Shell catalyst for producing alkenyl carboxylic acid esters with improved Pd distribution

Abstract

The present invention relates to a shell catalyst comprising Pd and Au, characterized by improved Pd distribution, and also to two processes for producing said catalyst, and a process for producing vinyl acetate monomer using said catalyst.

Description

[Technical Field]

[0001] The present invention relates to a shell catalyst containing Pd and Au, characterized by an improved distribution of Pd. The present invention also relates to two methods for producing this catalyst and a method for producing vinyl acetate monomer using this catalyst. [Background technology]

[0002] Shell catalysts have been used for many years in various catalytic processes. They are characterized by the fact that catalytically active species are distributed not throughout the entire catalyst support, but only in the shell region around the center of the catalyst support.

[0003] One application area is the production of vinyl acetate monomer (VAM) by the reaction of ethylene, acetic acid, and oxygen. Shell catalysts containing Pd and Au compounds as catalytic active species, and which can also contain various accelerators, are widely used here.

[0004] Therefore, Patent Document 1 (WO2008 / 145388A1) describes the production of a Pd-containing shell catalyst and an Au-containing shell catalyst in which the application of catalytic active species is carried out by spray impregnation of a fluidized bed of catalyst support. The resulting shell-like region of catalytic active species has a nearly constant distribution of catalytic active species.

[0005] In Patent Document 2 (WO2005 / 065821A1), the pore structure of the catalyst support is supported by absorption of a solution containing catalytically active species. Alternatively, a mixture of catalytically active species and a binder material is coated onto the surface of the catalyst support. The distribution of catalytically active species is unfavorable because it either spreads deeply into the interior of the support or forms an outer layer where the distribution is very uniform over a relatively large area of ​​the coated shell. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] WO2008 / 145388A1 [Patent Document 2] WO2005 / 065821A1 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Shell catalysts containing Pd and Au, characterized by improved Pd concentrations, are still sought after for improved catalytic performance. [Means for solving the problem]

[0008] This objective is achieved by a shell catalyst containing Pd and Au, wherein the palladium concentration profile in the shell catalyst matches an asymmetric Gaussian distribution, the maximum palladium concentration is within 0 to 40 micrometers from the geometric surface of the catalyst body, the palladium is present in a region of shell thickness 30 to 200 μm, the full width at half maximum (FWHM) of the concentration distribution is 10 to 70 μm, and the asymmetry of the Gaussian distribution is characterized by a ratio of 0.05 to 0.55 between the left-hand value of the FWHM and the right-hand value.

[0009] The present invention further provides a first method for producing a shell catalyst according to the present invention. The first method includes the following steps: (a) A step of recirculating the catalyst support bed and heating the bed to a temperature of 60°C to 120°C during the recirculation operation; (b) A step of spraying the dissolved Pd-containing precursor compound and the dissolved Au-containing precursor compound onto the recirculating catalyst bed, wherein, when applied simultaneously, the temperature is 5°C to 30°C, preferably 7°C to 25°C, and most preferably 10°C to 20°C lower than the temperature in step (a), and when applied continuously, the temperature of the first application is 5°C to 30°C, preferably 7°C to 25°C, and most preferably 10°C to 20°C lower than the temperature in step (a).

[0010] The catalyst according to the present invention can also be produced by a second production method according to the present invention. The second production method includes the following steps: (a) A step of recirculating the catalyst support bed and bringing the bed into contact with sprayed water at a temperature in the range of 55°C to 110°C; (b) A step of spraying the dissolved Pd-containing precursor compound and the dissolved Au-containing precursor compound onto the recirculating catalyst bed, either continuously or simultaneously, wherein if applied simultaneously, the temperature is the same as in step (a), and if applied continuously, the temperature of the first application is the same as in step (a). [Effects of the Invention]

[0011] Surprisingly, the method according to the present invention makes it possible to produce shell catalysts in which the Pd distribution inside individual catalyst molded bodies is improved, the Pd concentration distribution is in the form of an asymmetric Gaussian distribution, the maximum Pd concentration is within a range of 0 to 40 micrometers from the surface of the catalyst molded body, palladium is present in a region of shell thickness of 30 to 200 μm, the full width at half maximum of the concentration distribution is 10 to 70 μm, and the asymmetry of the Gaussian distribution is characterized by a ratio of the left value of the full width at half maximum to the right value of the full width at half maximum of 0.05 to 0.55. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows the experimental data points for Pd concentration for catalyst 1 of the example, and a plot of the sigmoid function determined by the same measurement method used to determine the starting point of the geometric surface after measuring the xsurface. [Figure 2] Figure 2 shows a plot of the curve for catalyst 1 obtained using experimental data points for Pd concentration and an appropriate fitting function in the example. [Figure 3] Figure 3 shows a plot of the curve for catalyst 2 obtained using experimental data points for Pd concentration and an appropriate fitting function in the example. [Figure 4]Figure 4 shows a plot of the curve of Catalyst 3 obtained using the experimental data points of Pd concentration and an appropriate fitting function in the examples. [Figure 5] Figure 5 shows the curves of Catalysts 1, 2, and 3 obtained using an appropriate fitting function in the examples. [Figure 6] Figure 6 shows the selectivities at different space-time yields of Catalysts 1 and 2, and the plots of their trend lines, in the reaction of acetic acid, ethylene, and oxygen to obtain vinyl acetate monomer in the examples.

Mode for Carrying Out the Invention

[0013] In the present specification, the shell catalyst is a catalyst molded body containing Pd and Au, wherein the Pd compound and the Au compound are present in the outer region of the carrier as catalytic active species, forming a so-called shell, and the inside of the catalyst molded body is substantially free of the Pd compound and the Au compound. The shell usually shows a high concentration of catalytic active species in a shallow region of the catalyst molded body.

[0014] Regarding the two methods according to the present invention, the shell catalyst is in the form of a catalyst molded body after step (b), and prior to this, the catalyst carrier is involved.

[0015] The maximum value of the Pd concentration in the shell catalyst is within the range of 0 to 40 micrometers, preferably 5 to 40 micrometers, preferably 5 to 35 micrometers, particularly preferably 5 to 30 micrometers, from the geometric surface of the catalyst molded body in each case.

[0016] The shell catalyst includes a Pd-containing shell having a thickness of 30 to 200 micrometers, preferably 40 to 180 micrometers, particularly preferably 50 to 160 micrometers, and most preferably 60 to 140 micrometers.

[0017] In one embodiment, the shell catalyst has a Pd concentration profile with a full width at half maximum (FWHM) in the range of 45 to 65 μm. In another embodiment, the shell catalyst has a Pd concentration profile in an asymmetric Gaussian distribution, and the ratio of the left value of the FWHM to the right value of the FWHM is in the range of 0.05 to 0.55, preferably 0.05 to 0.45, and particularly preferably 0.05 to 0.35.

