Effect of Synthetic Route and Metal Oxide Promoter on Cobalt-Based Catalysts for Fischer–Tropsch Synthesis

Article abstract of DOI:10.1007/s10562-018-2537-7

A hydrothermal technique was employed in order to produce a novel coordination polymer [Co_0.42Ni_0.40Zn_0.68(btc)(H₂O)₆] (1). The complex (1) was characterized by elemental analysis, and FT-IR spectroscopy; and its structure was determined by single crystal X-ray diffraction (XRD). Alumina-supported Co–Ni–Zn and silica catalysts were prepared by thermal decomposition of respective inorganic precursors (fabricated or synthesized catalysts) and through impregnation method as reference catalysts. The evaluation of catalytic activity of these catalysts was carried out at a fixed bed reactor for Fischer–Tropsch synthesis. The performance of the synthesized catalysts was much better than the catalysts which were produced by the impregnation procedure, those that were characterized by scanning electron microscopy (SEM), XRD, and BET specific surface area. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-018-2537-7

Catalysis Letters
https://doi.org/10.1007/s10562-018-2537-7
Effect of Synthetic Route and Metal Oxide Promoter on Cobalt-Based
Catalysts for Fischer–Tropsch Synthesis
Sania Saheli1 · Ali Reza Rezvani · Azim Malekzadeh · Michal Dusek · Vaclav Eigner
1
2
3
3
Received: 27 June 2018 / Accepted: 27 August 2018
©
Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
A hydrothermal technique was employed in order to produce a novel coordination polymer [Co Ni Zn (btc)(H O) ]
0
.42 0.40
0.68
2
6
(
1). The complex (1) was characterized by elemental analysis, and FT-IR spectroscopy; and its structure was determined
by single crystal X-ray diffraction (XRD). Alumina-supported Co–Ni–Zn and silica catalysts were prepared by thermal
decomposition of respective inorganic precursors (fabricated or synthesized catalysts) and through impregnation method as
reference catalysts. The evaluation of catalytic activity of these catalysts was carried out at a fixed bed reactor for Fischer–
Tropsch synthesis. The performance of the synthesized catalysts was much better than the catalysts which were produced
by the impregnation procedure, those that were characterized by scanning electron microscopy (SEM), XRD, and BET
specific surface area.
Graphical Abstract
Keywords Catalytic performance · Fischer–Tropsch synthesis · Inorganic precursor · Metal oxide promoter · Mixed metal
catalyst
1
Introduction
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-018-2537-7) contains
supplementary material, which is available to authorized users.
Fischer–Tropsch synthesis (FTS) is a catalytic polymeriza-
tion reaction through which clean fuels can be produced
from natural gas, biomass and coal [1–3]. Catalysts based
on cobalt, nickel, iron and ruthenium are considered efficient
compounds for hydrogenation of carbon monoxide [4–6]
despite the fact that group VIII transition metals catalyze
the FTS.
*
Ali Reza Rezvani
Ali@hamoon.usb.ac.ir
1
2
3
Department of Chemistry, University of Sistan
and Baluchestan, P. O. Box 98135-674, Zahedan, Iran
School of Chemistry, Damghan University (DU), Damghan,
Iran
Owing to their low water–gas shift activity, long life and
high selectivity into aliphatic hydrocarbons [7, 8], cobalt-
based catalysts are particularly useful for the FTS. Promoters
Institute of Physics, Czech Academy of Sciences, Na
Slovance 2, 18221 Prague 8, Czech Republic
Vol.:(0
1
123456789)
3

S. Saheli et al.
have a number of advantages for Co-based catalysts in the
FTS; for example, Rytter et al. [9] found that nickel deeply
affects the catalytic activity and can be used as a promoter of
reduction and activity (with loading>5 wt%). Ishihara et al.
cooper grid with carbon film. H -temperature programmed
2
reduction (H -TPR) experiments were carried out using a
2
NanoSORD NS91 (made by Sensiran Co., Iran) apparatus.
H -TPR experiments were conducted on 50 mg of each cata-
2
[
10, 11] proved that an alloy of cobalt and nickel reinforces
lyst placed in a U-shaped quartz reactor. Prior to each TPR
run, the catalyst was degassed in a flow of 10 sccmAr at
300 °C for 1 h, and it was cooled down to room temperature
under the same atmosphere. The sample was then reduced by
hydrogen adsorption, and leads to an increase in the catalytic
activity. With regard to these results and other investigations
[
12, 13], nickel can be employed as a promoter in FTS. In
addition, another possible promoter for cobalt-based cata-
lysts is zinc, which can reduce cobalt–support interaction,
thereby affecting cobalt reducibility [14, 15].
10 sccm of 5.0% H /Ar mixture while the temperature was
2
−
1
raised to 900 °C with a heating rate of 10 °C min .
