Palladium nanoparticles supported on mesoporous natural phosphate: An efficient recyclable catalyst for nitroarene reduction

Article abstract of DOI:10.1002/aoc.5117

We report the preparation of palladium nanoparticles supported on mesoporous natural phosphate (Pd@NP) using a wetness impregnation method. The prepared catalyst was characterized using various techniques. Furthermore, the reduction and preparation of the palladium nanoparticles was followed using UV–visible spectra. Based on the Scherrer equation, the crystallite size of the as-synthesized palladium nanoparticles was 10.88?nm. The performance of the synthesized catalyst was investigated in the reduction of 4-nitrophenol as a model substrate to 4-aminophenol using NaBH₄ as a hydrogen source. Moreover, catalytic reduction of various nitroarenes was studied and monitored using UV–visible spectroscopy and gas chromatography. The Pd@NP catalyst showed a high activity for the selected reaction and could be recycled.

Full text of DOI:10.1002/aoc.5117

Received: 30 April 2019
DOI: 10.1002/aoc.5117
Revised: 14 June 2019
Accepted: 23 June 2019
F U L L P A P E R
Palladium nanoparticles supported on mesoporous natural
phosphate: An efficient recyclable catalyst for nitroarene
reduction
1
,2
1
2
Ayoub Abdelkader Mekkaoui
| Sanaa Jennane | Abderrazak Aberkouks |
2
3
2
2
Brahim Boualy | Ahmad Mehdi | Mustapha Ait Ali | Larbi El Firdoussi |
1
Soufiane El Houssame
1
Laboratoire de Chimie, Modélisation et
We report the preparation of palladium nanoparticles supported on mesopo-
rous natural phosphate (Pd@NP) using a wetness impregnation method. The
prepared catalyst was characterized using various techniques. Furthermore,
the reduction and preparation of the palladium nanoparticles was followed
using UV–visible spectra. Based on the Scherrer equation, the crystallite size
of the as‐synthesized palladium nanoparticles was 10.88 nm. The perfor-
mance of the synthesized catalyst was investigated in the reduction of 4‐
Sciences de l'environnement, Université
Sultan Moulay Slimane, Faculté
Polydisciplinaire de Khouribga, BP 145,
25000 Khouribga, Morocco
2
Département de Chimie, Faculté des
Sciences Semlalia, Laboratoire de Chimie
de Coordination et de Catalyse, BP 2390,
40001 Marrakech, Morocco
3
Institut Charles Gerhardt Montpellier,
nitrophenol as a model substrate to 4‐aminophenol using NaBH as a hydro-
UMR 5253, Chimie Moléculaire et
Organisation du Solide, Université
Montpellier, Place E. Bataillon, 34095
Montpellier Cedex 5, France
4
gen source. Moreover, catalytic reduction of various nitroarenes was studied
and monitored using UV–visible spectroscopy and gas chromatography. The
Pd@NP catalyst showed a high activity for the selected reaction and could
be recycled.
Correspondence
Soufiane El Houssame, Laboratoire de
Chimie, Modélisation et Sciences de
l'environnement, Université Sultan
Moulay Slimane, Faculté Polydisciplinaire
de Khouribga, BP 145, 25000 Khouribga,
Morocco.
KEYWORDS
heterogeneous catalysis, mesoporous natural phosphate, nitroarene reduction, palladium
nanoparticles, supported catalyst
Email: hous_soufiane@hotmail.com
[
13–16]
1
| INTRODUCTION
counterparts
and continue to generate intense inter-
[
17–21]
est for their application as catalysts.
Supported catalysts play a crucial role according to their
Among noble metals used as catalysts, palladium has
high surface area, controllable porosity and well‐defined
structure. They are used in a large number of industrial
been exploited in various catalytic reactions like coupling
[1]
[22,23]
reactions and hydrogenation.
Previously, we have
processes for base chemicals productions (refining, petro-
carried out the allylic substitution of optically active nat-
[2]
[24]
chemicals and syngas) and fine chemistry. Various sup-
ports were developed for their preparation, such as
ural terpenic olefins using palladium(0).
Teranishi and
[
25]
Miyake
reported a sustainable method for the prepara-
[
3–6]
[7]
[8,9]
[10]
mineral oxides,
charcoals,
polymers,
clays
tion of palladium nanoparticles without the need for a
reducing reagent. Among the various supports reported
in the literature, natural supports have been paid much
attention due to inexpensive valuable resource and
[
11,12]
and phosphate derivatives.
While various metal par-
ticles have been reported in the literature, metal nanopar-
ticles have significant properties compared to their bulk
Appl Organometal Chem. 2019;e5117.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.5117

