Reduction of Carbon Dioxide in γ Ray Irradiated Carbon Dioxide: Water System Containing Cu2+ and SO32-

Article abstract of DOI:10.1246/cl.2000.572

Enhancing effect of various metal powders, metal oxides, metal ions, and inorganic anions on reduction of CO2 in γ ray irradiated CO2-water systems were investigated. Experimental results showed that Cu²⁺ and SO3^2- have large enhanci

Full text of DOI:10.1246/cl.2000.572

5
72
Chemistry Letters 2000
Reduction of Carbon Dioxide in γ Ray Irradiated Carbon Dioxide : Water System Containing
2
+
2-
Cu and SO
3
†
†
†
Xing-Zheng Wu,* Masanori Hatashita, Yuji Enokido, and Hidetake Kakihana
Department of Materials Science and Engineering, Faculty of Engineering, Fukui University, 3-9-1 Bunkyo, Fukui 910-8507
†
Research Department, the Energy Research Center, Wakasa Bay, 64-52-1 Nagatani, Tsuruga, Fukui 914-0192
(Received March 9, 2000; CL-000237)
a block of wood, and then placed around a 60Co γ ray source
(the Institute of Scientific and Industrial Research, Osaka
University) for a certain period at room temperature. Dose rate
Enhancing effect of various metal powders, metal oxides,
metal ions, and inorganic anions on reduction of CO in γ ray
2
irradiated CO -water systems were investigated. Experimental
2
2+
2-
–1
results showed that Cu and SO3 have large enhancing effect.
Furthermore, their synergical enhancing effect was found. The
enhancing factor was about 100-fold.
of the γ ray irradiation was about 1 kGy h . After the irradia-
tion, the pipette tube was immersed into water. The tip end was
scrupulously opened in the water, and a gas sample of 100 µL
of the gas phase in the tube was taken by a syringe needle. It
was immediately injected into a gas chromatograph (Hitachi G-
3500) with a separation column (3 mm ID × 2 m, GL Science)
Many researchers are endeavoring to develop effective
methods for removing or fixing CO in the atmosphere. For
of active carbon, a methanizer for converting CO and CO into
2
2
1-3
example, several chemical approaches such as catalytic, elec-
methane, and an FID detector. The detection limits of the GC
for CO, CH , and C H were about 5 ppm.
trochemical,4 and photochemical methods are being widely
-6
7,8
4
2
6
investigated to fix CO . In general, it is very difficult to con-
Table 1 shows concentrations of CO, CH , and C H
2
4 2 6
vert CO to a reduced substance such as hydrocarbon because it
detected from various CO -water systems after 18 hours irradia-
2
2
has the lowest reactivity among the carbon containing com-
pounds. On the other hand, ionizing radiation is known to often
tion of γ ray. The concentration ranges in Table 1 are obtained
from 4–6 radiation experiments carried out in different days.
stimulate chemical reactions. It has been reported that CO can
2
9
be decomposed by ionizing radiation at room temperature,
although the decomposition efficiency is very low due to the
regeneration of CO by the recombination reactions of the radi-
2
1
0,11
cals and atom produced during the irradiation.
Recently, γ ray induced CO reduction to CO and hydro-
2
carbon such as CH and C H are reported in a water containing
4
2
6
Fe powder.1
2,13
If CO could be reduced efficiently by the aid
2
of radiation exposure, it would be eminently meaningful to the
mankind. Firstly, radiation from spent nuclear fuels as well as
radioactive wastes, which is being or will be a severe environ-
mental problem, could be utilized effectively. Secondly, it
could be used for decreasing CO in the atmosphere. Thirdly, if
2
hydrocarbon compounds could be further produced, CO could
2
be used as a source of clean fuels and important chemical mate-
rials. Based on this consideration, we are carrying out the γ ray
irradiation experiments to find an effective CO reduction sys-
2
tem. Our first endeavor is to investigate enhancing effect of
various inorganic chemicals on the γ ray induced CO reduc-
2
tion. A small amount (0.02 g) of each chemical such as Fe,
FeSO , FeCl , Fe O , Cu powder, CuO, CuSO , CuCl , NiSO ,
4
3
2
3
4
2
4
ZnSO , ZnS, CdS, TiO , CoCl , Ag SO , Al powder, Na SO ,
4
2
2
2
4
2
3
or NaNO was introduced into a glass pipette tube with 10 cm
2
long tip part (internal diameter: 2 mm) and 5 cm long bottom
part (internal diameter: 7 mm), which was sequentially washed
-3
with water, 0.1 mol dm HCl, and water in an ultrasonic water
bath and heated in a 300 °C oven for 10 min, beforehand. The
bottom part was then heat-sealed with a high temperature gas
burner. About 2 mL water was introduced into the pipette tube,
and the chemical in the pipette tube was dissolved or dispersed
in the water. After the solution or suspension in the pipette tube
was bubbled with CO gas for about 30 min, middle of the tip
2
part was also heat-sealed. The volume of gas phase in the
pipette tube was about 0.5 mL. The pipette tubes were fixed on
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
573
Glass pipette tubes filled with air, water, and CO -bubbled
coexist (its G value was about 0.1). The enhancing factor is