The design of synthetic procedures for catalysts that
are suitable for FTS is technologically very important. An
appropriate method used in applying inorganic complexes
to produce mixed metal oxides exhibits some advantages
such as smaller particle sizes, higher surface area and
homogenous dispersion of metals [16–21]. In this work, a
new inorganic complex [Co Ni Zn (btc)(H O) ] was
2.2 Synthesis of Complex 1
1,3,5-Benzenetricarboxylic acid (105 mg, 0.5 mmol) was
dissolved in 10 ml of distilled water, followed by addition
of NaOH (40 mg, 1 mmol). Then it was stirred 30 min at
room temperature. An aqueous solution of Co(NO ) ⋅6H O
3
2
2
(291 mg, 1.0 mmol), Ni(NO ) ⋅6H O (290 mg, 1 mmol) and
0
.42 0.40
0.68
2
6
3 2
2
prepared and the complex was used for the fabrication of
inorganic precursors. Then, the mixed metal oxides result-
ing from thermal decomposition of inorganic precursors
were evaluated for catalytic activity in FTS, and were com-
pared with reference catalysts which were generated by the
impregnation procedure; and the physicochemical charac-
terizations were determined by Brunauer–Emmett–Teller
method (BET), X-ray diffraction (XRD) and scanning elec-
tron microscopy (SEM).
Zn(NO ) ⋅6H O (297 mg, 1.0 mmol) was appended to the
3 2 2
above-mentioned solution and was stirred 30 min at room
temperature. The resulting solution was placed in a Parr-
Teflon lined stainless steel vessel. It was sealed and heated
to 130 °C for 3 days and then cooled to the room tempera-
ture. Colorless crystals of 1 were obtained by filtration and
they were dried in air. The yield was 75%. Anal. Calc. for
C H Co Ni
O
Zn : C, 8.01; H, 1.12. Found: C,
9
15
0.42 0.40 12.06 0.68
8.04; H, 1.08%.
2.3 X‑ray Structure Determination
2
Experimental
Single crystal of approximate dimensions
0.04×0.06×0.37 mm for complex 1 was used for the deter-
mination of crystal structure on SuperNova diffractometer
equipped with mirror monochromated Mo Kα radiation
(λ=0.71073 Å). A total of 11,665 reflections were collected
in the range of 3.39°<θ<29.71° at 95 (10) K, of which 3363
independent ones [R = 0.0206] were used. The crystal
2
.1 Materials and Instruments
All purchased chemicals and solvents were of reagent grade
and were used without further purification; elemental analy-
ses were carried out by using a Leco, CHNS-932 elemen-
tal analyzer. The FT-IR spectra were measured with Perkin
Elmer (spectrum two) spectrophotometer as KBr disks in the
(
int)
structure was solved by direct methods with the Superflip
−
1
4
000–400 cm range, and simultaneous thermal analysis
program [22] and was refined by full-matrix least squares on
2
(
STA) was made by usingRheometric Scientific ARES, at
F using the program Jana 2006 [23]. All hydrogen atoms
−
1
a heating rate of 10 °C min . Powder diffraction data were
recorded on a Bruker D8 ADVANCE the 2θ range from
present in the structure model were discernible in differ-
ence Fourier maps and could be refined to reasonable geom-
etry; nevertheless, hydrogen atoms attached to carbon were
constraint at geometrically expected positions. Positions
of water hydrogen atoms were refined using an O–H bond
restraint 0.88 Å with s.u. 0.001, and H–O–H angle restraint
105° with s.u. 1.0. All non-hydrogen atoms were refined
using harmonic refinement, while for hydrogen atoms iso-
tropic ADPs were used with U (H) = 1.2U (C, O). The
1
0° to 80°, and the morphology of the catalysts was studied
on MIRA3 TESCANFE SEM,operatingwith an accelerat-
ing voltage of 15 kV. The BET surface areas of the samples
were measured by N physi-sorption using anASAP 2020
2
apparatus. Each sample was degassed under nitrogen atmos-
phere at 350 °C for 4 h. The images were recorded with
transmission electron microscope (TEM) Philips CM120
with a LaB6 cathode at acceleration voltage 120 kV. TEM
is equipped with a CCD camera Olympus Veleta. Powdered
samples were prepared by dispersing in water under ultra-
sonic treatment. Drop of suspension was evaporated on
iso
eq
crystallographic dataare summarized in Table 1.
The mixed site disorder was observed in the structure,
and the coordinates and ADPs of the mixed site atoms
were made equal. Since the refinement of the metal ratios
1
3

Effect of Synthetic Route and Metal Oxide Promoter on Cobalt-Based Catalysts for Fischer–Tropsch…
Table 1 Crystallography data for [Co0.42Ni0.40Zn0.68 (btc)(H O) ]
2
6
2.4 Synthesis of [Co0.42Ni0.40Zn0.68 (btc)(H O) ]/SiO
2
2
6
Precursor
Complex
1
Empirical formula
Formula weight
Crystal system
Space group
C H Co0.42Ni0.40O12.06Zn
15
408.9
Monoclinic
C2
0.04×0.06×0.37
17.3699 (6)
12.9305 (4)
111.830 (3)
1349.97 (8)
4
2.012
95
11,665/3363
0.021
−22 ≤ h 24≤
9
0.68
To prepare [Co Ni Zn (btc)(H O) ]/SiO precursor,
0
.42 0.40
0.68
2
6
2
0
5
.6 g silica was added to an aqueous solution containing
.2 g of the complex 1. The mixture was stirred and evapo-
rated at 60 °C in a rota-evaporator for 5 h. The resulting
precipitate was filtrated and then it was dried in an oven
at 120 °C for 12 h.
