Structural Influence of Ordered Mesoporous Carbon Supports for the Hydrogenation of Carbon Monoxide to Alcohols
Kim et al.
1980s, many researchers have screened over sixty elements
in the periodic table as promoters of the Rh-based cata-
lyst for improvement of the catalytic activity and selec-
tivity to C2+ oxygenates.13 However, high loading amount
(> 4–5 wt%) and high price of precious Rh metal have
prevented its application and commercialization even if
the higher selectivity and energy efficiency of Rh-based
catalyst to C2+ alcohols.25 Therefore, it is essential devel-
opment of more active Rh-based catalyst to reduce the
catalyst cost.
ordered mesoporous silica (OMS) templates were synthe-
sized according to the previous reports.31ꢀ32 A series of
OMCs were synthesized by using a templating synthesis.
Rod-type ordered mesoporous carbons, were prepared by
the complete filling of the mesopores of SBA-15 and KIT-
6 OMS hard templates, respectively.31 Briefly, OMSs were
filled with furfuryl alcohol as 85% of OMSs total pore vol-
ume. The samples containing furfuryl alcohol were placed
in an oven at 35 ꢀC for 1 h and then at 100 ꢀC for 1 h. The
resultant polymer/composite samples were further heated
ꢀ
Besides active metals and promoters, catalyst supports
are one of the important factors to effect on the cat-
alytic activity and selectivity for the direct conversion of
syngas to alcohols. It is due to structural properties of
support materials (pore structure, surface area, pore size,
pore volume, etc.), and unique interaction between active
components and catalyst supports.8ꢀ13 Most researches for
the catalytic performance of STA reaction has used sil-
ica oxides as supports, and other typical inorganic oxides
(Al2O3, TiO2, ZrO2, V2O3, CeO, MgO etc.) have been also
tested.2ꢀ7ꢀ26ꢀ27 Recently, Bao’s group demonstrated that a
promoted Rh-based catalyst using multi-wall carbon nano-
tubes (MWCNTs) as a support, and shows improving the
selectivity of C2+ oxygenates due to the favorable ther-
mal and electron conductive properties, as well as confine-
ment of active metal in MWCNT’s nanochannels.15 More
recently, other carbonaceous materials such as ordered
at 350 C for 2 h. After the samples were cooled to room
temperature, the samples were subsequently more filled
with furfuryl alcohol as 55% of OMSs total pore volume
and we then carried out drying and heating as in the first
case, followed by pyrolysis at 900 ꢀC with N2 flow for 2 h.
The CMK-3 and CMK-8 OMCs were recovered from the
silica template by an aqueous HF/ethanol mixture solution.
The hollow-type OMCs, CMK-5 (2-D hexagonal structure)
and CMK-9 (3-D cubic structure), were prepared by the
incomplete filling of the SBA-15 and KIT-6 mesopores
as following description. Silica templates were filled with
furfuryl alcohol as 100% of OMS’s total pore volume.
Carbonization of tꢀhe furfuryl alcohol/ONS samples were
carried out at 10ꢀ0 C for 1 h, followed by pyrolysis under
vacuum at 900 C. Silica templates of prepared CMK-5
and CMK-9 were removed in the same manner as was
used for CMK-3 and CMK-8.
Delivered by Publishing Technology to: West Virginia University/ Health Sci Ctr LIb
mesoporous carbons (OMC), carbon fibers, activated car-
IP: 110.80.157.193 On: Thu, 05 Nov 2015 02:09:53
bons, and graphitic mesoporous carbons has been exam-
Copyright: American Scientific Publishers
ined for direct conversion of syngas to alcohols.8ꢀ13ꢀ28–30
2.2. Preparation of Catalysts
Among the these carbonaceous materials, the ordered
mesoporous carbon materials could apply as model or
reference support materials in study to achieve useful
information about the behavior of carbonaceous catalysts
during the reaction, and effect of physicochemical proper-
ties on the catalytic reaction due to their uniform pore size
distribution and ordered mesopore structure, which can be
easily investigated by various analytic techniques such as
transmission electron microscopy, gas physisorption, and
X-ray diffraction analysis.31
In the present work, we synthesized a series of ordered
mesoporous carbon materials (OMCs) with structurally
well-defined carbonaceous supports as reference support
materials in syngas-to-alcohols reaction and prepared pro-
moted Rh-OMC catalysts with low amount of precious Rh
metal. We focus on the effects of the different mesopore-
structures and texture properties of OMCs on the direct
conversion of syngas-to-alcohols, which are investigated in
a fixed-bed reactor.
The Mn, Li, and Fe promoted Rh catalysts supported on
OMCs (RMLF/OMCs) were prepared by a simple incip-
ient wetness method using water as a solvent. The Rh
metal and promoters were added in a weight ratio of
Rh:Mn:Li:Fe = 1:1:0.075:0.05 according to Bao’s paper.15
1 g of OMC supports were impregnated with water con-
taining required amounts of RhCl3, Mn(NO3ꢁ2, LiNO3,
and Fe(NO3ꢁ3, which accounted for 2 times the OMCs
total pore volume. After impregnation, the samples were
dried at 35 ꢀC for 1 h followed by 60 ꢀC for 6 h in ambient
air to remove solvent. Before the STA reaction, the pre-
pared catalysts were reduced via heating under a hydrogen
flow rate of 20 ml min−1. The reduction temperature was
linearly increasedꢀfrom room temperature to 330 ꢀC with a
ꢀ
heating rate of 2 C min−1 and then maintained at 330 C
for 2 h. The samples were subsequently cooled with a
nitrogen flow for 1 h. For comparison, the Mn, Li, and Fe
promoted Rh catalysts supported on commercial activated
carbon (Darco Co.) was also prepared by the incipient
wetness method, and multi-wall carbon nanotubes (MWC-
NTs, Applied Carbon Nano Techn. Co., inner diameter:
6–10 nm, outer diameter: ∼ 120 nm, length: ∼ 10 ꢂm)
was prepared by the literature.15 The samples for using
activated carbon and MWCNT supports are denoted as
RMLF/AC and RMLF/CNT, respectively.
2. EXPERIMENTAL DETAILS
2.1. Synthesis of OMC Supports
SBA-15 (2-dimensional (2-D) hexagonal P6mm structure)
¯
and KIT-6 (3-dimensional (3-D) cubic Ia 3 d structure)
7512
J. Nanosci. Nanotechnol. 13, 7511–7518, 2013