[0018] Recirculating the catalyst bed is typically done using a suitable fluidized bed apparatus. Such apparatuses are sold by Glatt GmbH (Binsen, Germany), Aeromatic-Fielder AG (Büdendorf, Switzerland), FluidAir Inc (Aurora, Illinois, USA), Huettlin GmbH (Steinen, Germany), Umang Pharmatech Ltd. (Maharaschlein, Germany), and Romaco Pharmatechnik GmbH (Karlsruhe, Germany). Fluidized bed apparatuses particularly preferred for carrying out the process according to the present invention are commercially available from Romaco Pharmatechnik GmbH under the trade names Innojet® Ventilus or Innojet® AirCoater. These apparatuses include a cylindrical container with a fixed and immovable base, in which a spray nozzle is mounted. The base consists of circular vanes mounted in a stepped, overlapping manner. The process air flows horizontally and with a circumferential flow component toward the outward-facing container wall, between the individual blades into the container.

[0019] This forms a so-called sliding air layer, in which the molded catalyst support is initially carried outward towards the container wall. On the outer container wall, process air is provided, directed vertically upwards, to guide the catalyst support. Upon reaching the upper end, the catalyst support returns along a path tangential to the center of the base, passing through a spray mist from a nozzle in the process. After passing through the spray mist, the above operation resumes. The control of the process air provides the basis for a substantially homogeneous toroidal fluidized bed-like recirculation operation of the catalyst support.

[0020] In the manufacturing method according to the present invention, it is preferable to create a fluidized bed in which the recirculating molded body moves along an elliptical or toroidal path. In the prior art, the point at which the bed particles transition to a state in which they can move completely freely (fluidized bed) is called the minimum fluidization point, and the associated fluid velocity is called the minimum fluidization velocity.

[0021] In the manufacturing method according to the present invention, the fluid velocity is preferably up to four times the minimum fluidization velocity, preferably up to three times the minimum fluidization velocity, and more preferably up to twice the minimum fluidization velocity.

[0022] In the manufacturing method according to the present invention, the catalyst support is recirculated in the fluidized bed along an elliptical or toroidal path, preferably a toroidal path. According to the present invention, "elliptical recirculation" means that the catalyst support in the fluidized bed moves along an elliptical path in the vertical plane, where the first and second axes have different sizes. In the case of "toroidal recirculation," the catalyst support in the fluidized bed moves along an elliptical path in the vertical plane, where the first and second axes have different sizes, and along a circular path in the horizontal plane, where the radii have different sizes.

[0023] On average, in the case of "elliptic recirculation," the catalyst support moves along an elliptic path in the vertical plane, and in the case of "toroidal recirculation," it moves along a toroidal path; that is, the catalyst support moves helically along the surface of a torus having a vertical elliptic cross-section.

[0024] In one embodiment, an acetate is applied to the catalyst support before coating the Pd-containing precursor compound and the Au-containing precursor compound. This is preferably done using a solution containing the acetate. The solvent used to prepare the solution is preferably water, more preferably deionized water. The acetate used is typically an alkali metal acetate, preferably potassium acetate.

[0025] The application of the acetate solution can be carried out by any method known in the prior art, such as wet chemical impregnation, pore filling (initial wetting), and any type of spray impregnation.

[0026] The application of acetate is preferably carried out before step a) of the manufacturing method according to the present invention.

[0027] When the acetate is in the form of an alkali metal acetate, the amount of alkali metal added is in an appropriate stoichiometric ratio to the acetate anion.

[0028] After applying the acetate-containing solution, it is preferable to dry the material in the atmosphere, dilute air, or inert gas at a temperature range of 70°C to 120°C, more preferably 80°C to 110°C, and most preferably 90°C to 100°C. The drying time for the acetate-containing carrier is preferably in the range of 10 to 100 minutes, more preferably 30 to 60 minutes.

[0029] The drying of the acetate-containing carrier can be carried out in a conventional drying apparatus or in a coating apparatus. When drying is carried out in a coating apparatus, it is preferable that the carrier is kept in a steady state within it, that is, that it is kept in motion. When a moving bed or fluidized bed apparatus is used, the carrier preferably does not move within the moving bed or fluidized bed during drying.

[0030] In step (b), the dissolved Pd precursor compound and the dissolved Au precursor compound are applied to a catalyst support bed that undergoes recirculation.

[0031] Examples of preferred Pd precursor compounds are water-soluble Pd salts. Particularly preferred are Pd precursor compounds selected from the group consisting of Pd(NH3)4(HCO3)2, Pd(NH3)4(HPO4), ammonium Pd oxalate, Pd oxalate, Pd(K2 oxalate)2, Pd(II) trifluoroacetate, Pd(NH3)4(OH)2, Pd(NO3)2, H2Pd(OAc)2(OH)2, Pd(NH3)2, Pd(NH3)4(NO3)2, H2Pd(NO2)4, Na2Pd(NO2)4, Pd(OAc)2, and newly precipitated Pd(OH)NO2.

[0032] When newly precipitated Pd(OH)2 is used, it is preferably prepared as follows: A 0.1% to 40% by weight aqueous solution is preferably prepared from tetrachloropalladium. Then, preferably, a base is added to this aqueous solution until a brown solid, i.e., Pd(OH)2, precipitates. To prepare a solution to be coated onto a catalyst support, the newly precipitated Pd(OH)2 is isolated, washed, and dissolved in an alkaline aqueous solution.

[0033] The compound Pd(NH3)4(OH)2 is preferably prepared as follows: A precursor compound, for example, Na2PdCl4, is precipitated with potassium hydroxide as described above to obtain palladium hydroxide and precipitate, which are filtered and washed, and then dissolved in ammonia water to obtain Pd(NH3)4(OH)2.

[0034] The manufacturing method according to the present invention can also use nitrite Pd compounds. Preferred nitrite Pd precursor compounds can be obtained, for example, by dissolving Pd(OAc)2 in a NaNO2 or KNO2 solution.

[0035] A preferred example of an Au precursor compound is a water-soluble Au salt. According to a particularly preferred embodiment of the method according to the present invention, the Au precursor compound is selected from the group consisting of KAuO2, NaAuO2, CsAuO2, NMe4AuO2, KAuCl4, (NH4)AuCl4, HAuCl4, KAu(NO2)4, NaAu(NO2)4, CsAu(NO2)4, KAu(OAc)3(OH), NaAu(OAc)3(OH), CsAu(OAc)3(OH), HAu(NO3)4, and Au(OAc)3. It is preferable to precipitate the oxide / hydroxide from an acidic solution of gold, wash and isolate the precipitate, and dissolve it in acetic acid or KOH to produce new Au(OAc)3 or KAuO2 each time.

[0036] In the specification of the present invention, the dissolved Pd-containing precursor compound and the Au-containing precursor compound are understood to be compounds that exist in a dissolved form in a solvent, preferably water, an aqueous base, or an aqueous acid.

[0037] In the specification of this invention, salts are described as water-soluble if they are sufficiently soluble in water, aqueous bases, or aqueous acids.

