US 3639647 A
Description (OCR text may contain errors)
United States Patent C) US. Cl. 252-439 18 Claims ABSTRACT OF THE DISCLOSURE Highly dispersed alloy materials of nickel and molybdenum and/ or tungsten having a very high surface area are made by the controlled reduction of a mixture of compounds of the metals in a reducing atmosphere. These alloys and their sulfides are useful in catalysis such as hydrocracking, hydrogenation-dehydrogenation and hydroisomerization.
This invention relates to novel alloys of nickel with molybdenum and tungsten and their sulfides of very high surface areas, to methods of making these materials, and to their use as catalysts.
Nickel and tungsten and nickel and molybdenum form metallurgical alloys by the fusion of a mixture of powders of the two metals. Alloys of these metals are also prepared by the cathodic electrodeposition of the metals from solutions containing the metals. However, alloys formed by these techniques have essentially no surface area and are not suitable as catalyst materials.
It is well recognized in the metallurgical arts that a temperature greater than 500 C. is required to reduce molybdenum oxide to molybdenum metal with hydrogen and a temperature greater than 650 C. is required to reduce tungsten oxide to tungsten metal with hydrogen. Furthermore, it s known that nickel tungstate and nickel molybdate are reduced to the metals in hydrogen only at a temperature in excess of 500 C. However, at these high temperatures the resulting alloys are sintered or fused to a product having essentially no surface area. In experimenting with mixed oxides of nickel and tungsten or nickel and molybdenum we found that significant amounts of nickel tungstate or nickel molybdate are formed when the oxides are heated at a temperature above about 400 C. When these mixed oxides of nickel and tungsten or nickel and molybdenum are heated in the presence of hydrogen at a temperature such as 400 C., a highly exothermic reaction takes place resulting in the production of some free nickel metal together with nickel tungstate or nickel molybdate but only a small amount, if any, of alloy is formed.
In the face of this knowledge we have made the surprising discovery that substantial amounts of the alloys of nickel and tungsten or nickel and molybdenum are produced by subjecting a mixture of reducible compounds of the metals, preferably the hydrated mixed oxides, to a controlled temperature treatment in a reducing atmosphere. The resulting product is a fine, highly dipersed powder of high surface area containing substantial amounts of an alloy of nickel and tungsten and/or molybdenum which can be sulfided to produce mixed metallic sulfides of very high surface areas. The exceptionally high surface area of these new materials is a distinguishing characteristic of substantial significance in their catalytic efiicacy. In some instances the surface area exceeds 200 square meters per gram.
These novel alloy materials include nickel-tungsten alloys, nickel-molybdenum alloys and nickel-tungsten- "ice molybdenum alloys. In their broadest range these alloy materials will possess from about 5 to about mol percent nickel, while in their preferred range they will have from about 30 to about 85 mol percent nickel. Furthermore, the mol ratio of nickel to the second component, that is molybdenum and/or tungsten, in the alloy material can vary between about 50 to 1 and about 0.2 to 1 in the broad range and between about 15 to 1 and about 1 to 1 in the preferred range. These alloys are formed by the controlled reduction of reducible compounds such as a mixture of the hydrated oxides of the metals in a reducing atmosphere at relatively mild conditions. The resulting product is a mixture of the alloy or mixed alloys together with a minor amount of metal oxide or mixed metal oxides. We were surprised to discover the presence of tungsten and/or molybdenum metal in the final product as the result of the relatively mild reduction conditions employed particularly in view of the rigorous conditions required for the separate reduction of these relatively intractable metals. We were also surprised to discover that alloy materials of significant surface area were not produced by following the procedures of our invention when either iron or cobalt was substituted for the nickel.
In accordance with our preferred procedure for pro ducing the alloys, the material undergoing reduction is initially heated at a relatively low base temperature in a reducing atmosphere and is then heated at a higher temperature in a reducing atmosphere to complete the treatment. This initial reduction is conducted between about C. and about 250 C., preferably a maximum of about 200 C. The reduction is then carried out at a temperature above about 250 C. and up to about 600 C. for the final reduction treatment. The maximum temperature for superior alloy formation and surface area is preferably restricted to a temperature of about 450 C. and most preferably a maximum temperature of about 400 C. particularly for those compositions containing tungsten.
