LOW PRESSURE CATALYTIC HYDROGENATION OF CARBONYL-CONTAINING COMPOUNDS AND CATALYSTS THEREFOR

Abstract: Process for the hydrogenation of carbonyl-containing compounds at mild conditions of temperature and pressure to produce alcohols is disclosed, employing palladium and zinc-containing catalysts. Methods for the preparation of the palladium and zinc-containing catalysts useful for the desired reductive conversion are also disclosed.

Description: - 1 - Description LOW PRESSURE CATALYTIC HYDROGENATION OF CARBONYL-CONTAINING COMPOUNDS AND CATALYSTS THEREFOR This invention relates to catalytic hydrogena— tion. In one aspect, the present invention relates to a process for the selective reduction of carbonyl- containing compounds to alcohols. In another aspect, the present invention relates to catalysts useful for the selective reduction of carbonyl—containing compounds to alcohols, and methods for preparing such catalysts. The catalytic hydrogenation of carbonyl- containing compounds, e.g., esters, to produce their corresponding alcohols, is potentially of great commercial value. Catalysts traditionally employed for such conversions include copper chromite based materials, frequently containing a promoter such as barium. Unfortunately, these catalysts typically require high pressure to achieve commercially attrac¬ tive reaction rates for the hydrogenation of esters, i.e., pressures in excess of 3000 psig. In addition, chromium and barium present toxicity and environ¬ mental concerns which must be dealt with if one is to economically and safely use these materials on a commercial scale. More recently, substantial amounts of research have been carried out in efforts to develop hydrogenation catalysts capable of reducing carbonyl- containing compounds, e.g., organic acids and esters, to alcohols at reduced pressures. While such catalysts are capable of promoting the hydrogenation of carbonyl—containing compounds to produce alcohols, one problem with such materials is the need to run at very low liquid hourly space velocities in order to achieve suitably high conversion levels. Another problem frequently encountered with such prior art low pressure catalyst systems when employed for the reduction of carbonyl—containing compounds such as aldehydes and etones, is their lack of selectivity to the desired alcohol product, such catalysts frequently being too active and thus producing product which results from reaction of substrate with additional hydrogen. Yet another problem encountered with such prior art low pressure catalyst systems, such as Raney nickel, is the ease of handling of such catalysts, which are frequently pyrophoric, and thus require special handling to avoid fire hazard. Objects of the Invention An object of the present invention, therefore, is a process for the low pressure, high selectivity, high activity hydrogenation of carbonyl—containing compounds to produce alcohols. Another object of the present invention is a catalyst system which is capable of promoting the hydrogenation of carbonyl—containing compounds at low reaction pressures. Still another object of the present invention is a catalyst system which is capable of promoting the hydrogenation of carbonyl—containing compounds at low reaction pressure, which catalyst system is readily prepared and requires no special handling pre— cautions. These and other objects of the present invention will become apparent from inspection of the detailed description and the appended claims which follow. Statement of the Invention In accordance with the present invention, it has been discovered that palladium supported on zinc oxide is an effective catalyst for the low pressure hydrogenation of carbonyl—containing compounds to selectively produce alcohols in high yield. In accordance with a particular embodiment of the present invention, it has been discovered that palladium and zinc supported on a carrier is an effective catalyst for the low pressure hydrogenation of carbonyl—containing compounds to selectively produce alcohols in high yield. In accordance with another embodiment of the present invention, it has been discovered that a catalyst prepared by first depositing palladium on a support, then reducing the palladium sufficiently to "stabilize" the palladium on the support, and then contacting the palladium—treated support with zinc is exceptionally effective for the low pressure hydrogenation of carbonyl-containing compounds to selectively produce alcohols in high yield. The invention hydrogenation process employs readily prepared, easily handled catalysts and enables a commercially important reaction, i.e., the conversion of carbonyl-containing compounds to alcohols, to be carried out at low reaction pressures, thereby reducing the cost of equipment required for the desired hydrogenation reaction and reducing the safety risks involved in such conversions. Detailed Description of the Invention In accordance with the present invention there is provided a method for preparing high activity, low pressure hydrogenation catalysts comprising palladium on zinc oxide, which method comprises: (a) contacting said zinc oxide support or a precursor thereof with .palladium or a reducible compound thereof; (b) optionally calcining the resulting palladium—treated zinc oxide support or precursor thereof in the presence of an oxygen—containing gas at a temperature in the range of 200 up to 400°C for a time sufficient to remove substantially all of the counter—ions associated with said palladium or reducible compound thereof and said zinc oxide support or precursor thereof; and (c) contacting the optionally calcined palladium—treated zinc oxide support with a reducing atmosphere under conditions sufficient to cause reduction of at least a portion of the palladium to less than the +2 oxidation state. In accordance with the present invention there is also provided a method for preparing supported high activity, low pressure hydrogenation catalysts comprising palladium and zinc on a support, which method comprises: (a) contacting said support with at least one of zinc or a reducible compound thereof and palladium or a reducible compound thereof; (b) optionally calcining the resulting palladium and/or zinc treated support in the presence of an oxygen—containing gas at a temperature in the range of 200 up to 4O0°C for a time sufficient to activate said palladium and/or said zinc component; (c) where palladium is employed in step (a), optionally contacting said palladium—treated support with a reducing atmosphere under conditions sufficient to cause reduction of at least a portion of the palladium to less than the +2 oxidation