Catalyst for production of hydrocarbons

A catalyst for converting synthesis gas composed of hydrogen and carbon monoxide to hydrocarbons. The catalyst includes cobalt in catalytically active amounts up to about 60 wt % of the catalyst and rhenium in catalytically active amounts of about 0.5 to 50 wt % of the cobalt content of the catalyst supported on alumina. A metal oxide promoter may be added.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to catalysts and more particularly to a 
catalyst for converting synthesis gas to hydrocarbons. 
2. Description of the Prior Art 
The reaction to convert carbon monoxide and hydrogen mixtures (defined 
herein as synthesis gas or syngas) to higher hydrocarbons over metallic 
catalysts has been known since the turn of the century. This reaction is 
commonly referred to as the Fischer-Tropsch or F-T synthesis. The F-T 
synthesis was exploited commercially during World War II in Germany. By 
1944 a total of nine F-T plants were operating in Germany, primarily using 
a catalyst composed of cobalt, magnesium oxide, thorium oxide and 
kieselguhr, in the relative proportions of 100:5:8:200. Later, most of the 
thoria was replaced by magnesia, primarily for economic reasons. 
Currently, commercial Fischer-Tropsch plants are operating in South 
Africa. These plants use a precipitated iron-based catalyst which contains 
various promoters to improve the stability and product distribution. 
The common F-T catalysts are nickel, cobalt and iron. Nickel was probably 
the first substance to be recognized as capable of catalyzing the reaction 
of syngas to hydrocarbons, producing mainly methane (see, for example, 
"The Fischer-Tropsch Synthesis" by R. B. Anderson, Academic Press (1984), 
p.2). Iron and cobalt are able to produce longer chain length hydrocarbons 
and are thus preferred as catalysts for the production of liquid 
hydrocarbons. However, other metals are also capable of catalyzing the F-T 
synthesis. Ruthenium is a very active catalyst for the formation of 
hydrocarbons from syngas. Its activity at low temperatures is higher than 
that of iron, cobalt or nickel; and it produces a high proportion of heavy 
hydrocarbons. At high pressures, it produces a high proportion of high 
molecular weight wax. Osmium has been found to be moderately active, while 
platinum, palladium and iridium exhibit low activities (see Pichler, 
"Advances in Catalysis", vol. IV, Academic Press, N.Y., 1952). Other 
metals which are active, such as rhodium, yield high percentages of 
oxygenated materials (Ichikawa, Chemtech, 6, 74 (1982)). Other metals that 
have been investigated include rhenium, molybdenum and chromium, but these 
exhibit very low activities with most of the product being methane. 
Various combinations of metals can also be used for synthesis. Doping 
cobalt catalysts with nickel causes an increase in methane production 
during F-T synthesis (see "Catalysis", vol. IV, Reinhold Publishing Co., 
(1956), p.29). In U.S. Pat. No. 4,088,671 to T. P. Kobylinski, entitled 
"Conversion of Synthesis Gas Using a Cobalt-Ruthenium Catalyst", the 
addition of small amounts of ruthenium to cobalt is shown to result in an 
active F-T synthesis catalyst with a low selectivity to methane. Thus, 
these references teach that the combination of two or more metals can 
result in an active F-T catalyst. In general, the catalysts of these 
teachings have activities and selectivities which are within the ranges of 
the individual components. 
Combinations of metals with certain oxide supports have also been reported 
to result in an improved hydrocarbon yield during F-T synthesis, probably 
due to an increase in the surface area of the active metal. The use of 
titania to support cobalt or cobalt-thoria is taught in U.S. Pat. No. 
4,595,703, entitled "Hydrocarbons from Synthesis Gas". In this case the 
support serves to increase the activity of the metal(s) toward hydrocarbon 
formation. In fact, titania belongs to a class of metal oxides known to 
exhibit strong metal-support interactions and, as such, has been reported 
to give improved F-T activity for a number of metals (see, for example, S. 
J. Tauster et al, Science, 211, 1121 (1981)). Combinations of titania and 
two or more metals have also been shown to yield improved F-T activity. In 
U.S. Pat. No. 4,568,663, entitled "Cobalt Catalysts In the Conversion of 
Methanol to Hydrocarbons and for Fischer-Tropsch Synthesis", combinations 
of cobalt, rhenium and thoria and cobalt and rhenium supported on titania 
are claimed useful for the production of hydrocarbons from methanol or 
synthesis gas. This patent also indicates that similar improvements in 
activity can be obtained when cobalt-rhenium or cobalt-rhenium-thoria is 
compounded with other inorganic oxides. However, titania is the only 
support specifically discussed. The typical improvement in activity gained 
by promotion of cobalt metal supported on titania with rhenium is less 
than a factor of 2. We have found that the addition of rhenium to cobalt 
metal supported on a number of other common supports results in similar 
improvements in activity. 
