CO
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Conversion into Methanol Using a6H-SiC
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With the ever increasing global requirement for energy on
one side and ever shrinking global energy sources on the
other side, research efforts are underway to develop envi-
ronmentally friendly sustainable and renewable energy
catalytic activity of different catalysts for water splitting
[15, 16]. Chen et al. [17] have successfully synthesized In
TaO photo-catalyst using an aqueous sol–gel method and
4
it was modified by loading with NiO and used for the
photo-catalytic reduction of CO into methanol [18]. WO
3
sources. In this line, transformation of CO into useful
2
2
products such as methanol, hydrogen, and methane is
highly advantageous and it will fulfill both goals: reduction
of greenhouse gases for global warming issue as well as
providing alternate renewable energy sources [2].
has been used also as a photo-catalyst in the UV region
[19, 20]. Silicon carbide has rarely been used in the photo-
catalytic conversion of CO into hydrocarbons.
2
In this work, granular a6H-SiC was applied as a photo-
catalyst in the conversion of CO into methanol in the
As CO is a very stable and inert molecule, Most of the
2
2
processes for converting it into value added compounds
require a lot of energy. Recent research has shown that
photo-catalysis is a promising method of converting CO2
into methanol; however finding a highly reactive and effi-
presence of 355 nm monochromatic laser radiation and a
broad band radiation source and the relative merit of these
two radiations in the production yield of methanol con-
verted from CO2 and the photonic efficiencies were
investigated. A special reaction cell aiming at the optimum
interaction of radiation and the catalyst was designed. CO2
dissolved in distilled water at 50 psi pressure and the a6H-
SiC catalyst was placed inside the water and exposed to
incident radiation. The 355 nm laser radiation was gener-
ated from the third harmonic of pulsed Nd:YAG laser and
the broadband band source was a xenon mercury (XeHg)
lamp. The production yield (conversion of CO2 into
methanol) was estimated by Gas Chromatographic analysis
(GC) of the water sample taken at a regular time intervals
of irradiation. The GC peak was calibrated to the known
molar concentrations of methanol in the millimole/liter
(mM) scale. The maximum concentration of methanol
produced was 1.25 mM with the laser irradiation and
0.375 mM with the XeHg lamp irradiation. The maximum
cient catalyst to reduce the CO molecule remains a chal-
2
lenge. Moreover, this process should be economically
viable and environmentally friendly to adopt this process
for an industrial scale, which demands the usage of inex-
pensive and abundant material and renewable energy
sources.
Semiconductor catalysts have been effectively used for
many photo-chemical processes such as bacterial disin-
fection, water purification, recycling of organic dyes,
conversion of methane into methanol and so on [3]. When
the photon energy (hm) of the incident radiation is more
than that of the band gap (E ) of the semiconductor, the
g
electrons from the valence band will be excited to
the conduction band leaving positively charged holes in the
valence band (VB). The electron hole pairs, generated by
photo-excitation can move to the surface of semiconductor
photonic efficiency of CO into methanol with the 355 nm
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•
particle to form a highly oxidizing radicals like OH
-
hydroxyl radical) and O2 (super-oxide radical). This
laser radiation was 1.95 and 1.16 % with the XeHg lamp.
This enhancement of photonic efficiency with the laser is
attributed to the inherent qualities of the laser beam. In
addition to the enhanced yield, the selectivity in the case of
the laser irradiation is very impressive as methanol is
practically the only product in the laser based photo-reac-
tion compared to other accompanying products in the case
of the broadband source. In order to estimate the band gap
and other characteristics of a6H-SiC, the optical charac-
terization and XRD of the photo-catalyst was carried out.
The results of the study demonstrated that the granular
silicon carbide is a promising catalytic material for photo-
(
process can pursue a number of chemical pathways that
could lead to variety of reaction products.
Several pathways and numerous catalytic materials have
been investigated by several researchers to develop effi-
cient catalytic materials for conversion of CO into useful
2
products such as ethers, methanol, dimethylether [4], pro-
pylene, ethylene, methane, CO based copolymers [5, 6]
2
and organic and inorganic carbonates [7].
Wang and coworkers [8] applied copper doped titania–
silica nanostructured photo-catalysts and achieved rela-
tively good CO2 conversion efficiency. Titania-based
catalytic conversion of CO into methanol in the presence
2
photo-catalysts have been used for CO photo-catalytic
2
of UV laser radiation.
reduction in the presence of H O to produce chemicals
2
such as methanol or methane [9, 10]. TiO film coated on
2
optical fiber using a dip-coating method was utilized for
2 Experimental
CO conversion as well [11]. A number of catalysts pre-
2
pared by loading indium on the oxides of vanadium, nio-
bium and tantalum have demonstrated quite good
improvement in their photo-catalytic activities due to a
decrease in their band gap [12–14]. It has been demon-
strated that nickel oxide loading promotes the photo-
2.1 Chemicals and Materials
Silicon carbide (Saint-Gobain, USA) with the grain size of
1.5 mM size granules was used without any further pro-
cessing. CO gas with the purity of 99.997 % was obtained
2
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