Palladated cyclodextrin and halloysite containing polymer and its carbonized form as efficient hydrogenation catalysts

Article abstract of DOI:10.1002/aoc.5213

β-Cyclodextrin (β-CD) and glycidyl methacrylate monomer were polymerized in the presence of functionalized halloysite nanoclay (Hal) to afford a polymeric network (Hal-P-CD) containing Hal and CD. Hal-P-CD was then applied as a catalyst support for the im

Full text of DOI:10.1002/aoc.5213

Received: 8 July 2019
DOI: 10.1002/aoc.5213
Revised: 26 July 2019
Accepted: 8 August 2019
F U L L P A P E R
Palladated cyclodextrin and halloysite containing polymer
and its carbonized form as efficient hydrogenation catalysts
Samahe Sadjadi1
| Fatemeh Koohestani1 | Bastien Léger2
| Eric Monflier2
1 Gas Conversion Department, Faculty of
Petrochemicals, Iran polymer and
Petrochemicals Institute, PO Box 14975‐
112, Tehran, Iran
2 Univ. Artois, CNRS, Centrale Lille,
ENSCL, Univ. Lille, UMR 8181, Unité de
Catalyse et de Chimie du Solide (UCCS),
F‐62300, Lens, France
β‐Cyclodextrin (β‐CD) and glycidyl methacrylate monomer were polymerized
in the presence of functionalized halloysite nanoclay (Hal) to afford a poly-
meric network (Hal‐P‐CD) containing Hal and CD. Hal‐P‐CD was then applied
as a catalyst support for the immobilization of Pd nanoparticles. The resulting
nanocomposite, Pd@Hal‐P‐CD, could serve as a catalyst for the hydrogenation
of nitrobenzene. The precise study by the preparation of control samples con-
firmed the contribution of CD as both phase transfer and capping agent, P
(polymer) and Hal to the catalysis. Moreover, the results confirmed the impor-
tance of CD: glycidyl methacrylate monomer ratio. Pd@Hal‐P‐CD was also car-
bonized to prepare Pd@Hal‐C. Notably, the characterization of Pd@Hal‐C
showed that carbonization led to the growth of mean diameter of Pd nanopar-
ticles, increase of Pd content and partial destruction of Hal. However, the cat-
alytic activity of Pd@Hal‐C was superior to Pd@Hal‐P‐CD. Pd@Hal‐C was also
highly recyclable and could be recovered and recycled for several reaction runs.
The study of the carbonization temperature showed that this factor affected the
nature of the resulting carbon and the catalyst prepared at elevated tempera-
ture showed higher catalytic activity.
Correspondence
Samahe Sadjadi, Gas Conversion
Department, Faculty of Petrochemicals,
Iran polymer and Petrochemicals
Institute, PO Box 14975‐112. Tehran, Iran.
Email: samahesadjadi@yahoo.com
Funding information
PHC GUNDISHAPUR 2018, Grant/Award
Number: 40870ZG; Iran National Science
Foundation, Grant/Award Number:
97009384; French Embassy; Center for
International Scientific Studies & Collab-
orations (CISSC); European Regional
Development Fund (ERDF); Conseil
Régional du Nord‐Pas de Calais
KEYWORDS
carbonization, cyclodextrin, halloysite, heterogeneous catalyst, hydrogenation
1 | INTRODUCTION
its applications, surface functionalization as well as for-
mation of composite with other components such as poly-
In recent years, the use of halloysite nanoclay (Hal) as a
catalyst support has gained growing interest and numer-
ous heterogeneous Hal‐based catalysts have been devel-
oped and successfully applied for promoting diverse
organic transformations ranging from hydrogenation to
coupling reactions.[1–7] Moreover, Hal has been utilized
for the preparation of novel photocatalysts.[8–10] The
excellent performance of Hal can be assigned to its distin-
guished physical and chemical properties, including bio‐
compatibility, tubular morphology, opposite electrical
charges and chemical composition on inner and outer
surfaces and high mechanical resistance.[5–7,11,12] In
attempt to improve the properties of Hal and broaden
mers, dendrimers and carbon materials have been
focused.[4,13,14]
β‐cyclodextrin (CD) is a cyclic oligosaccharide com-
posed of 7 glucose subunits with defined cone‐shape
structure, in which the exterior surface is hydrophilic,
while the interior space is hydrophobic. The non‐toxic,
bio‐compatible and relatively low cost of β‐CD broaden
its utility in various sectors such as food industry, design
of delivery systems and catalysis.[15–17] The contribution
of CD in the catalysis is mostly related to three main
domains. First, CD can effectively act as a capping agent
and prevent nano‐catalysts from aggregations. More
importantly, CD can host the hydrophobic substrates
Appl Organometal Chem. 2019;e5213.