2
of 12
MEKKAOUI ET AL.
[
26]
environmentally benign effect.
Various supported cat-
method. The performance of the prepared catalyst was
evaluated in the nitroarene reduction reaction using
alysts have been used but only few works are devoted to
natural phosphate as a support.
[27,28]
However, solid
NaBH as hydrogen source.
4
phosphates such as natural phosphate, hydroxyapatite
and fluorapatite have been prepared and used as cata-
[29,30]
lysts.
Recently, we reported an efficient method for
the preparation of β‐enaminoesters using hydroxyapatite
2 | MATERIALS AND METHODS
2.1 | Catalyst preparation
[31]
as catalyst.
‐Nitrophenol is considered as a commonly known
4
organic pollutant used for pesticide and dye production.
Its degradation is of great interest, especially in the treat-
2.1.1 | Mesoporous NP support
[32]
ment of wastewaters at room temperature.
Moreover,
it presents carcinogenic and genotoxic risks to humans
The NP that we used was obtained from Khouribga
[33]
[56]
and wildlife.
In contrast, the reduced product, 4‐
region (Morocco).
It was treated by techniques involv-
aminophenol, plays a crucial role as an important indus-
ing attrition, sifting, calcinations (900°C), washing and
re‐calcination. The treated NP has the following chemical
[34]
trial intermediate.
According to its significance, con-
siderable efforts have been dedicated to developing an
composition: CaO (54.12%), P O5 (34.24%), F (3.37%),
2
efficient and recyclable catalyst for the reduction of 4‐
SiO (2.42%), SO (2.21%), CO (1.13%), Na O (0.92%),
MgO (0.68%), Al O (0.46%), Fe O (0.36%), K O (0.04%)
2 3 2 3 2
2
3
2
2
[35]
nitrophenol.
Recent works have reported a green
method for the synthesis of supported metal nanoparticle
catalysts using a naturally sourced reducing agent for the
reduction of nitroarene compounds and organic dyes and
and several metals in the ppm range.
Prior to use, we ground and sieved the NP several
times in order to obtain a homogeneous size of particles
(Figure 1). In the course of our study, a size of less than
45 μm was chosen for the mesoporous support of palla-
dium nanoparticles.
[36]
removal of aromatic compounds.
Hence, this reaction
is considered as ‘model catalytic reaction’ or ‘benchmark’
to evaluate the catalytic activity of metal nanoparticles in
[37–40]
aqueous solution.
Various noble metals were stud-
ied and exhibited good catalytic activities towards this
[41–47]
reaction.
In addition, various investigations have described the
toxicity and mutagenicity of aromatic nitro com-
2.1.2 | Palladium nanoparticles
[44,45,48,49]
pounds.
Although some of these compounds
An aqueous solution of H PdCl (2.0 mM) was prepared
2
4
are high‐energy explosives, they are contained in many
by mixing PdCl (0.6 mmol), 0.2 M HCl (6 ml) and water
2
[46,50]
unexploded landmines worldwide.
Thus, removing
(294 ml). Quantities of 200 ml of H PdCl solution, 70 ml
2
4
such highly toxic pollutants by their reduction to aro-
matic amino compounds has attracted enormous atten-
tion in the chemical industry.
of water, 47 ml of ethanol and 0.22 g of sodium carboxy-
methylcellulose (CMC‐Na) were mixed and refluxed for
3 h under air. The palladium nanoparticle preparation
was followed using UV–visible spectroscopy. The
resulting monodispersed palladium nanoparticles were
used for the preparation of the Pd@NP catalyst.
[47,51]
As part of our studies directed towards the develop-
ment of new metal nanoparticles and new supported cat-
[52–54]
alysts,
we have focused our attention on the
preparation, characterization and catalytic application of
palladium nanoparticles supported on natural phosphate
(NP). NP, being the first mining sector in the Moroccan
kingdom, is a natural and low‐cost material that exhibits
interesting properties such as ionic substitution ability,
structural stability and high adsorption capacity, making
it an attractive and cost‐effective catalyst for several
chemical transformations. To the best of our knowledge,
NP has never been used as a support of metal nanoparti-
cles. Furthermore, Morales et al. mentioned that wetness
impregnation has never been applied for the synthesis of
[55]
catalysts used in the reduction of 4‐nitrophenol.
First,
we prepared palladium nanoparticles (Pd(0)) supported
on a mesoporous NP using a wetness impregnation
FIGURE 1 Particle size distribution after first and second sieving

MEKKAOUI ET AL.
3 of 12
2
.1.3 | Deposition of Pd(0) metal nanopar-
equipped with an energy‐dispersive X‐ray (EDX) detector.
Transmission electron microscopy (TEM) observations
were carried out at 100 kV (JEOL 1200 EXII). Samples were
prepared by embedding the hybrid material in AGAR 100
resin, followed by ultramicrotomy techniques and deposi-
tion on copper grids.
ticles on mesoporous NP
A solution of 200 ml of the prepared Pd(0) nanoparticles
(0.4 mmol) was added to 0.6 g of mesoporous NP to pre-
pare the Pd@NP catalyst (10%). Wetness impregnation
was carried out for 24 h followed by calcination at
6
00°C for 3 h (Scheme 1).
2.3 | General procedure of catalytic
reduction of nitroarenes
2
.2 | Catalyst characterization
The catalytic application of the prepared supported cata-
lyst was investigated in the reduction of 4‐nitrophenol
to 4‐aminophenol at room temperature. The reaction
was carried out with 100 mg of 4‐nitrophenol, a molar
Spectrophotometric analysis was conducted using a
double‐beam scanning spectrophotometer (Shimadzu
Biochrom). Fourier transform infrared (FT‐IR) transmit-
tance spectra were recorded in the wavenumber range
excess of NaBH and 40 mg of Pd@NP. The reduction
4
−
1
of 4‐nitrophenol was monitored by UV–visible spectros-
copy. The same conditions were used in the reduction
of various nitroarenes and in the study of the reusability
of the prepared catalyst. It is noteworthy that during the
course of catalytic reduction, the filtrate of the reaction
mixture remained colourless indicating that most proba-
bly no leaching of Pd occurred which improved the het-
erogeneous nature of the nanocatalyst.
4
00–4000 cm using a PerkinElmer FTIR‐2000. X‐ray dif-
fraction (XRD) data were collected at room temperature
using a D2 PHASER diffractometer, with the Bragg–
Brentano geometry, using Cu Kα radiation (λ = 1.5406 Å)
at 30 kV and 10 mA. The patterns were scanned through
steps of 0.010142 (2θ) in the 2θ range 5–70°. Cyclic volt-
ammetry (CV) study was performed between
1
500 mV/−500 mV and 1200 mV/300 mV with a carbon
paste electrode modified by our samples in 0.5 M H SO
2
4
−
1
electrolyte at a scan rate of 100 mV s . Textural character-
istics of the prepared samples such as Brunauer–Emmett–
Teller (BET) surface area and average pore diameter were
3 | RESULTS AND DISCUSSION
3.1 | Catalyst characterization
determined with the N adsorption–desorption technique
2
using a Micromeritics 3FLEX analyser. Prior to measure-
ments, all samples were degassed at 120°C during 12 h
under vacuum. Scanning electron microscopy (SEM) mea-
surements were obtained with a TESCAN VEGA3‐EDAX
3.1.1 | Palladium nanoparticles
UV–visible spectra of H PdCl solution before and after
2
4
reduction (with and without CMC‐Na) are depicted in
SCHEME 1 Method of Pd@NP catalyst
synthesis

