Patented Feb. 3, 1948 2,435,380

UNITED STATES PATENT OFFICE 2,435,380 PROCESS FOR PRE PARNG CATALYSTS Raymond C. Archibald, Berkeley, and Robert A. Trimble, El Cerrito, Calif., assignors to Shell E)evelopment Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application September 4, 1944, Serial No. 552,714 22 Claims. (C. 252-228.4) 2 This invention relates to an improved method tion of a salt of a thioacid of an element of group of preparing metal sulfide type catalysts which VI, left sub-group, with an aqueous Solution of a are especially suitable for carrying out dehydro salt of an iron group metal and acidifying to a genations, and to the improved catalysts obtained relatively low pH, said thioacid salt Solution Con by Such process, and pertains more particularly to taining an amount of sulfide ions at least equiva improved mixed metal sulfide type catalysts. lent to said iron-group metal, whereby the mixed Metal sulfides and especially tungsten sulfide sulfides of said group VI element and of Said has long been recognized as a valuable catalytic metal are precipitated. Thereafter, the insoluble agent for effecting hydrogenation and dehydro mixed sulfides are recovered and subjected to re genation reactions and its use, alone or in com 0. ducing conditions and then converted into a form bination with various metals or other metal sul suitable as catalyst. fides, has been variously reported. Numerous at Although the thioacid salt solution may be temptS have been made to improve the effective treated with a combined solution of an iron neSS of tungsten sulfide, and various combination group metal salt and an acid, a Superior catalyst catalystS. Consisting largely of tungsten sulfide as 5 is obtained by a stepwise addition of first the Well as many Specialized methods of preparation metal salt solution and then the acid. have been proposed. Combinations of tungsten Sufficient acid is added to yield a relatively low Sulfide with a sulfide of a metal of the iron group, pH at which the highest simultaneous insolu for example, iron, cobalt, or nickel sulfide, are bilities of the sulfides of both the group VI ele especially desirable. In such combination cata ment and the iron-group metal are obtained. lysts, the tungsten sulfide usually predominates, That is, the pH is adjusted to a proper balance but in Some instances, it is often the practice to between the optimum pH for greatest insolubility use a greater proportion of the sulfides of iron, of each of Said sulfides. In general, this pH is cobalt or nickel. Many ways of preparing these above about 1, since at higher acidities the iron combination catalysts have been heretofore pro group metal sulfide becomes quite Soluble. The p0Sed. However, prior methods have been un optimum upper limit of pH depends on the nature satisfactory for various reasons, such as high of the group VI element employed but is in gen loSSes of tungsten, low catalyst activity, pelleting eral less than 3. For example, the optimum range difficulties, low mechanical stability, high cost, for mixtures of sulfides of tungsten and an iron IOW Catalyst life, etc. 30 group metal is from 1 to 2. During the acidifica It is therefore an object of this invention to tion there is a considerable evolution of hydrogen provide an improved process of preparing com sulfide, and since this evolution substantially bination catalysts comprising mixtures of the sul stops when the pH is at the desired value, this fides of a metal of the left sub-group of group serves as a practical gauge for determining the VI of the periodic table, especially of tungsten, 35 point at which the addition of acid should be and of a metal of the iron group, i.e., Fe, Co, Ni. stopped. i Another object of the present invention is to Likewise, the temperature, at which the thio provide a method of preparing such combination acid salt solution is treated, is preferably closely catalysts, whereby losses of the expensive metal controlled to give a maximum annount of precipi compounds are reduced to a minimum. 40 tation of the insoluble sulfides. In general, the It is a further object of this invention to pro treating or precipitation temperature is main Wide improved combination catalysts of the metal tained below about 50° C. and above about 20° C. sulfide type which are mechanically more stable For optimum catalyst activity and minimum and are amenable to periodic regeneration to re loss of materials, it is preferable to prepare the move carbonaceous deposits by combustion with 45 thioacid salt solution by conversion of the salt, an OXygen-containing gas. especially the ammonium salt, of the acid of said It is still another object to provide an improved group VI element in alkaline solution with a Sul process for the catalytic conversion, especially de fiding agent, such as hydrogen sulfide, ammo hydrogenation, of organic compounds in the pres nium sulfide, sodium sulfide, etc. The sulfiding ence of such combination metal sulfide catalysts. 