The only other examples in the literature of catalysts involving mixtures 
of cobalt and rhenium refer to completely different chemical reactions. 
For example, in Soviet Union Pat. No. 610558, a catalyst composed of 
cobalt and rhenium supported on alumina is taught to result in improved 
performance for the steam reforming of hydrocarbons. Steam reforming of 
hydrocarbons is a process completely different from hydrocarbon production 
via F-T synthesis and is believed to proceed by a completely different 
mechanism. Although some steam reforming catalysts can convert synthesis 
gas to hydrocarbons, such catalysts are not selective for the production 
of high carbon-number hydrocarbons (C3 and above) during conversion of 
synthesis gas. In fact, most commonly used steam reforming catalysts 
contain nickel as their active metal, and nickel produces mostly methane 
when used for syngas conversion. 
SUMMARY OF THE INVENTION 
It has been found in accordance with the present invention that synthesis 
gas comprising hydrogen and carbon monoxide can be converted to liquid 
hydrocarbons by using a catalyst consisting of cobalt and rhenium 
supported on alumina. The catalyst preferably contains from about 5 to 60% 
cobalt and has a rhenium content between 0.5 and 50% of the amount of 
cobalt. The alumina preferably is gamma alumina. 
It has been found that the addition of small amounts of rhenium to 
catalysts consisting predominantly of cobalt supported on alumina 
unexpectedly results in greatly enhanced activity of this catalyst for 
hydrocarbon production from syngas. This is surprising in light of the 
fact that rhenium supported on alumina shows very low activity, with most 
of the product being methane. Furthermore, rhenium addition to cobalt 
supported on supports other than alumina results in catalysts with much 
lower activity levels. In addition, the more active cobalt plus rhenium 
catalyst maintains the high selectivity to higher hydrocarbons and the low 
selectivity to methane found with an alumina-supported cobalt catalyst. 
Both the high activity and the low methane production of cobalt-rhenium on 
alumina are unexpected in light of the facts that (1) rhenium shows very 
low activity for F-T synthesis, (2) the main products from F-T synthesis 
over a rhenium catalyst are methane and carbon dioxide, and (3) the use of 
alumina as a support for catalysts containing only cobalt results in no, 
or at best only a slight, increase in activity compared to the use of 
cobalt on other supports. Thus, for reasons not fully understood, the 
combination of cobalt and rhenium supported on alumina results in a 
catalyst which is significantly more active than either of the two 
individual metals supported on alumina or the combination of the two 
metals supported on other inorganic supports, such as silica, magnesia, 
silica-alumina, titania, chromia or zirconia. Furthermore, the product 
distribution with a high selectivity to C.sub.2 + hydrocarbons and low 
selectivity to methane and carbon dioxide would not have been predicted 
based on the known product distribution from rhenium catalysts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The catalyst of the present invention comprises as the active catalytic 
ingredients cobalt and rhenium supported on alumina with rhenium present 
in a relatively smaller amount than cobalt. This catalyst has been found 
to be highly active for the conversion of synthesis gas, a mixture of 
hydrogen and carbon monoxide, into a mixture of predominantly paraffinic 
hydrocarbons. As indicated above, it has long been known that cobalt is an 
active catalyst for the F-T synthesis. It is also known that the addition 
of rhenium to a cobalt catalyst supported on titania gives improved 
activity, even if rhenium by itself shows very low activity for F-T 
synthesis and produces methane as the main product. Surprisingly, we have 
found that the choice of support for the cobalt plus rhenium catalyst is 
very critical, and that the addition of rhenium to an alumina-supported 
cobalt catalyst gives a much higher improvement in activity than addition 
of rhenium to cobalt supported on other inorganic oxides. 
The cobalt is added to the alumina support in some amount up to about 60 wt 
% of the catalyst, including cobalt. Preferably, amounts between 5 and 45 
wt % are used; and more preferably between 10 and 40 wt %. The content of 
rhenium is between about 0.5 and 50 wt % of the cobalt content; preferably 
between 1 and 30 wt %; and more preferably from about 2 to around 20 wt %. 
