Patented June 25, 1946 2,402,684

UNITED STATES PATENT OFFICE 2,402,684 HYDROGENATION CATALYSTS AND METHODS OF PRE PARATION Frank Kerr signalgo, Wilmington, Del, assignor to E. I. du Pont de Nemours & Company, Wil mington, Del, a corporation of Delaware No Drawing. Application February 16, 1940, Serial No. 319,242 15 Claims. (C. 252-228.4) 2 This invention relates to metal sulfide catalysts Solution is added slowly an aqueous solution of for use in hydrogenation reactions and to meth Sodium polysulfide. The precipitated ferrous ods of preparing Such catalystS. m metal polysulfide is then filtered from the liquid The literature on the use of metal sulfide cat medium and washed with water to remove solu alysts for the destructive hydrogenation of car ble salts. The precipitate is protected from oxi bonaceous materials is very extensive. Such dation by the atmosphere by means of a liquid metal sulfides are prepared by a variety of meth medium such as water or organic solvents. The ods such as precipitation, decomposition of thio paste is then dried in a non-oxidizing atmos Salts, and heating metals or metal compounds phere of carbon dioxide, nitrogen, hydrogen, etc., with volatile sulfur-containing materials such as O and finally reduced in an atmosphere of hydro sulfur, hydrogen sulfide, carbon bisulfide, mer gen at a temperature of 50° to 200° C. Alter captans, etc. natively, the metal sulfide paste may be mixed The metal sulfide catalysts described in the with the material to be hydrogenated and the literature are active for the destructive hydro hydrogen treatment of the catalyst carried out genation of carbonaceous materials and desul 5 under hydrogen pressure at an elevated tem furization of petroleum and gases at high tem perature in a hydrogenation autoclave so as to gerature, as for example 300 to 600° C. These activate the catalyst in situ. The details of drastic conditions of temperature are not suit carrying out this invention will vary according able for carrying out certain desirable hydrogen to the particular ferrous metal sulfide prepared reductions of organic compounds, since extensive 20 and depending upon the type of material to be Cracking and hydrogenolysis results and mixtures hydrogenated. The following selected examples of hydrocarbons are obtained. It is therefore indicate more precisely the manner of practicing essential to the successful hydrogen reduction of this invention. The proportions of materials many organic Sulfur compounds that the catalysts used are expressed as parts by weight unless employed be active at low temperatures so that 25 Otherwise Stated. simple addition of hydrogen or cleavage by hy Eacample I drogen will occur without accompanying dis ruptive side reactions. The catalyst must of A catalyst active for the hydrogenation of sul course be immune to sulfur poisoning if sulfur fur compounds is prepared as follows: Two hun or sulfur compounds are involved. 30 dred thirty-seven parts of cobalt chloride hexa This invention has as an object the prepara hydrate was dissolved in 500 parts of water. To tion of certain new and useful sulfactive cat this was added rapidly with stirring a solution alysts. Another (bject is the preparation of a of 240 parts of sodium sulfide nonahydrate and new class of hydrcgenation catalysts. A further 64 parts of Sulfur in 900 parts of water. A black object is to prepare hydrogenation catalysts by 35 precipitate was formed which was filter and an economical and simple process. A still fur Washed with water to remove soluble salts. The , ther object is the preparation of hydrogenation precipitate was then further washed with alcohol catalysts that are active under mild conditions to free it from water. The cobalt polysulfide of temperature. Allother object is to develop cer must be protected from oxygen or air due to its tain new processes for the production of such 40 pyrophoric nature. The paste was then placed catalysts. Other objects will be apparent from in a tube fitted in an electric furnace and heated the reading of the following description of the in a stream of hydrogen. The evolution of hy invention. drogen Sulfide commenced at a temperature of These objects are accomplished by the fol 60° C. At 100° C. the evolution of hydrogen sul lowing invention which comprises treating a met 45 fide was very vigorous. As the temperature was al polysulfide, obtainabie by precipitation from slowly raised to 200° C., the evolution of hydrogen a Solution of a salt of a metal of the iron group Sulfide gradually decreased, and after 1 hour at of the periodic table, with hydrogen at a tem this temperature reduction was sufficiently com perature between 25° and 300° C. The treatment plete. This reduced catalyst must be protected with hydrogen Inay be carried out as a separate 50 from air, Since it is pyrophoric. Operation or in conjunction with the use of the The catalyst So prepared is unusually active metal sulfide as a hydrogenation catalyst. for the hydrogenation of sulfur compounds, as In practicing this invention a salt of a metal will be seen from the following example. A mix of the iron group of the periodic table is dis ture of 98 parts of cyclohexanone and 32 parts solved in water with stirring, and to the stirred 55 of Sulfur was heated in an autoclave with 9 parts