4
of 12
MEKKAOUI ET AL.
Figure 2a. The reduction reaction shows the presence of
peaks at 228 and 290 nm due probably to the presence
2
− [57]
of [PdCl ] .
The reduction without CMC‐Na showed
4
a decrease in intensity, confirming reduction of H PdCl4
2
to Pd(0). With CMC‐Na, there was no obvious absorption
peak of Pd(II) which revealed that the transition metal
precursor H PdCl was totally reduced to nano‐Pd(0).
2
4
The crystallinity of the as‐synthesized palladium nano-
particles (CMCNa‐Pd NPs) was examined using XRD
analysis. As depicted in Figure 2b, five distinct reflections
are present at 39.87° (111), 46.34° (200), 67.83° (220),
8
1.74° (311) and 86.40° (222) which are in a good agree-
ment with the five reflections of face‐centred cubic struc-
ture of Pd nanoparticles. The desired development track
of the nanocrystals may be specified by the strong reflec-
tion at (111), in contrast with the other four reflec-
FIGURE 3 FT‐IR spectra of pure NP and Pd@NP
[58]
verified by the absence of diffraction peak of Pd(II) in
the XRD pattern of non‐calcined Pd@NP (Figure 4).
Based on XRD study, the palladium species present
two oxidation states in our prepared Pd@NP. CV experi-
ments were carried out to study the predominant oxida-
tion state of palladium species supported on the NP. CV
tions.
Based on the half‐width of the (111) reflection,
the average crystallite size (10.88 nm) of the CMCNa‐Pd
NPs was calculated using the Scherrer equation
[59]
(supporting information, Data S1).
was performed with different samples (NP, PdCl , non‐
2
calcined Pd@NP and Pd@NP). Figure 5 shows the CV
3.1.2 | Pd@NP catalyst
curves
collected
during
experiments
between
The palladium nanoparticles were supported on mesopo-
rous NP using a wetness impregnation method followed
by calcination at 600°C.
1500 mV/−500 mV and 1200 mV/300 mV.
The study of palladium electrodes presents four spe-
cific zones. The first two zones represent the adsorption,
absorption and desorption of hydrogen while the other
two represent surface oxide formation, reduction and dis-
FT‐IR spectra of NP and Pd@NP catalyst (Figure 3)
showed for both samples many characteristic bands of
crystalline apatite (phosphate group bands at 470, 560–
[
63]
solution. Compared to other samples, our NP was inert
for CV study and did not present any significant peaks.
The prepared Pd@NP exhibited the presence of Pd(0)
both before and after calcination and also Pd(0) was the
predominant species according to CV peaks. This is con-
firmed by simple comparison between voltammograms
−
1 [60]
6
00, 960, 1030–1120 cm ).
In contrast to Hassine et al.,
[28]
XRD patterns of NP
and Pd@NP calcined at 600°C showed a difference
related to the presence of palladium in our catalyst
(
Figure 4). XRD patterns of Pd@NP indicate that palla-
[
61]
dium is present in two oxidation states, Pd(0)
Pd(II).
and
of Pd@NP and PdCl .
2
BET measurements are reported in Figure 6 and
Table 1. BET surface area values of NP and our prepared
[62]
The existence of Pd(II) species is probably due
to re‐oxidation of Pd(0) during the calcination. This is
2 4
FIGURE 2 (a) UV–visible spectra of H PdCl reduction with and without CMC‐Na. (b) XRD pattern of as‐synthesized Pd nanoparticles

