Process for the Oligomerization of Ethylene

The present invention relates to the use of a refractory metal oxide/silica supported nickel cluster catalyst to oligomerize ethylene. More particularly, this invention relates to the use of a catalyst obtained by contacting a refractory metal oxide/silica support with a nickel cluster in the oligomerization of ethylene to higher olefins at high rates and low pressures.

It is well known in the art to use a variety of catalysts to oligomerize ethylene to higher molecular weight olefins. The term "oligomerize" has been employed, and is employed herein to describe the conversion of lower olefins such as ethylene to olefinic products of higher molecular weight, e.g., to dimer, trimer, tetramer and the like. The reaction rate and product distribution obtained are highly dependent on the exact catalyst composition and the reaction conditions employed. Two such general classes of catalysts are the "Ziegler" types consisting of aluminum trialkyls and the "Zeigler-Natta" types consisting of aluminum alkyl halides and titanium halides. Major disadvantages of aluminum alkyl catalysts are their highly reactive and pyrophoric nature and the fact that they must be used at relatively high temperatures, e.g., 200.degree.-275.degree. C. and pressures, e.g., 2000-4000 psig (13,790 to 27,580 kPa). Although much milder reaction conditions are used when the aluminum alkyls are used in conjunction with titanium halides, the reaction rates of both of these prior art types of catalysts are not as high as desired.

Several heterogeneous supported cyclopentadienyl nickel catalysts have been employed to oligomerize ethylene to higher molecular weight olefins. One such process described in U.S. Pat. No. 3,459,826 to Barnett et al employs nickelocene, i.e., bis(cyclopentadienyl)nickel, and an inorganic oxide catalyst support. This process, however, requires pretreatment with elemental hydrogen and yields 84% dimer and trimer. Related processes using (.pi.-cyclopentenyl)cyclopentadienyl-nickel are described in U.S. Pat. No. 3,527,838 and U.S. Pat. No. 3,532,765, both to Barnett et al.

A non-pyrophoric nickel-supported catalyst is described by Masaru Ichikawa in an article entitled "Preparation and Catalytic Activities of Supported Nickel Clusters on a Silica Surface", J. Chem. Soc., Chem. Comm. (1976), pages 26 and 27. This article discloses tris(cyclopentadienyl)trinickel dicarbonyl and other nickel cluster compounds deposited on silica gel or Vycor glass No. 7930 followed by heating at 120.degree. C. as catalysts for olefin hydrogenation and for the "oxo" reaction. Vycor glass No. 7930 is understood to be 95.6 weight percent silica, 1.0 weight percent alumina, 2.25 weight percent boric acid, the remaining 0.25 weight percent being unidentified contaminants.

It has now been found that ethylene can be oligomerized to C.sub.4 and higher olefins, by intimately contacting ethylene in a liquid medium with a catalyst produced by contacting (a) a refractory metal oxide/silica support such as alumina/silica wherein the silica content of the support is from about 2 to about 95 weight percent and the metal oxide content of the support is from about 5 to about 98 percent with (b) a tris(cyclopentadienyl)trinickel dicarbonyl. The process is characterized by ease of catalyst handling, high activity, low operating temperatures and pressures, and the production of a relatively high proportion of oligomers higher than dimer, i.e., trimer, tetramer, pentamer, etc.

The tris(cyclopentadienyl)trinickel dicarbonyl used herein has the structure: ##STR1## wherein R, R' and R" can be the same or different C.sub.1 to C.sub.20 inclusive, hydrocarbon radicals, and n, n' and n" can be the same or different integers of 0 to 5, inclusive. The R, R' and R" hydrocarbon radicals can be saturated or unsaturated, they can include aliphatic, alicyclic and aromatic radicals such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl and naphthyl radicals. One or more of the cyclopentadienyl moieties in the foregoing tris(cyclopentadienyl)trinickel dicarbonyl can be substituted so as to form an indenyl moiety or a fluorenyl moiety.

