MXPA98008115A - Panel type catalytic for vin acetate synthesis - Google Patents

Abstract

A particularly useful catalyst in the preparation of unsaturated esters such as the reaction of ethylene, oxygen and acetic acid in a vapor phase to form vinyl acetate, the catalyst comprises a honeycomb carrier coated with silica and containing palladium and gold throughout the coating of silica, said catalysts show reduced pressure drop and a high yield of time and space for vini acetate

Description

PANEL TYPE CATALYST FOR SYNTHESIS OF VITILLATE ACETATE BACKGROUND OF THE INVENTION The present invention relates to a novel catalyst for producing unsaturated esters by the gas phase reaction. In particular, this invention is directed to a new catalyst and a method for using the same in the reaction of -Gasile phase of ethylene. oxygen and acetic acid to -formate vinyl acetate. It is known how to produce vinyl acetate by reacting ethylene »oxygen and acetic acid in a gas phase and in the presence of a catalyst consisting of palladium. gold and an alkali metal acetate supported on certain carrier materials such as silica. Such catalyst systems may exhibit high activity. The results using such palladium and gold catalysts have been somewhat inconsistent. This consistency seems to be based in some way on the pattern of distribution or profile of the components of the catalyst that are deposited on and in relation to the carrier. For example, when using known vinyl acetate catalyst systems consisting of a porous support with palladium and gold, metal components deposited in or near the interior of the carrier or in the central regions do not always contribute significantly to the reaction mechanisms »because the reagents are not able to diffuse rapidly within the central or inner regions of the porous catalyst chain. More important. the synthesis products of catalysts formed inside the catalyst must diffuse from the inside outwards, being again in contact with the active phase in the external region of the catalyst. Consequently »these products formed inside go through an additional reaction and are often converted into useless by-products. The most effective reactions occur when the catalytic metal is formed as a thin shell over the surface regions of the catalyst since diffusion of the reactants and products can be quickly achieved to provide good product productions and reduced formulation of derivatives . Several patents have been granted based on the desire to distribute more uniformly and anchor gold and palladium catalytic components within a narrow band on a carrier surface to provide a vinyl acetate catalyst having high production, good selectivity and long duration. . Examples of such patents include US Patents. Nos. 4,087,6225 4,048,096; 3,822,308; 3,775,342 and British Patent 1 »521,852. The basic method for forming a vinyl acetate catalyst containing palladium and gold deposited on a catalyst carrier consists of (1) impregnating the carrier with aqueous solutions of water soluble palladium and gold compounds »(2) precipitating the gold compounds and water-soluble palladium on the catalyst carrier by contacting the impregnated catalyst carrier with a solution of compounds capable of reacting with the water-soluble gold and palladium compounds to form the precious metal compounds not soluble in water, (3) washing the water-treated catalyst for removing anions that are released from the gold and palladium compounds initially impregnated during precipitation; and (4) converting gold and palatine compounds not soluble in water to free metals by treatment with a reducing agent. A final treatment may include (5) impregnating the reduced catalyst with an aqueous solution of alkali metal acetate and (S) drying the fi nal catalyst product 1. Attempts to provide a uniform distribution of palladium and gold metals on a carrier have included handling of the steps mentioned above. Particularly useful improvements in the preparation of highly active catalysts for the preparation of vinyl acetate are described in the patents issued in the public domain E.U.A. Patent Nos. 5,314, 858 and 5,332,710 which are incorporated herein by reference. These two patents describe methods for improving the distribution of palladium and gold on a carrier by handling the precipitation step (2), the "fixing" of water-soluble precious metal compounds to the carrier as water-insoluble compounds. In E.U.A. 5,314,858 »the fixation of precious metals on the carrier is achieved by using two separate stages of precipitation to avoid using large amounts of" fixative "compound. (The patent of E.U.A). 