50 agent is usually added in excess at this stage to Other objects and advantages of the presentin provide an amount of Sulfide ions at least equiva vention will be readily apparent from the follow lent to the iron-group metal subsequently added. ing description. It is especially desirable to carry out this con Briefly, the present invention comprises the version to the thio acid salt under closely con main steps of treating an aqueous alkaline Solu 55 trolled temperature conditions. Thus, the tem 2,435,880 3 perature should usually be maintained above may be used, it has been found that catalyst made about 35° C. but in general below about 55 C. with nickel chloride and nickel sulfate have lower Of the elements of the left-hand sub-group of catalyst activities than that prepared from nickel group VI of the periodic table which may be used, nitrate. For example, a catalyst prepared from those elements having an atomic weight at least nickel sulfate had an activity of 4-5% less than as great as molybdenum are more desirable. one prepared from nickel nitrate. Further, the Further, the process of the present invention is use of nickel chloride entails difficulties with cor particularly applicable to tungsten, and the pre rosion of mixing vessels with attending contami ferred salt of thiotungstic acid is the ammonium nation of the product with iron, etc. Although a Salt. 0 molal nickel to tungsten ratio of 2 to 0.5 is gen For purposes of illustration, the process will be erally most desirable, a ratio of 1.5 to 2 mols of described in more detail in relation to the prepa nickel to 1. nol of tungsten has been found to ration of mixed sulfides of tungsten and iron yield particularly effective catalysts for the selec group metals, especially nickel. :: - tive catalytic dehydrogenation of cyclohexane Tungsten is usually obtained commercially as type naphthenes. . tungstic acid or as tungstic oxide which may be in - Preferably thereafter, the tungsten in the the form of soluble tungstic acid or a less soluble . slurry of ammonium thiotungstate and nickel sul form. The tungstic acid or oxide is dissolved in fide is precipitated as tungsten trisulfide by the aqueous annonia, to form a Solution of am addition of a suitable acid, such as preferably sul monium tungState. A suitable procedure, espe 20 furic acid of, for example, 36% by weight cially. When using the less soluble form of tungstic strength. Sufficient acid is added to bring the pH acid, for preparing this solution is to suspend the of the slurry liquid to between about 1 and 2, tungstic acid in plain Water with stirring and especially between 1 and 1.5. There is a copious then add the aqueous ammonia. However, when evolution of hydrogen sulfide during acidification, the Soluble tungstic acid is used, the order of add 25 which practically ceases when sufficient acid has ing the ingredients is immaterial. It has been been added to give the desired pH. By carrying found preferable to use aqueous ammonia of, out the precipitation of tungsten in this specified for example, 10-35%, and especially, 28% pH range, minimum loSSes of both tungsten and Strength, in this preparation, since, When gaseous nickel are obtained. - ammonia, is substituted therefore, the sulfide pre 30 likewise, in order to obtain minimum losses of cipitate finally obtained is more granular and a the expensive metal compounds, the precipitation large portion of the tungsten stays in the filtrate by acidification is carried out preferably at a tem (either in solution or as a colloid). Only a por ..perature of 20 to 50° C. and especially betWeen tion of this tungsten in the filtrate Will separate 35 and 45° C. For example, with a precipitation on prolonged standing. Tests show definitely that 35 temperature of above 45 C. a blue filtrate coin this difference in action between aqueous and taining a considerable amount of tungsten Was gaseous ammonia is not due to differences in the obtained, whereas a yellow-green filtrate of low rates of addition of ammonia. The behavior is tungsten content was obtained With a precipita perfectly normal if the gaseous ammonia, is first tion temperature of below 45° C. -- dissolved in Water, and then the tungstic acid 40 Although it is generally more preferable to add added. The phenomenon, therefore, cannot be stepwise first the soluble nickel salt Solution and explained by the presence or absence of certain then the acid, it may be desirable, in some in impurities. stances, to combine the acid. With the -nickel salt The ammonium tungstate is then converted to solution before addition to the ammonium thio the thio acid salt, ammonium thiotungstate, by 45 tungState Solution. For example, Sinall streams reaction with a sulfiding agent. When using the of annoniuin thiotungState Solution and acid preferred hydrogen