Transition metal tris-dithiolene and related complexes as precursors to active catalysts

The present invention is based on the discovery that certain transition metal containing complexes thermally decompose to form solids containing the transmission metal, sulfur and carbon and that these transition metal, sulfur and carbon containing solids are particularly suitable as catalysts for hydrodesulfurization, hydrodenitrogenation and aromatics hydrogenation. The transition metal complexes that are thermally decomposed to novel catalysts are complexes of the type represented by the general formula ML.sup.n.sbsp.3, wherein M is selected from Mo, W, Re and mixtures thereof, L is a dithiolene or aminobenzenethiolate ligand, and n represents the total charge of the metal complexes, and is 0, -1, or -2.

FIELD OF THE INVENTION 
This invention relates generally to catalytic hydrotreating of petroleum 
feedstocks and more specifically to novel transition metal-containing 
catalysts especially suitable for hydrodesulfurization, 
hydrodenitrogenation, and aromatic hydrogenation. 
BACKGROUND OF THE INVENTION 
Transition metal tris-dithiolene complexes and the related 
ortho-aminobenzenethiolate complexes have been reported in the literature. 
See, for example, Burns, R. P. et al., Adv. Inorg. Chem. Radiochem., 22, 
p. 303-348 (1979) and references therein; and Gardner, Joseph K. et al., 
Inorg. Chem, 17, p. 897-904 (1978). Molybdenum tris-dithiolene complexes 
have been reported as catalysts for the isomerization of norbornadiene to 
quadricyclane. See R. B. King, J. Mol. Cat., 4 p. 361-373 (1978). 
SUMMARY OF THE INVENTION 
It has now been discovered that certain transition metal-containing 
complexes thermally decompose to form solids containing the transition 
metal, sulfur and carbon and that these transition metals, sulfur and 
carbon containing solids are particularly suitable as catalysts for 
hydrodesulfurization, hydrodenitrogenation and aromatics hydrogenation. 
The transition metal-containing complexes that are thermally decomposed to 
novel catalysts are complexes of the type represented by .the general 
formula ML.sup.n.sub.3 wherein M is a transition metal selected from Mo, 
W, Re or mixtures thereof and L is a dithiolate or aminobenzenethiolate 
ligand, and n represents the total charge of the metal complex, and is 0, 
-1, or -2.

DETAILED DESCRIPTION OF THE INVENTION 
The catalysts of the present invention are prepared by the thermal 
decomposition of transition metal tris-dithiolate and aminobenzenethiolate 
complexes of the type ML.sup.n.sub.3 in which M is a metal selected from 
Mo, W, Re and mixtures thereof, n represents the total charge of the metal 
complex and is 0, -1, or -2, and L is a ligand selected from dithiolene or 
aminobenzenethiolate ligands having the general formula 
##STR1## 
and in which R is selected from alkyl, aryl and alkyl aryl groups, and 
when the ligand, L, is a dithiolene, R may also be CF.sub.3 or CN. 
In general, when R is an alkyl group, it will have from 1 to about 12 
carbon atoms. When R is an aryl group, it will have 6 carbon atoms. 
Finally, when R is an alkylaryl group, it will have from about 7 to about 
18 carbon atoms. 
As will be readily appreciated, when n is other than zero, the complex will 
include a cation such as an ammonium, alkylammonium, and quaternary 
alkylammonium anion. 
Examples of preferred complexes include Mo(tdt).sub.3, Mo(abt).sub.3, 
(TEA.sup.+).sub.2 Mo(tdt).sub.3, W(abt).sub.3 and Re(abt).sub.3 wherein 
tdt is 3,4-toluene dithiolate, abt is ortho-aminobenzenethiolate, and TEA 
is tetraethylammonium anion. 
The preparation of these precursors is well known and does not form a part 
of this invention. Methods used to prepare them, for example, may be found 
by consulting the references cited above. 
These compounds have been found to be useful catalyst precursors in the 
preparation of catalysts for hydrodesulfurization (HDS), 
hydrodenitrogenation (HDN), and aromatics hydrogenation. For example, when 
charged into a batch-type stirred reactor containing a mixture of 5 weight 
percent dibenzothiophene (DBT) and decalin, Mo(tdt).sub.3 was effective in 
removing sulfur from the mixture. In another example, using a mixture 
containing 0.8 weight percent sulfur as DBT, 0.8 weight percent nitrogen 
as 1,2,3,4-tetrahydroquinoline (THQ), and 5 weight percent acenapthylene 
in decalin, Mo(abt).sub.3 was effective in removing nitrogen and 
hydrogenating the acenapthylene. 
