Toluene total oxidation over Pd and Au nanoparticles supported on hydroxyapatite

Article abstract of DOI:10.1016/j.crci.2015.07.015

The total oxidation of toluene was carried out in a series of catalytic systems composed of either palladium or gold, as active phase, with hydroxyapatite as supports. The influence of different parameters on the catalytic reactivity was investigated: the type of support, the active phase content, the preparation method, and the nature of the active phase. Hydroxyapatite supports, impregnated by the active phase, showed better reactivities than that of the classical alumina one. Moreover, low palladium content (0.25 wt%) is enough to get high toluene conversions at low temperatures. Two preparation methods were used to introduce the active phase on the support: the conventional wet impregnation and the nanoparticle deposition achieved by impregnation of a colloidal suspension of the noble metal using the surfactant HEA16Cl. Introducing palladium by either of these methods leads to similar catalytic efficiencies. In addition to this, palladium is much more active than gold, gold was not probably present under the form of highly dispersed nanoparticles. X-ray Photoelectron Spectroscopy (XPS) evidenced PdO presence on the surface of all our catalysts. Palladium impregnated on apatite by conventional method showed an improvement of catalytic reactivity after 13 h under reacting mixture, probably because of Pd(0) formation besides PdO. As a result and after a literature survey, our catalysts could be classified among the most reactive systems towards total oxidation of toluene.

Full text of DOI:10.1016/j.crci.2015.07.015

C. R. Chimie xxx (2016) 1e13
Contents lists available at ScienceDirect
Comptes Rendus Chimie
www.sciencedirect.com
Full paper/M eꢀ moire
Toluene total oxidation over Pd and Au nanoparticles
supported on hydroxyapatite
Oxydation totale du tolu ꢁe ne sur Pd et Au support ꢀe s sur hydroxyapatites
Dayan Chlala a, b, Madona Labaki , Jean-Marc Giraudon , Olivier Gardoll ,
a
,
*
b
b
Audrey Denicourt-Nowicki , Alain Roucoux c , Jean-François Lamonier
Laboratoire de Chimie-Physique des Mat ꢀe riaux (LCPM)/PR2N, Universit ꢀe Libanaise, Fanar, BP 90656 Jdeidet El Metn, Lebanon
c
,
d
,
d
b
a
b
Unit ꢀe de Catalyse et de Chimie du Solide, UMR CNRS 8181, Universit ꢀe de Lille 1, Sciences et Technologies (USTL), 59655 Villeneuve-
d'Ascq cedex, France
c
ꢀ
Ecole Nationale Sup ꢀe rieure de Chimie de Rennes, UMR CNRS 6226, 11, all ꢀe e de Beaulieu, CS 50837, 35708 Rennes cedex 7, France
Universit ꢀe Europ ꢀe enne de Bretagne, France
d
a r t i c l e i n f o
a b s t r a c t
Article history:
The total oxidation of toluene was carried out in a series of catalytic systems composed of
either palladium or gold, as active phase, with hydroxyapatite as supports. The influence of
different parameters on the catalytic reactivity was investigated: the type of support, the
active phase content, the preparation method, and the nature of the active phase.
Hydroxyapatite supports, impregnated by the active phase, showed better reactivities than
that of the classical alumina one. Moreover, low palladium content (0.25 wt%) is enough to
get high toluene conversions at low temperatures. Two preparation methods were used to
introduce the active phase on the support: the conventional wet impregnation and the
nanoparticle deposition achieved by impregnation of a colloidal suspension of the noble
metal using the surfactant HEA16Cl. Introducing palladium by either of these methods
leads to similar catalytic efficiencies. In addition to this, palladium is much more active
than gold, gold was not probably present under the form of highly dispersed nanoparticles.
X-ray Photoelectron Spectroscopy (XPS) evidenced PdO presence on the surface of all our
catalysts. Palladium impregnated on apatite by conventional method showed an
improvement of catalytic reactivity after 13 h under reacting mixture, probably because of
Pd(0) formation besides PdO. As a result and after a literature survey, our catalysts could be
classified among the most reactive systems towards total oxidation of toluene.
Received 8 June 2015
Accepted 30 July 2015
Available online xxxx
Keywords:
VOC catalytic oxidation
Toluene
Hydroxyapatite
Palladium
Gold
Nanoparticles
Colloidal suspension
©
2016 Acad eꢀ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
r e s u m e
Mots-cl ꢀe s:
Oxydation catalytique du COV
Tolu eꢁ ne
Hydroxyapatite
Palladium
L’oxydation totale du tolu eꢁ ne a eꢀ t eꢀ eꢀ tudi eꢀ e sur la phase active palladium ou or support eꢀ e
sur differents supports de type hydroxyapatite. L’influence de differents parametres sur la
r eꢀ activit eꢀ catalytique a eꢀ t eꢀ eꢀ tudi eꢀ e : le type de support, la teneur de la phase active, la
m eꢀ thode de pr eꢀ paration et la nature de la phase active. Les supports hydroxyapatite ont
montr eꢀ de meilleures performances que le support classique alumine. De plus, une teneur
en palladium de 0,25 % en masse est suffisante pour obtenir des conversions de tolu eꢁ ne
eꢀ lev eꢀ es aꢁ de faibles temp eꢀ ratures. Deux m eꢀ thodes de pr eꢀ paration ont eꢀ t eꢀ utilis eꢀ es pour
ꢀ
ꢀ
ꢁ
Or
Nanoparticules
Suspension colloïdale
*
Corresponding author.
E-mail addresses: dayanechlela@hotmail.com (D. Chlala), m.labaki@ul.edu.lb (M. Labaki), jean-marc.giraudon@univ-lille1.fr (J.-M. Giraudon), olivier.
gardoll@univ-lille1.fr (O. Gardoll), audrey.denicourt@ensc-rennes.fr (A. Denicourt-Nowicki), alain.roucoux@ensc-rennes.fr (A. Roucoux), jean-francois.
lamonier@univ-lille1.fr (J.-F. Lamonier).
http://dx.doi.org/10.1016/j.crci.2015.07.015
1
631-0748/© 2016 Acad eꢀ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

2
D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
introduire la phase active : l’impr eꢀ gnation par voie humide conventionnelle et le d eꢀ p o^ t de
nanoparticules par impr eꢀ gnation d’une suspension colloïdale du m eꢀ tal noble en utilisant le
HEA16Cl comme surfactant. L’introduction du palladium par l’une ou l’autre de ces
m eꢀ thodes conduit aꢁ des performances catalytiques similaires. Les r eꢀ sultats obtenus ont
montr eꢀ que le palladium est plus r eꢀ actif que l’or, l’or ne se trouvant pas, probablement,
sous forme de nanoparticules hautement dispers eꢀ es. L’ eꢀ tude par spectroscopie de
photo eꢀ lectrons induits par rayons X (SPX) a r eꢀ v eꢀ l eꢀ l’existence en surface de la seule esp eꢁ ce
PdO sur tous nos catalyseurs. Le syst eꢁ me palladium impr eꢀ gn eꢀ sur le support
hydroxyapatite par m eꢀ thode conventionnelle a montr eꢀ une augmentation de la conversion
du tolu eꢁ ne apr eꢁ s 13 h sous flux r eꢀ actionnel, probablement suite ꢁa la formation d’esp eꢁ ces
Pd(0) et leur coexistence avec PdO. Finalement, nos syst eꢁ mes catalytiques se sont av eꢀ r eꢀ s
e^ tre parmi les meilleurs parmi ceux eꢀ tudi eꢀ s dans la litt eꢀ rature portant sur l’oxydation
totale du tolu eꢁ ne.
©
2016 Acad eꢀ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
also have base and acid sites at the same time [34e36].
These properties make them good candidates to be used as
In the last decades, the drastically increasing
catalysts [37,38] or catalytic supports. Stoichiometric Hap
(Hap-S) has the chemical formula Ca10(PO (OH) where
the ratio Ca/P is of 1.67. Calcium deficient Hap (Hap-D) has a
Ca/P ratio less than 1.67 (Ca10ꢀx(HPO (PO
0 < x ꢁ 1), and carbonate-rich hydroxyapatite (Hap-E)
(Ca10ꢀyNa [(PO ][(OH)2ꢀ2x(CO ]) has Ca/P
ratio higher than 1.67.
To date, few studies [24,30,39e42] investigated Hap as a
catalyst or catalyst support for total VOCs oxidation. Aellach
et al. [30] assessed the effect of the stoichiometry of apatite
support (Hap-Sand Hap-D), and thatof the synthesis method
(coprecipitation and impregnation) on Co-Hap materials
performances towards the total oxidation of methanol. Wet
impregnation of cobalt on deficient Hap support (Hap-D)
leads to better catalytic results as a consequence of the better
environmental consciousness urged scientists to search for
more efficient methods to reduce pollutants. Volatile
Organic Compounds (VOCs), which are emitted by various
industrial processes and automotive exhausts, are the main
class of air pollutants [1] because of their harmful effects on
man’s health and environment [1,2]. Among the various
technologies available for VOCs abatement, especially for
low pollutant concentrations (<1%), catalytic oxidation is
cheaper and very efficient [2,3]. It consists of a complete
oxidizing of VOCs into carbon dioxide and water. By shifting
the temperature required for conventional thermal
incineration to lower values, this technology saves energy
as well as it minimizes the formation of harmful by-
products [1,2]. Therefore, highly active catalysts which
work at lower temperatures are required.
4
)
6
2
4
)
x
4
)6ꢀx(OH)2ꢀx,
y
4
)
6ꢀy(CO
3
)
y
3
)
x
a
3 4
reducibility of Co O species. Conversely, Nishikawa et al.