In addition to cobalt and rhenium, it is beneficial to include a small 
amount of a metal oxide promoter in an amount between about 0.1 and 5 wt 
%, and more preferably between about 0.2 and 2 wt %, based on the weight 
of the complete catalyst. The promoter is suitably chosen from elements in 
groups IIIB, IVB and VB of the periodic chart, the lanthanides and 
actinides. The promoter oxide can be chosen from, for example, Sc.sub.2 
O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3, Ce.sub.2 O.sub.3, Pr.sub.2 
O.sub.3, ZrO.sub.2, Ac.sub.2 O.sub.3, PaO.sub.2, Nd.sub.2 O.sub.3, 
CeO.sub.2, V.sub.2 O or Nb.sub.2 O.sub.5. The most preferable oxide is 
La.sub.2 O.sub.3, or a mixture of lanthanides, rich in lanthanum. Oxides 
like MnO or MgO can also be included. Whle not essential, the use of these 
metal oxides is common in the art, since they are believed to promote the 
production of products with higher boiling points, while maintaining or 
improving catalytic activity. However, the catalyst is highly active and 
selective without the addition of a promoter. 
The Catalyst Support 
The catalytically active metals and the promoter metal oxide, if present, 
are distended on alumina. Although other supports may be used, it has been 
found, for example, that silica, titania, chromia, magnesia, 
silica-alumina and zirconia produce catalysts with much lower activities. 
To be most effective when used as a support, alumina should be 
characterized by low acidity, high surface area, and high purity. These 
properties are necessary in order to enable the catalyst to have high 
activity and a low deactivation rate, and to produce high molecular weight 
hydrocarbon products. The surface area of the alumina support is at least, 
and preferably greater than, about 100 m.sup.2 /g; and more preferably at 
least about 150 m.sup.2 /g. The pore volume is at least, and preferably 
greater than, about than 0.3 cm.sup.3 /g. The catalyst support must be of 
high purity. That is, the content of elements, e.g. sulfur and 
phosphorous, that have a deleterious effect on catalytic activity must be 
kept low. The sulfur content of the catalyst support should be kept below 
100 ppm and preferably below 50 ppm. Although gamma alumina has generally 
been used and is preferred, a number of alumina structures, if prepared 
properly, can meet these conditions and are suitable supports. For 
example, eta-aluminna, xi-alumina, theta-alumina, delta-alumina, 
kappa-alumina, boehmite and pseudo-boehmite can all be used as supports. 
Catalyst Preparation 
The method of depositing the active metals and the promoter oxide on the 
alumina support is not critical, and can be chosen from various methods 
well known to those skilled in the art. One suitable method that has been 
employed is known as incipient wetness impregnation. In this method the 
metal salts are dissolved in an amount of a suitable solvent just 
sufficient to fill the pores of the catalyst. In another method, the metal 
oxides or hydroxides are coprecipitated from an aqueous solution by adding 
a precipitating agent. In still another method, the metal salts are mixed 
with the wet support in a suitable blender to obtain a substantially 
homogeneous mixture. In the present invention, if incipient wetness 
impregnation is used, the catalytically active metals can be deposited on 
the support using an aqueous or an organic solution. Suitable organic 
solvents include, for example, acetone, methanol, ethanol, dimethyl 
formamide, diethyl ether, cyclohexane, xylene and tetrahydrofuran. Aqueous 
impregnation is preferred when Co(NO.sub.3).sub.2 is used as the salt, 
while an organic solvent is the preferred solvent when the catalyst is 
prepared from cobalt carbonyl. 
Suitable cobalt compounds include, for example, cobalt nitrate, cobalt 
acetate, cobalt chloride and cobalt carbonyl, with the nitrate being the 
most preferable when impregnating from an aqueous solution. Suitable 
rhenium compounds include, for example, rhenium oxide, rhenium chloride 
and perrhenic acid. Perrhenic acid is the preferred compound when 
preparing a catalyst using an aqueous solution. The promoter can suitably 
be incorporated into the catalyst in the form, for example, of the nitrate 
or chloride. 
After aqueous impregnation, the catalyst is dried at 110.degree. to 
120.degree. C. for 3 to 6 hours. When impregnating from organic solvents, 
the catalyst is preferably first dried in a rotary evaporator apparatus at 
50.degree. to 60.degree. C. under low pressure, then dried at 110.degree. 
to 120.degree. C. for several hours longer. 
The dried catalyst is calcined under flowing air by slowly increasing the 
temperature to an upper limit of between 200 and 500.degree. C., 
preferably between 250.degree. and 350.degree. C. The rate of temperature 
increase is preferably between 0.5.degree. and 2.degree. C. per minute, 
and the catalyst is held at the highest temperature for a period of 2 to 5 
hours. The impregnation procedure is repeated as many times as necessary 
to obtain a catalyst with the desired metals content. Cobalt, rhenium and 
the promoter, if present, can be impregnated together, or in separate 
steps. If separate steps are used, the order of impregnating the active 
components can be varied. 
