WO2010060649A2 - Coated catalyst, method for the production thereof, and use thereof - Google Patents

Abstract

The invention relates to a coated catalyst comprising a catalyst support that contains ZrO2 and has a coating containing Pd and Au. The ratio between Au and Pd atoms in the coated catalyst ranges from 0.2 to 1.2. In order to provide a coated catalyst that has a relatively high alkenyl acetate activity, the maximum Pd concentration in the coated catalyst is 0.75 percent by weight.

Description

 Shell catalyst, process for its preparation and

use

The present invention relates to a coated catalyst comprising a ZrO ₂ -containing catalyst support having a shell in which Pd and Au are contained, wherein the Au / Pd atomic ratio of the shell catalyst is 0.2 to 1.2.

Alkenyl acetates are an important monomer building block in the synthesis of plastic polymers. The main applications of alkenyl acetates are i.a. the preparation of polyvinyl acetate, polyvinyl alcohol and polyvinyl acetal and the co- and terpolymerization with other monomers such as ethylene, vinyl chloride, acrylate, maleate, fumarate and vinyl laurate.

An alkenyl acetate can be prepared for example in the gas phase from acetic acid and ethylene by reaction with oxygen, the catalysts used for this synthesis preferably Pd as active metal, Au as a promoter and an alkali metal component as a co-promoter, preferably potassium in the form of the acetate. In the Pd / Au system of these catalysts, the metals Pd and Au are not present in the form of metal particles of the respective pure metal, but rather in the form of Pd / Au alloy particles of possibly different composition, although the presence of unalloyed particles are not excluded can. Alternatively to Au, for example, Cd or Ba can also be used as co-promoter.

At present, alkenyl acetates are produced predominantly by means of so-called shell catalysts in which the noble metals Pd and Au do not completely complete the catalyst support but penetrate only in a more or less wide outer region (shell) of the catalyst support (cf., for this purpose, EP 565 952 A1, EP 634 214 A1, EP 634 209 A1 and EP 634 208 A1), while those lying further inside Areas of the catalyst support are free of precious metals. With the aid of shell catalysts, a more selective reaction is possible in many cases than with catalysts in which the carriers are impregnated into the carrier core with active component ("fully impregnated").

The shell catalysts known in the prior art for the preparation of alkenyl acetates may be, for example, catalyst supports based on silica, alumina, aluminosilicate, titanium oxide or zirconium oxide (cf., for this purpose, EP 839 793 A1, WO 1998/018553 A1, WO 2000/058008 A1 and WO 2005/061107 Al). However, catalyst supports based on titanium oxide or zirconium oxide are currently scarcely used since these catalyst supports are not long-term stable with respect to acetic acid or are relatively expensive.

The majority of currently used catalysts for the preparation of alkenyl acetates are coated catalysts with a Pd / Au shell on a porous amorphous formed as a ball aluminosilicate on the basis of natural phyllosilicates, which are impregnated with potassium acetate as a co-promoter.

Such alkenyl acetate shell catalysts are usually prepared in a so-called chemical way in which the catalyst support with solutions of corresponding metal precursor compounds, for example by immersing the carrier in the solutions or by Incipient Wetness method (pore filling method), in which the carrier is loaded with a solution volume corresponding to its pore volume, is impregnated.

The Pd / Au shell of the catalyst is produced, for example, by first impregnating the catalyst support in a first step with a palladium chloride solution and then fixing the Pd component with NaOH solution onto the catalyst support in the form of a Pd hydroxide compound in a second step becomes. In a subsequent separate third step, the catalyst support is then impregnated with a gold chloride solution and then the Au component also fixed by means of NaOH. After fixing the noble metal components in the outer shell of the catalyst support of the carrier is then largely free of chloride and Na ions washed, then dried, calcined and finally reduced in the liquid or gas phase. The Pd / Au shell thus produced usually has a thickness of about 100 μm to 500 μm.

Usually, the catalyst support loaded with the noble metals is loaded with potassium acetate after the last fixation step or after the reduction step, with the loading of potassium acetate not only taking place in the outer shell loaded with precious metals, but rather completely impregnated with the co-promoter. The catalyst carrier used is predominantly a spherical carrier with the name "KA-160" from SÜD-Chemie AG, Munich, Germany, based on a natural layered silicate which has a BET surface area of about 160 m ² / g.

The alkenyl acetate selectivities achieved by means of the alkenyl acetate shell catalysts based on Pd and Au and KA-160 supports known in the prior art are approximately 90 mol .-% based on the supplied ethylene, wherein the remaining 10 mol .-% of the reaction products are substantially CO ₂ , which is formed by total oxidation of the organic starting materials / products.

It is desirable to provide alkenyl acetate catalysts which have relatively high alkenyl acetate activity. For this purpose, attempts are made in the prior art to further increase the proportion of known coated catalysts on the active metal Pd. Alkenyl acetate catalysts currently used in the art have a Pd content of 0.9 wt.% Or higher.

The object of the present invention is to provide a shell catalyst which has a relatively high alkenyl acetate activity.

This object is achieved by a shell catalyst comprising a ZrO ₂ -containing catalyst support with a shell in which Pd and Au are contained, wherein the Au / Pd atomic ratio of the shell catalyst is 0.2 to 1.2 and wherein the proportion of the shell catalyst Pd is less than or equal to 0.75% by weight.

Surprisingly, it has been found that the coated catalyst according to the invention has a relatively high alkenyl acetate activity in comparison with corresponding coated catalysts of the prior art, despite a relatively low active metal content.

In addition, it has been found that the catalyst according to the invention, despite its high alkenyl acetate activity, is characterized by a relatively high alkenyl acetate selectivity. In addition, the coated catalyst of the present invention is particularly cost effective because it requires less Pd to provide the same alkenyl acetate activity and at least the same alkenyl acetate selectivity as a corresponding prior art catalyst.

Shell catalysts are known in the art. For shell catalysts, a distinction is made between "egg shell" and "egg white" shell catalysts. An egg-shell catalyst is a shell catalyst in which the catalytically active substance is present in an outer shell of the catalyst support, the shell extending inwards from the outer surface of the support and the core of the catalyst support being free of catalytically active substance In an "egg-white" shell catalyst, however, an inner shell in a near-surface zone of the catalyst support is slightly loaded below the outer support surface with the catalytically active substance, wherein the not occupied with catalytically active substance outer shell scavenge catalyst poisons and so to protect the underlying, catalytically active substance from poisoning. Even with shell catalysts of the "egg-white" type, the core of the catalyst support is free of catalytically active substance.

The coated catalyst according to the invention is a peelable catalyst of "βgg-shβll" or "βgg-wh-Ltβ" -Tvρ, preferably an egg-shell type shell-type catalyst.

According to a preferred embodiment of the coated catalyst according to the invention, it is provided that the proportion of the coated catalyst in Pd 0.75 wt .-% to 0.15

Wt .-% is, preferably 0.70 wt .-% to 0.40 wt .-% and preferably 0.65 wt .-% to 0.45 wt .-%. In the abovementioned intervals, the coated catalyst according to the invention is characterized by a particularly high activity.

According to another preferred embodiment of the coated catalyst according to the invention, it is provided that the proportion of the coated catalyst in Pd is 0.75 wt .-% to 0.50 wt .-%, preferably 0.75 wt .-% to 0.55 wt. -%, and preferably 0.70 wt .-% to 0.60 wt .-%.

The proportion of the coated catalyst according to the invention to Pd is less than or equal to 0.75 wt .-%. In this case, the expression "proportion of the coated catalyst according to the invention on Pd" refers to the weight of Pd based on the weight of the coated catalyst, ie the sum of the weights of the catalyst support, the noble metals Pd and Au and the co-promoter or co-promoter compound, for example potassium acetate. Prior to determining the weight of the shell catalyst, the shell catalyst is preferably dried for a period of 1 hour at a temperature of 120 ^° C. under a nitrogen atmosphere to substantially remove any moisture and then analyzed.

According to a further preferred embodiment of the shell catalyst according to the invention, it is provided that the Au / Pd atomic ratio of the shell catalyst is 0.3 to 1.0, preferably 0.4 to 0.7. In the above-mentioned intervals, the coated catalyst of the invention is characterized by a relatively high

Alkenyl acetate selectivity from a relatively low use of Au. According to a further preferred embodiment of the shell catalyst according to the invention, it is provided that at least part of the ZrO ₂ contained in the catalyst support is present in the tetragonal modification. ZrO ₂ in the tetragonal modification causes the coated catalyst of the invention over a relatively long period of time by a relatively high alkenyl acetate activity is characterized.