[0038] The Pd precursor compound and Au precursor compound are preferably selected so as not to contain catalyst poisons. After coating with the noble metal compound, the catalyst molded body is preferably simply dried, preferably in the same fluidized bed coating apparatus in which the coating was performed. The precursor compound is particularly preferably substantially chloride-free.

[0039] "Substantially chloride-free" means that the molecular formula of the compound does not contain chlorides; however, this does not rule out the possibility that the compound may contain chloride impurities that are unavoidable as a result of manufacturing, for example. The chloride content in substantially chloride-free Pd and Au precursor compounds is a maximum of 125 ppm per weight percent of Pd and Au in the precursor compound.

[0040] The application of the Pd-containing precursor compound and the Au-containing precursor compound is carried out by sequential, i.e., continuous or simultaneous, spray application of the dissolved Pd-containing precursor compound and the dissolved Au-containing precursor compound onto a recirculating catalyst support bed.

[0041] This coating can be performed by simultaneously applying a Pd-containing precursor compound solution and an Au-containing precursor compound solution. Alternatively, it can also be performed by applying solutions of the Pd-containing precursor compound and the Au-containing precursor compound separately.

[0042] Alternatively, the process may be carried out by sequential coating, using a Pd-containing precursor compound solution in the first step and an Au-containing precursor compound solution in the second step, or using an Au-containing precursor compound solution in the first step and a Pd-containing precursor compound solution in the second step.

[0043] In one embodiment, when applied sequentially, the solution applied in the second step contains both a Pd-containing precursor compound and an Au-containing precursor compound.

[0044] If the shell catalyst contains multiple different catalytic active species, such as one or more active metals and promoting metals in the shell, the method according to the present invention may be applied to the catalyst support molded body the required number of times.

[0045] Alternatively, the manufacturing method according to the present invention can be carried out using a mixed solution containing different catalytically active species or their precursors as desired. Furthermore, in the manufacturing method according to the present invention, each solution of the catalytically active species or its precursor can be simultaneously sprayed onto the catalyst support.

[0046] The process gas used in the manufacturing method according to the present invention is typically air. In further embodiments, an inert gas, such as nitrogen, methane, short-chain saturated hydrocarbons, noble gases, preferably helium, neon, or argon, or halogenated hydrocarbons may be used, or a mixture of two or more of these may be used.

[0047] The heating of the catalyst support in steps (a) and (b) of the first manufacturing method according to the present invention makes it possible to control the width of the formed noble metal shell. This is because, when a combination of Pd-containing precursor compounds and Au-containing precursor compounds is applied, the evaporation of at least one solution, preferably an aqueous solution, applied in step (b) becomes faster depending on the temperature, or when Pd-containing precursor compounds and Au-containing precursor compounds are applied in succession, the evaporation of the first solution, preferably an aqueous solution, applied in step (b) becomes faster, thereby suppressing the diffusion of the noble metal into the support.

[0048] For example, at relatively high temperatures, the drying rate is relatively high, and the solution in contact with the catalyst support dries quickly. As a result, the solution applied to the catalyst support does not penetrate deeply into the support. Therefore, at relatively high temperatures, it is possible to obtain a relatively thin shell containing a large number of active species.

[0049] Surprisingly, in the first manufacturing method according to the present invention, it has been found that heating the catalyst support in step (a) to a temperature 5°C to 30°C, preferably 7°C to 25°C, and most preferably 10°C to 20°C higher than the coating temperature, or, in the case of sequential coating, higher than the temperature of the first coating in step (b), makes it possible to advantageously control the distribution of Pd, with the maximum Pd concentration being within a range of 0 to 40 micrometers from the surface of the catalyst molded body, palladium being present in a shell thickness region of 30 to 200 μm, and the full width at half maximum of the concentration distribution being 10 to 70 μm.

[0050] The temperature of the catalyst support set in process (a) / (b) is controlled by measuring the exhaust temperature / floor temperature and performing additional control as needed.

[0051] The temperature set in step (a) is in the range of 60°C to 120°C, preferably 65°C to 110°C, and particularly preferably 70°C to 100°C.

[0052] The coating temperature, or the initial coating temperature set in step (b) in the case of continuous coating, is in the range of 55°C to 115°C, preferably in the range of 55°C to 110°C, more preferably in the range of 60°C to 100°C, and particularly preferably in the range of 65°C to 90°C.

[0053] When applying the coatings sequentially, the second coating can be performed at the same temperature as the first coating. In one embodiment, the temperature during the second coating is 5°C to 30°C higher, preferably 5°C to 20°C higher, and most preferably 5°C to 10°C higher, than the temperature during the first coating.

[0054] In step (a) of the second manufacturing method according to the present invention, the spraying of water can be controlled so that the width of the formed noble metal shell is approximately the same. This is because the water evaporates during contact with the catalyst support, resulting in a temporary temperature drop of the catalyst support which is then corrected by the temperature control of the coating apparatus, and the subsequent application of the metal-containing aqueous solution can be carried out at the desired temperature. Therefore, the aqueous solution applied in step (b) can be evaporated more quickly, or in the case of continuous application, the first solution applied can be evaporated more quickly, thereby reducing the diffusion of the noble metal into the interior of the support.

[0055] For example, at relatively high temperatures, the drying rate is relatively high, and the solution in contact with the catalyst support dries quickly. As a result, the solution applied to the catalyst support does not penetrate deeply into the support. Therefore, at relatively high temperatures, it is possible to obtain a relatively thin shell containing a large number of active species.

[0056] The temperature of the catalyst support set in process (a) / (b) is controlled by measuring the exhaust temperature / floor temperature and performing additional control as needed.

[0057] The temperature set in step (a) is in the range of 55°C to 110°C, preferably 60°C to 100°C, and particularly preferably 65°C to 90°C.

[0058] The coating temperature, or the initial coating temperature set in step (b) in the case of continuous coating, is the same as in step (a), and is in the range of 55°C to 110°C, preferably 60°C to 100°C, and particularly preferably 65°C to 90°C.

[0059] When applying the coatings sequentially, the second coating can be performed at the same temperature as the first coating. In one embodiment, the temperature between the second and second coatings is 5°C to 30°C, preferably 5°C to 20°C, and most preferably 5°C to 10°C higher.

[0060] In the manufacturing method according to the present invention, the drying of the catalyst support sprayed with the solution is preferably carried out continuously using a process gas.

[0061] In one embodiment of the manufacturing method according to the present invention, the catalyst support is subjected to a fixation step after step (b) in which a catalytically active species or its precursor is immobilized on the catalyst support. Suitable means include spraying a caustic alkali solution onto the catalyst support bearing the noble metal compound, or immersing the catalyst support in a caustic alkali solution.

[0062] Next, a water treatment is performed to remove excess caustic alkali solution from the catalyst support. This step is particularly suitable when the coated Pd or any Au precursor compound contains components that act as catalyst poisons, such as the corresponding Pd or Au chloride, especially in the production of VAM.