Specific examples of nickel clusters which can be used include:

tris(cyclopentadienyl)trinickel dicarbonyl,

tris(methylcyclopentadienyl)trinickel dicarbonyl,

(methylcyclopentadienyl)bis(cyclopentadienyl)trinickel dicarbonyl,

bis(methylcyclopentadienyl)(cyclopentadienyl)trinickel dicarbonyl,

tris(pentamethylcyclopentadienyl)trinickel dicarbonyl,

(pentamethylcyclopentadienyl)bis(cyclopentadienyl)trinickel dicarbonyl,

bis(pentamethylcyclopentadienyl)(cyclopentadienyl)trinickel dicarbonyl,

(methylcyclopentadienyl)bis(pentamethylcyclopentadienyl)trinickel dicarbonyl,

bis(methylcyclopentadienyl)(pentamethylcyclopentadienyl)trinickel dicarbonyl,

tris(ethylcyclopentadienyl)trinickel dicarbonyl,

(ethylcyclopentadienyl)bis(cyclopentadienyl)trinickel dicarbonyl,

bis(ethylcyclopentadienyl)(cyclopentadienyl)trinickel dicarbonyl,

tris(n-propylcyclopentadienyl)trinickel dicarbonyl,

tris(iso-propylcyclopentadienyl)trinickel dicarbonyl,

tris(butylcyclopentadienyl)trinickel dicarbonyl,

tris(pentylcyclopentadienyl)trinickel dicarbonyl,

tris(indenyl)trinickel dicarbonyl,

(indenyl)bis(cyclopentadienyl)trinickel dicarbonyl,

bis(indenyl)(cyclopentadienyl)trinickel dicarbonyl,

(indenyl)bis(methylcyclopentadienyl)trinickel dicarbonyl,

bis(indenyl)(methylcyclopentadienyl)trinickel dicarbonyl,

(indenyl)bis(pentamethylcyclopentadienyl)trinickel dicarbonyl,

bis(indenyl)(pentamethylcyclopentadienyl)trinickel dicarbonyl,

wherein the indenyl moiety has the structure: ##STR2## wherein (R.sub.1) and (R.sub.2) are the same or different C.sub.1 to to C.sub.10 hydrocarbon radicals, n is an integer of 0 to 4, and x is an integer of 0 to 3,

tris(fluorenyl)trinickel dicarbonyl,

(fluorenyl)bis(cyclopentadienyl)trinickel dicarbonyl,

bis(fluorenyl)(cyclopentadienyl)trinickel dicarbonyl,

(fluorenyl)bis(methylcyclopentadienyl)trinickel dicarbonyl,

bis(fluorenyl)methylcyclopentadienyl)trinickel dicarbonyl,

(fluorenyl)bis(pentamethylcyclopentadienyl)trinickel dicarbonyl,

bis(fluorenyl)(pentamethylcyclopentadienyl)trinickel dicarbonyl,

wherein the fluorenyl moiety has the structure: ##STR3## wherein (R.sub.3), (R.sub.4) and (R.sub.5) can be the same or different C.sub.1 to C.sub.10 hydrocarbon radicals; y and z can be the same or different integers of 0 to 4; and a is 0 or 1. The (R.sub.1), (R.sub.2), (R.sub.3), (R.sub.4) and (R.sub.5) hydrocarbon radicals can be the same or different, saturated or unsaturated and include the hydrocarbon radicals as described for R, R' and R".

The metal oxide associated with the silica in the support may be defined by the formula M.sub.x O.sub.y wherein M is aluminum, magnesium, zirconium or thorium, x is an integer of from 1 to 2 and y is an integer of from 1 to 3. Specific examples of such compounds include Al.sub.2 O.sub.3, MgO, ZrO.sub.2, ThO.sub.2, etc.