sulfide as the sulfiding agent, solution of nickel nitrate may be mixed at the it may simply be bubbled into the ammonium proper relative rates. In addition to the fact that tungstate solution in an open container, although a catalyst so produced has a slightly lower activity a closed pressure-type. Vessel provided With stir than that prepared by the preferred stepwise ring means is usually more desirable. In order to precipitation, the nickel sulfide is precipitated form ammonium thiotungState rather than ami less readily at the higher acid concentration so monium dithiotungstate, the temperature should that there is an incomplete precipitation of nickel be maintained somewhat above about 35° C., pref sulfide from the acidified nickel solution, whereby erably at about 40-50°C. In general, the temper 5 5 higher losses of nickel to the filtrate result. ature should be maintained below 55° C. to pre She aqueous slurry is preferably allowed to age vent Crystallization of the ammonium thiotung for at least about half an hour to obtain more state. An excess of sulfide ion, preferably as complete precipitation of tungsten trisulfide. This ammoniun Sulfide, is required to be present in the ageing may be accompanied with stirring. w Solution. - - . 60 Thereafter, the precipitated sulfide mixture is To this basic solution of ammonium thiotung Separated from the acidic aqueous solution. This state is added a sufficient amount of a soluble salt is accomplished by filtering, such as in vacuum of a metal of the iron group to obtain a molal filters, Centrifuges, etc. Secondary filters, centri ratio of tungsten to the iron group metal of fuges, etc., or settling tanks may be used to recover about 1 to 2 up to 2 to 1, although ratios outside additional Sulfides from the primary filtrates, if of this range may sometimes be used. Nickel, desired. . . . . -- - - especially in the form of nickel nitrate, has been Preferably Without washing, or after washing found to be most suitable and may be added as with dilute acid so that the pH of the slurry is a more or less concentrated solution prepared, for not altered, the mixed sulfide precipitate, ob example, by dissolving nickel nitrate hexahydrate tained as a relatively dry filter cake or stiff mud, crystals in a minimum amount of water. The ex is then dried and roasted under conditions to re cess sulfide in the ammonium thiotungState Solu duce the tungsten trisulfide to tungsten disulfide. tion causes the precipitation of nickel sulfide (and The actual valence states of the metals of the possibly Small amounts of nickel thiotungstate). catalyst in its most active form are not known, Although nickel salts other than the nitrate 75 but it is believed that the tungsten is present as 2,435,880. 5 6 the disulfide, and the nickel as some sulfide, Sub The catalysts described above are especially sulfide or mixture of elementary nickel, and sul active and selective for the dehydrogenation of fides. It is also possible that a portion of the hydroaromatic naphthenes. Furthermore, they metals exist in the form of nickel thiotungState. have exceptionally long lives and when used to The sulfur content of the finished catalyst will treat such hydrocarbons under suitable condi normally vary between about 23% and 35% by tions may be continuously employed. Over long. weight of the finished catalyst and Will depend periods of time, for instance, 5000 hours or more, in part upon the tungsten to nickel ratio. For the before the conversion, drops to a level making re preferred catalysts having a molal nickel to tung generation advisable. Thus, the frequent regen sten ratio of 1.5–2.0, the final catalyst may be O eration of the catalyst is entirely unneceSSary. generally represented by the approximate for When, after a long period of use it becomes ad Inula, visable to regenerate the catalyst, this may be W. 1.5-2.ONis 3-4S done simply, without resort to the customary For example, with a molal nickel to tungsten burning with oxygen-containing gases (although ratio of 1.5 the whole catalyst can be represented 5. this method can, if desired, be employed effec approximately by the formula: tively) by passing a stream of sulfur dioxide (preferably diluted with an inert gas) through W. 15Ni3S the catalyst bed for a short time. This regenera tion, which may be conveniently executed in although small proportions of oxygen and other situ at temperatures of, for example, 400 C. to impurities may also be present. A sulfur content 600° C., may be repeated at intervals to maintain of 26 to 28% by Weight is particularly desirable the excellent catalytic activity over exceedingly for a catalyst with a nickel to tungsten molal long periods of time. Another suitable regenera ratio of 1.5, although this may change as the cat tion procedure comprising purging with steam, alyst is used. 25. treating with steam and air, and then resulfiding, The heat