[0063] In a preferred embodiment, the catalyst support obtained after step (b) is heat-treated at a temperature in the range of 300°C to 600°C, particularly for 1 to 6 hours, to convert the precursor compound into the corresponding hydroxide compound / oxide. In a further embodiment, the catalyst support obtained after step (b) is dried at a temperature in the range of 80°C to 200°C, preferably 100°C to 150°C.

[0064] In a further embodiment, the catalyst support obtained after step (b) is not subjected to a fixation step, but is dried at a temperature in the range of 80°C to 200°C, preferably 100°C to 150°C.

[0065] It is particularly preferable not to perform drying or heat treatment in the range of 300°C to 600°C after step (b) and before reduction in step (c).

[0066] In one embodiment, step (b) is followed by step (c), which includes heat-treating the catalyst molded body obtained after step (b) in a non-oxidizing atmosphere to reduce the metallic component of the precursor compound to an elemental metal.

[0067] The reduction in step (c) can be carried out in the fluidized bed coating apparatus itself or in a separate reduction reactor. When the reduction is carried out in the fluidized bed coating apparatus, it is typically done using a mixture of hydrogen and nitrogen in an amount of 2% to 5% by volume, at a temperature in the range of 70°C to 150°C, for example, for 30 minutes to 5 hours.

[0068] When carried out in a separate reduction reactor, it is typically done using a mixture of 2% to 5% by volume of hydrogen in nitrogen, for example, as a foaming gas, at a temperature preferably in the range of 70 to 500°C for 30 minutes to 5 hours.

[0069] Further suitable reducing agents include ethylene, CO, NH3, formaldehyde, methanol, and hydrocarbons, where the reducing agent may also be diluted with an inert gas, such as carbon dioxide, nitrogen, or argon. It is preferable to use a reducing agent diluted with an inert gas. It is preferable to use a mixture of hydrogen and nitrogen or argon, with a hydrogen content of 1% to 15% by volume.

[0070] In further embodiments, the reduction of noble metals in a pure nitrogen atmosphere can be carried out at a temperature in the range of 130°C to 200°C, preferably in the range of 140°C to 170°C.

[0071] In a further embodiment, the reduction of the noble metal may be carried out in a liquid phase, preferably using a reducing agent such as hydrazine, potassium formate, sodium formate, formic acid, H2O2, hypophosphorous acid, or sodium hypophosphorous acid.

[0072] The catalyst support used in the manufacturing method according to the present invention can take on various shapes, such as tablets, cylinders, rings, irregular pellets, or spheres. The catalyst support is preferably spherical. Its geometric shape allows for uniform rotation around the axis of the support during recirculation, and therefore, the catalyst active species solution can be uniformly impregnated into the catalyst support. The catalyst support used in the manufacturing method of the present invention is not a powdered material.

[0073] The spherical catalyst support has an arithmetic diameter in the range of 1 to 10 mm, preferably 3 to 9 mm, and particularly preferably 3 to 8 mm. In the specification of this application, the term "spherical" is understood to include ellipsoids in which the diameter along the pole-to-pole axis is smaller than the diameter along the corresponding equatorial axis. The ratio of the diameter along the pole-to-pole axis to the diameter along the equatorial axis is in the range of 0.9 to 1.0. The arithmetic diameter of these generally spherical bodies is determined using the pole-to-pole diameter.

[0074] The catalyst support typically comprises compounds from the group consisting of titanium oxide, silicon oxide, aluminum oxide, zirconium oxide, magnesium oxide, silicon carbide, magnesium silicate, zinc oxide, zeolite, layered silicates, or mixtures thereof. The catalyst support preferably comprises Si-Al mixed oxides, particularly Si-Al mixed oxides in the form of layered silicates, preferably layered silicates in the form of calcined acid-treated bentonite.

[0075] The proportion of these compounds or mixtures is typically at least 70% by weight, preferably at least 80% by weight, and most preferably at least 90% by weight, based on the weight of the catalyst support after ignition loss. In a particularly preferred embodiment, the catalyst support contains calcined acid-treated bentonite in a proportion of at least 70% by weight, preferably at least 80% by weight, most preferably at least 90% by weight, and most preferably at least 95% by weight, based on the weight of the catalyst support after ignition loss.

[0076] The term "natural layered silicate," which is also used as a synonym for "phyllosilicate" in the literature, refers to a tetrahedron of SiO4, derived from natural raw materials, and is either untreated or treated silicate mineral, with the general formula [Si2O5]. 2- In this layer, SiO4 tetrahedra are interconnected.

[0077] These tetrahedral layers alternate with so-called octahedral layers, and cations, particularly Al and Mg, are octahedralized with OH or O. For example, two-layer phyllosilicates and three-layer phyllosilicates are distinguished. In the specification of the present invention, preferred layered silicates include clay minerals, particularly kaolinite, beidelite, hectorite, saponite, nontronite, mica, vermiculite and smectite, with smectite and especially montmorillonite being particularly preferred. The definition of the term "layered silicate" can be found, for example, in "LehrbuchderanorganischenChemie," Hollemann Wiberg, de Gruyter, deedition, 2007 (ISBN 978-3-11-017770-1), or under the term "phyllosilicate" in "Roempp Lexikon Chemistry," 10th edition, Georg Thiem Verlag.

[0078] Typical treatments of the natural phyllosilicate carrier material before use include, for example, acid treatment and / or calcination. In the present invention, the natural, particularly preferred, layered silicate is bentonite. Bentonite is not, in a strict sense, a natural layered silicate, but rather a mixture mainly consisting of clay minerals containing layered silicates.

[0079] If the natural layered silicate is bentonite, it is understood that the natural layered silicate exists in the catalyst support either in the form of calcined acid-treated bentonite or as a component thereof.

[0080] Catalyst supports based on natural layered silicates, particularly acid-treated and calcined bentonite, in the form of molded articles, can be manufactured, for example, as follows: A mixture containing acid-treated (uncalcined) bentonite and water is compressed and molded using equipment well known to those skilled in the art, such as an extruder or a tablet press, to obtain a molded article, and then the uncured molded article is calcined to obtain a stable molded article.

[0081] The specific surface area of ​​the catalyst support depends in particular on the quality of the (raw) bentonite used, the acid treatment process of the bentonite used, i.e., the properties and quantity of the bentonite, the concentration of the inorganic acid used, the duration and temperature of the acid treatment, and the pressing pressure, calcination time, temperature and atmosphere.

[0082] Acid-treated bentonite can be obtained by treating bentonite with a strong acid, such as sulfuric acid, phosphoric acid, or hydrochloric acid. The definition of the term bentonite, as applied in the specification of this invention, is specified in Roempp, Lexikon Chemie, 10th edn., Georg Thieme Verlag. In this invention, particularly preferred bentonite is a natural aluminum-containing layered silicate containing montmorillonite as the main material. Bentonite is usually washed with water after acid treatment, dried, and crushed.

