A parallel colorimetric method for the rapid discovery and optimization of heterogeneous hydrodesulfurization catalysts

Article abstract of DOI:10.1021/ja034222j

A spectrophotometric based, parallel approach to screen heterogeneous catalysts for hydrodesulfurization has been developed. The method utilizes optical changes resulting from the hydrodesulfurization of 1,1′-binaphthothiophene to 1,1′-binaphthyl to determine catalyst activity. Hydrodesulfurization of 1,1′-binaphthothiophene to 1,1′-binaphthyl results in a loss of conjugation in the binaphthyl ring system. This results in a blue shift of more than 60 nm in the UV-vis spectrum. Since only small amounts of the HDS catalyst and 1,1′-binaphthothiophene are required, a large number of catalysts may be screened simultaneously. The synthesis of the 1,1′-binaphthothiophene and conditions for HDS catalyst screening are described. Copyright

Full text of DOI:10.1021/ja034222j

Published on Web 07/24/2003
A Parallel Colorimetric Method for the Rapid Discovery and Optimization of
Heterogeneous Hydrodesulfurization Catalysts
Chad L. Staiger, Douglas A. Loy,* Gregory M. Jamison,* Duane A. Schneider, and
Christopher J. Cornelius
Chem & Bio Technologies/Materials Chemistry Departments, Sandia National Laboratories,
P.O. Box 5800 MS 0888, Albuquerque, New Mexico 87185-0888, and Polymers and Coating Group,
MS E549, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Received January 17, 2003; E-mail: daloy@lanl.gov; gmjamis@sandia.gov
Scheme 1. Hydrodesulfurization of Benzothiophene
Scheme 2. Synthesis of Binaphthothiophene 1
Combinatorial and highly parallel methods for heterogeneous
catalyst discovery are quickly gaining importance to supplement
traditional methods for evaluating catalyst design and activity.1-6
The ability to determine the activity of a series of catalysts in a
chemical process simultaneously allows one to quickly identify and
optimize the most active catalyst compositions and conditions. In
this Communication, we report a colorimetric method to rapidly
screen heterogeneous catalysts for activity in the hydrodesulfur-
ization (HDS) of petroleum feedstocks. The relatively severe
temperatures (>250 °C) and pressures (>2500 kPa) required for
HDS called for a unique set of experimental criteria for the screen
to function properly.
HDS is a high temperature and pressure catalytic process to
remove sulfur from hydrocarbons.7 Sulfur-containing compounds
such as benzothiophenes are reacted with hydrogen in the presence
of an HDS catalyst to generate the corresponding desulfurized
hydrocarbon and H2S (Scheme 1). The oil industry relies heavily
on this process to lower the amount of sulfur in petroleum
feedstocks.7 Environmental and health concerns over SOx emissions
from the combustion of fossil fuels has forced oil refiners to
dramatically reduce the sulfur content in gasoline and diesel fuels.8
The increased need for ultraclean fuels has prompted new research
into more efficient HDS catalysts.9 While current HDS catalysts
are extraordinarily efficient at removing low molecular weight
sulfides and thiophenes, higher molecular weight sulfur compounds
(i.e., R-substituted dibenzothiophenes) resist reductive desulfuriza-
tion.10
Our highly parallel method for HDS catalyst evaluation utilizes
an optical change in a dye molecule to signal HDS activity. An
optical approach offers the advantage of avoiding laborious
analytical methods by simply being able to visually determine
activity or by employing facile absorbance/fluorescence methods.
Recently, the use of this reactive dye strategy to screen catalysts
for hydrosilylation,11 the Heck reaction,12 and electrocatalysts13 for
fuel cell applications has been described.
The design of dye molecules used to probe catalyst activity
should mimic the sulfur compounds that are more difficult to treat
by current HDS catalysts. In addition, the dye molecule needs to
meet an additional set of criteria to cope with high temperatures
(>250 °C) and pressures (>2500 kPa) used for HDS. This includes
low volatility to avoid cross talk between sample cells exposed to
a common set of reaction conditions. The dye molecule should be
thermally stable under the HDS conditions to avoid false positives
from decomposition events. Also, the HDS products should not
interfere with the optical response of the dye molecule to make
analysis unambiguous.
readily available in two steps from BINOL 2 (Scheme 2).14 BINOL
2 was deprotonated with NaH and reacted with dimethylthiocar-
bamoyl chloride to give intermediate bisthiocarbamate 3 in 86%
yield. Thermal rearrangement and subsequent intramolecular dis-
placement of bisthiocarbamate 3 at 400 °C gave thiophene 1 in
60-75% yield after SiO2 chromatography and crystallization.