Although this reduction procedure is considered to be a two-phase procedure in its broadest aspect, that is, the first phase being carried out at a temperature between about 100 C. and about 250 C. and the second phase being carried out at atemperature above about 250 C. and up to about 600 C., the actual operation can be carried out according to a variety of techniques. Thus the reduction treatment can be initiated at an initial temperature within the first phase of operation and raised at an appropriate rate in a series of steps or at a continuous rate to the maximum desired temperature. For example, the hydrogen reduction of the mixture of metal compounds can be initiated at 100 C. with the temperature raised at a rate of 2 C. per minute to a maximum temperature of 400 C. and then maintained at this final temperature of 400 C. for two hours. In another procedure, the reduction is carried out over a series of suitable finite temperature increments. For example, reduction can be initiated at 200 C. and at succeeding higher temperature levels such as 50 C. or 100 C. higher in each level until the maximum desired temperature is reached, provided that reduction at each temperature level is carried out for sufiicient time, such as two hours, to effectuate satisfactory reduction at each level.
If the initial reduction is initiated at a temperature above about 250 C., an uncontrolled highly exothermic reaction takes place resulting in overheating and consequent calcination and fusing of the material and/or tungstate or molybdate formation without significant alloy formation or surface area formation and without significant catalytic activity in the resulting material. We believe that the initial reduction in our preferred two-phase reduction treatment effects the highly exothermic phase of the reduction at a rate which prevents the aforementioned adverse elfects. It has been determined for superior re sults according to this two-phase procedure that the first phase treatment be conducted under such conditions that a highly exothermic reaction is substantially reduced or eliminated in the second phase of the treatment. Therefore, the temperatures and duration of treatment must be properly correlated in any specific procedure utilized in order to effectuate adequate reduction while avoiding these adverse effects.
As an alternate procedure, the mixed metal feed composition can be reduced at a constant relatively high temperature, for example 400 C. under conditions which control the exothermic reaction. One such procedure involves reduction with internal cooling of the material undergoing reduction. Another procedure involves the use of a hydrogen stream admixed with a significant quantity of an inert diluent gas such as nitrogen to limit the rate of reduction and carry off heat as it is generated. Also combinations of these procedures or equivalent procedures can be utilized.
The product after completion of the reduction treatment without further conditioning is highly pyrophoric upon exposure to air and must either be used in this state under water, hydrocarbon oil or their equivalent in the absence of oxygen or it must be partially deactivated. In this deactivation treatment we prefer to pass a stream of nitrogen containing a trace of oxygen, such as ppm, over the reduced product at room temperature or lower until the material has been stabilized against attack by air. Alternatively, a stream of carbon dioxide or other inert gas containing a minute amount of oxygen can also be used for deactivation. Following this deactivation procedure, exposure of the material to air at room temperature is accompanied by a warming of the material, indicating a still further mild oxidation of the material. Although this deactivation results in the partial oxidation of the material, it permits it to be further handled in atmospheric air and to be used for catalytic purposes as any conventional catalyst without special precautions.
The product of the first phase of the two-phase reduction procedure, that is reduction carried out at a temperature no higher than 250 C., is extremely pyrophoric upon exposure to air and therefore analysis of this material is impractical. We have found that this material cannot effectively be deactivated for use by the above specified procedure. We believe that the product of the first phase of this reduction procedure is a very intimate mixture of partially reduced oxides which are extremely reactive to reoxidation and that the second phase is required to increase the degree of reduction and place the material in a form which has less tendency to reoxidize. Even then, as pointed out, the final material must be subjected to a controlled partial reoxidation to permit it to be exposed to air.
We have discovered that the final temperature at which the reduction treatment is conducted influences the surface area of the final product. That is the higher the final temperature, the lower is the surface area until at a temperature at about 600 C. or above the material fuses and coalesces. However, the lower the final temperature of treatment the longer the period of treatment that is required. Therefore, the final temperature of treatment affects both the required time of treatment and the surface area of the final product.