Two groups of catalysts were widely used for the
oxidation of VOCs: noble metals (Pt, Pd, Rh, and Au) [4,5]
and transition metals (Mn, Co, Cu, Fe, and Ni) [6e10]. In
general, the catalytic activity of noble metals is higher than
that of transition metals [11e14]. Out of all noble metals,
Pd-based catalysts have been studied and showed high
activity, at relatively low temperatures, and selectivity
[39] found that stoichiometric Hap is more active than the
deficient one in toluene, ethyl acetate and iso-propanol
oxidative decomposition because of the higher quantity of
electrons trapped in vacancies, proved by Electron
Paramagnetic Resonance (EPR), which could be responsible
for the oxygen activation that oxidizes VOC. Xu et al. [40]
reported the adsorption and activation of formaldehyde by
2þ
towards CO
compounds (VOCs) with a high tolerance to moisture
15e20]. Therefore, they are promising catalysts for
2
2
and H O in the oxidation of volatile organic
hydroxyl groups bonded with the Ca
of the
hydroxyapatites. Sun et al. [41] confirmed that a higher
hydroxyl group content in Hap leads to better catalytic
conversions in formaldehyde oxidation since interaction
between Hap and formaldehyde was increased. Wang et al.
[24] showed that gold supported on hydroxyapatites
are highly active and stable catalysts for benzene and
formaldehyde oxidation and that hydroxyapatites stabilized
nano-gold particles via interaction with phosphate (at
[
practical applications. After the study done by Haruta [21],
supported gold catalysts have attracted much attention.
Many studies reported high activity of Au-supported
catalysts in VOCs oxidation [22e27] even in the presence
of moisture [27]. However, it is found that the support
nature [6e8, 28e30] and the preparation method [23,
ꢂ
ꢂ
3
0e32] play an important role in the improvement in the
T < 400 C) and hydroxyl groups (at T < 600 C). Qu et al. [42]
investigated the oxidation of formaldehyde on Hap modified
by copper. They concluded that small dispersed Cu(II)
catalyst’s efficiency, particularly in oxidation reaction.
Hydroxyapatite (Hap) based materials have attracted
much interest to be used in a variety of applications
because they are safe, non-toxic [33], inexpensive, and
readily available in the natural environment. Furthermore,
these compounds present a high chemical and thermal
stability and a weak solubility in water. In addition to this,
they have a structural flexibility; all the elements can be
exchanged if the charge balance is maintained, and they
2þ
clusters, formed from the substitution of Ca on the surface,
mainly catalyzed formaldehyde oxidation.
To the best of our knowledge, no reports in the literature
deal with toluene catalytic oxidation over noble metals
supported on Hap. Thus, the aim of the present study is to
investigate the effect of (1) the support’s nature (different
Hap supports and alumina), (2) the noble metal content, (3)
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
3
ꢂ
the preparation method (wet impregnation or nanoparticle
deposition), and (4) the noble metal nature (Pd or Au), on
total oxidation of toluene. Toluene was used as a VOC
model molecule because it is an aromatic molecule
typically found in emissions of several processes such as
printing, pressing, and petrochemical industries [43,44],
and also in Diesel exhaust gases [45]. Moreover, toluene has
an important Photochemical Ozone Creation Potential
dried and then kept for about 20 h in an oven at 80 C, in
order to have a complete evaporation of the water. The
ꢂ
prepared catalysts were calcined at 400 C for 4 h under
air. They are designated as: Pd /HapY or Au /HapY, where
x x
x represents the weight percentage of noble metal,
x ¼ 0.25 and 1, and Y the type of hydroxyapatite support
(S, D or E).
2 3
Pd species was also impregnated on g-Al O support for
(
POCP ¼ 67) [46], and like benzene, it has a high chemical
comparison purposes, with x ¼ 0.4. The reference alumina
lifetime [44,47]. Thus, it is relevant to decrease its
emissions in the atmosphere.
support was supplied by Alfa Aesar (purity: 99.97%; surface
2
ꢀ1
area ¼ 72 m g ), and also used as received.
2
.1.2.2. Hydroxyapatite-supported noble metal (0) nano-
2
. Experimental
clusters.
2
.1.2.2.1. Preparation of Pd@HEA16Cl suspension. 106.4 mg
2
2
.1. Catalysts preparation
(
0.304 mmol, 2 equiv) of N,N-dimethyl-N-cetyl-N-(2-
hydroxyethyl) ammonium chloride salt (HEA16Cl) were
dissolved in 30 mL of water (solution A). HEA16Cl is a
surfactant composed of a lipophilic chain of 16 carbons
with chloride as counter-ion. 14.8 mg (0.391 mmol,
.1.1. Preparation of the support material
Hydroxyapatite (Hap) was used as a support and was
prepared by a coprecipitation technique according to the
following equation:
2
.6 equiv) of sodium borohydride, NaBH
4
, were added to
solution A to prepare a solution called B. 44.7 mg
6
ðNH
4
ÞH
2
PO
4
þ 10CaðNO
3
Þ2 þ 14NH
2
O
4
OH/Ca10ðPO Þ6ðOHÞ2
4
2 4
(0.152 mmol) of Na PdCl were dissolved in 10 mL of water
ꢃðHapÞ þ 20NH
4
NO
3
þ 12H
(solution C). Solution B was added, under vigorous stirring,
to solution C. The reduction of palladium occurred
immediately, and the resulting suspension, Pd@HEA16Cl,
was kept under stirring during 24 h.
A 0.1 M (NH
4
)H
2
4
PO (SigmaeAldrich; 98%) solution was
added to 0.167 M Ca(NO
3
)
2
$4H
2
O (SigmaeAldrich; 99%)
ꢂ
solution at 80 C, under magnetic stirring, and the pH was
adjusted to 10 by adding ammonia solution (25%;
2.1.2.2.2. Wet impregnation of the nanoparticles. 1.6 g of
hydroxyapatite are stirred in 10 mL of water during 2 h.
Then, a given volume of Pd@HEA16Cl suspension is added to
the latter mixture to yield the desired metal content. The
resulting mixture is stirred for 24 h. Then, the obtained solid
is filtered, washed three times with 5 mL of water, dried in
Verbi eꢁ se).
A white suspension was obtained. The
suspension was further stirred for 1 h, then filtered and
washed with hot deionized water. The resultant solid was
ꢂ
ꢂ
dried at 80 C for 20 h and then calcined for 4 h at 400 C
under a flow of purified air. The as-prepared solid is
considered as the stoichiometric hydroxyapatite and is
designated by HapS.
ꢂ
ꢂ
an oven at 80 C, and finally calcined under air at 300 C.
The same procedure was applied for gold, but only on
the HapD support and with a gold content of 0.25 wt%. In
A deficient hydroxyapatite HapD was prepared by the
this case, Na
HAuCl .3H O.
The as-prepared catalysts will be designated hereafter
by Pd
@HapY (x ¼ 0.25 and 0.5) or Au0.25@HapD.
2 4
PdCl was replaced by the suitable amount of
same way with appropriate concentrations of (NH
and Ca(NO $4H
4 2 4
)H PO
4
2
3
)
2
2
O solutions in order to obtain Ca/P ¼ 0.9.
A sodium containing carbonate-rich apatite, denoted as
HapE, was also similarly synthesized where a suitable
x
amount of NaNO
Ca(NO $4H
3
(PROLABO; 99%) was added to
O solution in order to get a (Ca þ Na)/P ¼ 2.2
)
3 2
2
2.2. Characterization techniques
where Ca/P ¼ 1.8. Indeed, introducing excess of positive
charges into hydroxyapatite structure leads to the
Elemental analysis of noble metal loading and bulk Ca/P
ratio was performed, on the calcined solids, using
inductively coupled plasma e optical emission spectroscopy
(ICP-OES) on an Agilent Technologies 700 Series
spectrometer. Analysis was carried out at the REALCAT
platform (Lille 1 University). Prior to analysis, the solids
were treated by a mixture of concentrated hydrochloric and
nitric acids (70%e30%).
2
incorporation of carbonate ions, from atmospheric CO [34].
It is worth noting that carbonate ions can substitute either
the hydroxyl ions (type A) or the phosphate ions (type B)
[48,49].
2
.1.2. Introduction of noble metals
Two different methods were used to introduce noble
metals: the conventional wet impregnation and the wet
impregnation of metal (0) nanoclusters.
Structural analyses were carried out by X-ray diffraction
(XRD), at ambienttemperature, of the calcined solids. Powder
X-ray diffraction was recorded with Cu K
a
(
l
¼ 1.5418 Å)
2
.1.2.1. Conventional wet impregnation. The required
amount of Pd(NO $2H (FLUKA), or HAuCl .3H
ACROS) was dissolved in excess water to give the desired
radiation on a D8 Advance Bruker diffractometer. The
crystalline phases were determined by the comparison of the
registered patterns with the ICDD-JCPDS powder diffraction
files processed on EVA software. The diffraction patterns
3
)
2
2
O
4
2
O
(
Pd or the Au loading before being added to the suitable
amount of Hap support. The resulting mixture was stirred
ꢂ
ꢂ
were recorded in the 2
q range 10e80 witha stepof0.02 and
ꢂ
at 60 C, in a rotary evaporator, until the sample was
a count time of 1.5 s. The Fullprof Suite program was used for
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

4
D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
Rietveld refinement [50]. The ThompsoneCoxeHastings
t
Toluene conversion (C ) was calculated as follows:
pseudo-Voigt function was chosen for describing the peak
½
tolueneꢄ ꢀ ½tolueneꢄ
profiles. LaB
6
was used as a standard to derive the instrument
i
t
C
t
ð%Þ ¼
ꢃ 100
resolution [51]. Here, an isotropic size-broadening model
based onlinearcombination of spherical harmonics wasused
to simulate the size broadening, and 6 additional parameters
were refined. Out of this refinement, the individual size was
derived for each crystallographic plane.
½tolueneꢄ
i
where [toluene]
toluene inlet and outlet concentrations.