MEKKAOUI ET AL.
5 of 12
FIGURE 4 XRD patterns of NP, non‐
calcined Pd@NP and Pd@NP calcined at
6
00°C
identical to that of the NP support (Figure 7). The SEM
image of Pd@NP shows the presence of Pd(0) at the
nanoscale with a good distribution. The EDX results for
NP exhibited bands which indicate that our mesoporous
NP is a fluorapatite structure. Also, EDX results for
Pd@NP confirmed the presence of palladium and the
fluorapatite composition remains unchanged.
Element distribution in the hybrid was determined for
both our support and the prepared Pd@NP (Figure 8;
supporting information, data S2 and S3). The main ele-
ments contained in our NP (fluorapatite (Ca (PO ) F)
5
4 3
and other elements) were determined (supporting infor-
mation, data S2) and showed a good distribution. Conse-
quently, in the case of Pd@NP the same elements allow a
good dispersion and distribution of palladium nanoparti-
cles (Figure 8c).
The elemental composition of the prepared palladium
nanoparticles supported on mesoporous NP was deter-
mined using X‐ray fluorescence analysis (Table 2). The
major and trace elements were detected. The percentage
of palladium in Pd@NP was found to be 4.028%.
TEM studies were also carried out (Figure 9). A slight
difference in terms of morphology between NP and the
prepared Pd@NP was detected and all samples reveal dif-
ferent aspect of nano‐sized grain crystals. This was consis-
tent with the crystal size calculation according to XRD
analysis, which indicated that the crystallite sizes of NP
and Pd@NP were respectively about 63 and 67 nm. In
contrast to NP (Figure 9a,b), which reveals irregular
sphere‐like particles (i.e. length/diameter) and agglomer-
ated superstructures, the prepared palladium nanoparti-
cles supported on mesoporous NP (Figure 9c,d) present
well‐defined rod‐like particles. The difference in shape
is due to the preparation procedure (presence of CMC‐
Na during the impregnation). The particle sizes are
approximately those of natural apatite compared with
FIGURE 5 CV curves of carbon paste electrode modified with
NP, PdCl and calcined and non‐calcined Pd@NP performed
between (a) 1500 mV/−500 mV and (b) 1200 mV/300 mV at a scan
2
−
1
rate of 100 mV s
2
catalyst (Pd@NP) were respectively 14.893 and 3.754 m g
−
1
.
Consequently, the decrease of SBET of Pd@NP is
caused by the deposition of Pd nanoparticles and the
agglomeration of metal species during calcination. While
the average pore diameter and the pore volume confirm
that our support and our catalyst are mesoporous
materials.
[
64]
The SEM images of NP and Pd@NP calcined at 600°C
show that the surface morphology of the catalyst is not
synthetic ones. Figure 9a reveals a lamellar aspect with
a lamella size less than 1 nm. The analysis shows round

6
of 12
MEKKAOUI ET AL.
FIGURE 6 (a) Nitrogen adsorption isotherm and (b) pore diameter distribution of NP and Pd@NP calcined at 600°C
studied in a natural apatite as well as for lamellar aspect.
The metal deposition on the particle surface was in a
well‐defined nanosphere shape (Figure 9c) and the Pd
nanoparticles were distributed with a mean size of
TABLE 1 BET surface area, average pore diameter and pore
volume of NP and Pd@NP
BET surface
Sample area (m g
BET average pore Pore volume
2
−1
3
−1
)
diameter (nm)
(cm g )
11.81 nm, as shown in Figure 9f.
−
−
2
3
NP
14.893
3.754
7.327
7.236
2.728 × 10
4.693 × 10
The investigation of the analysis results confirms that
Pd@NP
the choice of the wetness impregnation method of palla-
dium nanoparticles onto mesoporous NP is advanta-
geous, particularly in terms of a good distribution and
[
27,28]
dispersion of Pd compared to previous works.
bright patches (holes) distributed randomly in all the par-
ticles (Figure 9b) mostly of size between 11 and 41 nm
(
Figure 9e), explaining the large surface area obtained
3.2 | Catalytic application
from BET analysis. However, even though many studies
have reported the presence of sphere‐like nanopores in
The catalytic activity of the Pd@NP nanoparticle catalyst
was evaluated for the reduction of 4‐nitrophenol, chosen
[65,66]
synthetic apatite,
in our case the nanopores are
FIGURE 7 SEM images (left) and EDX analysis (right) of (a) NP and (b) Pd@NP

MEKKAOUI ET AL.
7 of 12
FIGURE 8 EDX elemental mapping analysis of Pd@NP: (a) the studied area; (b) distribution of palladium nanoparticles and our NP
elements; (c) palladium nanoparticle distribution over support
TABLE 2 X‐ray fluorescence analysis of Pd@NP catalyst
band at 313 nm. After NaBH addition, the band is shifted
4
Element
Amount (wt%)
Element
Amount (ppm)
to 400 nm and the solution colour changed from light yel-
low to intense yellow due to nitrophenolate anion forma-
tion. When the Pd@NP catalyst was added into the
Mg
Al
Si
0.113
0.189
0.683
3.671
Ti
V
471.0
247.3
508.6
solution containing 4‐nitrophenol and NaBH , a new
4
Cr
peak appeared at about 300 nm corresponding to the for-
mation of 4‐aminophenol and the colour became trans-
parent. In the presence of mesoporous NP as catalyst,
no conversion of 4‐nitrophenol was observed.
Optimization of the amount of catalyst was carried out
(Figure 11). Different catalytic ratios, namely 10, 25, 40
and 50% (catalyst/substrate, w/w), were studied. It is well
noticed in this study that the first five minutes are crucial
P
Mn
Ni
11.7
418.7
S
0.196
4.146
Cu
70.8
Cl
Zn
As
341.9
20.0
Ca
29.079
Br
Sr
47.5
751.6
(
giving ≥50% of the final conversion) in the catalytic
Fe
Pd
0.368
4.028
Y
224.9
reduction of nitroarenes over our prepared Pd@NP.
Moreover, the conversion increases with amount of cata-
lyst, until 40% which gave a total conversion at 40 min.
The efficiency of the Pd@NP catalyst was compared
with that of other reported catalysts in the reduction of
4‐nitrophenol (Table 3). Our prepared Pd@NP exhibits a
higher catalytic activity and a shorter reaction time com-
Zr
Pb
33.6
28.5
Ag
0.140
U
171.1
as model substrate, at room temperature and in the pres-
ence of NaBH as reducing agent. The conversion of 4‐
nitrophenol in aqueous medium at room temperature is
very fast and simple, with the advantage of being able
to be monitored using UV–visible spectroscopy. The
results are shown in Figure 10.
4
[
67–70]
pared to other catalysts.
The scope and limitation of the catalytic system were
examined by testing the reduction of various nitroarenes
under the same conditions (Table 4). The reactions show
total conversions with different selectivity of the amino
product (Figure 12).
A total reduction of 4‐nitrophenol was observed after
4
0 min. In aqueous medium, 4‐nitrophenol exhibits a