3
Crystal size (mm )
a (Å)
b (Å)
β (°)
3
V (Å )
2
.5 Synthesis of Silica‑Supported Cobalt–Nickel–
Z
Zinc Catalyst, Co–Ni–Zn/SiO2
Dcalcd (g cm−3
T (K)
)
The cobalt–nickel–zinc catalyst was prepared by calci-
Reflections collected/unique
Rint
nating [Co Ni Zn
(btc)(H O) ]/SiO precursor at
2 6 2
0
.42
0.40
0.68
600 °C at the atmosphere of static air in an electric fur-
Limiting indices
nacemaintaining the temperature for 6 h.
−
−
17 ≤ k 17
8 ≤ l ≤ 8
2
.6 Synthesis of [Co0.42Ni0.40Zn0.68 (btc)(H O) ]/Al O
2 6 2 3
Tmin, Tmax
0.625, 0.925
0.697
0.019, 0.044, 1.37
0.22, −0.33
Precursor
(
sin θ/λ) (Å−1)
max
2
2
2
R[F >3σ(F )], wR(F ), S
Δρmax, Δρmin (e Å
The [Co Ni Zn
(btc)(H O) ]/Al O precursor was
2 6 2 3
0
.42 0.40
0.68
−
3
)
obtained by mixing 0.6 g of alumina with an aqueous solu-
tion containing 5.2 g of the complex 1. The suspension was
stirred and aged at 60 °C in a rota-evaporator for 5 h. The
final mixture was filtrated and dried in an oven at 120 °C
for 12 h.
was not possible due to the electronic similarities of three
present metals, the ratio determined by microprobe analy-
sis was used instead, and because the structure crystallized
in non-centrosymmetric space group, the Flack parameter
was refined with a resulting value of 0.460 (8).
Fig. 1 A general view of
compound 1. Symmetry code:
(
i) −x, y, −z+1; (ii) −x+1, y,
−
z+2
1
3

S. Saheli et al.
2
.7 Synthesis of Alumina‑Supported Cobalt–
Table 2 Selected bond lengths (Å) and bond angles (°) for
[
Co Ni Zn (btc)(H O) ]
0.42 0.40 0.68 2 6
Nickel–Zinc Catalyst, Co–Ni–Zn/Al O
2
3
M–Oa
M–O (Å)
O–M–Oa
O–M–O (°)
The [Co Ni Zn
(btc)(H O) ]/Al O was calcined at
2 6 2 3
0
.42 0.40
0.68
O1w–M1–O1wi
O1w–M1–O2w
O1w–M1–O2w
M1–O1w
M1–O1w
M1–O2w
M1–O2w
M1–O1
1.9983 (15)
1.9983 (15)
2.1170 (18)
2.1170 (18)
2.1557 (14)
2.1557 (14)
2.0952 (13)
2.1282 (17)
2.0796 (13)
2.1154 (16)
2.0407 (14)
2.0426 (14)
104.36 (7)
85.10 (7)
92.71 (7)
98.18 (6)
156.10 (6)
92.71 (7)
85.10 (7)
156.10 (6)
98.18 (6)
176.44 (6)
97.08 (6)
86.00 (6)
86.00 (6)
97.08 (6)
61.04 (5)
89.21 (6)
176.51 (6)
93.54 (6)
93.29 (5)
90.08 (5)
87.32 (6)
177.25 (5)
90.19 (6)
94.02 (6)
89.93 (6)
86.33 (5)
90.55 (5)
89.58 (6)
86.06 (6)
174.64 (6)
6
00 °C in an electric furnaceat the atmosphere of static air
i
for 6 h.
i
i
O1w–M1–O1
2.8 Preparation of Reference Catalysts
i
O1w–M1–O1
i
i
M1–O1
O1w –M1–O2w
The silica- or alumina-supported Co–Ni–Zn reference cata-
lysts werepreparedusing the impregnation method. The sup-
port (silica or alumina) wasimpregnated by using an aqueous
solution consisting of nickel nitrate, cobalt nitrate and zinc
nitrate. The suspension was stirred and heated at 60 °C in a
rota-evaporator and it was kept at this temperature for 5 h.