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SADJADI ET AL.
inside its cavity and shuffle them to the hydrophilic
media.[15–17] Beside, CD can be considered as an efficient
precursor for the formation of carbon materials.[18–20]
Considering the wide range of use of aniline deriva-
tives in the industrial sector, many attempts have been
devoted to the development of efficient protocols for the
synthesis of anilines through hydrogenation of nitroben-
zenes.[21] This chemical process is mostly promoted in
the presence of precious metals such as Pd. Taking the
economic and environmental concerns into account, the
use of heterogeneous precious metals has received
increasing attention. Heterogenization can simply be
achieved by immobilization of metallic species on the sur-
face of an appropriate support or through encapsulation
within the cavity of the porous support.[22–26]
2 | EXPERIMENTAL
2.1 | Materials
The materials applied for the preparation of the catalyst
included Hal, β‐CD, 3‐ (trimethoxysilyl) propyl methacry-
late (M), potassium peroxide sulphate (KPS), Pd (OAc)2,
sodium hydroxide, NaBH4, toluene, distilled water, chlo-
roform and MeOH, all was provided from Sigma‐Aldrich
and used as received without further purification. The
chemicals used for performing the catalytic experiments,
i.e. nitroarenes, were purchased from Sigma‐ Aldrich.
In the continuation of our research on the develop-
2.2 | Instruments
ment of efficient Hal‐based heterogeneous catalysts,[27–
29]
recently, we have reported a novel catalyst with the
To characterize the prepared catalyst as well as the con-
trol catalysts, the following instruments were applied:
XRD, ICP‐AES, TGA, BET, TEM, FTIR, Zeta potential
and Raman spectroscopy. To record FTIR spectra,
PERKIN‐ELMER‐Spectrum 65 instrument was employed.
ICP analyses were performed by using ICP analyzer
Varian, Vista‐pro. To verify the structure of the catalyst
and the control samples, their XRD patterns were
recorded using a Siemens, D5000. Cu Kα radiation from
a sealed tube. METTLER TOLEDO thermogravimetric
analysis apparatus (scanning rate of 10 °C.min−1 under
N2 atmosphere) was applied for studying thermal stability
of the catalyst. The Raman spectrometer was TEKSAN‐
N1–541 Spectrum at k = 532 nm instrument. The textural
property of the catalyst was investigated by performing
BET analysis using a Belsorp Mini II instrument. To pre-
pare the sample for this analysis, the degassing was car-
ried out at 100 °C for 2 hr. Transmission Electron
Microscopy (TEM) was accomplished on a Tecnai Micro-
scope (200 kV) to record the morphology of the catalyst
and control samples. In detail, the samples were depos-
ited onto a carbon coated copper grid. Pd nanoparticle
size distributions have been calculated from the measure-
ment of ~ 200 nanoparticles found in arbitrarily selected
area of the images using the program ImageJ. Zeta poten-
tial measurements were carried out in water suspension
using a Malvern Zetasizer Nano ZS. The calculations are
based on a Laser Doppler electrophoretic mobility of
metallic nanoparticles via the Helmholtz‐Smoluchowski
equation, ξ = (η/ε)μe, where η is the viscosity of the
suspending liquid, μe is the ratio between the velocity of
the nanoparticles and the magnitude under the employed
electric field, and ε the dielectric conductivity of H2O. For
each test, 5 mg of the composite was dispersed in 5 mL of
deionized H2O and maintained under ultrasonic irradia-
tion for half an hour prior to ZP analysis.
utility for coupling reaction, in which Pd nanoparticles
were immobilized on the composite of poly (glycidyl
methacrylate) and Hal, in which Hal was covered with
a shell of poly (glycidyl methacrylate).[30] The composite
was simply synthesized through functionalization of Hal
surface with 3‐(trimethoxysilyl) propyl methacrylate
followed by the polymerization with glycidyl methacry-
late (M) monomer. The high catalytic activity of the cata-
lyst motivated us to pursue our investigation on pol
(glycidyl methacrylate)‐ Hal composite and develop a
new catalyst based on that. On the other hand, our expe-
riences showed that combination of chemistry of CD and
Hal could increase the catalytic activity of the resulting
catalyst due to the role of CD as molecular shuttle and
formation of inclusion complex with the hydrophobic
substrate and transferring it to the aqueous media.[29,31,32]
Taking the previous results into account, a novel cata-
lytic system is designed and prepared based on the incor-
poration of Hal as a filler in a 3D polymeric network,
formed from polymerization of CD and glycidyl methac-
rylate monomer, followed by Pd nanoparticles immobili-
zation. The performance of the catalyst, Pd@Hal‐P‐CD,
was studied for the hydrogenation reaction of
nitroarenes. Moreover, comparing the catalytic activity
of the catalyst with that of some control catalysts, the
roles of Hal, CD and the polymeric network in the catal-
ysis as well as the effect of Hal:CD ratio were investi-
gated. In the following, Pd@Hal‐P‐CD was carbonized
and the catalytic activity of the resulting composite,
Pd@Hal‐C, was compared with that of Pd@Hal‐P‐CD.
Furthermore, the effect of carbonization temperature on
the catalytic activity of the catalyst was studied. In the
final section of this research, the recyclability of
Pd@Hal‐C that exhibited the highest catalytic activity as
well as its Pd leaching were examined.

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2.3 | Synthesis of the catalyst
2.3.4 | Carbonization of Pd@Hal‐P‐CD:
Synthesis of Pd@Hal‐C
2.3.1 | Hal functionalization with 3‐ (tri‐
methoxysilyl) propyl methacrylate: Syn-
thesis of Hal‐S
In the final stage of the synthesis of the catalyst, Pd@Hal‐
C, the as prepared Pd@Hal‐P‐CD was carbonized in fur-
nace under inert atmosphere for 4.5 hr (the first 4 hr at
450 °C and the last 2 hr at 750 °C). The schematic repre-
sentation of the procedure used for the synthesis of the
catalyst, Pd@Hal‐C, is depicted in Figure 1. Using ICP
analysis, the content of Pd in Pd@Hal‐C was calculated
To decorate Hal with 3‐ (tri‐methoxysilyl) propyl methac-
rylate, Hal (1.5 g) was dispersed in dry toluene (40 ml)
under ultrasonic irradiation (power of 120 W) for half
an hour. Subsequently, 3‐(tri‐methoxysilyl) propyl meth-
acrylate (1.5 g) was slowly added to the homogenized sus-
pension of Hal in toluene. The resulting mixture was then
heated and refluxed under inert atmosphere for 1 day.