Before use, the calcined catalyst is preferably reduced with hydrogen. This 
can suitably be done in flowing hydrogen at atmospheric pressure at a flow 
rate between 30 and 100 cm.sup.3 /min when reducing about 2 g of catalyst. 
The flow rate should suitably be increased for larger quantities of 
catalyst. The temperature is increased at a rate between 0.5.degree. and 
2.degree. C. per minute from ambient to a maximum level of 250.degree. to 
450.degree. C., preferably between 300.degree. and 400.degree. C., and 
maintained at the maximum temperature for about 6 to 24 hours, more 
preferably 10 to 24 hours. 
After the reduction step, the catalysts may be oxidized and rereduced 
before use. To carry out the oxidation step, the catalyst is treated with 
dilute oxygen (1-3% oxygen in nitrogen) at room temperature for a period 
of 1/2 to 2 hours before the temperature is increased at the same rate and 
to the same temperature as used during calcination. After holding the high 
temperature for 1 to 2 hours, air is slowly introduced, and the treatment 
is continued under air at the high temperature for another 2 to 4 hours. 
The second reduction is carried out under the same conditions as the first 
reduction. 
Hydrocarbon Synthesis 
The reactor used for the synthesis of hydrocarbons from synthesis gas can 
be chosen from various types well known to those skilled in the art, for 
example, fixed bed, fluidized bed, ebullating bed or slurry. The catalyst 
particle size for the fixed or ebullating bed is preferably between 0.1 
and 10 mm and more preferably between 0.5 and 5 mm. For the other types of 
operations a particle size between 0.01 and 0.2 mm is preferred. 
The synthesis gas is a mixture of carbon monoxide and hydrogen and can be 
obtained from any source known to those skilled in the art, such as, for 
example, steam reforming of natural gas or partial oxidation of coal. The 
molar ratio of H.sub.2 :CO is preferably between 1:1 to 3:1; and more 
preferably between 1.5:1 to 2.5:1. Carbon dioxide is not a desired feed 
component for use with the catalyst of this invention, but it does not 
adversely affect the activity of the catalyst. All sulfur compounds must, 
on the other hand, be held to very low levels in the feed, preferably 
below 1 ppm. 
The reaction temperature is suitably between 150.degree. and 300.degree. 
C.; and more preferably between 175.degree. and 250.degree. C. The total 
pressure can be from atmospheric to around 100 atmospheres, preferably 
between 1 and 30 atmospheres. The gaseous hourly space velocity, based on 
the total amount of synthesis gas feed, is preferably between 100 and 
20,000 cm.sup.3 of gas per gram of catalyst per hour; and more preferably 
from 1000 to 10,000 cm.sup.3 /g/h, where gaseous hourly space velocity is 
defined as the volume of gas (measured at standard temperature and 
pressure) fed per unit weight of catalyst per hour. 
The reaction products are a complicated mixture, but the main reaction can 
be illustrated by the following equation: 
EQU nCO+2nH.sub.2 .fwdarw.(--CH.sub.2 --).sub.n +nH.sub.2 O 
where (--CH.sub.2 --).sub.n represents a straight chain hydrocarbon of 
carbon number n. Carbon number refers to the number of carbon atoms making 
up the main skeleton of the molecule. In F-T synthesis, the products are 
generally either paraffins, olefins, or alcohols. Products range in carbon 
number from one to 50 or higher. 
In addition, with many catalysts, for example those based on iron, the 
water gas shift reaction is a well known side reaction: 
EQU CO+H.sub.2 O.fwdarw.H.sub.2 +CO.sub.2 
With cobalt catalysts the rate of this last reaction is usually very low. 
However, it is found that, even though rhenium catalysts exhibit a 
relatively high selectivity to carbon dioxide, the cobalt plus rhenium 
catalyst of this invention surprisingly does not have a higher selectivity 
to carbon dioxide than the cobalt only catalyst. 
The hydrocarbon products from Fischer-Tropsch synthesis are distributed 
from methane to high boiling compounds according to the so called 
Schulz-Flory distribution, well known to those skilled in the art. The 
Schulz-Flory distribution is expressed mathematically by the Schulz-Flory 
equation: 
EQU W.sub.i =(1-.alpha.).sup.2 i.alpha..sup.i-1 
where i represents carbon number, .alpha. is the Schulz-Flory distribution 
factor which represents the ratio of the rate of chain propagation to the 
rate of chain propagation plus the rate of chain termination, and W.sub.i 
represents the weight fraction of product of carbon number i. 