The selectivity towards CO (SCO2) was determined by:
i t
and [toluene] represent respectively
2
The textural properties were studied by
adsorptionedesorption measurements at liquid nitrogen
temperature. The experiences were performed in
N
2
½
CO
2
ꢄ ꢃ 100
t
S
CO2 ð%Þ ¼ 7
ꢃ ½tolueneꢄ ꢃ C
t
i
a
Micromeritics TriStar-II Surface Areas and Porosity
equipment. Before starting the analysis, the samples were
degassed at 150 C in vacuum. The sample weight was about
2 t 2
where [CO ] is the CO outlet concentration.
The specific rate r was taken as:
ꢂ
À
Á
ꢀ
1
5
00 mg.
X-ray photoelectron spectra (XPS) were recorded at
r mol toluene$g 1$hꢀ1
À
Á
F mol toluene$h
ꢃ C
t
ꢀ
¼
Pd
Weight of PdðgÞ
ꢀ9
ambient temperature with a residual pressure of 10 mbar
on two spectrometers: VG ESCALAB 220XL and KRATOS,
where
F
is the initial molar flow of toluene,
F ¼ 1.96 ꢃ 10 mol toluene per hour.
ꢀ
4
AXIS Ultra with monochromated Al K
and a hemispherical analyzer with constant
a
anode (1486.6 eV)
E/E. The
D
source power was kept at 300 W for ESCALAB and at 150 W
for KRATOS.
3. Results and discussion
All binding energies were calibrated by using
contaminant carbon as an internal standard (C1s ¼ 285 eV).
Peak fitting was processed with CasaXPS. The fitting pro-
cedure allowed to determine the peak position, height, and
width.
3.1. Characterization of the supports
Chemical analysis results, BET surface areas and pore
volumes of the supports are summarized in Table 1.
The ICP results show that HapS is nearly stoichiometric
since its Ca/P ratio is close to 1.67. HapD is slightly deficient
with Ca/P of 1.56 but not as lower as the targeted value of
2
.3. Catalysts evaluation
0.9. HapE showed Ca/P greater than the stoichiometric
Catalytic oxidation runs for abatement of toluene
value. Aellach et al. [30], Silvester et al. [36] and Lamonier
et al. [37] obtained similar results. It is worth noting that
even if we obtained deficient and rich hydroxyapatites, a
difference exists between the experimental ratios Ca/P and
the targeted ones. Diallo-Garcia [52] suggested that
whatever the initial ratio of the reactants is, there is a trend
towards the formation of the most stable phase, i.e., the
stoichiometric one. Hence, by a simple adjustment of the
initial reactants proportions, as in our work, it is hard to
obtain hydroxyapatites with important deficiency or
important excess of carbonates [52]. Some studies proved
that parameters such as the pH [35,53] and the temperature
of the synthesis [53] play an important role on the Ca/P ratio.
Silvester et al. [36] also reported that the increase in the Ca/P
ratio was accompanied by a linear increase in the carbon
content (not analyzed in our samples), which could
originate from the substitution of phosphate ions, located in
the apatite structure, by carbonate ones.
were performed in a continuous flow fixed bed Pyrex
micro-reactoratatmosphericpressure. About0.2 gofcatalyst
was placed in the reactor for each run. To obtain accurate and
stable gas flow rates, the mass flow controllers were used.
The concentration of toluene was 800 ppm, which was
controlled by the temperature of a home-made saturator and
the additional air stream. The flow rate of the gas mixture
ꢀ
1
through the reactor was 100 mL min , which gave a Gas
ꢀ1
Hourly Space Velocity (GHSV) of 15,000 h . All the lines
ꢂ
were sufficiently heated at 120 C to prevent the adsorption
and condensation of toluene and water in the tubes.
The micro-reactor is placed in an electrical furnace
which provides the required temperature for catalytic
reaction. Catalysts were evaluated in a temperature range
ꢂ
of 300 Ceroom temperature, with a rate decrease of
ꢂ
ꢀ1
0
.5 C min . Before each run, the samples were pretreated
ꢂ
ꢀ1
.
for 4 h at 300 C under an air flow of 75 mL min
For the stability tests, the catalyst was fed with the
Specific surface areas of the hydroxyapatite supports
2
ꢀ1
ꢂ
reactant mixture at 165 C, and the evolution of toluene
range between 110 and 120 m g . The value does not
conversion was followed for the next 45 h at the same
temperature.
significantly differ between the different supports.
However, HapD shows a trend to have a slightly higher
The concentrations of the inlet and outlet gas stream
were analyzed online by Gas Chromatography (7860A
Agilent Gas Chromatograph) equipped with a Thermal
Conductivity Detector (TCD) and Flame Ionization Detector
Table 1
Chemical analysis of HapY supports and their textural properties.
Catalyst Theoretical Experimental Surface
Pore volume
(cm
(
FID) and with two columns: Restek Shin Carbon ST/Silco
HP NOC 80/100 micropacked, to separate permanent gases
Air, CO and CO ) and a capillary column Cp-Wax 52 CB25
ꢀ1
3
ꢀ1
g )
Ca/P
Ca/P
area (m2
g
)
HapS
HapD
HapE
1.67
0.9
1.8
1.64
1.56
1.71
109
118
107
0.68
0.76
0.59
(
2
m, Ø ¼ 0.25 mm, to separate hydrocarbons and aromatic
compounds.
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
5
surface area. It is to be noted that the values we got are
higher than those found by some researchers who prepared
and calcined apatites at 400 C [30,37,54,55]. They are
When the Ca/P ratio increases, the amount of carbonates
increases e as stated in our introduction and in reference
[36] e and then the cell parameter a decreases. This
observation could be explained by the fact that carbonate
ions, which are smaller than phosphate ones, partially
substitute these latter in the apatitic structure (type B
substitution) [36,37,57].
ꢂ
rather close to those of Silvester et al. [36].
The volumes of the pores of the supports are in the
range of 0.6e0.8 cm3
g , where HapD shows a slightly
ꢀ1
higher value than that of the other supports.
The X-ray diffractograms of the different HapY supports
are depicted in Fig.1. All of the pure hydroxyapatites present
In addition, it is to be noted here that the cell parameter
c is slightly higher for the sodium containing apatite, HapE,
than for the other apatites. Such a result which reveals an
expansion in cell volume was already reported
[36,37,58,59] for sodium containing apatites.
diffraction lines due to crystalline hydroxyapatite phase
ꢂ
Ca
5
(PO
4
)
3
OH (JCPDS
n
01-086-0740) [56]. The three
/m
prepared HapY crystallize in a hexagonal system with P6
3
space group. All of the diffractograms are similar and no
crystalline phase other than hydroxyapatite was detected.
By using the structure model proposed by Hughes et al.
Cheng et al. [60] demonstrated that the substitution-type
has different impacts on the Hap structure: type-A
substitution leads to an elongation according to the a-axis
and a contraction according to the c-axis, whereas type-B
substitution leads to the reverse effect. The B substitution
will lower the crystallinity of the Hap.
Moreover, as it is shown in Table 2, the crystallite size
increases with the ratio Ca/P whereas the length/thickness
ratio follows the reverse order (3.5 for HapD, 3.4 for HapS
and 3.3 for HapE). This suggests that the anisotropic
elongated shape of HapY crystallites became more
spherical with the increase of Ca/P ratio. Our results are in
good agreement with those of Silvester et al. [36] who
showed an increase of the crystallite size with an increase
of Ca/P ratio or carbonate content. Moreover, these
researchers proved the elongated anisotropic shape of the
HapY crystallites and found it to become more spherical for
carbonate-rich apatites. It is to be reminded that in our
case, HapE is supposed to be the support the most rich in
carbonates and it has the highest Ca/P.
3
[56], the apatite structure was refined in the P6 /m space
group. A small difference was noticed between the value
observed and the theoretical one. The cell parameters, as
well as the crystallite sizes, were deduced from the Rietveld
refinement and listed in Table 2. The cell parameters were
deduced from the diffraction lines of (300) crystallographic
ꢂ
ꢂ
plane at 32.9 and of (004) crystallographic plane at 53.1 .
The crystallite sizes were deduced from (001) and (100)
crystallographic planes. The information on (001) plane
ꢂ
was deduced from (002) one at 25.8 (Fig. 1). The plane
100) is at 10.9 (Fig. 1).
ꢂ
(
3.2. Effect of support nature
In our previous work [61], the different supports HapY
were tested in toluene total oxidation and showed no
ꢂ
toluene conversion between 100 and 250 C. No oxidation
ꢂ
ꢂ
occurs below 250 C for HapE and below 290 C for HapS
and HapD [61]. It is also noted that without a catalyst, no
reaction occurs at all at a temperature that ranges between
ꢂ
5
0 and 400 C [61].
Light-off curves of Pd0.25/HapY and of palladium
impregnated on a classical alumina support are plotted in
Fig. 2. T10 and T90, the temperatures at which respectively
10% and 90% of toluene is converted, are listed in Table 3.
Table 2
Cell parameters and crystallite size of HapY supports determined using
Rietveld refinement.
Sample Cell parametersa
Crystallite size (nm) Length/
corresponding to thickness
the crystallographic ratio
plane
a (±0.002 Å) c (±0.002 Å) (001)
(100)
(001)/(100)
HapD 9.4293
6.8830
6.8873
6.8915
28
31
33
8
9
10
3.5
3.4
3.3
HapS
HapE
9.4163
9.4101
a
Fig. 1. X-ray diffractograms of the HapS, HapD, and HapE materials.
a calculated from the (300) line and c calculated from the (004) line.
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

6
D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
First, Pd addition, even with a low content of 0.25 wt%,
Table 3
Temperatures at 10% and 90% toluene conversions, respectively T10 and T90
enhanced the toluene conversion of the supports; toluene is
ꢂ
ꢀ1
ꢀ1
ꢂ
(
C), and the specific rates r (mol toluene.gPd
h
) at 150 C for the
ꢂ
not oxidized below 250 C on the HapY supports [61],
different studied catalysts.