The spectral properties of thiophene 1 and its major HDS product,
binaphthyl 4, are shown in Figure 1. The sulfur group in 1 constrains
the conformation of the binaphthyl ring to an approximate planar
geometry and imparts extended conjugation between the naphthyl
rings. Absorbance maxima can be observed at 353, 337, 313, 301,
276, and 236 nm by UV-vis spectroscopy in solution. The
absorption profile for the major HDS product, binaphthyl 4, shows
absorbance maxima at 293 and 283 nm and is optically transparent
beyond 330 nm. Therefore, the absorbance maxima at 353 nm for
thiophene 1 allows assessment of HDS catalyst activity without
interference from those HDS products which absorb in the long
UV-vis region.
Thiophene 1 was evaluated as a parallel screen for catalyst
activity using two known HDS catalysts (Table 1, entries 1-2)
and four noncatalysts (entries 3-6) expected to be inactive under
reaction conditions. The noncatalysts chosen are typical of solid
supports used for heterogeneous catalysis. A control or blank with
no catalyst (entry 7) was also used. To each reaction well (an open
1 dram glass vial) were added ∼30 mg of catalyst and a decalin
solution of thiophene 1 (2.00 mL, 5.0 × 10-5 M). All of the catalyst
solutions were bundled together and loaded into the same pressure
reactor. The void space inside the reactor was filled with decalin
to a level equal to that of the solution in the vials. The reactor was
sealed and charged with H2 and subjected to standard HDS
A molecule we envisioned to fit the above requirements for the
HDS screen was 1,1′-binaphthothiophene 1. This compound is
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J. AM. CHEM. SOC. 2003, 125, 9920-9921
10.1021/ja034222j CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
3). Activated charcoal is known to have a high capacity for
adsorbing thiophenes.15,16 In addition, this false positive could also
be discarded as a possible HDS catalyst by running a bulk reaction
and looking for HDS products by MS. The other noncatalysts
(entries 4-6), alumina, silica gel, and 4 Å molecular sieves, also
absorbed the dye to varying but much lesser degrees, as absorption
bands for thiophene 1 were still observed. Adsorption effects on
screening should be readily minimized through the use of higher
concentrations of 1.
This highly parallel method based on the change in optical
properties of binaphthothiophene 1 allows for the rapid and facile
screening of a variety of potential HDS catalysts simultaneously.
The dye should also be a useful diagnostic for individual catalyst
performance in more traditional and larger scale HDS experiments.
Both applications should result in greater productivity in the
discovery of more reactive catalysts for HDS processing of fuels.
Presently, we are developing derivatives of 1 with added alkyl
substituents to increase the steric environment around the sulfur.
This less reactive screening dye should make it possible to detect
subtle differences in catalyst activity and identify catalysts that will
more effectively remove sulfur from similarly adorned ben-
zothiophenes, the most resistant repositories of sulfur in petroleum-
based fuels. Furthermore, one could potentially apply this type of
colorimetric screen to assist with the discovery and optimization
of other catalytic systems such as hydrodenitrogenation and
dearomatization.
Figure 1. UV-vis absorption spectra of thiophene 1 (9.4 × 10-6 M, solid
line) and binaphthyl 4 (9.0 × 10-6 M, dashed line) in decalin.
Table 1. Average Percentage of Thiophene 1 Consumed during
HDS from Four Runs
entry
catalyst
% thiophene 1 consumeda
1
2
3
4
5
6
7
Ni/Mo on aluminab
Co/Mo on aluminab
activated charcoal
alumina
silica gel
4 Å molecular sieves
no catalyst
98.0 ( 0.8
95.8 ( 5.5
99.4 ( 0.9
35.2 ( 8.8
20.0 ( 6.8
11.8 ( 3.2
-0.7 ( 2.1
a Quantified from the absorbance at 353 nm using Beer’s law (ꢀ ) 14 400
cm-1 M-1). b Ni/Mo catalyst contained 9 wt % NiO and 32 wt % MoO3
balanced with Al2O3. Co/Mo catalyst contained 5 wt % CoO and 10 wt %
MoO3 balanced with Al2O3. Weight percentages determined by electron
microprobe.