5,332,710 discloses the fixation of precious metals by rotation of catalyzed impregnated carriers while the impregnated carriers are immersed in a reaction solution at least during the initial period of precipitation. Such a roto-dip process has been discovered to produce catalysts in which the metals of the precipitated carrier are more evenly distributed in a narrow band on the surface of the carrier. Other attempts to improve the catalytic activity have involved using catalyst carriers of particular pore size or particular figures. Catalyst carriers useful for producing vinyl esters are typically composed of silica, alumina, aluminum silicates or spinels. Silica is the preferred carrier material because the silica is porous and is a neutral carrier for deposition of precious metals. The carriers are usually formed as spheres, tablets or cylinders. The carriers in the form of spheres having diameters in the range of 4-B mm are frequently used. It is preferable, for the purpose of producing an unsaturated ester on an industrial scale, to increase the volume of raw gas material composed of olefin, organic carboxylic acid and oxygen passing through the catalyst as the catalytic activity increases. The catalytic activity is usually evaluated by space time production (PTE). One reason for increasing the volume of raw gas material passing through a catalyst is to avoid the formation of hot spots on the catalyst. Because the formation of unsaturated ester reactions is exothermic, an increase in catalytic activity can excessively heat portions of the catalyst. Inefficient heat distribution over a catalyst undesirably leads to side reactions such as carbon dioxide formation resulting in less selectivity for the formation of the unsaturated ester such as vinyl acetate. Unfortunately, an increase in the volume of raw gas material naturally creates a problem of falling pressure increase in the catalyst layer. This phenomenon of falling pressure increase has been a barrier against the commercially advantageous production of unsaturated esters, in particular when an attempt is made to use a high activity catalyst utilizing the existing equipment. Although the catalytic activity has been improved by modification of catalyst formation or modification of the carrier form or the like, there is still a major obstacle to achieving an economically advantageous method of producing unsaturated esters, including the pressure drop obstacle when increasing the volume of raw gas material to make efficient use of the catalytic activity increased in the present. EP 0464633 Al assigned to Kuraray Co. »Ltd. describes a catalyst developed with the aim of minimizing the pressure drop caused by an increase in the gas of raw material during the synthesis of unsaturated esters. EP 0464633 A1 discloses catalyst carriers for production of vinyl acetate consisting of at least one tubular channel and suggests that such carriers may consist of a hollow cylinder "a ring" a honeycomb or a block having crossed channels. Such carriers are detailed as silica and / or alumina compounds. The catalytic active agents on such carriers include elements selected from Group VIII of the Periodic Table such as palladium and also a promoter selected from Group lb such as gold. Preferably "a second promoter which is an alkali metal compound of an element selected from the Group is also used. EP 0464633 Al claims that hollow catalytic carriers have the advantage of good heat distribution and low pressure drop, thereby providing a higher reaction percentage and reducing the number of unwanted side reactions, and increasing the selectivity of reactions for desired end products. Although the honeycomb carriers are listed among the hollow tube carriers suggested in EP 0464633 Al, as far as the inventors are aware, honeycomb carriers have never been prepared commercially from alumina or silica. It is believed that all commercial honeycomb carriers such as for catalyst use consist of ceramics such as cordierite, a magnesium aluminosilicate.; ullita; an aluminosilicate; or mu 1 ta-cordier ta, a combination of magnesium-aluminosilicate aluminosilicate. Such material is too dense and non-porous to serve as the carrier for the gold and palladium metals used in the catalytic preparation of vinyl esters. The catalytic metals would not be sufficiently anchored to the ceramic carrier to provide an effective amount of catalytic active sites. It is further believed that even if the combs could be composed of silica or alumina, such carriers would not be practical in the processes for preparing unsaturated esters, especially in commercial operations. Under process conditions to prepare unsaturated esters. such silica or alumina carriers can crack or become too brittle to continue supporting the selective catalytic synthesis of unsaturated esters. Cracking or brittleness can also lead to uneven heat distribution and increased pressure drop. The patent of E.U.A. 4,764,498 describes formed articles containing silica and a process for their preparation. Although hollow catalysts are known, including a suggestion of combs having one or at least two passage channels for the synthesis of esters to For example, there is still a need for an improved honeycomb catalyst containing catalytic agents such as gold and palladium having improved durability, high activity, and improved selectivity for unsaturated esters. object of the present invention is to provide an improved honeycomb catalyst for selective synthesis of vinyl acetate Another object of the present invention is to provide a honeycomb catalyst having improved durability in commercial synthesis of unsaturated esters. of the present invention are set forth in the description that follows and will be apparent upon the practice of the present invention.

