Co-Ru catalysts with different composite oxide supports for Fischer–Tropsch studies in 3D-printed stainless steel microreactors

Article abstract of DOI:10.1016/j.apcata.2020.117838

Bimetallic Co-Ru on different mesoporous composite oxides (m-SiO₂-Al₂O₃, m-SiO₂-TiO₂, m-TiO₂-Al₂O₃) and CoRu-m-SiO₂-TiO₂ were synthesized by incipient wet-impregnation (IWI) and one-pot (OP) hydrothermal methods, respectively. Bimetallic catalysts were coated in the microchannels of 3D-printed stainless steel (SS) microreactors for Fischer-Tropsch (FT) studies. The physiochemical properties of the catalysts were examined by BET, XRD, SEM, TEM, TPR, TGA-DSC and XPS techniques. The TPR results showed that the method and the composite support had a profound effect on the reducibility of the active sites. All the catalysts resisted deactivation for first 50 h and 10Co5Ru/m-SiO₂-TiO₂ (IWI) was most stable with ～80 % CO conversion at the end of 60 h. The stability and activity of the catalysts were observed in the order: 10Co5Ru/m-SiO₂-TiO₂ (IWI) >10Co5Ru/m-SiO₂-Al₂O₃ (IWI) >10Co5Ru/m-Al₂O₃-TiO₂ (IWI) >10Co5Ru-m-SiO₂-TiO₂ (OP). The TPO and XRD analyses of the spent catalysts confirmed coking as a potential factor but not the only cause of catalyst deactivation over time.

Full text of DOI:10.1016/j.apcata.2020.117838

Applied Catalysis A, General 608 (2020) 117838
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Co-Ru catalysts with different composite oxide supports for Fischer–Tropsch
studies in 3D-printed stainless steel microreactors
S. Bepari , Xin Li , R. Abrokwah , N. Mohammad , M. Arslan , D. Kuilaa,b,*
a
b
a
b
a
a
Chemistry Department, Applied Sciences and Technology, Greensboro, NC, 27411, United States
b
Joint School of Nanoscience and Nanoengineering, North Carolina A&T State University, Greensboro, NC, 27411, United States
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bimetallic Co-Ru on different mesoporous composite oxides (m-SiO
2
-Al
2
O
3
, m-SiO
2
-TiO
2
, m-TiO
2
-Al
2
O ) and
3
FT synthesis
CoRu-m-SiO -TiO were synthesized by incipient wet-impregnation (IWI) and one-pot (OP) hydrothermal
2
2
CoRu catalyst
methods, respectively. Bimetallic catalysts were coated in the microchannels of 3D-printed stainless steel (SS)
microreactors for Fischer-Tropsch (FT) studies. The physiochemical properties of the catalysts were examined by
BET, XRD, SEM, TEM, TPR, TGA-DSC and XPS techniques. The TPR results showed that the method and the
composite support had a profound effect on the reducibility of the active sites. All the catalysts resisted deac-
Mesoporous composite oxide
SS microreactor
Silica-alumina
Alumina-titania
tivation for first 50 h and 10Co5Ru/m-SiO
2
-TiO
2
(IWI) was most stable with ∼80 % CO conversion at the end of
-TiO
(OP). The
6
0 h. The stability and activity of the catalysts were observed in the order: 10Co5Ru/m-SiO
2
2
(
IWI) > 10Co5Ru/m-SiO
2
-Al
2
O
3
(IWI) > 10Co5Ru/m-Al
2
O
3
-TiO
2
(IWI) > 10Co5Ru-m-SiO
2
-TiO
2
TPO and XRD analyses of the spent catalysts confirmed coking as a potential factor but not the only cause of
catalyst deactivation over time.
1
. Introduction
activity for a longer period due to the ability of Al
2
O support to sta-
3
bilize small metal clusters which would suppress the aggregation of Co-
metal particles during the reaction [13].
Depletion of petroleum resources, oil price fluctuation and global
warming have triggered researchers to focus on new approaches to
produce clean fuels [1]. Fischer–-Tropsch synthesis (FTS) is the process
Mesoporous materials have been successfully used as support for
Co-based catalyst due to their high surface areas and uniform pore size
distribution. The mesoporous nature of the support would help to
maximize the dispersion of active metal along with thermal, mechanical
and chemical stability of the FT catalyst [14]. Another advantage of a
mesoporous-structured catalyst is to provide maximum contact time
between active metal and reaction gas molecules [14]. The composite
metal oxide would facilitate CO conversion and product selectivity by
tuning the structural stability of the catalyst. The small particle size of
Co in the support is hampered by reducibility of the catalyst. In order to
enhance the reducibility and dispersion of Co particles, some transition
metals (e.g. Ni, Cu, Mo, V, Cr, Nb, Zr, Ti) including noble metals (e.g.
Ru, Re, Ir, Pd, Rh, Os, Au, Ag and Pt), rare earth metals (e.g. Ce, La, Sc,
Pr, Y), and alkali and alkaline earth metals (e.g. Li, Na, K, Rb, Cs, Ca
and Mg) have been used as a promoter for the supported Co-based
catalysts [15–25]. Some parameters which influence the promotional
effect of the elements on Co-based catalyst are: (1) the nature of the
support and its textural properties, (2) promoter and Co-loading, (3)
synthesis method of the catalyst and (4) FTS reaction conditions [26].
These parameters affect the active site, catalyst stability and Co-support
to generate liquid fuels from syngas (mixture of CO and H ) obtained
2
from oil-alternative resources such as natural gas (Gas To Liquid, GTL),
coal (Coal To Liquid, CTL) and biomass (Biomass To Liquid, BTL) [2].
The product selectivity of fuel and CO conversion depend on physio-
chemical features of the catalyst and reaction conditions [3]. In this
regard, Co-based catalysts are most attractive to produce linear hy-
drocarbons with C5+ chain length due to their high activity, good
stability and low water-gas shift activity [4,5]. The activity of the cat-
alyst depends on several factors such as Co-particle size, the support,
the presence of promoters, preparation method and pre-treatment
conditions [6]. Porous inorganic oxide supports with high surface area
such as SiO
catalysts [7]. Some researchers have investigated SiO
FTS due to its good stability and adequate porosity [8–10]. Other
supports such as TiO have been reported to promote the formation of
2
, Al
2
O
3
and TiO
2
are generally used to prepare Co-based
2
as support for
2
C oxygenates [11,12]. Alumina has also been utilized as supports for
2
Co-based FT catalysts because of its high thermal stability and the
strong resistance to attrition [13]. It also provides stable catalytic
⁎
Corresponding author.
E-mail address: dkuila@ncat.edu (D. Kuila).
https://doi.org/10.1016/j.apcata.2020.117838
Received 2 March 2020; Received in revised form 13 September 2020; Accepted 17 September 2020
Available online 20 September 2020
0926-860X/ © 2020 Elsevier B.V. All rights reserved.

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
interaction. However, it may be difficult to judge the effect of the
promoter on the activity of Co-based catalyst [17,18].
synthesis (to obtain 10 g of the catalyst after calcination); first, P123
was dissolved in 2 M HCl at 35 °C to obtain a clear solution designated
as solution “A”. A second solution designated as “B” was prepared by
dissolving CTAB in DI water and stirring at 35 °C until a colorless so-
lution was obtained. Solution B was then gently poured into solution A
while stirring for 30 min. Ethanol was gently added to the resulting
mixture. TEOS and TIPR were mixed and stirred in a separate beaker to
obtain a yellow solution and then added dropwise to the mixture while
stirring vigorously. This final mixture was covered with parafilm and
stirred for 20 h at 35 °C for aging under the fume hood. The final
aqueous mixture with pH = 1 was then aged at 80 °C in the oven for at
least 48 h (to dry) followed by air-drying under a fume hood for 24 h.
The sample (now a yellowish-white precipitate) was then oven-dried
again for 24 h at 98 °C. Finally, the dried material was calcined in a
furnace under air at 550 °C for 6 h.
Apart from the catalyst, the type of reactor also plays an important
role in FTS. The conventional reactor systems such as a tubular fixed-
bed reactor (TFBR), micro-fixed bed reactor and continuous stirred-tank
reactor (CSTR) have been widely used in FTS [26–29]. The Pearl and
Qatar petroleum corporation is working on GTL technology to produce
1
40000 bpd (barrel per day), which is an example of the profitable
economical scale of GTL processing [30]. There are some limitations of
the scale-up considerations to commercialize small scale industry into a
profitable process. This limitation has driven both industry and re-
searchers to find alternative technologies. Microstructured technology
is considered as an alternative for small and medium scale catalytic
processes. Many researchers and industries such as Velocys and Mi-
cromeritics have been actively doing research in this area [31–33].