In oligomerizing ethylene with the catalyst defined herein, the ethylene and catalyst are contacted with each other at a temperature in the range of about 20.degree. to about 250.degree. C., preferably about 50.degree. to about 170.degree. C., and a pressure of about one to about 70 atmospheres, preferably from about six to about 60 atmospheres, for about 10 minutes to about 12 hours, or longer, but preferably about 0.5 to about four hours. Thus, ethylene can be brought into contact with a slurry composed of said catalyst and one of the hydrocarbon solvents as defined hereinafter. The amount of catalyst required will range from about 0.1 milligram to about 1.0 gram of nickel in the catalyst per mole of ethylene, preferably from about 1.0 milligram to about 0.1 gram of nickel in the catalyst per mole of ethylene.

With reaction times on the order of about an hour, about 20 percent by weight of the olefins formed during oligomerization are C-8 or higher. Higher percentages of olefins higher than C-8 olefins can be obtained by ceasing ethylene addition to the reactor after about 0.4 to four hours, and allowing the product olefins to continue to react at an elevated temperature within the reaction temperatures defined above, e.g., above about 50.degree. C., for from about two to about 18 additional hours.

When the nickel supported catalyst is contacted with ethylene in an aromatic solvent, such as benzene, some alkylation of the solvent can occur. Thus, at a reaction temperature of about 150.degree. C., it has been found that about five percent by weight of the total product formed in the oligomerization of ethylene is a mixture of secbutylbenzene and diethylbenzenes. In order to avoid this undesirable side reaction, it is preferred to use a non-aromatic solvent, that is, an alicyclic or aliphatic solvent, such as heptane or cyclohexane when reaction temperatures of about 150.degree. C., or higher, are employed. However, the nickel cluster has a low solubility in alicyclic and aliphatic solvents, such as heptane and cyclohexane. Thus, when using such solvents, it is preferred to prepare the catalyst in situ in the oligomerization reactor by charging the nickel cluster as a solid to the reactor along with the silica/metal oxide support, adding the solvent which is also a solvent for the oligomerization reaction, and, after the nickel cluster has been deposited on the support, adding ethylene to the reactor.

The supported nickel catalyst and ethylene can be contacted in any suitable reaction vessel such as an autoclave or similar reaction vessel provided with suitable agitation means. Preferably, the reaction vessel is purged with an inert gas such as argon or nitrogen before the catalyst and ethylene are added.

At the end of the reaction period, the contents of the reaction vessel are cooled to a temperature of about -10.degree. to about 50.degree. C., preferably about 20.degree. to about 50.degree. C., after which unreacted ethylene is vented from the system and the pressure is reduced to about one to about five atmospheres. The reactor contents are then filtered to recover the solid catalyst. The solvent and ethylene oligomers can be separated and isolated, if desired, by conventional methods, such as fractional distillation, extraction, selective adsorption, etc. The reaction solvent, catalyst and any unreacted ethylene can be recycled to the reaction vessel.

A suitable support for the catalyst composition for use in the process of this invention is a metal oxide/silica support wherein the silica content is from about 2 to about 95 weight percent and the metal oxide content is from about 5 to about 98 weight percent. Preferably, the support comprises from about 15 to about 92 weight percent silica and about 10 to about 85 weight percent metal oxide; and most preferably from about 80 to about 92 weight percent silica and from about 10 to about 20 weight percent metal oxide. The metal oxide/silica supports include synthetic materials as well as acid-treated clays or even the crystalline alumina silicates known as molecular sieves, so long as the silica and alumina contents are within the ranges specified. Thus, any of the commercially available metal oxide/silicas having the proper silica to metal oxide ratios can suitably be used to prepare the compositions of this invention. The preferred alumina/silicas are coprecipitated from aqueous or alcoholic solutions of a silicate such as sodium silicate or silicic acid and an aluminum salt such as aluminum nitrate, aluminum sulfate or aluminum chloride. For example, an aqueous solution of silicic acid and aluminum nitrate produces a coprecipitate when treated with ammonium hydroxide at a controlled pH of about 8. Differing physical properties of the coprecipitates result by varying the pH during precipitation. The precipitates are an intimate comixture of silicon and aluminum oxides.