Acknowledgment. We thank Paul Hlava for electron micro-
probe analyses and Steve Meserole (Sandia) and John Greaves (UC-
Irvine) for MS analyses. Sandia is a multiprogram laboratory
operated by Sandia Corporation, a Lockheed Martin Company, for
the U.S. Department of Energy under contract DE-ACO4-
94AL85000. Los Alamos National Laboratory is supported by the
U.S. Department of Energy under contract with the University of
California W-7405-ENG-35.
conditions (300 °C at 5066 kPa). After these conditions were
maintained for 4 h, the reactor was cooled to room temperature
and each solution subjected to UV-vis analysis to evaluate catalyst
activity. Since some solvent in each vial was lost to evaporation
during the reaction, the contents of each vial were diluted to a
uniform volume to permit quantitative spectrophotometric measure-
ments.
Supporting Information Available: Experimental procedures for
the HDS catalyst screen and the syntheses of 1 and 3. This material is
available free of charge via the Internet at http://pubs.acs.org.
The HDS parallel catalyst screening using thiophene 1 under
the conditions described above is summarized in Table 1. Each
entry in Table 1 represents the average percentage of thiophene 1
consumed in four separate runs by a catalyst. As expected, the
known HDS catalysts, Ni/Mo and Co/Mo on alumina (entries 1
and 2), were shown to have consumed nearly 100% of the dye
molecule. The standard deviation for the amount of thiophene 1
consumed for each catalyst was small, indicating the HDS catalyst
screen was very reproducible from run to run. The vial containing
no catalyst (entry 7) showed no change in absorption profile,
indicating there was no cross talk of the dye between other vials in
the reactor. A control study using only decalin solutions of
thiophene 1 and decalin also confirmed the absence of dye
migration. However, cross talk of the major HDS product binaphthyl
4 was observed by MS. While this precludes direct analysis of the
HDS products for each catalyst under the conditions used in this
study, its presence in the other vials does not interfere with the
screen for catalyst activity if monitored as consumption of thiophene
1. Further refinement of the procedure by using higher boiling
solvents or lower HDS reaction temperatures or a modified reactor
design may very well eliminate migration of the solvent and HDS
products. Not too surprisingly, the dye had completely disappeared
from the solution containing the adsorbent, activated charcoal (entry
References
(1) Jandeleit, B.; Turner, H. W.; Uno, T.; Van Beek, J. A. M.; Weinberg, W.
H. Cattech 1998, 2, 101-123.
(2) Jandeleit, B.; Weinberg, W. H. Chem. Ind. (London) 1998, 795-798.
(3) Jandeleit, B.; Schaefer, D. J.; Powers, T. S.; Turner, H. W.; Weinberg,
W. H. Angew. Chem., Int. Ed. 1999, 38, 2494-2532.
(4) Senkan, S. Angew. Chem., Int. Ed. 2001, 40, 312-329.
(5) Thomas, J. M. Angew. Chem., Int. Ed. 1999, 38, 3588-3628.
(6) Weinberg, W. H.; Jandeleit, B.; Self, K.; Turner, H. Curr. Opin. Solid
State Mater. Sci. 1998, 3, 104-110.
(7) Kabe, T.; Ishihara, A.; Qian, W. Hydrodesulfurization and Hydrodeni-
trogenation: Chemistry and Engineering; Wiley-VCH: New York, 2000.
(8) U.S. Environmental Protection Agency. Tier 2/Gasoline Sulfur Final
Rulemaking. http://www.epa.gov/otaq/tr2home.htm (accessed Jan 2003).
(9) Hannerup, P. N. Chem. Ind. Dig. 1997, 10, 112-115.
(10) Shafi, R.; Hutchings, G. J. Catal. Today 2000, 59, 423-442.
(11) Cooper, A. C.; McAlexander, L. H.; Lee, D.; Torres, M. T.; Crabtree, R.
H. J. Am. Chem. Soc. 1998, 120, 9971-9972.
(12) Shaughnessy, K. H.; Kim, P.; Hartwig, J. F. J. Am. Chem. Soc. 1999,
121, 2123-2132.
(13) Reddington, E.; Sapienza, A.; Gurau, B.; Viswanathan, R.; Sarangapani,
S.; Smotkin, E. S.; Mallouk, T. E. Science 1998, 280, 1735-1737.
(14) Bandarage, U. K.; Simpson, J.; Smith, R. A. J.; Weavers, R. T. Tetrahedron
1994, 50, 3463-72.
(15) Salem, A. S. H.; Hamid, H. S. Chem. Eng. Technol. 1997, 20, 342-347.
(16) Takahashi, A.; Yang, F. H.; Yang, R. T. Ind. Eng. Chem. Res. 2002, 41,
2487-2496.
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