K-promoted Mo/Co- and Mo/Ni-catalyzed Fischer-Tropsch synthesis of aromatic hydrocarbons with and without a Cu water gas shift catalyst

Article abstract of DOI:10.1016/j.apcata.2014.04.044

The catalyst systems Mo/Co/K/ZSM-5 and Mo/Ni/K/ZSM-5, alone and with the added copper-based water gas shift catalyst, were used for the conversion of two CO/H₂ ratios in a batch reactor. GC analysis of the gas phase was used to determine CO conversion while GCMS and NMR studies were used to characterize the liquid products formed and liquid product selectivities. The liquids were hydrocarbons consisting mainly of alkyl substituted benzenes. Methyl substitution in the alkyl benzenes in the product liquid ranged from an average of 1.3 to 4.5 methyls per ring depending on reaction conditions and reactant gas mole ratios. The additional presence of the WGS catalyst significantly increased CO conversion in the reactions taking place at 280 °C from ～25% to ～90% while increasing selectivity toward higher average methyl substitution. Similar conversions and selectivities were observed with both a bio-syngas and a 50/50 mixture of H₂ and CO.

Full text of DOI:10.1016/j.apcata.2014.04.044

Applied Catalysis A: General 480 (2014) 93–99
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
K-promoted Mo/Co- and Mo/Ni-catalyzed Fischer–Tropsch synthesis
of aromatic hydrocarbons with and without a Cu water gas shift
catalyst
Rangana Wijayapalaa, Fei Yub, Charles U. Pittman Jr.a, Todd E. Mlsnaa,∗
a Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, USA
b Agricultural and Biological Engineering, Mississippi State University, Mississippi State, MS 39762, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The catalyst systems Mo/Co/K/ZSM-5 and Mo/Ni/K/ZSM-5, alone and with the added copper-based water
gas shift catalyst, were used for the conversion of two CO/H2 ratios in a batch reactor. GC analysis of the
gas phase was used to determine CO conversion while GCMS and NMR studies were used to characterize
the liquid products formed and liquid product selectivities. The liquids were hydrocarbons consisting
mainly of alkyl substituted benzenes. Methyl substitution in the alkyl benzenes in the product liquid
ranged from an average of 1.3 to 4.5 methyls per ring depending on reaction conditions and reactant
gas mole ratios. The additional presence of the WGS catalyst significantly increased CO conversion in the
reactions taking place at 280 ◦C from ∼25% to ∼90% while increasing selectivity toward higher average
methyl substitution. Similar conversions and selectivities were observed with both a bio-syngas and a
50/50 mixture of H2 and CO.
Received 25 November 2013
Received in revised form 23 April 2014
Accepted 26 April 2014
Available online 9 May 2014
Keywords:
Fischer–Tropsch
Biofuel
Synthesis gas conversion
Water gas shift
Molybdenum
© 2014 Elsevier B.V. All rights reserved.
Alkyl benzene synthesis
1. Introduction
from synthesis gas [6]. Similar mixed metal ZSM-5 catalyst systems
have been used to enhance selectivity to gasoline through increased
With increasing population, economic development and limited
supplies of fossil fuels, new approaches are needed to make renew-
able liquid fuels [1]. The catalytic conversion of biomass-derived
synthesis gas (CO + H2) to liquid hydrocarbons is an approach that
has been intensely studied for several decades [2,3]. The major
focus in gas-to-liquids (GTL) technology has been Fischer Tropsch
(FT) synthesis [4], which converts synthesis gas into liquid hydro-
carbon fuels (Eq. (1)). Traditionally, commercial catalysts used
cobalt, iron and ruthenium [4,5] though a variety of catalysts can
be used [4]. Molybdenum, on a zeolite (ZSM-5) support, has shown
promise for the conversion of synthesis gas to liquid hydrocarbons
[6] as have cobalt and nickel [2]. However these systems can pro-
duce a wide range of hydrocarbons (C1–C60) during the reaction
[6].
production of high-octane aromatic hydrocarbons by promoting
oligomerization, cracking, isomerization, and aromatization reac-
tions on ZSM-5 (Si/Al = 50) [2,7–11]. Anderson–Schulz–Flory (ASF)
polymerization kinetics is generally observed in FT product dis-
tributions [12]. Most FT catalysts produce aromatic hydrocarbons
by chain propagation reactions of initially formed low molecule
weight aliphatic hydrocarbons or alcohols followed by dehydra-
tions, cyclizations and dehydrogenations [13–15]. Thus, multistage
catalysis processes govern FT product distribution.