We prefer to use the coprecipitated hydrated metal oxides of the desired metals as the feed material to our reduction process. Other mixed reducible compounds of the metals such as the oxides, carbonates, acetates, oxalates, etc., are usable herein. It is preferred to use coprecipitated compounds of the metals in order to obtain a more intimate mixture, however, a mixture of the compounds which have been intimately mixed in the solid form, such as by grinding together the solid compounds of the metals, can also be utilized. In producing these metal containing feed mixtures, it is important to avoid the inclusion of any undesired cationic constituent which would remain in the final product after the reduction treatment.
The final product of the reduction treatment and deactivation as described contains a nickel-tungsten and/or molybdenum alloy as a major component. X-ray diffraction analysis of the preparation indicates that the alloy is a solid solution of molybdenum and/or tungsten in nickel in which the molybdenum and/or tungsten is incorporated into the basic nickel lattice. However, the term alloy is used herein in its broad general sense, that is, to include intermetallic compounds, solid solutions of the metals or mixtures thereof in crystalline or amorphous phases, or mixtures thereof.
Elemental analysis of this final product also indicates the presence of oxygen. The amount of oxygen that is present as the result of incomplete reduction of the material has not been determined separately from the amount that is incorporated in the deactivation procedure and upon subsequent exposure to air. The final product is determined to be one or more alloy phases in admixture with one or more metal oxide or suboxide phases in crystalline, partially crystalline and/ or amorphous phases. In the high nickel compositions such as those containing about four mols of nickel for each mol of the other metal, X-ray diffraction analysis indicates a strong alloy phase and a minor amorphous phase. As this mol ratio is re duced to about three, a small tungsten suboxide phase appears together with a strong alloy phase and a more significant amorphous phase. When the mol ratio is reduced further to about one, the crystalline tungsten suboxide phase becomes more significant together with a strong alloy phase and an equivalent amorphous phase. When the mol ratio is further reduced to about one-third, the tungsten suboxide phase predominates over the alloy phase along with the appearance of a tungsten and/or molybdenum metal phase and a reduced amorphous phase. These observations indicate that a mol ratio of nickel to the other metals of greater than about one is preferred for superior alloy formation. The alloy in our composition is the major constituent and constitutes greater than percent in the higher ranges of nickel content with the oxide phases being only a minor constituent. It has been observed, in general that the oxygen content decreases as the nickel content of the material increases.
When these materials containing the metal alloys are treated in a sulfiding atmosphere, such as one containing hydrogen sulfide, under sulfiding conditions, various sulfides of the metals are produced. The particular sulfide of nickel, of which there are several, that is produced is in part dependent upon the particular temperature used and the concentration of the hydrogen sulfide in the sulfiding gas. It is significant that the sulfiding operation produces the metal sulfides as a result of a sulfiding of the metals present as well as a significant sulfiding of the metal oxides and/or suboxides present in the material, therefore the oxygen content of the sulfided material is significantly lower than the oxygen content of the nonsulfided material. This sulfiding procedure is effected with only a slight reduction of the surface area of the alloy material, that is, the resulting sulfided product possesses an unusually high surface area. This sulfiding can be conveniently carried out at any suitable temperature such as a temperature between about 250 C. and about 400 C.
In order to point out more fully the nature of the present invention the following specific examples are set forth without any intention of limiting the invention.
EXAMPLE 1 A solution containing 65.5 grams of nickel nitrate hexahydrate and 6.3 grams of ammonium rnetatungstate, (NH W O -8H O in 375 ml. of water was mixed with 500 ml. of 8 molar ammonium hydroxide. The precipitate obtained by stirring and heating the mixture until the pH reached between 7 and 8 was filtered by suction and dried at 120 C. for hours. Analysis of this material, preparation 1, together with three other materials prepared in the same manner but using different proportions of the nickel and tungsten compounds are set forth in Table I. The water content was determined by thermal gravimetric analysis and the nonwater oxygen by difference. These materials are called hydrated metal oxides or metal oxide hydrates, although their precise structure Each of the preparations listed in Table I was separately packed in a tube and slowly reduced with hydrogen which was passed over each sample for two hours at each of the following temperatures in the sequence 250, 300, 350 and 400 C. at a gas hourly space velocity of approximately 200 hour- At the completion of each reduction cycle the sample tube was cooled to 78 C. and dried nitrogen was passed over the sample for three hours. Each tube was then left open to the atmosphere at C. for approximately 20 hours. The analysis in weight percent of the components of these resulting reduced materials following deactivation and exposure to air as well as surface area in square meters per gram is set forth in Table II.