However, very limited use of a microchannel microreactor has been
reported for FTS [34–38]. The use of microreactor is gaining attention
for FTS due to its high heat dissipation for exothermic reactions, effi-
cient mass transfer, high reaction throughput, precise control of hy-
drodynamics, portability and easy scale-up [39–43] of the reactions.
In this present work, three mesoporous oxide composites have been
investigated as supports for Ru promoted Co-based catalyst in FTS.
2.2.2. Mesoporous Al
Mesoporous Al
TIPR as the limiting reagent [47,49]. The molar composition of the
2
O
3
-TiO
2
(m-Al
2
O
3
-TiO
2
) support
2
O
3
-TiO was prepared using a one-pot process with
2
reagents used was 1 TIPR: 0.783 C Al 0.081 CTAB: 41 H O: 7.5
H
9 21
O
3
2
ethanol: 0.0167 Pl23: 5.981 HCl. For a typical synthesis (to obtain 10 g
of the catalyst after calcination); first, P123 was dissolved in 2 M HCl at
35 °C to obtain a clear solution designated as solution “A”. A second
solution designated as “B” was prepared by dissolving CTAB in DI water
and stirring at 35 °C until a colorless solution was obtained. Solution B
was then gently poured into solution A while stirring for 30 min to
Mesoporous SiO
2
-TiO
2
composite oxide is considered because SiO
2
2
tends to avail a large surface area and improves CO adsorption and TiO
enhances the formation of C
2
oxygenates [44]. Similarly, Al
2
O is an-
3
other good support for FT reaction due to its favorable mechanical and
tunable properties [45]. However, the strong interaction between the
obtain mixture C. In a separate beaker C
9
H
21
O Al was dissolved/stirred
3
Co-ion and Al
2
O
3
2
decreases reducibility of the metal. Incorporation of
in ethanol and heated at 80 °C until complete dissolution. The dissolved
both SiO and Al
2
O
3
can therefore optimize support properties and can
C
9
21 3
H O Al was added to TIPR and stirred vigorously to prevent pre-
increase the reducibility of the Co catalyst [46]. Another important
reason for selecting the mesoporous composite supports is to explore
any synergistic effects of the supports on catalyst activity [47]. Usually
a small amount of ruthenium is added to cobalt catalysts to increase
reducibility and dispersion of Co active sites. The physiochemical
properties of all catalysts were characterized by several characteriza-
cipitation and was designated solution ‘D’. Solution D which was quite
viscous was then added dropwise to the mixture ‘C’ and stirred vigor-
ously. This final mixture was covered with parafilm and stirred for 20 h
at 35 °C for aging under the fume hood. The final aqueous mixture with
pH = 0.5 was then aged at 80 °C in the oven for at least 48 h (to dry)
followed by air-drying under a fume hood for 24 h. The sample (now a
greyish precipitate) was then oven-dried again for 24 h at 98 °C. Finally,
the dried material was calcined in a furnace under air at 400 °C for 4 h.
tion techniques such as N
2
adsorption-desorption isotherm, H
2
-tem-
perature programmed reduction (H
2
-TPR), X-ray diffraction (XRD),
Transmission electron microscopy (TEM), Scanning electron micro-
scopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray
photoelectron spectroscopy (XPS). All Co-based catalysts were tested to
measure their catalytic activities in terms of syngas or CO conversion
and product selectivity for FTS in 3D printed stainless steel (SS) mi-
crochannel microreactors.
2.2.3. Mesoporous SiO
Mesoporous SiO -Al
TEOS as the limiting reagent [47,48]. In an actual preparation, the
molar composition of the reagents used was 1 TEOS: 0.589 C Al
O: 7.5 ethanol: 0.0167 Pl23: 5.981 HCl. For a typical
2
-Al
2
2 3
O
O
3
(m- SiO
2
-Al
2
O
3
) support
2
was prepared using a one-pot process with
9
H
21 3
O
0.081 CTAB: 41 H
2
synthesis (to obtain 10 g of the catalyst after calcination); the first P123
was dissolved in 2 M HCl at 35 °C to obtain a clear solution designated
as solution “A”. A second solution designated as “B” was prepared by
dissolving CTAB in DI water and stirring at 35 °C until a colorless so-
lution was obtained. Solution B was then gently poured into solution A
while stirring for 30 min to obtain mixture C. In a separate beaker
2
. Experimental methods
2.1. Materials
For the mesoporous composite support synthesis, aluminum iso-
propoxide C
9
H
21
O
3
Al, tetraethyl orthosilicate (TEOS) and titanium
C
9
H
21
O Al was dissolved/stirred in ethanol and heated at 80 °C until
3
isopropoxide (TIPR) as a precursor of alumina, SiO
2
and TiO
2
were
complete dissolution. The dissolved C
H
9 21
O Al was added to TEOS and
3
purchased from Sigma-Aldrich, USA. Pluronic P123 as a structure agent
and Cetyl trimethyl ammonium bromide (CTAB) were also procured
from Sigma-Aldrich, USA. Anhydrous ethanol and hydrochloric acid
stirred vigorously to prevent precipitation and was designated solution
‘D’. Solution D which was quite viscous was then added dropwise to the
mixture ‘C’ and stirred vigorously. This final mixture was covered with
parafilm and stirred for 20 h at 35 °C for aging under the fume hood.
The final aqueous mixture with pH = 1.5 was then aged at 80 °C in the
oven for at least 48 h (to dry) followed by air-drying under a fume hood
for 24 h. The sample (now a greyish precipitate) was then oven-dried
again for 24 h at 98 °C. Finally, the dried material was calcined in a
furnace under air at 550 °C for 6 h.
(
HCl) were purchased from Fischer Scientific, USA. The active metals
precursors, cobalt nitrate hexahydrate [Co(NO
Ruthenium Chloride [RuCl . xH O], were acquired from Alfa Aesar,
USA. Deionized water (DI water) was used as a solvent.
3
)
2
.6H O] and
2
3
2
2
.2. Different support synthesis
.2.1. Mesoporous SiO -TiO (m-SiO
2
2
2
2
-TiO
2
) support
2.2.4. One-pot synthesis of mesoporous Co-Ru-m-SiO
2
-TiO
2
Mesoporous SiO -TiO was prepared using a one-pot process with
2
2
Cobalt-ruthenium based bi-metallic nanocatalysts supported by
TEOS as the limiting reagent [48,49]. In an actual preparation, the
composite oxides of SiO
2
and TiO were synthesized using a one-pot
2
molar composition of the reagents used was 1 TEOS: 0.752 TIPR 0.081
hydrothermal procedure. TEOS, TIPR, P123, HCl were used in a molar
ratio of 1: 0.752: 0.081: 41: 7.5: 0.01679: 5.981, respectively. The
CTAB: 41 H O: 7.5 ethanol: 0.01679 Pl23: 5.981 HCl. For a typical
2
2

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
quantity of metal precursor was calculated based on the weight per-
centage of metal to be incorporated into the catalysts. In a typical
synthesis process, the weighed surfactant (CTAB) was dissolved in de-
ionized water at 30 °C and stirred until the solution becomes clear. A
second mixture with HCl and P123 was prepared at 30 °C stirred until
clear solution. The two solutions were mixed and stirred rigorously for
presence of Air at 100 ml/min. The oxidation states of all catalysts were
determined by X-ray photoelectron Spectroscopy (Model: Escalab Xi+-,
Make: Thermo Scientific, West Sussex, UK).
2.5. Microreactor fabrication
3
0 min. A separate solution was prepared by dissolving metal pre-
3D printing technology was used to fabricate microchannel micro-
reactors and respective cover channels as described previously [38].
Basically, they are designed by AutoCAD software is shown in our
previous work [38]. The microreactor has 11 microchannels of
500 μm × 500 μm × 2.4 cm as reaction zone in between them. The
stainless steel microreactor is assembled in a heating block with inlet
and outlet channels which facilitates syngas to pass through it.
cursors in ethanol and stirring approximately for 30 min. The dissolved
metal solution was gently poured into the solution mixture and stirred
vigorously for 30 min. TMOS, the limiting reagent for this chemical
synthesis, was added dropwise into the mixture while stirring con-
tinuously for another 30 min, followed by adding TIPR dropwise stirred
for another 30 min. The mixture was then stirred for another 3 h, fol-
lowed by aging for 24 h at 110 °C. The aged material was dried in air for
2
4 h then dried in an oven at 110 °C for 24 h. This dried catalyst was
2.6. Catalyst loading into the microreactor
calcined at 550 °C for 16 h with a heating rate of 2 °C/min to remove the
surfactant. It was then cooled to room temperature at a rate of 2 °C/
min.