ꢂ
whereas, T90 is in the range of 178e190 C, when 0.25 wt% of
ꢂ
ꢂ
ꢂ
Sample
T
10 ( C)
T
90 ( C)
r at 150
C
Pd is present. Many scientists got such results [5,62e66].
Second, Pd0.25/HapY are more active than Pd0.4/Al O .
2 3
ꢀ
1
ꢀ1
h )
(mol toluene g
Pd
Pd0.25/HapS
Pd0.25/HapD
Pd0.25/HapE
146
141
150
154
163
147
178
182
190
181
198
180
0.05
0.06
0.04
0.007
0.01
0.04
Therefore, our supports with low palladium content are
more performant than classical alumina one with a two-fold
higher palladium content. Third, it could be said that
Pd0.25/HapD and Pd0.25/HapS have similar toluene
conversions with a trend for Pd0.25/HapD to be more active
than Pd0.25/HapS at lower reaction temperatures, where
toluene conversions are low, and to be slightly less active
than it at higher reaction temperatures. Pd0.25/HapE is rather
less active than both other apatites supporting palladium. It
is worth mentioning that the toluene conversion difference
between the different HapY supports is slight and could be
linked to the slight difference in their Ca/P ratio which will
result in a slight difference in their chemical properties. The
1
Pd /HapS
Pd0.4/Al O3
2
Pd0.25@HapE
activity of Pd was controlled through the acid-base
property of the support and through the electronic
interaction between support and Pd which is linked to
palladium dispersion on the support.
Furthermore, PdO formation on the hydroxyapatite
surface was evidenced, in all our samples, hereafter, by XPS.
No Pd(0) was detected. Hence, it could be postulated that
PdO interaction with acidic supports leads to a slight
enhancement of toluene oxidation. Indeed Popova et al. [8]
and Aellach et al. [30] emphasized the role of the acidic
centers of the catalysts in the toluene oxidation. The
activity in total toluene oxidation is related to the
interaction of the aromatic electrons of toluene with these
acidic centers, increasing the possibility of an electrophilic
attack of adsorbed oxygen and combustion of toluene
molecules, the electrons trapped in vacancies of apatites
are supposed to be responsible for oxygen activation [39].
Moreover, Tidahy et al. [29] reported that the activity of
Pd should be controlled by the reducibility of PdO by the
hydrocarbon and then through the electronic interaction
between the support and palladium. Since the reduction
step is an important factor for catalytic activity in total
oxidation reactions, these researchers concluded that the
pre-treatment of the used support could influence the
electronic interaction between palladium particles and the
corresponding support.
comparison of the specific rates (r) obtained on the different
ꢂ
studied systems at 150
C (Table 3) confirmed the
aforementioned trends: r increased by four to six times
when the reaction was performed on Pd0.25/HapY instead of
Pd0.4/Al
In addition, for low conversions, toluene was mainly
oxidized into CO . Secondary products obtained are benzene
2 3
O .
2
and some traces of non-identified hydrocarbons. No CO was
detected consistent with the ability of supported Pd
catalysts to catalyse the CO oxidation [67e70]. When
toluene conversion reaches 100%, selectivity towards CO
2
was 100%, in all the studied cases. Rooke et al. [64] obtained,
in the presence of noble metals, some CO and benzene as
major by-products during toluene total oxidation.
Okumura et al. [28] investigated the metalesupport
interaction between palladium and the different oxide
supports (MgO, Al O , SiO , SnO , ZrO , Nb O , WO ) with
2 3 2 2 2 2 5 3
different acid-base properties. They reported that the
combustion activity over Pd loaded on the strongest acidic
(
WO
over Pd on weak acid-base ones (SnO
Nb ). Therefore, it was considered that the combustion
3
) or basic (MgO) support was lower than when it was
2
, Al , SiO and
2
O
3
2
2
O
5
3.3. Effect of palladium content
Fig. 2 also compares toluene conversion data over two
different palladium contents loaded on the same support,
HapS. As already mentioned, adding Pd improved
significantly support ability to oxidize toluene, since
ꢂ
toluene conversion was of 100% at 200 C. However,
increasing palladium loading from 0.25 wt% to 1 wt% does
not lead to a better enhancement in the catalytic oxidation
of toluene. The same trend was observed whatever the
support nature or the preparation method used was
(
results not shown). The specific rate on Pd0.25/HapS
decreased about seven times (Table 3) when palladium
content was increased to 1 wt%, Pd /HapS. For 100% toluene
conversion, toluene was selectively converted into CO and
O.
.5 wt% Pd/LaMnO
Pd/LaMnO versus toluene oxidation according to the work
of Musialik-Piotrowska et al. [71]. However, Hosseini et al.
63] obtained a higher activity for 1.5 wt% Pd over
nanostructured mesoporous TiO eZrO (20 wt%e80 wt%)
1
2
H
2
0
3
was slightly less active than 0.1 wt%
3
[
Fig. 2. Toluene conversion versus reaction temperature on: Pd0.25/HapY,
Pd /HapS, and a classical catalyst Pd0.4/Al
1
2
O
3.
2
2
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
7
than for 0.5 wt% Pd one. Besides, Okumura et al. reported
that when Pd dispersion decreased, the catalytic activity in
the toluene oxidation decreased [28]. A comparison of the
specific surface areas of the reference [71] e range
2
ꢀ1
1
3
5e20 m g e with those of the reference [63] e about
2
ꢀ1
72 m
palladium content is increased, the palladium species are
still well dispersed on TiO eZrO , whereas when more
palladium is loaded on LaMnO , palladium was no more
g
e , leads us to conclude that even when the
2
2
3
dispersed and thus some palladium species were probably
not accessible to the reactants and consequently no
enhancement in toluene conversion could be observed.
Then higher palladium loading on hydroxyapatite led
certainly some palladium sites to be not accessible to
reactants.
Li et al. [72] investigated catalytic oxidation of toluene
over Pd-based FeCrAl wire mesh monolithic catalysts
prepared by electrodes plating method, with palladium
loadings of 0, 0.1, 0.2, 0.3, 0.4, and 0.5 wt%. For a catalyst
Fig. 3. Toluene conversion versus reaction temperature on Pd0.25/HapE and
Pd0.25@HapE.
without palladium, no toluene conversion was denoted. For
ꢂ
0
.1 wt% of palladium, T50 was about 215 C. Increasing
ꢂ
lower chemisorption energy was linked to a lower intrinsic
activity [62]. Furthermore, some other researchers [74]
palladium loading to 0.2 wt% leads to a shift of T50 to 206 C.
A further increase to 0.5 wt% does not lead to significant
improvement. Thus, these researchers regarded 0.3e0.4 wt
18
16
proved by O/ O isotopic exchange study that gold did
not promote the dissociation of dioxygen.
%
as a suitable palladium loading.
Furthermore, it is now well-known that the catalytic
activity and selectivity of gold-based catalysts strongly
depend on particles size, which in turn, depends mainly on
the preparation method. Gold is catalytically active only
under the form of ultrafine highly dispersed particles on
metallic oxide supports [62e64]. Conventional preparation
methods, such as wet impregnation, one of the methods
used in our case, do not lead to the formation of such active
particles [75]. Sintering of gold nanoparticles is one of the
most important limitations to their catalytic performances.
Our results show that even incorporating gold by colloidal
suspension does not lead to good catalytic results. It could
be then suggested that the latter preparation method does
not give rise to the formation of highly dispersed gold
nanoparticles. Of course, more deep characterization of
gold catalysts should be carried out in order to check this
3
.4. Effects of preparation method and nature of noble metal
The two preparation methods we used were compared
in terms of toluene conversion versus reaction temperature
in Fig. 3. Light-off temperatures are slightly shifted to lower
values for nanoparticle deposition method when toluene
conversions become higher than 20%. For lower toluene
conversions, both catalysts exhibit similar behaviors.
2
Selectivity towards CO and other products are comparable
between the two preparation methods.
Since a catalytic result similar to that of conventional
impregnation was obtained,
a
palladium colloidal
suspension can be successfully used to deposit Pd
nanoparticles on a hydroxyapatite support. To the best of our
knowledge, this type of impregnation on hydroxyapatite
support has never been used, and further investigations are
needed to improve this methodology approach. Indeed, for
higher Pd loading (0.5 wt%), it has been difficult to deposit
the targeted Pd content (see the characterization part).
The toluene conversion versus reaction temperature is
shown in Fig. 4 for catalysts loaded with Pd and Au. It is
clearly seen that Au0.25@HapD is far less active than
ꢂ
Pd0.25@HapD. Toluene oxidation starts at 250 C on
Au0.25@HapD and the conversion is only at about 10% at
ꢂ
ꢂ
3
00 C whereas at 200 C it is at 100% on Pd0.25@HapD.
Many researchers obtained better catalytic activities for
palladium-supported catalysts than gold ones in total
oxidation of toluene, independently of the preparation
method [5,62,63,65,66,73]. They explained the as-obtained
catalytic trend by the oxidation mechanism. They
suggested that VOC oxidation over supported noble metal
catalysts usually involves the dissociative adsorption of
oxygen [12,62,63]. They found, accordingly, that oxygen
chemisorption energy is lower for gold catalysts than for
other studied noble metals, including palladium, and that
Fig. 4. Toluene conversion versus reaction temperature on Au0.25@HapD and
Pd0.25@HapD.
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

8
D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
hypothesis and also to verify the eventual influence of other
parameters (oxidation state, supportemetal interaction,
reducibility…) on gold catalytic performances in our case.