y 2,402,684 3 of the catalyst described above. The autoclave 4. was charged with hydrogen at 2,000 lbs./sq. in. lbs. per sq. in. The autoclave was then heated pressure and agitated and heated to 175° C. Un to a temperature of 150 C. for 3 hours, but dure der these conditions the pressure in the autoclave ing this period there was no apparent hydrogen dropped very rapidly, and it was necessary to absorption. The temperature was raised accord add hydrogen from time to time to maintain the ingly to 170° C. and the pressure decreased only pressure in the range from 1,000 to 2,000 lbs./sq. 400 lbs. in 3 hours. No further hydrogen absorp in. The total pressure drop in three hours tion was noted. The contents of the autoclave amounted to 2,100 lbs./sq. in, after which no were then filtered to separate the catalyst and further hydrogen absorption was noted. On 0 worked up as described above. Cyclohexanethiol cooling the autoclave and filtering the product was obtained in Only 3.6% yield, indicating that from the catalyst there was obtained cyclo little reaction had occurred. hexanethiol in 74% conversion. I believe this Eacample IV type of hydrogenation reaction proceeds as An active nickel sulfide catalyst was prepared follows: 5 catalyst as follows: Ninety parts of nickel sulfate hexa (1) S -- H --> HS hydrate was dissolved in 250 parts of water and to the stirred Solution there was added a solution (2) RC=O + HS - R2C=S -- HaO of 80 parts of sodium sulfide nonahydrate and catalyst 21 parts of Sulfur dissolved in 300 parts of water. (3) RCs-S -- - RaCHS 20 The black precipitate was filtered and washed Eacample II Several times with Water to remove the soluble It will be noted that in reducing the cobalt salts. Fifteen parts of the nickel sulfide so pre polysulfide with hydrogen, as described in the pared was charged into an autoclave with 100 preceding example, the evolution of hydrogen parts of pentadecanone-8, 33 parts of sulfur, and sulfide commenced at 60° C. and was very vigor 25 50 parts of acetic acid. Hydrogen was admitted ous at 100° C. It is evident, therefore, that the to the autoclave to a pressure of 2,300 lbs./sq. in. reduction with hydrogen can conveniently be and the autoclave heated to 150° C. while being carried out under the conditions used for hy agitated. After a few minutes hydrogen was drogenation reactions. This is shown by the absorbed rapidly at this temperature but after following experiment. A solution of 237 parts of 30 One-half hour reaction became slower. The ten cobalt chloride was precipitated with a solution perature was then raised to 200° C. and further of 240 parts of sodium sulfide Saturated with absorption of hydrogen occurred until after a sulfur. The precipitate was filtered and washed total time of 2.5 hours no further absorption of with water and finally with alcohol. Ten parts hydrogen was noted. On working up the reaction of this unreduced precipitated cobalt polysulfide 35 mixture pentadecanethiol-8 was obtained in 80% was charged into a hydrogenation autoclave yield. with 98 parts of cyclohexanone and 32 parts of Eacample V sulfur. Hydrogen was admitted to the autoclave to a pressure of 2,000 lbs./sq. in and the auto Ten parts of cobalt polysulfide catalyst pre clave was heated to 150. Hydrogen was ab 40 pared as in Example II and made into a thick sorbed slowly at first while the cobalt polysul paste with acetic acid was charged into an auto fide was being reduced to the active catalyst. clave, together with 90 parts of methyl butyl After a few minutes, however, a rapid absorption ketOne and 32 parts of sulfur. Hydrogen was of hydrogen took place and more hydrogen was forced into the autoclave to a pressure of 2,000 added to maintain the pressure above 1,000 45 lbs./sq. in. and the autoclave heated to 150 C. lbs./sq. in. After 4 hours no more hydrogen was At this temperature the absorption of hydrogen absorbed, and on working up the contents of the became very rapid and additional hydrogen was autoclave cyclohexanethiol was obtained in an added to maintain the pressure in the range of amount corresponding to a conversion of 80% of 1,200-2,000 lbs./sq. in. After 1.5 hours the ab the cyclohexanone. 50 Sorption of hydrogen had ceased, indicating the The freshly precipitated cobalt polysulfide completion of the reaction. After removing the contained 1.65 parts of sulfur per part of cobalt. catalyst, the contents of the autoclave were dis The catalyst after use was found to be reduced tilled and there was obtained hexanethiol-2 in an to a material having 1 part of cobalt to 0.76 part amount corresponding to 66% conversion from of sulfur. This is the active form of the catalyst. 