The catalyst was loaded into the microchannels of the microreactor
using a PVA solution containing the catalyst and acetic acid. The mi-
croreactor was dip-coated in the PVA solution, sonicated for about
5 min and dried in air. Then the microreactor was calcined ex-situ in the
presence of air at 550 °C for 6 h with heating and cooling rates of 1 °C/
min to remove the acetic acid and PVA. The calcined microreactor was
finally loaded into the reaction block and reduced prior to FT reactions
2.3. Composite oxide supports for metal impregnation
The theoretical ratio of each oxide within the mixed oxide compo-
site support was 50 wt%. The metal precursor salt solutions were added
to the already calcined supports by incipient wet-impregnation (IWI)
method. Stoichiometric molar ratios of cobalt nitrate and ruthenium
chloride were mixed according to the desired loading and dissolved in
water to prepare the aqueous solution. The volume of the solution used
for each composite support was determined by the total pore volume of
the catalyst from BET analysis. The aqueous solutions of cobalt and
ruthenium salts were mixed with each composite support and stirred
vigorously before drying at 90 °C, followed by calcination at 350 °C for
2.7. Catalyst activity test
FTS was carried out in a Stainless-Steel microchannel microreactor
at four different temperatures (180, 210, 240 and 270 °C) and 1 atm
-
1
with an H /CO molar ratio of 2. We maintained 12,000 h GHSV for
2
each reaction. The LabVIEW software was used to control the reaction
parameters (temperature, flow rate and pressure). The gas flow rate was
controlled by Cole-Parmer mass flow controller with 0.2 ml/min of CO
6
h. All the synthesized catalysts after calcination are expected to
contain 10 wt% Co and 5 wt% Ru.
and 0.4 ml/min of H . Nitrogen was used as a carrier gas and its flow
2
rate was controlled by Aalborg mass flow controller within the range of
0 to 10 ml/min. The upstream and downstream pressures were mon-
itored by pressure gauge continuously. The stream of product gases was
directly fed to the GC-MS (Model: 7890B GC and 5977A MSD; Make:
Agilent Technologies). Before the FTS, the catalyst loaded micro-
reactors were reduced ex-situ in Carbolite Gero tubular furnace in
2.4. Catalyst Characterization
The N adsorption-desorption isotherms of all catalysts were mea-
2
sured by the BET surface area analyzer (Model: 3Flex, Make:
Micromeritics, USA) instrument at constant liquid N temperature
−196 °C). The surface areas and pore size distributions were calcu-
2
(
presence of 10 % H and Ar mixture. In order to compensate for the loss
2
lated by
N
2
adsorption-desorption isotherm using the Brunauer-
of catalyst reactivity during transfer of the microreactor into the
heating block, the catalyst loaded microreactor was again reduced in-
situ at 350 °C for 6 h before the start of the FTS. The reactions reached a
steady state after one hour. CO conversion and hydrocarbon selectivity
were calculated based on the following equations [37,38]:
Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) method. The X-
ray diffraction was carried out using a powder X-Ray diffractometer
(
Model: Bruker AXS). The detection limit of the instrument was in the
range of 10-80° with a step interval of 0.02° using a Cu Kα1 radiation
source with a wavelength of 1.5406 Å. Peaks observed in these spectra
were used to identify the catalyst metals, their oxidation state, and
morphology. Temperature programmed reduction was performed using
a chemisorption analyzer (Mode: 3Flex, Make: Micromeritics, USA).
Although production of CO
important, CO
2
from the water gas shift reaction is
2
selectivity was not included in the calculation because
the primary objective was to understand the effect of different meso-
porous mixed composite oxide support and the Co, Ru metals on CO
conversion and hydrocarbon selectivity [37].
0
.05 g of sample material was measured and placed into a chemisorp-
tion tube on top of a covering layer of quartz wool beneath a quartz
filter cap upon which the sample was placed. The sample was then
3. Results and discussion
placed under a 10 % H /Ar (1:9wt %) flow of 50 ml/min and a ramp
2
rate of 10°C/min from room temperature to 800 °C to determine re-
ducibility of the metal oxides. Synthesized materials were imaged using
a ZEISS Auriga Focused Ion Beam Scanning Electron Microscope
3.1. Catalyst characterization
3.1.1. N adsorption–desorption isotherms
2
(
FIBSEM) provided by the Joint School of Nanoscience and
Low-temperature N adsorption-desorption isotherms for three dif-
2
Nanoengineering. These images were used to draw conclusions of the
average particle size, morphology and topography of each catalyst. The
Transmission Electron Microscopy (TEM) was carried out by Thermo
Fischer Talos (Model: F200X). The field emission system was operated
at 200 kV. The decomposition temperature of polymer-templates, used
in the mixed composite support preparation, was determined by
Thermogravimetry and Differential scanning Calorimetry (TGA-DSC)
ferent mesoporous supports and CoRu based catalysts are shown in
Fig. 1(a). The BET surface areas are shown in Table 1. The isotherms of
mSiO
and CoRu/m-SiO
mAl -TiO and CoRu/Al
classification [50,51]. Isotherms of all samples have hysteresis loops of
different types: mSiO -Al is H1 type; mSiO -TiO and mAl -TiO
are H type; and all metal containing catalysts are H4 type [52]. In-
corporation of CoRu into the supports did not affect the shape of the
2
-Al
2
O
3
,
mSiO
2
-TiO
2
,
CoRu/m-SiO
2
-Al
2
O
3
,
CoRu/m-SiO
2
-TiO
2
2
-TiO
2
(OP) correspond to type IV, whereas those of
2
O
3
2
2
O
3
-TiO are of Type II, according to IUPAC
2
2
2
O
3
2
2
2
O
3
2
(
Model: TA instruments, New castle, DE, USA). Sample was heated to
000 °C at a heating rate of 10°C/min. The analysis was done in
3
1
3

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
Fig. 1. (a) N
2
adsorption-desorption isotherms and (b) pore size distributions of three different mesoporous supports and CoRu-loaded catalysts.
isotherm significantly, but it changed the type of hysteresis loop. It is
the result of partial filling of metal clusters into the pores of the sup-
ports, which did not substantially change the porous matrix but reduced
the pore volume and the pore shapes [53]. The mesoporous SiO
2
-Al
2 3
O
and SiO supports exhibited higher pore volumes and surface
areas, establishing the expansion of mesopores upon introducing Al
52] and Ti into mesoporous SiO framework. The capillary con-
2
-TiO
2
[
2
densation between adsorption and desorption of N occurred at liquid
2
nitrogen temperature in the pores, producing this kind of isotherm
pattern [54]. The corresponding supports and catalysts pore size dis-
tribution curves are shown in Fig. 1(b). The distribution curve shows
that the pore sizes of CoRu/m-SiO
2
-Al
(IWI) and CoRu- m-SiO
are similar but little bit smaller than the supports (m-SiO
2
O
3
(IWI), CoRu/m-SiO
-TiO (OP) catalysts
-Al , m-
2
-TiO
2
(
IWI), CoRu/m-Al
2
O
3
-TiO
2
2
2
2
2 3
O
SiO -TiO and m-Al
2
2
2
O
3
-TiO
2
), indicating that pores of the supports are
partially occupied by the added metal oxides. This confirmed a partial
loss of the structural integrity of the mixed oxide supports upon in-
corporation of the metals (see the SEM image in supplementary sec-
tion).
3
.1.2. Temperature programmed reduction (TPR)
The H -TPR profiles of the supported CoRu based catalysts are
2
shown in Fig. 2. TPR studies were carried out to understand the re-
ducibility of supported CoRu particles. The reduction profiles of cata-
lysts were obtained under the flow of 10 % H /Ar. Supplemental Fig. S1
2
shows the H
supports. No reduction peaks are observed for the supports. In Fig. 2,
the TPR profile of CoRu/m-SiO -Al (IWI) catalyst showed the re-
duction peaks around 326 °C and 448 °C that correspond to formation of
metallic Co via two-step reduction of Co crystals [Co
= 3CoO + H and CoO + H = Co + H O] with intermediate
2
-TPR profiles of the bare mesoporous composite oxide
2
O
2 3
Fig. 2. H -TPR profiles of all composite oxides supported CoRu catalysts.
2
3
2
O
4
3
O
4
+
H
2
2
O
2
formation of CoO species [55,56]. The peak at 190 °C corresponds to
reduction of RuO
2
to Ru° [57]. In the case of the CoRu/m-SiO
2
-TiO
2
Table 1
N adsorption-desorption analysis data of different mixed composite supports and catalysts.