ZrO ₂ occurs in three modifications. At room temperature ZrO _{2 is} in monoclinic modification, at a temperature above 1170 ⁰ C is ZrO ₂ in tetragonal modification before and above 2370 ⁰ C to the melting point at 2690 ⁰ C ZrO _{2 is} in cubic modification.

According to a preferred embodiment of the shell catalyst according to the invention, it is provided that at least 50% by weight of the ZrO ₂ contained in the catalyst support is present in tetragonal modification. Since the proportion of ZrO ₂ contained in the catalyst support with tetragonal modification by X-ray diffractometry (XRD) is determined, the said proportion refers only to X-ray diffractive ZrO ₂ , which is included in the catalyst support according to the invention.

It was found that the inventive

Coated catalyst in the alkenyl acetate synthesis the less ZrO? liberated, ie, washed out, the greater the proportion of the carrier to ZrO _{2 which} is present in the tetragonal modification. Accordingly, it is provided according to a preferred embodiment of the coated catalyst according to the invention that at least 50 wt .-% of ZrO ₂ contained in the catalyst support are present in the tetragonal modification, preferably 50 wt .-% to 100 wt .-%, more preferably from 70% to 100%, even more preferably from 85% to 100%, more preferably from 90% to 100%, more preferably 92% by weight to 100% by weight, and more preferably 93% by weight to 100% by weight. The above proportions refer to the X-ray diffractive ZrO ₂ contained in the carrier. A proportion of 100% by weight tetragonal ZrO ₂ , which is particularly preferred according to the invention, means that in a corresponding XRD diffractogram only signals of tetragonal ZrO _{2 are} identifiable and no signals of ZrO ₂ monoclinic or cubic modification.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that in an XRD diffractogram of the carrier the ratio of the intensity of the signal at 2theta of 28.2 ° to the intensity of the signal at 2 theta of 30.2 ° is less than or equal to 1 , preferably less than 0.5, preferably less than 0.3, even more preferably less than 0.05 and even more preferably 0. It is further preferred that the XRD diffractogram of the support is free of signals of cubic ZrO ₂ . At 2theta of 28.2 °, the highest intensity peak (hkl 111) of monoclinic ZrO ₂ , at ₂ theta of 30.2 ° lies the highest intensity peak (hkl 101) of tetragonal ZrO ₂ . The XRD diffractogram is a so-called XRD differential diffractogram. The XRD differential diffractogram is generated by taking an XRD diffractogram from a ZrO ₂ -containing and a reference catalyst support under the same conditions and subtracting the XRD diffractogram of the reference catalyst support from that of the ZrO ₂ -containing catalyst support. The reference catalyst support is prepared analogously to the ZrO ₂ -containing catalyst support, with the exception that the Reference catalyst carrier is not added to Zr. The XRD diffractograms are preferably measured on a BRUKER axs powder X-ray diffractometer, Model D4 Endeavor, in Bragg Brentano geometry. The device parameters are preferably: Cu-K _a iph _a 1.5406 A, current 40 kV, current 40 mA and the scan parameters: continous scan, 2theta from 5 ° to 90 °, increment = 0.03 ° 2theta, time per Step = 0.5 s, divergence slit = variable 12 mm, antiscattering slit = variable 12 mm, sample rotation: 30 rpm.

Tetragonal zirconia has a relatively high specific surface area. However, the stable at room temperature phase is the monoclinic zirconia, which has a relatively low specific surface area. By simply incorporating undoped zirconium hydroxide into a support matrix comprising a layered silicate and subsequent calcination, it has been possible to produce and stabilize the surface-rich tetragonal ZrO ₂ phase in high yield. Thus, with relatively little use of expensive zircon, a relatively high specific zirconia surface is provided in the catalyst support. A prior art catalyst support prepared by impregnating a catalyst support with a zirconium salt solution and then calcining it is X-ray amorphous with respect to the zirconium. This usually means that the zirconium is present in the form of nanocrystalline particles and / or in amorphous form.

According to a further preferred embodiment of the coated catalyst according to the invention, it is provided that the ZrO ₂ is present in particulate form. Lies in the catalyst carrier ZrO ₂ in the tetragonal

Modification before, the ZrO _{2 is contained} in the carrier in particulate form. Otherwise, the ZrO ₂ in the carrier may in principle also be contained in the form of individual ZrO ₂ units, which are incorporated, for example, in the structure of the carrier. However, it is preferred that the ZrO ₂ in the

Catalyst support is present in particulate form. As a result, a solid incorporation of ZrO ₂ in the carrier and thus a largely low ZrO ₂ release of the catalyst support is ensured in acetic acid.

If the ZrO ₂ in the catalyst support of the catalyst according to the invention in particulate form, it is provided according to a further preferred embodiment of the catalyst according to the invention that the ZrO _{2 has} a mean particle diameter d ₅₀ of at most 50 microns, preferably a mean particle diameter d ₅₀ of a maximum of 30 microns and more preferably a mean particle diameter d ₅₀ of 20 microns maximum. The determination of the mean particle diameter d ₅₀ is determined by means of electron microscopy (EDX). For this purpose, the maximum dimensions of the 50 largest identifiable ZrO ₂ particles are measured in a 1 mm × 1 mm arbitrarily selected region of an EDX spectrum of the catalyst support and from this the d ₅₀ value is determined. The EDX measurement is preferably carried out on a scanning electron microscope LEO 430VP, equipped with an energy-dispersive spectrometer from Bruker AXS. For the measurement, the catalyst support is cut through, glued onto an aluminum sample holder and then vapor-deposited with carbon. The detector preferably is a nitrogen-free silicon drift chamber detector (XFlash ^® 410) with a

Energy resolution of 125 eV for the manganese K _a i _Pha line is used. The thus determined d ₅₀ value is usually much larger than the actual d ₅₀ value in the Catalyst supports incorporated ZrO ₂ particles. The actual d ₅ o value _did s _ä # chiich one would measure, if the ZrO ₂ particles may detach from the support and would be measured, corresponding to 0.8 to 2 times the in the process for preparing the Catalyst carrier used zirconium hydroxide. From this, and based on the intensity of the XRD reflections for the tetragonal ZrO _{2, it} can be concluded how large the proportion of ZrO ₂ particles in the catalyst support which are X-ray diffractive in terms of size (approximately greater than 50 Angstrom).

According to a further preferred embodiment of the coated catalyst according to the invention, it is provided that the ZrO _{2 is} uniformly or statistically evenly distributed in the catalyst support.

It has been found that the more uniformly the ZrO _{2 is distributed} in the matrix of the carrier, the lower the ZrO ₂ release of the catalyst carrier in acetic acid. By matrix is meant the solid matter of the carrier surrounding the pores. In the event that the catalyst support contained in the coated catalyst according to the invention does not consist of ZrO ₂ , it is therefore provided according to a further preferred embodiment of the coated catalyst according to the invention that the ZrO _{2 is} uniformly distributed in the matrix of the carrier, preferably homogeneously distributed.

According to a further preferred embodiment of the coated catalyst according to the invention, it is provided that the ZrO _{2 is present} in the catalyst support in a proportion of 1% by weight to 30% by weight, based on the weight of the catalyst support. If ZrO _{2 is present} in the catalyst support in an amount of less than 1% by weight, the alkenyl acetate activity of the coated catalyst according to the invention is only slightly increased, while above a fraction of 25% by weight the increase in the activity of the catalyst with a marked decrease in alkenyl acetate selectivity. Accordingly, it is provided according to a further preferred embodiment of the catalyst according to the invention that the ZrO ₂ in the catalyst support in a proportion of 1 wt .-% to 25 wt .-% is contained based on the weight of the catalyst support, preferably with a share of 5 Wt .-% to 20 wt .-% and more preferably in a proportion of 8 wt .-% to 15 wt .-%.

The catalyst support contained in the coated catalyst according to the invention may consist of ZrO ₂ or ZrO ₂ other ingredients such as one or more metal oxides selected from the group consisting of SiO ₂ , MgO, Al ₂ O ₃ , aluminosilicate, TiO ₂ , fumed silica and Nb ₂ O ₅ .

According to a further preferred embodiment of the coated catalyst according to the invention, it is provided that the catalyst support comprises a natural layered silicate.