Many studies identified advantages of using bi-functional cata-
lysts to convert synthesis gas to high carbon number gasoline range
hydrocarbons [16–19]. Alkali metal promotion can enhance cat-
alytic activity. For example, potassium has long been used as the
promoter with several FT catalysts [20]. Water gas shift (WGS) cat-
alysts can decrease H2O while increasing the effective H2/CO ratio
[21] (Eq. (2)). Cu-based WGS catalysts have been widely employed
commercially since the early 1960s and exhibit high activity and
selectivity [22]. Some are reported to maintain catalyst activity
under reaction conditions required for FT conversions [23–25]. The
commercial Cu-based catalyst (HiFUEL W220 used in this study)
was previously used to catalyze the WGS reaction at low tempera-
tures (170–250 ◦C) and low carbon monoxide concentrations, in the
(2n + 1)H2 + nCO → CnH(2n+2) + nH2O
(1)
Molybdenum-zeolite FT catalysts have been used to produce
aromatics and branched/cyclized alkanes, olefins and oxygenates
∗
Corresponding author. Tel.: +1 662 617 5553.
E-mail address: tmlsna@chemistry.msstate.edu (T.E. Mlsna).
http://dx.doi.org/10.1016/j.apcata.2014.04.044
0926-860X/© 2014 Elsevier B.V. All rights reserved.

94
R. Wijayapala et al. / Applied Catalysis A: General 480 (2014) 93–99
‘low-temperature’ CO-shift process [26–28]. Furthermore, another
study reports high CO conversion activity extends up to 500 ◦C
using this same W220 catalyst [29].
Silico) packed column and a MXT-1 (60 m 0.53 mm ID 5.00 ␮m) cap-
illary column were employed for separation of inorganic gases and
light hydrocarbons. Gas phase product structures were identified
by comparing retention times to known standards. Liquid and solid
hydrocarbons were extracted from the reactor using ethyl acetate
(Sigma Aldrich, LC–MS Grade) and then analyzed using GCMS (Agi-
lent 7890A) equipped with DB-1 column (GC, DB-1–60 m 0.32 mm
1.0 ␮m). The major hydrocarbon products were identified by com-
paring GC retention times and MS fragmentation patterns both with
authentic standards and the NIST 08 MS library. Quantification was
done using naphthalene as an internal standard. After quantita-
tion, the hydrocarbons were separated for structural identification
by removing the ethyl acetate through distillation. Hydrocarbons
were analyzed by proton NMR (Bruker, 300 MHz) to determine the
alkyl/aromatic ring substitution ratio.
H2O + CO ꢀ H2 + CO2
(2)
Here we present novel mixed catalyst systems combining a
Mo/Co/K/ZSM-5 or Mo/Ni/K/ZSM-5 catalyst with this Cu-based
W220 low temperature WGS catalyst for the FT converting both
bio-syngas and a H2/CO (50/50) ratio syngas with remarkable selec-
tivity to methylated benzene ring products.
2. Experimental
2.1. Catalyst preparation
The Mo/Co/K zeolite catalyst was prepared using incipi-
ent wetness impregnation [6]. The ammonium form of ZSM-5
(SiO2/Al2O3 = 50) (50.0 g) obtained from Zeolyst International was
dried for 24 h and then impregnated with an aqueous solution
containing 4.60 g of (NH4)6Mo7O24·4H2O (Sigma Aldrich). This
Mo/ZSM-5 was then impregnated with an aqueous solution with
12.35 g of Co(NO3)2·6H2O (Sigma Aldrich). Finally this Mo/Co/ZSM-
5 was impregnated with an aqueous solution with 1.25 g of K2CO3
(Sigma Aldrich). The same procedure was followed for making
the Mo/Ni/K zeolite catalyst, using 7.78 g Ni(NO3)2·6H2O (Sigma
Aldrich) in place of the Co. The samples were then calcined in air at
500 ◦C for 3 h and pelletized into 0.45–0.8 mm particles for activity
tests. The designated (after calcination) loading was 5 wt.% for Co,
or Ni with 5 wt.% Mo and 1.4 wt.% K. The WGS catalyst was pur-
chased from Alfa Aesar (Copper based low temperature water gas
shift catalyst, HiFUEL W220 pellets 3.1 mm × 3.1 mm).
