22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
In situ monitoring of the oxidation of adsorbed species on surfaces exposed to
plasma using FTIR and DRIFT
Z. Jia1, C. Barakat1, F. Thevenet2 and A. Rousseau1
1
LPP, Ecole Polytechnique, UPMC, Université Paris Sud, CNRS, Palaiseau, France
2
Université Lille Nord-de-France & Mines Douai, CE, F-59508 Douai, France
Abstract: We report here the use of FTIR (transmission) and DRIFT (reflectance) to
monitor adsorbed VOC and their oxidation onto catalytic surfaces such as CeO 2 . The
dynamic of adsorption under ozone flow is reported. Intermediates are identified.
Keywords: CeO 2 , VOCs decomposition, plasma-catalysis, FTIR, DRIFT
1. Introduction
Environmental issues and especially air pollution are
nowadays a major matter of concern. The numerous
pollutants involved and the low concentrations which
have to be treated represent a huge challenge. In particular,
the cleaning of indoor air requires a low energetic cost
technique with the lowest possible by-products emission.
A dielectric barrier discharge with coaxial geometry is
used to generate highly oxidizing species at low energetic
cost. The dielectric barrier distributes the microdischarges throughout the discharge volume initiating the
chemical reactions by reactive species like ions, radicals
and activated molecules.
Alternatively to the conventional and widely studied
plasma catalyst-coupling, a sequential approach is put into
place, where pollutants are first adsorbed on a
porous/catalytic material and surface regeneration is
followed by switching on the plasma for a brief period.
We evaluate the performances of a two-stage
configuration, with the catalyst placed downstream from
the discharge zone, limiting ozone as the main oxidative
species able to interact with the material surface.
In our previous studies, different parameters are
investigated, such as the injected power, the relative
humidity [1] , the type of VOC and the type of catalytic
materials. In-plasma and post-plasma configuration are
studied [2-3]. The gas phase and the adsorbed phase are
independently monitored using two infrared systems. The
analysis of the chemical composition of the gas phase is
performed using an FTIR cell and the in situ surface
analysis of adsorbed species and intermediates is followed
using a DRIFTS cell [3]. We report here the use of FTIR
(transmission), DRIFT (reflectance) to monitor adsorbed
VOC and Sorbent TRACK “direct in situ monitoring of
adsorbed species on the surface under plasma
exposure” and their oxidation onto catalytic surfaces such
as CeO 2 .
of the gas phase composition; and (2) Diffuse Reflectance
Infrared Fourier Transform Spectroscopy for the in-situ
analysis of the adsorbent/catalyst surface, as shown in
Fig.1.
CeO 2 catalyst is placed downstream a dielectric barrier
discharge and is subsequently exposed to ozone
considered as the main oxidative species generated by
non-thermal plasma and able to interact with the material
surface at room temperature.
Figure 1. Schemes of the experimental setups: (a) as
phase studies using FTIR analysis and (b) surface studies
using DRIFTS analysis.
3. Results
The acetone breakthrough/flushing curve obtained is
reported in Fig. 2. The amount of acetone irreversibly
adsorbed on CeO 2 is 3.2 ± 0.3 µmol/m2.
2. Experimental set-up
The oxidation of acetone is monitored using two
parallel and complementary infrared diagnostics: (1)
Fourier Transform Infrared Spectroscopy for the analysis
O-5-4
1
Acetone concentration (ppm)
200
Breakthrough cuve
150
100
50
Flushing
0
Mixting cuve
0
50
100
150
200
250
Time (min)
Furthermore, the absorption displayed at 1427cm-1
which is strengthened with acetone exposed time is most
likely assignable to δCH vibrations in –CH2-C=O groups
of diacetone alcohol (DAA)-like species. This δCH
absorption, together with the ν(C=O) absorption at 1628
cm-1 may imply formation of DDA species.
We show in Figure 4 the normalized logarithmic peak
areas of the acetone ((ν (CH) at 2970 cm-1) absorption
band as a function of time for different ozone
concentration.
Figure 2. Acetone breakthrough curve and flushing curve
monitored on CeO2 surface.
Fig.3 show a DRIFT spectra of dehydrated ceria
powder (28 mg of ceria powder with 1h pretreatement at
673K: BET surface ~ 50 m2/g) with dry air and exposed
to 200 ppm acetone for 60min.
Figure 4. Plots of the normalized logarithmic peak areas
of the acetone ((ν (CH) at 2970 cm-1) absorption band as
a function of time for different ozone concentration.
4. Acknowledgement
The authors gratefully acknowledge Plas@Par,
ALKOTHERM and DGA for financial support
Figure 3. DRIFT spectra in the (A) 4000-2500 cm-1 and
(B)2000-1200 cm-1 range of the sample CeO2 under
500ml/min in dry air at 300K.
5. References
[1] L. Sivachandiran , F. Thevenet , P. Gravejat , A.
Rousseau, Chemical Engineering Journal 214 (2013) 17–
26
[2] L. Sivachandiran , F. Thevenet, A. Rousseau, Plasma
Chemistry & Plasma Processing, (2013)
[3] C. Barakata, P. Gravejat, O. Guaitella, F. Thevenet, A.
Rousseau, Applied Catalysis B: Environmental 147 (2014)
302– 313
With the increase of acetone absorption time, The v(CH)
(2971 and 2928 cm-1) and ν(C=O) (1693cm-1)
respectively shift to 2964, 2918 and 1674 cm-1. These
shifts together with the new bandes at 2932, 2873, 1674,
1628, 1578, 1470, 1427 lead support to the acetone Aldol
condensation species (mesityl oxide). In addition, the
very broad band appearing between 3609 and 3524 cm-1
can be assigned to adsorbed H 2 O, the products of acetone
aldol-condenstation reaction followed by dehydration.
2
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