The term "natural layered silicate", for which the term "phyllosilicate" is also used in the literature, is understood in the context of the present invention to originate from natural sources, untreated or treated silicate mineral in which Si0 ₄ tetrahedra, which structural Form the basic unit of all silicates which are crosslinked in layers of the general formula [Si ₂ O ₅ ] ^{2 "} These tetrahedral layers alternate with so-called octahedral layers in which a cation, especially Al and Mg, is octahedrally surrounded by OH or O. It will be For example, a distinction is made between two-layer phyllosilicates and three-layer phyllosilicates. Phyllosilicates preferred in the context of the present invention are clay minerals, in particular kaolinite, beidellite, hectorite, saponite, nontronite, mica, vermiculite and smectites, with smectites and in particular montmorillonite being particularly preferred. Definitions of the term "layered silicates" can be found, for example, in "Lehrbuch der anorganischen Chemie", Hollemann Wiberg, de Gruyter, 102nd Edition, 2007 (ISBN 978-3-11-017770-1) or in "Rompp Lexikon Chemie", 10. Edition, Georg Thieme Verlag under the term "phyllosilicate".

Typical treatments to which a natural layered silicate is subjected prior to use as a carrier material include, in particular, treatment with acids, in particular mineral acids such as, for example, hydrochloric acid, and / or calcining.

A particularly preferred natural layered silicate in the context of the present invention is montmorillonite, which is preferably used in the form of a bentonite.

Bentonites are mixtures of various clay minerals containing predominantly montmorillonite (about 50% by weight to 90% by weight). Other accompanying minerals can i.a. Quartz, mica and feldspar.

According to a further preferred embodiment of the Schaienkatalysators invention, it is provided that the natural phyllosilicate is an acid-activated phyllosilicate.

Acid-activated phyllosilicates are known in the art (see Rompp Lexikon Chemie, 10th edition, Georg Thieme Verlag, term "bentonite") Increase catalyst carrier is the natural

Layered silicate in the carrier, preferably in the form of an acid-activated layered silicate. It is further preferred that the acid-activated phyllosilicate is acid-activated montmorillonite which, according to the invention, is more preferably contained in the carrier in the form of an acid-activated bentonite.

According to the invention, the proportion of the catalyst support of natural layered silicate is greater than or equal to 50% by weight, preferably 55% by weight to 95% by weight, preferably 60% by weight to 90% by weight, more preferably from 65% to 85% and more preferably from 70% to 80% by weight, based on the weight of the catalyst support.

According to a further preferred embodiment of the coated catalyst according to the invention, it is provided that the natural phyllosilicate present in the catalyst support has an SiO ₂ content of at least 65% by weight, preferably one of at least 80% by weight and more preferably one of 90% by weight % to 95% by weight. This ensures a high chemical resistance of the catalyst support in the alkenyl acetate synthesis.

In the gas-phase synthesis of an alkenyl acetate from acetic acid and ethene, a relatively low Al ₂ O ₃ content in the natural layered silicate hardly adversely affects, while at high Ai ₂ O ₃ contents must be expected with a significant decrease in the pressure of the catalyst support. According to a preferred embodiment of the catalyst according to the invention, the natural sheet silicate therefore contains less than 5% by weight Al ₂ O ₃ , preferably from 0.1% by weight to 3.5% by weight and preferably from 0.3% by weight to 3.0% by weight, based on the weight of the natural layered silicate present in the carrier. According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support has an acidity of from 1 .mu.l / g to 150 .mu.l / g.

The degree of acidity of the catalyst support may favorably influence the activity of the catalyst of the present invention in the gas-phase synthesis of an alkenyl acetate of acetic acid and ethene. According to a further preferred embodiment of the catalyst according to the invention, it is therefore provided that the catalyst support has an acidity of 1 .mu.l / g to 150 .mu.l / g, preferably an acidity of 5 .mu.l / g to 130 .mu.l / g, preferably an acidity of 10 .mu.val / g to 100 μval / g, and more preferably an acidity of 20 μval / g to 60 μval / g. The acidity of the carrier can be increased, for example, by impregnation of the catalyst or carrier with acid.

The acidity of a catalyst support is determined as follows: I g of the finely ground catalyst support is mixed with 100 ml of water (with a pH blank) and extracted with stirring for 15 minutes. It is then titrated with 0.01 N NaOH solution at least until pH 7.0, wherein the titration is carried out stepwise; Namely, 1 ml of the NaOH solution is added dropwise to the extract (1 drop / second), then waited 2 minutes, read the pH, 1 ml of NaOH is added dropwise, etc. The blank value of the water used is determined and the acidity Calculation corrected accordingly. The titration curve (ml 0.01 NaOH versus pH) is then plotted and the point of intersection of the titration curve at pH 7 is determined. The molar equivalents are calculated equiv in 10 ^"6 / g of support, resulting from the consumption of NaOH for the intersection at pH 7: 10 ml of 0.01 N NaOH,.

Total acid: = μval / g

1 carrier

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support has an average pore diameter of 8 nm to 30 nm.

In order to keep the pore diffusion limitation of the catalyst according to the invention substantially low, it is provided according to a further preferred embodiment of the catalyst according to the invention that the catalyst support has an average pore diameter of 8 nm to 30 nm, preferably one of 10 nm to 20 nm and more preferably one of 10 nm to 15 nm. The mean pore diameter is determined according to DIN 66134 (determination of the pore size distribution and the specific surface area of mesoporous solids by nitrogen sorption (method according to Barrett, Joyner and Halenda (BJH)).

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support has a specific surface area of less than or equal to 180 m ² / g.

It has been found that the alkenyl acetate selectivity of the catalyst according to the invention is the higher with virtually constant activity of the catalyst, the smaller the specific surface area of the catalyst support. According to a particularly preferred embodiment of the catalyst according to the invention, it is therefore provided that the catalyst support has a specific surface area of less than or equal to 180 m ² / g, preferably one of less than or equal to 160 m ² / g, preferably less than or equal to 140 m ² / g, more preferably less than or equal to 137 m ² / g, more preferably less than / equal to 135 m ² / g, even more preferred a of less than or equal to 133 m ² / g and particularly preferably a of less than / equal to 130 m ² / g. The specific surface of the support is according to DIN 66131 (determination of the specific

Surface of solids by gas adsorption according to Brunauer, Emmett and Teller (BET)) and DIN 66132 determined by nitrogen.

According to the invention it is further preferred that the

Catalyst support has a specific surface area of from 60 m ² / g to 180 m ² / g, preferably from 65 m ² / g to 160 m ² / g, preferably from 70 m ² / g to 140 m ² / g, more preferably from 70 m ² / g to 120 m ² / g, more preferably from 70 m ² / g to 110 m ² / g and most preferably from 80 m ² / g to 100 m ² / g.

The size of the specific surface area, the average pore diameter, the integral pore volume, etc. of the catalyst carrier depends on the case where the

Catalyst support comprises a natural layered silicate, in particular the quality of the natural layered silicate used, the acid treatment process, i. for example, the nature and the relative to the layered silicate amount and the concentration of the mineral acid used, the acid treatment time and the temperature, the compression pressure and the calcination time and temperature and the calcination from.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support has a hardness of greater than or equal to 55 N, preferably a hardness of 55 N to 65 N and particularly preferably a hardness of 57 N to 63 N. The determination of hardness

(Pressure hardness) is carried out on spherical samples (diameter: 5 mm) by means of the tablet hardness tester 8M from Dr. Ing. Schleuniger Pharmatron AG (Switzerland). Before the measurement, the samples are dried over a period of 2 h at a temperature of 130 ⁰ C. Hardness is calculated as the average of 100 measurements. For the measurements, the following selectable parameters of the 8M Tablet Hardness Tester are set as follows:

Hardness (dimension): N

Distance to the sample: 5.00 mm

Time delay: 0.80 s

Feed type: 6 D

Speed: 0.60 mm / s

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support has an integral pore volume of from 0.25 ml / g to 0.7 ml / g.

It was found that the alkenyl acetate selectivity of the catalyst according to the invention is dependent on the integral pore volume of the catalyst support. Therefore, it is preferred that the catalyst support has an integral pore volume of 0.25 ml / g to 0.7 ml / g, preferably one of 0.3 ml / g to 0.55 ml / g, and preferably one of 0.35 ml / g to 0-5 ml / g. The integral pore cleavage is determined according to DIN 66134 (determination of the pore size distribution and the specific surface area of mesoporous solids by nitrogen sorption (method according to Barrett, Joyner and Halenda (BJH)). According to a further preferred embodiment of the catalyst according to the invention, it is provided that at least 80% of the integral pore volume of the catalyst support is formed by mesopores and macropores, preferably at least 90% and preferably at least 95%. This counteracts a reduced activity of the catalyst according to the invention caused by diffusion limitation, in particular a shell catalyst with a relatively large shell thickness. Here, the terms "micropores", "mesopores" and "macropores" are understood to mean pores having a diameter of less than 2 nm, a diameter of 2 nm to 50 nm and a diameter of greater than 50 nm Mesopores and macropores at the integral pore volume are determined on the basis of the pore volume distribution of the catalyst support according to the invention, which is determined according to DIN 66134 (determination of the pore size distribution and the specific surface of mesoporous solids by nitrogen sorption (method according to Barrett, Joyner and Halenda (BJH)).