treatment may be carried out in tWO has also proved exceedingly satisfactory. stages, i. e., drying and then reducing, whereby As illustrative of the process of the present in less treating gas is required and less catalyst is Wention, the following example is given: lost as fine dust. The wet filter cake may be Into a kettle containing 46.5 gallons of Water dried by heating at about 100° C. or higher until 30 the evolution of steam starts to decrease. There was added, with stirring, 64.5 pounds of soluble after the treating-gas flow is started and the tungstic acid to form a Suspension. To this was temperature increased. The reduction may be added 186 pounds (about 24.5 gallons) of 28% carried out, for example, in a rotating drum, at aqueous annonia,. Whereby the tungstic acid was a temperature of about 250° C.-500° C. in the completely dissolved except for a slight. Opales presence of a stream of hydrogen or hydrogen cense. The kettle was closed tightly and warmed sulfide, or a mixture of hydrogen and hydrogen to about 40 C. Then the tungsten was con sulfide, or other reducing gas, such as natural Werted to annonium thiotungState and an excess. gas. The heat treatment is continued for a long of ammonium sulfide provided by the addition of enough period to reduce the tungsten trisulfide 40 hydrogen sulfide until 67 pounds had been dis to the disulfide and to produce preferably a cata solved. Cooling was necessary during the addi lyst which may be readily compressed into pel tion of hydrogen sulfide to keep down the pres lets for use. The treating time is determined by Se. the pilability of the catalyst, the rate of flow of In another Wessel 155 pounds of nickel nitrate hexahydrate. Was dissolved in a minimum volume the reducing gas, etc. and may, for example, be 45 less than 15 ninutes for a 200 grain laboratory of Water (about 9A gallons). This solution of batch at a hydrogen flow rate of 0.003 cubic foot nickel nitrate was slowly added to the solution of per minute, and 6 to 8 hours for a 40-pound batch annonium thiotungState in the closed kettle, at a hydrogen flow rate of 0.3 cubic foot per nin whereupon a black precipitate, largely nickel sul ute. As the roasting is COintinued, the Catalyst 50 fide, was formed with slight evolution of hydro passes through three stages relative to its pilla gen Sulfide. bility. Under-treated catalyst is difficult to pill The tungsten Was then precipitated as: tung because it sticks to the pill machine die with the Sten trisulfide by the addition of Sulfuric acid of result that the Surface of the pill becomes dull 36% by weight strength until the pH of the slurry and Scored, and extreme pressures are required 55 Was about 1.2. Large Volumes of hydrogen sulfide to eject the pill from the die. Further roasting Were evolved during the acidification. treatinent resultS in pills that are very hard and Stirring in the closed kettle was continued dur Shiny and require no lubricant or binder. After ing all of the above operations and for about A Still further treatment the pills are still hard and hour after acidification while maintaining the Shiny, but Very brittle so that they split on ejec temperature between 40 C. and 45° C. The tion from the die. A correctly treated catalyst 60 Slurry Was then Withdrawn from the kettle and can be pilled with ease. It is believed that pill the precipitate separated from the mother liquor ability is a function of the sulfur content, which With an imperforate basket-type centrifuge. decreases during roasting. The precipitate cake (containing approxi When the desired pillability has been attained 65 mately 50-70% water) was charged to a cal in a batch of catalyst under treatment, the cata cining kiln of a design permitting heating to lyst, is cooled in an inert atmosphere, such as 425 C. in an atmosphere of hydrogen. A resi nitrogen, renoved from the drier in the form of dence time of about 6 hours at 400-425 C. in a granules and powder, crushed or granulated to Stream of hydrogen was required to reduce the the proper mesh for feeding to the pill machine, O Sulfides to the desired state. and compressed into tablets. If desired, the cata After cooling to room temperature and flush lyst may be pilled with a binder and/or a rela ing With inert gas, the granules were crushed to. tively inert extender and/or a small proportion, less than 20 mesh and formed into. 4 inch by for example 0.25% to 0.5% of one of the conven 4 inch pills by compression. tional lubricants. 