2.3. Catalyst characterizations
The catalyst surface areas were determined by N2 BET
(Monosorb Quantachrome). Prior to these measurements, the sam-
ples were pretreated at 280 ◦C under flow of 30% nitrogen in helium.
Atomic absorption (AAS) analyses were conducted using Mo, Ni,
Co, Cu, K standards (Sigma-Aldrich AAS standards) to quantitate
each metal’s composition. An acid digestion was performed on 0.1 g
of catalyst using 50.0 mL of 1:1 70% HNO3 (Sigma-Aldrich)/95%
H2SO4 (Sigma-Aldrich). Metals were dissolved from the catalyst
into the acid for 24 h with stirring and then diluted 10 fold with
deionized water prior to AAS analysis. Catalyst morphologies were
investigated with a Carl Zeiss EVO50VP variable pressure scan-
ning electron microscope (SEM) equipped with a Bruker Quantax
200× flash energy-diffusive X-ray spectroscopy (EDX) spectrome-
ter system, which simultaneously provided the surface elemental
composition information with spot size of 10 nm. The accelerating
voltage was 15 kV with a working distance of 10 mm.
2.2. Catalytic activity tests
All reactions were performed in a 500 mL stainless steel static
reactor equipped with an autoclave catalyst basket located 8.5 cm
above the bottom of the reactor (Fig. S1). Temperature was mea-
sured internally near the catalyst basket and was controlled
with a Parr 4843 Reactor Controller. The catalyst (either 8.0 g
of the metal/ZSM-5 or 4.0 g each of the WGS and metal/ZSM-
5) was used with two different syngas feeds: H2/CO (50:50)
(mol% H2—46.76%, CO—47.41%, N2—5.83%) and bio-syngas (mol%
H2—17.82%, N2—46.03%, CO—22.65%, CH4—1.76%, C2H4—0.25%,
O2—0.88%, CO2—10.59%). Bio-syngas was produced in a continuous
process conducted in the industrial gasifier located in Mississippi
State University [30]. The catalyst was loaded and the reactor was
purged with the reaction gas at ambient temperature. The reactant
gas was used to pressurize the reactor so that 1000 psig would be
achieved when reaching the selected reaction temperature (initial
ambient temperature pressure of 480 psig for a reaction tempera-
ture of 350 ◦C and 540 psig for a reaction temperature of 280 ◦C).
Table 1 summarizes 16 reactions. These reactions studied the four
catalyst combinations with both the 50/50 H2/CO and bio-syngas at
each of the two reaction temperatures. The reactor was then held at
a reaction temperature of either 280 ◦C or 350 ◦C for 18 h. Pressure
was monitored with time.
3. Results and discussion
3.1. Characterization of the catalyst samples
The catalyst surface areas, metal and carbon compositions are
listed in Table 2. Impregnating ZSM-5 with metals significantly
reduced the surface area from 422 m2/g to approximately 300 m2/g,
indicating that the added metals block some zeolite channels
resulting in lower surface area. No significant surface area change
was observed when comparing metal-impregnated zeolite cata-
lysts before and after the catalytic reactions. This implies negligible
surface coking of the FT catalysts. In contrast, the Cu-based water
gas catalyst underwent significant surface area reduction possibly
due to coking or surface reconstruction. However, the WGS catalyst
did not exhibit significant loss in activity after 3 recycles as seen in
Section 3.2.3, and no significant increase in mass was observed for
the mixed catalysts after the reaction. The AAS analysis confirmed
metal composition at expected 1:1 wt ratios for Mo/Co and Mo/Ni
catalysts after calcination. The SEM images of Mo/Co/K/ZSM-5 and
Mo/Ni/K/ZSM-5 and EDX analysis are illustrated in Fig. 1. The EDX
surface analysis shows the presence of Mo, Co, K and Ni metals on
the catalyst surfaces.