Upon completion of the reaction, the solid was filtered
off, washed with toluene several times and dried in oven
at 80 °C for 1 day.
to be 0.19 mmol.g−1
.
It is worth noting that for the synthesis of the control
catalysts, Pd@Hal, Pd@P, Pd@P‐CD, Pd@Hal‐CD,
Pd@Hal‐P, the same procedure was used, except Hal, P
and P‐CD were applied as catalyst support, respectively.
Moreover, to elucidate the role of the ratio of the mono-
mers in the catalysis, Pd@Hal‐P‐CD catalyst with CD:M
ratio of 6:3 was also prepared. To study the effect of car-
bonization temperature, apart from the main catalyst that
was carbonized at 450–750 °C (Pd@Hal‐C750), another
catalyst (Pd@Hal‐C600) was prepared, in which carboni-
zation was performed at 450–600 °C.
2.3.2 | Polymerization of CD and glycidyl
methacrylate in the presence of Hal‐S:
Synthesis of Hal‐P‐CD
Hal‐S (1.5 g) was first dispersed in the mixture of distilled
water and toluene with the aid of ultrasonic irradiation.
Then, a solution of CD (5 g in 10 mL distilled water)
and KPS (0.1 g) were added to the Hal‐S suspension.
The obtained mixture was stirred under inert atmosphere
for 15 min. Subsequently, M monomer (4 g) was injected
to the mixture. Then, the polymerization reaction was
carried out at 70 °C for 1 day. At the end of the reaction,
the precipitate was collected and washed with distilled
water repeatedly. To further purify the product and
remove unreacted monomers, the solid was subjected to
Soxhlet extraction with chloroform for 72 hr. Finally,
the product, Hal‐P‐CD, was obtained after drying in oven
at 80 °C for 12 hr.
2.4 | Hydrogenation reaction
The hydrogenation of nitro compounds and formation of
the corresponding anilines was carried out as follow: the
catalyst (3 wt. %) was introduced to the mixture of nitro
compound (1 mmol) in deionized water (2 ml) in a glass
reactor. Then, the temperature of the mixture was ele-
vated to 60 °C and hydrogen gas was purged into the
reaction vessel (H2 pressure of 1 atm). After that, the mix-
ture was stirred vigorously (700 rpm) and the progress of
the reaction was monitored via TLC. At the end of the
reaction, the catalyst was separated via simple filtration,
washed with H2O for several times and dried at 95 °C
overnight for reusing in the consecutive reaction runs.
To obtain the anilines, the solvent was evaporated. To
identify the organic products, their melting/boiling point
and FTIR spectra were compared with those of the
authentic samples.
2.3.3 | Immobilization of Pd nanoparticles
on Hal‐P‐CD
To immobilize Pd nanoparticles on Hal‐P‐CD support,
Hal‐P‐CD (7 g) was homogeneously dispersed in dry tolu-
ene (30 mL) by using ultrasonic irradiation of power
100 W. Subsequently, a solution of Pd (OAc)2 (0.75 g in
20 ml toluene) as Pd precursor was added to the afore-
mentioned suspension in a dropwise manner. The
resulting mixture was then stirred for 1 day. Upon com-
pletion of the reaction, a solution of NaBH4 (0.65 g in
30 ml EtOH) was introduced to the mixture in a dropwise
manner. After stirring for 1 hr, the precipitate was filtered
off, washed and dried at 70 °C in oven for 12 hr.
3 | RESULTS AND DISCUSSION
3.1 | Catalyst characterization
To verify the formation of the Pd@Hal‐P‐CD as well as
Pd@Hal‐C, their FTIR spectra were recorded (Figure 2).
As depicted, the FTIR spectrum of Pd@Hal‐P‐CD exhib-
ited the characteristic bands at 1729 cm−1 that can be
assigned to the –C=O functionality in the backbone of
the P, 3440 cm−1 that can be due to the –OH functionality

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SADJADI ET AL.
FIGURE 1 The schematic representation of the procedure used for the synthesis of the catalyst
stretching and Al‐O‐Si vibration of the incorporated Hal
respectively (Figure 2). Moreover, the two small bands
at 3737 and 3675 cm−1 can be assigned to the internal
hydroxyl groups of Hal. Other characteristic bands of
Hal overlapped with that of P‐CD.[33] The formation of
Pd@Hal‐C can be confirmed by comparing the FTIR
spectrum of the catalyst with that of Pd@Hal‐P‐CD. More
precisely, the disappearance of the characteristic band of
P (the band at 1729 cm−1) can indicate the successful car-
bonization. The bands at 2925 cm−1 and 3440 cm−1 in the
FTIR spectrum of Pd@Hal‐C can be attributed to the –
CH2 and –OH functionalities in C. Noteworthy, the Hal
characteristic band at 1027 cm−1 is shifted to
1091 cm−1, indicating the coverage of Al in Hal structure
with carbon.[34] Moreover, the band at 910 cm−1 that is
indicative of Al‐OH bending vibration disappeared in
the FTIR spectrum of Pd@Hal‐C. This can be attributed
to the thermal treatment of Hal‐P‐CD.[34]
FIGURE 2 FTIR spectra of Hal, Pd@Hal‐P‐CD and Pd@Hal‐C
of CD as well as the hydroxyl groups of the opened epoxy
rings and 2925 cm−1 (‐CH2 stretching). Noteworthy, the
short characteristic bands at 1027 cm−1 and 580 cm−1
can also be observed that can be attributed to the Si–O
To further characterize the catalyst, the TGA thermo-
gram of Pd@Hal‐C was recorded and compared with that

SADJADI ET AL.