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the proportion of the pores of the carrier with a diameter of 6 nm to 50 nm at the integral pore volume is more than 66%, preferably from 66% to 80% and particularly preferably from 68%. up to 75%. The percentages are from the

Pore size distribution to be determined according to DIN 66134 (determination of the pore size distribution and the specific surface area of mesoporous solids by nitrogen sorption (method according to Barrett, Joyner and Halenda (BJH)).

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the Catalyst support has a bulk density of more than 0.3 g / ml, preferably a greater than 0.35 g / ml and more preferably a bulk density of 0.35 g / ml to 0.6 g / ml.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support is formed as a shaped body.

In principle, the catalyst support may have any form which is known to those skilled in the art for the purpose of the invention. For example, the catalyst support may be formed as a sphere, cylinder, perforated cylinder, trilobium, ring, star, torus or strand, preferably as a rib strand or star strand.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support has a maximum dimension of 1 mm to 25 mm, preferably a maximum dimension of 3 mm to 15 mm.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support is formed as a sphere.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the ball has a diameter of 2 mm to 10 mm, preferably a diameter of 4 mm to 8 mm.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the catalyst support with at least one oxide of a metal selected from the group consisting of Hf, Ti, Si, La, Nb, Ta, W, Mg, Re, Y and Fe, preferably with HfO ₂ . By doping, the activity of the catalyst according to the invention can be increased.

It is particularly preferred that the catalyst support is doped with HfO ₂ and / or that the ZrO ₂ is doped with Y ₂ O ₃ , La ₂ O ₃ and / or SiO ₂ . The doping of ZrO ₂ causes a relatively high acetic acid resistance of ZrO ₂ . The HfO ₂ doping causes an increase in the activity of the catalyst according to the invention.

According to an alternative embodiment, it is provided that the ZrO ₂ contained in the catalyst support is free of a doping oxide which stabilizes the tetragonal phase of the ZrO ₂ , preferably free of La ₂ O ₃ , SiO ₂ and Y ₂ O ₃ .

Even without appropriate doping, the tetragonal ZrO ₂ can be stable in the carrier.

According to a further preferred embodiment of the catalyst according to the invention, it is provided that the proportion of the catalyst support to doping oxide is between 0.1 wt .-% and 20 wt .-%, preferably 1 wt .-% to 10 wt .-% and preferably 3 Wt .-% to 8 wt .-% based on the weight of the catalyst support. The doping can be effected, for example, by surface doping, as known from the prior art, or the metal oxide / metal oxides can / can be incorporated into the matrix of the catalyst support.

According to a further preferred embodiment, it may be provided that the water absorbency of the catalyst support is 40% to 75%, preferably 50% to 70% calculated as weight increase by Wasseraufnähme. The Absorbency is determined by soaking 10 g of the carrier sample with deionized water for 30 minutes until gas bubbles no longer escape from the carrier sample. Then, the excess water is decanted and the soaked sample is blotted with a cotton cloth to free the sample from adherent moisture. Then the water-loaded carrier is weighed and the absorbency calculated according to:

(Weight (g) - weight (g)) x 10 = water absorbency (%)

According to a further preferred embodiment of the shell catalyst according to the invention, it is provided that the thickness of the shell is 30 μm to 500 μm, preferably 50 μm to 200 μm and particularly preferably 75 μm to 150 μm. It was found that the alkenyl acetate selectivity of the coated catalyst according to the invention in the aforementioned intervals is comparatively high while at the same time having relatively high activity of the catalyst. The thickness of the shell can be measured, for example, by means of a light microscope or by means of EDX.

The present invention further relates to a process, in particular a process for the preparation of the coated catalyst according to the invention, comprising

- generating a fluidized bed of catalyst supports by means of a gas, wherein the catalyst supports move in the fluidized bed on an elliptical or toroidal path;

Spraying the catalyst support moving in the fluidized bed on an elliptical or toroidal orbit with a first solution in which a Pd precursor is dissolved; Spraying the catalyst support moving in the fluidized bed on an elliptical or toroidal orbit with a second solution in which an Au precursor is dissolved.

It has been found that coated catalysts prepared according to the process of this invention can have a relatively thin shell of relatively uniform thickness and relatively uniform noble metal distribution, resulting in a relatively high alkenyl acetate selectivity of the catalyst.

The process according to the invention is carried out by producing a fluidized bed in which the catalyst supports move in an elliptical or toroidal path, or in other words in which the catalyst supports rotate elliptically or toroidally. To give an idea of how the catalyst supports move in the fluidized bed, in "elliptical orbit" the catalyst supports in the fluidized bed move in a vertical plane on an elliptical orbit of slightly varying major and minor axis size "Toroidal orbital" the catalyst supports in the fluidized bed move in a vertical plane on an elliptical orbit of slightly varying size of the major and minor axes and in a horizontal plane on a circular orbit of slightly varying size of the radius. On average, the catalyst supports move "elliptically" in a vertical plane on an elliptical path, "toroidal" on a toroidal path, that is, a catalyst support helically traverses the surface of a vertical elliptical sectioned torus. In the prior art, the transition of the particles of a bed to a state in which the particles are completely free to move (fluidized bed), referred to as a relaxation point (fluidized point) and the corresponding fluid velocity as loosening speed. According to the invention it is preferred that in the process according to the invention the fluid velocity (of the gas) is up to 4 times the relaxation rate, preferably up to 3 times the relaxation rate and more preferably up to 2 times the relaxation rate.

According to an alternative embodiment of the method according to the invention, it may be provided that the

Fluid velocity up to 1.4 times the log of the rate of deceleration, preferably up to 1.3 times the log of the rate of deceleration, and more preferably up to 1.2 times the log of the rate of deceleration.

The interaction of spraying with the fluid bed elliptical or toroidal circulation of the

Catalyst support causes, in contrast to working in a conventional fluidized bed, that the individual catalyst carriers pass through the spray nozzle in approximately the same frequency. In addition, the circulation process also ensures that the individual catalyst carriers perform a rotation about their own axis, which is why the

Va h => T vσa * - / -> v <- rä πor Vio oz-inHoT-c! πl o i r> Vimä (lή α TΠ i t- T.nonnπ H rmmrStern H prh.

The catalyst supports moving in the fluidized bed on an elliptical or toroidal orbit can, in the process according to the invention, be treated first with the first solution containing the Pd precursor and then with the second, the Au precursor-containing solution, to be sprayed. Alternatively, the catalyst supports may be sprayed first with the second and then with the first solution. Alternatively, it can also be provided that the catalyst supports are sprayed simultaneously with the first and with the second solution, for example by means of two single-fluid nozzles or by means of a two-fluid nozzle. According to the invention it is particularly preferred that the catalyst supports are sprayed first with the first and then with the second solution.

In the method according to the invention run the

Catalyst support in the fluidized bed elliptical or toroidal order. However, it is particularly preferred that the catalyst supports in the fluidized bed move on a toroidal path.

In a further preferred embodiment, the method according to the invention further comprises

- Drying of sprayed with the first and / or second solution catalyst support.

The drying of the catalyst carrier sprayed with the solution (s) preferably takes place continuously in the process according to the invention by means of the gas for the production of the fluidized bed, which is why relatively small shell thicknesses can be obtained in a technically simple manner. However, it can also be provided that, after spray impregnation with continuous drying or without drying, a separate drying step is carried out. For example, in the first case, the temperature of the

Gas or the catalyst support set the drying rate and thus, for example, the thickness of the shell In the second case, it can be dried by any drying method known to those skilled in the art.

According to the invention it is preferred that the drying takes place at a temperature of 20 ⁰ C to 200 ⁰ C, preferably between 40 ⁰ C and 150 ⁰ C and particularly preferably between 70 ⁰ C and 120 ⁰ C, both at atmospheric pressure and in vacuo can be dried. It can be dried both in air and under inert gas.

According to a further preferred embodiment, the method according to the invention further comprises

Calcination of the catalyst supports sprayed with the first and / or second solution at a temperature at which the metal component of the metal precursor / precursor sprayed onto the catalyst supports is converted into an oxidic form.

