22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Development of fluidized spray plasma (FSP) device to deposit nanostructural
catalysts on ceramic beads
M. Nikravech, K. Baba and C. Lazzaroni
LSPM–CNRS, Institut Galilee, Université Sorbonne Paris Cité, Paris 13, Av. J. B. Clément, FR-93430 Villetaneuse,
France
Abstract: The Fluidized Spray Plasma is a new device to produce nanostructured catalysts
on the surface of ceramic beads from cheap and abundant starting precursors. The basic
principle of this method based on the association of plasma reactivity, the properties of
spray pyrolysis technique and those of fluidized bed reactors is described. Characteristics
of ZnO-Cu catalysts deposited on alumina beads’ surface are presented.
Keywords: catalysts, spray,pPlasma, fluidized bed, ZnO-Cu
1. Introduction
Nanomaterials are known to exalt chemical properties
that appear weakly on massif materials. The development
of new methods to elaborate nanostructured catalysts
materials is under focus across research programs to
develop high and new chemical reactivity. Several
methods, as metal organic chemical vapor deposition,
plasma enhanced chemical vapor deposition, using
plasma’s reactivity have been developed since decades.
These methods use, generally, the staring materials that
have high vapor pressure and that can be introduced into
the plasma reactor in the form of vapor. However,
metalorganic compounds are expensive and their handling
is delicate. Deposition of catalyst materials using low
vapor-pressure materials has been developed since
decades by various techniques such as sol-gel,
impregnation, polyol etc. Each method is adapted for
preparation of a specific range of materials. Spray
pyrolysis is another effective technique that allows the
elaboration of nano-powders by the use of precursors
(nitrates and chlorides), that are cheap and abundant but
having low vapor-pressure. In spray pyrolysis, the starting
material is injected in the form of an aerosol into a heated
reactor. The association of plasma reactivity with the
spray pyrolysis’ properties allowed to setup Spray Plasma
device to elaborate materials at relatively low (room)
temperature, on the surface of plane substrates [1, 2].
Nevertheless, fluidized beds are effective techniques to
deposit materials on the surface of granular ceramic
substrates. The association of plasma reactivity with spray
pyrolysis’s properties and those of fluidized bed permits
the elaboration of nano-catalysts on the surface of ceramic
beads. At our knowledge, such a process has not been yet
reported. In this paper, we aim to present this new method
based on the association of plasma’s reactivity with those
of spray pyrolysis to deposit catalyst materials on the
surface of alumina beads.
The mechanisms of nitrate aerosol transformation in
low-pressure plasma are described in reference [3]. To
resume, during their injection in a vacuum reactor the
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aqueous aerosol evaporates leading to reduce the radius of
droplets. Oxygen and water’s vapor around the droplets,
submitted to the reactivity of electrons in plasma, results
in forming highly oxidant O° and OH° radicals. Then,
these species diffuse inside the droplets to transform
nitrates and chlorides precursors into oxides. The sprayed
droplets during their fly inside the fluidized bed are
projected on the surface of fluidized beads. As each
droplet contains almost few molecules of precursors, the
projected droplets form a nanostructured layer that is
transformed to oxide by the reactive species of plasma.
2. Experimental setup
In order to produce catalysts on the surface of ceramic
granular substrates, a new device, named Fluidized Spray
Plasma (FSP) process, was developed. This process,
presented in Fig. 1, is a variant of Spray Plasma device
described in [2]. The FSP device is composed of
3 distinguished parts: (i) fluidized bed plasma reactor, (ii)
spray and injection device, (iii) vacuum pump and
pressure gauge. The fluidized bed plasma reactor is
constituted of an external cylindrical quartz tube (50 mm
in diameter and 500 mm in length). To produce plasma,
an inductive coil rolled around this tube permits the
coupling of the electromagnetic power supplied by a
radiofrequency generator (Hüttinger Trumpf Qinto 3013,
3 kW, 13.5 MHz). A second concentric quartz tube of
30 mm in diameter, containing the fluidized particles, put
in the center of plasma close to the inductive coils.
A carrier gas composed of argon and oxygen (95%-5%),
circulating inside this inner tube, allows fluidizing the
solid beads. In this work, two types of beads were tested
successfully: spherical alumina beads of 2 mm in
diameter offered by SASOL CO. and cylindrical alumina
with 3 mm in length and 2 mm in diameter. Mass flow
meters (Bronkhorst) were used to measure and control the
gas flows. An ultrasonic nebulizer (MGA 1000 frequency
1 MHz) was used to transform the precursor solution to a
spray of droplets with 1 to 5 micrometers in diameter. The
precursor solution is composed of solid zinc nitrate
1
Zn(NO 3 ) 2 99.999 (Aldrich), solid cupper nitrate
Cu(NO 3 ) 2 (Aldrich) and bi-distilled water. The
composition of this solution is an important factor to fix
the stoichiometry of the final deposit. Argon (flow rate
200 mL/min) is used to form the fluidized bed with
alumina beads. The spray is injected into the reactor
through a conditioning device equipped with a pulsed
valve insulating the nebulizer from the plasma chamber.
The opening pulse of the valve is programmed to admit
the spray inside the reactor during one second. At this
time, the flow rate reaches a sufficient value to fluidize
the beads particles inside the plasma. A pump (ADP 81
Alcatel) permits to vacuum the reactor at 50 Pa. The
pressure is measured by a MKSA Baratron pressure
sensor.
Figure 2. SEM photograph of ZnO-Cu deposited by
Fluidized Spray Plasma technique on alumina pellet’s
surface.