75 This preparation produced approximately 100 2,435,880, 7 8 pounds of finished catalyst having a composition lent to said metal and said acid being in suff represented approximately by W2Ni4S. - cient amount to obtain a pH of between 1 and 3, The invention claimed is: - the precipitation being carried out at a temper 1. An improved process for preparing a catalyst ature below about 50 C., removing the water of mixed sulfides of an element of the left Sub : from the precipitate of mixed sulfides, and sub group of group VI of the periodic table and of a jecting the resulting dried sulfides to reducing metal of the iron-group, comprising the Steps of conditions. - treating an aqueous alkaline solution of a salt 6. An improved process for preparing a catalyst of a thioacid of said element. With an aqueous of mixed sulfides of an element of the left sub Solution of a Water-soluble salt of said metal and 10. group of group VI of the periodic table and of With a water-soluble acid to precipitate the Sul a metal of the iron-group comprising the steps fides of said element and of said metal, said thio of converting the acid salt of said element in an acid Salt Solution containing sulfide ions in an aqueous alkaline solution to a salt of the thio amount at least equivalent to Said metal and said acid with an excess of a Sulfiding agent at a tem acid being in sufficient amount to obtain a pH of 5 perature of about 35° to 50° C., treating said between and 3 at which the sulfide of said ele thioacid Salt Solution. With an aqueous solution of ment is substantially insoluble the precipitation a Water-soluble salt of Said metal and with a being carried out at a temperature below about Water-Soluble acid to precipitate the sulfides of . 50° C., removing the water from the precipitate Said element and of Said metal, said acid being of mixed sulfides, and subjecting the resulting 20 in sufficient amount to obtain a pH of between dried sulfides to reducing conditions. 1 and 3, the precipitation being carried out at a 2. An improved process for preparing a catalyst temperature below about 50° C. removing the of mixed Sulfides of an element of the left sub Water from the mixed sulfide precipitate, and group of group VI of the periodic table and of a subjecting the resulting-dried sulfides to reducing metal of the iron-group, comprising the steps of Conditions. treating an aqueous alkaline solution of a salt of 25 7. An improved process for preparing a catalyst a thioacid of said element with an aqueous so of mixed sulfides of an element of the left sub lution of a Water-Soluble salt of said metal and group of group VI of the periodic system and With a Water-soluble acid to precipitate the Sul of a metal of the iron-group, comprising the steps fides of said element and of said metal, said thio 30 of treating an aqueous alkaline solution of a salt acid Salt Solution containing. Sulfide ions in an of the thioacid of said element first with an aque amount at least equivalent to said metal and said Ous Solution of a water-soluble salt of said metal, acid being in sufficient amount to obtain a pH Said thioacid salt solution containing sulfide ions of between l and 2 the precipitation being carried in an amount at least equivalent to said metal, Out at a temperature below about 50° C. 35 whereby a precipitate of the sulfide of said metal 3. An improved process for preparing a catalyst is formed, then adding a water-soluble acid to of mixed sulfides of an element of the left sub the resultant slurry until the evolution of hydro group of group VI of the periodic table and of a gen Sulfide caused by the acidification has sub metal of the iron-group, comprising the steps of stantially ceased whereby a sulfide of said ele treating an aqueous alkaline solution of a salt of 40 ment is precipitated, the amount of said acid a thioacid of Said element with an aqueous so being sufficient to maintain a pH of between 1 iution of a water-soluble salt of said metal and and 3 and the precipitation being carried out at With dilute mineral acid to precipitate the sul a temperature below about 50° C. removing the fides of said element and of said metal, said thio Water from the precipitate of mixed sulfides and acid Salt solution containing sulfide ions in an 45 Subjecting the resulting dried sulfides to reduc amount at least equivalent to said metal and said ing conditions. acid being in sufficient amount to obtain a pH 8. An improved process for preparing a catalyst of between 1 and 3, the precipitation being car of mixed sulfides of an element of the left sub ried out at a temperature below about 50° C. group of group VI of the periodic system and of 4. An improved process for preparing a catalyst 50 a metal of the iron-group, comprising the steps of mixed sulfides of an element of the left sub of treating an aqueous alkaline solution of a salt group of group VI of the periodic table and of of the thioacid of said element with an aqueous a metal of the iron-group, comprising the steps Solution of a Water-soluble salt of said metal and of treating an aqueous alkaline solution of a With a Water-soluble acid to precipitate the sul Salt of a thioacid of Said element with an aque 55 fides of said element and of said metal, said thio ous Solution of a water soluble salt of said metal acid Salt Solution