By calcining a fixation of the Pd, the Au or the Pd and the Au component is achieved on the catalyst support on the one hand, on the other hand, these metals can be converted relatively easily from the oxidic form in the metallic state.

In the context of the present invention, the calcination can be carried out, for example, in a temperature range from 200 ^° C. to 1000 ^° C., preferably in a temperature range from 300 ^° C. to 800 ^° C., more preferably in a temperature range from 350 ^° C. to 750 ^° C. particularly preferably in a temperature range from 400 ^° C. to 500 ^° C. The calcination time is usually in the range of 1 minute to 48 hours, preferably in the range of 30 minutes to 12 hours, and more preferably in the range of 1 hour to 7 hours, with a calcination time of 2 hours to 5 hours is particularly preferred.

According to the present invention, the calcination of the metal precursors sprayed catalyst supports may preferably be carried out under a protective gas, while the metal precursors e.g. decompose to 0 oxidation state metal by autoreduction. As a result, a separate reduction step can be avoided.

According to the present invention, it is particularly preferred that the protective gas is a gas selected from the group consisting of the noble gases, CO ₂ , nitrogen and

Mixtures of two or more of the aforementioned. Under protective gas gases or gas mixtures are understood that can be used as an inert protective atmosphere, for example, to avoid unwanted chemical reactions. In the context of the present invention, the noble gases helium, neon, argon, krypton or xenon can be used as the protective gas, or mixtures of two or more of the abovementioned, with argon being particularly preferred as protective gas. In addition to the noble gases or in addition to these, for example, nitrogen can also be used as protective gas. An inert gas atmosphere which is particularly preferred according to the method of the present invention comprises the noble gas argon and nitrogen.

According to a further preferred embodiment, the method according to the invention further comprises - Transfer the Pd component of the Pd precursor and the

Au component of the Au precursor in the oxidation state 0

According to the present invention, it is preferred that the conversion of the metal component of the metal precursor into the oxidation state 0 by means of a reducing agent.

Gaseous or vaporizable reducing agents such as H ₂ , CO, NH ₃ , formaldehyde, methanol and hydrocarbons are preferably used, wherein the gaseous reducing agents may also be diluted with inert gas such as carbon dioxide, nitrogen or argon. Preferably, an inert gas-diluted reducing agent is used. Preference is given to mixtures of hydrogen with nitrogen or argon, preferably with a hydrogen content of between 1% by volume and 50% by volume.

The amount of reducing agent is preferably selected so that during the treatment period at least the necessary for the complete transfer of the metals equivalent is passed over the catalyst. However, preference is given to

Excess reducing agent passed over the catalyst to ensure rapid and complete transfer.

Preferably, the metal is depressurized, ie at an absolute pressure of about 1 bar, transferred to the oxidation state 0. For the production of technical quantities of catalyst, a rotary kiln or fluidized bed reactor is preferably used in order to ensure a uniform reduction. According to the present invention, the conversion of the metals into the oxidation state 0 preferably takes place at a temperature of 100 ^° C. to 450 ^° C.

The conversion of the metals into the oxidation state 0 can, in principle, be carried out at any temperature which is known to the person skilled in the art as suitable for the purpose according to the invention. In the context of the present invention, the conversion of the metals into the oxidation state 0 can be carried out in a temperature range from 100 ^° C. to 500 ^° C., preferably in a temperature range from 150 ^° C. to 450 ^° C., and more preferably in a temperature range from 200 ^° C. up to 400 ^° C.

The conversion of Pd and Au into the oxidation state 0 can also be carried out in situ, ie in the process reactor, or also ex situ, ie in a special reduction reactor. The ex situ conversion can be carried out, for example, with 5% by volume of hydrogen in nitrogen, for example by means of forming gas, at temperatures in the range from preferably 150 ^° C. to 400 ^° C. over a period of 5 hours.

The conversion of Pd and Au into the oxidation state 0 can preferably also be carried out by wet-chemical means, for example by means of an aqueous solution of alkali metal hypophosphite.

According to a further preferred embodiment of the method according to the invention, it is provided that the first solution and the second solution are one and the same solution.

Are in the inventive method the

Catalyst support sprayed with a solution in which both the Pd precursor and the Au precursor contained dissolved is, then the precursors can be applied to procedural particularly simple way on the carrier.

According to a further preferred embodiment of the method according to the invention, it is provided that the Pd precursor is Pd (NH ₃ J ₄ (OH) ₂ .

The Pd precursor may, in principle, be any Pd-containing substance known to the person skilled in the art for the purpose according to the invention. According to the invention, preference is given to the Pd precursor being selected from the group consisting of Pd (NH ₄ ) ₄ (OH) ₂ , Pd (NH ₃ J ₄ (OAc) ₂ , H ₂ PdCl ₄ , Pd (NH ₃ ) ₄ ( HCO ₃ ) _{2 /} Pd (NH ₃ J ₄ (HPO ₄ ), Pd (NHa) ₄ Cl ₂ , Pd (NH ₃ ) ₄ -oxalate, Pd-oxalate, Pd (NO ₃ ) ₂ , Pd (NH ₃ ) ₄ (NO ₃ ) ₂ , K ₂ Pd (OAc) ₂ (OH) ₂ , Na ₂ Pd (OAc) ₂ (OH) ₂ , Pd (NH ₃ ) ₂ (NO ₂ ) ₂ , K ₂ Pd (NO ₂ J ₄ , Na ₂ Pd (NO ₂ J ₄ , Pd (OAc) ₂ , K ₂ PdCl ₄ , (NH ₄ J ₂ PdCl ₄ , PdCl ₂ and Na ₂ PdCl ₄ , with Pd (NH ₃ ) ₄ (OH) _{2 being} particularly preferred The corresponding complex salts with ethylenediamine or ethanolamine as ligand can also be used instead of NH _3. Besides Pd (OAc) ₂ , other carboxylates of palladium can also be used, preferably the salts of aliphatic monocarboxylic acids having 3 to 5 carbon atoms, for example the propionate - or the butyrate salt.

According to a further preferred embodiment of the method according to the invention, Pd nitrite precursors may also be preferred. Preferred Pd nitrite precursors are, for example, those obtained by dissolving Pd (OAc) ₂ in a NaNO ₂ solution.

According to a further preferred embodiment of the method according to the invention, it is provided that the Au precursor is KAuO ₂ . The Au precursor may in principle be any Au-containing substance which is known to the person skilled in the art for the purpose according to the invention as being suitable. According to the invention it is preferred that the Au precursor is selected from the group consisting of KAuO ₂ , HAuCl ₄ , KAu (NO ₂ ) ₄ , AuCl ₃ , KAuCl ₄ , NaAuCl ₄ , KAuCl ₄ , KAu (OAc) ₃ (OH) , HAu (NO ₃ J ₄ , NaAuO ₂ , NMe ₄ AuO ₂ , RbAuO ₂ , CsAuO ₂ , NaAu (OAc) ₃ (OH),

RbAu (OAc) ₃ OH, CsAu (OAc) ₃ OH, NMe ₄ Au (OAc) ₃ OH and Au (OAc) ₃ , with KAuO _{2 being} particularly preferred. It may be advisable to prepare Au (OAc) ₃ or KAuO ₂ fresh by precipitating the oxide / hydroxide from a solution of gold acid, washing and isolating the precipitate and taking up the same in acetic acid or KOH.

According to a further preferred embodiment of the method according to the invention, it is provided that the first solution and the second solution are aqueous solutions.

Suitable solvents for the precursors are all pure solvents or solvent mixtures in which the selected precursors are soluble and which after application to the catalyst support of the same can be easily removed by drying again. Preferred solvents for metal acetates as precursors are, for example, acetone or unsubstituted carboxylic acids, in particular acetic acid, and for the metal chlorides especially water or dilute hydrochloric acid.

If the precursors are not sufficiently soluble in pure solvents such as acetone, acetic acid, water or dilute hydrochloric acid or mixtures thereof, alternatively or in addition to the solvents mentioned, others may be used

Solvent or solvent additives find application. In a particularly preferred embodiment, the inventive method is carried out using a device which is adapted to generate by means of a gas, a fluidized bed of a particulate material, wherein the particles of the material move in the fluidized bed on an elliptical or toroidal path. Such devices are described, for example, in the documents WO 2006/027009 A1, DE 102 48 116 B3, EP 0 370 167 A1, EP 0 436 787 B1, DE 199 04 147 A1, DE 20 2005 003 791 U1, the contents of which are referenced in US Pat the present invention is incorporated.