After that, the resulting mixture was filtrated and dried in
an oven at 120 °C for 12 h, and the precursor was calcined
at 600 °C for 5 h.
i
i
M2–O3w
M2–O4w
M2–O5w
M2–O6w
M2–O3
O1w –M1–O2w
i
O1w –M1–O1
i
i
O1w –M1–O1
i
O2w–M1–O2w
O2w–M1–O1
i
M2–O6
O2w–M1–O1
i
O2w –M1–O1
O2w –M1–O1
i
i
i
O1–M1–O1
O3w–M2–O4w
O3w–M2–O5w
O3w–M2–O6w
O3w–M2–O3
O3w–M2–O6
O4w–M2–O5w
O4w–M2–O6w
O4w–M2–O3
O4w–M2–O6
O5w–M2–O6w
O5w–M2–O3
O5w–M2–O6
O6w–M2–O3
O6w–M2–O6
O3–M2–O6
2.9 Catalytic Activity Measurements
The catalytic performances of the catalysts for the Fis-
cher–Tropsch reaction were carried out in a fixed bed micro
reactor operating at the atmospheric pressure. The reactor
tube was made of stainless steel with an internal diameter
of 1.7 cm. In each run, 0.8 g of the catalyst was loaded to
the reactor and reduced in a mixture of hydrogen/nitro-
−
1
gen gas (with a flow rate of 30 mL min for each gas) at
4
00 °C for 8 h. The N /H was then replaced for the syn-
2 2
thesis gas H /CO (2:1), and the Fischer–Tropsch reaction
2
was carried out at the temperature range of 200–300 °C and
−
1
GHSV=2700 h . The gas chromatograph (Thermo ONIX
UNICAM PROGC+), equipped with sample loop, two ther-
mal conductivity detectors (TCD) and one flame ionization
detector (FID), was employed for online analysis of the reac-
tant and product streams. The TCD was used for the analysis
a
M stands for Co, Ni and Zn since all the atom types share identical
coordinates the bond lengths and angles will be equal for all of them
of H and CO, and the analysis of hydrocarbons was carried
Symmetry code: (i) −x, y, −z+1
2
out by FID. The contents of the sample loop were automati-
cally injected into a capillary column, and each run of GC
analysis lasted more than 30 min. CO conversion and selec-
tivity of the products were two parameters for evaluating
the catalytic performance, calculated with the help of the
following equations:
3 Results and Discussion
3.1 Characterization of the Complex
3
.1.1 Crystal Structure
ꢀ
ꢁꢂMols of COin
ꢃ
(
I) CO conversion % =
ꢃꢄ∕Mols of COinꢅ × 100
ꢂ
−
Mols of COout
The complex 1, which is a coordination polymer with two
symmetry-distinct mixed-sites metal centers containing
cobalt(II), nickel(II) and zinc(II) cations,crystalizes in the
monoclinic system with the non-centrosymmetric space
group C2. As shown in Fig. 1, four oxygen atoms from water
molecules and two oxygen atoms from carboxylate groups
surround each metal center .The Co(II), Ni(II) and Zn(II)
(
II) Selectivity of j product (%)
ꢁꢂ
Mols of j product∕ Mols of CO
ꢀ
ꢃ
=
in
−ꢂ
ꢃꢄꢅ
Mols of COout
× 100
(
j:hydrocarbon).
1
3

Effect of Synthetic Route and Metal Oxide Promoter on Cobalt-Based Catalysts for Fischer–Tropsch…
Fig. 2 The view of hydrogen
bonding network in the com-
pound 1
Table 3 Hydrogen bonds data
D–H⋯A
D–H (Å)
H⋯A (Å)
D⋯A (Å)
D–H⋯A (°)
for [Co Ni Zn (btc)
0
.42 0.40
0.68
(
H O) ] (Å, °)
O1w–H1o1w⋯O4i
O1w–H2o1w⋯O5w
O2w–H1o2w⋯O3w
O2w–H2o2w⋯O4
O3w–H1o3w⋯O2
O3w–H2o3w⋯O1
O4w–H1o4w⋯O1
O4w–H2o4w⋯O5
O5w–H1o5w⋯O5
2
6
0.880 (19)
0.88 (2)
0.88 (2)
1.96 (2)
1.78 (3)
2.01 (3)
2.832 (2)
2.643 (3)
2.868 (2)
2.838 (2)
2.614 (2)
2.8696 (18)
2.882 (2)
2.6706 (19)
2.5472 (19)
2.7731 (18)
3.119 (2)
171 (2)
165 (2)
164.9 (18)
177.6 (17)
157.0 (16)
171.6 (18)
174 (2)
ii
iii
iv
0.880 (15)
0.880 (19)
0.880 (9)
0.880 (16)
0.880 (9)
0.880 (15)
0.880 (7)
0.88 (2)
1.959 (15)
1.781 (17)
1.996 (7)
2.006 (17)
1.793 (10)
1.726 (15)
1.899 (8)
2.48 (2)
v
vi
iii
175 (2)
154.3 (15)
172.4 (19)
130.3 (14)
171 (2)
vii
O5w–H2o5w⋯O4
O6w–H1o6w⋯O4
O6w–H2o6w⋯O2
viii
ix
0.880 (13)
1.862 (12)
2.7337 (19)
Symmetry codes: (i) −x+1/2, y−3/2, −z+1; (ii) −x, y−1, −z+1; (iii) −x+1/2, y−1/2, −z+1; (iv)
x−1/2, y−3/2, z−1; (v) x+1/2, y+1/2, z+1; (vi) x+1/2, y+1/2, z; (vii) x−1/2, y−1/2, z−1; (viii)
x−1/2, y−1/2, z; (ix) −x+1/2, y+1/2, −z+2
ions are six-coordinated in a distorted octahedral geometry,
and all bond distances and bond angles correspond well with
values found in other cobalt(II), nickel(II) and zinc(II) com-
plexes [24–26]. Selected bond lengths and bond angles are
listed in Table 2.