8
of 12
MEKKAOUI ET AL.
FIGURE 9 TEM images of (a, b) NP with (e) pore size distribution and (c, d) Pd@NP calcined at 600°C with (f) Pd nanoparticle
distribution
FIGURE 11 Optimization of amount of catalyst in 4‐nitrophenol
reduction
FIGURE 10 UV–visible absorption spectra of 4‐nitrophenol
reduction
extension (Figure 13) which could be due to the agglom-
To investigate the reusability of Pd@NP and the effect
of Pd particle size, the catalytic performance was evalu-
ated in four consecutive cycles. The catalyst exhibited a
high activity over the four cycles with a reaction time
eration phenomenon of Pd particles. Comparing Pd@NP
after the first and the fourth runs, SEM imaging showed
relatively dispersed nanoparticles (Figure 14). However,
SEM imaging of the catalyst after four cycles showed

MEKKAOUI ET AL.
9 of 12
TABLE 3 Comparison of catalytic performance of other palla-
dium catalysts in reduction of 4‐nitrophenol
Catalyst
Time
Ref.
[
[
[
[
67]
68]
69]
70]
HMMS‐NH
2
‐Pd
60 min
5.5 h
Polymer‐anchored Pd(II) complex
PdCu/graphene
Pd‐FG
1.5 h
12 min
40 min
Pd@NP
Present work
FIGURE 13 Kinetics of 4‐nitrophenol reduction during recycling
of Pd@NP catalyst
a
TABLE 4 Pd@NP catalytic performance for reduction of various nitroarenes
b
b
Entry Nitroarene
Aminoarene
Solvent (water–ethanol) Time (h) Conversion (%) Selectivity (%)
1
2
3
4
5
6
7
8
9
1
1
Nitrobenzene
Aniline
7/3
2
99
99
99
99
99
99
99
99
99
99
99
99
99
99
70
70
96
80
96
70
82
96
Nitroaryl‐himachalene Aminoaryl‐himachalene 7/3
12
4‐Nitrotoluene
3‐Nitrophenol
4‐Nitrophenol
4‐Nitroanisole
2‐Nitroaniline
4‐Nitroaniline
4‐Nitrobenzaldehyde
4‐Toluidine
7/3
0.8
3‐Aminophenol
4‐Aminophenol
4‐Anisidine
Water
Water
7/3
0.7
0.7
1.5
1.5
1.5
2
2‐Phenilenediamine
4‐Phenilenediamine
4‐Aminobenzylalcohol
Water
Water
Water
0
1
Methyl 3‐nitrobenzoate Methyl 3‐aminobenzoate 7/3
3,5‐Dinitrosalicylic acid 3,5‐Diaminosalicylic acid Water
1.5
1.5
a
Reaction conditions: nitroarene 100 mg, molar excess of NaBH
4
and 40 mg of Pd@NP at room temperature.
b
Conversion and selectivity were determined by GC using dodecane as an internal standard.
FIGURE 12 UV–visible spectra of studied nitroarenes: (a) nitrobenzene, (b) nitroaryl‐himachalene, (c) 4‐nitrotoluene, (d) 3‐nitrophenol,
e) 4‐nitroanisole, (f) 2‐nitroaniline, (g) 4‐nitroaniline, (h) 4‐nitrobenzaldehyde, (i) methyl 3‐nitrobenzoate and (j) 3,5‐dinitrosalicylic acid
(

10 of 12
MEKKAOUI ET AL.
FIGURE 14 SEM images and EDX
spectra of recycled catalyst after (a) first
run and (b) fourth run
agglomerated particles which could affect the catalytic
performance (Table 5). Moreover, the identity of the
recovered catalyst was studied using powder XRD analy-
sis (Figure 15) which shows that the crystallinity of the
catalyst remains similar to that of fresh catalyst with
absence of Pd(II) peak. This is due to its reduction by
the presence of excess of NaBH4 during nitroarene
reduction.
4 | CONCLUSIONS
In summary, novel palladium nanoparticles (Pd(0)) were
synthesized without the use of any reducing agent. The
preparation was monitored by UV–visible spectroscopy
and offers significant advantages such as mild reaction
conditions. Afterwards, the palladium nanoparticles were
supported on a mesoporous NP support to prepare a cat-
alyst (Pd@NP). The prepared catalyst exhibits marked
activity, good reusability and stability in the reduction
of 4‐nitrophenol and other nitroarenes in aqueous
medium and at room temperature.
TABLE 5 EDX palladium ratio of Pd@NP during recycling
Pd@NP
Pd (wt%)
Pd (at%)
As prepared
First cycle
1.40
2.5
0.32
0.4
ACKNOWLEDGEMENT
We thank Prof. Dr Önder Metin from Koç University of
Istanbul for helpful comments and critical reading of
the manuscript.
Fourth cycle
4.5
1.1
ORCID
Ayoub Abdelkader Mekkaoui https://orcid.org/0000-0002-
7
336-1961
Soufiane El Houssame
522
https://orcid.org/0000-0003-1319-
8
REFERENCES
FIGURE 15 XRD patterns of fresh and recycled Pd@NP catalyst
[1] K. P. De Jong, Curr. Opin. Solid State Mater. Sci. 1999, 4, 55.