55 the ketone. In contrast to these results obtained with a The used catalyst was still active and can be used catalyst prepared according to this invention, again without undergoing further reduction. the following experiment shows the inferior per Eacample III formance of a cobalt monosulfide such as is de By way of contrast the above experiment Was 60 scribed in the literature. Cobalt monosulfide was duplicated except that a cobalt Sulfide catalyst prepared by precipitation from a solution of co prepared by the methods disclosed in U. S. balt chloride by means of a solution containing Patents 1932,186; 1955,829; 1960,977; 2,038,599; an equivalent amount of Sodium monosulfide. and 2,12,382 was used. The black precipitate of cobalt monosulfide was Seventy-five parts of CP cobaltic oxide was filtered, washed with water, and made into a heated in a stream of hydrogen sulfide at a tem paste with acetic acid. Ten parts of this cobalt perature of 350° C. for 4 hours. The product monosulfide was charged, together with 90 parts was a dark grey, friable mass which was then of methylbutyl ketone and 32 parts of sulfur, into finely pulverized before use. Five parts of the an autoclave. Hydrogen was added to a pres cobalt sulfide catalyst prepared in this manner 70 sure of 2,000 lbs./sq. in. and the autoclave heated was charged into a hydrogenation autoclave to to 150° C. Hydrogen was absorbed during the gether with 60 parts of cyclohexanone and 30 initial half hour, and the absorption ceased there parts of sulfur. The autoclave was agitated and after. The temperature was then raised to 175 hydrogen was introduced to a pressure of 2,000 C. but no further absorption of hydrogen oc S curred. After COOling the autoclave the contents 2,402,684 6 were worked up as described previously and there Eacample VIII was obtained hexanethiol-2 in an amount corre By Way of contrast, the above experiment was sponding to 27% conversion from the ketone. A repeated using a cobalt sulfide catalyst prepared comparison of this result with that obtained in by the method described in U. S. Patents 2,127,383 the preceding example shows the greater catalytic and 2,038,599. activity of the catalyst prepared by reducing co-, Sixty parts of Cobalt nitrate hexahydrate was balt polysulfide. dissolved in 200 parts of water and stirred with Eacample VI an excess of ammonium sulfide solution. The black precipitate was filtered and washed free This difference in activity of monosulfides pre 10 from Soluble Salts with water and then heated in pared according to prior art methods for obtain a current of hydrogen sulfide at a temperature of ing sulfactive catalysts and catalysts prepared 200 C. for 12 hours. The black powder was then according to this invention was also encountered finely ground. Fifteen parts of the cobalt sulfide in the case of nickel and iron sulfides. For exam prepared in this manner was charged into an ple, the behavior of two preparations of iron Sul 5 autoclave with 150 parts of cottonseed oil. Hy fide is given below. An iron sulfide catalyst was drogen was then added to the autoclave to a pres prepared according to my method as follows. A sure of 3,000 lbs. per sq. in. and the autoclave solution containing. 80 parts of sodium sulfide heated to 200° C. for 4 hours. During this period nonahydrate and 21 parts of sulfur in 300 parts very slight hydrogen absorption was apparent. of water was added with stirring to a solution 20 The contents of the autoclave were filtered from of 95 parts of ferrous sulfate heptahydrate in the catalyst. The product obtained in this man 250 parts of water. The black precipitate is fil ner was a liquid at ordinary temperatures. It had tered, washed several times with water and finally an iodine number of 89, indicating that very little with alcohol. Fifteen parts of the sulfide so pre hydrogenation had occurred. pared was charged into an autoclave, together 25 Eacample IX with 100 parts of pentadecanone-8, 33 parts of sulfur, and 50 parts of acetic acid. Hydrogen One hundred twenty-five parts of cyclohexa was added to the autoclave to a pressure of 2,000 none and 15 parts of reduced cobalt polysulfide lbs./sq. in. and the autoclave heated to a tem catalyst prepared as described in Example I were perature of 150-200° C. After 7 hours the total 30 charged into an autoclave which was then heated pressure drop had amounted to 1,800 lbs./sq. in. to 200° C. under a hydrogen pressure of 3,400 On working up the reaction product, there was lbs./sq. in. After six hours the absorption of obtained pentadecanethiol-8 in 50% conversion hydrogen had ceased, and the total pressure drop from the ketone. The reduced catalyst was found had amounted to 1,800 lbs./sq. in. After filtering to contain 1 part of iron to 1.2 parts of sulfur. off the catalyst, there was obtained by distilla One hundred forty parts of ferrous sulfate tion a mixture containing 82% of