Preferably, the support is calcined prior to contact with the nickel cluster as by heating at a temperature of from about 200.degree. C. to about 800.degree. C. and, more preferably, from about 450.degree. C. to about 650.degree. C. for a period of from about one to about 24 hours, or even longer, but preferably about four to about 12 hours. The calcining operation can be conducted in air, but is preferably conducted in an inert atmosphere such as in a stream of argon or nitrogen. Following the calcining operation, the support is cooled slowly in an inert atmosphere and stored in the absence of air.

The calcined support is then contacted in the absence of air with the nickel cluster, that is, a tris(cyclopentadienyl)trinickel dicarbonyl. The nickel cluster defined by the chemical formula (.eta..sup.5 -C.sub.5 H.sub.5).sub.3 Ni.sub.3 (CO).sub.2, wherein .eta. is the Greek letter eta, used herein, can be prepared by the method of E. O. Fischer et al described in Chem. Ber., 91, 1725 (1958). This compound is a solid at room temperature and is not sensitive to air. The structure of the nickel cluster consists of a triangle of nickel atoms with a cyclopentadienyl ligand bonded to each nickel in a pentahapto fashion and two triply-bridging carbon monoxide ligands. This complex has the structure represented above when each of n, n' and n" has a value of O.

One method of contacting the support with the nickel cluster is to use a solution of the nickel cluster in a liquid hydrocarbon solvent which is non-reactive. Examples of such solvents include pentane, hexane, heptane, cyclopentane, cyclohexane, benzene, toluene, and xylene. The amount of nickel cluster used is not critical and can vary widely as long as the nickel content of the product obtained from the reaction of the nickel cluster with the support is within the range of about 0.001 to about five weight percent, preferably within the range of about 0.05 to about two weight percent.

The nickel cluster and the support are contacted at a temperature of from about 20.degree. to about 200.degree. C. for a period of about 10 minutes to about 12 hours and, more preferably, for about 15 minutes to about one hour at a temperature of from about 20.degree. to about 100.degree. C. The temperature and time can vary widely depending upon the solubility-temperature profile of the solvent and nickel cluster. They can be contacted in any suitable reaction vessel such as an autoclave.

As previously mentioned, the nickel cluster has a low solubility in certain aliphatic and alicyclic solvents such as heptane and cyclohexane. This may result in a very slow transfer and/or an incomplete transfer of the nickel cluster from solution to the support. Thus, when using such solvents, a different method of contacting the nickel cluster and the support is preferably used. According to this method, instead of adding the nickel cluster as a solution to the reaction chamber, it is charged as a solid with the support. After purging the reaction chamber with an inert gas such as argon or nitrogen, the solvent is then added to the reaction chamber.

Following the necessary contact time to effect deposition of the nickel cluster onto the support, the resultant catalyst composition can be separated from the solvent diluent and stored, preferably in an inert atmosphere, until ready for use. Separation can be accomplished by conventional techniques such as filtration, centrifugation, and decantation. The catalyst composition can be dried in an inert atmosphere. Alternatively, the catalyst composition can be used to oligomerize ethylene in the solvent diluent in which it was prepared.

It is preferred to activate or preactivate the catalyst composition prior to contact with the ethylene, unless temperatures exceeding 100.degree. C. were used in the reaction of the nickel cluster with the support in which case the activation or preactivation is unnecessary. Activation and preactivation of the catalyst can be accomplished by heating it in an inert atmosphere at a temperature between about 70.degree. and about 200.degree. C., preferably between about 100.degree. to about 170.degree. C., for from about five minutes to about 4 hours, or longer, but preferably about 20 minutes to about one hour. The term "activation" as used herein refers to an operation performed in situ in the oligomerization reactor prior to the addition of the ethylene; and the term "preactivation" refers to an operation performed external to the oligomerization reactor.

The use of the catalyst compositions in the process of this invention results in several advantages over prior art ethylene oligomerization catalysts. Thus, their use in the oligomerization of ethylene avoids the use of the highly reactive, pyrophoric aluminum alkyls. Nickel oligomerization catalysts ordinarily do not result in the production of significant amounts of higher olefins than dimers. The catalysts described herein, however, when used to oligomerize ethylene results in the production of significant amounts of oligomers higher than dimers, that is, oligomers having up to about 20 carbon atoms. Moreover, higher reaction rates are attained at lower temperatures and pressures than with prior art catalysts.