MEKKAOUI ET AL.
11 of 12
[
2] O. Deutschmann, H. Knözinger, K. Kochloefl, T. Turek,
Ullmann's Encyclopedia of Industrial Chemistry, Wiley‐VCH,
Weinheim 2009.
Jennane, B. Boualy, N. Fdil, A. Karim, L. El Firdoussi,
J. Mater. Environ. Sci. 2017, 8(S), 4778.
[
25] T. Teranishi, M. Miyake, Chem. Mater. 1998, 10, 594.
[
[
[
[
3] X. Zhou, Q. Chen, Y. Tao, H. Weng, J. Nat. Gas Chem. 2011, 4,
[
26] a)M. Nasrollahzadeh, E. Mehdipour, M. Maryami, J. Mater. Sci.
Mater. Electron. 2018, 29(19), 17054; b)S. S. Momeni, M.
Nasrollahzadeh, A. Rustaiyan, J. Colloid Interface Sci. 2017,
3
50.
4] K. Shimura, T. Miyazawa, T. Hanaoka, S. Hirata, Appl. Catal.
Gen. 2014, 475, 1.
499, 93; c)B. Khodadadi, M. Bordbar, M. Nasrollahzadeh,
5] S. Shubhra Acharyya, S. Ghosh, R. Singh, R. Bal, J. Adv. Catal.
Sci. Technol. 2014, 1, 15.
J. Colloid Interface Sci. 2017, 490, 1; d)B. Khodadadi, M.
Bordbar, A. Yeganeh‐Faal, M. Nasrollahzadeh, J. Alloys
Compd. 2017, 719, 82; e)M. Maryami, M. Nasrollahzadeh, E.
Mehdipour, S. M. Sajadi, Sep. Purif. Technol. 2017, 184, 298; f)
M. Khazaei, A. Khazaei, M. Nasrollahzadeh, M. R. Tahsili, Tet-
rahedron 2017, 73, 5613; g)Z. Issaabadi, M. Nasrollahzadeh, S.
M. Sajadi, J. Clean. Prod. 2017, 142, 3584.
6] E. Del Río, D. Gaona, J. C. Hernández‐Garrido, J. J. Calvino,
M. G. Basallote, M. J. Fernández‐Trujillo, J. A. Pérez‐Omil, J.
M. Gatica, J. Catal. 2014, 318, 119.
[
7] A. Abdedayem, M. Guiza, A. Ouederni, C. R. Chim. 2015, 18,
1
00.
[
27] F. El Aroui, S. Lahrich, A. Farahi, M. Achak, L. El Gaini, M.
[
[
8] B. Tamami, S. Ghasemi, Appl. Catal. Gen. 2011, 393, 242.
Bakasse, A. Bouzidi, M. A. El Mhammedi, Electroanalysis
9] A. Di Giuseppe, M. Crucianelli, M. Passacantando, S. Nisi, R.
Saladino, J. Catal. 2010, 276, 412.
2014, 26, 1751.
[
[
[
28] A. Hassine, S. Sebti, A. Solhy, M. Zahouily, C. Len, M. N.
[
[
[
[
10] N. Lahbabi, Z. Rais, M. Hajjaji, S. Kacim, Afr. Sci. Rev. Int. Sci.
Technol. 2009, 05, 14.
Hedhili, A. Fihri, Appl. Catal. Gen. 2013, 450, 13.
29] S. Sebti, M. Zahouily, H. Lazrek, J. Mayoral, D. Macquarrie,
11] J. Xi, Y. Zhang, Q. Xia, X. Liu, J. Ren, G. Lu, Y. Wang, Appl.
Catal. Gen. 2013, 459, 52.
Curr. Org. Chem. 2008, 12, 203.
30] Y. E. L. Bouabi, A. Farahi, M. Achak, M. Zeroual, K. Hnini, S.
El Houssame, M. Bakasse, A. Bouzidi, M. A. El Mhammedi,
J. Taiwan Inst. Chem. Eng. 2016, 66, 33.
12] S. Rostamizadeh, A. M. Amani, G. H. Mahdavinia, N. Shadjou,
Chin. Chem. Lett. 2009, 20, 779.
13] F. Frederix, J. Friedt, K. Choi, W. Laureyn, A. Campitelli, D.
[
[
[
31] A. Louroubi, H. Ouahine, B. Boualy, M. Ait Ali, L. El Firdoussi,
Mondelaers, G. Maes, G. Borghs, Anal. Chem. 2003, 75, 6894.
J. Adv. Catal. Sci. Technol. 2016, 13, 63.
[
[
14] M. Brust, C. J. Kiely, Colloids Surf. A 2002, 202, 175.
32] G. Booth, Ullmann's Encyclopedia of Industrial Chemistry,
Wiley‐VCH, Weinheim 2000.
15] C. H. Ho, J. Tobis, C. Sprich, R. Thomann, J. C. Tiller, Adv.
Mater. 2004, 16, 957.
33] G. Eichenbaum, M. Johnson, D. Kirkland, P. O'Neill, S. Stellar,
J. Bielawne, R. DeWire, D. Areia, S. Bryant, S. Weiner, D.