about 100-fold comparing to the system without them. This
result suggests that Cu and SO3 have synergical enhancing
2
water were firstly irradiated to investigate the backgrounds of
the production of CO and CH . No detectable CO, CH , and
2+
2-
4
4
C H were found in the irradiated air and water. However,
effect in the CO reduction. Although the exact reaction mech-
2
6
2
about 40–55 ppm CO and 5–10 ppm CH were detected after
anisms remain to be investigated, above results suggest that it
might be a meaningful method to find out an effective CO2
reduction system by considering the synergical enhancing effect
of various chemicals.
4
1
8 h-irradiation in the CO -bubbled water. This means that a
2
part of CO was reduced to CO and even CH in the CO bub-
2
4
2
bled water by the irradiation. Secondly, the reported CO -water
2
system containing Fe powder was investigated. As shown in
Although CO production was greatly enhanced by the exis-
2+
2-
footnotes of Table 1, no CO but a large amount of CH and
tence of Cu and SO3 , neither increase of CH nor C H was
4
4 2 6
C H were detected before the irradiation. This means that a
observed. In all of the systems, the maximum CH concentra-
4
2
6
2
+
part of CO was reduced to CH and C H in the system even
tion was observed in the system containing Cu , its G value
2
4
2
6
-
4
without the irradiation. After the irradiation CO was increased
was about 10 . It is well known that various active species
to about 60–80 ppm, but both CH and C H were decreased in
containing H such as H·, H, ·OH, and H are easily generated in
4
2
6
2
1
4
comparison with those before the irradiation. The increase of
CO in the system with Fe powder comparing with that without
Fe powder suggests that Fe powder has a little enhancing effect
in the CO reduction to CO. The decrease of CH and C H
6
γ ray irradiated water. The production of CH is expected
4
from the reaction of these active species with CO or reduction
2
product CO. However, as stated above CH will be decom-
4
posed meanwhile in the irradiation of γ ray. The experimental
results suggest that the decomposition might be more easier
than the production. Accordingly, some inhibitors to the
decomposition reaction might be required to the production of
CH4.
2
4
2
after the irradiation might be due to the decomposition effect of
the γ ray, by which many organic compounds are known to be
decomposed.14 Therefore, in the system with Fe powder, CH4
and C H were not produced by the irradiation of γ ray. Its
2
6
detail will be reported elsewhere.
In addition to Fe powder, other chemicals of Fe (Fe , Fe ,
The CO concentration was increased with both the irradia-
2+
3+
tion time and the dose rate of γ ray. However, the CH concen-
4
2
+
Fe O , Fe O ), Cu (powders of Cu, CuCl and CuO, Cu ) and
tration seems to be independent of irradiation time, but
increased with the decrease of the dose rate. The details and the
reaction mechanisms will be reported later.
2
3
3
4
3
+
Al (Al powder, Al ) were also added into the CO bubbled
2
water to investigate their enhancing effects. The chemicals of
Cu and Al were tried since a Cu electrode and Al particles have
been reported to be efficient in the electrochemical reduction of
The authors thank Dr. T. Yamamoto and Dr. S. Okuda of
Osaka University for their helps in carrying out the experiments
4
15
CO2 and H gas evolution in γ ray irradiated water, respec-
2
6
0
tively. Furthermore, semiconductor particles (TiO , ZnS, and
using Co γ ray resource and related facility. The authors
would also thank Mr. S. Murata and Mr. Y. Iwasaki of Fukui
University for their help in the experiments.
2
CdS ) were also investigated since photocatalytic reduction of
1
6,17
CO has been reported.
Experimental results show that the
2
largest amount of CO and CH were produced in the system
4
containing Cu2+ in these chemicals. The Cu might act as a
2+
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2
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the other hand, most of these chemicals have little enhancing
2
(
effect in CH production.
4
Other metal ions such as Ni2+, Co2+, Mn2+, Zn2+, Ag+,
2+
+
2+
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4
5
2
+
that of Cu . In addition to metal ions, reductive inorganic
6
7
8
9
2
-
-
anions SO3 and NO2 were also investigated. Carbon dioxide
1
0
is known to be decomposed by γ ray as follows,
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1
1
1
0
1
2
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2
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Phys. Chem., 44, 349 (1994).
2
2
-
2+
in the system with SO3 is larger than that containing Cu .
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stable compound such as SO4 would enhance the CO reduc-
14
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2-
2
1
5
tion efficiency.
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16
17 J. C. Hemminger, R. Carr, and G. A. Somorjai, Chem. Phys.
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2
+
2-
concentration of CO was detected when Cu and SO3 were