In a typical reaction, pressure decreased rapidly over the first
few hours before the drop in pressure slowed and stopped within
15 h. After the pressure stabilized, the reactor was allowed to cool
to room temperature where the final pressures ranged from 175 to
450 psig. Sample plots of the pressure versus time for different cat-
alysts are given in Fig. S2. The effluent gas was collected into a 1 L
Tedlar bag and analyzed using a gas chromatograph (SRI 8610C)
equipped with thermal conductivity (TCD) and flame ionization
(FID) detectors. A shincarbon ST 100/120 (2 m 1 mm ID 1/16ꢀꢀ OD
3.2. Reaction products
3.2.1. CO conversion and CO2 selectivity
Catalyst activity tests were performed using the dual catalyst
systems (WGS + ZSM-5/Mo/Co/K or WGS + ZSM-5/Mo/Ni/K) and
these were compared to the performance of the ZSM-5/Mo/Co/K
or ZSM-5/Mo/Ni/K catalyst used alone. Collected gas samples were
analyzed as described in Section 2.2. These analyses were used for

R. Wijayapala et al. / Applied Catalysis A: General 480 (2014) 93–99
95
Table 1
Reaction conditions for the dual catalyst systemsa.
Catalyst
Syngas
Temperature (◦C)
Reaction abbreviation
280
350
280
350
280
350
280
350
280
350
280
350
280
350
280
350
MoCo 50/280
MoCo Bio/280
MoCo 50/350
MoCo Bio/350
MoCo/WGS 50/280
MoCo/WGS Bio/280
MoCo/WGS 50/350
MoCo/WGS Bio/350
MoNi 50/280
MoNi Bio/280
MoNi 50/350
MoNi Bio/350
MoNi/WGS 50/280
MoNi/WGS Bio/280
MoNi/WGS 50/350
MoNi/WGS Bio/350
50/50 Syngas
Bio-syngas
50/50 Syngas
Bio-syngas
50/50 Syngas
Bio-syngas
50/50 Syngas
Bio-syngas
Mo/Co/K (8 g)
WGS (4 g) + Mo/Co/K (4 g)
Mo/Ni/K (8 g)
WGS (4 g) + Mo/Ni/K (4 g)
a
All reactions were run for 18 h with initial reaction pressures of 1000 psig in a 500 mL autoclave.
CO conversion and product selectivity calculations using Eqs. (3)
and (4). Nitrogen was used as the internal standard. Reaction tem-
peratures were maintained for 18 h for each of the reactions listed
in Table 1 before cooling to ambient temperature.
were significantly lower than that of the 50/50 H2/CO (initially, the
H2 pressure is 36% and CO is 46% that of the 50/50 H2/CO initial
pressures). The consistently larger pressure drop associated with
the 50/50 H2/CO compared to the bio-syngas can be attributed, in
part, to the presence of the 46% N2 present in the bio-syngas. The
overall yields of the gaseous hydrocarbons (methane, ethane and
propane) range from 4.6 to 20.0% of CO consumed. Selectivity to
these gaseous hydrocarbons is lower at higher temperatures and
in the presence of the WGS catalyst (4.6 to 7.1%).
ꢀ
ꢀ
ꢁ
ꢀ
ꢁꢁ
CC0O CN2 /CN0 − CCO CN0 /CN
2
2
2
ꢀ
ꢁ
conversion of CO % =
( )
× 100
(3)
CC0O CN2 /CN0
2
ꢀ ꢀ
ꢁ
ꢀ
ꢁꢁ
ꢁ
n
Ci CN0 /CN − Ci0 CN2 /CN0
3.2.2. Liquid product yields with single vs. dual catalyst systems
Liquid reaction products were analyzed as described in Section
2.2. Both single and dual catalyst systems resulted in significant
alkyl-substituted aromatic hydrocarbon production. Methyl ring-
substitution greatly dominated with a small amount of ethyl and
isopropyl substitution also observed. A greater average number of
methyl groups per ring were observed in reactions with the dual
catalyst systems (Fig. 2). All reactions were stopped after 18 h at
280 or 350 ◦C; during this time the reaction pressure had stabi-
lized. Catalyst weight changes before and after the reactions were
negligible. Analysis of the amounts of each gas phase product was
performed using GC with nitrogen as an internal standard to deter-
mine relative ratios. Then the ideal gas laws (pressure, temperature
and volume were known for all reactions) were applied to obtain
the gas product stoichiometries and yields.