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of pristine Hal and Pd@Hal‐P‐CD (Figure 3). The weight
losses in the thermogram of pristine Hal included the loss
at ~140 °C that is due to the loss of water in Hal structure
and the loss related to the Hal dehydroxylation
(~540 °C).[35,36] As illustrated, Hal‐P‐CD exhibited lower
thermal stability compared to Hal. In more detail, besides
loss of water (at ~ 100 °C), two more losses were observed
at 290 (19.5 wt.%) and 380 °C (37.9 wt.%). These weight
losses can be assigned to the degradation of P‐CD. As
shown in (Figure 3), upon carbonization and formation
of Pd@Hal‐C, the thermal stability significantly
increased. This observation can further confirm the suc-
cessful carbonization of P‐CD.
26.7°, 35.4°, 55.6° and 62.1°, JCPDS No. 29–1487 (labelled
as H)) can be observed.[37,38] However, the intensities of
these peaks are dramatically decreased and small shift
can also be seen. According to the literature, the decrease
in the intensity of Hal characteristic bands can be
assigned to the thermal treatment.[34,39] On the other
hand, the slight shift of the Hal characteristic bands can
be attributed to the intercalation of P chain between the
silicate layers of Hal.[40] Moreover, the Pd characteristic
bands can be observed at 2θ = 41.1 °, 45.5°, 68.7°, 79.6°,
and 87° (labelled as P) that can be assigned to the
{111},[41] {200}, {220}, {311} and {222} planes of Pd (JCPDS,
No.46–1043).[42] Apart from Hal and Pd characteristic
bands, an additional band at 2θ = 24.2° appeared and
that can be attributed to the formation of graphite‐like
carbon structure (crystalline carbon).[43] Regarding
Pd@Hal‐P‐CD, only a broad band at 2θ = 13–20° can be
detected in the XRD pattern that can be assigned to the
amorphous P‐CD. The absence of the characteristic bands
of Hal and Pd can be attributed their low content in the
composite.[44]
To shed more light to the structure of the catalyst, the
XRD patterns of pristine Hal, Pd@Hal‐P‐CD and
Pd@Hal‐C were recorded and compared (Figure 4). As
illustrated in Figure 4, in the XRD pattern of Pd@Hal‐
C, the characteristic bands of Hal (2θ = 11.5°, 20.2°,
The N2‐adsorption–desorption isotherm of Pd@Hal‐C,
depicted in Figure S1, exhibited type IV isotherm, indicat-
ing the porous nature of Pd@Hal‐C. The BET analysis
showed that the specific surface area of the catalyst was
193 m2 g−1
.
In order to have a better idea of the dispersion and the
size of Pd nanoparticles dispersed onto the support, TEM
characterization of the different synthesized samples has
been done. First, the TEM images of Pd@Hal clearly
show that the structure of the Hal nanotubes is preserved
after the deposition of the metal nanoparticles (The Pd
nanoparticles are deposited on the Hal tubes, Figure
S2). Nevertheless, the dispersion of the Pd nanoparticles
onto the support is not so good even if no aggregation is
observed. If Pd nanoparticles were supported on the
FIGURE 3 TGA thermograms of Hal, Pd@Hal‐P‐CD and
Pd@Hal‐C
FIGURE 4 XRD patterns of Hal,
Pd@Hal‐P‐CD and Pd@Hal‐C

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SADJADI ET AL.
Hal‐P‐CD polymer, considering a CD:M molar ratio of
5:4, a good dispersion of Pd nanoparticles is observed
with a mean diameter of 6.6
3.2 nm (Figure 5 and
Figure S3). As shown in Figure 5, the Pd nanoparticles
(black spots) can be observed on the polymeric sheet.
This better dispersion of Pd nanoparticles could be
explained by the strongest interaction between the Pd
metallic salt and the Hal‐P‐CD polymer in the organic
phase. It should be noticed that it is not possible to see
the structure of Hal nanotube in this sample coming from
the fact that the Hal is well embedded in P‐CD polymer.
If the CD:M molar ratio is increased from 5:4 to 6:3, the
dispersion of Pd nanoparticles is greatly altered (Figure
S4). Indeed, large aggregates are observed and conse-
quently, a poor dispersion of Pd nanoparticles is obtained.