BRIEF DESCRIPTION OF THE INVENTION It has now been discovered that a catalyst consisting of a honeycomb carrier having a silica coating applied thereto and in which the silica coating supports palladium and gold is particularly useful for the synthesis of unsaturated esters such as vinyl esters. from ethylene, low carboxylic acids with 2-4 carbon atoms and oxygen in a gas phase at elevated temperature and at normal or high pressure. The use of the honeycomb catalyst of this invention results in more activity as well as lower pressure drop across the catalyst. A better steam flow to provide a better heat distribution and to avoid unwanted side reactions is achieved in relation to catalysts suggested above. The silica-coated honeycomb carriers of the present invention eliminate problems of cracking and brittleness that could occur in hypothetical honeycomb carriers purely silica or alumina compounds, especially under commercial conditions used to prepare vinyl ester. Moreover, because commercial ceramic panels such as cordierite are not porous enough to effectively contain catalytic metals such as palladium and gold for vinyl acetate synthesis, the honeycomb carriers of this invention are coated with porous silica. Neutral provide a suitable bed for anchoring the catalytic agents »and also have an area of increased area within the cells of the honeycomb for a more uniform absorption of the catalytic agents. What has been discovered is that a greater catalytic activity with respect to the formation of vinyl esters such as vinyl acetate by the process of reacting ethylene, a lower carboxylic acid and oxygen in a gas phase can be maintained and that the selectivity of the vinyl ester can be improved with a honeycomb catalyst of this invention as described more fully below.

IO DETAILED DESCRIPTION OF THE INVENTION The improved catalyst of the present invention consists of a honeycomb carrier coated with at least one layer of silica and palladium and gold catalysts supported on the silica coating. The carrier material for catalysts of the present invention has a honeycomb structure. For example, such a carrier can be formed as drums, blocks or cylinders having tubular cells »square or hexagonal cells» as in a honeycomb »extending over the entire length of the carrier. The cell density per carrier can be from a scale of 100 cells /6.45 cms * to 400 cells / 6.45 c * preferably from 200 cells / 6.45 cm * to 400 cells / 6.45 cm *. The size of the honeycomb carrier can vary and will depend on the size of the reactor used to synthesize an unsaturated ester. The material of the honeycomb carrier can be made of any strong material such as metals or ceramic material. Such metals include, but are not limited to, aluminum »titanium, cobalt» steel and the like. Ceramic materials include but are not limited to aluminum silicate such as aluminum magnesium aluminosilicate such as cordierite, a combination of agnesium aluminosilicate aluminosilicate such as cordieri ta-ul 1 ta and the like. Such ceramic carriers are described in U.S. Patents. US. 3,894,965; 3, B73,469J 3,856,707; and 4,056.4B9 whose full description is incorporated herein by reference. The most useful materials for providing the honeycomb are non-porous or low porosity materials that can withstand the conditions of the process used in the synthesis of unsaturated esters under commercial operations. The honeycomb catalytic carriers of the present invention will typically have a pore volume as measured by mercury porosimetry of less than 0.4 cc / g. Although porosities greater than 0.4 cc / g are useful, such porous carriers may not need, but preferably have, the silica coating. The carriers can be formed by any suitable method including, for example, molding, pressing, extrusion or die stamping, etc. Because the most desired carrier materials are relatively non-porous, the catalytic carrier, including cell surfaces of the honeycomb catalyst carrier, are covered with at least one layer of silica to provide a porous bed to receive the palladium catalytic agents. and gold The silica layer increases the surface area of each cell of the honeycomb carrier such that when a catalyst agent is applied to each cell the catalytic material is evenly distributed over the surface of each cell resulting in improved selectivity for a product end of the desired reaction during the synthesis of unsaturated esters. Additionally, a decreased pressure drop in the cells of the honeycomb carrier reduces the