The known volume of extracting solvent and GCMS results
on collected liquid samples were used to determine stoichio-
metries and product selectivities. As a specific example, 8.0 g of
Mo/Co/K/ZSM-5 catalysts were placed in the reaction basket. The
reactor was then charged with 478 psig of CO/H2 (50/50) at ambi-
ent temperature. Upon heating to 350 ◦C, the reaction pressure
reached 1000 50 psig. After 18 h followed by cooling to 25 ◦C,
the reactor pressure was ∼225 psig. No catalyst weight change
was observed. The gas phase product was collected and analyzed
2
2
2
ꢀ
ꢁ
ꢀ
selectivity of product i %
( )
=
CC0O CN2 /CN0 − CCO CN0 /CN
2
2
2
× 100
(4)
CC0O —initial CO concentration (moles/L) (in syngas); CCO—final CO
concentration; CN0 —initial N2 concentration; CN —final N2 con-
centration; Ci0 —initial product i concentration; Ci—final product i
concentration; n—number of carbon atoms in product i.
2
2
Table 3 illustrates that CO conversion is low at 280 ◦C with
the FT catalyst alone (20–30%) but increases dramatically with the
addition of the water gas shift catalyst (85–92%). A less dramatic
increase in CO conversion with the addition of the WGS catalyst
is also observed at 350 ◦C (68–80% to 83–90%). The WGS equilib-
rium produces CO2 and H2 but H2 is also being consumed during
hydrocarbon formation along with CO. Therefore, the gas prod-
uct compositions are continually being changed as liquid products
form. Also the various rates of hydrocarbon formation (hence loss
of CO and H2) and the WGS rates are different and they change with
time, in part because the partial pressures of the gaseous reagents
are changing with time. In general, similar CO conversions and
product selectivities were observed for both the 1/1 syngas H2/CO
(50/50) and the bio-syngas (∼18/23). While the bio-syngas H2/CO
ratio is close to that of 50/50, the partial pressures of H2 and CO
Table 2
Catalysts’ elemental analyses and surface areas.
Surface area (m2/g)
Catalyst
Elemental analysisb (wt%)
Used catalystc (wt%)
C
Calcined
Useda (m2/g)
Mo
Co
Ni
K
Cu
ZSM-5
422
299
302
84.6
–
291
299
59.1
–
–
4.24
–
–
–
4.08
–
–
–
–
–
–
ZSM-5/Mo/Co/K
ZSM-5/Mo/Ni/K
Cu based WGS
4.19
4.25
–
1.16
1.23
–
0.23
0.31
3.45
–
38.15
a
Catalysts were used in 18 h reactions with initial reaction pressures of 1000 psig at 350 ◦C, with H2/CO mole ratio 50/50 syngas prior to BET analysis.
Elemental analyses (atomic absorption) were performed on catalysts after calcination and before reactions with syngas.
Carbon analysis performed on used catalyst.
b
c

96
R. Wijayapala et al. / Applied Catalysis A: General 480 (2014) 93–99
Fig. 1. SEM images of (a) Mo/Co/K/ZSM-5 and (b) Mo/Ni/K/ZSM-5 catalysts (top) and their EDX analyses (bottom) before use in reactions with synthesis gas. The arrows
indicate EDX analysis positions and the circles indicate the EDX spot size (10 nm). No difference was observed between the EDX spectra collected at different spots, indicating
good metal dispersion and showing homogeneity is reached within 78.5 nm2 spot areas on the catalyst.
Table 3
CO conversion and product selectivity in the gas phase for all 16 reaction conditions.