state; (d) optionally contacting said support again with at least one member selected from the group consisting of palladium or a reducible compound thereof and zinc or a reducible compound thereof; with the proviso that said support is ultimately contacted with both palladium and zinc; (e) optionally calcining the resulting palladium and zinc treated support in the presence of an oxygen-containing gas at a temperature in the range of 200° up to 00°C for a time sufficient to activate said palladium and said zinc component; and thereafter (f) contacting the zinc and palladium—treated support with a reducing atmosphere under conditions sufficient to cause reduction of at least a portion of the palladium to less than the +2 oxidation state. As suggested by the above—described method for catalyst preparation, support can be contacted simultaneously with appropriate palladium and/or zinc components; or support can be contacted with one component followed by a subsequent contacting with the other component; or support can be treated via multiple contacting (with optional calcination/— reduction treatments between contacting) with one or both of the palladium and zinc catalyst components. In accordance with the present invention there is further provided a presently preferred method for preparing supported high activity, low pressure hydrogenation catalysts comprising palladium and zinc on a support, which method comprises: (a) contacting said support with palladium or a reducible compound thereof; (b) contacting said palladium—treated support with a reducing atmosphere under conditions sufficient to form highly dispersed, supported zerovalent palladium; (c) contacting said supported zerovalent palladium with zinc or a reducible compound thereof; and thereafter (d) optionally calcining the resulting palladium and zinc treated support in the presence of an oxygen—containing gas at a temperature in the range of 200° up to 00°C for a time sufficient to remove undesired counter—ions and/or ligands, thereby activating said zinc component. In accordance with another embodiment of the present invention, there is provided a process for the low pressure hydrogenation of carbonyl-containing compounds of specified structure to produce the corresponding alcohols, which process comprises contacting the carbonyl-containing compounds with a catalyst comprising 0.01 up to 20 weight percent palladium on a zinc oxide—containing support in the presence of hydrogen under hydrogenation conditions. Catalysts employed in one embodiment of the present invention comprise palladium on zinc oxide support. A wide variety of techniques for contacting palladium and zinc oxide are suitable. For example, palladium can be applied directly to preformed zinc oxide employing such techniques as incipient wetness, wet impregnation., metal atom evaporation, precipitation, or appropriate precursors of palladium and zinc can be coprecipitated, then calcined to remove the counter ions introduced by the precursor compounds, and, finally, reduced to convert the palladium to an active form. Catalysts employed in another embodiment of the present invention comprise palladium and zinc on a carrier or support. A wide variety of techniques for contacting support with palladium and zinc are contemplated for use in the practice of the present invention. For example, palladium or a palladium precursor can be applied directly to support employing such techniques as incipient wetness, wet impregnation, ion exchange, metal atom evaporation, precipitation; then zinc or a zinc precursor can be similarly applied to support; or support can be contacted with both zinc and palladium at the same time; or appropriate precursors of palladium and zinc can be coprecipitated in the presence of support, and then calcined and/or reduced to convert the palladium and zinc to an active form. In accordance with he presently preferred method for preparing supported catalyst, after support has been contacted with palladium or a palladium precursor, and before the support is further treated with zinc, the palladium—treated support is subjected to reducing conditions sufficient to fix the palladium on the support in a highly dispersed and reduced state so that redispersion of the palladium does not occur upon exposure to corrosive zinc species such as nitrates. For example, this can be accomplished by subjecting the palladium—treated support under a hydrogen atmosphere at a temperature in the range of about 25 up to 400°C. A wide range of zinc compounds are suitable zinc oxide precursors for use in the practice of the present invention, e.g., zinc nitrate, zinc halides, zinc acetate, zinc carbonate, and the like. When zinc oxide is employed as catalyst support, a variety of zinc oxide compounds can be directly employed as catalyst support. Typically, such preformed zinc oxide materials will contain an impurity content no greater than about 5%. Preferred zinc oxide compounds employed as catalyst supp »ort will contain at least 60% zinc oxide by weight, with up to 40% by weight of inert materials such as: Si0 2 , A1 2 0 3 , and " Ti0 2 being employed as inert diluents and as catalyst binders. When supported catalyst is contemplated for use in the practice of the invention process, a wide range of inorganic materials can be employed as support for the invention Pd/Zn catalyst. Exemplary materials are relatively non—acidic in that they do not promote significant levels of such undesired side reaction as transesterification, alcohol dehydra— tion, ester hydrolysis, and the like. Such materials include silica (SiO.), titania (Ti0 9 ), carbon (C), rare earth oxides (e.g., La 0 , CeO ), alumina (Al 0 ) , and the like, as well as mixtures of any two or more thereof. The surface area of the catalyst supports employed in the practice of the present invention can vary widely. Preferably, support materials employed in the practice of the invention will have surface 2 areas of at least about 1 m /g. Of course, those of skill in the art also recognize that higher surface area materials will generally produce higher activity catalysts than lower surface area catalysts having comparable composition. When zinc oxide support is prepared by calcina¬ tion of a precipitated zinc oxide precursor, tempera¬ tures in the range of about 200 up to 400°C are generally employed. Such temperature is maintained for a time sufficient to remove substantially all the counter ions introduced by the zinc oxide precursor (and the palladium compound employed) to form the catalyst. Times in the range of about 2 up to 8 hours or longer are generally effective for this purpose. Suitable sources of