The products produced by the catalyst of this invention generally follow 
the Schulz-Flory distribution, except that the yield of methane is usually 
higher than expected from this distribution. This indicates that methane 
is apparently produced by an additional mechanism. 
It is well known, and also shown in one of the following examples, that 
rhenium alone is a low activity catalyst for Fischer-Tropsch synthesis 
producing a product which is predominantly methane. On the other hand, 
cobalt is a well known catalyst for producing higher carbon number 
hydrocarbons. In U.S. Pat. No. 4,568,663, it has been shown that adding 
small amounts of rhenium to cobalt supported on titania improves the 
catalytic activity. In the present invention, it has been found that the 
hydrocarbon yield obtained by adding rhenium is surprisingly much larger 
for an alumina supported cobalt catalyst than that obtained from cobalt 
and rhenium on several other inorganic supports. The improved activity is 
followed by no deleterious effect on the selectivity to methane. 
The catalyst of this invention is further described in the following 
examples. 
Experimental Work 
The following examples describe the preparation of various catalysts and 
the results obtained from testing these catalysts for conversion of 
synthesis gas into hydrocarbons. 
Before being tested, each catalyst was given a pretreatment consisting of 
reduction by passing hydrogen over the catalyst at a rate of 3000 cm.sup.3 
/g/h while heating the catalyst at a rate of 1.degree. C./min to 
350.degree. C. and maintaining this temperature for 10 hours. In the 
tests, synthesis gas consisting of 33 vol % carbon monoxide and 67 vol % 
hydrogen was passed over 0.5 g of the catalyst at atmospheric pressure at 
temperatures of 185.degree., 195.degree. and 205.degree. C. according to 
the following schedule: 
9 hr. 50 min. at 195.degree. C. 
4 hr. 20 min. at 205.degree. C. 
4 hr. 30 min. at 185.degree. C. 
9 hr. 50 min. at 195.degree. C. 
The flow rate of synthesis gas was 1680 cm.sup.3 /g of catalyst/h. Products 
from the reactor were sent to a gas chromatograph for analysis. Catalysts 
were compared based on the results over the period from 10 to 30 hours on 
stream. 
EXAMPLE 1 
Catalyst Containing Cobalt But No Rhenium 
This example describes the preparation of a control cobalt catalyst which 
was used for comparative purposes. This catalyst was prepared as follows: 
A solution was prepared by dissolving 17.03 g of cobalt nitrate, 
Co(NO.sub.3).sub.2.6H.sub.2 O, and 0.76 g of mixed rare earth nitrate, 
RE(NO.sub.3).sub.3, where RE stands for rare earth with a composition of 
66% La.sub.2 O.sub.3, 24% Nd.sub.2 O.sub.3, 8.2% Pr.sub.6 O.sub.11, 0.7% 
CeO.sub.2, and 1.1% other oxides (Molycorp 5247), in 30 ml of distilled 
water. The total solution was added with stirring to 25 g of Ketjen CK300 
gamma-alumina which had been calcined 10 hours at 500.degree. C. The 
prepared catalyst was then dried for 5 hours in an oven at a temperature 
of 115.degree. C. The dried catalyst was then calcined in air by raising 
its temperature at a heating rate of 1.degree. C./minute to 300.degree. C. 
and holding at this temperature for 2 hours. The finished catalyst 
contained 12 wt % cobalt and 1 wt % rare earth oxide with the remainder 
being alumina. This catalyst is referred to as preparation "a" in Table I. 
The above procedure was repeated to produce preparation "b" catalyst in 
Table I. 
The results of the tests with this catalyst are shown in Table I. In this 
and the following tables, selectivity is defined as the percent of the 
carbon monoxide converted that goes to the indicated product. 
TABLE I 
______________________________________ 
CO 
Con- C.sub.2 + 
CH.sub.4 
CO.sub.2 
Temp. Prep- version Selectivity 
Selectivity 
Selectivity 
.degree.C. 
aration % % % % 
______________________________________ 
185 a 7 91.1 7.2 1.7 
b 11 91.8 7.1 1.1 
195 a 12 90.0 8.9 1.1 
b 18 90.2 9.0 0.8 
205 a 21 87.7 11.3 1.0 
b 29 86.7 12.4 0.9 
______________________________________ 
This example shows that a cobalt catalyst exhibits good selectivity to 
ethane and longer chain length hydrocarbons and low selectivity to methane 
and carbon dioxide. 