(Fig. 3.) creating a zig-zag polymeric chain. The 3D packing
of the structure is shown in Fig. 4.
3.1.2 FT-IR Spectrum
Several inter-molecular and intra-molecular hydrogen
bonds stabilize the crystal structure (Fig. 2). The coordinated
water molecules act as donors in hydrogen bonds, whereas
oxygen atoms of carboxylate groups and those of other water
molecules are used as the acceptors of the bond. For further
details on hydrogen bonding, refer to Table 3.
The FT-IR spectrum of 1 (Fig. 5) displays a broad band at
−
1
3456 cm which is assigned to the stretching vibrations of
the coordinated water molecules. The strong band which is
−
1
observed at 1615 cm is the result of deprotonation of car-
−1
boxyl groups [27, 28], and the band at 3195 cm is assigned
to C–H stretching vibration of the benzene ring [29]. Lack
−
1
The metallic center which is located at a twofold crystal-
lographic axis coordinates carboxylate in a bidentate mode,
whereas the center that is located at a general symmetry
position connects two carboxylates by two ꢀ-oxo bridges
of vibrations at the 1700 cm indicates that the carboxylic
groups are fully deprotonated. The anti-symmetric ν (COO)
a
stretching vibrations of the carboxylate groups appear
−
1
at 1522 and 1472 cm , while the symmetric stretching,
−
1
ν (COO), emerges at 1372 and 1434 cm . The frequency
s
1
3

S. Saheli et al.
Fig. 3 A view of infinite zigzag chain in 1
differences (Δν) are 150 and 38 cm−1 indicating the pres-
3.2 Catalysts Characterization
ence of monodentate and bidentate coordination mode of
the carboxylate groups to the metallic centers, respectively
3.2.1 FT-IR Spectrum
1
[
30]. The band which appears at 719 cm− belongs to the
δ(COO) vibration.
The FT-IR spectra of the silica- and alumina-supported
Co–Ni–Zn synthesized catalysts are illustrated in Fig. 7. In
3.1.3 Thermal Analysis
the FT-IR spectrum of Co–Ni–Zn/SiO catalyst, the broad
2
−
1
bond at 3421 cm belongs to the OH stretching mode of
The thermal stability of complex 1 was investigated by ther-
mogravimetric analysis (TGA), Fig. 6. Two weight losses
at the temperature region of 80–260 °C are brought about
by eliminating the water molecules, with a total weight loss
of about 26.6% (calcd. 26.4%). The two ultimate steps of
weight losses occur while the temperature is being increased
to 540 °C, and they are attributed to the decomposition of
physically adsorbed water; in addition, the H–OH bending
−
1
vibration appears at 1610 cm [31]. The strong band at
−
1
909 cm is assigned to the asymmetric stretching mode of
−
1
Si–O–Si, and the bands observed at 468, 581and 671 cm
are imputed to the stretching vibrations of Ni–O, Zn–O
and Co–O, respectively [32–34].
In the FT-IR spectrum of alumina-supported Co–Ni–Zn
catalyst, the OH stretching vibration and the H–OH bend-
ing mode of physically adsorbed water appear at 3415
H btc ligands. No further weight loss occurs until 800 °C
3
indicating an inorganic residuum in the form of metal oxides.
Further evaluationof the complex thermal behavior was
conducted by differential scanning calorimetry (DSC)
−
1
and 1618 cm , respectively. The bending vibration
−
1
of Al–O–Al emerges at 1117 cm , and the stretching
modes of Ni–O, Zn–O and Co–O appear at 450, 583and
(
Fig. 6). Multiple endo- and exo-thermic effects in the
−
1
DSC curve matched TGA results. The endothermic peak
observed at the temperature region of 80–260 °C is related
to the removal of coordinated water molecules, and two
exothermic peaks at the temperature region 400–540 °C
are attributed to successiveburning of organic parts.
672 cm , respectively.
3.2.2 X-ray Powder Diffraction
The Co–Ni–Zn catalysts obtained through calcination of
inorganic precursors were characterized by X-ray powder
diffraction. The X-ray diffractograms of the silica- and
alumina-supported Co–Ni–Zn synthesized catalysts have
been shown in Fig. 8. The identified phases for both syn-
thesized Co–Ni–Zn catalysts were similar, and contained
1
3

Effect of Synthetic Route and Metal Oxide Promoter on Cobalt-Based Catalysts for Fischer–Tropsch…
Fig. 4 The 3D network of complex 1
6
5
5
4
4
3
3
2
2
0
5
0
5
0
5
0
5
0
1
10
00
90
110
1
90
70
50
8
7
6
5
4
3
0
0
0
0
0
0
30
a
10
20
b
-10
-30
1
0
0
4
000
3400
2800
2200
1600
1000
400
2
0
120
220
320
Temperature (
420
520
)
620
720
Wavenumber cm-1
Fig. 5 The FT-IR spectrum of complex 1
Fig. 6 TGA (a) and (b) DSC plots of complex (1)
1
3