cyclohexanol, heptahydrate was dissolved in 1000 parts of water together with some unhydrogenated cyclohexa and hydrogen sulfide gas bubbled through the One, solution. Some precipitate was formed. A solu catalyst tion of 170 parts of sodium monosulfide nona 40 R2C=O - E - RCHO hydrate in 700 parts of water was added drop In the foregoing examples I have indicated cer wise with stirring. The final solution was then tain specific procedures for preparing highly ac treated again with hydrogen sulfide gas for one tive ferrous group metal sulfide catalysts. It is half hour, The precipitate was filtered and apparent that one skilled in the art may vary the washed several times with water. Fifteen parts 45 procedure used for preparing the catalysts with of the sulfide so prepared was charged into an Out departing from the scope of this invention. autoclave, together with 100 parts of penta For example, the ferrous group metal may be de decanone-8, 33 parts of sulfur, and 50 parts of rived from any suitable salt, such as, for ex acetic acid. The autoclave was heated to 150° C. 50 ample, the chloride, sulfate, nitrate, acetate, bro under a hydrogen pressure of 1,800 lbs./sq. in. mide, etc. The Valence of the metal in the orig After the absorption of hydrogen had ceased, the inal salt may be any of the common valences temperature was gradually raised to 200 C. until in which the metals exist. For example, cobaltous no further absorption of hydrogen occurred. On or cobaltic salts may be used, nickelous or nickelic, working up the reaction mixture there was ob or ferrous or ferric salts. tained pentadecanethiol-8 in 10% conversion 55 The soluble polysulfide used as the precipi from the pentadecanone-8, , tant may vary likewise. For example, the pos The ferrous metal sulfide catalysts prepared itive ion of the sulfide may be that of any of the according to this invention are also active for alkali metals such as sodium, potassium, lith other hydrogenations, as is shown by the follow ium, etc., and also the ammonium ion. It is also ing examples. 60 Within the Scope of this invention to use other Eacample VII soluble metal polysulfides, as for example those of the alkaline earth metalsIn preparing barium, catalystscalcium, One hundred fifty parts of cottonseed oil was strontium, and the like. charged, together with 15 parts of cobalt poly 65 according to this invention, any convenient sulfide prepared as in Example II, into an auto amount of sulfur may be contained in the poly clave and hydrogen was added to a pressure of sulfide solution so long as it is more than one 3,000 lbs./sq. in. The temperature was raised to atom of sulfur for each two univalent positive 200° C. and after two hours the absorption of ions or for each single divalent metal ion, etc. I hydrogen had ceased. After removing the con prefer, however, to use Solutions of sodium or tents from the autoclave and filtering off the cat ammonium polysulfide that contain between two alyst, there was obtained the hydrogenated fat and four atoms of sulfur for each two positive which melted at 44-50° C. and showed an iodine univalentions. These polysulfide solutions may number of 44.5 as compared with 113 for the orig be obtained by a variety of methods. I have found inal unhydrogenated oil. 75 it convenient to dissolve the alkali monosulfide 2,402,684 7 8 in water and stir this solution with an amount of the same apparatus that is used for the subse free sulfur calculated to yield the polysulfide de quent hydrogenation reaction. Moreover, the sired until solution is complete. The alkali poly- . material to be catalytically hydrogenated may be. sulfides may also be obtained by heating the hy present also, so that both the reduction of the drated monosulfides with free sulfur until the catalyst and the hydrogenation for which it is sulfur dissolves and thereafter diluting the mix to be used may be carried out in a single opera ture with water. tion, as illustrated in the foregoing examples. The precipitation may be carried out, as I have It is likewise a part of this invention to pre indicated, by adding the polysulfide solution to pare the ferrous metal sulfides individually or the cold, stirred, aqueous solution of ferrous O in combination with each other. For example, group metal salt. However, other procedures may active hydrogenation catalysts are obtained by be adopted. For example, the metal salt may be reducing precipitated mixtures of cobalt and added to the polysulfide solution and the precip nickel, cobalt and iron, nickel and iron poly . itation may be carried out not only at room ten sulfides. Moreover, the catalysts may be sup perature but at higher or lower temperatures. 