Gas product selectivityc
Reaction abbreviationa
Final pressure (psig) at 25 ◦
C
CO % conversionb
CO2
CH4
C2H6
C3H8
MoCo 50/280
MoCo Bio/280
MoCo 50/350
MoCo Bio/350
MoCo/WGS 50/280
MoCo/WGS Bio/280
MoCo/WGS 50/350
MoCo/WGS Bio/350
MoNi 50/280
MoNi Bio/280
MoNi 50/350
MoNi Bio/350
MoNi/WGS 50/280
MoNi/WGS Bio/280
MoNi/WGS 50/350
MoNi/WGS Bio/350
32.9
25.1
75.9
66.6
91.3
85.2
88.4
83.0
28.6
19.5
81.7
63.2
88.6
91.4
88.7
87.9
350
450
225
350
225
400
175
325
350
450
200
350
250
400
175
325
34.2
42.4
39.7
44.5
42.7
47.9
43.2
39.1
24.1
27.4
35.8
35.6
58.1
51.3
43.2
41.6
6.7
9.5
4.4
5.7
3.0
4.5
2.8
3.8
7.6
10.0
5.8
4.2
3.8
3.6
2.8
2.8
4.4
5.9
3.0
3.1
2.0
4.1
1.9
2.5
5.1
7.7
3.9
4.8
2.5
4.1
1.8
2.1
0.3
2.7
0.3
1.2
0.2
1.0
0.1
1.0
0.3
3.3
0.4
1.1
0.2
0.8
0.1
0.7
a
See Table 1 for explanation.
Calculated using Eq. (3).
Calculated using Eq. (4). Products were confirmed by comparing GC retention times with standards.
b
c

R. Wijayapala et al. / Applied Catalysis A: General 480 (2014) 93–99
97
Mo/Co/K-ZSM-5, 350°C
a.
8.E+05
7.E+05
6.E+05
5.E+05
4.E+05
3.E+05
2.E+05
1.E+05
0.E+00
13
18
23
28
33
38
Time (min)
Mo/Co/K-ZSM-5 + WGS, 350°C
b.
8.E+06
7.E+06
6.E+06
5.E+06
4.E+06
3.E+06
2.E+06
1.E+06
0.E+00
13
18
23
28
33
38
Time (min)
Fig. 2. GCMS showing the liquid phase product distributions obtained in reactions catalyzed by (a) Mo/Co/K (73.9% CO conversion) alone and (b) Mo/Co/K + WGS (88.9% CO
conversion) catalysts. Both reactions used 50/50 syngas at 1000 psig initial reaction pressure at 350 ◦C for 18 h.
using GC to determine a 76% CO conversion and the selectivities
given in Table 3 (reaction MoCo 50/350). All liquid products were
carefully extracted from the autoclave with three separate 8 mL
aliquots of ethyl acetate, which were placed in a 25 mL volumetric
flask. This solution was diluted precisely to 25 mL with addi-
tional ethyl acetate. Naphthalene (0.1 M) was used as an internal
standard and GCMS analysis determined the product distribution
and selectivity of the liquid phase. Concentrations of aliphatic and
methyl-substituted benzenes (Liquid Product mole% are shown in
Fig. 3) were calculated through comparison with known naph-
thalene concentrations after determining the analyte response
factors. Aromatic hydrocarbon mol% increase with the dual cata-
lyst systems, and with increasing temperatures as shown in Fig. 3.
Aromatic to aliphatic carbon moles ratios have been calculated (Fig.
S4) to verify this observation. The extent of methyl substitution,
percentage of converted CO transformed into liquid product and
percentage of initial CO converted to liquid is compared in Table 4.
The extent of methyl substitution in the liquid products was
tracked using proton NMR. After extracting the liquid products,
ethyl acetate was evaporated and NMR analysis was performed on
the remaining crude product mixture. The CH3 number gives the
average number of methyl substituents per benzene ring. It was
calculated using the integrated areas of aromatic (6.8–8 ppm) and
aliphatic protons (2–3 ppm) in the 1HNMR spectrum of each crude
mixture. The equation given in Fig. 4 caption was used to calcu-
late the average number of methyl groups per aromatic ring (CH3
number).
Table 4 data shows that the CH3 number increases slightly using
the 50/50 syngas mixture versus using the bio-syngas mixture.
A more dramatic increase in CH3 number is observed with the
Fig. 3. Percent CO conversion and carbon mol% present within each product in all reactions employing both dual and single catalyst systems.

98
R. Wijayapala et al. / Applied Catalysis A: General 480 (2014) 93–99
Table 4
Alkylated aromatic hydrocarbon product yields after 18 h.