S. Saheli et al.
◊
▲
□
a
◊
▲
□
◊
▲
□
◊
◊
▲
□
▲
◊
▲
□
▲
□
a
b
10
20
30
40
50
60
70
80
4
000
3400
2800
2200
1600
1000
400
2
Tetha
Wavenumber cm-1
Fig. 9 The XRD patterns of Co–Ni–Zn/SiO (a) and Co–Ni–Zn/
2
Al O (b) reference catalysts produced by impregnation proce-
2
3
dure. (open square: ZnCo O , filled triangle: Co O , open diamond:
b
2
4
3
4
NiCo O )
2
4
ZnCo O (characteristic peaks at 2θ = 16.1°, 31.9°, 37.2°,
2
4
5
2
6.5°, 59.3°, 65.1°, 74.7°), Co O (characteristic peaks at
3 4
θ = 31.9°, 37.2°, 56.5°, 59.3°, 65.1°) and NiCo O (char-
2
4
acteristic peaks at 2θ = 20.9°, 31.9°, 37.2°, 56.5°, 59.3°,
6
5.1°).
4
000
3400
2800
2200
1600
1000
400
The diffractograms of reference catalysts constructed by
Wavenumber cm-1
impregnation method have been illustrated in Fig. 9. Char-
acteristic peaks of NiCo O at 2θ = 31.2°, 37.2°, 44.8°,
2
4
Fig. 7 The FT-IR spectra of Co–Ni–Zn/SiO (a) and Co–Ni–Zn/
55.7°, 59.3°, 65.1° are observed; the peaks observed at
2θ = 19.1°, 31.2°, 37.2°, 44.8°, 55.7°, 59.3°, 65.1° are
related to overlapping of phases Co O and ZnCo O .
2
Al O (b) catalysts obtained by thermal decomposition of inorganic
2
3
precursors
3
4
2
4
3
.2.3 Scanning Electron Microscopy
○
◊
▲
■
The morphology of the synthesized and reference catalysts
was investigated by scanning electron microscopy (SEM),
and their SEM micrographs have been shown in Figs. 10 and
11, respectively. The morphological properties of the synthe-
sized catalysts and those of reference catalysts are different,
and they have smaller particle sizes and less agglomeration
for the fabricated catalysts.
◊
□
■
♦
♦
◊
▲
□
○
■
○
♦
◊
◊
▲
□
■
□
♦
◊
▲
□
▲
□
a
b
□
■
♦
○
○
3
.2.4 Brunauer–Emmett–Teller
10
20
30
40
50
60
70
80
2
Tetha
Textural properties of the catalysts constructed by thermal
decomposition of inorganic precursor and those of the ref-
erence catalysts prepared by the impregnation method have
been displayed in Table 4. As observed in Table 4, synthe-
sized catalysts have higher surface areas in comparison to
reference catalysts. These results were in agreement with
the SEM observation which showed the particle sizes of
the fabricated catalysts were less than those of the reference
catalysts.
Fig. 8 The XRD patterns of Co–Ni–Zn/SiO (a) and Co–Ni–Zn/
2
Al O (b) constructed catalysts prepared by thermal decomposition
2
3
of inorganic precursors. (ν: NiO, filled triangle: Co O , open circle:
3
4
ZnO, filled diamond: Ni Zn O, open square: ZnCo O , open dia-
0
.8
0.2
2
4
mond: NiCo O )
2
4
Ni Zn O and NiO (characteristic peaks for their overlap
0
.8
0.2
at 2Ɵ = 37.2°, 43.3°, 62.5°, 74.7°, 78.8°), ZnO (charac-
teristic peaks at 2θ = 31.9°, 34.7°, 47.5°, 62.5°, 68.7°),
1
3

Effect of Synthetic Route and Metal Oxide Promoter on Cobalt-Based Catalysts for Fischer–Tropsch…
Fig. 10 SEM images of synthe-
sized catalysts: a Co–Ni–Zn/
SiO and b Co–Ni–Zn/Al O
2
2
3
3
.2.5 Transmission Electron Microscopy
range. The reduction peak around 660 °C corresponds to
0
the reduction of ZnO to Zn [35–42].
The TEM images of the synthesized and reference catalysts
are displayed in Fig. S1. The average crystallite sizes were
respectively 15 and 22 nm for the fabricated catalysts with
the SiO and Al O support, while for the reference cata-
The H -TPR profiles of both reference catalysts reveal
2
multiple overlapping peaks because of different reduction
steps (Fig. S3). It can be seen that both reference cata-
lysts have the same reduction peaks at 300 to 400 °C and
400–700 °C, and this is related to the reduction of Co O ,
2
2
3
lysts these values were 38 and 40 nm. This result shows that
preparation of Co–Ni–Zn catalysts via thermal decomposi-
tion of inorganic precursors yields smaller crystallite sizes.