An X-ray diffraction analysis indicates that a major crystalline component in preparations 1, 2 and 3 and a minor component in preparation 4 is a solid solution of tungsten in nickel. This solid solution or alloy retains the basic nickel lattice with an expanded cubic unit cell in accommodation of the larger atomic radius of the tungsten. The unit cell size of this crystalline alloy was determined to be constant within the limits of error of the measurements even though the over-all nickel-tungsten ratio varied from sample to sample. A poorly crystallized tungsten suboxide phase appears in a minor amount in preparation 2, in greater amount in preparation 3, and in major amount in preparation 4. Also observed in the pattern for preparation 1 was a poorly crystallized or amorphous phase which was more predominant in preparations 2 through 4. A significant amount of nonalloyed tungsten metal was identified in the pattern of preparation 4. The d spacings and relative intensities of the X-ray EXAMPLE 3 The procedure of Example 1 was followed using varying proportions of nickel nitrate hexahydrate and ammonium molybdate. The analysis of the nickel-molybdenum oxide hydrates produced thereby are set forth in Table III.
TABLE III Ni, Mo, 0, H20. weight weight weight weight percent percent percent percent Preparation:
EXAMPLE 4 The materials resulting from the procedures of Example 3 were reduced in accordance with the procedures of Example 2. The analysis in weight percent of the reduced material after deactivation and exposure to air is set forth in Table IV.
TABLE IV Ni/Mo,
mol/ N1 M0 0 mol SA Preparation:
The nickel-molybdenum alloy formed in preparations 5, 6 and 7 of Table IV has an X-ray dilfraction pattern very similar to that shown under Example 2 for the nickeltungsten alloy. The principal difierence is that the lines of the nickel-molybdenum pattern are broader and more asymmetrical than those for nickel-tungsten, which suggests that the nickel-molybdenum solid solution obtained is not as homogeneous in composition or is not as well crystallized as the nickel-tungsten solid solution or alloy.
Nickel-tungsten-molybdenum alloys are produced using the same procedures as described in Examples 1 to 4 from the hydrated metal oxide mixture obtained by precipitation from a solution of suitable compounds of the three metals.
EXAMPLE 5 Preparation 2 of Table I was reduced at 250 C. for two hours and at 300 C. for two hours using the same general procedure set forth in Example 2. Without deactivation or exposure to air, the sample was then subjected to a stream of hydrogen sulfide in hydrogen in a volumetric ratio of 1 to 4 at 300 C. and a space velocity of about 300 vol./vol./hr. for two hours. The resulting product contained nickel sulfide and tungsten sulfide but no combined nickel-tungsten sulfide as determined by X-ray diffraction analysis. It analyzed as 31.5 Weight percent nickel, 35.1 percent tungsten, 27.7 percent sulfur and 5.6 percent oxygen and possessed a surface area of 46.4 m. /g. Additional experiments showed that the sulfide species and the surface areas are affected by the temperature of the sulfiding, the concentration of the hydrogen sulfide and the composition of the reduced alloy composition.
EXAMPLE 6 The procedures of Example 5 were followed using preparation 7 of Table III. The reduction was at 250 C. for two hours and 300 C. for two hours. Sulfiding was carried out at 350 C. for two hours. The product contained a nickel sulfide and molybdenum sulfide but no combined nickel-molybdenum sulfide. The product analyzed as 27.3 weight percent nickel, 35.9 percent molybdenum and 36.8 percent sulfur. The sulfided mixture had a surface area of 35 mF/g.
The various metal alloy and metal sulfide materials, examples of which are described above, are useful as catalysts in various hydrocarbon reactions including bydrogenation-dehydrogenation such as the gas phase dehydrogenation of cyclohexane, hydrocracking and hydroisomerization. The following examples describe uses of these materials as catalysts.
EXAMPLE 7 n-Octane was hydrocracked in separate runs using preparation l of Table II and preparation 6 of Table IV and compared with nickel metal prepared from dry nickel hydroxide by the procedures set forth in Example 2. These catalysts were pelleted to to mesh size. Hydrocracking was carried out at 400 C. and at atmospheric pressure using a liquid hourly space velocity of n-octane of 0.43 hour and a hydrogen to n-octane mol ratio of 1.5.