According to the invention particularly preferred devices are sold by the company Innojet Technologies under the names Innoj et ^® Ventilus or Innojet ^® AirCoater. These devices comprise a cylindrical container with a fixed and immovably installed container bottom, in the middle of which a spray nozzle is mounted. The floor consists of circular lamellae, which are gradually mounted one above the other. The process air flows between the individual slats horizontally eccentrically with a circumferential

Outflow component in the direction of the container wall into the container. In the process, so-called air sliding layers form, on which the catalyst carriers are initially transported outwards in the direction of the container wall. On the outside of the container wall, a vertically aligned process air flow is guided, which deflects the catalyst carrier to the exterior. Obsn arrived bsv / egsn the catalyst carrier back on a more or less tangential path towards the center of the soil, in the course of which they pass the spray of the nozzle. After passing the spray, the described movement process starts again. The described process air supply provides the basis for a largely homogeneous, toroidal fluidized bed-like circulation of the catalyst support.

In a further preferred embodiment, the apparatus 2 has nozzles ("circular segment nozzles") mounted on an inner ring offset by 180 ° separating two toroidally circulating fluidized beds This preferred embodiment allows separate feeding of solutions (e.g. Pd solutions), so that Pd and Au can be simultaneously coated from separate stock solutions.

In order to accomplish a catalyst support fluidized bed in which the catalyst supports rotate elliptically or toroidally, it is provided in a procedurally simple and thus cost-effective manner that according to a further preferred embodiment of the method according to the invention, the apparatus comprises a process chamber with a bottom and a side wall, wherein the gas is introduced through the bottom of the process chamber, which is preferably constructed of a plurality of superposed, overlapping annular guide plates, between which annular slots are formed, is introduced with a horizontal, radially outwardly directed component of movement in the process chamber for generating the catalyst carrier fluidized bed.

By introducing gas into the process chamber with a horizontal, radially outwardly directed component of motion, elliptical circulation of the catalyst supports in the fluidized bed is effected. If the structures in the fluidized bed are to rotate toroidally, then the catalyst carriers must additionally be subjected to a circumferential component of motion which forces the carriers onto a circular path. The method of the present invention, therefore, according to a preferred embodiment, involves applying a circumferential flow component to the gas introduced into the process chamber.

The circumferential component of motion can the

Catalyst carriers are imposed, for example, by arranged on the side wall correspondingly aligned guide rails for deflecting the catalyst carrier. According to a preferred embodiment of the method according to the invention, however, it is provided that a circumferential flow component is imposed on the gas introduced into the process chamber. As a result, the generation of the fluidized bed in which the catalyst carriers rotate toroidally, procedurally simple guaranteed.

In order to impose the circumferential flow component on the gas introduced into the process chamber, it can be provided according to a further preferred embodiment of the method according to the invention that appropriately shaped and aligned gas guide elements are arranged between the annular guide plates. Alternatively or additionally, it can be provided that the circumferential flow component is imposed on the gas introduced into the process chamber by introducing additional gas with an obliquely upwardly directed component of motion through the bottom of the process chamber into the flow chamber. m ± j. u, v \ j ±. .. u ^ o wci- o c -i ui> - j- -i ± u £ j.

Side wall of the process chamber.

It may be provided that the spraying in the

Fluid bed circulating carrier is carried out with the solution by means of an annular gap nozzle which sprays a spray cloud, wherein the plane of symmetry of the spray cloud in parallel or substantially parallel to the plane of the device floor. Due to the 360 ° circumference of the spray cloud, the catalyst carriers moving down in the middle can be sprayed particularly uniformly with the solution. The annular gap nozzle, ie its mouth, is preferably completely embedded in the fluidized bed.

According to a further preferred embodiment of the method according to the invention, it is provided that the annular gap nozzle is arranged centrally in the bottom of the container and the mouth of the annular gap nozzle is embedded in the fluidized bed. This ensures that the free path of the droplets of the spray cloud to impinge on a catalyst support is relatively short and corresponding to the drops relatively little time remains to coalesce into larger drops, which could counteract the formation of a largely uniform shell thickness.

According to a further preferred embodiment of the method according to the invention, provision may be made for a gas support pad to be produced on the underside of the spray cloud. The bottom-side pad keeps the soil surface largely free of sprayed solution, which means that almost the entire sprayed solution is introduced into the fluidized bed, so that hardly any spray losses occur.

According to a further preferred embodiment of the method according to the invention, it is provided that the gas for generating the fluidized bed is selected from the group consisting of air, oxygen, nitrogen and the noble gases and mixtures of the above gases. According to a further embodiment of the method according to the invention, it is preferred that the spraying of the catalyst support with the first and / or second solution at a temperature of 50 ⁰ C to 120 ⁰ C, preferably at a temperature of 55 ⁰ C to 90 ⁰ C and Most preferably at a temperature of 60 ⁰ C to 80 ⁰ C is performed.

In order to prevent premature drying of droplets of the spray cloud, provision may be made for the gas to be enriched with the solvent of the first, of the second or of the first and of the second solution before introduction into the device, preferably in a range of 10%. up to 50% of the saturation vapor pressure (at process temperature). In this case, the solvent added to the gas and solvent can be separated from the drying of the catalyst support by means of suitable cooling units, condensers and separators from the gas and recycled by means of a pump in the solvent enrichment.

The present invention further relates to a shell catalyst according to the invention, obtainable by means of the method according to the invention.

The present invention further relates to the use of a coated catalyst according to the invention or a coated catalyst according to the invention, which is obtainable by the process according to the invention, in which

The following description of a preferred apparatus for carrying out the method according to the invention and the description of trajectories of catalyst supports is used in conjunction with the drawings to explain the invention. Show it: Fig. IA is a vertical sectional view of a preferred

Apparatus for carrying out the method according to the invention;

FIG. 1B shows an enlargement of the area framed in FIG. 1A and marked with the reference symbol IB; FIG.

Fig. 2A is a perspective sectional view of the preferred

Device in which the trajectories of two elliptically rotating catalyst carrier are shown schematically;

Fig. 2B is a plan view of the preferred apparatus and trajectories of Fig. 2A;

3A is a perspective sectional view of the preferred device, in which the trajectory of a toroidal circulating catalyst carrier is shown schematically.

Fig. 3B is a plan view of the preferred device and the trajectory of FIG. 3A.

FIG. 1A shows a device, which is designated overall by the reference numeral 10, for carrying out the method according to the invention.

The apparatus 10 includes a container 20 having an upstanding cylindrical side wall 18 enclosing a process chamber 15.

The process chamber 15 has a bottom 16, below which an inflow chamber 30 is located. The bottom 16 is composed of a total of seven annular superposed ring plates as baffles. The seven ring plates are placed one above the other so that an outermost ring plate 25 forms a lowermost ring plate on which then the other six inner ring plates, each lying underneath partially overlapping, are placed.

For the sake of clarity, only a few of the total of seven ring plates are provided with reference numerals, for example, the two superimposed annular plates 26 and 27. This overlapping and spacing between two annular plates each have an annular slot 28 formed by the process air 40 as a gas with a predominantly horizontal directed movement component can pass through the bottom 16.

In the central uppermost inner ring plate 29, an annular gap nozzle 50 is inserted in the central opening from below. The annular gap nozzle 50 has an orifice 55 which has a total of three orifice gaps 52, 53 and 54. All three orifice gaps 52, 53 and 54 are aligned so that they approximately parallel to the bottom 16, so spray approximately horizontally with a 360 ° Umfassungswinkel. Alternatively, the spray nozzle may be constructed such that the spray cone extends obliquely upward. Via the upper gap 52 and the lower gap 54, spray air is expelled as the spray gas, through the middle gap 53 the solution to be sprayed.

The annular gap nozzle 50 has a rod-shaped body 56 which extends downwards and contains the corresponding channels and supply lines, which are known per se and therefore not shown in the drawing. The annular gap nozzle 50 For example, it may be formed with a so-called rotary annular gap, in which walls of the channel through which the solution is sprayed rotate relative to each other to prevent clogging of the nozzle, so that sprayed uniformly from the gap 53 over the 360 ° surrounding angle can be.

The annular gap nozzle 50 has a conical head 57 above the mouth gap 52.

In the area below the mouth gap 54, a frusto-conical wall 58 is present, which has numerous openings 59. As can be seen from Fig. IB, the bottom of the frusto-conical wall 58 rests on the innermost ring plate 29 such that between the bottom of the frusto-conical wall 58 and the underlying, with this partially overlapping ring plate 29, a slot 60 is formed through the process air 40 can pass through.