5 ported on carriers such as kieselguhr, silica gel, While solvents such as alcohols and liquid am alumina, magnesia, or on metallic supports. For monia may be used as precipitation media, I pre liquid-phase batch hydrogenation, it is preferable fer to use water. The amount of water used in that the catalyst be in finely divided form. the precipitation and also the relative proportion However, for continuous liquid and vapor phase of the reagents may be varied considerably. The hydrogenations, the catalyst may be formed into precipitate may be washed with water to remove 20 pellets, briquets, and the like, preferably prior soluble salts, but in some cases it is convenient to the hydrogen treatment. to use the crude precipitated mixture directly. The use of the metal sulfides prepared as here Since the precipitated polysulfides rapidly oxidize in described as catalysts for hydrogenation re in contact with oxygen or air, it is preferable to 25 actions, regardless of the nature of the material protect them against oxidation by an inert at hydrogenated or the conditions under which the mosphere or liquid, such as Water, alcohol, ben hydrogenation reaction is carried out, constitutes Zene, and the like. a part of this invention. In preparing catalysts by the methods de The exact nature of the metal sulfides prepared scribed, some free sulfur may be precipitated 30 according to this invention is not known. It is along with the ferrous group metal sulfide. It is well known that alkali polysulfides do not con usually not necessary to separate the sulfur from sist of a single chemical species. For example, the metal sulfide but this may be accomplished a solution of sodium polysulfide corresponding to if desired by extracting the crude precipitate the formula Na2S3 probably contains such species with solvents for Sulfur, as for example benzene, 35 as Na2S2, Na2S3, Na2S4, and Na2S5. Consequently carbon bisulfide, Solutions of ammonium or So the ferrous group metal sulfide obtained by mix dium monosulfides. When alkali polysulfides are ing such a solution with a solution of a ferrous employed as precipitants, some ferrous group group metal salt may be a mixture of several metal hydroxide may be formed together with different species. During the treatment of the the insolubde sulfide. The presence of the metal 40 metal sulfide with hydrogen, hydrogen sulfide hydroxide is not harmful to the activity of the is evolved indicating a reduction of higher sul catalyst, but if desired the metal sulfide may be fides to lower sulfides. As shown by way of ex obtained in purer form by digesting the crude ample, a sample of precipitated cobalt sulfide precipitate with dilute organic or dilute mineral that had been extracted with dilute acid to re acid such as dilute sulfuric acid at ordinary or 45 move any cobalt hydroxide and with hot benzene elevated temperatures to dissolve the metal hy to remove any free sulfur contained 1 part of droxide, leaving the acid-insoluble metal sul cobalt to 1.65 parts of sulfur. After treating this fide. material with hydrogen, the catalyst contained The hydrogen treatment of the precipitated 1 part of cobalt to 0.76 part of sulfur. The cat sulfide may be effected with considerable lati 50 alyst may be in reality a mixture of cobalt sul tude. A paste of the precipitated sulfide may be fides of different cobalt-sulfur ratios. Similarly, heated in a current of hydrogen to remove the a sample of nickel sulfide after hydrogen treat Water or other liquid medium and the heating ment contained 1 part of nickel to 1.05 parts of continued in hydrogen until the evolution of hy Sulfur. It may be that greater reduction occurs drogen sulfide has largely ceased. I have found SS on the surface of the catalyst particles than at these metal polysulfides to be unusually reactive the interior. Hence the invention is not limited toward hydrogen, so that it is sufficient to carry to exact compositions. The ferrous group metal out the hydrogen treatment at relatively low tem Sulfides prepared according to the methods de peratures in excess of 25 C. and especially in Scribed, regardless of empirical composition, are the range from 75 to 200° C. However, the hy 30 active hydrogenation catalysts at unusually low drogen treatment may be carried out at tem temperatures. peratures above 200° C. if desired, but excessively The ferrous group metal sulfides prepared ac high temperatures above 300° C. may impair the cording to this invention are especially useful as activity of the catalysts. The duration of the catalysts for hydrogenation reactions involving hydrogen treatment necessary to activate the 85 Sulfur compounds. For example, organic disul catalyst may vary considerably and less time will fides, thioketones, and thioaldehydes may be be required the higher the temperature at which Smoothly hydrogenated to the corresponding the treatment with hydrogen is done. Usually thiols by means of the catalysts prepared accord less than One hour is necessary at temperatures ing to this invention. Furthermore, the hydro between 150 and 200° C. and at atmospheric 70 genation of aldehydes, ketones, and nitriles in pressure. The metal sulfides may be treated with the presence of hydrogen sulfide to