The nickel converted 68 percent of the n-octane to 100 percent gas product, primarily methane, the nickel-tungsten catalyst converted 33 percent of the n-octane to 50 percent liquid product, and the nickel molybdenum converted 45.4 percent of the n-octane to 68 percent liquid product. The liquid product in both instances was mainly C and C hydrocarbons with a minor fraction of ethyl benzene. These results illustrate the significant difference in catalytic effect between the alloy materials and the nickel metal. These results also further indicate that the nickel is combined in the two metal component catalysts since gas formation would be the product with free nickel.
EXAMPLE 8 Preparation 3 of Table II and a nickel catalyst prepared as described in the preceding example were compared in the hydroisomerization of l-hexene at a temperature of 350 C. and atmospheric pressure using a liquid hourly space velocity of 1.0 based on the l-hexene and a hydrogen to l-hexene mol ratio of 7.5. In each instance the catalyst was 10 to mesh size. The nickel converted 23 percent of the l-hexene with a selectivity of 53 percent to branched C acyclic compounds, while the nickel-tungsten catalyst converted 50 percent of the 1- hexene with a selectivity of 88 percent to branched C acyclic compounds.
EXAMPLE 9 Preparation 2 of Table II in powder form and a powdered nickel catalyst prepared as described in Example 7 were compared in the liquid phase hydrogenation of 1- hexene. In each experiment 0.5 gram of the catalyst was added to a mixture f0 0.1 6 mol of l-hexene, 0.25 mol of acetic acid and 0.25 mol of methanol in a 100 ml. stainless steel autoclave. Hydrogen was then introduced at 150 p.s.i.g. and the temperature was raised to 100 C. and held there for three hours. The nickel-tungsten catalyst hydrogenated 81 percent of the l-hexene while no hydrogenation occured with the nickel catalyst.
As indicated these novel catalytic materials can be used in a powdered form or in pelleted or extruded form. Additionally they can be mixed with suitable solid diluents or dispersants. These dispersants can provide a separate catalytic function in addition to that provided by the metal alloy when in use or they can be catalytically inert. Examples of such materials are alumina, silicaalumina, carbon, silicon carbide, granular or powdered polymeric materials such as fiuorinated hydrocarbon polymer, etc.
These dispersed alloy materials can be produced by directly mixing the powdered alloy material with the dispersant or by mixing the unreduced metal ocmpounds, such as the hydrated metal oxides, with the dispersant and then reducing the resulting mixture in the described manner. These dispersed mixtures can contain any suitable proportion of alloy material and dispersant, desirably about 5 to about 50 volume percent of the alloy material and more desirably about 10 to 30 volume percent of the alloy material. The following examples relate to dispersed catalysts.
EXAMPLE 10 45.9 grams of preparation 2 of Table I were mixed with 137.4 grams of a commercially available high surface area silica-alumina containing 75 percent silica and 25 percent alumina. The mixture was cooked in boiling water for five hours and then dried at 120 F. The mixture was then formed into 10 to 20 mesh pellets and reduced according to the procedures of Example 2. Next, grams of the reduced mixture were charged to a reactor and treated for one hour at 600 F. and at one atmosphere pressure with a hydrogen-hydrogen sulfide mixture containing eight percent hydrogen sulfide. Following this an FCC furnace oil was passed over the catalyst at a liquid hourly space velocity of 2.0 and at a temperature of 600 F. and a pressure of 1000 p.s.i.g. together with 10,000 s.c.f. of hydrogen per barrel of charge. During an eight hour run 19 percent of the furnace oil was cracked.
EXAMPLE 11 Preparation 3 of Table H was dispersed with the silicaalumina used in the preceding example using the same proportions and procedures. This material was used for the hydroisomerization of l-hexene at the same conditions used in Example 8, resulting in 83 percent conversion with an 88 percent selectivity to branched C acyclic compounds.
In another example powdered alloy material, such as preparation 2 of Table II or preparation 2 of Table IV, is mixed with powdered Teflon (fluorocarbon resin produced by E. I. du Pont de Nemours Company) in suitable proportions such as an equal volume mix. After thorough mixing the mixture is cast into a sheet and used in fuel cells as a catalyst.