Another explanation that could be postulated to explain
the lower toluene conversion on gold impregnated
supports compared to palladium homologous ones is the
presence of chloride which is known to cause sinterization
of gold particles, thus turning them less active or even
inactive [55,58].
who studied different palladium loadings on Hap. In a
previous study [61], whenwe impregnate 2.5 wt% copper on
different HapY, we obtain specific surface areas slightly
lower than those of the corresponding supports and pore
volumes similar to those of them. This observation was
explained by the high dispersion of copper as suggested by
XRD study [61]. A similar explanation could be stated for our
present catalysts.
Fig. 5 gives examples of the XPS spectra obtained for our
samples. All our palladium-based samples exhibited the
same XPS spectra (not all shown in Fig. 5). A peak centered at
3
.5. Characterization of noble metal based catalysts
336.9 eV was obtained and assigned to Pd3d5/2 core level.
This binding energy value is similar to those reported for
Pd3d5/2 of PdO in the literature [28, 79e81]. No peak due to
other palladium oxidation states was detected. The Full
Width at Half Maximum (FWHM) of the XPS peak was
nearly the same in all the studied cases. Thus, our two
synthesis methods lead to PdO and not to Pd(0) formation. It
seems that Pd(0) anchored on hydroxyapatites by the metal
nanoparticle deposition method was oxidized, at least, for
the species present on the surface, into PdO, after calcination
under air. It is also noted that no chloride species was
Since gold-based catalyst showed lower reactivities than
palladium ones towards toluene oxidation, characterization
has been focused on palladium-based materials. The results
of chemical analysis of palladium-based catalysts are
summarized in Table 4.
Chemical analyses show that the amount of Pd found in
the low Pd loading samples is generally in agreement with
the quantities introduced in solutions. However, for high Pd
content (Pd /HapS and Pd0.5@HapE), palladium loading is
1
somehow lower than the nominal content.
X-ray diffractograms of the different noble metal based
catalysts are the same as those of the supports (figures not
shown). After impregnation of noble metals, no crystalline
x
evidenced on the surface of our Pd @HapY samples. It is
then concluded that all chloride ions, whose origin is the
precursor used, were removed by filtration and subsequent
washings. XPS study of Pd introduced by different methods
on mixed cobalt-aluminum oxide prepared by hydrotalcite
route: coprecipitation, wet impregnation, ion exchange, and
thermal combustion, also revealed the presence of PdO as
the only surface palladium species [81].
5 4 3
phase other than Ca (PO ) OH was detected by XRD and
hence the crystalline structure of the hydroxyapatite did not
change as a consequence of noble metal addition. No
diffraction line due to PdO or Pd(0) species was observed.
Similar results after noble metal impregnation on
hydroxyapatite have been obtained by different research
groups [76e78]. They reported that impregnation of noble
metals did not change the support structure, and that no
XRD line ascribable to noble metal or oxide phase was
observed because, probably, of the relatively low noble
metal amount and/or the too small size of the diffracting
domains.
Specific surface areas and the volumes of the pores are
also listed in Table 4.
Surface areas of the supports decreased upon
introduction of noble metals, whatever the preparation
method was. When the metal content increases, in the
range we studied, it is not accompanied by a further
Table
5 summarizes binding energies and atomic
surface ratios given by XPS.
A presence of N species is detected on the surface of the
impregnated samples. N could be due to some residual
nitrate coming from Pd(NO ) .2H O, the palladium
3 2 2
precursor used in this method, not fully decomposed by
calcination.
The Ca/P ratio obtained from XPS is lower than that
obtained from ICP. Similar results were obtained by
Diallo-Garcia [52] and Silvester et al. [36] and were
explained by the fact that Ca species are less exposed to the
1
decrease in surface area since Pd0.25/HapS and Pd /HapS
show similar surface areas, also Pd0.25@HapE and
Pd0.5@HapE. Pore volumes of the different HapY slightly
decreased after noble metal introduction. All these results
are consistent with the results obtained by Cheikhi et al. [55]
Table 4
Chemical analysis and textural properties of Pd-based hydroxyapatites.
Catalyst
Experimental content
of noble metal (%) ICP (m
Surface area Pore volume
2
ꢀ1
3
ꢀ1
g )
g
)
(cm
Pd0.25/HapS
Pd0.25/HapD
Pd0.25/HapE
Pd /HapS
1
Pd0.25@HapD 0.22
0.24
0.26
0.30
0.81
93
95
99
91
92
96
92
0.59
0.72
0.52
0.57
0.55
0.53
0.55
Pd0.25@HapE
Pd0.5@HapE
0.23
0.34
1
Fig. 5. Pd3d5/2 XPS spectra of Pd /HapS and Pd0.25/HapE materials.
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
9
surface than phosphates, at least within the 10 nm analysis
depth limit of the XPS technique. Conversely, Pd/(Ca þ P),
Pd/Ca, and Pd/P XPS ratios are higher than those of ICP
ones, indicating that both Ca and P of the surface were
covered by Pd species. However, Pd/(Ca þ P) and Pd/Ca
obtained by XPS for Pd0.25@HapE are lower than those of
ICP. It is thought that some diffusion (of palladium species
towards the bulk, and of calcium species towards the
surface) could occur. This hypothesis should be later
verified.
3
.6. Stability tests
The stability of the catalysts is crucial for a practical
application. Fig. 6 shows, for Pd0.25/HapE and Pd0.25@HapE,
the evolution of toluene conversion versus reaction time at
ꢂ
165 C for 45 h. Pd0.25@HapE exhibits a decrease of toluene
Fig. 6. Time-on-stream plot of toluene conversion over Pd0.25/HapE and
Pd0.25@HapE catalysts. Feed composition: 800 ppm toluene in air,
conversion from 30% to 10% during the first three hours
under the stream. A stabilization of the value of toluene
conversion followed this decrease. Conversely, Pd0.25/HapE
showed a fluctuation of the toluene conversion between 10
and 20% during the first three hours of the reaction, and
later a stabilization of the conversion at approximately 10%.
After about 13 h under the stream, toluene conversion
increases gradually to reach 100% over this catalyst at the
ꢂ
temperature: 165 C.
test, only PdO species were evidenced and no Pd(0) was
detected. After stability tests, both PdO and Pd(0) were
evidenced on the catalysts' surfaces. Hence, the higher
catalytic reactivity after some time under stream was
explained by the existence of Pd(0) besides PdO. Indeed,
many researchers demonstrated that the presence of both
PdO and Pd(0) is responsible for the good performances in
oxidation reactions [83, 86e88]. PdO was partially reduced
into Pd(0) under toluene/air flow and therefore the cata-
lytic activity was improved. However, the catalyst was
neither fully reduced because of oxygen presence nor fully
oxidized because of the continuous feed of toluene [81]. It
2
5th hour and remained stable till the end of the stability
test. The deactivation process observed during the first
three hours for both catalysts could be explained by coke
formation [82], by the blocking of the active palladium sites
by water [83], and by poisoning or fouling of the catalyst
[84]. Nevertheless, some researchers stated that the partial
deactivation by water vapor of Pd supported on mixed
cerium-zirconium-yttrium oxide support is reversible [85].
The characterization of our systems after 3 h under stream
should be carried out in order to clarify the reason of the
observed deactivation.
However, after 13 h under the stream, Pd0.25/HapE
showed a non-conventional behavior. Such behavior was
not very common in literature where either no deactivation
or some deactivation was noted for palladium-based
catalysts under a stream of VOC diluted in air. As we
know, only Li et al. [81] obtained a behavior, under stream
of 800 ppm of toluene diluted in air, similar to that of
ꢂ
ꢂ
took Li et al. [81] 5 h at 240 C and it took us 13 h at 165 C to
reach the chemical equilibrium of PdOePd(0) in toluene/air
atmosphere.
Up till now, we did not have a clear explanation of the
difference between the behaviors under time on stream of
our two catalysts. We could suggest that Pd0.25@HapE
needs more time to reach the equilibrium PdOePd(0),
probably because palladium and support interaction is
different than in Pd0.25/HapE. This hypothesis is suggested
by the previously mentioned XPS results where some
palladium species is thought to diffuse towards the bulk.
Yet it should be verified later by different characterization
studies before and after stability tests.
Pd0.25/HapE in our case during their work on Pd/Co
3
AlO
(
mixed cobalt-aluminum oxide prepared by hydrotalcite
route) where palladium was introduced in the system
according to three different methods: impregnation, wet
ion exchange, and thermal combustion. These researchers
performed an XPS study to determine the states of Pd on
the surface before and after the stability tests. Before the
3.7. Comparison of our catalytic systems with literature ones
The reaction temperature, at which 50% of inlet toluene
was oxidized, T50, was used to compare the performances
Table 5
Binding energies, atomic surface ratios, and Full Width at Half Maximum (FWHM) data from XPS.