The molybdenum tris-dithiolene and related complexes may be thermally 
decomposed by heating the complex at elevated temperatures generally in 
excess of about 200.degree. C., and preferably in the range of about 
250.degree. to 350.degree. C., in a reducing atmosphere such as one 
containing hydrogen. The decomposition preferably is conducted in the 
presence of a solvent. Indeed, the precursors may be thermally decomposed 
in the petroleum hydrocarbon being catalytically hydrotreated. 
The molybdenum, tungsten and rhenium trisdithiolene and related complexes 
are examples of catalyst precursor molecules in which sulfur and carbon 
are covalently bound in the metal complex. We refer to these molecules as 
"inner sphere" sulfur-and carbon-containing precursors. The advantageous 
nature of these complexes as catalyst precursors is believed to derive 
from the presence of this "inner sphere" sulfur and carbon during the 
decomposition to form the active catalytic material. 
The precursors, of course, may be used either singly or mixed with one 
another for forming catalysts of the present invention. 
The invention will be further understood by reference to the following 
examples. 
EXAMPLE 1 
Molybdenum tris(toluene-3,4-dithiolate) was prepared by the following 
procedure: 
Toluene-3,4-dithiol (5.9 g, 0.38 mole) was dissolved in a solution 
containing 15 ml 5% aqueous sulfuric acid and 135 ml 95% ethyl alcohol. A 
solution of Na.sub.2 MoO.sub.4 (2.49 g, 0.126 mole) in 150 ml water was 
added rapidly with strong stirring. After stirring for 40 min, the mixture 
was extracted 2 times with 250 ml CHCl.sub.3. The extracts were washed 
with water, and dried over anhydrous MgSO.sub.4. The chloroform solution 
was mixed with 200cc dry silica gel, and solvent removed under reduced 
pressure. The resulting mixture was poured onto a column of dry silica 
(60.times.7 cm) Elution with 2:1 hexane/CHCl.sub.3 gave 1.85 g pure Mo 
(tdt).sub.3. 
EXAMPLE 2 
The following describes the preparation of molybdenum 
tris(aminobenzenethiolate). o-Aminobenzenethiol (2.2 g) was dissolved in 
10 ml 5% H.sub.2 SO.sub.4 and 90 ml 95% ethanol. A solution of Na.sub.2 
MoO.sub.4 (1.62 g) was poured into the aminobenzenethiol solution with 
vigorous stirring. After 10 minutes, the stirring was stopped, and the 
mixture allowed to stand for 30 min. Filtration gave (after drying) 2.8 g 
green solid Mo(abt).sub.3. 
EXAMPLE 3 
Bis(tetraethylammonium)-molybdenum-tris (toluene-3,4-dithiolate) was 
prepared as follows: Mo(tdt).sub.3 (2.03 g) was dissolved in 120ml 
tetrahydrofuran under inert atmosphere. A solution of n-butyllithium (4.6 
ml, 1.5M solution in hexane) was added slowly. After stirring 1/2 hour, 
tetraethyl ammonium bromide (excess) was dissolved in 50 ml methanol, and 
added. The product (1.4 g. blue-black solid) was precipitated by addition 
of 250 ml diethylether, filtered, and dried. 
EXAMPLE 4 
Rhenium tris-aminobenzenethiolate (Re(abt).sub.3) was prepared as follows: 
A solution containing 5.0 g. (0.017 mole) of potassium perrhenate in 500 ml 
hot water was added to a solution of 6.0 ml o-aminobenzenethiolate and 50 
ml 5% H.sub.2 SO.sub.4 in 500 ml 95% ethanol. After heating for one hour 
at 100.degree. C., the resulting brown crystalline material was filtered, 
washed with ethanol and ether, and dried. This solid was dissolved in 500 
ml acetone, filtered and the filtrate diluted with 250 ml water. After 
standing for 3 days, the precipitated dark blue needles of Re(abt).sub.3 
were filtered and dried. 