Pd@Hal‐C was furnished from the carbonization at
750 °C of Pd@Hal‐P‐CD and the TEM characterization
clearly showed that the carbonization resulted in the
increase of the size of the Pd nanoparticles. In the TEM
images of this catalysts, the large Pd nanoparticles on
the carbon sheet are observable. Indeed, the mean diam-
eter of the Pd nanoparticles increased from 6.6 3.2 nm
to 26.0 12.6 nm (Figure S5) keeping the good dispersion
of Pd nanoparticles onto the support. It was found that in
the sample with higher amount of CD in P‐CD, the
increase of the size of Pd nanoparticles after the carboni-
zation step was less pronounced (with final mean diame-
ter of 20.9 15.2 nm, Figure S6) with a good dispersion of
Pd nanoparticles onto the support.
The increase of the hydrophobicity of the material
after the carbonization step has also been confirmed by
zeta potential measurement (Figure S7). Indeed, the zeta
potential value of Pd@Hal dispersion is about −45.8 mV.
This value is classical for a Hal support dispersed into
water because of the negative charge on the outer surface
of this material. This value for Pd@Hal‐P‐CD was about
−47.5 mV, very similar to that of Pd@Hal. Nevertheless,
after the carbonization step, this zeta potential is decreas-
ing from −47.5 to −38.6 mV. This decrease could be
explained by the increase of the hydrophobicity of the
surface of the catalyst coming from the formation of a
carbon layer onto the Hal surface.
3.2 | Catalyst activity
Encouraged by the results of our previous report,[30] in
which Hal‐P showed high performance as catalyst sup-
port, a novel catalytic system was designed. On the con-
trary of the previous report that polymer covered Hal
tubes, in this study a polymeric network was targeted, in
which Hal tubes were dispersed through covalent bond-
ing. Another novelty of the presented catalyst was
FIGURE 5 TEM images at different magnifications and size
distribution of Pd@Hal‐P‐CD catalyst

SADJADI ET AL.
7 of 13
incorporation of CD as co‐monomer and formation of a co‐
polymer of P‐CD. The aim of this design was benefiting
from the capability of CD for the encapsulation of the
hydrophobic substrate and serving as phase transfer agent
to make the reaction possible in aqueous media.
To investigate the catalytic activity of the catalyst, the
hydrogenation of nitrobenzene was targeted as a model
catalytic reaction. Initially, the reaction variables were
optimized by studying their effects on the reaction yield
(Table S1). The optimization tests showed that
performing hydrogenation in the presence of catalytic
amount of Pd@Hal‐P‐CD (3 wt.%) in water as solvent at
60 °C and hydrogen gas as reducing agent resulted in a
conversion of 80% and a selectivity of 100% towards ani-
line after 75 min.
Armed with the optimum reaction condition and with
the aim of studying the contribution of P, CD and Hal,
several control catalysts including, Pd@P, Pd@Hal,
Pd@Hal‐P, Pd@P‐CD and Pd@Hal‐CD were synthesized
and their catalytic activities for promoting hydrogenation
of nitrobenzene were compared with that of Pd@Hal‐P‐
CD (Table 1).
As shown in Table 1, the catalytic activity of Pd@Hal
was insignificant (Entry 8, Table 1). This observation
was quite expectable as bare Hal cannot effectively immo-
bilize Pd nanoparticles.[5] The catalytic activity of Pd@P
(Entry 9, Table 1) was also very low, but higher than that
of Pd@Hal. The higher activity of Pd@P could be attrib-
uted to the presence of several functionalities in the back-
bone of polymer network that could act as anchors for Pd
nanoparticles. The catalytic activity of Pd@Hal‐P (Entry
5, Table 1) was superior compared to Pd@Hal and
Pd@P, confirming the positive effect of composite forma-
tion of Hal and P on the catalytic activity of the resulting
catalyst. According to the literature, this could stem from
the synergism between two components of the compos-
ite.[27] Interestingly, Pd@Hal‐P‐CD (Entry 3, Table 1)
exhibited high catalytic activity that was remarkably
superior compared to that of three above‐mentioned cat-
alysts. According to the literature, this observation can
be assigned to the role of CD as a phase transfer agent
and its capability to form inclusion complex with the
hydrophobic substrate and transfer it to the aqueous
media.[15–17] Moreover, CD can induce its effect through
acting as capping agent for Pd nanoparticles and
preventing them from aggregation. This can be confirmed
from TEM results that showed Pd nanoparticle with
mean diameter of 6.6 3.2 nm and good dispersion.
To further investigate the contribution of CD to the
catalysis, Pd@Hal‐CD (Entry 6, Table 1) and Pd@P‐CD
(Entry 7, Table 1) were also prepared and their catalytic
activities were compared with that of the CD‐free coun-
terparts. As tabulated, the catalytic activity of Pd@Hal‐
CD was superior to that of Pd@Hal catalyst, emphasizing
the role of CD in the catalysis. Notably, this effect was not
pronounced in the case of Pd@P‐CD.
Confirming the contribution of CD to the catalysis, the
effect of the content of CD on the catalyst backbone was
studied by changing the ratio of CD: M monomer in the
course of formation of Pd@Hal‐P‐CD. In this line, two
catalysts with the ratios of 5:4 and 6:3 of CD:M were pre-
pared (Entries 3 and 4, Table 1) and their catalytic activ-
ities were examined. The results showed that the
optimum ratio of CD:M was 5:4 and increase of this ratio
to 6:3 decreased the catalytic activity. This issue can be
justified by the TEM results. As discussed above, increase
of CD:M from 5:4 to 6:3 resulted in large aggregates and
consequently, a poor dispersion of Pd nanoparticles. This
can lead to the inferior catalytic activity. This observation
can show that there is an optimum amount for the con-
tent of CD and further increase of this value can have a
converse effect on the observed catalytic activity.