Sample
Binding energy (eV)
Atomic ratios
Ca/P XPS (ICP)
Ca 2p
P2p
O1s
N1s
Pd3d5/2 (FWHM/eV)
Pd/(Ca þ P) XPS (ICP)
Pd/Ca XPS (ICP)
Pd/P XPS (ICP)
Pd
1
/HapS
347.7
347.6
347.4
347.2
134.0
133.6
133.5
133.1
531.4
531.9
531.4
531.2
399.4
399.8
399.9
e
336.9 (1.9)
337.1 (2.5)
337.1 (1.7)
336.6 (2.2)
1.46 (1.64)
1.38 (1.64)
1.50 (1.71)
1.46 (1.71)
0.010 (0.007)
0.005 (0.002)
0.008 (0.002)
0.001 (0.002)
0.017 (0.010)
0.008 (0.003)
0.013 (0.003)
0.002 (0.004)
0.024 (0.017)
0.012 (0.005)
0.019 (0.005)
0.003 (0.002)
Pd0.25/HapS
Pd0.25/HapE
Pd0.25@HapE
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

10
D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
Table 6
Pd weight percentage (wt%), Pd dispersion (%), toluene content in air (ppm), Gas Hourly Space Velocity GHSV (hꢀ1) or Volume Hourly Space Velocity VHSV
3
ꢀ1 ꢀ1
ꢂ
(
m
kg
h
), and temperature at 50% toluene conversion, T50 ( C), on our catalysts and different palladium systems from the literature.
cat
GHSV (h 1) (VHSV) (m3 kg
ꢀ
ꢀ1 ꢀ1
h
)
ꢂ
T50 ( C)
Reference
Catalyst
Pd (wt%) (% dispersion)
Toluene (ppm)
cat
Pd/HapS
Pd/HapD
Pd/HapE
Pd@HapE
Pd/HBEA
Pd/NaBEA
Pd/CsBEA
Pd/HFAU
Pd/NaFAU
Pd/CsFAU
0.25
0.25
0.25
0.25
0.5 (18)
0.5 (19)
0.5 (28)
0.5 (21)
0.5 (25)
0.5 (12)
0.5 (15)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
800
800
800
15,000
15,000
15,000
15,000
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(60)
(1200)
(1200)
(1200)
(1200)
(1200)
(1200)
(1200)
(1200)
(60)
168
168
174
168
159
177
230
162
155
152
196
230
251
256
280
240
210
201
207
250
240
155
180
210
210
525
325
280
325
375
325
425
277
200
235
220
217
220
220
210
220
240
250
220
360
335
290
167
178
450
230
225
250
170
180
165
175
206
213
193
191
194
200
211
207
206
183
187
The present work
The present work
The present work
The present work
800
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
9500
9500
9500
9500
9500
9500
9500
9500
1000
1000
1000
1000
975
65,90
65,90
65,90
65,89e90
65,89e90
65,89e90
65,90
5,65,90
63,65
63,65
63,65
73
73
73
91
29
29
29
29
92
92
28
28
28
28
28
28
28
28
64
64
66
Pd/ZrO
2
Pd/TiO
Pd/TiO
Pd/TiO
Pd/TiO
Pd/TiO
2
macro mesoporous
2
eZrO
eZrO
eZrO
2
2
2
(80/20)
(50/50)
(20/80)
2
2
2
(non porous)
(5%)eTiO
(5%)eTiO
prepared from Ta(OEt)
Pd/Nb
Pd/V
Pd/Ta
2
O
5
2
2
O
5
2
2
O
5
5
Pd/mesoporous ZrO
Pd/mesoporous ZrO
Pd/mesoporous ZrO
2
2
2
0.5 (54)
0.5 (64)
0.5 (40)
0.5 (30)
0.5
-400
-600
Pd/ZrO
2
ref.
Pd/Hierarchically porous Ta
Pd/Hierarchically porous Nb
Pd/MgO
2
O
5
2
O
5
0.5
0.5 (14.1)
0.5 (4.1)
0.5 (16.5)
0.5 (21.5)
0.5 (1.2)
0.5 (3.6)
0.5 (3.1)
0.5 (16.5)
0.5
0.5
0.5
0.5
1 (14-16)
1 (28-38)
0.5
0.5
0.5
Pd/Al
Pd/ZrO
Pd/SiO
Pd/SnO
2
O
3
2
2
2
Pd/Nb
Pd/WO
Pd/ZrO
2
O
5
5
3
2
Pd/TiO
Pd/Nb
2
2
O
(3%)eTiO
2
(60)
(60)
(60)
16000
16000
(30)
(30)
(30)
Pd/CeO
Pd/CeO
2
(0.5%)eTiO
(5%)eTiO
IMP
LPRD
Al calcined at 290
Al calcined at 450
2
2
2
66
62
62
14
14
14
14
a
Pd/TiO
Pd/TiO
PdeMg
PdeMg
2
a
2
975
ꢂ
ꢂ
b
3
3
C
C
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
170
1500
270
270
270
270
1220
1220
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
b
b
Pd/Mg
Pd/Al
Pd/ eAl
3
Al
b
2
O
3
0.5
1
(30)
g
2
O
3
15000
19000
19000
19000
10000
10000
[6.36]e
26000
50000
50000
50000
50000
18000
18000
32000
32000
32000
32000
32000
32000
32000
32000
32000
32000
32000
80
93
93
93
94
94
c
LePd
LTePd
LePdT
Pd/SBA-15
Pd/LaSBA-PS
0.5 (24.8)
0.5 (12.6)
0.5 (9.6)
0.5 (29)
0.5 (12)
5 (78)
0.3
0.1
0.1
0.1
0.1
c
c
d
d
Pd/MCM-41
Pd/ZSM-5
95
96
97
97
97
97
71
71
Pd extracted solvent/
g
-Al
-Al
Pd extracted solvent/cordierite
PdCl aqueous solution/cordierite
2
O
3
PdCl
2
aqueous solution/
g
2
O
3
2
Pd/LaMnO
Pd/LaMnO
Pd/ZSM-5
Pd/KIT-6
Pd/ZK-3%
Pd/ZK-6%
Pd/ZK-12%
Pd/ZK-24%
Pd/ZK-mixed
Pd/SBA-15
Pd/SBA-15-T
Pd/SC-8.74
Pd/SC-17.3
3
3
0.1
0.5
0.48 (21)
0.49 (30)
0.49 (41)
0.48 (49)
0.50 (47)
0.47 (35)
0.49 (27)
0.49 (31)
0.48 (29)
0.49 (64)
0.51 (53)
86,98
86,98
f
f
98
98
98
98
98
99
99
99
f
f
f
f
g
g
g
g
99
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
11
Table 6 (continued )
GHSV (h 1) (VHSV) (m3 kg
ꢀ
ꢀ1 ꢀ1
h
)
ꢂ
T50 ( C)
Reference
Catalyst
Pd (wt%) (% dispersion)
Toluene (ppm)
cat
g
Pd/SC-29.6
Pd/SC-38.2
Pd/SC-79.1
Pd/FeCrAl
Pd/FeCrAl
Pd/FeCrAl
0.47 (42)
0.48 (38)
0.5 (34)
0.1
0.2
0.5
0.90
0.99
1.01
0.95
1000
1000
1000
~975
~975
~975
800
800
800
800
~2090
32000
32000
32000
10000
10000
10000
30000
30000
30000
30000
10000
199
198
205
215
206
203
220
263
253
280
159
99
99
99
72
72
72
81
81
g
g
h
h
h
i
Pd/Co
Pd/Co
Pd/Co
Pd/Co
3
AlO (COP)
3
AlO (IMP)
3
AlO (WIE)
3
AlO (TCB)
i
i
81
81
87
i
Pd/CeO
2
0.5
a
Pd deposited on commercial TiO
2
either by impregnation (IMP) or by Liquid Phase Reduction Deposition (LPRD).
Al signifies Pd incorporated into a Mg Al support prepared by hydrotalcite route. Pd/Mg Al signifies Pd impregnated on the same support.
Pd impregnated on Kraft lignin activated by H PO without thermal treatment (L-Pd) and after thermal treatment (LT-Pd). L-Pd after thermal treatment
b
c
Pd-Mg
3
3
3
3
4
is designated by L-PdT.
d
PS signifies post-synthesis; a solution of lanthanum nitrate was added to a calcined SBA-15.
e
f
ꢀ3
This value corresponds to the concentration of toluene (gtoluene
m
) divided by the catalyst weight (g).
KIT-6 is a porous material prepared from the initial sol without addition of ZSM-5. ZK-x% corresponds to biporous materials ZSM-5 and KIT-6 with
different weight percentages, x, of ZSM-5. ZK-mixed designs a mechanical mixture of ZSM-5 (12 wt%) and KIT-6.
g
2 2
T signifies that the sample was not reduced by H . All the other samples of this reference were reduced by H after calcination under air. SC-x signifies
SBA-15 with different x ¼ Si/Al ratios.
h
FeCrAl are wire mesh monolithic catalysts.
Co AlO is a cobalt-aluminum mixed oxide prepared by hydrotalcite route. COP: Coprecipitation, IMP: Impregnation, WIE: Wet Ion Exchange, TCB:
3
i
Thermal Combustion Method.
of our palladium catalysts with other palladium ones
studied in literature in total oxidation of toluene, in
conditions similar to ours. The results are summarized in
Table 6 from which we concluded that our systems are
among the most active found in literature. The palladium
catalysts which exhibited a catalytic behavior similar to or
higher than ours are mainly composed of mesoporous
supports or of zeolite supports with high surface areas
HEA16Cl as surfactant can be successfully used to deposit
Pd nanoparticles on a hydroxyapatite support; similar
catalytic performances have been obtained in the presence
of Pd-based catalysts prepared using either this
methodology approach or the conventional metal salt
impregnation. PdO species were evidenced on the support
surfaces of both preparation methods and no Pd(0) was
detected. It was also found that palladium is more active
than gold towards the studied reaction. Finally, it is
concluded that the catalytic performances are mainly
related to the high dispersion of active species as well as to
supportemetal interaction. Palladium supported on
hydroxyapatites by conventional method showed an
increase of toluene conversion after 13 h under stream
whereas palladium impregnated via a colloidal suspension,
did not show such behavior. It is thought that Pd(0)
formation after a given time under the air-toluene mixture
is responsible for this catalytic reactivity improvement.
However, after impregnating a colloidal suspension, some
interaction between palladium and support might probably
exist inhibiting such catalytic reactivity enhancement. It is
also shown that our catalytic systems compete with the
best palladium systems studied in literature, evidencing
that hydroxyapatite could be an alternative support to
conventional ones (alumina, zeolite…) for catalytic VOC
removal.
2
ꢀ1
(
Pd/HFAU, Pd/NaFAU and Pd/CsFAU, with 414e714 m g
)
[89,90]. Hence, to enhance our catalytic performances, we
suppose to synthesize mesoporous hydroxyapatite. By such
a synthesis, an increase in surface area of the apatite
supports will occur leading to an increase of palladium
dispersion.