2
2
Catalysts and support
Surface area (m /g)
Pore diameter (nm)
Avg. pore volume (cc/g)
m-SiO
2
2
-Al
2
O
3
654.78
594.02
225.85
192.46
230.83
97.80
5.33
6.08
8.26
4.92
4.55
7.11
4.11
0.87
0.90
0.46
0.24
0.26
0.17
0.56
m-SiO
-TiO
2
m-Al
2
O
3
-TiO
2
1
1
1
1
0Co5Ru/m-SiO
2
2
-Al
2
O
3
(IWI)
(IWI)
(IWI)
(OP)
0Co5Ru/m-SiO
-TiO
2
0Co5Ru/m-Al
2
O
3
-TiO
2
0Co5Ru-m-SiO
2
-TiO
2
552.92
4

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
(
IWI) catalyst, reduction of all metal oxides was achieved at a lower
pot procedure, no such peak is observed. Low angle XRD of m-Al
2
O -
3
temperature (< 400 °C). The reduction for the formation of stable CoO
intermediate is not clear due to overlaps of two reduction peaks. This
was probably caused by the presence of Ru which lowered the reduc-
tion temperature via hydrogen spillover effect or even direct Co-Ru
interactions [58–60]. The presence of Ru also possibly facilitated re-
TiO support was not performed because this sample does not contain
2
ordered pores as observed in mesoporous silica. Fig. 3 (B) shows the
XRD patterns of different catalysts. The diffraction peaks at various 2θ
angles such as 19.05°, 31.27°, 36.78°, 44.89°, 59.21° and 65.14° cor-
respond to Co
3
O
4
with cubic structure, indicating that Co
3
O is the
4
duction of Co species by dissociating H
2
molecule to give active hy-
primary crystalline cobalt species [69,70]. Some weak peaks at
2θ = 28.31° and 54.29° correspond to RuO with tetragonal structure
[71,72]. The weak intensity peaks of RuO are possibly observed due to
interaction of Ru with Co species. This appears to be consistent with the
TPR results. The anatase phase of TiO is observed at a 2θ angle of
25.36° and 48.60° for only CoRu/m-SiO -TiO (IWI) [73]. However, in
the case of CoRu-m-SiO -TiO (OP) catalyst, only one peak for anatase
phase of TiO at
drogen atoms [61]. Dissociation of H
2
that leads to the hydrogen spil-
2
lover effect was mainly influenced by the support characteristics,
distribution of the metals, interactions between two metals, and the
adsorption capacity of the catalysts [62–64]. More specifically, the
2
2
spillover effect of CoRu/m-SiO
2
-TiO
2
(IWI) was due to the combined
2
2
effect of high surface area (Table 1) and the relatively weaker ruthe-
nium-support interactions observed in the XPS analysis (Table 4). This
2
2
2
at 25.36° and a very weak intensity peak of Co
3 4
O
is evident in the mesoporous SiO
2
-TiO
2
composite oxide support, where
36.78° are observed. This could be due to the fact that the one pot
procedure produces ordered cage-like frameworks (see isotherms in
Section 3.1.1) which may tend to shield the metal oxides from the in-
cident X-rays. Table 3 shows the average crystal size of different crystals
Ru played an important role to reduce the reduction temperature. The
peak around 160 °C was attributed to reduction of RuO to Ru° for the
CoRu/m-Al -TiO catalyst. Another peak at about 330 °C was as-
signed to reduction of Co to Co [1]. However, a different TPR profile
was obtained for CoRu-m-SiO -TiO (OP) catalyst. Several reduction
2
2
O
3
2
3
O
4
of Co
3
O
4
, RuO
2
and TiO . Modified Scherrer equation, as described
2
2
2
elsewhere [74], is used to determine the average crystal size. The
average crystal sizes of CoRu/m-SiO -Al (IWI), CoRu/m-SiO -TiO
(IWI), CoRu/m-Al -TiO (IWI) and CoRu-m-SiO -TiO (OP) catalysts
are shown in Table 3. The average crystal sizes of Co and RuO for
CoRu/m-SiO -Al (IWI) and CoRu/m-SiO -TiO (IWI) are almost
same. This suggests the uniform distribution of metal particles over the
large surface areas of the supports. In the case of CoRu/m-Al -TiO
steps occurred at a higher temperature suggesting that this support has
a strong interaction with the Co species. The two peaks around 602 °C
and 838 °C are attributed to the reduction of cobalt titanates and sili-
cates mixed metal oxides [65]. Four distinct reduction peaks were ob-
served at temperature below 400 °C. These peaks are basically attrib-
2
2
O
3
2
2
2
O
3
2
2
2
3
O
4
2
2
2
O
3
2
2
uted to the reduction of RuO
2
and Co
3
O
4
. The presence of Ru lowered
2
O
3
2
the reduction temperature of cobalt [66]. Thus, the variation of me-
soporous support and catalyst preparation methods play an important
role in the reduction of CoRu species.
(IWI) and CoRu-SiO
2
-TiO (OP) catalysts, the average crystal size is
2
quite large. It suggests that the metal oxide has a weak interaction with
the support, which can easily agglomerate resulting in a poor/less
uniform distribution.
Table 2 shows the H
analysis. The highest H
Al (IWI) catalyst and it suggests the presence of maximum amount
of reducible species. In contrast, the lowest H consumption was ob-
served for CoRu-SiO -TiO (OP) catalyst. The catalyst contains a greater
2
2
consumption of different catalysts during TPR
consumption was observed for CoRu/m-SiO
2
-
In general, the crystal sizes of noble metals are known to be smaller
than that of transition elements; it depends on structural rearrange-
ments (e.g. substitutional, interstitial, and intermetallic alloy forma-
tion) in the presence of other metals. The first possibility is that the
relatively larger number of Co species outcompeted the Ru oxides for
the binding sites of the support which could lead to agglomeration of
O
2 3
2
2
2
number of non-reducible species or in other words very difficult to
reduce. Table 2 also shows the reduction degree (%) of different cata-
lysts. The reducibility of the Co based catalyst has been observed in the
temperature range of 150 to 400 °C [67]. This temperature range is used
because it covers most of the reaction temperatures used for FT
synthesis. Based on our TPR results shown in Table 2, the highest re-
the Ru oxide crystallites. The 6.5 nm crystal size of the TiO anatase
2
phase is very small compared to the other metal oxides. This suggests a
strong interaction between SiO and TiO . The implication is that the
addition of SiO to TiO stabilized the anatase phase which hindered
the chain growth and hence agglomeration of the TiO crystallites [75].
2
2
2
2
duction degree is observed for CoRu/m-SiO
2
-TiO
2
(IWI) catalyst. The
-Al (IWI)
2
main reduction peak at 448 °C is observed for CoRu/m-SiO
2
2 3
O
catalyst. This temperature is outside the reduction temperature range
3
.1.4. Transmission electron microscopy (TEM)
The TEM images of Co-Ru catalysts with different mesoporous
mixed composite supports prepared by IWI and that of CoRuSiO -TiO
(
150 to 400 °C). So, the reduction degree (%) of CoRu/m-SiO
2
2 3
-Al O
(
IWI) catalyst is low.
2
2
prepared by one-pot (OP) are shown in Fig. 4. The dark spots corre-
spond to the metal oxides formed over the mesoporous support. These
micrographs do not reveal information about distinct particle dis-
tribution of Ru-Co mixed oxide phases. However, the images of calcined
IWI catalysts exhibited some agglomeration of metal oxides over dif-
ferent supports [See also the SEM images in Supplemental Fig. S4]. The
metal oxides can block partially or completely the pores of the support
leading to a partial structural degradation of the mixed oxide supports
3
.1.3. X-ray diffraction (XRD)
XRD analysis was carried out to ascertain the metal oxide crystal
phases present in the catalysts. Fig. 3 (A) exhibits the low angle XRD
patterns of different mesoporous oxide supports. In the case of m-SiO
Al support, the well-resolved peak at 2θ = 1.4° is observed. This is
2
-
O
2 3
the characteristics of mesoporous material [plane (1 1 0)] with 2D-
hexagonal structure [68]. However, for m-SiO
2
-TiO prepared by one-
2
Table 2
The H
2
consumption and reduction degree at 150–400 °C for the prepared catalysts.
a
Reduction degree (%)b
Catalysts
2
H Consumption (μmol/g)
1
1
1
1
0Co5Ru/m-SiO
2
2
-Al
2
O
3
(IWI)
(IWI)
(IWI)
(OP)
324.09
273.01
271.48
153.23
47.74
95.27
92.53
34.46
0Co5Ru/m-SiO
-TiO
2
0Co5Ru/m-Al
2
O
-TiO
3 2
2 2
0Co5Ru-m-SiO -TiO
a
The H
2
consumption (μmol/g) was defined as the measured amount of H
2
consumption in TPR peak /theoretical H
2
con-
sumption (μmol H
2
/g) × 100.
b
The degree of reduction (%) was defined according to the literature [67] as the measured amount of H
2
consumption
between 150-400 °C in TPR peak /theoretical H
2
consumption (μmol H /g) × 100.