TABLE 1 The comparison of the catalytic activity of the catalyst
for hydrogenation of nitrobenzene with that of control samplesa
Entry
Catalyst
Yield. [%]b
1
2
Pd@Hal‐C750
Pd@Hal‐Cc
Pd@Hal‐P‐CD
Pd@Hal‐P‐CDd
Pd@Hal‐P
100
60
80
50
35
35
22
10
20
92
3
4
5
6
Pd@Hal‐CD
Pd@P‐CD
7
Motivated by the previous results on the high catalytic
activity of Hal‐carbon composites,[28,32] in the second part
of this study, it was elucidated whether carbonization of
Pd@Hal‐P‐CD has a positive effect on the catalytic activity
of the catalyst. In this line, Pd@Hal‐P‐CD was carbonized,
characterized and the catalytic activity of the resulting cat-
alyst, Pd@Hal‐C, for promoting the hydrogenation of the
model reaction under similar reaction condition was mea-
sured (Entry 1, Table 1) and compared with that of
Pd@Hal‐P‐CD. Notably, the characterization of Pd@Hal‐
C showed that carbonization resulted in significant
8
Pd@Hal
9
Pd@P
10
Pd@Hal‐C600e
aReaction conditions: Substrate (1 mmol), catalyst (3 wt%), H2O (2 ml), agi-
tation (700 rpm) at 60 °C.
bIsolated yields.
cThe catalyst prepared by carbonization of Pd@Hal‐P‐CD synthesized by
using CD:M ratio of 6:3.
dPd@Hal‐P‐CD prepared by using CD:M ratio of 6:3.
eThe catalyst prepared via carbonization at lower temperature (450–600 °C).

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SADJADI ET AL.
change in the structure of the catalyst. More precisely,
upon carbonization, the Hal structure was affected and
partially destructed (as shown in the XRD pattern). On
the other hand, due to the low yield of carbonization
(about 20%), the content of Pd in the Pd@Hal‐C increased
significantly compared to that of Pd@Hal‐P‐CD (almost
four fold). Consequently, for the same catalyst weight,
the amount of Pd is higher with Pd@Hal‐C than with
Pd@Hal‐P‐CD. However, carbonization resulted in the
aggregation of Pd nanoparticles to some extent and
increase of the Pd nanoparticles mean size (Figure S5).
Moreover, the thermal stability of the catalyst as well as
its hydrophobicity increased (Figure S7). All of these
changes can affect the catalytic activity and their combina-
tional effects led to the increase of the catalytic activity of
Pd@Hal‐C compared to its non‐carbonized counterpart.
Considering these results and in attempt to clarify
whether incorporation of Hal in the structure of Pd@Hal‐
C has any contribution to the catalysis, carbonization of
Hal free sample, i.e. Pd@P‐CD, was performed to see
whether Hal‐free catalyst could lead to a catalyst with sim-
ilar catalytic activity. To this purpose, CD and M monomer
were polymerized in the absence of Hal and then carbon-
ized and used as a catalyst for promoting the model reac-
tion. It was found that the presence of Hal could both
improve the yield of polymerization and the catalytic activ-
ity of the resulting catalyst. According to the literature, this
observation can be attributed to the effect of Hal on the
resulting polymer.[45,46] Hence, although Hal is partially
destroyed in the course of carbonization, its incorporation
was beneficial for achieving the best catalytic activity.
Notably, the carbonization of Pd@Hal‐P‐CD with
higher content of CD (Entry 2, Table 1) led to a catalyst
with moderate catalytic activity. This result further con-
firmed the importance of ratio of CD:M on the catalytic
activity. Moreover, according to the literature, this obser-
vation can be assigned to the effect of CD as precursor on
the nature of the final carbon.[20]
It was assumed that carbonization can influence the
nature of the resultant carbon. To verify this postulate,
the Raman spectra of both samples were recorded and
compared (Figure 7). As depicted, in the Raman spectra
of two samples two bands, a D‐band at 1327 cm−1 and a
G‐band at 1615 cm−1, can be observed. According to the
literature, the D band can be indicative of the sp3 config-
uration that can be attributed to presence of intrinsic
defects and the G‐band is due to the graphitic car-
bon.[47–49] The comparison of two Raman spectra showed
that the ID/IG value for Pd@Hal‐C600 and Pd@Hal‐C750
were 0.92 and 0.84 respectively. This result can indicate
that the C obtained at elevated temperature has more gra-
phitic nature.
Noteworthy, the XRD pattern of Pd@Hal‐C600 is dis-
tinguishable from Pd@Hal‐C750 (Figure 8). More pre-
cisely, in the XRD pattern of Pd@Hal‐C600, a band at
2θ = 20–22.8° can be observed. According to the previous
reports, the observed broad band can be assigned to the
(002) reflection of C, implying that the catalyst can also
contain a number of amorphous compounds.[50] Compar-
ing the C characteristic bands in two XRD patterns of
Pd@Hal‐C600 (the broad band at 2θ = 20–22.8° and a
small band at 2θ = 25°) and Pd@Hal‐C750 (a sharp band
at 2θ = 25°), it can be concluded that the natures of C in
these samples are different. This issue was further con-
firmed via Raman spectroscopy.