4
. Conclusion
Three hydroxyapatites were synthesized with three
different Ca/P ratios: Ca/P ¼ 1.64 (stoichiometric HapS),
Ca/P ¼ 1.56 (deficient HapD) and Ca/P ¼ 1.71 (rich HapE).
The potential of these materials as catalyst support for
palladium and gold was tested in the reaction of toluene
total oxidation. Four parameters were investigated: the
support’s nature, the active phase nature, its content, and
the way of incorporating it on the support.
Hydroxyapatite supports lead to more efficient catalysts
ꢂ
than classical alumina one does, because at 150 C, the
specific rates on apatites supports were four to six times
higher (for Pd content of 0.24e0.30 wt%) than the specific
rate on alumina support (0.4 wt% of Pd). Even if palladium
improved toluene conversion obtained on the support,
increasing palladium loading above 0.25 wt% did not result
Acknowledgments
Mrs. D. Chlala acknowledges the award of a doctoral
fellowship by the Agence Universitaire de la Francophonie
(AUF) e R eꢀ gion du Moyen-Orient. Mrs. M. LABAKI is also
in further improvement, Pd
1
/HapS giving a specific rate, at
grateful to this institution for research fellowship. This
work was also supported by a grant from the project PHC
CEDRE 2015 N 32933QE.
ꢂ
150 C, ~7 times lower than Pd0.25/HapS. Furthermore, it
ꢂ
was shown that palladium colloidal suspension with
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

12
D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
Chevreul
institute
(FR
2638),
Minist eꢁ re
de
[34] J.C. Elliot, Structure and Chemistry of the Apatites and Other Cal-
cium Orthophosphates, Elsevier, Amsterdam, 1994.
l'Enseignement Sup eꢀ rieur et de la Recherche, R eꢀ gion
Nord e Pas de Calais and FEDER are acknowledged for
[35] T. Tsuchida, J. Kubo, T. Yoshioka, S. Sakuma, T. Takeguchi, W. Ueda, J.
Catal. 259 (2008) 183.
supporting and funding this work.
[36] L. Silvester, J.-F. Lamonier, R.-N. Vannier, C. Lamonier, M. Capron, A.-
S. Mamede, F. Pourpoint, A. Gervasini, F. Dumeignil, J. Mater. Chem.
A 2 (2014) 11073.
The authors also want to warmly thank Dr. Rose-No e€ lle
VANNIER for Rietveld refinements, Mrs. Martine
TRENTESAUX for her technical help in XPS spectra recording
and Mrs. Laurence BURYLO for XRD measurements. Special
thanks to Mrs. Ferial SROUR NEMR to her excellent
proofreading.
[37] C. Lamonier, J.-F. Lamonier, B. Aellach, A. Ezzamarty, J. Leglise, Catal.
Today 164 (2011) 124.
[
38] L. Silvester, J.-F. Lamonier, J. Faye, M. Capron, R.-N. Vannier,
C. Lamonier, J.-L. Dubois, J.-L. Couturier, C. Calais, F. Dumeignil, Catal.
Sci. Technol. 5 (2015) 2994.
[39] H. Nishikawa, T. Oka, N. Asai, H. Simomichi, T. Shirai, M. Fuji, Appl.
Surf. Sci. 258 (2012) 5370.
[
40] J. Xu, T. White, P. Li, C. He, Y.-F. Han, J. Am. Chem. Soc. 132 (2010)
3172.
41] Y. Sun, Z. Qu, D. Chen, H. Wang, F. Zhang, Q. Fu, Chin. J. Catal. 35
2014) 1927.
1
References
[
(
ꢀ
[
1] Agence de l'Environnement et de la Maîtrise de l'Energie (ADEME),
[42] Z. Qu, Y. Sun, D. Chen, Y. Wang, J. Mol. Catal. A Chem. 393 (2014)
182.
Les Compos eꢀ s Organiques Volatils, R eꢀ duction des eꢀ missions de COV
dans l'industrie, Dunod, Paris, 2013.
[43] L.A. Palacio, J. Vel aꢀ squez, A. Echavarría, A. Faro, F. Ram o^ a Ribeiro,
[
2] S. Ojala, S. Pitk €a aho, T. Laitinen, N.N. Koivikko, R. Brahmi, J. Ga aꢀ lov aꢀ ,
L. Matejova, A. Kucherov, S. P €a iv €a rinta, C. Hirschmann, T. Nevanper a€ ,
M. Riihim €a ki, M. Piril a€ , R.L. Keiski, Top. Catal. 54 (2011) 1224.
M. Filipa Ribeiro, J. Hazard. Mater. 177 (2010) 407.
[44] C.-H. Kuo, S.-M. Chen, Ind. Eng. Chem. Res. 35 (1996) 3973.
[45] F. Diehl, J. Barbier Jr., D. Duprez, I. Guibard, G. Mabilon, Appl. Catal. B
95 (2010) 217.
[46] R.G. Derwent, M.E. Jenkin, S.M. saunders, M.J. Pilling, Atmos. Envi-
ron. 32 (1998) 2429.
[47] S. Vigneron, P. Deprelle, J. Hermia, Catal. Today 27 (1997) 229.
[48] M.E. Fleet, Calcium phosphate: Structure, Synthesis, Properties and
Applications, Nova Science Publishers, 2012, p. 41.
[49] F. Ren, Y. Leng, Key Eng. Mater. 493e494 (2012) 293.
[50] J. Rodriguez-Carjaval, Recent Developments of the Program
FULLPROF, in: Commission on Powder Diffraction, 26,
International Union of Crystallography (IUCr) Newsletter,
2001, p. 12.
[51] P. Thompson, D.E. Cox, J.B. Hastings, J. Appl. Crystallogr. 20 (1987) 79.
[52] S. Diallo-Garcia, PhD thesis, Universit eꢀ de Pierre et Marie Curie,
Paris, October 2012.
[53] S. Raynaud, E. Champion, D. Bernache-Assollant, P. Thomas, Bio-
materials 23 (2002) 1065.
[54] M. Riad, S. Mikhail, Catal. Sci. Technol. 2 (2012) 1437.
[55] N. Cheikhi, M. Kacimi, M. Rouimi, M. Ziyad, L.F. Liotta, G. Pantaleo,
G. Deganello, J. Catal. 232 (2005) 257.
[56] J.M. Hughes, M. Cameron, K.D. Crowley, Am. Mineral. 74 (1989) 870.
[57] A. Krajewski, M. Mazzocchi, P.L. Buldini, A. Ravaglioli, A. Tinti,
P. Taddei, C. Fagnano, J. Mol. Struct. 744e747 (2005) 221.
[58] S. Kannan, J.M.G. Ventura, A.F. Lemos, A. Barba, J.M.F. Ferreira,
Ceram. Int. 34 (2008) 7.
[59] R.M. Wilson, J.C. Elliott, S.E.P. Dowker, R.I. Smith, Biomaterials 25
(2004) 2205.
[60] Z.H. Cheng, A. Yasukawa, K. Kandori, T. Ishikawa, Langmuir 14
(1998) 6681.
[
[
[
[
[
[
[
3] J. Quiroz Torres, S. Royer, J.-P. Bellat, J.-M. Giraudon, J.-F. Lamonier,
ChemSusChem 6 (2013) 578.
4] J.K. Edwards, B. Solsona, P. Landon, A.F. Carly, A. Herzing, C. Kiely,
G.J. Hutching, J. Catal. 236 (2005) 69.
5] M. Hosseini, S. Siffert, H.L. Tidahy, R. Cousin, J.-F. Lamonier,
A. Aboukaïs, A. Vantomme, B.-L. Su, Catal. Today 122 (2007) 391.
6] M. Labaki, S. Siffert, J.-F. Lamonier, E.A. Zhilinskaya, A. Aboukaïs,
Appl. Catal. B 43 (2003) 261.
7] F. Wyrwalski, J.-F. Lamonier, S. Siffert, A. Aboukaïs, Appl. Catal. B 70
(
2007) 393.
ꢀ
8] M. Popova, A. Szegedi, Z. Cherkezova-Zheleva, A. Dimitrova, I. Mitov,
Appl. Catal. A 381 (2010) 26.
9] J. Quiroz, J.-M. Giraudon, A. Gervasini, C. Dujardin, C. Lancelot,
M. Trentesaux, J.-F. Lamonier, ACS Catal. 5 (2015) 2260.
[
10] R. Averlant, S. Royer, J.-M. Giraudon, J.-P. Bellat, I. Bezverkhyy,
G. Weber, J.-F. Lamonier, ChemCatChem 6 (2014) 152.
[
[
[
11] P. Gelin, M. Primet, Appl. Catal. B 39 (2002) 1.
12] J.J. Spivey, Ind. Eng. Chem. Res. 26 (1987) 2165.
13] T. Maillet, C. Solleau, J. Barbier, D. Duprez, Appl. Catal. B 14 (1997)
85.
[
14] J. Carpentier, J.-F. Lamonier, S. Siffert, E.A. Zhilinskaya, A. Aboukaïs,
Appl. Catal. A 234 (2002) 91.
[
[
[
15] S.S. Kim, K.H. Park, S.C. Hong, Appl. Catal. A 398 (2011) 96.
16] S. Zuo, Q. Huang, R. Zhou, Catal. Today 139 (2008) 88.
17] J.M. Giraudon, A. Elhachimi, F. Wyrwalski, S. Siffert, A. Aboukaïs,
J.F. Lamonier, G. Leclercq, Appl. Catal. B 75 (2007) 157.
18] P. Papaefthimiou, T. Ioannides, X.E. Verykios, Appl. Therm. Eng. 18
[
[
(
1998) 1005.
19] K. Nomura, K. Noro, Y. Nakamura, H. Yoshida, A. Satsuma, T. Hattori,
Catal. Lett. 58 (1999) 127.