the corre hydrogen at ordinary pressure or at superatmos Sponding thiols proceeds readily using the cat pheric pressures, and inert gases or vapors may alysts herein described. These catalysts are also be present. It is obvious that this hydrogen re useful for the hydrogen reduction of nitrates, duction of the catalyst may be accomplished in S nitrites, and a variety of unsaturated groups such 2,402,684 10 as ethylenic, acetylenic, nitro, and carbonyl bringing together in solution a salt of a metal of groups. Moreover, these reductions can be car the iron group of the periodic table and an inor red, out in the presence of sulfur impurities or ganic polysulfide, thereby precipitating a poly acids, which prevent the use of ordinary metal sulfide of said metal and then treating said metal hydrogenation catalysts. polysulfide with hydrogen at a temperature be The metal sulfides prepared according to this tween 25 and 200° C. invention are active hydrogenation catalysts at 6. The process in accordance with claim 5 char unusually low temperatures and at the same time acterized in that the treatment with hydrogen are immune to poisoning by sulfur or its con is continued until there is substantially no more pounds. This combination of properties makes O evolution of hydrogen sulfide. practicable for the first time the catalytic hy 7. The process in accordance with claim 5 char drogen reduction of certain sulfur compounds to acterized in that the treatment with hydrogen is the corresponding thiols, thus affording a new carried out at a temperature within the range and highly economical method for obtaining of 75° to 200° C. these compounds. Moreover, the catalysts are s 8. The process in accordance with claim 5 char resistant to poisoning and attack by Organic acterized in that the metal salt is a cobalt salt. acids, dilute mineral acids, alkalis, annonia, 9. The process in accordance with claim 5 char and amines, enabling one to carry out hydro acterized in that the metal salt is a nickel salt. genation reactions in the presence of these sub 10. The process in accordance with claim 5 stances which in certain cases have hitherto re 20 characterized in that the rhetal Salt is an iron Salt. quired the use of noble metal catalysts. The 11. A process for the preparation of ferrous unusual stability of these catalysts allows them group metal sulfide catalysts which comprises to be used repeatedly for hydrogenation reactions bringing together in an aqueous solution a salt with little decrease in activity. of a metal of the iron group of the periodic table It is apparent that many widely different emi 25 and an alkali polysulfide, and thereafter treat bodiments of this invention may be made without ing the precipitated metal polysulfide with hy departing from the spirit and scope thereof and drogen at a temperature between 25 and 200 C. therefore it is not intended to be limited except 12. The process in accordance with claim 11 as indicated in the appended claims. characterized in that the alkali polysulfide is a claim: . 30 sodium polysulfide containing between 2 and 4 1. The process for the preparation of ferrous atoms of sulfur for each 2 positive univalent ions. group metal sulfide catalysts which comprises 13. The process in accordance with claim 11 reacting a precipitated polysulfide of a metal of characterized in that the alkali polysulfide is an the iron group of the periodic table with hy ammonium polysulfide containing between 2 and drogen at a temperature between 25 and 200° C. 35 4 atoms of sulfur for each 2 positive univalent 2. The process in accordance with claim 1 char ions. acterized in that, the reaction is carried out at a 14. The process in accordance with claim 11 temperature between 75° and 200 c. characterized in that the precipitate is digested 3. The process for the preparation of ferrous with a dilute acid under non-oxidizing condi group metal sulfide catalysts which comprises 40 tions so as to remove any metal hydroxide there bringing a precipitated polysulfide of a metal of from. the iron group of the periodic table into contact 15. A metal sulfide hydrogenation catalyst that with hydrogen at a temperature between 75° and is active at relatively low temperatures and in the 200 C. and continuing said contact until there is presence of sulfur compounds, said catalyst being stantially no more evolution of hydrogen sul 45 obtained by bringing together in solution a salt de. of a metal of the iron group of the periodic table 4. The process in accordance with claim 1 char with an inorganic polysulfide thereby precipitat acterized in that the precipitated metal polysul ing a metal polysulfide, and thereafter treating fide is obtained by precipitation from a solution the said precipitated metal polysulfide with hy of a salt of said metal. drogen at a temperature between 25 and 200 C. 5. A process for the preparation of ferrous group metal sulfide catalysts, which comprises FRANK KERR SIGNAIGO.