containing sulfide ions in an and With a water-Soluble acid to precipitate the amount at least equivalent to said metal and Sulfides of said element and of said metal, said Said acid being in sufficient amount to obtain thioacid salt. Solution containing sulfide ions in a pH of between 1 and 3 the precipitation being an amount at least equivalent to said metal and 60 carried out at a temperature of 20° to 50° C., sep Said acid being in sufficient amount to obtain arating the precipitate of mixed sulfides from a pH of between 1 and 2, the precipitation being the major portion of the water in the slurry, carried out at a temperature below about 50° C. drying the separated precipitate, and heating the 5. An improved process for preparing a catalyst dried precipitate at a temperature of 250-500° C. of mixed sulfides of an element of the left, sub 65 in a reducing atmosphere. group of group VI of the periodic table, said ele 9. An improved process for preparing a combi ment having an atomic weight at least as great nation catalyst of mixed sulfides of tungsten and as molybdenun, and of a metal of the iron-group of a metal of the iron group comprising the steps comprising the steps of treating an aqueous al Of treating an aqueous. alkaline solution of a salt kaline Solution of a salt of a thioacid of said ele 70 of thiotungstic acid with an aqueous solution of ment With an aqueous solution of a water-soluble a Water-soluble salt of said metal and with Salt of Said metal and with a water-solubie acid Sulfuric acid to precipitate an insoluble sulfide to precipitate the sulfides of said element and of tungsten and the Sulfide of said metal, said of Said metal, said thioacid salt solution con thiotungstic acid salt solution containing sulfide taining sulfide ions in an amount at least equiva 75 ions in an amount at least equivalent to said 2,435,380 9 O metal and said acid being in sufficient amount to tion of ammonium thiotungstate with an aqueous obtain a pH of between 1 and 2, the precipitation solution of a water-soluble salt of said metal and being carried out at a temperature between about with a dilute mineral acid to precipitate tungsten 35° C. and 459 C. removing, the Water from the trisulfide and the sulfide of said metal, said thio precipitate of mixed sulfides and subjecting the tungstate Solution containing Sulfide ions in an resulting dried sulfides to reducing conditions. amount at least equivalent to said metal and said 10. An improved process for-preparing a com acid being in sufficient amount to obtain a pH of bination catalyst of mixed sulfides of tungsten. between 1 and 2, the precipitation being carried and of a metal of the iron-group comprising the out at a temperature below about 50° C. separat steps of treating.an-aqueous alkaline solution of ing the precipitate of mixed sulfides from the a salt of thiotungstic-acid with an aqueous solu major portion of the water, in the slurry, drying tion of a water-soluble salt of said metal and with the separated precipitate, and heating the dried an acid to precipitate tungsten trisulfide and the precipitate at a temperature of 250-500 C. in a sulfide of said metal, said thiotungstic acid Salt stream of reducing gas comprising hydrogen to solution containing sudfide ions in an amount at 5 reduce the sulfur content. least equivalent to said metal and said acid being 14. The process of claim 13, wherein said re in sufficient amount to obtain a pH of between 1 ducing gas comprises a mixture of hydrogen and and 2, and the precipitation being carried out at hydrogen Sulfide. a temperature below about 4.5 C, removing the 15. An improved process for preparing a COm water from the precipitate of mixed sulfides, and 20 bination catalyst of mixed Sulfides of tungsten Subjecting the resulting dried Sulfides to reducing and nickel, comprising the steps of treating an conditions aqueous alkaline Solution of a Salt of thiotungstic 1. An improved process for preparing a com acid with an aqueous Solution of a water-Soluble bination catalyst of mixed sulfides of tungsten nickel Salt and with an acid to precipitate tung and a metal of the iron-group comprising the 25 sten trisulfide and nickel Sulfide, said thiotungstic steps of introducing aqueous ammonia into an acid salt Solution containing sulfide ions in an aqueous suspension of tungstic acid to form an amount at least equivalent to said nickel and said alkaline Solution of ammonium tungstate, Con acid being in Sufficient amount to obtain a pH of verting said tungstate to ammonium thiotung between 1 and 2, the precipitation being carried State With an excess of hydrogen Sulfide at a ten 30 out at a temperature below about 50 C. removing perature above about 35 C., treating said solu the water from said mixed sulfide precipitate, and tion of ammonium thiotungstate with an aqueous subjecting said dried sulfides to reducing condi solution of a