A critical feature of the invention is that the support in the catalyst composition must contain the silicate and metal oxide within the specified ranges. As shown in Example 4 which follows, if tris(cyclopentadienyl)trinickel dicarbonyl is deposited on either pure silica or pure alumina, the resultant composition will not oligomerize ethylene. Example 5 which follows illustrates that if the amount of silica and the amount of alumina is outside the ranges specified for this invention, the resultant composition will not oligomerize ethylene.

The following examples illustrate the best mode contemplated for carrying out this invention. In the examples, the amount of nickel in the catalyst is reported as weight percent elemental nickel based upon the total catalyst weight. The activities reported were calculated based upon the weight of elemental nickel supplied by the nickel complex. All percentages are by weight unless otherwise indicated.

An alumina/silica support was prepared by calcining an alumina/silica mixture comprising 87 weight percent silica and 12 weight percent alumina under argon at 550.degree. C. for 24 hours. Subsequently, 1.50 grams of the calcined support was transferred under argon to a 300 cc Magnedrive autoclave which had been previously purged with argon. The autoclave was sealed and again purged with argon by three successive argon pressuring-venting cycles. Into a separate clean, dry bottle was accurately weighed 0.0560 gram of tris(cyclopentadienyl)trinickel dicarbonyl. The bottle was fitted with a rubber septum and purged with argon for greater than 0.5 hour. Dry, oxygen-free benzene which had been purified by distillation under argon from sodium benzophenone ketyl was syringed into the bottle and the resulting solution comprising a total volume of about 98 ml. was syringed under argon into the autoclave containing the silica/alumina support. The contents of the autoclave were stirred at 500 r.p.m. at 22.degree. C. for 0.5 hour to allow adsorption of the tris(cyclopentadienyl)trinickel dicarbonyl onto the alumina/silica support. Heating was commenced and the contents of the autoclave maintained at 150.degree. C. for 30 minutes. The weight percent of nickel on the support was 1.48. Ethylene was added to the autoclave to a total pressure of 500 psig (3448 kPa), as needed, to always maintain a pressure of 450-500 psig (3103 to 3448 kPa). The temperature was maintained at 150.degree..+-.2.degree. C. After 1.0 hour the autoclave was rapidly cooled to 20.degree. C. and the product mixture removed and analyzed by gas chromatographic techniques. The results are reported in Table I. An activity of 1576 grams of oligomer per gram of nickel per hour was found.

A catalyst composition was prepared under the conditions described in Example 1 using 2.24 grams of the same alumina/silica, 0.061 gram of tris(cyclopentadienyl)trinickel dicarbonyl and 112 ml. of benzene. After stirring these materials in the autoclave for 0.5 hour at room temperature and an additional 0.5 hour at 150.degree. C., the temperature was adjusted to 125.degree. C. Ethylene was admitted to the autoclave and maintained at a pressure of 450-500 psig (3103 to 3448 kPa) for 1.0 hour. The autoclave contents were cooled, removed and examined by gas chromatographic techniques. The results are reported in Table II. An activity of 2481 grams of oligomer per gram of nickel per hour was observed.

A benzene solution containing 0.01 gram of tris(cyclopentadienyl)trinickel dicarbonyl was stirred with 2 grams of an alumina/silica support comprising 87 weight percent silica and 12 weight percent alumina. The support having a surface area of 450 m.sup.2 /g. had been calcined under purified argon flow at 550.degree. C. for about 18 hours. A gradual decrease in the intense yellow-brown color of the solution due to the presence of tris(cyclopentadienyl)trinickel dicarbonyl was observed. After one hour, the solution became colorless and the alumina/silica support had changed color from white to brown-black, indicating complete adsorption of the tris(cyclopentadienyl)trinickel dicarbonyl onto the support. The resultant supported nickel cluster was transferred under argon to a pressure reactor wherein it was thermally activated by heating at 150.degree. C. This catalyst was then used to oligomerize ethylene at a reaction temperature of 150.degree. C. for one hour and an ethylene pressure of 35 atmospheres. After one hour, the reaction mixture was rapidly cooled to 5.degree. C. and the gases were vented from the system. The liquid reaction product was analyzed and the results are set forth in Table III. The C-6 product was analyzed by capillary column gas chromatography and the results, which indicate the presence of relatively large amounts of internal olefins, are set forth in Table IV.