2
5

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
Fig. 3. XRD analyses: (A) Low angle XRD of mesoporous composite support; (B) WAXRD of different mesoporous composite oxides supported CoRu based catalysts.
Table 3
[79]. This phase transition is consistent with our XRD diffraction pat-
Crystal size calculation* based on XRD data.
terns described in Section 3.1.3 which showed that only the SiO -TiO
2
2
2
(
IWI) composite matrix possessed a substantial proportion of the TiO
Catalysts
Crystal Size (nm)
anatase crystal structure. No change in weight loss was observed above
Co
3
O
4
RuO
2
TiO
2
500 °C, indicating that all the composite oxides were thermally stable.
1
1
1
1
0Co5Ru/m-SiO
2
2
-Al
2
O
3
(IWI)
(IWI)
(IWI)
(OP)
21.37
17.98
23.51
40.42
88.54
87.24
38.66
–
–
0Co5Ru/m-SiO
-TiO
2
6.53
–
3
.1.6. X-ray photoelectron spectroscopy (XPS)
0Co5Ru/m-Al
2
O
3
-TiO
2
The chemical states of cobalt and ruthenium in mixed oxide sup-
0Co5Ru-m-SiO
2
-TiO
2
38.68
ports were determined from XPS studies. The Fig. S3 shows the spectra
for the mixed oxide supports Si 2p centered at 153 eV, Ti centered at
*
Using Modified Scherrer equation [74].
4
64 eV and O 1s at 531 eV which confirms the presence of two supports
Table 4
in the catalyst. Table 4 lists the position of transition states of cobalt
and ruthenium in all the composite supports. In Table 4, the difference
in the binding energies of Co 2p spectra for Co 2p3/2 and Co 2p1/2 peak
intensities indicate interaction of Co metal with different types of
support. This suggests that the microstates of Co electronic transitions
are also dependent on the type of support. The results clearly show that
the interaction is greatly dependent on the type of the composite sup-
port. This is also consistent with the TPR results (Section 3.1.2) showing
different reduction temperatures for Co metal when the support is
changed. The XPS spectra for Co 2p and Ru 3d are shown in Fig. 6a and
b, respectively. The deconvolution of Co 2p in Co 2P1/2 and Co2p3/2
with a satellite peak is shown for all samples indicating the presence of
The transition states of cobalt and ruthenium in all the mesoporous composite
oxides supports.
Catalyst
Co 2p1/2 (eV)
Co 2p3/2 (eV)
Ru 3d3/2 (eV)
1
1
1
0Co5Ru /SiO
2
2
-Al
-TiO
-TiO
2
O
3
796.03
795.86
795.94
781.05
780.86
780.69
284.3
284.1
284.6
0Co5Ru /SiO
2
0Co5Ru /Al
2
O
3
2
and hence a decrease in the surface area. The decrease in surface area
caused by incorporation of metal oxides as well as the partial loss/de-
gradation of the support structure are consistent with the results of N
2
two Co-oxidation states in Co
are shifted to higher binding energies when compared to the other two
catalysts showing the strong metal-support interactions in SiO -Al
and hence Ru oxidation state is
3
O
4
[80]. The peaks in CoRu/SiO
2
2
-Al O
3
adsorption-desorption isotherms. In the case of calcined OP catalyst, the
TEM image shows that metal oxides were well distributed over the
support. The agglomerated metal oxides particles on the support could
decrease scattering contrast between the pore and the walls of the
support [76,77].
2
O
2 3
4
+
support [38]. The presence of RuO
2
confirmed by Ru 3d spectra with a binding energy centered around
2
84 eV. In the case of cobalt catalysts, the binding energy suggests that
2+ 3+
both Co
and Co
species are present in the catalyst framework
3
.1.5. Thermogravimetry and differential scanning calorimetry (TGA-DSC)
[81]. This is also consistent with the TPR profiles for the reduction of
metals in three different supports. It was also noticed that XPS spectra
for Ru exists in Ru 3d3/2 transition state which is shown in Fig. 6b.
However, no significant differences in binding energies for Ru were
observed when compared to Co 2p spectra in different mesoporous
supports. It is conspicuous that the XPS intensities varied among the
catalysts. Usually in XPS, the peak intensity is a measure of how much
of each element is present at the outermost surface of the material.
Thus, differences in metal-support interactions which affect the degree
of exposure and distribution of the active sites impacts the spectral
Fig. 5 shows the TGA-DSC profiles of as-synthesized (not calcined)
mixed oxide mesoporous supports. The first weight loss below 190 °C is
due to the removal of volatile solvents used for the catalyst preparation
and water/moisture adsorbed on the support surfaces. The second
weight loss between 190 °C and 240 °C were caused by the decom-
position of the pluronic acid (P123) template used for synthesis. The
third weight loss from 250 °C to 380 °C was due to the decomposition of
the surfactant-CTAB [78]. The differences in the weight losses (peak
heights) of the P123 and CTAB are due to their different molar con-
centrations used for the synthesis in Section 2.2. In the case of Fig. 6b,
the additional exothermic weight loss from 400 °C to 500 °C could be
intensities significantly. In CoRu-Al
2
O
3
-TiO
2
sample, the peak in-
tensities of Co and Ru are less compared to the other catalysts in-
dicating that very small amount of the metals are present on the surface
of the material. It can therefore be speculated that most of the Co and
attributed to phase transition of amorphous TiO
2
to the crystalline
anatase polymorph similar to observations made by Deshmane et al.
6

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
Fig. 4. TEM images of Co-Ru catalysts with different mesoporous mixed composite supports prepared by incipient wetness impregnation (IWI) and one-pot (OP)
methods: (a) 10Co5Ru/m-Al
2
O
3
-TiO
2
(IWI); (b) 10Co5Ru/m-SiO
2
-TiO
2
(IWI); (c) 10Co5Ru/m-SiO
2
-Al
2
O
3
(IWI); (d) 10Co5Ru-m-SiO
2
-TiO (OP).
2
Ru particles may have been entrapped within the mesoporous frame-
work, shielding them from the incident X-rays.
3.2.3. m-SiO
2
-TiO
2
(IWI) catalysts
Fig. 9 shows the effect of reaction temperature on CoRu/m-SiO
2
-
TiO (IWI) catalyst activity in terms of CO conversion and product se-
2
lectivity. CO conversion increased initially up to 210 °C, then decreased
at higher temperature. At higher temperature, the catalyst was active
for reverse water gas shift reaction. Methane selectivity was constant
throughout the temperature range. Initially at 180 °C, the formation of
ethane was more. However, when the temperature is increased, the
ethane selectivity decreased a little, then it increased again. No propane
was observed at 180 °C. Propane started to form around 210 °C. Highest
CO conversion of 68.59 % was observed at 210 °C. In conclusion, CoRu/
3
.2. Fischer–Tropsch synthesis (FTS)
.2.1. m- SiO -Al (IWI) catalysts
3
2
2 3
O
The effect of reaction temperature on different mesoporous com-
posite oxide supported CoRu catalysts activity was investigated to know
the optimum reaction temperature for CO conversion and hydrocarbon
selectivity of each catalyst. The reactions were carried out at four dif-
ferent temperatures (180, 210, 240 and 270 °C) and at 1 atm with a H /
2
m-SiO
2
-TiO (IWI) catalyst showed promising activity in terms of CO
2
CO molar ratio of 2. The FT reaction mainly produced methane, ethane
and propane, which are in reasonable agreement with previous work on
FT synthesis at 1 atm [82].
conversion when compared to the catalysts impregnated on other
mixed mesoporous supports. Interestingly, TPR study showed that this
catalyst was completely reduced below 400 °C (Figure 2). So, we
Fig. 7 shows the effect of temperature on CoRu/m-SiO
2
-Al
2
O cat-
3
compare CoRu/m-SiO
2
-TiO
2
(IWI) with CoRu/m-SiO
2
-TiO (OP) cata-
2
alyst activity in terms of CO conversion and selectivity towards hy-
lyst for FT studies to investigate the effect of preparation procedure on
the catalyst’s activity (next below).
drocarbons. CO conversion increased initially up to 210 °C, then it de-
creased at higher temperature (> 210 °C). Methane, CH , selectivity
4
was almost constant throughout the experimental range of temperature.
CO conversion decreased more at temperatures greater than 210 °C
3
.2.4. m-SiO
2
-TiO
Fig. 10 shows the effect of reaction temperature on CoRu/m-SiO
(OP) catalyst activity in terms of CO conversion and product se-
2
(OP) catalysts
2
-
because of reverse water gas shift reaction (CO
2
+ H
2
= CO + H O,
2
TiO
2
ΔH298 = 41 kJ/mol) that is thermodynamically feasible at higher
temperatures. FT synthesis shows propane formation starting at 210 °C,
while ethane and propane selectivity were almost constant throughout
the temperature range up to 210 °C. The highest CO conversion was
lectivity. CO conversion increased with the increase of reaction tem-
perature up to 210 °C, then decreased. This was possibly due to reverse
water gas shift reaction at higher temperature. Methane and ethane
selectivity were almost constant throughout the temperature range.