The outer ring 25 is spaced from the wall 18 so that process air 40 can enter the process chamber 15 in the direction of the arrow indicated by the reference numeral 61 with a predominantly vertical component and thereby the process air 40 entering the process chamber 15 through the slots 28 gives relatively strong upward component.

The right-hand half of FIG. 1A shows which conditions form in a run-in state in the device 10.

From the mouth gap 53 exits a spray cloud 70 of the solution, the horizontal mirror plane is approximately parallel to Ground level runs. Through the openings 59 in the frusto-conical wall 58 passing air, which may be, for example, process air 40, forms on the underside of the spray cloud 70, a supporting air flow 72 from. The process air 40 passing through the numerous slots 28 forms a radial flow in the direction of the wall 18, from which the process air 40 is deflected upward, as shown by the arrow indicated by the reference numeral 74. From the deflected process air 40, the catalyst carriers are guided in the area of the wall 18 upwards. The process air 40 and the catalyst carriers to be treated then separate from each other, with the process air 40 being discharged through outlets, while the catalyst carriers move radially inwardly as indicated by arrows 75 and vertically downwardly toward the conical head 57 of the annular die 50 due to gravity hike. There, the moving catalyst carriers are deflected, passed to the top of the spray cloud 70 and treated there with the sprayed medium. The sprayed catalyst carrier then move back towards the wall 18 and away from each other, as to

Leaving the spray cloud 70 at the annular orifice gap 53, the catalyst carriers a circumferentially larger space is available. In the area of the spray cloud 70, the catalyst carriers to be treated meet with the sprayed solution and are moved away from each other in the direction of movement of the wall 18, treating them very evenly and harmoniously with the heated process air 40, ie. dried.

FIG. 2A shows two possible trajectories of two elliptically circulating catalyst supports by means of the curve progressions denoted by the reference symbols 210 and 220. The elliptical trajectory 210 has relatively large changes in the size of the major and minor axis compared to an ideal elliptical path. The elliptical trajectory 220, in contrast, has relatively small changes in the size of the major and minor axes and describes nearly an ideal elliptical trajectory without any circumferential (horizontal) motive component, as shown in FIG. 2B.

In FIG. 3A, a possible trajectory of a toroidally circulating catalyst carrier is shown by means of the curve course indicated by the reference numeral 310. The toroidal trajectory 310 describes a section of the surface of a nearly uniform torus whose vertical section is elliptical and whose horizontal section is annular. FIG. 3B shows the movement path 310 in plan view.

The following examples serve to illustrate the invention.

Examples 1 and 2:

500.0 g of an acid-treated dried powdered bentonite (acid-activated bentonite) with the main constituent montmorillonite as phyllosilicate were mixed with a quantity corresponding to 61.875 g of ZrO ₂ (Example 1) or with a quantity corresponding to 132 g of ZrO ₂ (Example 2) on commercial Zr ( OK) ₄ with a d _iö value of about 1 _.mu.m , - a d _E0 value of about 5 .mu.m and with a d ₉₀ value of 7 .mu.m and with 10 g of a conventional organic binder / pore former mixed together.

The resulting mixture was mixed with water and processed by means of a mixer into a dough, from which spherical shaped bodies (d = 5 mm) were produced by means of a tablet press under pressure. For curing, the balls were dried and calcined at a temperature of 650 ⁰ C over a period of 5 h. After calcination, the moldings were treated with 20% hydrochloric acid over a period of 30 hours, washed extensively with water and calcined at a temperature of 600 ^° C. for a period of 5 hours. The moldings thus obtained have the characteristics listed in Table 1 (Example 1) or Table 2 (Example 2):

Table 1:

Tabelle 2:

Table 2:

Beispiel 3 :

Example 3:

70 g catalyst carrier according to Example 1 were measured by temperature-controlled at a temperature of 90 ⁰ C air in a fluidized bed reactor of the type ^"® Innojet Aircoater 25" Innojet Technologies, Steinen, Germany in a

Fluidized bed state offset in which the catalyst carrier toroidal circulated.

After the catalyst supports were heated to a temperature of 90 ⁰ C, the toroidal were circulating

Catalyst support over a period of 0.5 h with a solution prepared from 150 ml of water and 11.35 g of a 8.82% Pd (NH ₃ ) ₄ (OH) ₂ solution (based on Pd 4.5%) sprayed ,

After the solution had been sprayed onto the supports, the loaded catalyst supports were calcined in air over a period of 2 hours at a temperature of 350 ^° C.

After the catalyst supports had been calcined, they were again placed in a fluidized bed state in which the catalyst supports toroidally circulated by means of air heated to a temperature of 90 ° C. in said device. After the catalyst supports had been heated to a temperature of 90 ^° C., the toroidally circulating catalyst supports were prepared over a period of 0.5 h with a solution of 150 ml of water and 4.4 g of an 8.44% strength KAuO ₂ solution ( based on Au 6.2%) sprayed.

To reduce the noble metal components, the catalyst supports were exposed to a mixture of 5% by volume of hydrogen in nitrogen over a period of 5 hours and at a temperature of 200 ^° C. After reducing, the catalyst supports were impregnated with an aqueous potassium acetate solution by the incipient wetness method and then dried under a nitrogen atmosphere for a period of 1 hour at a temperature of 120 ^° C. The proportion of the coated catalyst thus obtained was 2 , 6 wt .-% (calculated on the amount of potassium acetate used).

The theoretical loading of the supports with Pd is 0.73% by weight and 0.39% by weight Au, the experimental loading was 0.66% by weight Pd and 0.36% by weight Au (by means of Inductively Coupled plasma (ICP) determined; Au / Pd atomic ratio: 0.29).

The shell thickness was 124 μm (mean value).

38 catalyst balls were in a fixed bed tube reactor at a temperature of 153 ⁰ C at 10 bar with a feed gas flow of 550 ml / min composed of 15 vol .-% HOAc, 6 vol .-% O ₂ , 39 vol .-% C ₂ H ₄ acted in N ₂ and the reactor effluent analyzed by gas chromatography.

The selectivity (to ethylene Alkylenacetat) is calculated according to the formula S (C ₂ H ₄₎ = mole Alkenylacetat / (mole Alkenylacetat + CO ₂ mole / 2). The space-time yield is obtained as g alkenyl acetate / 1 catalyst / h. The oxygen conversion is calculated according to (mole O ₂ in-mole O ₂ out) / mole O ₂ in.

The catalyst according to the invention shows a selectivity S (C ₂ H ₄ ) of 91.0% and a space-time yield (determined by gas chromatography) of 922 g alkenyl acetate / 1 catalyst / h at an oxygen conversion of 64.0%. Example 4:

70 g catalyst carrier according to Example 2 were measured by temperature-controlled at a temperature of 90 ⁰ C air in a fluidized bed reactor of the type ^"® Innojet Aircoater 25" Innojet Technologies, Steinen, Germany in a

Fluidized bed state offset in which the catalyst carrier toroidal circulated.

After the catalyst supports were heated to a temperature of 90 ⁰ C, the toroidal were circulating

Catalyst support over a period of O, 5 h with a solution prepared from 150 ml of water and 3.58 g of a 8.82% Pd (NH ₃ ) ₄ (OH) ₂ solution (based on Pd 4.5%) sprayed.

After the solution had been sprayed onto the supports, the loaded catalyst supports were calcined in air over a period of 2 hours at a temperature of 350 ^° C.

After the catalyst supports had been calcined, they were again placed in a fluidized bed state in which the catalyst supports toroidally circulated by means of air heated to a temperature of 90 ° C. in said device. After the catalyst support were heated to a temperature of 90 ⁰ C, the toroidally circulating catalyst carrier over a period KAuö ₂ solution (were of O, 5 h with a solution made of 150 ml of water and 3.84 g of a 8.44% strength by weight based on Au 6.2%) sprayed.

To reduce the noble metal components, the catalyst supports were exposed to a mixture of 5% by volume of hydrogen in nitrogen over a period of 5 hours and at a temperature of 200 ^° C. After reducing, the catalyst supports were impregnated with an aqueous potassium acetate solution by the incipient wetness method and then dried under a nitrogen atmosphere for a period of 1 hour at a temperature of 120 ^° C. The proportion of the coated catalyst thus obtained was 2 , 6 wt .-% (calculated on the amount of potassium acetate used.

The theoretical loading of the supports with Pd is 0.23% by weight and 0.34% by weight Au; the experimental loading was 0.21 wt.% Pd and 0.31 wt.% Au (determined by (ICP); Au / Pd atomic ratio: 0.8).

The shell thickness was 130 μm (mean value).