The following example illustrates that when tris(cyclopentadienyl)trinickel dicarbonyl is deposited on either pure silica or pure alumina, the resultant composition will not oligomerize ethylene.

In a series of experiments, designated A through G, benzene solutions of tris(cyclopentadienyl)trinickel dicarbonyl in the amounts set forth in Table V were deposited on the supports indicated in that table in an appropriate reaction vessel under the conditions described in Example 1. In Experiments A-E, the silica support had a surface area of 350 m.sup.2 /g.; and in Experiments F and G, the alumina support had a surface area of 200 m.sup.2 /g. Ethylene was added to the reaction vessel to a pressure as indicated in the table and the reaction was conducted at the temperatures and for the length of time indicated in Table V.

In each experiment, the activity, g. oligomer/g. Ni.times.hr., was found to be 0.

In the following example, Experiments I and J illustrate the effect of varying the amounts of silica and alumina in the support and Experiments H and K illustrate the effect of using an amount of silica and an amount of alumina outside the ranges of this invention:

Four different supports were prepared by isolating a 100-200 mesh fraction and calcining under identical conditions, i.e., each support was fluidized in a stream of argon at 550.degree. C., for 5 hours. These calcined supports were used in experiments conducted in an identical manner by charging 2.0 grams of the support and 0.01 gram of solid tris(cyclopentadienyl)trinickel dicarbonyl under argon to a 300 cc. autoclave. Purging was accomplished with 3 successive pressure-vent cycles using argon. Cyclohexane (50 ml.) was weighed and syringed into the autoclave under argon. The contents were stirred at ambient temperature for 2.0 hours and were then rapidly heated to 150.degree. C. and maintained at that temperature for 30 minutes. Ethylene was then added to a total pressure of 500 psig (3448 kPa) and maintained at this temperature for 1.0 hour. The autoclave was then rapidly cooled to 5.degree. C. and the liquid contents were collected in a tared, cooled bottle and analyzed immediately by gas chromatography. The results of these experiments are shown in Table VI. In this table, experiment H used a support comprising 85 weight percent silica and 15 weight percent alumina; experiment I used a support comprising 98 weight percent silica and 2 weight percent alumina; experiment J utilized a support comprising 15 weight percent silica and 85 weight percent alumina; and experiment K utilized a support comprising 2 weight percent silica and 98 weight percent alumina. In each experiment, the weight percent of nickel on the support was 0.21.

As seen from Table VI, the dominant effect of the SiO.sub.2 :Al.sub.2 O.sub.3 ratio was to decrease activity at the two extremes, i.e., 2:98 (Experiment K) and 98:2 (Experiment I) yielding activities of 5 and 0 respectively.

A 500 ml. 3-neck round bottom flask was fitted with a magnetic stirring bar, a gas inlet, a stopper and a rubber septum. The flask was purged with argon and an alumina/silica support (2.1 grams) comprising 87 weight percent silica and 12 weight percent alumina which had been calcined at about 550.degree. C. under argon was placed in the flask. The flask was then purged with a constant flow of argon. Into a separate bottle was weighed 0.0607 gram of tris(cyclopentadienyl)trinickel dicarbonyl. The bottle was filled with a magnetic stirring bar, sealed with a rubber septum and then purged with a constant argon flow. Benzene (70 ml.) which had been purified by distillation under argon from sodium benzophenone ketyl (70 ml.) was syringed into the bottle and stirred to dissolve the nickel complex. The resulting dark yellow-brown solution was syringed into the flask containing the alumina/silica under a constant flow of argon and the resulting suspension was stirred to allow adsorption of the nickel complex onto the alumina/silica support. After 2 hours at room temperature (22.degree. C.), the suspension was filtered under argon to yield a clear orange-brown solution which was a different color from the original solution of tris(cyclopentadienyl)trinickel dicarbonyl. The supported catalyst was recovered as an orange-brown solid. The weight percent of Ni on the support was 0.27. The supported catalyst was added to an autoclave along with 50 ml. of heptane and ethylene was added to the autoclave to a total pressure of 500 psig (3448 kPa). The temperature was maintained at 150.degree. C. for 2.0 hours. The autoclave was then rapidly cooled and the product mixture removed and analysed by gas chromatographic techniques. The results are reported in Table VII.