[0083] The BET surface area of ​​the catalyst support is 10 to 600 m². 2 / g, preferably 20-400m 2 / g, particularly preferably 80-170m 2 The value is / g. The BET surface area is determined by a single-point method by nitrogen adsorption according to DIN66132.

[0084] In one embodiment, the total pore volume of the catalyst support not coated with the precursor compound is measured according to DIN66133 (Hg porosimetry) to be at least 0.1 ml / g, preferably at least 0.18 ml / g, and more preferably at least 0.4 ml / g. In further embodiments, the total pore volume is in the range of 0.1 ml / g to 0.8 ml / g, preferably in the range of 0.18 ml / g to 0.6 ml / g, and particularly preferably in the range of 0.35 to 0.55 ml / g.

[0085] The catalyst support used in the manufacturing method of the present invention has a hardness of at least 20N, preferably at least 30N, particularly preferably at least 40N, and most preferably at least 50N.

[0086] The proportion of Pd in ​​the catalyst according to the present invention is in the range of 0.2% to 2.0% by weight, preferably 0.4% to 1.75% by weight, and particularly preferably 0.7% to 1.5% by weight, based on the weight of the reduced catalyst molded body containing the precious metal after drying loss.

[0087] The proportion of Au in the catalyst according to the present invention is in the range of 0.1% to 1.2% by weight, preferably 0.2% to 1.0% by weight, and most preferably 0.3% to 0.8% by weight, based on the total weight of the catalyst molded body after reduction and drying loss.

[0088] In a preferred embodiment, the Au / Pd atomic ratio of the catalyst molded article according to the present invention is in the range of 0.01 to 1.2, preferably in the range of 0.05 to 1.0, more preferably in the range of 0.1 to 0.8, and particularly preferably in the range of 0.15 to 0.6.

[0089] The shell catalyst of the present invention preferably contains an alkali metal compound as an accelerator, preferably a potassium, sodium, cesium, or rubidium compound, and particularly preferably a potassium compound. Suitable and particularly preferred potassium compounds include potassium acetate (KOAc), potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), and potassium hydroxide (KOH), and preferably potassium acetate (KOAc).

[0090] The potassium compound can be applied to the catalyst support / catalyst molded body either before or after the reduction of the metal components to Pd and Au metals.

[0091] In a preferred embodiment, the potassium compound is applied before the application of the noble metal compound, and particularly preferably before step (a).

[0092] In this case, care must be taken to ensure that heat treatment in subsequent steps such as coating, fixing, or reduction of the precursor compound is performed only if the potassium compound is not decomposed to its oxide or is only slightly decomposed, because potassium oxide is only slightly converted to potassium acetate under the reaction conditions of the VAM reaction.

[0093] The catalyst support / catalyst molded body is preferably exposed only to temperatures below 200°C.

[0094] When the catalyst molded article according to the present invention contains an alkali metal acetate, preferably potassium acetate, the amount of alkali metal acetate in the catalyst bed is 0.1 to 0.7 mol / l, preferably 0.3 to 0.5 mol / l.

[0095] In a preferred embodiment, the catalyst molded body of the present invention has an alkali metal / Pd atomic ratio in the range of 1 to 16, more preferably in the range of 2 to 13, and particularly preferably in the range of 3 to 10. Preferably, the lower the alkali metal / Pd atomic ratio, the smaller the surface area of ​​the catalyst molded body.

[0096] Considering the low pore diffusion limitation, in a more preferred embodiment of the Pd / Au catalyst according to the present invention, the catalyst molded body may have an average pore diameter of 8 to 50 nm, preferably 10 to 35 nm, and preferably 11 to 30 nm.

[0097] The acidity of the catalyst molded body can have an effect that is advantageous to the activity of the catalyst according to the present invention. In a more preferred embodiment of the catalyst according to the present invention, the catalyst molded body has an acidity in the range of 1 to 150 μval / g, preferably in the range of 5 to 130 μval / g, and particularly preferably in the range of 10 to 100 μval / g.

[0098] The acidity of the catalyst molded body is measured as follows: 1 g of finely ground catalyst molded body is mixed with 100 ml of water (with a pH blank value) and extracted for 15 minutes while stirring.

[0099] Next, the mixture is titrated with a 0.01n NaOH solution to at least pH 7.0. The titration involves steps such as first adding 1 ml of NaOH solution to the extract dropwise (1 drop / second), then waiting for 2 minutes, reading the pH, and adding another 1 ml of NaOH dropwise. Determine the blank value of the water to be used and correct the acidity calculation accordingly.

[0100] Next, the titration curve (0.01 ml NaOH against pH) is plotted, and the intersection point of the titration curve at pH 7 is determined. The molar equivalent is calculated using a 10⁻⁶ equiv / g carrier and is obtained from the NaOH consumption at the intersection point at pH 7.

[0101]

number

[0102] The shell catalyst is preferably spherical or substantially spherical. The sphere has a diameter in the range of 1 to 10 mm, preferably 3 to 9 mm, and particularly preferably 3 to 8 mm.

[0103] To enhance the activity of the Pd / Au catalyst according to the present invention, the catalyst molded body can be doped with at least one oxide of a metal selected from the group consisting of Zr, Hf, Ti, Nb, Ta, W, Mg, Re, Y, and Fe, preferably ZrO2, HfO2, or Fe2O3. The proportion of the doped oxide in the catalyst molded body is preferably 0.1% to 20% by weight, preferably 1.0% to 18% by weight, and preferably 4% to 16% by weight, based on the weight of the catalyst molded body.

[0104] In a more preferred embodiment of the catalyst molded body according to the present invention, the water absorption rate of the catalyst molded body is calculated as the weight increase due to water absorption, and is 40% to 75%, preferably 50% to 70%.

[0105] The water absorption capacity is determined by impregnating a 10g catalyst mold with deionized water for 30 minutes until no more bubbles are released from the sample. Then, the excess water is drained, and the impregnated sample is lightly wiped dry with a cotton cloth to remove any adhering moisture. Next, the water-containing catalyst mold is weighed, and the absorption rate is calculated according to the following formula. (Final weight (g) - Initial weight (g)) x 10 = Water absorption capacity (%)

[0106] The BET surface area of ​​the shell catalyst is 10-600 m². 2 / g, preferably 20-400m 2 / g, particularly preferably 80-170m 2 The value is / g. The BET surface area is determined by a single-point method by nitrogen adsorption according to DIN66132.

[0107] In one embodiment, the total pore volume of the shell catalyst not coated with the precursor compound is measured according to DIN66133 (Hg porosimetry) to be at least 0.1 ml / g, preferably at least 0.18 ml / g, and more preferably at least 0.4 ml / g. In further embodiments, the total pore volume is in the range of 0.1 ml / g to 0.8 ml / g, preferably in the range of 0.18 ml / g to 0.6 ml / g, and particularly preferably in the range of 0.35 to 0.55 ml / g.