EXAMPLE 2 
Catalyst Containing Rhenium But No Cobalt 
This example describes a rhenium catalyst prepared for comparative 
purposes. The procedure employed was the same as for Example 1 except that 
the solution contained 0.33 g of perrhenic acid, HReO.sub.4 as 82.5% 
aqueous solution, and 0.54 g of rare earth nitrate to make 24 ml of 
solution which then was added to 20 g of calcined alumina. The finished 
catalyst contained 1 wt % rhenium and 1 wt % rare earth oxide with the 
remainder being alumina. 
The results of the tests with the catalyst of Example 2 are shown in Table 
II. 
TABLE II 
______________________________________ 
CO C.sub.2 + CH.sub.4 CO.sub.2 
Temp. conversion Selectivity 
Selectivity 
Selectivity 
.degree.C. 
% % % % 
______________________________________ 
185 0.3 20 30 50 
195 0.3 19 31 50 
205 0.3 19 31 50 
______________________________________ 
EXAMPLE 3 
Catalyst Containing Rhenium But No Cobalt 
Repetition of the procedure from Example 2, except that 0.83 g of perrhenic 
acid were used, gave a catalyst containing 4 wt % rhenium. The results of 
the tests with the catalyst of Example 3 are shown in Table III. 
TABLE III 
______________________________________ 
CO C.sub.2 + CH.sub.4 CO.sub.2 
Temp. conversion Selectivity 
Selectivity 
Selectivity 
.degree.C. 
% % % % 
______________________________________ 
185 0.3 20 30 50 
195 0.3 19 31 50 
205 0.3 19 31 50 
______________________________________ 
The results from Examples 2 and 3 show that catalysts containing rhenium 
but no cobalt have very low activity for producing desirable liquid 
hydrocarbons from synthesis gas. Furthermore, about half the product is 
carbon dioxide, and most of the hydrocarbon product is methane. 
EXAMPLES 4 THROUGH 11 
Catalysts Containing Both Cobalt And Rhenium 
The preparation procedure of Example 1 was employed except that varying 
amounts of perrhenic acid were added to the solution. This produced a 
series of catalysts containing 12 wt % cobalt and 0.1, 0.2, 0.3, 0.5, 1.0, 
2.0, 4.0, and 8.0 wt % rhenium in addition to 1.0 wt % rare earth oxide. 
The results of the tests with the catalysts of Examples 4 through 11 at 
195.degree. C. are shown in Table IV and further illustrated in FIG. 1. 
FIG. 1 shows the effect on carbon monoxide conversion of adding rhenium to 
catalysts containing 12% cobalt. 
TABLE IV 
______________________________________ 
C.sub.2 + 
CH.sub.4 
CO.sub.2 
CO Selec- 
Selec- 
Selec- 
Example 
Co Re conversion 
tivity 
tivity 
tivity 
No. wt % wt % % % % % 
______________________________________ 
4 12 0.1 26 89.8 9.6 0.6 
5 12 0.2 29 88.9 10.4 0.7 
6 12 0.3 27 88.2 11.0 0.8 
7 12 0.5 31 88.3 10.9 0.8 
8 12 1.0 33 87.7 11.4 0.9 
9 12 2.0 31 85.7 13.3 1.0 
10 12 4.0 28 84.7 14.2 1.1 
11 12 8.0 25 84.5 14.2 1.3 
______________________________________ 
As can be seen from comparison of the results in Table I with Table IV and 
FIG. 1, the addition of small amounts of rhenium to a cobalt supported on 
alumina catalyst significantly increases the conversion of the carbon 
monoxide in the feed. Levels of rhenium as low as 0.1 wt % result in 
approximately doubling the CO conversion. The exact level of Re for 
optimum activity is very important, as the rate of carbon monoxide 
conversion increases rapidly at low rhenium addition levels, reaches a 
maximum and then decreases gradually at levels greater than 1 wt % 
rhenium. However, even at the highest rhenium level investigated (8%), a 
clear improvement in conversion is evident when compared to the catalyst 
not containing rhenium. 
It is important that the increase in activity occur without a corresponding 
increase in either the methane or the carbon dioxide selectivities. Table 
IV shows that the increase in carbon monoxide conversion is not 
accompanied by any substantial change in either the selectivities to 
methane or carbon dioxide. Thus, after rhenium addition the principal 
reaction products are still desirable hydrocarbons. 
EXAMPLES 12 THROUGH 25 
Catalysts Containing Both Cobalt and Rhenium 
The preparation procedure of Example 1 was employed except that varying 
amounts of cobalt nitrate and perrhenic acid were added to the solution. 
This produced a series of catalysts containing from 3.0 to 40 wt % cobalt 
and from 0 to 5.0 wt % rhenium in addition to 1.0 wt % rare earth oxide. 
