Chemical Papers
example, Zirconium (Zr) as a metal promoter facilitates cata-
et al. (2005) showed that Zr enhances the catalyst activity
toward the higher hydrocarbons. Moreover, the presence
of Zr modifes the strong cobalt–support interaction, and
consequently facilitates the catalyst reduction at lower tem-
peratures (Jongsomjit et al. 2003).
economical aspects. The synthesized catalysts were tested
in a fxed-bed reactor in FTS conditions and the catalyst
properties were characterized by XRD, H2-TPR, BET, and
HRTEM techniques.
Experimental
Moreover, it is very important to achieve a FTS catalyst
with a reasonable price, from economical point of view.
Hence, the addition of mineral oxides (e.g., TiO2, SiO2,
and Al2O3) as catalyst modifers into cobalt-based catalyst,
which is commonly used as support, has a lower price and
more availability. Additionally, it is reported, in some of the
patent literatures from the well-known companies that they
eral oxides (Rytter and Holmen 2016). Moreover, a range of
as a support modifer on FTS process. Savost’yanov et al.
(2016) studied the impact of Al2O3 as a promoter of Co/SiO2
on C5+ formation. They illustrated that the addition of Al2O3
to Co/SiO2 promotes the catalyst activity and C5+ selectiv-
ity. Keyvanloo et al. (2014) discussed the efect of SiO2 as a
stabilizer on diferent catalysts supported by alumina. They
observed that SiO2 efectively stabilizes the alumina mate-
rial against the transformation of γ-Al2O3 to α-Al2O3. In
more recent work of this team (Rahmati et al. 2018), the
FTS performance of cobalt catalyst on silica-stabilized alu-
mina support has been compared with the other commercial
cobalt-based catalyst. Therefore, it has been reported the
alumina-supported cobalt catalyst with silica stabilizer has
high surface area, larger pore volume, larger pore size, and
unique bimodal pore enhanced mass transfer during FTS
reaction in comparison with alumina-supported cobalt cata-
lyst. In addition, it has high thermal stability that enables the
removal of most surface hydroxyl groups by calcinations
at very high temperature. Wu et al. (2015) doped Co/SiO2
catalyst with TiO2 and ZrO2 as promoter. They demonstrated
that dispersion of active metal improved through TiO2 addi-
tion. In other words, TiO2 acts as a structural promoter, and
therefore increases metal–support interaction.
Catalyst preparation
The γ-alumina support has 209 m2/g surface area,
0.518 cm3/g pore volume, and 9.55 nm pore size. To inves-
tigate the silica efect on Co–Ru–Zr/γ-Al2O3 catalyst, the
γ-alumina support was mixed with diferent ratio of col-
loidal silica (Sigma-Aldrich, 40 wt% suspension in H2O) to
provide 0, 5, 10, and 15 wt% of silica on γ-Al2O3 support.
The supports after mixing with diferent ratios of SiO2 were
dried at 110 ̊C for 24 h, then subjected to 350 ̊C in a furnace
for 3 h. Ammonium zirconium (IV) carbonate solution in
H2O (Sigma-Aldrich, contains 1–2% tartaric acid as stabi-
lizer) was used as precursor to add 3 wt% Zr to the prepared
supports by incipient wetness impregnation method. Then
it was dried in an oven at 110 °C for 24 h and then cal-
cined at 350 °C for 3 h. In the next step, 0.2 wt% Ru and
13 wt% Co added by co-impregnation method using Ru(NO)
(NO3)3 (Acros organics in diluted nitric acid 0.01 ml/ml) and
Co(NO3)2.6H2O (Merck, purity>97%) as precursor, respec-
tively. Finally, samples were dried in an oven at 110 °C for
24 h, and subsequently, calcined at 350 °C in air for 3 h.
Catalyst characterization
BET surface area, pore volume and mean pore diameter were
determined using an ASAP 3020 instrument of Micromerit-
ics. The samples were degassed under vacuum at 300 °C for
2 h before measurement. H2 temperature-programmed reduc-
tion (TPR) experiments were performed in a quartz reactor
using a mixture of 20% H2/80% Ar (v/v) as the reducing
gas. About 0.5 g catalyst was packed in the quartz reactor.
The catalyst sample was heated from room temperature to
800 °C at a heating rate of 5 °C/min. The fow rate of mixed
gas was adjusted to 50 ml/min. The hydrogen consumption
was monitored by the change of thermal conductivity of
the efuent gas stream. The morphology for the prepared
catalysts was observed using Philips Tecnai 20 microscope
operating at 200 kV. Powder X-ray difraction (XRD) pattern
of fresh catalyst was produced with a Philips PW1840 X-ray
difractometer with monochromatized Cu (Kα) radiation for
determining of cobalt phases. The average size of the Co3O4
crystallites in the catalysts was calculated using the Scherrer
equation from the line broadening of a Co3O4 at 2θ of 36.88.
Despite all these studies, there is a lack of informa-
tion on the addition of some mineral oxides as a modifer
on γ-Al2O3-supported cobalt catalyst. Hence, this paper
mainly discusses the efect of silica addition as a support
modifer on the activity and selectivity of the catalyst in
FTS process. The presence of Ru and Zr materials enact
as promoters of cobalt/γ-Al2O3 catalyst. It was speculated
that SiO2 augmentation to Co–Ru–Zr/γ-Al2O3 catalyst
intervene the strong interaction between the cobalt and
γ-Al2O3 and facilitate Co reducibility and dispersion,
simultaneously. As a result, the catalyst performance in
terms of activity and selectivity improves to rationalize the
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