Highest CO conversion of 47.99 % was observed at 210 °C. This catalyst
showed lower activity than the catalyst prepared by IWI method. This is
likely due to a smaller number of reducible Co and Ru metals in the
catalyst prepared by one-pot method and consistent with our TPR stu-
dies (Figure 2) where the reduction peaks at higher temperature are
observed. As the metals in the sample prepared by OP method involved
stronger interaction with the mesoporous support, it was difficult to
7
4.7 % at 210 °C.
3.2.2. m-Al
2
O
3
-TiO
2
(IWI) catalysts
As shown in Fig. 8 for CoRu/m-Al
2
O
3
-TiO (IWI) catalyst, CO con-
2
version increased up to 210 °C, then it decreased at higher temperature.
Consequently, methane selectivity decreased initially up to 210 °C, then
it increased at higher temperature. The formation of methane at higher
temperature revealed that catalyst was active for methanation reaction.
Ethane selectivity increased up to 210 °C, then it decreased at higher
temperature. Highest CO conversion and ethane selectivity were 61.98
reduce them with H . t. Thus, the catalyst support and the method of
2
preparation play an important role in catalyst activity studies.
In all cases, maximum amount of methane was produced when
compared to other hydrocarbons. This is most likely due to the fact that
%
and 14.84 %, respectively at 210 °C.
7

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
Fig. 5. TGA-DSC profiles of: (a) as-synthesized m-SiO
2
-Al
O
2 3
; (b) as-synthesized m-SiO
2
2
-TiO ; (c) as-synthesized m-Al
2
O
3
-TiO
2
supports.
FT reactions were carried out at atmospheric pressure. The high se-
lectivity to methane might be explained by the Anderson-Schulz-Flory
mechanism [83,84]. The methane formation was possible at several
metal active sites during hydrogenation but not active for FT synthesis.
For Co based catalyst, methane formation mainly depends on partial
temperature as well as partial pressure of H
2
could help to suppress the
formation of methane [86]. Formation of large amount of methane
relative to ethane and propane indicates very limited/low poly-
merization on the active sites. This suggests that the rate of initial
surface carbide formation (via CO decomposition) is faster than the rate
pressure of CO,
H
2
,
2
H O
and temperature [85]. So, increasing
of formation of hydrocarbon chain extenders (—CH
2
—CH groups)
2
Fig. 6. XPS spectra of (a) Co 2p (b) Ru 3d of all CoRu bimetallic catalysts.
8

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
Fig. 7. Effect of temperature on CO conversion and product selectivity in FT
Fig. 10. Effect of temperature on CO conversion and product selectivity in FT
synthesis using 10Co5Ru/m-SiO
2
-Al
2
O
3
(IWI) catalyst (Conditions: H
2
/CO = 2,
synthesis using 10Co5Ru-m-SiO
2
-TiO
2
(OP) catalyst (Conditions: H /CO = 2,
2
-
1
-1
1
atm, 12000 h GHSV).
1 atm, 12000 h GHSV).
by the deposition of carbon on the catalyst active sites via CO decom-
position. Evidently, retardation or disruption of the chain growth pre-
vents formation of higher hydrocarbons [87,88] at 1 atm due to coke
formation. In this study, product formation mainly depended on dif-
ferent mesoporous support. Propane was observed for mesoporous
SiO
2
-Al
2
O
3
and SiO
2
-TiO supported IWI catalysts. Thermodynamically,
2
the lower olefins are produced in FT synthesis at higher pressure
89,90]. However, this work was done at 1 atm. So, we found only
lower alkanes.
[
3.3. Continuous time-on-stream behavior of all catalysts
In order to know the time-on-stream behavior or stability of the
catalysts, all the catalysts were tested for 60 h at 210 °C, 1 atm with H
2
to CO molar ratio of 2. Fig. 11 shows the stability study of all catalysts
based on CO conversion. After initial drop on CO conversion, all the
catalysts showed good stability during 60 h operation. Highest CO
Fig. 8. Effect of temperature on CO conversion and product selectivity in FT
synthesis using 10Co5Ru/m-Al -TiO (IWI) catalyst (Conditions: H /CO = 2,
atm, 12000 h GHSV).
2
O
3
2
2
conversion, ∼75 %,was achieved with 10Co5Ru/m-SiO
2
-TiO (IWI)
2
-
1
1
catalyst. Lowest CO conversion (53 %) was observed with 10Co5Ru-
SiO -TiO (OP) catalyst. This result suggests that the method for the
catalyst preparation played an important role on stability studies. For
0Co5Ru/m-SiO -Al (IWI) catalyst, ∼65 % CO conversion was
2
2
1
2
2 3
O
obtained. In the case of 10Co5Ru/m-Al
2
O
3
-TiO catalyst, 55 % CO
2
conversion was achieved during 60 h stability studies. Thus, the type of
support has a great influence on the deactivation rate of the catalyst
during FT synthesis [86]. Iglesia et al. reported that the type of support
Fig. 9. Effect of temperature on CO conversion and product selectivity in FT
synthesis using 10Co5Ru/m-SiO -TiO (IWI) catalyst (Conditions: H /CO = 2,
atm, 12000 h GHSV).
2
2
2
-
1
1
[
87]. Thus, carbidization causes clogging of metal active sites with
carbon deposits that ultimately disrupts polymerization to higher hy-
drocarbons. Therefore, the increase in methane selectivity with the
decrease in selectivity towards ethane and propane was possibly caused
Fig. 11. Time-on-Stream behavior of all catalysts (Conditions: H
2
/CO = 2,
-1
2
10 °C, 1 atm, 12000 h GHSV).
9

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
Table 5
Carbon content (wt.%) based on temperature range of 200 to 600 °C of all spent
catalysts.
Catalyst
Carbon content (wt.%)
Spent 10Co5Ru/m-SiO
2
2
-Al
2
O
3
(IWI)
(IWI)
(IWI)
(OP)
0.61
3.44
2.85
2.24
Spent 10Co5Ru/m-SiO
-TiO
2
Spent 10Co5Ru/m-Al
2
O
3
-TiO
2
2 2
Spent 10Co5Ru-m-SiO -TiO
can be utilized to enhance the stability of the catalyst to resist deacti-
vation [4]. In summary, the stability and ability of the catalysts to
withstand deactivation were observed in the order: 10Co5Ru/m-SiO
2
-
TiO
2
(IWI) > 10Co5Ru/m-SiO
2
2
-Al O
3
(IWI) > 10Co5Ru/m-Al
2
O
3
-TiO
2
(
IWI) > 10Co5Ru-m-SiO -TiO
2
2
(OP).
3.4. FT studies with catalyst supports only
In order to know the negative reaction control of the FT synthesis,
reactions were also carried out with three different mesoporous com-
posite supports. Fig. S5 shows CO conversion on the bare supports at
2
10 °C and 1 atm with H /CO molar ratio of 2. No hydrocarbon for-
2
mation and CO conversion were observed with the bare catalyst sup-
ports indicating that the supports did not influence the hydrocarbon
product distribution.
3
.4.1. Characterization of spent catalysts
The spent catalysts were examined by temperature programmed
(
TPO-DSC) carbon oxidation in air and XRD analysis to ascertain the
possible causes in the decline of the catalyst activity over time. Table 5
compares percent carbon deposition of the catalyst after continuous
6
0 h on-stream. The TGA-DSC thermal profiles of the spent catalysts are
shown in supplemental Fig. S2.
Fig. 12. XRD of spent CoRu catalysts on different mesoporous composite oxides
Interestingly, there was no linear correlation between the carbon
deposition and loss of catalyst activity after 60 h. Based on the amount
supports.
of carbon deposited on the active sites, 10Co5Ru/m-SiO
2
-Al
2
O (IWI)
3
catalyst should have shown the highest activity and long-term stability.