palladium are any compounds which are reducable when subjected to reducing conditions. Since many palladium compounds are convertible to the oxide form upon calcination under the above—described conditions, and the oxides of palladium are readily reduced, many palladium compounds are useful for catalyst preparation. Exemplary palladium compounds include the palladium halides, palladium acetate, palladium nitrate, palladium ammine complexes, organometallic complexes of palladium, and the like. When the palladium and/or zinc components of the invention supported catalyst are provided as precursor moieties, it is preferred to subject the Pd/Zn—treated support to a calcination treatment at temperatures in the range of about 200 up to 400°C. Such temperature is maintained for a time sufficient to activate the zinc and the palladium components used to form the catalyst. Times in the range of about 2 up to 8 hours or longer are generally effective for this purpose. Finally, the Pd/Zn—treated support can optionally be subjected to a reducing atmosphere under condi— tions sufficient to cause reduction of at least a portion of the palladium to less than the +2 oxidation state. When the zinc component of the presently preferred supported catalyst (i.e., where palladium is "fixed" on the support before zinc eis applied) is provided as a precursor moiety, it is preferred to subject the Pd/Zn—treated support to a calcination treatment at temperatures in the range of about 200 up to 400°C. Such temperature is maintained for a time sufficient to remove undesired counter—ions and/or ligands, thereby activating the zinc component used to form the catalyst. Times in the range of about 2 up to 8 hours or longer are generally effective for this purpose. The term "carbonyl-containing compounds" as employed in this specification is intended to include compounds of the structure wherein R is a C -C Q alkyl or substituted alkyl radical; or a C_—C_ 0 alkenyl or alkynyl radical or substituted derivative thereof; wherein said substituted groups include ethers, amines, additional carbonyl groups, aryl groups, hydroxyl groups and alkoxy groups; and Z=H , R', wherein R' is defined the same as R, and is selected independently of R, OR 1 , wherein R' is as defined above, X, wherein X is any one of the halogens, or NR" , wherein each R" is independently selected from H or R* ; with the proviso that R and Z can be joined as part of a polymethylene or hydrocarbyl— or heteroatom— substituted polymethylene radical, poly-carbonyl analogs of such carbonyl-containing compounds; and mixtures of any two or more thereof. Preferred carbonyl-containing compounds are compounds selected from the group consisting of: (a) Y0 2 C—A—C0 2 Y , wherein A is an alkylene moiety, an alkenylene moiety, or an alkynylene moiety having 1 up to 20 carbon atoms, or substituted derivative thereof, or a cycloalkyl or cycloalkenyl moiety having 4—12 carbon atoms or substituted derivative thereof; and wherein each Y is independently a C up to C alkyl, alkenyl or alkynyl radical or substituted derivative thereof; (b) B-C0 2 Y wherein B is an alkyl, alkenyl or alkynyl radical, or substituted derivative thereof, having 1 up to 20 carbon atoms; and wherein Y is defined as above; wherein Z is an alkyl, alkenyl or alkynyl radical having 1 up to 20 carbon atoms or substituted derivatives thereof; and mixtures of any two or more thereof. Exemplary carbonyl-containing compounds which satisfy the above formulae include alkyl oleates, dialkyl adipates, propionaldehyde, dialkyl cyclo— hexane dicarboxylates, alkyl acrylates, alkyl propionates, alkyl isobutyrates, alkyl normal butyrates, alkyl acetates, nonanal, dialkyl butane dicarboxylates, alkyl methacrylates, alkyl crotonates, alkyl isocrotonates, alkyl sorbates, alkyl cinnamates, maleic anhydride, alkyl fumarates, dialkyl succinates, succinic anhydride, alkyl glutarates, dialkyl malonates, dialkyl octanedioates, dialkyl decanedioates, dialkyl dodecanedioates, alkyl laurates, alkyl myristates, alkyl palmitates, alkyl stearates, alkyl linoleates, alkyl linolenates, alkyl isovalerates, alkyl normal valerates, alkyl caproates, alkyl caprylates, alkyl 2—ethylhexanoates, dialkyl cyclohexanedioates, γ-butyrolactone, alkyl phenylacetates, alkyl cyclohexane carboxylates, alkyl pyruvates, alkyl glycolates, alkyl oxalates, alkyl formates, alkyl lactates, alkyl citrates, glyceride esters, and the like. Typical alkyl groups employed have from 1 up to 20 carbon atoms, with alkyl groups having 1 up to 6 carbon atoms being preferred. The hydrogenation process of the present inven- tion involves contacting at least one of the above- described carbonyl-containing compounds with at least one of the above—described palladium/zinc oxide catalysts in the presence of hydrogen under hydrogenation condtions. Hydrogenation conditions typically employed in the practice of the present invention are set forth below. The process of the present invention can be operated in a variety of configurations. Depending on the substrate to be hydrogenated, the preferred method of opeation is frequently in a fixed bed flow reaction system. If the vapor pressure of the substrate to be hydrogenated is sufficiently high at reaction temperature, the desired method of operation may be vapor phase, i.e., all reactants and products exist in the gaseous phase. For other substrates, the desired method of operation may be a trickle bed configuration. Regardless of the method of opera¬ tion, the desired time of contact between the reactants and catalyst components can be varied as desired to achieve the desired level of reaction. In typical fixed bed operation, pressures in the range of 100—10,000 psig will be employed. Preferably, the pressure will be in the range of 100—2500 psig. Similarly, temperatures in the range of 25—400°C can be used, with a more perferred range of 100-290°C. While the feed rate of the substrate will be varied to control the level of conversion, normal liquid hourly space velocities (LHSV) will be in the range of about 0.01-100 h — , with a preferred range of 0.1-20 h . The molar ratio of hydrogen to substrate will typically be in the range of 1:1 to 1000:1 with a preferred range of 2:1 to 100:1. Alternatively the invention may be conducted in a slurry phase reactor. In slurry phase operation, the ratio of carbonyl-containing compound to catalysts employed can vary widely, with ratios as low as 1:1 or lower being operable, but not economically attractive; and ratios as high as 10,000:1 and higher also being operable, but generally providing relatively low conversions unless very long contact times are employed. Preferred