On the other hand, in the XRD pattern of Pd@Hal‐
C600, the Hal characteristic bands are more pronounced
compared to Pd@Hal‐C750. This observation is in good
agreement with the literature,[34,39] in which it was con-
firmed that the disappearance of Hal characteristic bands
is pronounced upon thermal treatment at elevated
temperatures.
Finally, the effect of carbonization condition on the
catalytic activity of the resulting catalyst was studied by
comparing the catalytic activity of Pd@Hal‐C600 and
Pd@Hal‐C750 (Table 1, entries 10 and 1). As tabulated,
the carbonization temperature can affect the catalytic activ-
ity and Pd@Hal‐C750 exhibited higher catalytic activity.
To further investigate the effect of carbonization tem-
perature, the TGA thermogram of Pd@Hal‐C600 and
Pd@Hal‐C750 were compared (Figure 6). As shown, the
thermal stability of Pd@Hal‐C750 was higher than that
of Pd@Hal‐C600. In the TGA thermogram of Pd@Hal‐
C600, an additional loss stage can be detected at 310 °C,
indicating that carbonization of P‐CD cannot be com-
pleted by treatment at 600 °C and the degradation of the
remaining P‐CD resulted in the observed loss stage.
FIGURE 6 TGA thermograms of Pd@Hal‐C600 and Pd@Hal‐
C750

SADJADI ET AL.
9 of 13
FIGURE 7 The Raman spectra
Pd@Hal‐C600 and Pd@Hal‐C750
FIGURE 8 XRD patterns of Pd@Hal‐
C600 and Pd@Hal‐C750
Measurement of the zeta potential value of Pd@Hal‐
C750 and Pd@Hal‐C600 (Figure S7) showed that this
value for Pd@Hal‐C600 was slightly higher (−33.4 mV)
than that of Pd@Hal‐C750.
Finding Pd@Hal‐C as the best catalyst, the selectivity
of the catalyst towards nitro reduction was studied. To
this purpose, 4‐nitroacetophenone was hydrogenated as
a substrate with two functional groups. Gratifyingly, the
result showed that 4‐nitroacetophenone underwent the
hydrogenation reaction to afford 4‐aminoacetophenone
as a sole product. Although the yield of this reaction
was lower (80%) than that of the model one, observation
of no by‐product can confirm high selectivity of the cata-
lyst towards nitro group.
In the next step, the catalytic activity of Pd@Hal‐C was
compared with some of previously reported catalysts
reported for the hydrogenation of nitrobenzene (the
model substrate), Table 2. As tabulated, this reaction
has been subjected to numerous studies and various cata-
lysts have been applied for promoting this hydrogenation
reaction using different reducing agents, including
hydrogen gas and chemical reducing agents under differ-
ent reaction conditions. The catalysts tabulated in Table 2
exhibited high catalytic activities for hydrogenation of
nitrobenzene. However, some of the reported catalysts
are efficient at high H2 pressure. On the other hand, in
some of the listed procedures chemical reducing agents
or toxic organic solvents are used. Taking the environ-
mental issues into account, use of low pressure of hydro-
gen gas as hydrogen source is more appealing.
Furthermore, use of water as environmentally benign sol-
vent renders the reaction more promising. Considering
these points as well as high catalytic activity and recycla-
bility of Pd@Hal‐C, it can be concluded that this catalyst
can be classified as one of the efficient catalysts with util-
ity for the hydrogenation of nitroarenes.
3.3 | Catalyst recyclability
Confirming high catalytic activity of the catalyst, it was
studied whether Pd@Hal‐C was a recyclable catalyst. In

10 of 13
SADJADI ET AL.
TABLE 2 The comparison of the catalytic activities of Pd@Hal‐C with some of previously reported catalysts for the hydrogenation of
nitrobenzene
Temperature
(°C)
Time (h:min) Reducing
agent
Yield
(%)
Entry Catalyst
Solvent
Ref
1
Pd@Hal‐C750 (3 wt%)
Pd@Hal/di‐ureaa (1.5 wt%)
Pd/PPh3@FDU‐12b (8.33 × 10−4 mmol Pd) 40
60
50
H2O
1:15
1:00
1:00
3:00
2:00
H2/1 atm
H2/1 bar
H2/10 bar
H2/1 atm
H2/40 atm
100
100
99
This work
[52]
2
H2O
[53]
[54]
[55]
[56]
[57]
[58]
[59]
[60]
[57]
[57]
3
EtOH
THF
EtOH
4
PdNP(0.5%)/Al2O3 (0.3 g)
APSNPc (1 mol%)
r.t.
100
100
5
r.t.
r.t.
6
Pd‐(CH3)2NHBH3 (6 mol%)
Pd/graphene
H2O/MeOH 0:10
H2O/EtOH 1:30
(CH3)2NHBH3 99
7
50
r.t
50
r.t.