resistance to vapor flow during the vapor reaction phase allowing better penetration of the cells vapor and contact with the catalytic agents inside the cells , thus increasing the production of a desired final product. The specific surface area of the silica coating can vary from 50 to 500 m * / g (measured according to BET) and is formed of micropores hg a pore volume as measured by mercury porosimetry of about 0.3 to about 1.0. cc / g »or which at least 6054 has a diameter of about 40 to approximately 400 angstroms. The silica coating the surface of each cell can be applied to the honeycomb carrier by any suitable method in the art. A method for coating the silica on a carrier is by a wet coating. An aqueous slurry of silica is prepared and the slurry is coated on the honeycomb carrier as a multiple layer or layers according to the art. The methods used to apply the aqueous silica paste can include spray coating or bathing the honeycomb carrier in a silica paste followed by drying the silica at a temperature of about 100 to 150 ° C in a conventional oven. A sufficient amount of silica is coated on the carrier in such a way that the silica coating ranges from about 1554 to 5054 by weight, preferably, from about 2054 to 4054 by weight of the completed catalyst. In accordance with this invention, the silica layer is thoroughly impregnated with the catalytic metals by known methods. Preferably, an aqueous solution containing a water-soluble gold-soluble palladium compound and water-soluble gold is used as impregnating agents. Separate solutions of palladium and gold compounds can also be used successively, but it is less convenient to proceed in this way. Palladium chloride (II), palladium (II) sodium chloride, palladium (II) nitrate or palladium (II) sulfate are suitable examples of water-soluble palladium compounds, while auric chloride (III) ) or tetrachloroauric acid (III) can be used as water-soluble gold compounds. Tetrachloroauric acid (III) and palladium (II) sodium chloride are preferred because of their good solubility in water. The amounts of these compounds used are such to provide almost 1.5 to B.O g of palladium and almost 0.5 to 8.0 g of gold per liter of finished catalyst. The gold present in the catalyst will be around 654 to 20054 by weight in relation to the amount of palladium. Catalysts containing even greater or lesser amounts of precious metals relative to those described above may be useful in the formation of vinyl acetate by ethylene reaction, oxygen and acetic acid in a vapor phase while the catalyst consists of a honeycomb carrier with a silica coating supporting the palladium and gold metals. After impregnation of the carrier with the water-soluble gold and palladium compounds, the impregnated carrier can be dried prior to fixing the palladium and gold compounds as water soluble compounds on the carrier, or fixing the compounds of the Palladium and gold can be achieved while the carrier is still wet with the impregnation solution. The fixing solution contains an alkaline solution »for example. an aqueous solution of alkali metal hydroxides »alkali metal bicarbonates and / or alkali metal carbonates. It is particularly preferred to use aqueous solutions of sodium hydroxide or potassium hydroxide. By treatment with an alkaline solution, the water-soluble precious metal compounds are converted to water-insoluble compounds which are believed to be oxides and / or hydroxides. at least where the alkaline solution is a solution of sodium hydroxide or potassium hydroxide. The alkaline fixing solution can simply be spilled on the impregnated carriers and the treated carriers allowed to remain until the precipitation of the water-insoluble metal compounds is complete. The volume of the fixing solution is equal to the dry absorbency of the carrier and the amount of alkaline compound used is in excess on a molar basis which is required to react with all precious metal impregnated compounds. The catalytic activity. such as for the formation of vini acetate, it can be maintained and the side reactions related to the formation of carbon dioxide can be reduced if the de fi ning step is divided into at least two separate stages of treatment with alkaline fixing solution. . In each separate fixation treatment, the amount of alkaline reactive compound is no more than that equal to the molar amount required to react with all the precious metal compounds that are present on the carrier as a water-soluble compound. No excess reactive