[0108] The shell catalyst has a hardness of at least 20N, preferably at least 30N, particularly preferably at least 40N, and most preferably at least 50N.

[0109] In a more preferred embodiment of the catalyst molded body according to the present invention, at least 80%, preferably at least 85%, and preferably at least 90% of the total pore volume of the catalyst molded body may be formed by mesopores and macropores.

[0110] This prevents a decrease in the activity of the catalyst molded body according to the present invention, which can result from diffusion restriction, especially in the case of relatively thick shells. The terms micropore, mesopore, and macropore are understood to mean pores having a diameter of less than 2 nm, a diameter in the range of 2 to 50 nm, and a diameter greater than 50 nm, respectively.

[0111] The present invention further relates to a method for producing alkenyl carboxylic acid esters, particularly VAM or allyl acetate monomers, using the shell catalyst according to the present invention. The method for producing VAM can be carried out by passing acetic acid, ethylene, and oxygen or an oxygen-containing gas through the catalyst molded body according to the present invention.

[0112] This is generally carried out by passing a gas containing acetic acid, ethylene, and oxygen or an oxygen-containing gas through the catalyst molded body according to the present invention at a temperature in the range of 100°C to 200°C, preferably in the range of 120°C to 200°C, and at a pressure in the range of 1 to 25 bar, preferably in the range of 1 to 20 bar, thereby allowing the unconverted reaction products to be recirculated.

[0113] The oxygen concentration is advantageously kept below 10% by volume. However, dilution with an inert gas such as nitrogen or carbon dioxide may also be advantageous. Carbon dioxide is particularly suitable for dilution because it is formed in small amounts during the VAM synthesis process and accumulates in the circulating gas.

[0114] The obtained vinyl acetate is isolated using a suitable method, for example, as described in US5,066,365A. A similar process has also been published for allyl acetate. In such vinyl acetate production methods, it is known that accelerators lost during catalyst use can be replenished by post-adding an accelerator that may be present in the catalyst, such as potassium acetate KOAc.

[0115] This can also be done during the process of producing alkenyl carboxylic acid esters, in which case the accelerator acetate compound is mixed with or supplied separately by metering to the acetic acid and / or potassium acetate supplied to the production method.

[0116] The present invention will now be described more specifically with reference to several embodiments, but these are not limiting in any way.

[0117] Figure 1 shows experimental data points for Pd concentration for catalyst 1 of the example, and x surface After the measurement, a plot of the sigmoid function, determined by the same measurement method used to determine the starting point of the geometric surface, is shown.

[0118] Figure 2 shows a plot of experimental data points for Pd concentration and the curve for catalyst 1 obtained using an appropriate fitting function.

[0119] Figure 3 shows a plot of the curve for catalyst 2 obtained using experimental data points for Pd concentration and an appropriate fitting function.

[0120] Figure 4 shows a plot of the curve for catalyst 3 obtained using experimental data points for Pd concentration and an appropriate fitting function.

[0121] Figure 5 shows the curves for catalysts 1, 2, and 3 obtained using an appropriate fitting function.

[0122] Figure 6 shows the selectivity of catalysts 1 and 2 at different space-time yields in the reaction of acetic acid, ethylene, and oxygen to obtain vinyl acetate monomer, along with their trend lines. [Examples]

[0123] Measurement method Pore ​​volume: Pore volume was measured by mercury porosimetry according to DIN 66133 in the pressure range of 1 to 2000 bar. BET surface area: The BET surface area was measured according to DIN66135. To measure the micropore volume and micropore surface area, the nitrogen adsorption isotherm at the temperature of liquid nitrogen (77K) was measured using the MicromeriticsASAP2020M instrument.

[0124] Elemental distribution in the support: The distribution of Pd and Au in the catalyst molded body was determined by cutting the support in half to create a cross-section of the spherical catalyst molded body. This made it possible to determine the spatial distribution of the metals using EDX spectroscopy (Energy Dispersive X-ray spectroscopy), also known as EDX spectroscopy, with an electron microscope. By moving a Pd-sensing measurement head across the sample, it was possible to determine the distribution of each element along a line from the outer surface to the center of the catalyst molded body.

[0125] The measurements were performed using a LEO1530 electron microscope connected to a QuantaxEDX unit equipped with a BrukerXFlash4010 detector. The measurement conditions were as follows: Acceleration voltage (EHT): 20kV Opening: 120μm Operating distance: Approximately 16mm (ideal for SEM-EDX shape) SEM detector: SE2 Magnification: Low (e.g. 55x) Measurement time: 10-15 minutes

[0126] The starting point for the measurement was set at least 80 μm from the outer edge of the sample, and the measurement was performed from there toward the center of the sphere. The length of the measurement line was 1600 μm.

[0127] The measurement of various catalyst shapes is generally carried out such that the starting point of the measurement is set at least 80 μm from the starting point of the geometric surface of the sample, from which the sample head moves vertically towards the original geometric surface of the sample and then moves across the sample.

[0128] This made it possible to determine the shell thickness of Pd. The inner end of the shell thickness was defined as the point where the intensity was first less than the total of the bremsstrahlung and had a value three times the standard deviation thereof.

[0129] The start of the geometric surface of the measured catalyst formed body was determined by fitting the following function to the intensities of the inner and outer bremsstrahlung along the measurement line at various points x.

[0130]

Equation

[0131] rate is a measure of the gradient at the inflection point, base corresponds to the intensity I of the outer bremsstrahlung of the catalyst formed body, and max corresponds to the intensity I of the bremsstrahlung outside the region containing no noble metal inside the catalyst formed body, i.e., outside the noble metal shell region.

[0132] The inflection point x0 of this sigmoid function determines the outer end of the shell. To determine the concentration distribution of the noble metal along the subsequent measurement line, the x0 value is subtracted from the measured value x, and all a series of measurements start from the point x surface = 0 μm on the outer surface.

[0133] FIG. 1 shows a graph of the sigmoid function determined by the same method as for determining the start of the geometric surface after measuring the intensity and x surface for Catalyst 1 of the example.

[0134] This ensures that a sufficient number of catalyst formed bodies are individually measured to define their outer surfaces.

[0135] The concentration distribution of palladium precious metal along the line was determined by calculating the arithmetic mean of the intensity at point x from individual measurements, and then fitting the concentration distribution of the precious metal to the obtained measurements using the Gaussian function described below.

[0136]

number

[0137] x max =Position of the peak maximum value A = Determine the peak height max = Determine the asymmetry of the concentration distribution rate = Determines the asymmetry of the concentration distribution

[0138] The values ​​of the half-width (FWHM) of the Pd concentration distribution can also be determined as follows. Here, the FWHM is the difference between two points along the measurement line at half the maximum intensity. The value on the left of the FWHM is therefore the difference between the first point on the measurement line that has half the maximum intensity and the point that has the maximum intensity, and the value on the right of the FWHM is the difference between the point that has the maximum intensity and the second point on the measurement line that has half the maximum intensity.