water-soluble Salt of said metal and tions. With an acid to precipitate tungsten trisulfide and 16. The process of claim 15, wherein Said Wa the Sulfide of Said metal, Said thiotungState solu 35 ter-soluble nickel salt is nickel nitrate. tion containing Sulfide ions in an amount at least 17. The process of claim 15, wherein said Solu equivalent to said metal and said acid being in tion of nickel Salt is first added to the thiOtungstic Sufficient amount to obtain a pH of between 1. acid salt solution and then the acid is added to and 2, the precipitation being carried out at a the resultant nickel sulfide-containing liquid. temperature below about 50° C. removing the Wa 40 18. The process of claim 15, wherein said acid ter from the precipitate of mixed sulfides and is dilute mineral acid. subjecting the resulting dried Sulfides to reducing 19. The process of claim 15, wherein said acid conditions. is Sulfuric acid. 12. An improved process for preparing a Com 20. An improved process for preparing a con bination catalyst of mixed Sulfides of tungsten bination catalyst of mixed Sulfides of tungsten and a metal of the iron-group comprising the and nickel, comprising the steps of treating an Steps of introducing adueous annonia, into an adueous alkaline Solution of a Salt of thiOtungstic aqueous Suspension of tungstic acid to form an acid with an aqueous Solution of a Water-Soluble alkaline solution of ammonium tungState, con nickel salt and with an acid to precipitate tung Verting Said tungState to annonium thiotung 50 sten trisulfide and nickel sulfide, Said thiotungstic state with an excess of hydrogen Sulfide at a tem acid Salt solution containing sulfide ions in an perature above about 35° C., treating said solution amount at least equivalent to said nickel and said of ammonium thiotungstate with an aqueous acid being in sufficient amount to obtain a pH Solution of a water-Soluble Salt of said metal and of between 1 and 2, the precipitation being car With a Water-Soluble acid to precipitate tungsten 55 ried out below a temperature of about 50 C., trisulfide and the sulfide of said metal, said thio removing the water from the precipitate of tung tungState solution Containing sulfide ions in an sten trisulfide and nickel sulfide, and subjecting amount at least equivalent to Said metal and said the resulting dried precipitate to reducing con acid being in Sufficient amount to obtain a pH ditions to reduce the tungstein trisulfide to tung of between 1 and 2, the precipitation being car 60 sten disulfide and the nickel sulfide to a nickel ried out at a temperature between 20 and 50° C. Sub-Sulfide. separating the precipitate of mixed sulfides from 21. The process of claim 9, wherein the re the major portion of the water in the slurry, dry duction is continued until the product has a ing the separated precipitate, and heating the composition approximately represented by the dried precipitate at a temperature of 250-500° C. 65 formula, in a stream of reducing gas. 13. An improved process for preparing a com bination catalyst of mixed sulfides of tungsten 22. A catalyst, especially suitable for dehydro and a metal of the iron-group comprising the genating conversions of hydrocarbons of the type Steps of introducing aqueous ammonia, into an O of cyclohexane-type naphthenes, consisting aqueous SLISpension of tungstic acid to form an essentially of a reduced mixed sulfide prepared by alkaline solution of ammonium tungstate, con the process comprising the steps of treating an Verting said tungstate to ammonium thiotung aqueous alkaline solution of a salt of thiotungstic State With an exceSS of hydrogen Sufide at a ten acid with an aqueous solution of a Water-soluble perature above about 35° C., treating said solu 75 salt of nickel and with an acid and thereby form 2,485,880 2 - ing a precipitate containing an insoluble sulfide of tungsten and a sulfide of nickel, said thiotung UNITED STATES PATENTS . . . stic acid salt solution containing sulfide ions Number Name ...... Date: in an amount at least equivalent to said nickel 1862,949-r Al------June i4, 1932 and said acid being in sufficient amount to ob- 5 2,026,819 Boswell ------Jan. 7, 1936 tain at pH of between 1 and 2, the precipitation 2,037,781 Grosse ------Apr. 21, 1936 being effected at a temperature below about 50° 2,075,172 Buell et al. ------Mar. 30, 1937 C. approximately represented by the formula 2,094,128 Tazier et al. ------Sept. 28, 1937 2,105,665 Lazier et al. ------Jan. 18, 1938 W.15-2Ni 3-4s O 2,123,623 Brown ------July 12, 1938 2,159,511 Pier et al...------May 23, 1939 RAYMOND C. ARCHIBAL.D. 2,192,125 Brown et al...... Feb. 27, 1940 ROBERTA. TRIMBLE, 2,215,876 Herold et al.------Sept. 24, 1940 REFERENCEs CITED OTHER REFERENCEs The following references are of record in the Analytical Chemistry, Treadwell-Hall, vol I, file of this patent: - 7th ed., Wiley & Sons, 1930, page 184. . . . ---