carbonyl-containing compound:catalysts ratios fall within the range of about 1:1 up to 1,000:1, with ratios in the range of about 2:1 up to 100:1 being most preferred because good levels of conversion of the carbonyl-containing compounds are obtained without requiring excessive amounts of catalysts, or extremely long contact times. While the invention hydrogenation process can be carried out in the absence of solvent, it is presently preferred to perform the process in the presence of a suitable solvent. Suitable solvents are compounds which are fluid and in which the carbonyl-containing starting material is soluble at reaction temperature, and which are non—reactive under hydrogenation conditions. Preferred solvents are those which are fluid and in which the carbonyl- containing starting material is soluble at room temperature. Exemplary solvents include aromatic solvents such as toluene; alcohols such as methanol; ethers such as diphenyl ether and tetrahydrofuran; and the like. When employed, the volume/volume ratio of solvent to substrate can vary widely, typically falling in the range of about 5:95 to 95:5. In a preferred embodiment of the present invention, hydrogenation of carbonyl-containing compounds is carried out with small amounts of water (i.e., 0.01 up to about 2 wt. % water based on the total weight of reactants and solvent) present in the reaction mixture. It has been found that selectivity to hydrogenation (as opposed to transesterification between reactant and product) products is greatly improved by the presence of such small quantities of water in the reaction mixture. Following hydrogenation, the desired product can be recovered and purified using conventional techniques well known to those of skill in the art. For example, catalysts can be removed from the reaction mixture by filtration, decantation and the like. By-products and unreacted starting material as well as solvent, if employed, can be separated from the product by distillation, recrystallization, solvent/solvent extraction, and the like. The invention will now be described in greater detail by reference to the following non—limiting examples. EXAMPLE 1 - Catalyst Preparation a. Pd on ZnO Support A sample of 1 wt % Pd supported on ZnO was prepared as follows: A solution of Pd was prepared by dissolving 20 g of Pd(N0 ) in 50 -ml of H 2 0 and 16 g of HNO- . This solution was diluted to 750 ml and added to 925 g of powdered ZnO. The resulting mixture was heated at 90°C in air until dry. The sample was then calcined at 200°C for two hours prior to catalytic evaluation. Approximately 1 cc of powdered sample was loaded into a plug flow micro- reactor and heated to 300°C in flowing hydrogen. The catalyst was held at 300°C for two hours prior to evaluation for hydrogenation of carbonyl-containing compounds. b. Pd—Zn on SiO- Support A sample of 1 wt % Pd on Davison Grade 59 SiO was prepared by dissolving 0.48 grams (g) of Pd(N0 ) in 29.4 mL of water and adding the resulting solution to about 20 g of the solid SiO support material. The resulting solid sample was dried in air at 90°C for 30 minutes and then further calcined in air at 350°C for 12 hours. This result¬ ing Pd/SiO ? catalyst was split into separate fractions for zinc addition. Zinc was added by dissolving the appropriate amount of zinc nitrate in a small amount of water and adding this solution to the Pd/SiO- sample. The resulting solid was dried at 90°C in air and then calcined at 200°C for several hours prior to evaluation for hydrogenation of carbonyl-containing compounds. c. Pd—Zn on SiO, with Intervening Reduction of Pd A sample of 2.8 wt % Pd on Davison Grade 59 SiO was prepared by dissolving 7 grams (g) of [Pd(NH ) ]C1 in 25 mL of water and adding the resulting solution to about 100 g of the SiO„ 2 support material which was suspended in about 2,000 mL of water containing sufficient NH,0H to 4 adjust the pH to about 11.0. After soaking for about two hours at room temperature, the SiO ? was recovered by filtration, washed with about 400 mL of water, then dried in air at 120°C for about 18 hours and then further treated to reducing conditions as follows: (a) 500 standard cubic centimeters per minute (seem) of argon for about 1 hour at room temperature; (b) 500 seem of argon for an additional 1 hour at 120°C; (c) 500 seem of argon for an additional 1 hour at 260° ; (d) argon flow was replaced with hydrogen and catalyst temperature increased; hydrogen flow was maintained for about 1.5 hours after the temperature had reached about 400°C; then (e) the catalyst was allowed to cool to about 380°C, the hydrogen flow replaced with about 500 seem of argon, and catalyst then allowed to cool to room temperature under continued argon flow. The resulting Pd/SiO catalyst was split into separate fractions for zinc addition. Zinc was added by dissolving the appropriate amount of zinc nitrate [Zn(NO_) 2 -6H 2 0] in about 50 mL of water and adding this solution to 20 g portions of the Pd/SiO- sample. The resulting solid was dried initially by stirring to steam bath temperature, followed by heating to about 120°C in air and then calcined in flowing air at 200°C for 3 hours prior to evaluation for hydrogenation of carbonyl-containing compounds. EXAMPLE 2 - Methyl Acetate Hydrogenation; Effect of Water in the Feed Catalyst prepared as described in Example la was employed for the vapor phase hydrogenation of methyl acetate. All evaluations were conducted using a hydrogen/ester ratio of 4.0 and a gas hourly space velocity (GHSV; volume of gas/volume of catalyst/hr) of 30,180 hr — . The effect of water content in the feed is demonstrated by the results presented in Table I. Table I Catalytic Hydrogenation over Pd/ZnO *MeOH - methanol EtOH = ethanol EtOAc = ethyl acetate The results set forth in Table I demonstrate that the addition of small amounts of water to the reaction mixture promotes improved catalyst per¬ formance by reducing the occurrence of undesired transesterification by—product formation. EXAMPLE 3 - Hydrogenation of Methyl Acetate a. Pd on ZnO Catalyst Catalyst prepared as described in Example 1 was evaluated in the manner described in Example 2. The water content of the feed was approximately 1% by weight for all of the runs carried out. Results from these evaluations are presented in Table II: Table II Catalytic Evaluation of Pd/ZnO Methyl Acetate Hydrogenation *MeOH = methanol EtOH = ethanol EtOAc = ethyl acetate The results set forth in Table II demonstrate that Pd/ZnO catalyst is effective for the conversion of esters with high selectivity to the corresponding alcohols at pressures below 1000 psig. In addition, excellent catalyst performance is obtained under a variety of the reaction parameters, i.e., tempera¬ ture, pressure and feed composition. b. Supported Pd-Zn Catalysts Catalysts prepared as described in Example lb f_nd lc were employed for the vapor phase hydrogenation of methyl acetate. Catalytic evaluations were conducted in a vapor phase micro—reactor system using 1—2 cc of powdered catalyst. Methyl acetate feed was pumped into a heated chamber which was purged with the hydrogen feed gas. Typical GHSV were in the range of 30,000 h , with H 2 /ester ratios in the range of 3.6 up to 4.5 being typical. Product analysis of exit stream from the reactor was accomplished by gas chromatography. Results obtained at 300°C, 750 psig, at conversions of <20% are presented in Table III. Table II I Methyl Acetate Hydrogenolysis 2. 