Desai‐Krieger, P. Guzzie‐Peck, D. C. Evans, A. Tonelli, Regul.
Toxicol. Pharmacol. 2009, 55, 33.
[
[
[
16] H. R. Moon, J. H. Kim, M. P. Suh, Angew. Chem. 2005, 44, 1261.
17] C. T. Campbell, S. C. Parker, D. E. Starr, Science 2002, 298, 811.
18] A. B. R. Mayer, J. E. Mark, S. H. Hausner, Angew. Makromol.
Chem. 1998, 259, 45.
[34] S. C. Mitchell, R. H. Waring, Ullmann's Encyclopedia of Indus-
[
19] M. Zhao, R. M. Crooks, Angew. Chem. Int. Ed. 1999, 38, 364.
trial Chemistry, Wiley‐VCH, Weinheim 2000.
[
20] S. Praharaj, S. Nath, S. K. Ghosh, S. Kundu, T. Pal, Langmuir
[35] K. Esumi, R. Isono, T. Yoshimura, Langmuir 2004, 20, 237.
2
004, 20, 9889.
21] C. Shi, M. Cheng, Z. Qu, X. Bao, Appl. Catal. Environ. 2004, 51,
71.
[
36] a)H. Veisi, S. Kazemi, P. Mohammadi, P. Safarimehr, S.
Hemmati, Polyhedron 2019, 157, 232; b)M. Nasrollahzadeh,
M. Sajjadi, M. Maham, S. M. Sajadi, A. A. Barzinjy, Mater.
Res. Bull. 2018, 102, 24; c)M. Nasrollahzadeh, M. Sajjadi, S.
M. Sajadi, Chin. J. Catal. 2018, 39, 109; d)S. M. Sajadi, K. Kolo,
S. M. Hamad, S. A. Mahmud, A. A. Barzinjy, S. M. Hussein,
ChemistrySelect 2018, 3, 12274; e)S. M. Sajadi, K. Kolo, S. M.
Abdullah, S. M. Hamada, H. S. Khalida, A. T. Yassein, Surf.
Interfaces 2018, 13, 205; f)S. M. Sajadi, K. Kolo, S. M. Hamad,
S. A. Mahmud, M. Pirouei, K. Amjadian, K. M. Khalid, IET‐
Nanobiotechnology 2018, 13, 124; g)S. M. Sajadi, K. Kolo, M.
Pirouei, S. A. Mahmud, J. A. Alia, S. M. Hamad, RSC Adv.
[
[
1
22] a)B. M. Choudary, S. Madhi, N. S. Chowdari, M. L. Kantam, B.
Sreedhar, J. Am. Chem. Soc. 2002, 124, 14127; b)H. Veisi, N. H.
Nasrabadi, P. Mohammadi, Appl. Organometal. Chem. 2016, 30,
8
2
6
90; c)S. Lebaschi, M. Hekmati, H. Veisi, J. Colloid Interface Sci.
017, 485, 223; d)E. Farzad, H. Veisi, J. Ind. Eng. Chem. 2018,
0, 114; e)H. Veisi, M. Pirhayati, A. Kakanejadifard, P.
Mohammadi, M. R. Abdi, J. Gholami, S. Hemmati,
ChemistrySelect 2018, 3, 1820; f)S. Hemmat, L. Mehrazin, M.
Pirhayati, H. Veisi, Polyhedron 2019, 158, 414.
[
[
23] a)J. M. Thomas, B. F. G. Johnson, R. Raja, G. Sakar, P. A.
Midgley, Acc. Chem. Res. 2003, 36, 20; b)B. A. Khakiania, K.
Pourshamsiana, H. Veisi, Appl. Organometal. Chem. 2015, 29,
2
018, 8, 35557; h)M. Maryami, M. Nasrollahzadeh, E.
Mehdipour, S. M. Sajadi, Int. J. Hydrogen Energy 2016, 41,
1236.
2
2
59; c)H. Veisi, M. Ghadermazi, A. Naderi, Appl. Organometal.
[
[
[
37] P. Hervés, M. Pérez‐Lorenzo, L. M. Liz‐Marzán, J. Dzubiella, Y.
Chem. 2016, 30, 341; d)H. Veisi, S. Najafi, S. Hemmati, Int. J.
Biol. Macromol. 2018, 113, 186.
Lu, M. Ballauff, Chem. Soc. Rev. 2012, 41, 5577.
38] S. Wunder, Y. Lu, M. Albrecht, M. Ballauff, ACS Catal. 2011, 1,
24] a)S. El Houssame, L. El Firdoussi, S. Allaoud, A. Karim, Y. Cas-
tanet, A. Mortreux, J. Mol. Catal. A 2001, 168, 15; b)S. El
Houssame, H. Anane, L. El Firdoussi, A. Karim, Cent. Eur. J.
Chem. 2008, 6(3), 470; c)S. El Houssame, A. A. Mekkaoui, S.
9
08.
39] T. Aditya, A. Pal, T. Pal, Chem. Commun. 2015, 51, 9410.
[40] N. Pradhan, A. Pal, T. Pal, Colloids Surf. A 2002, 196, 247.