[0139] Measurement of elemental concentrations: Elemental concentrations were determined by dokimastic digestion using copper cupellation and subsequent ICP-AES analysis, and calculated based on the catalyst molded body after drying at 120°C for 2 hours.

[0140] Hardness Measurement: The hardness of the catalyst molded bodies was measured using a Dr. Schleuniger Pharmatron AG8M tablet hardness tester, with the average value of 99 bodies being used. The catalyst molded bodies were dried at 130°C for 2 hours before measurement. The instrument settings were as follows: Hardness:N Distance to catalyst molded body: 5.00 mm Delay time: 0.80 seconds Feed type: 6D Speed: 0.60mm / sec

[0141] The following examples illustrate the present invention.

[0142] Example 1: Catalyst 1 100 g of bentonite-containing catalyst support KA-160 (available from Clariant) was weighed and impregnated with a mixture of 39.3 g of 2 mol KOAc solution and 18.1 g of deionized water according to the pore filling method (incipient wetness).

[0143] The mixture was dried in a fluidized bed dryer at 90°C for 35 minutes, then cooled to room temperature and transferred to an Innojet IAC025 coating apparatus. The KOAc-impregnated carrier was operated in a fluidized bed using process gas. Subsequently, 36.8 g of deionized water was sprayed onto the catalyst carrier at a spray rate of 4 g / min. The process air was temperature-controlled to 70°C.

[0144] Next, 7.0 g of cesium aurate aqueous solution (4.7 wt% Au) was diluted with deionized water to prepare 50 g of coating solution, which was then applied to the catalyst support in the coating apparatus during the first coating step at a spray rate of 4 g / min and a process air temperature of 70°C.

[0145] Next, in the second coating step, 2.7 g of aqueous cesium aurate (4.7 wt% Au) and 38.9 g of tetraamine palladium hydroxide solution (3.4 wt% Pd) were diluted with deionized water to make 80 g of coating solution, which was then applied to the catalyst support at a spray rate of 4 g / min and a process air temperature of 70°C.

[0146] The catalyst support was held in a fluidized bed. After further static drying in a fluidized bed dryer (90°C / 35 mins), the catalyst molded body was statically reduced in a tubular furnace using a forming gas (2% H2 in N2) at 100°C for 45 minutes.

[0147] Elemental analysis of the catalyst molded body revealed the following proportions: Pd: 1.3% by weight Au: 0.46% by weight

[0148] The distribution of precious metals was measured using a scanning electron microscope LEO1530 equipped with an energy-dispersive spectrometer from BrukerAXS. To measure the concentration of precious metals across the thickness of the shell, the catalyst molded body was cut, bonded to an aluminum sample holder, and then carbon deposited.

[0149] The detector used was the XFlash® 410, a nitrogen-free silicon drift chamber detector with an energy resolution of 125 eV for manganese K-alpha rays. The following parameters were used for the measurements.

[0150] Scan resolution: 500 dots Data point spacing: 1.8 μm Magnification: 200x Beam voltage: 20kV Beam current: 20nA Input pulse rate: 50,000 pulses / second Line scan measurement time: 200 seconds

[0151] The shell thickness of the 10 spherical bodies of the shell catalyst manufactured as described above was measured.

[0152] The maximum Pd concentration was 23 micrometers below the geometric surface of the shell catalyst. The shell thickness of Pd was 130 micrometers, and the shell thickness of Au was 93 micrometers.

[0153] The full width at half maximum (FWHM) for Pd was 60 micrometers, with the left-hand value being 16 micrometers and the right-hand value being 44 micrometers. The ratio of the left-hand value to the right-hand value was 0.37. The Pd concentration curve is shown in Figure 2.

[0154] Example 2: Catalyst 2 100 g of bentonite-containing catalyst support material KA-160 (available from Clariant) was weighed and impregnated with a mixture of 39.3 g of 2 mol KOAc solution and 18.1 g of deionized water according to the pore filling method (initial wetness). After static drying in a fluidized bed dryer at 90°C for 35 minutes, the mixture was cooled to room temperature and transferred to an Innojet IAC025 coating apparatus.

[0155] The KOAc-impregnated carrier was operated in a fluidized bed using process gas. The process air was temperature-controlled to 90°C and held for 2 minutes before starting the spray application of the cesium aurate aqueous solution. 7.0 g of cesium aurate aqueous solution (4.7 wt% Au) was diluted with deionized water to prepare 50 g of coating solution. In the first coating step, this solution was applied to the catalyst carrier in the coating apparatus at a spray rate of 4 g / min. Upon starting the spray operation, the process air temperature was lowered from 90°C to 15°C, then further reduced to 70°C, and subsequently maintained at this temperature.

[0156] Next, in the second coating step, a mixture of 2.4 g of aqueous cesium aurate (4.7 wt% Au) and 38.9 g of tetraamine palladium hydroxide solution (3.4 wt% Pd) was diluted with deionized water to obtain 80 g of coating solution, which was then applied to the catalyst support at a spray rate of 4 g / min and a process air temperature of 70°C.

[0157] The catalyst support was held in a fluidized bed. After further static drying in a fluidized bed dryer (90°C / 35 mins), the catalyst molded body was statically reduced in a tubular furnace using a forming gas (2% H2 in N2) at 100°C for 45 minutes.

[0158] The elemental analysis of the catalyst molded body showed the following proportions. Pd: 1.3% by weight Au: 0.43% by weight

[0159] The distribution of precious metals was measured in the same manner as in Example 1. The maximum Pd concentration was 30 micrometers below the geometric macroscopic surface of the shell catalyst. The Pd shell thickness was 129 micrometers. The full width at half maximum (FWHM) of Pd was 50 micrometers. The left value of the FWHM was 16 micrometers, and the right value was 34 micrometers. The ratio of the left value to the right value of the FWHM was 0.45. The Pd concentration curve is shown in Figure 3.

[0160] Comparative Example 1: Catalyst 3 100 g of bentonite-containing carrier material KA-160 (available from Clariant) was weighed and impregnated with a mixture of 39.3 g of 2 mol KOAc solution and 18.1 g of deionized water according to the pore filling method (initial wetness).

[0161] After standing drying in a fluidized bed dryer at 90°C for 35 minutes, the mixture was cooled to room temperature and transferred to an Innojet IAC025 coating apparatus. Using process gas, the KOAc-impregnated carrier was subjected to fluidized bed operation, heated to 70°C and maintained for 2 minutes, after which an aqueous cesium laurate solution was spray-coated.

[0162] In this spray coating process, 7.0 g of cesium aurate aqueous solution (4.7 wt% Au) was diluted with deionized water to obtain 50 g of coating solution, which was then applied to the catalyst support in the coating apparatus at a spray rate of 4 g / min during the first coating step. The process air temperature dropped by 15°C, but was raised to 71°C and maintained at that temperature.