compound is used. Preferably, the amount of reactive compound used in each fixing step is less than the molar amount required to react with all water-soluble precious metal compounds. Each fixing step is conducted by further impregnating the dried carrier impregnated with alkaline fixing solution in an amount equal to approximately the dry absorbency of the carrier. The amount of the alkaline compound contained in the solution is preferably such that the radius of alkali metal to anion of the precious metal compound soluble in water is about 0.7 ai: i molar in the first stage and preferably almost 0.2 to 0.9: 1. molar in the second stage. Preferably the total amount of alkali metal to anion varies from about 1.2 to 1.6: 1 molar for the complete fixing step. Following the treatment in the first fixation step, the treated carriers are allowed to stand for a sufficient period to allow precipitation of the water-insoluble precious metal compounds. The period of time may vary but typically ranges from about 2 hours to about 8 hours before the carrier is again treated with the second portion of the alkaline fixing solution. Following the treatment in the second fixation step, the treated supports are allowed to stand again for at least an additional 2 hours, preferably at least 4 hours and can withstand complete precipitation for about 16 hours. The treatment in the second fixing stage can be equivalent to that of the first stage in which the treated and partially fixed carrier is impregnated with fixing solution at the desired alkaline concentration and in a total volume of solution again equivalent to the dry absorbency of the carrier. Alternatively, the carrier can be impregnated in the second fixing stage by a process called rotation immersion described in the U.S. patent. No. 5,332,710, issued July 26, 1994 to Nicolau et al., And assigned to Hoechst Celanese Corporation, the entire disclosure of which is hereby incorporated by reference in its entirety. In the rotation immersion, the catalysts once fixed are immersed in an alkaline fixing solution and stirred or rotated therein during the initial stages of precipitation of the precious metal compounds not soluble in water. The rotation or stirring of a carrier in an alkaline fixing solution preferably lasts at least about 1/2 hour from the initial treatment and, more preferably, at least one hour. The spin immersion treatment may take up to approximately 4 hours before the treated carriers are allowed to stand in the fixing solution to ensure that complete precipitation of the precious metal compounds not soluble in water takes place. Any type of rotation or stirring equipment can be used since the exact apparatus used is not critical. The rotation is preferably sufficient such that all the surfaces of the impregnated carriers are uniformly contacted with alkaline fixing solution. The rotation is preferably not so rough that the current abrasion of non-water soluble precious metal compounds takes place and that water-insoluble compounds are worn off the surface of the carrier. In any case, it is believed that a small degree of abrasion of the precious metal compounds not soluble in water works to more evenly distribute the precious metal compounds not soluble in water on the surface of the carrier. The rotation is around 1 to 10 rpm and can still be higher depending on the exact carrier used and the amount of precious metal to be deposited on the carrier. RPMs are variable and may also depend on the apparatus used for the rotation, the size and shape of the support, the type of carrier »metal charges» etc »but preferably falls within the guidelines expressed above, although a small amount of abrasion can be beneficial »is not such that compounds not soluble in water are wasted off the surface of the carrier. After fixation and precipitation, the carriers are washed with deionized water to remove anions, such as chlorides, which are still contained on the carrier and released from the initial impregnation solution. The washing is continued until all the anions are removed from the carrier. To ensure a substantially complete removal of anions, such as chlorine ions, from the catalyst, the wash effluent is tested with silver nitrate after each wash. The washing is continued until the silver nitrate tests are negative, that is, there is no conversion to silver chloride. The catalyst is then dried at temperatures not exceeding nearly 150 ° C under an inert atmosphere such as a continuous