As indicated, the surface area of the resulting alloy materials is affected by the maximum temperature of the reduction treatment. This feature permits a significant control of the final surface area of the material. For catalytic purposes it is desirable to prepare a final product with a surface area of at least one square meter per gram, however, it is preferred that the material have a surface area of at least 20 m. g. In carrying out the reduction hereunder any suitable reducing atmosphere can be used including hydrogen, carbon monoxide, mixtures of hydrogen and carbon monoxide, mixtures of these with diluent gases, etc.
It is to be understood that the above disclosure is by way of specific example and that numerous modifications and variations in the alloy materials and methods for their preparation and utilization are available to those of ordinary skill in the art without departing from the true spirit and scope of our invention.
1. A catalyst consisting of metallic nickel, a second metallic component selected from the class consisting of molybdenum, tungsten and mixtures thereof, the mol ratio of nickel to said second component being between about 50 to l and about 0.2 to 1, and less than 25 percent of an oxide or oxides of said metals, said nickel and said second component associated together as -an alloy, and said catalyst having a surface area of at least about one square meter per gram.
2. A catalyst in accordance with claim 1 on a solid catalyst support.
3. A catalyst in accordance with claim 2 in which the second component is tungsten.
4. A catalyst in accordance with claim 2 in which the second component is molybdenum.
5. A catalyst in accordance with claim 2 in which the mol ratio of nickel to said second component is from about 15 to one to about one to one.
6. A composition in accordance with claim 2 in which the surface area is at least about 20 m. g.
7. A catalyst in accordance with claim 1 in which the mol ratio of nickel to said second component is from about 15 to one to about one to one.
8. A method for producing the catalyst of claim 1 which comprises heating a mixture of reducible compounds of said metals in a reducing atmosphere at a first temperature between about 100 and 250 C. and further heating the partially reduced mixture in a reducing atmosphere at a second temperature above about 250 C. and up to about 600 C.
9. A method for producing the catalyst of claim 2 Which comprises heating a mixture of reducible compounds of said metals in the presence of said solid catalyst support in a reducing atmosphere at a first temperature between about 100 and 250 C. and further heating the partially reduced mixture in a reducing atmosphere at a second temperature above about 250 C. and up to about 600 C.
10. A method in accordance with claim 9 in which said reducing atmosphere contains hydrogen and said second temperature is between about 300 and 500 C.
11. A method in accordance with claim 10 in which said second component is molybdenum.
12. A method in accordance with claim 10 in which said second component is tungsten.
13. A method of producing sulfided alloys of nickel and a second component selected from the group consisting of molybdenum, tungsten and mixtures thereof which comprises heating a mixture of reducible compounds of nickel and a second component selected from the group consisting of molybdenum, tungsten and mixtures thereof, the mol ratio of nickel to the second component as the metals being between about to 1 and about 1 to .1, in a reducing atmosphere at a first temperature between about 100 and about 250 C., further heatmg the partially reduced mixture in a reducing atmosphere at a second temperature above about 250 and up to about 600 C., and finally heating the reduced product in a sulfiding atmosphere at a temperature between about 250 C. and about 400 C.
14. A method for producing sulfided alloys in accordance with claim 13 in which the reducible compounds of nickel and the second component are on a solid catalyst support.
15. A method in accordance with claim 14 in which said second component is molybdenum.
16. A method in accordance with claim 14 in which said second component is tungsten.
17. The sulfided catalyst consisting of the sulfided alloy of nickel and a second component selected from the group consisting of molybdenum, tungsten and mixtures thereof as produced by the method of claim 13.
18. The supported sulfided catalyst consisting of the sulfided alloy of nickel and a second component selected from the group consisting of molybdenum, tungsten and mixture thereof on a solid catalyst support as produced by the method of claim 14.
References Cited UNITED STATES PATENTS 2,650,906 9/1953 Engel et a1. 252-470 2,744,052 5/1956 Nozaki 25243'9 X 2,948,687 8/1960 Hadley 252470 PATRICK P. GARVIN, Primary Examiner US. Cl. X.R.
252-470; l70; 208--l.l2; 26 0-68165