8% Pd-Zn/ SiO Catalyst 300°C 700 psig H, /Ester = 3.0 Rate (umole/g—cat sec) Catalyst MeOH EtOH EtOAc Total* A. Supported Catalyst Prepared as described in Example lb: Pd/Si0 2 1-21 0.016 0.073 0.089 Pd-Zn/Si0 2 2.74 0.024 0.85 0.87 (1:1)** Pd-Zn/Si0 2 6.48 0.12 2.25 2.37 (1:2)** Pd-Zn/Si0 2 3.09 0.00 0.84 0.84 (1:5)** Pd-Zn/Si0 2 2.31 0.012 0.68 0.69 (1:10)** Zn/Si0 2 0.00 0.00 0.00 0.00 B. Supported Catalyst Prepared as Described in Example lc: Pd-Zn (1:0) 21. 3.5 2.1 5.6 Pd-Zn (1:1) 46. 24. 14. 38. Pd-Zn (1:2) 48. 16. 19. 35. Pd-Zn (1:5) 6.7 0.7 2.8 3.5 Pd-Zn (1:10) 2.6 .08 1.1 1.2 Table III (Cont'd) Rate (-mnole/g—cat sec) Catalyst MeOH EtOH EtOAc Total* Pd-Zn (1:0) 0.0 0.0 0.0 0.0 Comparative Example*** Pd-Zn (1:2) 8.7 3.7 3.1 6.8 MeOH — Methanol, EtOH = Ethanol, EtOAc = Ethyl Acetate *Total = Rate EtOH + Rate EtOAc **The numbers in parenthesis indicate the atomic ratio of Pd:Zn. ***Catalyst was prepared by treating Si0 2 with NH4OH and Pd( H3) Cl 2 (pH - 11.0) for 80 minutes, filtering the solid material from solution, rinsing with water, and drying in air at 120°C for 24 hours. Zinc was added by dissolving an appropriate amount of zinc nitrate in a small amount of water and adding this to the Pd/Si0 sample. The resulting solid was dried at 90°C in air and then calcined at 200°C for three hours prior to evaluation for catalytic activity. The results set forth in Table III demonstrate that supporting palladium and zinc on silica results in catalysts with performance superior to the corresponding supported monometallic samples. C. Catalysts Employed Using Ion—Exchange Technique A series of catalysts similar to those described in Example lb were prepared except that the Pd was added using an ion exchange technique and the Pd loading level was 2.8 wt %. The catalysts were prepared by treating the SiO sample with NH OH and Pd(NH 3 ) Cl (pH = 11.0) for 80 minutes, filtering the solid material from solution, rinsing with water, and drying at 120°C for 24 hours. Addition of zinc was accomplished according to the procedure of Example 1. The resulting samples were calcined for about 3 hours at about 200°C prior to evaluation for catalytic activity. Results from this catalytic evaluation using the conditions employed in Example 2 are presented in Table IV. Table IV MeOH = Methanol, EtOH = Ethanol, EtOAc = Ethyl Acetate *Total = Rate EtOH + Rate EtOAc The results set forth in Table IV indicate that catalysts prepared by ion exchange of the palladium component exhibit activity for the low pressure hydrogenation of carbonyl compounds. In addition, it is evident that catalyst performance is dependent on the Pd-Zn ratio. At lower Pd—Zn ratios, selectivity to the alcohol is enhanced, but the overall rate of hydrogenation. is lower than observed at higher Pd-Zn ratios. Thus, the Pd-Zn ratio can be used to adjust the rate of hydrogenation. D. Effect of Varied Pd Loading Level A series of catalysts were prepared using the procedure described in Example 3c except that the palladium loading level was varied from 1—5 wt % and the Pd—Zn atomic ratio was held constant at 1:2. These catalysts were evaluated as set forth in Example 2. For comparison, results from a 1% Pd on ZnO supported catalyst described in Example la are shown. Data from this latter catalyst were collected under identical conditions except that the total pressure was 730 psig. Table V Methyl Acetate Hydrogenation Rate (mnole/g—cat sec) Catalyst MeOH EtOH EtOAc Total* 1% Pd-Zn/Si0 2 2.8% Pd-Zn/Si0 2 5% Pd-Zn/Si0 2 1% Pd/ZnO MeOH = Methanol, EtOH = Ethanol, EtOAc = Ethyl Acetate *Total = Rate EtOH + Rate EtOAc These results demonstrate that higher palladium loading levels give catalysts having dramatically higher activity for ester hydrogenation. E. Effect of Water Addition on Supported Pd-Zn Catalyst __ Catalyst prepared as described in Example 3d and containing 5 weight % Pd was evaluated as described in Example 3b, except the ester feed (methyl acetate) 0886 25 - was supplemented with 1 weight % (based on the total weight of liquid feed) of water. The results of this experiment and a comparison in which no water was added to the feed are summarized in Table VII. Table VII In the absence of water, transesterification product, ethyl acetate, represents more than 70% (14 out of 19 moles) of the reaction product; while in the presence of water, transesterification product represents only about 40% of the reaction product. Thus, the presence of water is seen to supress transesterification and thereby give improved selectivity to the desired direct hydrogenation product. EXAMPLE 4 - Hydrogenation of Methyl Propionate a. Pd/ZnO Catalyst The catalyst prepared as described in Example la was evaluated in the same manner as described in Example 2 for the hydrogenation of methyl propionate. Reaction parameters and results from this evaluation are given below. Temperature - 333°C Pressure — 710 psig H 2 /ester - 4.8 GHSV - 29,178 h ~ l Conversion — 16. % methanol propanol Rate (τ__moles/g—cat sec): 12. 