Table 6
However, 10Co5Ru/m-SiO
2
-TiO
2
(IWI) catalyst which had about 6
Crystal size* calculated from XRD data.
times as much coking compared to the former showed the highest long-
term stability. The trend suggests that although coking was one of the
potential causes of deactivation, other factors such as method of pre-
paration, composition of mixed oxide support, oxidation, sintering,
support degradation and attrition also played a role. Under our ex-
perimental conditions, we think the dominant effect of the stability of
mixed oxide support outweighed the coke deactivation effect. Another
Catalysts
Crystal size (nm)
Co
3
O
4
RuO
2
TiO
–
2
Spent 10Co5Ru/m-SiO
2
2
-Al
2
O
3
(IWI)
(IWI)
(IWI)
(OP)
9.12
–
Spent 10Co5Ru/m-SiO
-TiO
2
17.76
12.6
5.88
14.04
–
Spent 10Co5Ru/m-Al
2
2
O
3
-TiO
2
9.71
6.08
Spent 10Co5Ru-m-SiO
-TiO
2
14.08
16.98
factor could be the relative ease of reducibility of 10Co5Ru/m-SiO
TiO (IWI) catalyst (i.e. below 400 °C) as discussed in Section 3.1.2.
Fig. 12 shows the XRD pattern of all spent catalysts. The crystal
structures changed permanently, and formation of an amorphous
structure is observed. The peak intensities of Co , RuO and TiO
crystals are also reduced. The cubic face-centered structure of carbon
2
-
*
Using Modified Scherrer equation [74].
2
(
IWI), 10Co5Ru/m- Al
catalysts. The BET results showed that catalyst surface areas decreased
upon impregnation of metals on the mixed oxide supports. Co and
RuO crystals in the catalysts were observed by XRD studies. Variation
in reduction temperature due to different mesoporous composite oxide
support-metal interaction was identified by H -TPR analysis. The cat-
alyst preparation method also affected the reduction temperature of
2
O
3
-TiO
2
(IWI), and 10Co5Ru-m-SiO
2
-TiO (OP)
2
3
O
4
2
2
O
3 4
(
JCPDS 81-2220) peaks are found in the spent catalysts. This result
2
confirmed that carbon was deposited on the catalyst surface during the
reaction. Table 6 shows the crystal size of all metal oxides after the FT
reactions. The crystal size is quite reduced in the spent catalysts.
2
metal oxides. Among all catalysts studied, CoRu/m-SiO
2
-TiO (IWI)
2
catalyst showed promising activity for FT synthesis. Although coking is
a potential cause of deactivation, other factors such as method of pre-
paration, oxidation, composition of mixed oxide support, sintering,
support degradation and attrition also played a role in the stability of
the catalysts.
4
. Conclusions
Stainless steel microchannel microreactors prepared using 3D-
printed technology were used for FT synthesis using three different
mesoporous composite oxides supported CoRu catalysts. The catalysts
were coated in the microchannels of the microreactors. Catalysts were
prepared using incipient wet-impregnation and one-pot hydrothermal
synthesis methods. Very different physicochemical properties were
CRediT authorship contribution statement
observed for 10Co5Ru/m-SiO
2
-Al
2
O
3
(IWI), 10Co5Ru/m-SiO
2
-TiO
2
S. Bepari: Conceptualization, Data curation, Investigation, Writing -
10

S. Bepari, et al.
Applied Catalysis A, General 608 (2020) 117838
original draft, Software. Xin Li: Data curation, Formal analysis,
Resources. R. Abrokwah: Methodology, Supervision, Writing - review
171.
[
[
[
33] T. Mazanec, S. Perry, L. Tonkovich, Y. Wang, Nat. Gas Convers. Vii 147 (2004) 169.
34] Y. Sun, Z. Jia, G. Yang, L. Zhang, Z. Sun, Int. J. Hydrogen energy 42 (2017) 29222.
35] Y. Sun, G. Yang, L. Zhang, Z. Sun, Chem. Eng. Process Process Intensif. 119
(2017) 44.
&
editing. N. Mohammad: Methodology, Data curation, Formal ana-
lysis. M. Arslan: Visualization. D. Kuila: Conceptualization, Writing -
[
[
36] S. Mehta, V. Deshmane, S. Zhao, D. Kuila, Ind. Eng. Chem. Res. 53 (2014) 16245.
37] R.Y. Abrokwah, M.M. Rahman, V.G. Deshmane, D. Kuila, Mol. Catal. 478 (2019)
review & editing.
1
10566.
Declaration of Competing Interest
[38] N. Mohammad, S. Bepari, S. Aravamudhan, D. Kuila, Catalysts 9 (2019) 872.
39] A. Gavriilidis, P. Angeli, E. Cao, K.K. Yeong, S.S.Y. Wan, Chem. Eng. Res. Des. 80
[
(
2002) 3.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
[40] X. Ouyang, R. Besser, Catal. Today 84 (2003) 33.
[41] V. Hessel, P. Lob, H. Lowe, Stud. Surf. Sci. Catal. 159 (2006) 35.
[
[
[
42] R. Guettel, T. Turek, Chem. Eng. Sci. 64 (2009) 955.
43] A. Holmen, H.J. Venvik, R. Myrstad, J. Zhu, D. Chen, Catal. Today 216 (2013) 150.
44] L. Han, D. Mao, J. Yu, Q. Guo, G. Lu, Catal. Commun. 23 (2012) 20.
Acknowledgements
[45] X. Sun, X. Zhang, Y. Zhang, N. Tsubaki, Appl. Catal. A Gen. 377 (2010) 134.
[
[
[
[
46] Y. Zhang, S. Nagamori, S. Hinchiranan, T. Vitidsant, N. Tsubaki, Energy Fuels 20
(
2006) 417.
This work is performed at North Carolina A&T State University and
Joint School of Nanoscience and Nanoengineering, a member of the
Southeastern Nanotechnology Infrastructure Corridor (SENIC) and
National Nanotechnology Coordinated Infrastructure (NNCI), which is
supported by the National Science Foundation (Grant ECCS-1542174).
The authors acknowledge the funding received from National Science
Foundation, NSF CREST (#260326) and University of North Carolina,
Research Opportunity Initiative, UNC-ROI (#110092). The authors also
gratefully acknowledge the help from Dr. Kristen Dellinger for XPS
studies and Dr. Cynthia S. Day of Wake Forest University, North
Carolina, USA for XRD studies of the spent catalysts. We thank Prof.
Moti Herskowitz of Ben-Gurion University of the Negev, Israel, for
useful discussions.
47] S. Bepari, R. Stevens-Boyd, N. Mohammad, Xin Li, R. Abrokwah, D. Kuila, Mater.
Today (2020), https://doi.org/10.1016/j.matpr.2020.04.582.
48] S.A. Salihi, R. Abrokwah, W. Dade, V. Deshmane, T. Hossain, D. Kuila, Int. J.
Hydrogen Energy 45 (2020) 14183.
49] R.Y. Abrokwah, W. Dade, S.L. Owen, V. Deshmane, M. Rahman, D. Kuila, Effects of
Mesoporous Supports and Metals on Steam Reforming of Alcohols, E-Publishing,
CRC, New York, 2019, pp. 93–106.
[
50] A. Corma, M. Navarro, T. Perez-Pariente, J. Chem. Soc. Chem. Commun. (1994)
1
47.
[51] K.S.W. Sing, Pure Appl. Chem. 54 (1982) 2201.
[
[
52] H.M. Gobara, Egypt. J. Pet. 21 (2012) 1.
53] B. Huang, C.H. Bartholomew, S.J. Smith, B.F. Woodfield, Microporous Mesoporous
Mater. 165 (2013) 70.
[54] V. Vosoughi, S. Badoga, A.K. Dalai, N. Abatzoglou, Fuel Process. Technol. 162
(2017) 55.
[
[
55] G. Jacobs, Y. Ji, B.H. Davis, D. Cronauer, A.J. Kropf, C.L. Marshall, Appl. Catal. A
Gen. 333 (2007) 177.
56] G. Jacobs, T.K. Das, Y.Q. Zhang, J.L. Li, G. Racoillet, B.H. Davis, Appl. Catal. A Gen.
233 (2002) 263.
References
[
[
57] J. Panpranot, J.G. Goodwin Jr., A. Sayari, Catal. Today 77 (2002) 269.
58] S.K. Beaumont, S. Alayoglu, C. Specht, W.D. Michalak, V.V. Pushkarev, J. Guo,
N. Kruse, G.A. Somorjai, J. Am. Chem. Soc. 136 (2014) 9898.
59] W.C. Conner Jr., J.L. Falconer, Chem. Rev. 95 (1995) 759.
60] J. Hong, E. Marceau, A.Y. Khodakov, L. Gaberova, A. Griboval-Constant,
J.S. Girardon, C.L. Fontaine, V. Briois, ACS Catal. 5 (2015) 1273.
61] S. Mandal, S. Maity, P.K. Gupta, A. Mahato, P. Bhanja, G. Sahu, Appl. Catal. A Gen.
[
1] Y.S. Noh, K.-Y. Lee, D.J. Moon, Catal. Today (2019), https://doi.org/10.1016/j.
cattod.2019.08.035.
[
[
[
[
2] F. Bertella, P. Concepcion, A. Martinez, Catal. Today 289 (2017) 181.