Liquid product (mol%)a
CH3 numberb
Reaction abbreviation
Mol% of converted
CO in Liq. Prod.c
Mol% of initial CO
converted to Liq. Prod.d
C6
C7
C8
C9
C10
C11
C12
MoCo 50/280
MoCo Bio/280
MoCo 50/350
MoCo Bio/350
MoCo/WGS 50/280
MoCo/WGS Bio/280
MoCo/WGS 50/350
MoCo/WGS Bio/350
MoNi 50/280
MoNi Bio/280
MoNi 50/350
MoNi Bio/350
MoNi/WGS 50/280
MoNi/WGS Bio/280
MoNi/WGS 50/350
MoNi/WGS Bio/350
11.0
13.6
7.1
19.2
2.0
1.9
0.7
1.5
6.4
8.9
3.8
5.2
3.1
4.5
2.7
2.2
16.1
17.7
16.5
25.5
1.1
3.0
1.7
2.7
14.0
14.2
8.8
13.9
1.3
1.3
1.6
2.3
41.1
42.2
41.7
35.5
0.7
1.9
1.0
2.8
39.9
40.4
38.7
39.8
2.5
1.4
0.4
4.9
27.8
23.9
28.1
15.1
5.7
17.8
10.2
15.3
33.9
31.8
39.9
34.9
6.8
1.3
0.8
2.5
2.2
69.4
64.9
46.9
51.2
2.2
1.7
5.1
3.3
71.0
78.8
64.3
60.0
1.7
1.1
2.9
1.6
18.6
9.9
37.9
25.9
2.5
1.9
2.7
2.2
14.1
7.0
1.0
0.7
1.3
0.8
2.6
0.5
1.7
0.7
1.1
1.2
1.1
0.6
1.2
0.7
0.3
0.4
2.2
1.8
2.1
1.3
4.2
4.1
4.5
4.3
2.5
2.3
3.4
2.9
4.2
4.1
4.3
4.2
45.0
39.8
46.2
40.3
44.5
43.5
52.6
46.5
52.2
55.6
45.4
52.8
38.9
41.0
46.4
41.2
13.4
10.1
34.1
26.7
40.2
37.2
46.8
38.6
12.5
11.1
36.2
33.4
34.7
37.5
41.0
36.2
6.2
10.0
13.4
20.7
16.8
a
Mol% of this fraction in the collected liquid product.
b
c
Average methyl substitution of the liquid products were calculated using proton NMR data as described in Fig. 3.
Percentage of the converted CO that is collected as liquid hydrocarbon product.dPercentage of initial CO that is collected as liquid hydrocarbon product.
Fig. 4. Proton NMR spectrum of the liquid product produced using the Mo/Co/K + WGS catalysts, 50/50 H2/CO at 1000 psig initial pressure at 350 ◦C for 18 h (a–c = aromatic
protons, d–h = substituted methyl protons). CH3 number = 6 × (y/(y + 3x)), x = a + b + c , y = d + e + f + g + h where the integrated number of aromatic protons (from
(
)
(
)
1HNMR) x = a + b + c and number of aliphatic protons y = d + e + f + g + h. The ratio of methyl substituted to unsubstituted carbons on the aromatic ring is y/3:x.
addition of the WGS catalyst (from approximately 2.3 to 4.2). Traces
of methanol (0.1–0.25%) were formed at both 280 and 350 ◦C using
the dual catalyst (FT + WGS) system. Significant dimethyl ether for-
mation was observed in a test reaction when using the WGS catalyst
alone in the reaction with 50/50 syngas at 350 ◦C. The percent of
dimethyl ether in the products peaked after 3 h and then decreased
to near zero after 18 h (Fig. S3). Dimethyl ether is the bimolecu-
lar dehydration product of methanol. Both methanol and dimethyl
ether can function to methylate aromatic rings over acidic cat-
alytic sites, serving as the source of methyl groups on the aromatic
products. This activity contributes to the observed increase in CH3
number with the dual FT/WGS catalyst system over using the FT
alone.
It is interesting to note that the percent of consumed CO that is
converted to liquid (% CO Converted into Liq. Prod., Table 4) varies
only modestly in the reactions with changes in H2/CO mole ratio
syngas and temperature. A slight increase in CO conversion to liq-
uid was observed using the Mo/Co/K catalyst with the WGS catalyst
verses a decrease using Mo/Ni/K with the WGS catalyst. The percent
of initial CO converted to liquid (% Initial CO converted to Liq. Prod,
Table 4) increased dramatically with increasing temperature and
with the presence of the WGS catalyst. Both dual catalyst systems
produced predominately tetra- and penta-methyl benzene deriva-
tives at both 280 and 350 ◦C. Using the FT catalyst alone produced
primarily di- and tri-methyl benzene derivatives. This trend was
observed with either syngas type.