The results of the tests with the catalysts of Examples 12 through 25 at 
195.degree. C. are shown in Table V. 
TABLE V 
______________________________________ 
C.sub.2 + 
CH.sub.4 
CO.sub.2 
CO Selec- 
Selec- 
Selec- 
Example 
Co Re Conversion 
tivity 
tivity 
tivity 
No. wt % wt % % % % % 
______________________________________ 
12 3 0.0 5 90.7 8.1 1.2 
13 3 0.25 4 87.2 10.4 2.4 
14 6 0.0 12 90.0 8.9 1.1 
15 6 0.5 16 88.2 10.8 1.0 
16 9 0.0 15 90.0 9.1 0.9 
17 9 0.75 25 88.1 11.1 0.8 
18 20 0.0 20 89.3 9.8 0.9 
19 20 0.5 40 87.9 11.1 1.0 
20 20 1.0 46 86.1 12.9 1.0 
21 20 5.0 42 83.9 14.8 1.3 
22 40 0.0 20 89.3 9.7 1.0 
23 40 1.0 56 85.0 13.2 1.8 
24 40 2.0 58 84.3 13.7 2.0 
25 40 5.0 60 81.9 15.7 2.4 
______________________________________ 
The results in Table V show that for cobalt catalysts without rhenium, 
there is a significant increase in activity in going from 3% cobalt to 6% 
cobalt. However, only modest increases in activity occur from this point 
up to cobalt loadings of as high as 40%. At a cobalt loading of 3%, the 
addition of rhenium does not improve the catalytic activity, but the 
improvement upon rhenium addition is significant for higher cobalt 
loadings. In fact, the improvement in activity due to the addition of 
rhenium increases as the cobalt content increases as shown in FIG. 2. 
EXAMPLES 26 AND 27 
Cobalt/Rhenium Catalysts with Promoters 
To illustrate the use of promoters other than rare earth oxides, the 
following catalysts were prepared. The preparation procedure used to 
prepare the catalyst of Example 8 was used except that zirconium nitrate, 
Zr(NO.sub.3).sub.4, or vanadyl oxalate, VO(C.sub.2 O.sub.4 H).sub.3, was 
substituted for the rare earth nitrate. The results of tests at 
195.degree. C. with the catalysts of examples 26 and 27 are shown in Table 
VI. In addition to the promoter, these catalysts contained 12% cobalt and 
1% rhenium and were supported on alumina. 
TABLE VI 
______________________________________ 
C.sub.2 + 
CH.sub.4 
CO.sub.2 
CO Selec- 
Selec- 
Selec- 
Example conver- tivity 
tivity 
tivity 
No. Promoter sion % % % % 
______________________________________ 
26 ZrO.sub.2 (0.75 wt %) 
31 87.9 11.3 0.8 
27 V.sub.2 O.sub.5 (0.56 wt %) 
26 89.4 9.8 0.8 
______________________________________ 
EXAMPLES 28 THROUGH 41 
Cobalt/Rhenium Catalysts On Other Supports 
For comparison with alumina, several catalysts were prepared on other 
supports. The preparation procedure used to prepare the catalyst of 
Example 8 was repeated, but without the addition of rare earth oxide. The 
titanium-supported catalysts were prepared on titania calcined at both 
500.degree. C. and 600.degree. C. After calcination at 600.degree. C., the 
titania is mainly in the crystalline rutile form; while after calcination 
at 500.degree. C. the anatase:rutile ratio is about 1:1. The catalysts 
prepared on the titania support calcined at these two temperatures showed 
exactly the same catalytic activity. 
The supports used were: Davison Grade 59 silica; Degussa P25 titania; Alpha 
Chemicals No. 88272 chromia; magnesia prepared by calcining Fischer basic 
magnesium carbonate; American Cyanamid AAA Silica-Alumina; and Alpha 
Chemicals 11852 zirconia (containing 2% alumina). Information on the 
composition of the catalysts prepared on the different supports is given 
in Table VII. 
TABLE VII 
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Weight of Materials in 
Composition of 
Weight of 
Impregnating 
Finished 
Example Support 
Solution, g Catalyst, wt % 
No. Support 
g Co(NO.sub.3).sub.2 
HReO.sub.4 * 
Co Re 
__________________________________________________________________________ 
28 Silica 20 13.47 -- 12 -- 
29 Silica 20 13.62 0.38 12 1.0 
30 Titania** 
25 16.84 -- 12 -- 
31 Titania** 
24.64 16.78 0.46 12 1.0 
32 Titania*** 
25 16.84 -- 12 -- 
33 Titania*** 
24.64 16.78 0.46 12 1.0 
34 Chromia 
20 13.47 -- 12 -- 
35 Chromia 
21.3 14.51 0.40 12 1.0 
36 Magnesia 
21.59 14.54 -- 12 -- 
37 Magnesia 
14.54 10.67 0.29 12 1.0 
38 Silica- 
20 13.47 -- 12 -- 
Alumina 
39 Silica- 
20 13.62 0.38 12 1.0 
Alumina 
40 Zirconia 
20 13.47 -- 12 -- 
41 Zirconia 
20 13.62 0.38 12 1.0 
__________________________________________________________________________ 
*Weight of 82.5% perrhenic acid solution. 