9.0 These results demonstrate that Pd/ZnO is an effective catalyst for the hydrogenation of methyl propionate to propanol and methanol. Note the very high reaction rates obtained even under non—optimized reaction conditions. b. Supported Catalyst Prepared as Described in Example lb: The catalyst prepared as described in Example 3d and containing 5 weight % was used for the hydrogena¬ tion of methyl propionate to produce n—propanol, employing the procedure set forth in Example 3b, except that methyl propionate was used instead of methyl acetate. The conversion of methyl propionate to n—propanol proceeded at a rate of about 14 ιιmoles/g—cat sec, thereby demonstrating that Pd—Zn/SiO catalyst is effective for the hydrogenation of methyl propionate. EXAMPLE 5 — Hydrogenation of Methyl n-Butyrate The catalyst prepared as described in Example la was evaluated in the same manner as described in Example 2 for the hydrogenation of methyl n—butyrate. Reaction parameters and results from this evaluation are given below. The results demonstrate that Pd/ZnO is an effective catalyst for the hydrogenation of methyl n—butyrate to n—butanol and methanol. EXAMPLE 6 - Hydrogenation of Methyl i-Butyrate The catalyst prepared as described in Example la was evaluated in the same manner as described in Example 2 for the hydrogenation of methyl i—butyrate. Reaction parameters and results from this evaluation are given below. Temperature - 334°C Pressure — 725 psig H 2 /ester — 5.7 GHSV - 28,372 h~l Conversion — 25. % methanol i—butanol Rate (-μjnoles/g—cat sec): 2.9 6.0 These results demonstrate that Pd/ZnO is an effective catalyst for the hydrogenation of methyl i—butyrate to i—butanol and methanol. Even under these non-optimized reaction conditions, the per pass conversion was 25%. EXAMPLE 7 - Hydrogenation of Ethyl Acetate a. Pd/ZnO Catalyst The catalyst prepared as described in Example la was evaluated in the same manner as described in Example 2 for the hydrogenation of ethyl acetate. Reaction parameters and results from this evaluation are given below. Temperature - 332°C Pressure - 725 psig H 2 /ester - 4.9 GHSV - 29,100 h-1 Conversion — 16. % Ethanol Rate (μmoles/g—cat sec): 16.7 These results demonstrate that Pd/ZnO is an effective catalyst for the hydrogenation of ethyl acetate to ethanol. Note the high selectivity and very high rate of reaction even under these non—optimized conditions. b. Supported Catalyst Prepared as Described in Example lb: The catalyst prepared as described in Example 3d and containing 5 weight % * Pd was used for the hydrogenation of ethyl acetate according to the procedure set forth in Example 3b, except that ethyl acetate was used instead of methyl acetate. The conversion of ethyl acetate to ethanol proceeded at a rate of about 30 ■ μmoles/g—cat sec, thereby demonstrating that Pd—Zn/SiO is an effective catalyst for the hydrogenation of ethyl acetate. EXAMPLE 8 — Hydrogenation of 1,4—Dimethylcyclohexane Dicarboxylate A catalyst was prepared in the same manner as described in Example la. For catalytic evaluation, 260 cc of catalyst (14X40 standard mesh particles) was loaded into a 1 inch fixed bed reactor. The sample was treated in a hydrogen flow while heating the catalyst to reaction temperature. The system pressure was then increased to the desired reaction pressure. The ester feed consisted of 10 wt% 1,4— dimethylcyclohexane dicarboxylate (DMCD) in 1— odecanol. Catalytic evaluation was conducted using a liquid feed rate of 80 g/h, 290°C, 1250 psig, and a 1000 standard cubic centimeters (seem) hydrogen flow. Under these conditions, the DMCD conversion was 93.3%. The observed products were 60 mol % cyclohexanedimethanol (CHDM) and 40 mole % 1—methyl, 4—dodecyl, cyclohexanedicarboxylate. The above—described catalyst.and reaction set—up were employed in the same manner as described except that the reaction conditions were changed to a liquid feed rate of 13 g/h, 300°C, 1250 psig, and 130 seem hydrogen. Under these conditions, the observed conversion of DMCD was 99.5% with 93.3% molar selectivity to CHDM. These results demonstrate that Pd/ZnO is a very effective catalyst for the selective hydrogenation of DMCD to CHDM. EXAMPLE 9 - Effect of Support Surface Area on Catalyst Performance Catalyst samples were prepared as described in Example la except that various sources of ZnO were used for the catalyst support. Table VI Catalytic Evaluation of Pd/ZnO Methyl Acetate Hydrogenation, *MeOH = methanol EtOH = ethanol EtOAc = ethyl acetate These results demonstrate that a variety of zinc oxide—containing support materials are useful supports for the Pd/ZnO catalyst of the present invention. In addition, the results show that the rate of reaction with Pd/ZnO catalyst is greatly improved with higher surface area support. EXAMPLE 10 - Catalyst with Modified Catalyst Support: ZnO Al 2 Q.3 ZnO/Al 0„ was prepared by dissolving 365 g of zinc nitrate in 800 ml of water at 60°C. A solution of Na 2 C0 3 (160 g/700 ml) was slowly added to the Zn solution while stirring to precipitate the Zn. The resulting precipitate was washed in 1000 ml of water, filtered and dried at 90°C. The resulting solid was heated in a flow of air at 350°C for four hours. A portion of this solid (50 g) was added to 32 g of aluminum hydrate and 200 ml of water. This mix was blended for 20 minutes, filtered, and finally heated in a flow of air at 350°C for four hours. The resulting powder had a BET surface area of 79. 2 m /g. The final Pd/ZnO, A1 2 0 3 catalyst was prepared by adding an aqueous solution containing 0.24 g of Pd nitrate to 10 g of the ZnO/Al 0 3 support material, drying the resulting mixture at 90°C, and then heating in a flow of air at 250°C for four hours. The catalyst was evaluated for methyl acetate hydrogenation activity as described in Example 2. The reaction parameters employed and results obtained were as follows: Temperature - 332°C Pressure — 720 psig H 2 /ester — 4.1 Wt% H 2 0 - 0.0 GHSV - 30,180 h-1 Methyl Acetate conversion - 12.0% Product Rate moles/ —cat sec These results indicate that alumina can be added to the preparation of invention catalyst, if desired. It is of note that high selectivity to the desired hydrogenation products, methanol. and ethanol, are obtained even at the high rates of reaction achieved with the Pd/ZnO-Al 0 catalyst. EXAMPLE 11 - Diethyl Adipate Hydrogenation A hydrogenation reaction was conducted as described in Example 8 except that diethyl adipate was used in place of DMCD and the catalyst volume was 100 cc. Operation conditions are given below: Temperature - 300°C Pressure — 1233 psig H Feed Rate — 760 seem Liquid Feed Rate — 189 ml/hr Analyses of the liquid product stream gave the following results: Dodecyl alcohol — 92% Diethyl adipate - 2.2% 1,6—hexanediol — 2.8% C, products — 3.