3.2.3. Catalyst deactivation
The MoCoK, MoNiK, MoCoK + WGS and MoNiK + WGS catalysts
were each recyled through three reactions at 350 ◦C in order to eval-
uate catalyst deactivation. A 50/50 syngas mixture was used. The
CO conversions remained essentially unchanged for MoCoK and
100
90
80
70
60
1st
50
2nd
40
3rd
30
20
10
0
MoCoK
MoNiK
MoCoK+WGS MoNiK+WGS
Fig. 5. Catalyst deactivation tests using 50/50 CO/H2 at 350 ◦C showing CO con-
versions in three reaction cycles over MoCoK and MoNiK catalysts, both with and
without the WGS catalyst present. A larger descrease in CO conversion is observed
with the dual catalyst systems.

R. Wijayapala et al. / Applied Catalysis A: General 480 (2014) 93–99
99
70
60
50
40
30
20
10
0
C6
C7
C8
C9
C10
C11
C12
1st
2nd
3rd
1st
2nd
3rd
1st
2nd
3rd
1st
2nd
3rd
Mo/Co/K
Mo/Ni/K
Mo/Co/K+WGS
Mo/Ni/K+WGS
Fig. 6. Product selectivities (mol%) employing MoCoK, MoNiK, MoCoK + WGS and MoNiK + WGS catalysts at 350 ◦C upon recycling.
MoNiK used alone (Fig. 5). A small but steady drop in CO conver-
sion occurred for the hybrid FT + WGS catalysts. Since WGS catalyst
showed a substantial loss of surface area during a single reaction
cycle at 350 ◦C (Table 2), its ability to enhance conversion likely
drops with time, accounting for this observation.
(DE-FG3606GO86025) and U.S. Department of Agriculture under
Award (AB567370MSU).
Appendix A. Supplementary data
The product selectivities as a function of catalyst recycle at
350 ◦C are shown in Fig. 6. Selectivities in the liquid products are
represented as mol% of compounds having each specified carbon
number relative to the total number of moles of all liquid com-
pounds. The selectivities remained essantially constant over three
reaction cycles, even for the hybrid catalysts.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
2014.04.044.
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Novel catalyst systems have been developed for the conver-
sion of 1/1 H2/CO and bio-syngas into aromatic hydrocarbons.
Potassium-activated Mo/Ni or Mo/Co on a ZSM-5 support, both
alone and with a WGS catalyst present, exhibited good batch CO
conversions and remarkable selectivities to alkyl benzenes. The
CO conversions for the FT/WGS catalyst systems were ∼90% at
280 ◦C, a surprising increase verses using the FT catalyst alone
(∼25%). Remarkable selectivities were found for tetra- and penta-
methylbenzene with the FT/WGS catalyst systems, where these
compounds made up over 80% of the liquid products. The amount of
liquid hydrocarbon product increased with temperature. Using the
dual FT/WGS catalyst system, the percent of initial CO converted
into liquid hydrocarbon ranged from a low of 10.7% (280 ◦C MoCo)
to a high of 48.2% (350 ◦C MoCo/WGS). The carbon molar ratio of
aromatic to aliphatic hydrocarbons (aromatic/aliphatic) increased
with temperature and with the dual catalyst systems from a low of
0.4 (280 ◦C MoCo) to a high of 6.7 for (350 ◦C MoNi/WGS). Includ-
ing the WGS catalyst significantly improves CO conversion while
increasing hydrogen use efficiency. Future work will focus on opti-
mizing reactions conditions in a flow reactor. The H2/CO ratio will
be varied. Pressures will be held constant and studied between
1000 and 3000 psi, higher pressures (up to 2000 psi), and higher
temperatures, and gas hourly space velocities will be investigated.
Acknowledgments
This work was performed through the Sustainable Energy
Research Center at Mississippi State University and is sup-
ported by the U.S. Department of Energy under Awards