20] W.S. Epling, G.B. Hoflund, J. Catal. 182 (1999) 5.
[61] D. Chlala, M. Labaki, J.-M. Giraudon, J.-F. Lamonier, J. Catal. Mat. Env.
11 (2014) 35.
[
[
[
[62] V.P. Santos, S.A.C. Carabineiro, P.B. Tavares, M.F.R. Pereira,
21] M. Haruta, T. Kobayashi, H. Sano, N. Yamada, Chem. Lett. (1987) 405.
22] S. Minic oꢁ , S. Scir eꢁ , C. Crisafulli, R. Maggiore, S. Galvagno, Appl. Catal.
J.J.M. oꢀ rf ~a o, J.L. Figueiredo, Appl. Catal. B 99 (2010) 198.
[63] M. Hosseini, S. Siffert, R. Cousin, A. Aboukaïs, Z. Hadj-Sadok, B.-L. Su,
C. R. Chimie 12 (2009) 654.
[64] J.C. Rooke, T. Barakat, M. Franco Finol, P. Billemont, G. De Weireld,
Y. Li, R. Cousin, J.-M. Giraudon, S. Siffert, J.-F. Lamonier, B.L. Su, Appl.
Catal. B 142e143 (2013) 149.
[65] T. Barakat, J.C. Rooke, H.L. Tidahy, M. Hosseini, R. Cousin, J.-F. Lamonier,
J.-M. Giraudon, G. De Weireld, B.-L. Su, S. Siffert, ChemSusChem 4
(2011) 1420.
[66] T. Barakat, V. Idakiev, R. Cousin, G.-S. Shao, Z.-Y. Yuan, T. Tabakova,
S. Siffert, Appl. Catal. B 146 (2014) 138.
[67] A.S. Ivanova, E.V. Korneeva, E.M. Slavinskaya, D.A. Zyuzin,
E.M. Moroz, I.G. Danilova, R.V. Gulyaev, A.I. Boronin, O.A. Stonkus,
V.I. Zaikovskii, Kinet. Catal. 55 (2014) 748.
[68] X. Liu, R. Wang, L. Song, H. He, G. Zhang, X. Zi, W. Qiu, Catal.
Commun. 46 (2014) 213.
[69] J. Wang, M. Wang, M. Shen, J. Wang, G. Wei, H. Li, J. Rare Earths 32
(2014) 1114.
[70] E.J. Peterson, A.T. DeLARiva, S. Lin, R.S. Johnson, H. Guo, J.T. Miller,
J.H. Kwak, C.H.F. Peden, B. Kiefer, L.F. Allard, F.H. Ribeiro, A.K. Datye,
Nat. Commun. 5 (2014) article number 4885.
B 28 (2000) 245.
[
23] S. Scir eꢁ , S. Minic oꢁ , C. Crisafulli, C. Satriano, A. Pistone, Appl. Catal. B
40 (2003) 43.
[
24] Y. Wang, B.-B. Chen, M. Crocker, Y.-J. Zhang, X.-B. Zhu, C. Shi, Catal.
Commun. 59 (2015) 195.
25] D.Y.C. Leung, X. Fu, D. Ye, H. Huang, Kinet. Catal. 53 (2012) 239.
26] Y.-C. Hong, K.-Q. Sun, K.-H. Han, G. Liu, B.-Q. Xu, Catal. Today 158
[
[
(
2010) 415.
27] B.-B. Chen, C. Shi, M. Crocker, Y. Wang, A.-M. Zhu, Appl. Catal. B
32e133 (2013) 245.
28] K. Okumura, T. Kobayashi, H. Tanaka, M. Niwa, Appl. Catal. B 44
2003) 325.
[
[
[
1
(
29] H.L. Tidahy, M. Hosseini, S. Siffert, R. Cousin, J.-F. Lamonier,
A. Aboukaïs, B.-L. Su, J.-M. Giraudon, G. Leclercq, Catal. Today 137
(
2008) 335.
[
[
[
[
30] B. Aellach, A. Ezzamarty, J. Leglise, C. Lamonier, J.-F. Lamonier, Catal.
Lett. 135 (2010) 197.
31] A. Aboukaïs, S. Aouad, H. El-Ayadi, M. Skaf, M. Labaki, R. Cousin,
E. Abi-Aad, Scientific World J. 2013 (2013) 6. Article ID 824979.
32] M. Labaki, J.F. Lamonier, S. Siffert, E.A. Zhilinskaya, A. Aboukaïs,
Colloid Surf. A 227 (2003) 63.
[71] A. Musialik-Piotrowska, H. Landmesser, Catal. Today 137 (2008)
357.
[72] Y. Li, Y. Li, Q. Yu, L. Yu, Catal. Commun. 29 (2012) 127.
33] H.R. Low, M. Avdeev, K. Ramesh, T.J. White, Adv. Mater. 24 (2012)
4175.
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015

D. Chlala et al. / C. R. Chimie xxx (2016) 1e13
13
[
73] T. Barakat, J.C. Rooke, M. Franco, R. Cousin, J.-F. Lamonier, J.-
M. Giraudon, B.-L. Su, S. Siffert, Eur. J. Inorg. Chem. (2012) 2812.
74] P. Lakshmanan, F. Averseng, N. Bion, L. Delannoy, J.-M. Tatibou e€ t,
[87] D.-S. Lee, Y.-W. Chen, J. Taiwan Inst. Chem. E 44 (2013) 40.
[88] F. Yin, S. Ji, P. Wu, F. Zhao, C. Li, J. Catal. 257 (2008) 108.
[
[89] H.L. Tidahy, S. Siffert, J.-F. Lamonier, R. Cousin, E.A. Zhilinskaya,
C. Louis, Gold Bull. 46 (2013) 233.
A. Aboukaïs, B.-L. Su, X. Canet, G. De Weireld, M. Fr eꢁ re, J.-
[
[
75] G.C. Bond, D.T. Thompson, Gold Bull. 33 (2000) 41.
76] M.I. Domínguez, F. Romero-Sarria, M.A. Centeno, J.A. Odriozola,
Appl. Catal. B 87 (2009) 245.
M. Giraudon, G. Leclercq, Appl. Catal. B 70 (2007) 377.
[90] H.L. Tidahy, S. Siffert, F. Wyrwalski, J.-F. Lamonier, A. Aboukaïs,
Catal. Today 119 (2007) 317.
[
77] Z. Boukha, M. Kacimi, M. Ziyad, A. Ensuque, F. Bozon-Verduraz, J.
Mol. Catal. A Chem. 270 (2007) 205.
78] N. Takarroumt, M. Kacimi, F. Bozon-Verduraz, L.F. Liotta, M. Ziyad,
J. Mol, Catal. A Chem. 377 (2013) 42.
[91] J.C. Rooke, T. Barakat, J. Brunet, Y. Li, M. Franco Finol, J.-F. Lamonier, J.-
M. Giraudon, R. Cousin, S. Siffert, B.-L. Su, Appl. Catal. B 162 (2015) 300.
[92] J.C. Rooke, T. Barakat, S. Siffert, B.-L. Su, Catal. Today 192 (2012) 183.
[93] J. Bedia, J.M. Rosas, J. Rodríguez-Mirasol, T. Cordero, Appl. Catal. B 94
(2010) 8.
[94] K. Bendahou, L. Cherif, S. Siffert, H.L. Tidahy, H. Benaïssa,
A. Aboukaïs, Appl. Catal. A 351 (2008) 82.
[95] G.M. da Silva, H.V. Fajardo, R. Balzer, L.F.D. Probst, A.S.P. Lov oꢀ n,
J.J. Lov oꢀ n-Quintana, G.P. Valença, W.H. Schreine, P.A. Robles-
Dutenhefner, J. Power Sources 285 (2015) 460.
[96] C. He, P. Li, J. Cheng, Z.-P. Hao, Z.-P. Xu, Water Air Soil Pollut. 209
(2010) 365.
[97] J.-B. Kim, J.-I. Park, H.S. Kim, Y.J. Yoo, J. Ind. Eng. Chem. 18 (2012) 425.
[98] C. He, L. Xu, L. Yue, Y. Chen, J. Chen, Z. Hao, Ind. Eng. Chem. Res. 51
(2012) 7211.
[
[
[
[
79] T.R. Barr, J. Phys. Chem. 82 (1978) 1801.
80] S.C. Kim, W.G. Shim, Appl. Catal. B 92 (2009) 429.
81] P. Li, C. He, J. Cheng, C. Yan Ma, B. Juan Dou, Z. Ping Hao, Appl. Catal.
B 101 (2011) 570.
82] J. Jacquemin, S. Siffert, J.-F. Lamonier, E.A. Zhilinskaya, A. Aboukaïs,
Stud. Surf. Sci. Catal. 142 A (2002) 699.
[
[
[
[
[
83] B. Stasinska, A. Machocki, K. Antoniak, M. Rotko, J.L. Figueiredo,
F. Gonçalves, Catal. Today 137 (2008) 329.
84] S. Ojala, U. Lassi, M. H a€ rk o€ nen, T. Maunula, R. Silvonen, R.L. Keiski,
Chem. Eng. J. 120 (2006) 11.
85] W. Tan, J. Deng, S. Xie, H. Yang, Y. Jiang, G. Guo, H. Dai, Nanoscale 7
(
2015) 8510.
86] C. He, J. Li, X. Zhang, L. Yin, J. Chen, S. Gao, Chem. Eng. J. 180 (2012)
6.
[99] C. He, F. Zhang, L. Yue, X. Shang, J. Chen, Z. Hao, Appl. Catal. B
111e112 (2012) 46.
4
Please cite this article in press as: D. Chlala, et al., Toluene total oxidation over Pd and Au nanoparticles supported on hy-
droxyapatite, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2015.07.015