50
50
NaBH4
H2/1 bar
NaBH4
NaBH4
NaBH4
NaBH4
91
90
98
99
98
85
8
Pd0‐AmP‐MCFd (0.5 mol%)
EtOAc
H2O/EtOH 1:30
H2O 2:00
1.15
9
Pd NPs/RGO (6 mg)
10
11
12
PdNP@PPh2‐PEGPIILPe (0.05 mol%
PdCu/graphene (2 mol% Pd)
PdCu/C (2 mol% Pd)
H2O/EtOH 1:30
H2O/EtOH 1:30
aPd immobilized on functionalized Hal
bPd NPs (1.1 nm) with triphenylphosphine (PPh3) cross‐linked in the nanopore of FDU‐12
cactivated palladium sucrose nanoparticles
dPd nanoparticles supported on aminopropyl‐functionalized siliceous mesocellular foam
ePalladium nanoparticles stabilized by lightly cross‐linked phosphine‐decorated polymer immobilized ionic liquids (PIIL) and their PEGylated counterparts
(PEGPIIL)
this line, at the end of the hydrogenation reaction of
nitrobenzene in the presence of fresh Pd@Hal‐C, the cat-
alyst was simply separated from the reaction mixture and
washed. After drying in oven at 90 °C, the recovered cat-
alyst was subjected to the next run of hydrogenation reac-
tion under similar reaction conditions. The recovery‐
reusing cycle was repeated for 6 reaction runs and the
yield of aniline after each recycling was calculated and
compared with that of the fresh Pd@Hal‐C. The results
(Figure 9) exhibited that Pd@Hal‐C could be successfully
recycled for five reaction runs with slight loss of activity.
However, further recycling up to sixth reaction run led to
the significant loss of the catalytic activity.
To further investigate the effect of recycling on
Pd@Hal‐C, the recycled Pd@Hal‐C after 6 reaction runs
was characterized with TEM, ICP and FTIR spectros-
copy. The ICP analysis showed that recycling of the cat-
alyst for 5 times led to the low Pd leaching. However,
this value reached to its maximum point (7 wt% initial
Pd loading) upon sixth recycling. The FTIR spectrum
FIGURE 9 The recycling result of
Pd@Hal‐C750 catalyst

SADJADI ET AL.
11 of 13
of the recycled Pd@Hal‐C (Figure 10) confirmed the
structural stability of the catalyst in the course of the
reaction. More precisely, the FTIR spectrum of the
recycled catalyst exhibited the characteristic bands of
the fresh catalyst.
It should be noticed that the TEM characterization of
the recycled catalyst has been performed (Figure S8). No
aggregation of Pd nanoparticles was observed onto the
support after several runs and moreover, the size of Pd
nanoparticles was not greatly altered after the 6th run
with a mean diameter about 27.2 10.7 nm. This analysis
is a proof that the Pd nanoparticles are efficiently
adsorbed onto the composite.
postulated that CD could act not only as a phase transfer
agent, but also as a capping agent for the Pd nanoparti-
cles. Moreover, the synergism between the components
could improve the catalytic activity of the nanocomposite
compared to the individual components. It was also con-
firmed that the ratio of the monomers played an impor-
tant role in the Pd particle size and the catalytic activity
of the final catalyst. The carbonization of Pd@Hal‐P‐CD
was also carried out to afford a new composite,
Pd@Hal‐C that exhibited superior catalytic activity com-
pared to Pd@Hal‐P‐CD. Characterization of Pd@Hal‐C
confirmed significant structural change such as growth
of Pd nanoparticles, increase of Pd content and partial
destruction of Hal upon carbonization. The study on the
carbonization temperature indicated that carbonization
at elevated temperature could lead to the formation of a
catalyst with higher catalytic activity. It was also found
out that although Hal was partially destroyed in
Pd@Hal‐C, its presence in the backbone of the catalyst
could improve the catalytic activity.
3.4 | Hot filtration test
The last part of this study was dedicated to the investiga-
tion of the nature of the catalyst species. To this purpose,
conventional hot filtration test was performed.[51] Briefly,
the catalyst was removed from the reaction mixture after
a short reaction time and the progress of the hydrogena-
tion reaction was monitored in the filtrate. As the reaction
did not proceed in the absence of the catalyst, it can be
concluded that the true catalyst was heterogeneous and
did not proceed through Pd leaching and re‐deposition.
ACKNOWLEDGMENTS
The TEM in Lille (France) are supported by the Conseil
Régional du Nord‐Pas de Calais and the European
Regional Development Fund (ERDF). This work has been
supported by the Center for International Scientific Stud-
ies & Collaborations (CISSC) and French Embassy in Iran
and Hubert Curien French‐Iranian partnership “PHC
GUNDISHAPUR 2018” n° 40870ZG. S. Sadjadi appreciate
Iran National Science Foundation for the Individual
given grant, No. 97009384.
4 | CONCLUSIONS
With the aim of taking advantage of Hal, P and CD chem-
istry, a novel composite, Pd@Hal‐P‐CD, was prepared by
polymerization of β‐CD and M monomer in the presence
of functionalized Hal, followed by Pd immobilization.
The resulting nanocomposite showed high catalytic activ-
ity for promoting hydrogenation reaction of nitrobenzene
in aqueous media, superior compared to that of Pd@Hal‐
P, Pd@Hal‐CD, Pd@P‐CD, Pd@Hal and Pd@P. It was
CONFLICT OF INTEREST
There are no conflicts to declare. The Iranian authors
declare that none of them are employed by a government
agency that has a primary function other than research
and/or education. Moreover, none of them are official
representative or on behalf of the government.
ORCID
Samahe Sadjadi https://orcid.org/0000-0002-6884-4328
Bastien Léger https://orcid.org/0000-0003-2411-1162
Eric Monflier https://orcid.org/0000-0001-5865-0979
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