[0163] Next, in the second coating step, a mixture of 2.4 g of aqueous cesium aurate (4.7 wt% Au) and 38.9 g of tetraamine palladium hydroxide solution (3.4 wt% Pd) was diluted with deionized water to obtain 80 g of coating solution, which was then applied to the catalyst support at a spray rate of 4 g / min and a process air temperature of 70°C.

[0164] The catalyst support remained in the fluidized bed. After further static drying in a fluidized bed dryer (90°C / 35 min), the catalyst was statically reduced in a tubular furnace using a forming gas (2% H2 in N2) at 100°C for 45 minutes.

[0165] The elemental analysis of the catalyst showed the following proportions. Pd: 1.3% by weight Au: 0.43% by weight

[0166] The distribution of precious metals was measured in the same manner as in Example 1. The maximum Pd concentration was 43 micrometers below the surface of the shell catalyst. The Pd shell thickness was 183 micrometers. The full width at half maximum (FWHM) of Pd was 73 micrometers. The left value of the FWHM was 27 micrometers, and the right value was 46 micrometers. The ratio of the left value to the right value of the FWHM was 0.60. The Pd concentration curve is shown in Figure 4.

[0167] Example 3: Reactor Test Test results regarding the activity, selectivity, and yield of catalysts 1, 2, and 3 in the synthesis of vinyl acetate monomer.

[0168] For catalyst testing, 2.9 g of each catalyst was packed into a 5.7 ml reactor and then heated to 138°C under inert gas. At this temperature, the inert gas stream was replaced with streams of acetic acid, ethylene, and oxygen, which were passed through the reactor. At regular intervals, samples of the discharge stream were taken downstream of the reactor and analyzed by gas chromatography.

[0169] After a 24-hour reaction at 138°C, the reactor temperature was raised to 140°C and maintained for another 12 hours. Subsequently, the temperature was further increased to 142°C, 144°C, and 146°C, and finally returned to 140°C. Each reaction period lasted 12 hours, and the pressure was 5-6 barg. The components used were ethylene 45%, O2 6%, CO2 0.9%, methane 9%, acetic acid 15.5%, and the remainder being N2.

[0170] Table 1 and Figure 6 show the selectivity / activity of catalysts 1, 2, and 3 according to the O2 conversion rate. Catalysts 1 and 2, produced according to the present invention, clearly have much higher activity, selectivity (at the same activity level), and yield than comparative catalyst 3. This is also evident in Figure 6, which shows a plot of VAM selectivity according to space-time yield.

[0171] [Table 1]

Claims

1. The shell catalyst has a palladium concentration profile, which is in the form of an asymmetric Gaussian distribution, the maximum palladium concentration is within a range of 0 to 40 micrometers from the geometric macroscopic surface of the catalyst molded body, the palladium is present in a shell thickness region of 40 to 180 μm, the full width at half maximum (FWHM) of the concentration distribution is 10 to 70 μm, the ratio of the left value of the FWHM to the right value of the FWHM is 0.05 to 0.55, the Pd percentage is in the range of 0.2% to 2.0% by weight, and this weight percentage is based on the total weight of the catalyst molded body after reduction and drying loss. Here, the palladium concentration profile is the palladium concentration curve obtained by following the procedure below: Using EDX spectroscopy (Energy Dispersive X-ray), the EDX intensity I (Intensity) of palladium is measured for multiple shell catalysts, starting from the outer edge of the shell catalyst's cross-section and moving toward the center of the shell catalyst. The starting point x 0 on the surface of the shell catalyst is determined by fitting the following sigmoid function to the EDX intensity I obtained at each measurement point x: [Math 2] Subtract the x 0 value from the measured x so that all measured values ​​start from the outer surface point x surface = 0 μm; and The palladium concentration distribution is determined by calculating the arithmetic mean of the intensity I at point x, and then fitting the palladium precious metal concentration distribution to the obtained measurement using the following Gaussian function (x = max = position of the maximum peak, A = peak height): [Math 3] A shell catalyst comprising Pd and Au, characterized by the above.

2. The shell catalyst according to claim 1, wherein the maximum Pd concentration is in the range of 5 to 40 micrometers from the surface of the shell catalyst.

3. The shell catalyst according to claim 1, further comprising an alkali metal acetate.

4. The shell catalyst according to claim 1, wherein the proportion of Au is in the range of 0.1% by weight to 1.2% by weight.

5. (a) A step of recirculating the catalyst support bed, wherein the bed is heated to a temperature of 60°C to 120°C before or after the recirculation; (b) A step of spraying the dissolved Pd-containing precursor compound and the dissolved Au-containing precursor compound onto the recirculating catalyst bed, wherein, when applied simultaneously, the temperature is 5°C to 30°C lower than the temperature in step (a), and when applied continuously, the temperature of the first application is 5°C to 30°C lower than the temperature in step (a). A method for producing a shell catalyst containing Pd and Au as described in claim 1, including the method described in claim 1.

6. The manufacturing method according to claim 5, further comprising step (c), after step (b), a step of reducing the metal component of the precursor compound to an elemental metal by heat-treating the catalyst support obtained in step (b) in a non-oxidizing atmosphere.

7. The manufacturing method according to claim 5 or 6, wherein the coating temperature, or in the case of continuous coating, the initial coating temperature in step (b), is in the range of 55°C to 115°C.

8. The manufacturing method according to claim 5, wherein in step (b), a dissolved Au-containing precursor compound is applied in the first step, and a dissolved Pd-containing precursor compound is applied in the second step.

9. The manufacturing method according to claim 5, wherein the acetate is applied to the catalyst support before applying the Pd-containing precursor compound and the Au-containing precursor compound.

10. (a) A step of recirculating the catalyst support bed and bringing the bed into contact with sprayed water at a temperature in the range of 55°C to 110°C; (b) A step of spraying the dissolved Pd-containing precursor compound and the dissolved Au-containing precursor compound onto the recirculating catalyst bed, either continuously or simultaneously, wherein if applied simultaneously, the temperature is the same as in step (a), and if applied continuously, the temperature of the first application is the same as in step (a). A method for producing a shell catalyst containing Pd and Au as described in claim 1, including the method described in claim 1.

11. The manufacturing method according to claim 10, further comprising step (c) after step (b), wherein the catalyst support obtained in step (b) is heat-treated in a non-oxidizing atmosphere to reduce the metal component of the precursor compound to an elemental metal.

12. The manufacturing method according to claim 10 or 11, wherein in step (b), a dissolved Au-containing precursor compound is applied in the first step, and a dissolved Pd-containing precursor compound is applied in the second step.

13. The manufacturing method according to claim 10, wherein the acetate is applied to the catalyst support before applying the Pd-containing precursor compound and the Au-containing precursor compound.

14. A method for producing an alkenylcarboxylic acid ester using the shell catalyst described in claim 1.

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