Toluene decomposition by DBD-type plasma combined with metal oxide catalysts supported on ferroelectric materials

Article abstract of DOI:10.1166/jnn.2013.7001

We investigated toluene decomposition with a single-stage plasma catalytic system operated at atmospheric pressure and working at reduced temperature (T <75 °C), where a synergistic catalyst was integrated on ferroelectric BaTiO₃ beads with a high dielectric constant. The catalyst species were characterized by FE-SEM and XPS before and after the experiment. The MnO₂/BaTiO₃ catalyst showed high stability in igniting plasma during destruction of toluene for 230 hours in a lifetime test. Copyright

Full text of DOI:10.1166/jnn.2013.7001

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Nanoscience and Nanotechnology
Vol. 13, 4146–4149, 2013
Toluene Decomposition by DBD-Type Plasma
Combined with Metal Oxide Catalysts
Supported on Ferroelectric Materials
Jin Guk Jeong1ꢀ2, Hyeong Seok Lee1ꢀ3, Youngjin Kang4,
Ki Bong Lee2ꢀ∗, and Jung Whan Yoo1ꢀ∗
1Eco-Composite Materials Center, Korea Institute of Ceramic Engineering and Technology, Korea
2Department of Chemical and Biological Engineering, Korea University, Seoul, 153-801, Korea
3Department of Chemical Engineering, Hanyang University, Seoul, 153-801, Korea
4Department of Chemistry and Division of Science Education, Kangwon National University, 153-801, Korea
We investigated toluene decomposition with a single-stage plasma catalytic system operated at
atmospheric pressure and working at reduced temperature (T < 75 ꢀC), where a synergistic catalyst
was integrated on ferroelectric BaTiO3 beads with a high dielectric constant. The catalyst species
were characterized by FE-SEM and XPS before and after the experiment. The MnO2/BaTiO3 cata-
lyst showed high stability in igniting plasma during destruction of toluene for 230 hours in a lifetime
test.
Keywords: Plasma Catalytic System, Ferroelectric Materials, VOC, Catalyst.
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1. INTRODUCTION
the most attention because of its high ozone decompo-
sition activity.1 Moreover, ferroelectric materials, such as
packed beads, are key the proper functioning of plasma
catalytic systems.6 The transported charge that leads to
excitation, dissociation, or ionization in a plasma reaction
is proportional to the dielectric constant of ferroelectric
materials. Rico et al. described a hybrid catalytic-DBD
plasma reactor for the steam reforming of methanol.10
They demonstrated that copper–manganese oxide catalysts
on ferroelectric material interacted synergistically and pro-
posed this system as an efficient alternative to conven-
tional catalytic reactions for the reforming of methanol.
However, a major disadvantage of this configuration is the
faster deactivation of the catalyst as a result of carbona-
ceous deposits.6
Control of volatile organic compound (VOC) emission
has become an important issue in that VOCs are not
only hazardous to human health, but also harmful to
the environment.1ꢀ2 Conventional techniques used to
decompose VOCs include adsorption and thermal and
thermo-catalytic oxidation.3 An alternative method for
VOC decomposition is non-thermal plasma (NTP) gener-
ated at atmospheric pressure, which is an energy-saving
approach.2–5 NTP is a combination of energetic elec-
trons, radicals, ions, and excited active species as well as
radiation.7 In NTP, the electrical energy is primarily used
to produce energetic electrons without heating. However,
NTP abatement of VOCs shows low selectivity to total oxi-
dation (CO2 and H2O) and may result in the formation of
undesirable and sometimes toxic by-products.7 To improve
the efficiency of the NTP technique, catalysts can be incor-
porated into the plasma.8 In the catalytic plasma technique,
there is synergy between plasma excitation and catalysis
when the catalyst is placed in the discharge.3
In this study, we investigated toluene decomposition
using a single-stage plasma catalytic system operated at
atmospheric pressure and reduced temperature (T < 75 ꢀC),
where the synergetic catalyst was integrated on ferroelec-
tric BaTiO3 beads with a high dielectric constant.
Numerous catalysts have been studied in this context.
The catalysts are typically metal oxides such as MnO2,
SiO2, Al2O3, Co3O4, TiO2, Ag2O, and CuO, among others.
Among these various metal oxides, MnO2 has attracted
2. EXPERIMENTAL DETAILS
The dielectric materials used were alumina (Al2O3), SiO2
glass, and barium titanate (BaTiO3) beads purchased from
Alfa Aesar. Metal oxide catalysts were prepared by mix-
ing an aqueous solution of copper nitrate, cobalt nitrate,
∗Authors to whom correspondence should be addressed.
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doi:10.1166/jnn.2013.7001