flow of nitrogen. The fixed and washed material is then treated with a reducing agent in order to convert precious metal compounds that are present to their metallic form. The reduction can be carried out in a liquid phase »for example» with aqueous hydrazine hydrate. or in a gas phase, for example, with hydrogen or hydrocarbons, for example, ethylene. If the reduction is carried out with a hydrazine hydrate solution, the reaction is preferably snowed out at normal temperature. If the reduction is carried out in the gaseous phase, it is advantageous to carry out the reaction at an elevated temperature, for example, of 100 or 200 ° C when reduced with ethylene. The reducing agent is used in excess to ensure that all precious metal compounds are converted to their metallic form. Depending on the use for which the catalyst is designed, the catalyst can also be provided with custom additives. For example, additions of alkali metal salts such as acetates are advantageous when the catalyst is used for the preparation of unsaturated esters from olefins, oxygen and organic acids. In such cases, the catalysts can be impregnated with an aqueous solution of potassium acetate, sodium acetate, lithium acetate, rubidium acetate or cesium acetate and then dried. Preferably, the potassium acetate is the alkali metal salt employed. The catalysts according to the present invention can be used with particular advantages in the preparation of vinyl acetate from ethylene, oxygen and acetic acid in the gas phase. For this purpose, the catalysts according to the present invention which are of a metal or ceramic honeycomb carrier coated with silica material and containing palladium, gold or alkali metal acetates additives are particularly suitable. In the preparation of vinyl acetate, such catalysts are also distinguished by high activity and selectivity and by long duration, particularly under commercial operating conditions. When the vinyl acetate is prepared using catalysts of the present invention, a stream of gas containing ethylene, oxygen or air and acetic acid is passed over the catalyst. The composition of the gas stream can be varied within wide limits, taking into account explosive limits. For example. the molar radius of ethylene to oxygen may be from about 80:20 to 98: 2 and the molar radius of acetic acid to ethylene may be from about 100: 1 to 1: 100 and the gaseous alkali metal acetate content may be almost 2-200 ppm. in relation to the acetic acid used. The gas stream could also contain other inert gases, such as nitrogen, carbon dioxide and / or saturated hydrocarbons. The reaction temperatures which can be used are high temperatures, preferably those in the range of about 150 ° C to 220 ° C. The pressure used can be a pressure of about 1 to about 20 atmospheres manometry. The following examples are intended to further illustrate the present invention and are not intended to limit the scope of the invention.

EXAMPLES 1 AND 2 The catalysts of examples 1 and 2 were prepared according to the method of the present invention. The cordierite honeycomb carriers were provided by Corning Inc. and coated with silica by Prototeck Corp. of Needhamm, Mass. Sufficient silica was applied on each carrier such that the silica consists of about 2054 by weight of the total weight of the completed catalyst. Cordierite 9475, the cordierite honeycomb carrier of Example 1 had a cell density of 400 cells / 6,425 cm * and weight almost 62.9 g, and cordierite EX-20, the cordierite honeycomb carrier of Example 2 had a cell density of 200 cells / 6,425 crn2 and weight almost 75.6 g. Each honeycomb carrier was a cylinder about 45 mm in diameter and almost 70 mm long. The absorbency of the silica coating on the carrier of Example 1 was 19,254 while the absorbency of the silica coating on the carrier of Example 2 was 19,654. In both examples, each honeycomb carrier coated with silica was impregnated with an aqueous solution containing palladium sodium chloride and tetrachloroauric acid. A sufficient amount of palladium sodium chloride and tetrachloroauric acid were impregnated onto each carrier such that each carrier in the final catalyst was tried to have almost 6.6 g / 1 of palladium and almost 3.0 g / 1 of gold. The impregnated carriers were then treated with an aqueous solution of sodium hydroxide having a concentration of about 8 g / 1. The volume of the sodium hydroxide solution was equal to the absorbance of the dry support in the fixing step. Each treated carrier