% The results show that Pd/Zno is effective for the conversion of dibasic esters such as diethyl adipate to the corresponding diol. EXAMPLE 12 - Methyl Oleate Hydrogenation a. Pd/ZnO Catalyst Hydrogenation of methyl oleate was carried out as described in Example 11 except that the liquid feed contained pure methyl oleate. The liquid feed rate was 68 ml/hr and the reaction temperature was 290°C. Analysis of the product mixture gave the following results. Methyl oleate - 4.1 wt % Stearyl Alcohol - 42 wt % Oleyl Alcohol - 50 wt % These results demonstrate the utility of Pd/ZnO for the conversion of methyl oleate to a mixture of C-18 alcohols at low pressure. Of particular note is the fact that a significant portion of the hydrogena¬ tion product is the unsaturated product, oleyl alcohol. Isolation of this product is particularly noteworthy in view of the fact that the material has been subjected to reducing conditions in the presence of a catalytic material (i.e., Pd) which is generally quite effective for double bond hydrogenation. Thus, hydrogenation in accordance with the present invention is seen to be selective for reduction of carbon—oxygen double bonds (i.e., carbonyl bonds) relative to carbon—carbon double bonds. b. Supported Catalyst Prepared as Described in Example lb: Fifty cc's of a 5% Pd (Pd-Zn ratio of 1:2) on SiO catalyst (prepared as described in Example 3d was loaded into a 1" tubular reactor. After catalyst was pre—treated at 1200 psig at 300°C in a flowing hydrogen atmosphere for 12 hours, methyl oleate feed was pumped into the tubular reactor (maintained at 300°C) at the rate of about 1.4 mL/minute with a hydrogen flow of about 744 standard cubic centimeters per minute. Under the above conditions, a 9% conversion of methyl oleate was obtained with nearly quantitative selectivity to a 2:1 mixture of oleyl alcohol and stearyl alcohol. These results demonstrate that Pd—Zn/SiO is an effective catalyst for the selective hydrogenation of methyl oleate; with the carbon—carbon unsaturation being retained in about 2/3 of the reduced product. EXAMPLE 13 — Hydrogenation of Propionaldehyde A Pd/ZnO catalyst prepared as described in Example la was evaluated for the vapor phase hydrogenation of propionaldehyde in a micro reactor system. Approximately 1 cc of catalyst was charged ' to the reactor and pretreated as described in previous example ' s. The reaction parameters employed and results obtained were as follows: Temperature - 130°C Pressure — 800 psig H 2 /Aldehyde - 4.0 • GHSV - 30,000 h-1 Propionaldehyde conversion — 49.0% Product Selectivity, wt % CH CH 2 CH OH 45 2-methyl—2—pentenal 55. The results demonstrate the utility of Pd/ZnO catalyst for the conversion of propionaldehyde to propanol. EXAMPLE 14 — Hydrogenation of Nonanal A 1% Pd on ZnO catalyst prepared as described in Example la was evaluated for the slurry phase hydrogenation of nonanal. Nonanal (4g) was mixed with toluene (75 ml) and 1% Pd/ZnO (1 g). This mixture was placed in a stirred autoclave and heated to 100°C under 100 psig hydrogen pressure. The system was pressurized to 1500 psig and the mixture stirred for two hours. The autoclave was then cooled, vented and the resulting product mixture analyzed by gas chromatography (GC). For the comparative example, 1 g of a commercially available 1% Pd/AI D was substituted for the Pd/ZnO . Pd/ZnO exhibits substantially higher activity and selectivity than Pd/Al_0 3 under identical conditions for the hydrogenation of nonanal. The examples have been provided merely to illustrate the practice of our invention and should not be read so as to limit the scope of our invention or the appended claims in any way. Reasonable varia¬ tions and modifications, not departing from the essence and spirit of our invention, are contemplated to be within the scope of patent protection desired and sought.

Claims: Claims We Claim: 1. A method for preparing high activity, low pressure hydrogenation catalysts comprising palladium and zinc on a support, said method comprising: (a) contacting said support with at least one of zinc or a reducible compound thereof and palladium or a reducible compound thereof; (b) optionally calcining the resulting palladium and/or zinc treated support in the presence of an oxygen—containing gas at a temperature in the range of 200 up to.400°C for a time sufficient to activate said palladium and/or said zinc component; (c) where palladium is employed in step (a), optionally contacting said palladium- treated support with a reducing atmosphere under conditions sufficient to cause reduction of at least a portion of the palladium to less than the +2 oxidation state; (d) optionally contacting said support again with at least one member selected from the group consisting of palladium or a reducible compound thereof and zinc or a reducible compound thereof, with the proviso that said support is ultimately contacted with both palladium and zinc; (e) optionally calcining the resulting palladium and zinc treated support in the presence of an oxygen—containing gas at a temperature in the range of 200° up to 400°C for a time sufficient to activate said palladium and said zinc component; and thereafter (f) contacting the zinc and palladium-treated support with a reducing atmosphere under conditions sufficient to cause reduction of at least a portion of the palladium to less than the +2 oxidation state. 2. A method in accordance with Claim 1 wherein said contacting step (a) comprises contacting said support with palladium or a reducible compound thereof; wherein optional step (b) is omitted; wherein step (c) comprises contacting said palladium—treated support with a reducing atmosphere under conditions sufficient to form highly dispersed, supported zerovalent palladium; wherein optional step (d) comprises contacting said supported zerovalent palladium with zinc or a reducible compound thereof; and thereafter; optionally carrying out steps (e) and (f). 3. A method in accordance with Claim 1 wherein the quantity of said palladium employed is in the range of 0.01 up to 20 wt %, calculated as the metal and based on the total weight of palladium, zinc and support. 4. A method in accordance with Claim 3 wherein the atomic ratio of Pd to Zn falls within the range of about 0.01 up to 10. 5. A method in accordance with Claim 1 wherein said support has a surface area of at least about 1 2. m /g. A method in accordance with Claim 5 wherein said support is selected from the group consisting of: Si0 2 Ti0 2 C, Rare earth oxides, A A11 ΛΛ ,, as well as mixtures of any two or more thereof.. 7. A method in accordance with Claim 5 wherein said support is silica. 8. A method in accordance with Claim 7 wherein the quantity of palladium employed is in the range of 0.5 up to 6 weight %, calculated as the method and based on the total weight of palladium, zinc, and support. 9. A method in accordance with Claim 8 wherein the atomic ratio of Pd to Zn falls within the range of about 0.2 up to 5.0. 10. A method in accordance with Claim 1 wherein said calcination is carried out for a time in the range of about 0.5 up to 8 hours. 11. A method in accordance with Claim 2 wherein said reducing atmosphere comprises active hydrogen. 12. A method in accordance with Claim 11 wherein said contacting with a reducing atmosphere is carried out at a temperature in the range of 25 up to 400°C for a time sufficient to form highly dispersed, supported zerovalent palladium. 