Jeong et al.
Toluene Decomposition by DBD-Type Plasma
and manganese nitrate (purchased from Aldrich) to obtain
5 wt% solution. After 1 hour of stirring, the solutions were
evaporated, dried, and then calcined at 500 ꢀC for 4 h. The
catalysts were characterized by field emission scanning
electron microscopy (FE-SEM) and X-ray photoelectron
spectroscopy (XPS).
NTP reaction system alone. Toluene conversion increased
from zero to a certain value at a well-defined applied volt-
age for each packed material. In the case of plasma alone
(without packed materials), increasing the input voltage
from 4 to 7 kV increased the toluene conversion rates,
which reached 25% at 5.5 kV and 78% at 7 kV. The
toluene conversion rate was similar to that of Al2O3, SiO2
glass beads, and plasma alone at all voltages. However,
the conversion of toluene using BaTiO3 beads with high
dielectric constant (ꢁ ≈ 1,500) as a ferroelectric material
was enhanced compared to that of SiO2 glass (ꢁ ≈ 5) and
Al2O3 (ꢁ ≈ 9) beads at the same voltage. As reported
previously, the higher the relative dielectric constant, the
higher the conversion efficiency.10
We next investigated the synergistic catalytic perfor-
mance of MnO2, Co3O4, and CuO on ferroelectric BaTiO3
beads with respect to toluene conversion. Toluene con-
version as a function of applied voltage is presented in
Figure 2. Toluene conversion increased monotonically up
to 6 kV and MnO2/BaTiO3 was the most active of all the
catalysts tested with complete toluene conversion achieved
at 5 kV. The toluene conversion efficiency of the catalysts
at 5 kV was as follows: MnO2/BaTiO3 > Co3O4/BaTiO3 >
CuO/BaTiO3 > BaTiO3 · MnO2 is a metal oxide catalyst
and has potential activity in redox reactions.8ꢀ11 Metal ions
(Mnn+), oxides (O2−) and defect sites of various oxidation
states are exposed on the surface of MnO2 particles.
The plasma-catalyst reactor has been used in the present
work to incoporate the catalyst inside the plasma discharge
zone. The reactor consisted of a stainless steel high-voltage
electrode with a diameter of 16 mm and a quartz tube
with an outer diameter and wall thickness of 22 mm and
1 mm, respectively. The gap distance (2 mm) between the
electrodes was filled with 50 g of catalyst (beads) with an
average size of 1 mm. The gas flow rate was maintained
at 1 L/min with 100 ppm toluene in air balance. An AC
power supply with a voltage that could be varied between
1 and 20 kV and a frequency that could be carried between
10 and 20 kHz was used to ignite the plasma. The con-
centration of toluene in the outlet of the reactor at each
applied voltage was measured with a gas chromatograph
(Agilent 6890 N).
3. RESULTS AND DISCUSSION
We initially investigated the effect of beads as a pack-
ing material between the electrodes. Firstly, to evaluate
the effects of the Al O , SiO glass, and BaTiO beads
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2
3
3
MnO2 also has various degrees of coordination unsatu-
on toluene decomposition, tolueneIwPa:s5p.6a2ss.1ed55th.8ro2uOghn:thMe on, 06 Jun 2016 20:22:50
ration, and it has acid and base properties. Therefore, the
Copyright: American Scientific Publishers
packed reactor without igniting the plasma discharge. No
synergistic effect of manganese oxide and BaTiO3 with
regard to the acceleration of the decomposition of O3 to
active oxygen species facilitated toluene conversion and
was energy-efficient due to the low amount of input volt-
age consumed by the plasma catalytic system.
conversion of toluene was detected under our experimen-
tal conditions. Toluene conversion as a function of average
applied voltage with packed Al2O3, SiO2 glass, BaTiO3
beads, or plasma alone is shown in Figure 1. Toluene
was mainly decomposed to CO2 and CO gaseous prod-
ucts. Small amounts, less than 1% hydrocarbon or inter-
mediate oxidation products were detected in the effluent
gas. The combined reaction system with plasma and cata-
lyst enhanced total oxidation product selectivity rather than
The long-run performance of the synergistic MnO2/
BaTiO3 catalyst inside the plasma discharge zone operated
at a constant voltage of 5.0 kV for 230 h is shown in
Figure 3. The fact that this process was driven at low tem-
ꢀ