38 catalyst spheres were in a fixed bed tubular reactor at a temperature of 147.6 ⁰ C in 10 bar with a feed gas stream of 550 ml / min composed of 15 vol .-% HOAc, 6 vol .-% O _2, 39 vol .-% C ₂ H ₄ acted upon in N ₂ and the reactor effluent analyzed by gas chromatography.

The catalyst according to the invention shows a selectivity S (C ₂ H ₄ ) of 95.7% and a space-time yield (determined by gas chromatography) of 408 g alkenyl acetate / 1 catalyst / h at an oxygen conversion of 28.5%.

Claims

claims A coated catalyst comprising a ZrO ₂ -containing Catalyst support having a shell in which Pd and Au are contained, wherein the Au / Pd atomic ratio of the shell catalyst is 0.2 to 1.2, characterized in that the proportion of the shell catalyst in Pd is less than or equal to 0.75 wt. % is. 2. coated catalyst according to claim 1, characterized in that the proportion of the coated catalyst of Pd 0.75 wt .-% to 0.15 wt .-% is. 3. coated catalyst according to one of the preceding claims, characterized in that the Au / Pd atomic ratio of the shell catalyst is 0.3 to 1.0. 4. coated catalyst according to one of the preceding claims, characterized in that at least 50 wt .-% of the ZrO ₂ contained in the catalyst support are present in tetragonal modification. 5. coated catalyst according to one of the preceding claims, characterized in that the ZrO ₂ is present in particulate form. 6. coated catalyst according to one of the preceding claims, characterized in that the ZrO _{2 is} uniformly distributed in the catalyst support. 7. coated catalyst according to one of the preceding claims, characterized in that the proportion of the catalyst support to ZrO ₂ 1 wt .-% to 30 wt .-% is. 8. coated catalyst according to one of the preceding claims, characterized in that the catalyst support comprises a natural layered silicate. 9. coated catalyst according to one of the preceding claims, characterized in that the natural phyllosilicate is an acid-activated phyllosilicate. 10. coated catalyst according to claim 8 or 9, characterized in that the proportion of the catalyst support of natural phyllosilicate is at least 50 wt .-%. 11. coated catalyst according to one of claims 8 to 10, characterized in that the natural phyllosilicate contained in the catalyst support has a SiO ₂ content of at least 65 wt .-%. 12. coated catalyst according to one of claims 8 to 11, characterized in that the natural phyllosilicate contained in the carrier contains less than 5 wt .-% Al ₂ O ₃ . 13. A coated catalyst according to any one of the preceding claims, characterized in that the catalyst support has an acidity of 1 μval / g to 150 μval / g. 14. A coated catalyst according to any one of the preceding claims, characterized in that the catalyst support has an average pore diameter of 8 nm to 30 nm. 15. coated catalyst according to one of the preceding claims, characterized in that the Catalyst support has a specific surface area of less than or equal to 180 τn ² / g. 16. coated catalyst according to one of the preceding claims, characterized in that the catalyst support has a specific surface area of 180 m ² / g to 60 m ² / g. 17. coated catalyst according to one of the preceding claims, characterized in that the catalyst support has a hardness of greater than or equal to 55 N. 18. coated catalyst according to one of the preceding claims, characterized in that the catalyst support has an integral pore volume of 0.25 ml / g to 0.7 ml / g. 19. coated catalyst according to one of the preceding claims, characterized in that at least 80% of the integral pore volume of the catalyst support of mesopores and macropores are formed. 20. coated catalyst according to one of the preceding claims, characterized in that the catalyst support has a bulk density of greater than 0.3 g / ml. 21. coated catalyst according to one of the preceding claims, characterized in that the catalyst support is formed as a shaped body. 22. coated catalyst according to one of the preceding claims, characterized in that the Catalyst support has a maximum dimension of 1 mm to 25 mm. 23. coated catalyst according to claim 21 or 22, characterized in that the catalyst support is a ball. 24. coated catalyst according to claim 23, characterized in that the ball has a diameter of 2 mm to 10 mm. 25. coated catalyst according to one of the preceding claims, characterized in that the catalyst support is doped with at least one oxide of a metal selected from the group consisting of Hf, Ti, Nb, Ta, W, Mg, Re, Y and Fe. 26. coated catalyst according to claim 25, characterized in that the proportion of the catalyst support to doping 1 wt .-% to 20 wt .-% is. 27. Shell catalyst according to one of the preceding Claims, characterized in that the thickness of the shell is 30 microns to 500 microns. 28. A process for the preparation of a coated catalyst according to any one of claims 1 to 27, comprising Generating a fluidized bed of catalyst carriers by means of a gas, wherein the catalyst carriers move in the fluidized bed on an elliptical or toroidal path; - Spraying moving in the fluidized bed on an elliptical or toroidal path A catalyst support comprising a first solution in which a Pd precursor is dissolved; Spraying the catalyst support moving in the fluidized bed on an elliptical or toroidal orbit with a second solution in which an Au precursor is dissolved. 29. The method according to claim 28, characterized in that the catalyst carriers move in the fluidized bed on a toroidal path. 30. The method according to claim 28 or 29, characterized in that the method further comprises - Drying of sprayed with the first and / or second solution catalyst support. 31. The method according to any one of claims 28 to 30, characterized in that the method further comprises Calcination of the catalyst supports sprayed with the first and / or second solution at a temperature at which the metal component of the metal precursor / precursor sprayed onto the catalyst supports is converted into an oxidic form. 32. The method according to any one of claims 28 to 31, characterized in that the method further comprises - Transferring the Pd component of the Pd precursor and the Au component of the Au precursor in the oxidation state 0th 33. The method according to any one of claims 28 to 32, characterized in that the first solution and the second solution are one and the same solution. 34. The method according to any one of claims 28 to 33, characterized in that the Pd precursor Pd (NH ₃ J ₄ (OH) ₂ is. 35. The method according to any one of claims 28 to 34, characterized in that the Au precursor KAuO ₂ . 36. The method according to any one of claims 28 to 35, characterized in that the first solution and the second solution are aqueous solutions. 37. The method according to any one of claims 28 to 36, characterized in that the method using a Device (10) is arranged, which is adapted by means of a gas (40) to produce a fluidized bed of a particulate material, wherein the particles of the material move in the fluidized bed on an elliptical or toroidal path. 38. The method according to claim 37, characterized in that the device (10) comprises a process chamber (15) having a bottom (16) and a side wall (18), wherein the gas (40) through the bottom (16) of the process chamber ( 15), which is preferably constructed of a plurality of overlapping, overlapping annular guide plates (25, 26, 27, 23), between which annular slots (28) are formed, with horizontal, radially outwardly directed component of movement into the process chamber (15 ) is introduced to produce the catalyst support fluidized bed. 39. Method according to claim 38, characterized in that a circumferential flow component is imposed on the gas (40) introduced into the process chamber (15). 40. Method according to claim 39, characterized in that the circumferential flow component is imposed on the gas (40) introduced into the process chamber (15) by means of guide elements arranged between the annular guide plates (25, 26, 27, 29). 41. Method according to claim 39 or 40, characterized in that the peripheral flow component is imposed on the gas (40) introduced into the process chamber (15) by introducing additional gas (61) through the bottom (16) of the process chamber (15) obliquely upward movement component is introduced into the process chamber (15). 42. The method according to any one of claims 38 to 41, characterized in that the spraying moving in the fluidized bed on an elliptical or toroidal path Catalyst support with the solution by means of an annular gap nozzle (50) is performed, which sprays a spray cloud (70) which is substantially parallel to the plane of the bottom (16). 43. The method according to claim 42, characterized in that the annular gap nozzle (50) is arranged centrally on the bottom (16) and the mouth (55) of the annular gap nozzle (50) is embedded in the fluidized bed. 44. The method of claim 42 or 43, characterized in that on the underside of the spray cloud (70), a Gasstützpolster (72) is accomplished. 45. The method according to any one of claims 28 to 44, characterized in that the gas (40) is selected from the group consisting of air, oxygen, nitrogen and the noble gases and mixtures of the above gases. 46. The method according to any one of claims 28 to 45, characterized in that the spraying of the catalyst support with the first solution and / or with the second solution at a temperature of greater than or equal to 60 ⁰ C is performed. 47. The method according to any one of claims 38 to 46, characterized in that the gas (40) before the introduction into the process chamber (15) is enriched with the solvent of the first, the second or the first and second solution. 48. coated catalyst according to one of claims 1 to 27 obtainable by means of a method according to any one of claims 28 to 47. 49. Use of a coated catalyst according to any one of claims 1 to 27 or according to claim 48 in the production of alkenyl acetates.