**Calcined at 500.degree. C. 
***Calcined at 600.degree. C. 
A series of tests was conducted to evaluate the activities of the catalysts 
of the above examples in converting synthesis gas into hydrocarbons. The 
results of the tests with the catalysts of Examples 28 through 41 at 
195.degree. C. are shown in Table VIII. The results from catalysts 
prepared on alumina are included for comparison. 
TABLE VIII 
______________________________________ 
CO 
Ex- Con- 
am- ver- C.sub.2 + 
CH.sub.4 
CO.sub.2 
ple Co Re sion Selec- Selec- Selec- 
No. % % Support % tivity % 
tivity % 
tivity % 
______________________________________ 
1 12 -- Al.sub.2 O.sub.3 
12 90.0 8.9 1.1 
8 12 1 Al.sub.2 O.sub.3 
33 87.7 11.4 0.9 
28 12 -- SiO.sub.2 
11 90.1 8.7 1.2 
29 12 1 SiO.sub.2 
12 88.1 10.7 1.2 
30 12 -- TiO.sub.2 * 
11 87.6 11.8 0.6 
31 12 1 TiO.sub.2 * 
17 86.5 12.8 0.7 
32 12 -- TiO.sub.2 ** 
11 87.6 11.7 0.7 
33 12 1 TiO.sub.2 ** 
17 85.8 13.5 0.7 
34 12 -- Cr.sub.2 O.sub.3 
1 83.5 15.5 1.0 
35 12 1 Cr.sub.2 O.sub.3 
2 80.8 12.3 6.9 
36 12 -- MgO 0.3 20.0 30.0 50.0 
37 12 1 MgO 0.3 19.1 30.9 50.0 
38 12 -- SiO.sub.2 /Al.sub.2 O.sub. 3 
5 76.3 22.2 1.5 
39 12 1 SiO.sub.2 /Al.sub.2 O.sub.3 
6 78.6 19.8 1.6 
40 12 -- ZrO.sub.2 
4 80.9 16.3 2.8 
41 12 1 ZrO.sub.2 
7 78.8 18.7 2.5 
______________________________________ 
*Support calcined at 500.degree. C. 
**Support calcined at 600.degree. C. 
The catalysts in Table VII were prepared to test the teaching that various 
inorganic supports are acceptable for preparing cobalt plus rhenium F-T 
catalysts. An examination of the data in Table VIII leads to the 
surprising conclusion that the type of support is extremely important and 
that vast differences in activity exist between catalysts prepared on one 
support and catalysts of the same catalytic metals content on another 
support. More surprisingly, only cobalt plus rhenium on alumina showed a 
commercially attractive activity level and selectivity. 
Catalysts on magnesia and chromia exhibited extremely low activities, both 
with and without rhenium. Catalysts on zirconia and silica-alumina showed 
somewhat higher activities, but selectivity to C.sub.2 + hydrocarbons was 
poor. These catalysts showed only modest improvements in activity upon the 
addition of rhenium. 
Catalysts without rhenium supported on silica and titania showed activity 
levels close to comparable cobalt on alumina catalyst. However, upon 
addition of rhenium, the alumina catalyst showed a surprising increase in 
activity from about 15% carbon monoxide conversion to 33% carbon monoxide 
conversion; whereas, the silica supported catalyst showed only a very 
small increase in activity from 11% carbon monoxide conversion to 12% 
carbon monoxide conversion, while the titania supported catalyst showed a 
larger, but still modest, gain in activity from 11% carbon monoxide 
conversion to 17% carbon monoxide conversion. 
From these examples, plus those presented previously, it can be concluded 
that the catalytic activity of a cobalt catalyst supported on alumina is 
greatly improved by adding minor amounts of rhenium, as long as the cobalt 
level is greater than about 5 wt %. Although improved activity from 
rhenium addition is also observed for some other supports, the activity 
level achieved by adding rhenium to a catalyst supported on alumina is 
much higher than for other supports. This result is surprising and would 
not have been predicted based on teachings in the prior art.