EXAMPLES 5, 6 and 7 
The precursors of Examples 1 through 3 were made into 20-40 mesh (U.S. 
Sieve size) particles and placed in an autoclave reactor basket. The 
autoclave was charged with 100 cc's of 5 weight percent dibenzothiophene 
(DBT) in decalin. The autoclave was heated at 350.degree.0 C. while 
flowing hydrogen through the reactor at 100 cc's per minute with a 750 rpm 
spinning rate for the basket. The concentrations of DBT and products were 
determined by gas chromatography. The results are shown in Table I below. 
TABLE I 
______________________________________ 
HDS 
Experiment Precursor Activity* 
______________________________________ 
Ex. 5 Mo(tdt).sub.3 
93 
Ex. 6 Mo(abt).sub.3 
41.5 
Ex. 7 (TEA).sub.2 Mo(tdt).sub.3 
76 
Comp. Ex. 8 (NH.sub.4).sub.2 MoS.sub.4 
28 
______________________________________ 
*(.times.10.sup.16 molecules DBT/g precursor sec) 
COMATIVE EXAMPLE 8 
Molybdenum sulfide catalyst was prepared as follows: Ammonium 
tetrathiomolybdate (NH.sub.4).sub.2 MoS.sub.4, (10 g) was heated at 
350.degree. C. for two hours under a flow of gas consisting of 15% H.sub.2 
S in H.sub.2. The resulting MoS2 was cooled under H.sub.2 S/H.sub.2 gas to 
100.degree. C., then cooled to room temperature under nitrogen. 
Following the procedure of Examples 5, 6 and 7, 1 gram of molybdenum 
sulfide prepared in this way was used in the hydrodesulfurization of DBT. 
The results are also shown in Table I. 
EXAMPLE 9 
This example illustrates the ex-situ formation of an active HDS/HDN 
catalyst (preforming). A sample of Mo(abt).sub.3 (2 g) was placed in a 300 
cc autoclave with 200 ml decalin. The autoclave was pressurized to 225 psi 
with H.sub.2, and then heated to 350.degree. C. for several hours. After 
cooling to room temperature, the reactor contents were filtered, and the 
black solid catalyst washed with toluene, dried in vacuo, and used in 
subsequent testing. The surface area of this material was determined to be 
71.2 m.sup.2 /g. Elemental analysis of the catalyst gave the following 
results: C, 6.67%; H, 1.12%; N, 0.68%; Mo, 45.72%; S, 35.07%. 
EXAMPLES 10, 11 and 12 
The precursor of Examples 2 and 4, and the preformed catalyst from Example 
9, were placed in separate autoclaves. Each autoclave was charged with 100 
cc's of feed containing 0.8 wt. percent sulfur as dibenzothiophene, 0.8 
wt. percent nitrogen as 1,2,3,4-tetrahydroquinoline, and 5 wt. percent 
acenapthylene. The autoclave was heated at 350.degree. C., while flowing 
H.sub.2 through the reactor at 100 cc's per minute. The mixture of feed 
and catalyst was stirred at 750 rpm. Concentrations of desulfurized 
products (biphenyl and cyclohexyl benzene), denitrogenated products 
(propylbenzene, propylcyclohexane, propylcyclohexene), and 
hexahydroacenapthylene were determined by gas chromatography of samples of 
the product withdrawn from the reactor at intervals during each 7 hour 
run. Zero-order rates of HDS, HDN, and hydrogenation are shown in Table 
II. 
TABLE II 
______________________________________ 
HDS HDN Hydrogenation 
Experiment 
Catalyst Activity Activity 
Activity 
______________________________________ 
Ex. 10 Mo(abt).sub.3 
15.2 31 23 
(Ex. 2) 
Ex. 11 Re(abt).sub.3 
9.4 70.5 45 
(Ex. 4) 
Ex. 12 Mo(abt).sub.3 
5.1 17.1 10.8 
(Ex. 8) 
Comp. Ex. 13 
MoS.sub.2 
1.0 23 5.0 
______________________________________ 
COMATIVE EXAMPLE 13 
The procedure of Examples 10, 11 and 12 were followed, except that the 
catalyst from Comparative Example 8 was employed. The results are shown in 
Table II.