Figure 3. X-ray diffraction pattern of ZnO layers
deposited by Spray Plasma method.
Figure 1. Spray PlasmaFluidized bed experimental
setup.
3. Characteristics of ZnO-Cu catalysts’ layers
Aqueous solutions of 0,1 M Zn(NO 3 ) 2 containing
Cu(NO 3 ) 2 equivalent to 10% and 20% weight of Cu (II)
were prepared to deposit ZnO-Cu10% and ZnO-Cu20%
catalysts. Sets of 8 grams of commercial alumina (Alpha)
cylindrical beads of 3 mm in diameter and 5 mm in length
were put in the Fluidized Spray Plasma reactor. The
precursor spray was projected by the bottom of the
fluidized bed during 30 minutes. The plasma power was
fixed at 300 W. The particles were then annealed at
400 °C under argon vacuum 1 mbar for 2 hours.
After these treatments a green-blue color of the layer on
the surface of beads, witnessing the effective covering of
alumina beads with ZnO-Cu, was observed. The SEM
micrograph of the layers on the alumina beads’ surface,
presented on Fig. 2 shows the presence of particles with
diameter less than 100 nm. Grazing X-ray diffraction of
ZnO layers deposited on plan glass substrate, Fig. 3,
shows that the deposits are well structured and the ZnO
crystallites are c-axe’s oriented.
2
The MET photograph of these structures, presented on
Fig. 4, shows that the mean diameter of crystallites is
around 20 nm and that is confirmed by Williamson-Hall
method [4].
Figure 4. TEM photograph of ZnO layers deposited by
Spray Plasma method.
The temperature programmed reduction (TPR) analysis
of the deposits was carried out between 40°C and 800 °C.
The results depicted for several samples of ZnO- Cu show
the presence of two maxima at 250 °C and 460 °C,
corresponding to two types of Cu-O bonds, Fig. 5. The
first maximum corresponds to CuO and the second one to
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Cu 2 O oxides. Nevertheless, it is noteworthy to highlight
that ZnO-Cu, deposited by impregnation method (carried
out during this study), presented just one maximum at 250
°C, pointing out that the elaboration’s method plays great
influence on the quality of deposited materials.
These catalysts were tested during dry reforming of
methane in plasma-catalysts reactor. The results,
presented in a second paper in ISPC-22, showed that the
conversion rates of CH 4 and CO 2 reach respectively 60%
and 45%. Main gas products are CO, H 2 C 2 H 4 , C 2 H 6 .
Liquid products were detected. The analysis of these
liquids revealed the production of methanol, ethanol,
acetic acid, n-butanone, acetone as main liquid products.
Acknowlegments
Acknowoledgements are due to Programme Energie
CNRS-2009, to Commissariat Général à l’Investissement
(CGI) and to Agence National pour la Recherche (ANR).
Figure 5. Temperature programmed reduction (TPR)
analysis of ZnO-Cu catalysts synthetized by Fluidized
Spray Plasma process. A1 (ZnO-10%Cu, plasma gas : Ar)
reduced in H 2 flow at 200 °C for 2 hours , B1 (ZnO10%Cu, plasma gas : Ar), B2 (ZnO-10%Cu, plasma gas :
Ar + 20% O 2 ), B3 (ZnO-20%Cu, plasma gas : Ar).
The ICP analysis of samples measuring the percentage
of Cu and Zn, presented on Table 1, revealed the low
concentrations of these elements, compared to alumina
concentration (the layers are formed mainly on the surface
of alumina beads). The results show that the ratios of
Cu/Zn are about 13% and 21%, respectively obtained
with the precursor solutions containing 10% and 20 % Cu
nitrate. These results show that the catalyst’s composition
corresponds globally to the composition of the precursor’s
solution. However, the X-ray elemental analysis,
performed on several points of the beads’ surface, had
revealed inhomogeneous Cu/Zn ratios.
References
[1] Miralai, S. F., Avni, R., Franke, E., Morvan, D.,
Amouroux, J., & Nickel, H. (1995). European patent No
9500518. Munich, Germany: European Patent Office.
[2] Mehrdad Nikravech, Spray Plasma device, a new
method to process nanostructured layers. Application to
deposit ZnO thin layers. Journal of Nanoscience and
Nanotechnology, 10, 1171–1178 (2010). DOI:
10.1166/jnn.2010.1870.
[3] Mehrdad Nikravech, Kamal Baba, Bernard
Leneindre, Frédéric Rousseau, Role of reactive species in
processing materials at laboratory temperature by spray
plasma devices, Chemical Papers 66 (5) 502–510 (2012)
DOI: 10.2478/s11696-012-0158-y
[4] K. Baba, C. Lazzaroni, O. Brinza, M. Nikravech
Effect of zinc nitrate concentration on structural and
optical properties of ZnO thin films deposited by Spray
Plasma device. Thin Solid Films 558 (2014) 62–66.
Table 1. ICP analysis of deposit catalysts :A1 (ZnO10%Cu, plasma gas : Ar) reduced in H 2 flow at 200 °C
for 2 hours , B1 (ZnO-10%Cu, plasma gas : Ar), B2
(ZnO-10%Cu, plasma gas : Ar + 20% O 2 ), B3 (ZnO20%Cu, plasma gas : Ar).
Samples : wt% of Cu/Zn
in precursor
11%
B1
Cu %
Zn %
0,018
0,129
Cu/Zn in
catalysts
14%
B2
11%
0,022
0,173
13%
B3
25%
0,02
0,093
21%
A1
11%
0,014
0,102
14%
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