3
4
NiCo O and ZnCoO phases, like synthesized catalysts.
2
4
4
According to TPR and XRD results, one point that makes
synthesized catalysts different from reference catalysts is
the existence of NiO and ZnO phases in the synthesized
catalysts. In fact, these phases serve as promoters in the
catalysts. The ZnO phase reduces cobalt-support interac-
tion and affects cobalt reducibility; furthermore, the NiO
phase amplifies the hydrogen adsorption. Hence, these
phases affect catalyst activity and improve the catalytic
activity of synthesized catalysts.
3.2.6 Reducibility Studies (H -TPR)
2
The H -TPR profiles of the synthesized catalysts have
2
been shown in Fig. S2. The reduction peak observed in
the range of 300–420 °C corresponds to the reduction of
Co O to CoO, NiCo O to NiCoO and NiO to Ni. At this
3
4
2
4
2
3
+
2+
temperature region, Co and Zn of ZnCoO phase were
4
2
+
0
reduced to Co and Zn , respectively. For the NiCoO ,
2
the broad peak at 420–635 °C is assigned to co-reduction
3.3 Catalytic Performance
2
+
0
2+
0
of Co to Co and Ni to Ni , Additionally, the reduc-
0
tion of CoO to Co occurred at the same temperature
Hydrogenation of carbon monoxide at the presence of the
synthesized and reference catalysts was conducted at the
1
3

S. Saheli et al.
Fig. 11 SEM images of refer-
ence catalysts: a Co–Ni–Zn/
SiO and b Co–Ni–Zn/Al O
2
2
3
Table 4 BET results of synthesized and reference catalysts
90
80
Synthesized sample BET surface Reference sample BET surface
2
−1
2
−1
area (m g
)
area (m g
)
70
Co–Ni–Zn/SiO2
116
96
Co–Ni–Zn/SiO2 60
Co–Ni–Zn/Al O 58
60
Co–Ni–Zn/Al O3
2
2
3
50
40
3
0
atmospheric pressureat the temperature range 200–300 °C
with H /CO ratio of 2.
20
10
0
2
As shown in Fig. 12, the CO conversion of the catalysts
increases with the temperature, and the CO conversion of
the synthesized Co–Ni–Zn/SiO and –Al O catalysts is
3
00
280
260
240
2
2
3
220
200
Temperature
higher in comparison to the reference catalysts at all stud-
Co-Ni-Zn/Al2O3 synthesized
Co-Ni-Zn/Al2O3 reference
Co-Ni-Zn/SiO2 synthesized
Co-Ni-Zn/SiO2 reference
ied temperatures.
The catalytic performance of the catalysts that is pre-
pared by different procedures grows with an increase in
temperature from 200 to 300 °C (Figs. 13, 14). While
the selectivity to the olefin and paraffin is reduced with
Fig. 12 Influence of reaction temperature on CO conversion percent-
ages of fabricated and reference catalysts
1
3

Effect of Synthetic Route and Metal Oxide Promoter on Cobalt-Based Catalysts for Fischer–Tropsch…
50
40
30
20
10
0
40
a
a
30
20
10
0
2
00
220
240
Temperature
260
280
300
200
220
240
Temperature
C3H6
260
C2H6
280
300
CH4
C2H4
C3H6
C2H6
C3H8
CH4
C2H4
C3H8
40
30
20
10
0
b
50
40
30
20
10
0
b
2
00
220
240
260
280
300
Temperature
CH4
C2H4
C3H6
C2H6
C3H8
200
220
240
260
280
300
Temperature
CH4
C2H4
C3H6
C2H6
C3H8
Fig. 14 Effect of different reaction temperatures on the catalytic per-
formance of reference catalysts (a Co–Ni–Zn/SiO , b Co–Ni–Zn/
2
Al O )
Fig. 13 Effect of different reaction temperatures on the catalytic per-
2
3
formance of synthesized catalysts (a Co–Ni–Zn/SiO , b Co–Ni–Zn/
2
Al O )
2
3
8
0
0
0
0
0
7
6
5
4
an increase in temperature, the methane selectivities of
both constructed and reference catalysts grow. The results
revealed that the optimal operating temperature of the
catalysts is 260 °C. At this temperature, the Co–Ni–Zn/
SiO and Co–Ni–Zn/Al O synthesized catalysts, pre-
2
2
3
30
pared by thermal decomposition of inorganic precursor,
have higher selectivity to light olefin products and lower
methane selectivity. Moreover, the paraffin selectivity
is favorable at the optimum temperature. Selectivity to
C H is 46% and 40% for silica and alumina supported,
2
0
0
0
1
0
5
10
15
20
25
30
2
4
Time (h)
Co-Ni-Zn/Al2O3 synthesized
Co-Ni-Zn/Al2O3 reference
Co-Ni-Zn/SiO2 synthesized
Co-Ni-Zn/SiO2 reference
respectively. In addition, propylene selectivity of synthe-
sized catalysts is about 16%. The selectivity into paraffin
(
C –C ) of synthesized catalyst obtains about 19% and
2 3
Fig. 15 Stability test of synthesized and reference catalysts
1
7% for silica and alumina supported, respectively. As the
data show, the synthesized catalysts have acceptable activ-
ity in FT reaction due to the catalyst physicochemical fea-
tures. It can be seen that from SEM results of synthesized
catalysts, these catalysts have low degree of agglomera-
tion and small particle sizes, which is in good agreement
with the results obtained from XRD. Moreover, the syn-
thesized catalysts have high surface area. According to
the explained catalysts feature, it can be concluded that
the catalyst physicochemical features affect the catalysts
activity. Comparing both synthesized catalysts, it can be
concluded that the catalytic performance of Co–Ni–Zn/
SiO is slightly better than alumina-supported Co–Ni–Zn
2
catalyst. On the other hand, in both reference catalysts,
methane selectivity is higher compared to the fabricated
catalysts, and the production amount of olefins and paraf-
fins is lower. All these data reveal that catalysts production
through thermal decomposition of inorganic precursors
1
3