base was allowed to remain for almost 24 hours. After fixation, each base of treated carrier was thoroughly washed with deionized water to remove the chlorine ions at accepted levels. The washing was continued until the washed fluid could no longer react with silver nitrate. The percentage of water flow for washing was almost 200 croViuin. for approximately 5 hours. Each catalyst was dried under a continuous stream of nitrogen at a temperature of no more than about 150 ° C. Each dried catalyst was reduced with ethylene at a temperature of about 150 ° C. The reducing gas contained almost 554 ethylene in nitrogen and was passed over the catalysts for almost 5 hours at atmospheric pressure. Each reduced catalyst was impregnated with an aqueous solution containing almost 10 g of potassium acetate in a volume of solution equal to the absorbency of the carrier. Each catalyst was dried at a temperature no higher than about 150 ° C. The vinyl acetate was prepared using the catalysts prepared in Examples 1 and 2 according to the following procedure. Each honeycomb catalyst was placed into separate baskets suitable in size to support a simple honeycomb catalyst. The baskets with the catalysts were placed in a Berty reactor. A thermocouple was placed on the top and bottom of each catalyst during the synthesis of vi acetate or to measure the temperature. Each catalyst was heated by an electric heating mantle placed around the basket holding the catalyst. The catalyst of Example 1 was maintained at approximately 192 ° C and the catalyst of Example 2 was maintained at about 195 ° C. A gas mixture formed of about 50 normal liters (measured to NTP) of ethylene, 10 normal liters of oxygen, 49 normal liters of nitrogen and almost 50 grams of acetic acid was traveled under a pressure of about 12 atmospheres on each catalyst. Product analysis was achieved by on-line gas chromatographic analysis combined with off-line liquid product analysis by condensation of the product stream at 10 ° C to obtain an optimum analysis of the final products. The results of the analysis of the products of each catalytic synthesis are established in Table 1 below. The honeycomb catalysts of examples 1 and 2 had high space-time production for vinyl acetate, respectively, of 434 g / l / hr and 367 g / l / hr, and comparable selectivities of COa.

TABLE 1

Claims (17)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A catalyst for producing vinyl esters consisting of a ceramic honeycomb carrier having cells extending over the entire length of the carrier; the carrier being provided with silica coating within at least the cells, the catalyst further comprising palladium metal and gold metal distributed throughout the length of the silica coating.
2. 2. The catalyst according to claim 1, further characterized in that the carrier consists of alu inosium magnesium icoate »aluminosil cato» or a combination of aluminosilicate magnesium licate-aluminosilicate.
3. 3. The catalyst according to claim 2, further characterized in that the magnesium aluminosilicate is cordierite.
4. 4. The catalyst according to claim 2. further characterized because the aluminosilicate is very small.
5. 5. The catalyst according to claim 2, further characterized in that the aluminosilicate magnesium aluminosilicate 1 icato is cordierite-muí lita.
6. 6. The catalyst according to claim 1 »further characterized in that it further comprises an alkali metal acetate uniformly distributed throughout the length of the silica coating.
7. 7. The catalyst according to claim 6, further characterized in that the alkali metal acetate consists of potassium acetate, sodium acetate, lithium acetate, palladium acetate or cesium acetate.
8. 8. The catalyst according to re-indication 7, further characterized in that the alkali metal acetate is potassium acetate.
9. 9. The catalyst according to claim 1, further characterized in that the silica coated cells of the catalyst carrier have an area area of about 50 m * per gram to about 500 * per gram.
10. 10. The catalyst according to claim 1, further characterized in that the catalyst carrier has a density of 100 cells per 6.45 ero * to 400 cells per 6.45 cm *.
11. 11. The catalyst according to claim 10. further characterized in that the catalyst carrier has a density of about 200 cells per 6.45 cm * to 400 cells per 6.45 cm *.
12. 12. The catalyst according to claim 1, further characterized in that the silica coating consists of about 1554 to 5054 by weight of the catalyst.