peratures (maximum temperature of 75 C) indicates that
Fig. 1. Toluene conversion as a function of the average applied voltage
Fig. 2. Toluene conversion as a function of average applied voltage for
for packed Al2O3, SiO2 glass, BaTiO3 beads, or plasma alone.
MnO2, Co3O4, or CuO on the ferroelectric BaTiO3 beads.
J. Nanosci. Nanotechnol. 13, 4146–4149, 2013
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Toluene Decomposition by DBD-Type Plasma
Jeong et al.
plasma catalytic reactor than before the reaction. Zhang
et al. demonstrated that glow discharge treatment leads to
higher and more stable dispersion of active species over
the support.10 Furthermore, we found that the catalyst we
used had good activity and stability, consistent with previ-
ous studies.
The chemical states of MnO2/BaTiO3 before and after
the plasma catalytic reaction for 230 h were examined by
XPS analysis. The Mn 2p and O 1s XPS spectra before
and after the reaction are shown in Figures 5(a) and (b),
respectively. The binding energy of the Mn 2p peak was
determined to be at 642 and 653 eV for both catalysts,
indicating that the +2 and +4 oxidation states were well
preserved after the reaction (Fig. 5(a)).2ꢀ5 The binding
energies of the O 1s peaks at 530 (O2−) and 533 eV
(OH−) of both catalysts were also preserved after the reac-
tion. However, the O 1s peak at 530 eV had a lower
energy after the reaction. It has been shown that ultrafine
particle catalysts have a less perfect crystal lattice when
a large number of oxygen vacancies are present, which
induces higher catalytic activity.12 Some unusual chemi-
cal activities have been reported for cases where plasma
species were involved in the catalyst surface reactions,
which has motivated efforts to apply plasmas directly to
obtain more effective catalysts.13–14 We demonstrated that
plasma enhanced the dispersion of the active species of
Fig. 3. The lifetime performance of the MnO2/BaTiO3 catalyst in a
plasma catalytic reaction at 5.0 kV for 230 h.
almost all toluene was converted by the plasma catalytic
reaction without the requirement for additional external
heating. As seen from the figure, the MnO2/BaTiO3 cat-
alyst maintained the same activity throughout the course
of the reaction. This confirms the long-run stability of the
MnO2/BaTiO3 catalyst in plasma during the destruction of
VOCs.6
SEM images of MnO2/BaTiO3 before and after the
plasma catalytic reaction at 5.0 kV for 230 h are shown in
Figure 4. The MnO2 particles on the BaTiO3 were much
smaller and more dispersed after the 230 h reaction in the
MnO and improved the stability as well as the activity of
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2
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the catalysts.
Copyright: American Scientific Publishers
Fig. 4. The SEM images of MnO2/BaTiO3 for 230 h; before (a) and
Fig. 5. The XPS spectra of MnO2/BaTiO3 before and after reaction for
after reaction (b).
230 h; (a) Mn 2p spectra and (b) O 1s spectra.
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Jeong et al.
Toluene Decomposition by DBD-Type Plasma
4. CONCLUSION
3. J. V. Durme, H. V. Langenhove, and J. Dewulf, Appl. Catal.
B-Environ. 78, 324 (2008).
We investigated toluene decomposition in a plasma cat-
alytic system where a catalyst was integrated on ferroelec-
tric BaTiO3 beads. The order of toluene conversion at 5 kV
was MnO2/BaTiO3 > Co3O4/BaTiO3 > CuO/BaTiO3 >
BaTiO3. In a lifetime test, the MnO2/BaTiO3 catalyst
showed high stability in igniting plasma during the
destruction of toluene for 230 hours.
4. H. H. Kim, H. Einaga, and A. Ogata, Appl. Catal. B-Environ. 46, 87
(2003).
5. N. B. Mandache, V. I. Parvulescu, and M. Magureanu, Appl. Catal.
B-Environ. 74, 270 (2007).
6. Ch. Subrahmanyam, A. Renken, and L. K. Minsker, Chem. Eng. J.
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Acknowledgment: This work was supported by Eco-
technopia 21 project of Korea Environmental Industry and
Technology Institute (KEITI).
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Received: 23 November 2011. Accepted: 4 May 2012.
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J. Nanosci. Nanotechnol. 13, 4146–4149, 2013
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