13. A method in accordance with Claim 1 wherein ≤aid reducing atmosphere comprises active hydrogen. 14. A method in accordance with Claim 13 wherein said contacting with a reducing atmosphere is carried out at a temperature in the range of 25 up to 400°C for a time sufficient to reduce at least a portion of the palladium to less than the +2 oxidation state. 15. The catalyst prepared by the method of Claim 1. 16. The catalyst prepared by the method of Claim 2. 17. The catalyst prepared by the method of Claim 6. 18. The catalyst prepared by the method of Claim 9. 1 . 9. A process for the low pressure hydrogenation of carbonyl-containing compounds to produce the corresponding alcohol, wherein said carbonyl- containing compounds have the structure: wherein R is a C -C alkyl or substituted alkyl radical; or •a C —C alkenyl or alkynyl radical or a substituted derivative thereof; wherein said substituted groups include ethers, amines, additional carbonyl groups, aryl groups, hydroxyl groups and alkoxy groups; and Z=H, R 1 , wherein R' is defined the same as R, and is selected independently of R, OR', wherein R' is as defined above, X, wherein X is any one of the halogens, or NR" 9 , wherein each R" is independently selected from H or R* ; with the proviso that R and Z can be joined as part of a polymethylene or hydrocarbyl— or heteroatorn—substituted polymethylene radical, poly—carbonyl analogs of such carbonyl— containing compounds; and mixtures of any two or more thereof; said process comprising contacting said carbonyl- containing compounds with an optionally supported palladium and zinc containing catalyst comprising 0.01 up to 20 wt % palladium calculated as the metal and based on the total weight of catalyst; and wherein the atomic ratio of Pd to Zn falls within the range of about 0.01 up to 10; wherein said contacting is carried out in the presence of hydrogen under hydrogenation conditions. 20. A process in accordance with Claim 19 wherein said contacting is carried out in the further presence of iη the range of 0.01 up to 2.0 wt % water, based on the total weight of reactants and solvent charged to the reactor. 21. A process in accordance with Claim 19 wherein said hydrogenation conditions comprise a temperature in the range of 25 up to 400°C, and a pressure in the range of 100 up to 10,000 psig. 22. A process in accordance with Claim 19 wherein the hydrogen partial pressure falls within the range of 100 up to 10,000 psig. 23. A process in accordance with Claim 19 wherein said hydrogenation conditions comprise a temperature in the range of 100 up to 290°C and a pressure in the range of 100 up to 2500 psig. 24. A process in accordance with Claim 19 wherein the liquid hourly space velocity falls within the range of about 0.01 up to 100 h 25. A process in accordance with Claim 19 wherein the weight ratio of carbonyl-containing compound to catalyst falls within the range of 1:1 up to 10,000:1. 26. A process in accordance with Claim 19 wherein the carbonyl-containing compound is selected from the group consisting of: (a) Y0 2 C—A—C0 2 Y , wherein A is an alkylene moiety, an alkenylene moiety, or an alkynylene moiety having 1 up to 20 carbon atoms, or substituted derivative thereof, or a cycloalkyl or cycloalkenyl moiety having 4—12 carbon atoms or substituted derivative thereof; and wherein each Y is independently a C. up to C 1 alkyl, alkenyl or alkynyl radical or substituted derivative thereof; (b) B-C0 2 Y wherein B is an alkyl, alkenyl or alkynyl radical, or substituted derivative thereof, having 1 up to 20 carbon atoms; and wherein Y is defined as above; wherein Z is an alkyl, alkenyl or alkynyl radical having 1 up to 20 carbon atoms or substituted derivatives thereof; and mixtures of any two or more thereof. 27. A process in accordance with Claim 26 wherein the carbonyl-containing compound comprises a dialkyl adipate. 28. A process in accordance with Claim 27 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 29. A process in accordance with Claim 26 wherein the carbonyl-containing compound comprises a dialkyl cyclohexanedicarboxylate. 30. A process in accordance with Claim 29 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 31. A process in accordance with Claim 26 wherein the carbonyl-containing compound is selected from the group consisting of an alkyl oleate, an alkyl stearate, an alkyl linoleate, an alkyl linolenate, an alkyl α—eleostearate, an alkyl β—eleostearate, and mixtures of any two or more thereof. 32. A process in accordance with Claim 31 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 33. A process in accordance with Claim 26 wherein the carbonyl-containing compound comprises a dialkyl butanedicarboxylate. 34. A process in accordance with Claim 33 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 35. A process in accordance with Claim 26 wherein the carbonyl-containing compound comprises a glycerol ester. 36. A process in accordance with Claim 35 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 37. A process in accordance with Claim 26 wherein the carbonyl-containing compound comprises a dialkyl glutarate. 38. A process in accordance with Claim 37 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 39. A process in accordance with Claim 26 wherein the carbonyl-containing compound is selected from the group consisting of dialkyl fumarates, succinates, maleates, and mixtures of any two or more thereof. 40. A process in accordance with Claim 39 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 41. A process in accordance with Claim 26 wherein the carbonyl-containing compound comprises an alkyl decanoate. 42. A process in accordance with Claim 41 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 43. A process in accordance with Claim 26 wherein the carbonyl-containing compound comprises an alkyl dodecanoate. 44. A process in accordance with Claim 43 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms. 45. A process in accordance with Claim 26 wherein the carbonyl-containing compound is selected from the group consisting of alkyl acetates, propionates, butyrates, valerates, caproates, and mixtures of any two or more thereof. 46. A process in accordance with Claim 45 wherein said alkyl radical has in the range of 1 up to 6 carbon atoms.

Inventors: GUSTAFSON BRUCE LEROY, MERCER PATRICIA LEE NIXON, NELSON GREGORY OTIS, WEHNER PAUL SHERMAN, GUSTAFSON, BRUCE, LEROY, MERCER, PATRICIA, LEE, NIXON, NELSON, GREGORY, OTIS, WEHNER, PAUL, SHERMAN
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1988
Main classification: B01J23
IPC codes: B01J23, C07B61, C07C29, C07C31