13. 13. The catalyst according to claim 1 »further characterized in that the silica coating comprises from about 2054 to 4054 by weight of the catalyst.
14. 14. The catalyst according to claim 1, further characterized in that the cells consist of a tubular, square or hexagonal shape.
15. 15. The catalyst according to claim 1. further characterized in that the amount of palladium metal consists of about 1.5 gm per liter to about 8.0 gm per liter of the catalyst.
16. 16. The catalyst according to claim 1, further characterized in that the amount of gold metal consists of about 0.5 gm per liter to about 0.8 gm per liter of the catalyst.
17. 17. The catalyst according to claim 1. further characterized in that the amount of gold metal in the catalyst comprises from about 654 to about 20054 by weight relative to the amount of palladium metal. IB.- The catalyst according to claim 1 »further characterized in that the pore volume of the carrier consists of less than about 0.4 cc / g as measured by mercury porosimetry. 19.- The catalyst in accordance with 2B Vindication 1 further characterized in that the silica coating has micropores with a pore volume of about 0.3 to about 1.0 cc / g. 20. A method for preparing an unsaturated ester which comprises reacting in a gaseous phase an olefin, an organic acid carboxy and oxygen in the presence of a catalyst, the catalyst consisting of a ceramic honeycomb carrier having cells extending over the entire length of the carrier, the carrier being provided with a silica coating within at least the cells »the catalyst further comprising more of palladium metal and gold metal distributed throughout the length of the silica coating . 21. The method of compliance with the claim 20 »further characterized in that the olefin is ethylene. 22. The method according to the claim 21"further characterized in that the molar ratio of ethylene to oxygen is about 80:20 to 98: 2. 23. The method according to claim 20, further characterized in that the organic carboxylic acid is acetic acid. 24. The method according to claim 23 »further characterized in that the molar ratio of acetic acid to ethylene is from about 100: 1 to 1: 100. 25. The method according to claim 20, further characterized in that the unsaturated ester is prepared at a temperature of about 150 to 220 ° C. 26. The method according to claim 20, further characterized in that the silica coated cells of the catalyst carrier have an area area of about 50 m * / g to approximately 500 m * / g. 27.- The method of compliance with the claim 20, further characterized in that the catalyst carrier has a density of about 100 to 400 cells / 6.45 cm *. 2B.- The method according to claim 20, further characterized in that the catalyst carrier has a density of from 200 to 400 cells / 6.45 cm *. 29. The method according to claim 20, further characterized in that the silica coating comprises from about 1554 to 5054 by weight of the catalyst. 30. The method according to claim 20, further characterized in that the silica coating comprises from about 2054 to 4054 by weight of the catalyst. 31. The method according to claim 20, further characterized in that the reaction is carried out at a pressure of about 1 to 20 manometric atmospheres. 32.- The method of compliance with the claim 20, further characterized in that the amount of palladium metal is from about 1.5 gm / 1 to B.O gm / 1 of the catalyst. 33.- The method according to claim 20, further characterized in that the amount of gold metal consists of about 0.5 gm / 1 to 8.0 gm / 1 of the catalyst. 34.- The method according to claim 20, further characterized in that the amount of gold metal in the catalyst consists of about 654 to approximately 20054 by weight in relation to the amount of palladium metal. 35. The method according to claim 20, further characterized in that the cells consist of a tubular, square or hexagonal shape. 36. The method according to claim 20, further characterized in that said honeycomb carrier consists of cordierite, small cell or cordieri ta-mul combination i i ta. RESUME OF THE I V? IPN A catalyst particularly useful in the preparation of unsaturated esters such as the reaction of ethylene »oxygen and acetic acid in a vapor phase to form vinyl acetate; the catalyst comprises a honeycomb carrier coated with silica and containing palladium and gold throughout the silica coating; said catalysts show reduced pressure drop and a high time and space yield for vinyl acetate. P98-1000f SRZ / xa1 * ehp * p »mr *.