S. Saheli et al.
based on complex 1 is a promising procedure due to good
active phase dispersion, small particle size, low degree of
agglomeration and formation of promoter phases.
performance of a Co/SiO2 catalyst in Fischer–Tropsch slurry
reactor synthesis. Catal Lett 100:105–116
5
6
7
.
.
.
Davis BH (2003) Fischer-Tropsch synthesis: relationship between
iron catalyst composition and process variables. Catal Today
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4:83–98
Mirzaei AA, Kiai RM, Atashi H, Arsalanfar M, Shahriari S (2012)
Kinetic study of CO hydrogenation over co-precipitated iron–
nickel catalyst. J Ind Eng Chem 18:1242–1251
3.4 Stability Test
Dry ME (2002) The fischer–tropsch process: 1950–2000. Catal
Today 71:227–241
The stability (Fig. 15) of the constructed catalysts was
studied at 260 °C, and that of the reference catalysts was
evaluated at 300 °C because they display the maximum
CO conversion at this temperature. The catalysts prepared
by thermal decomposition were stable for 10 h atopti-
mal operating temperature (260 °C). The stability test
of the constructed catalysts was continued for 30 h, and
only a slight decrease in the activity of the catalysts was
observed. The activity of the reference catalysts was rela-
tively constant for 7 h, and during the following 30 h, the
activity decreased faster than for the synthesized catalysts.
8. De La Osa AR, De Lucas A, Romero A, Valverde JL, Sánchez
P (2011) Fischer–Tropsch diesel production over calcium-pro-
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2
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(
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4
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nickel as promotor in cobalt Fischer–Tropsch synthesis catalysts.
Top Catal 58:896–904
The Co–Ni–Zn mixed metal catalysts were produced by ther-
mal decomposition of their inorganic precursors and were
compared with the reference catalysts prepared by the impreg-
nation method. The different preparation procedure causes
smaller particle size, higher surface area and lower agglom-
eration of the catalysts fabricated by thermal decomposition.
The catalytic performance tests of both types of catalysts were
1
1
1
1
4. Feyzi M, Khodaei MM, Shahmoradi J (2012) Effect of preparation
and operation conditions on the catalytic performance of cobalt-
based catalysts for light olefins production. Fuel Process Technol
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5. Du J, Yan J, Hong J, Zhang Y, Chen S, Li J (2015) Catalytic
performance of Co/Zn–Al O Fischer–Tropsch catalysts: a com-
2
3
parative study of zinc introduction methodologies. RSC Adv
5:60534–60540
6. Saheli S, Rezvani AR, Malekzadeh A (2017) Study of structural
and catalytic properties of Ni catalysts prepared from inorganic
complex precursor for Fischer–Tropsch synthesis. J Mol Struct
1144:166–172
carried out at the temperature range 200–300 °C with H :CO
2
ratio of 2:1. The results show higher selectivity to desirable
products and better stability for the fabricated catalysts.
7. Saheli S, Rezvani AR, Malekzadeh A, Dusek M, Eigner V (2018)
Novel inorganic precursors [Co4.32 Zn1.68 (HCO2)18(C2H8N)6]/
SiO2 and [Co4.32 Zn1.68 (HCO2)18(C2H8N)6]/Al2O3 for Fis-
cher–Tropsch synthesis. Int J Hydrogen Energy. https://doi.
org/10.1016/j.ijhydene.2017.11.019
Acknowledgments The authors are grateful to University of Sistan and
Bluchestan for the support of this work. The crystallographic part was
supported by the Project 18-10504S of the Czech Science Foundation
using instruments of the ASTRA lab established within the Operation
program Prague Competitiveness—Project CZ.2.16/3.1.00/24510.
18. Farzanfar J, Rezvani AR (2015) Inorganic complex precursor
route for preparation of high-temperature Fischer–Tropsch syn-
thesis Ni–Co nanocatalysts. Res Chem Intermed 41:8975–9001
1
9. Razmara Z, Rezvani AR, Saravani H (2017) Fischer–Tropsch
reaction over a Co -Ni-Mn/SiO nanocatalyst prepared by thermal
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