12 of 12
MEKKAOUI ET AL.
[
41] K. Esumi, K. Miyamoto, T. Yoshimura, J. Colloid Interface Sci.
002, 254, 402.
[58] Y. Piao, Y. Jang, M. Shokouhimehr, I. S. Lee, T. Hyeon, Small
2007, 3, 255.
2
[
42] a)P. Zhao, X. Feng, D. Huang, G. Yang, D. Astruc, Coord.
Chem. Rev. 2015, 287, 114; b)H. Veisi, S. B. Moradi, A. Saljooqi,
P. Safarimehr, Mater. Sci. Eng. C 2019, 100, 445; c)H. Veisi, S.
Razeghi, P. Mohammadi, S. Hemmati, Mater. Sci. Eng. C
[59] P. G. Scherrer, Nachrichten Math. Phys. 1918, 2, 98.
[
[
60] B. O. Fowler, Inorg. Chem. 1974, 13, 207.
61] S. Harish, J. Mathiyarasu, K. L. N. Phani, V. Yegnaraman,
Catal. Lett. 2009, 128, 197.
2
019, 97, 624.
[
62] F. El Aroui, S. Lahrich, A. Farahi, M. Achak, L. El Gaini, B.
Manoun, M. Bakasse, A. Bouzidi, M. A. El Mhammedi,
J. Taiwan Inst. Chem. Eng. 2014, 45, 2725.
[
[
43] Y.‐C. Chang, D.‐H. Chen, J. Hazard. Mater. 2009, 165, 664.
44] a)M. Rocha, C. Fernandes, C. Pereira, S. L. H. Rebelo, M. F. R.
Pereira, C. Freire, RSC Adv. 2015, 5, 5131. b)M.
Nasrollahzadeh, Z. Issaabadi, R. Safari, Sep. Purif. Technol.
[63] M. Grdeń, M. Łukaszewski, G. Jerkiewicz, A. Czerwiński,
Electrochim. Acta 2008, 53, 7583.
2
019, 209, 136.
[64] B. Hosseini, S. M. Mirhadi, M. Mehrazin, M. Yazdanian, M. R.
[
[
[
45] P. Zhang, C. Shao, Z. Zhang, M. Zhang, J. Mu, Z. Guo, Y. Liu,
Kalantar Motamedi, Trauma Mon. 2017, 22, 36139.
Nanoscale 2011, 3, 3357.
[
[
65] M. Mujahid, S. Sarfraz, S. Amin, Mater. Res. 2015, 18, 468.
46] Q. Wang, W. Jia, B. Liu, A. Dong, X. Gong, C. Li, P. Jing, Y. Li,
66] J. Guo, F. Dong, S. Zhong, B. Zhu, W. Huang, S. Zhang, Catal.
Lett. 2018, 148, 359.
G. Xu, J. Zhang, J. Mater. Chem. A 2013, 1, 12732.
47] S. K. Ghosh, M. Mandal, S. Kundu, S. Nath, T. Pal, Appl. Catal.
Gen. 2004, 268, 61.
[
[
[
[
67] P. Wang, F. W. Zhang, Y. Long, M. Xie, R. Li, J. T. Ma, Catal.
Sci.Technol. 2013, 3, 1618.
[
48] V. Purohit, A. K. Basu, Chem. Res. Toxicol. 2000, 13, 673.
68] M. Islam, P. Mondal, A. S. Roy, K. Tuhina, Transition Met.
Chem. 2010, 35, 427.
[
49] US Department of Health and Human Services, Public Health
Service, Agency for Toxic Substances and Disease Registry,
69] A. K. Shil, D. Sharma, N. R. Guha, P. Das, Tetrahedron Lett.
1
995.
2
012, 53, 4858.
70] Z. M. Wang, C. L. Xu, G. Q. Gao, X. Li, RSC Adv. 2014, 4,
3644.
[
[
50] J. C. Oxley, Explosive Effects and Applications, Springer, New
York 1998.
1
51] a)A. S. Travis, Chemistry of Anilines, Part 1, John Wiley, New
York 2007. b)Ö. Metin, H. Can, K. Şendil, M. S. Gültekin,
J. Colloid Interface Sci. 2017, 498, 378.
SUPPORTING INFORMATION
[
[
[
52] M. A. Harrad, P. Valerga, M. C. Puerta, I. Houssini, M. Ait Ali,
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
L. El Firdoussi, A. Karim, Molecules 2011, 16, 367.
53] A. Farrouji, A. Eddine, S. Bouzit, B. Boualy, A. Mehdi, L.
Firdoussi, M. Ait Ali, Int. Res. J. Pure Appl. Chem. 2015, 8, 190.
54] a)A. Aberkouks, A. A. Mekkaoui, B. Boualy, S. El Houssame,
M. Ait Ali, L. El Firdoussi, Adv. Mater. Sci. Eng. 2018, 2018,
1
; b)A. Aberkouks, A. A. Mekkaoui, B. Boualy, S. El Houssame,
M. Ait Ali, L. El Firdoussi, Mater. Today Proc. 2019, 13, 453.
How to cite this article: Mekkaoui AA, Jennane
S, Aberkouks A, et al. Palladium nanoparticles
supported on mesoporous natural phosphate: An
efficient recyclable catalyst for nitroarene
reduction. Appl Organometal Chem. 2019;e5117.
https://doi.org/10.1002/aoc.5117
[
[
55] M. V. Morales, M. Rocha, C. Freire, E. Asedegbega‐Nieto, E.
Gallegos‐Suarez, I. Rodríguez‐Ramos, A. Guerrero‐Ruiz, Car-
bon 2017, 111, 150.
56] Natural phosphate (NP) comes from Khouribga Region
(
Morocco); it is readily available (raw or treated) from the Cen-
tre for Studies and Research of Mineral Phosphates
CERPHOS), 37 Bd My Ismail, Casablanca, Morocco.
(
[
57] D. Berger, G. A. Trăistaru, B. Ş. Vasile, I. Jitaru, C. Matei, UPB
Sci. Bull. Ser. B 2010, 72, 113.