3] O.A. Kungurova, A.A. Khassin, S.V. Cherepanova, A.A. Saraev, V.V. Kaichev,
N.V. Shtertser, G.K. Chermashentseva, E.Y. Gerasimov, E.A. Paukshtis,
O.V. Vodyankina, T.P. Minyukova, G. A-J, Appl. Catal. A Gen. 539 (2017) 48.
4] E. Iglesia, Appl. Catal. A Gen. 161 (1997) 59.
[
5
57 (2018) 55.
[
[
[
[
[
[
[
[
[
[
62] C.-H. Chen, C.-C. Huang, Microporous Mesoporous Mater. 109 (2008) 549.
63] F. Roessner, U. Roland, J. Mol. Catal. A Chem. I12 (1996) 401.
64] R. Kramer, M. Andre, J. Catal. 58 (1979) 287.
5] M.E. Dry, Catal. Today 71 (2002) 227.
6] E. Rytter, N.E. Tsakoumis, A. Holmen, Catal. Today 261 (2016) 3.
7] A.Y. Khodakov, W. Chu, P. Fongarland, Chem. Rev. 107 (2007) 1692.
8] W.M. Chen, Y.J. Ding, D.H. Jiang, Z.D. Pan, H.Y. Luo, Catal. Lett. 104 (2005) 177.
9] D.H. Jiang, Y.J. Ding, Z.D. Pan, W.M. Chen, H.Y. Luo, Catal. Lett. 121 (2008) 241.
65] T.N. Phaahlamohlaka, M.W. Dlamini, M.W. Mogodi, D.O. Kumi, L.L. Jewell,
D.G. Billing, N.J. Coville, Appl. Catal. A Gen. 552 (2018) 129.
66] G. Jacobs, W. Ma, B.H. Davis, Catalysts 4 (2014) 49.
[
[
[
[
[
[
[
10] X.H. Mo, J. Gao, N. Umnajkaseam, J.G. Goodwin Jr., J. Catal. 267 (2009) 167.
11] S.C. Chuang, J.G. Goodwin Jr., I. Wender, J. Catal. 95 (1985) 435.
12] A. Erdohelyi, F. Solymosi, J. Catal. 84 (1983) 446.
67] Y.P. Li, T.J. Wang, C.Z. Wua, X.X. Qin, N. Tsubaki, Catal. Commun. 10 (2009) 1868.
68] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. Fredrikson, B. Chmelka, G.D. Stucky,
Science 279 (1998) 548.
13] K. Shimura, T. Miyazawa, T. Hanaoka, S. Hirata, J. Mol. Catal. A Chem. 394
[
[
69] X.Y. Zhao, H.Y. Zhang, J. Chen, L.J. Li, Y.K. Liew, B.R.M. Nordin, Chem. Cat. Chem.
(
2012) 22.
4
(2012) 265.
[
14] S. Mandal, S. Maity, P.K. Gupta, A. Mahato, P. Bhanja, G. Sahu, Appl. Catal. A Gen.
70] V.R.R. Pendyala, G. Jacobs, W. Ma, J.L.S. Klettlinger, C.H. Yen, B.H. Davis, Chem.
Eng. J. 249 (2014) 279.
5
57 (2018) 55.
[
[
[
[
15] R. Oukaci, A.H. Singleton, J.G. Goodwin Jr., Appl. Catal. A Gen. 186 (1999) 129.
16] A.Y. Khodakov, Catal. Today 144 (2009) 251.
[
[
[
[
[
[
71] A. Sari, Chem. Eng. J. 244 (2014) 317.
72] A. Haghtalab, A. Mosayebi, Int. J. Hydrogen Energy 39 (2014) 18882.
73] K. Jalama, Catal. Commun. 74 (2016) 71.
17] A.Y. Khodakov, W. Chu, P. Fongarland, Chem. Rev. 107 (2007) 1692.
18] B.Y.F. Morales, B.M. Weckhuysen, J.J. Spivey, K.M. Dooley (Eds.), Catalysis, RSC
Publishing, 2006, pp. 1–40.
74] A. Monshi, M.R. Foroughi, M.R. Monshi, WJNSE 2 (2012) 154.
75] C.H. Kwon, J.H. Kim, I.S. Jung, H. Shin, K.H. Yoon, Ceram. Int. 29 (2003) 851.
76] N. Osakoo, R. Henkel, S. Loiha, F. Roessner, J. Wittayakun, Catal. Commun. 56
[
[
19] E. Rytter, N.E. Tsakoumis, A. Holmen, Catal. Today 261 (2016) 3.
20] T. Jermwongratanachai, G. Jacobs, W.D. Shafer, V.R.R. Pendyala, W. Ma,
M.K. Gnanamani, S. Hopps, G.A. Thomas, B. Kitiyanan, S. Khalid, B.H. Davis, Catal.
Today 228 (2014) 15.
(
2014) 168.
[
[
77] J. Taghavimoghaddam, G.P. Knowles, J. A.L.Chaffee, Mol. Catal. A Chem. 358
2012) 79.
78] R.Y. Abrokwah, V.G. Deshmane, S.L. Owen, D. Kuila, Adv. Mat. Res. 1096 (2015)
(
[
[
21] K. Shimura, T. Miyazawa, T. Hanaoka, S. Hirata, Appl. Catal. A Gen. 494 (2015) 1.
22] O.L. Eliseev, M.V. Tsapkina, O.S. Dement’eva, P.E. Davydov, A.V. Kazakov,
A.L. Lapidus, Kinet. Catal. 54 (2013) 207.
1
61.
[
[
[
[
[
[
[
[
79] V.G. Deshmane, R.Y. Abrokwah, D. Kuila, J. Mol. Catal. A. Chem. 408 (2015) 202.
80] D.G. Castner, P.R. Watson, I.Y. Chan, J. Phys. Chem. 93 (1989) 3188.
81] S.C. Petitto, M.A. Langell, J. Vac, Sci. Technol. A 22 (2004) 1690.
82] A. Dinse, M. Aigner, M. Ulbrich, G.R. Johnson, A.T. Bell, J. Catal. 288 (2012) 104.
83] H. Schulz, Catal. Today 214 (2013) 140.
[
[
[
[
[
23] H. Ming, B.G. Baker, M. Jasieniak, Appl. Catal. A Gen. 381 (2010) 216.
24] J.H. Den Otter, S.R. Nijveld, K.P. De Jong, ACS Catal. 6 (2016) 1616.
25] J. Cheng, P. Hu, P. Ellis, S. French, G. Kelly, C.M. Lok, J. Catal. 257 (2008) 221.
26] V. Vosoughi, A.K. Dalai, N. Abatzoglou, Y. Hu, Appl. Catal. A Gen 547 (2017) 155.
27] M. Sarkari, F. Fazlollahi, H. Ajamein, H. Atashi, W.C. Hecker, L.L. Baxter, Fuel
Process Technol. 127 (2014) 163.
84] T.I. Sibianu, D. Berger, C. Matei, I. Calinescu, U.P.B. Sci. Bull. 78 (2016) 39.
85] H. Schulz, E.V. Steen, M. Claeys, Stud. Surf. Sci. Catal. 81 (1994) 455.
86] N. Mohammad, R.Y. Abrokwah, R.G. Stevens-Boyd, S. Aravamudhan, D. Kuila,
Catal. Today (2020), https://doi.org/10.1016/j.cattod.2020.02.020.
87] S. Zhao, V.S. Nagineni, N.V. Seetala, D. Kuila, Ind. Eng. Chem. Res 47 (2008) 1684.
88] H. Schulz, Top. Catal. 26 (2003) 73.
[
[
28] F.G. Botes, J.W. Niemantsverdriet, J. van de Loosdrecht, Catal. Today 215 (2013)
1
12.
29] S. Chambrey, P. Fongarland, H. Karaca, S. Piche, A. Griboval-Constant,
D. Schweich, F. Luck, S. Savin, A.Y. Khodakav, Catal. Today 171 (2011) 201.
30] D.A. Wood, C. Nwaoha, B.F. Towler, J. Nat. Gas. Sci. Eng. 9 (2012) 196.
31] S.R. Deshmukh, A.L.Y. Tonkovich, K.T. Jarosch, L. Schrader, S.P. Fitzgerald,
D.R. Kilanowski, J.J. Lerou, T.J. Mazanec, Ind. Eng. Chem. Res. 49 (2010) 10883.
32] L.C. Almeida, O. Sanz, J. Dolhaberriague, S. Yunes, M. Montes, Fuel 110 (2013)
[
[
[
[
[
[
89] D.B. Bukur, X. Lang, A. Akgerman, Z. Feng, Ind. Eng. Chem. Res. 36 (1997) 2580.
90] J. Chen, C. Yang, ACS Omega 4 (2019) 22237.
[
11