Using the procedure described in Example 1, additional catalyst compositions were prepared using the support, the amount of tris(cyclopentadienyl)trinickel dicarbonyl, and the amount of benzene shown in Table VIII. The weight percent of Ni on the support in the resultant composition is also set forth. In Examples 7 to 9, the support had a surface area of 425-450 m.sup.2 /g; and in Example 10, the support had a surface area of 487 m.sup.2 /g.

Each of these catalysts were used to oligomerize ethylene under the conditions described in Example 1, except that in Example 8, the reactor contents were cooled to 125.degree. C. before the addition of ethylene and the reaction was run at that temperature; and in Example 9, the reactor contents were cooled to 100.degree. C., ethylene was added, the temperature was then raised to 125.degree. C. and maintained for 30 minutes, and finally the temperature was raised to 150.degree. C. and held there for 1.6 hours.

Using the procedure described in Example 5, additional catalyst compositions were prepared using the support, the amount of tris(cyclopentadienyl)trinickel dicarbonyl and the amount of heptane or cyclohexane shown in Table X. The weight percent of Ni on the support in the resultant composition is also set forth. In Examples 11 and 12, heptane was substituted for the cyclohexane of Example 5. In each example, the support had a surface area of 425-450 m.sup.2 /g.

Each of these catalysts were used to oligomerize ethylene under conditions described in Example 5, except that in Example 11, the reactor contents were cooled to 25.degree. C. before the addition of ethylene, the contents were slowly heated to 150.degree. C. after the addition of ethylene, and the reaction was run for 1.8 hours; and in Example 14, the addition of ethylene was stopped after one hour, and the autoclave contents were allowed to react overnight at 150.degree. C. Analysis of the liquid products of Example 14 indicated an olefin concentration of about 55 percent by weight in cyclohexane. The results of analysis of the product obtained in each example are reported in Table XI.

Using the procedure described in Example 5, a catalyst composition was prepared using 2.01 grams of a support comprising 87 weight percent silica and 12 weight percent alumina and a benzene solution of 0.01 gram of solid tris(cyclopentadienyl)trinickel dicarbonyl. The contents of the reactor were stirred overnight and benzene was removed at a temperature of about 25.degree. C. under high vacuum, i.e., a pressure of 10.sup.-3 mm. of mercury. The weight percent of nickel on the support was 0.20. The reactor was purged with argon and 40 ml. of heptane were added. Ethylene was then added to a total pressure of 500 psig (3448 kPa) and the reactor contents were heated to 190.degree. C. and maintained at this temperature for 3.7 hours. The results of analysis of the product are reported in Table XII.

The following example was performed to illustrate that when tris(cyclopentadienyl)trinickel dicarbonyl is not used in conjunction with a support, the resultant composition will not oligomerize ethylene.

Solid tris(cyclopentadienyl)trinickel dicarbonyl (0.11 g.) was charged to a reaction vessel. There were then added 109 ml. of benzene. Ethylene was added and the contents of the reaction vessel were heated to 150.degree. C. and maintained at that temperature for 3.2 hours. The ethylene pressure was maintained at 1000 psig (6896 kPa) throughout the reaction. The activity, g. oligomer/g. Ni.times.hr., was found to be 0.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore, and as defined in the appended claims.