Pd stabilized on nanocomposite of halloysite and β-cyclodextrin derived carbon: An efficient catalyst for hydrogenation of nitroarene

Article abstract of DOI:10.1016/j.poly.2019.114210

Carbon nanospheres, CCDs, were fabricated using β-cyclodextrin as carbon precursor. The as prepared CCD was then hybridized with halloysite nanotubes (Hal) through hydrothermal treatment to furnish a nanocomposite, Hal-CCD that was subsequently applied as

Full text of DOI:10.1016/j.poly.2019.114210

Polyhedron 175 (2020) 114210
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Pd stabilized on nanocomposite of halloysite and b-cyclodextrin derived
carbon: An efficient catalyst for hydrogenation of nitroarene
Samahe Sadjadi a, , Fatemeh Ghoreyshi Kahangi , Majid M. Heravi c
⇑
b
a
Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemicals Institute, PO Box 14975-112, Tehran, Iran
Department of Chemistry, University Campus 2, University of Gilan, Rasht, Iran
Department of Chemistry, School of Science, Alzahra University, PO Box 1993891176, Vanak, Tehran, Iran
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Carbon nanospheres, CCDs, were fabricated using b-cyclodextrin as carbon precursor. The as prepared
CCD was then hybridized with halloysite nanotubes (Hal) through hydrothermal treatment to furnish
a nanocomposite, Hal-CCD that was subsequently applied as support to stabilize Pd nanoparticles.
Investigation of the catalytic activity of palladated nanocomposite, Pd@Hal-CCD, for the hydrogenation
reaction of nitrobenzenes confirmed that Pd@Hal-CCD could efficiently promote the hydrogenation reac-
tion under mild reaction condition. Moreover, the catalyst was recyclable and showed slight Pd leaching
upon reusing. The comparison of the catalytic activity of Pd@Hal-CCD with that of Pd@Hal and Pd@CCD
indicated the superior catalytic activity of the former. The observed high catalytic activity of the catalyst
was attributed to its higher Pd loading and water disperse ability. Additionally, the results confirmed that
the ratio of Hal:CCD could affect the catalytic activity and the best result was obtained by using Hal:CCD
ratio of 1:2.
Received 29 June 2019
Accepted 27 October 2019
Available online 1 November 2019
Keywords:
b-Cyclodextrin
Nanospheres
Halloysite
Heterogeneous catalysts
Hydrogenation
Ó 2019 Elsevier Ltd. All rights reserved.
1
. Introduction
In recent years, utilization of natural halloysite nanotubes (Hal)
Using host-guest chemistry of CD, various state of the art catalysts
can be designed and developed for performing the reaction in
aqueous media [18–20]. On the other hand, CDs can be considered
as potent carbon precursors to form carbon materials [21–23].
Synthesis of anilines through reduction of nitro compounds is a
utile reaction, applicable for the production of more sophisticated
chemicals [24]. This hydrogenation reaction is mostly promoted by
precious metal-based catalysts in the presence of hydrogen gas or
chemical reducing agent. To render this chemical transformation
more economic and environmentally benign, the precious metals
are mostly stabilized on supports. Considering the importance of
catalyst support on the catalytic performance and recyclability of
the catalyst, development of efficient supports that prevent from
coverage of catalyst active sites and/or exert catalytic activity is
of great importance [25–29].
In the continuation of our efforts on disclosing the application
of Hal for the catalytic purposes [12,30–32], herein we wish to
report a novel nanocomposite based on hydrothermal treatment
of Hal with carbon nanospheres derived from CD as carbon precur-
sor. To furnish this nanocomposite, Hal-CCD, the CCD was first pre-
pared through hydrothermal treatment of CD followed by
carbonization under inert atmosphere. Subsequently, CCD was
treated with Hal under hydrothermal condition to furnish Hal-
CCD. In the next part of this research, Hal-CCD was utilized as sup-
port for the immobilization of Pd nanoparticles. The resulting
in diverse fields of research such as catalysis and drug delivery wit-
nessed tremendous growth [1–8]. This issue is due to the remark-
able physiochemical properties of Hal such as high thermal and
mechanical stability, availability, non-toxicity and more impor-
tantly, its tubular morphology that allows Hal to encapsulate var-
ious guest molecules [2,9–11]. For catalytic purposes, the
promissing results have been achieved when Hal was surface mod-
ified or applied in combination with other materials in hybrid or
composite forms [12–14]. In this context various catalytic compos-
ites of Hal such as Hal-dendrimer, Hal-polymers and Hal-carbon
materials have been reported [14].
Among oligosaccharides, cyclodextrins (CDs) that possess cyclic
structures have received considerable attention due to their unique
properties, i.e. having a hydrophilic exterior surface and hydropho-
bic cavity [15–18]. The interior cavity of CD can be exploited to
host diverse range of molecules such as biologically active species.
⇑
Corresponding author at: Gas Conversion Department, Faculty of Petrochem-
icals, Iran Polymer and Petrochemicals Institute, PO Box 14975-112, Tehran, Iran.
Tel.: 982148666; fax: +982144787021-3.
E-mail addresses: s.sadjadi@ippi.ac.ir, samahesadjadi@yahoo.com (S. Sadjadi),
m.heravi@alzahra.ac.ir (M.M. Heravi).
https://doi.org/10.1016/j.poly.2019.114210
0
277-5387/Ó 2019 Elsevier Ltd. All rights reserved.

2
S. Sadjadi et al. / Polyhedron 175 (2020) 114210
nanocomposite, Pd@Hal-CCD was then employed as a catalyst for
promoting hydrogenation of nitrobenzene under mild reaction
condition. The role of CCD and Hal in the catalysis and the effect
of Hal:CCD ratio on the catalysis as well as the recyclability of
the catalyst were also investigated.
then stirred at room temperature for 3 h. In the next step, a solu-
tion of 0.075 g NaBH in 10 mL water was added into the Hal-
CCD and Pd(OAc) suspension in a dropwise manner and the
resulting mixture was stirred for 2 h. Finally, the solid material
was filtered off, washed with water and dried in oven at 60 °C
for 12 h. The schematic procedure of the synthesis of the catalyst
is illustrated in Fig. 1.
Pd loading of Pd@Hal-CCD was measured via ICP-AES analysis.
The sample preparation procedure for ICP analysis is as follow: a
mixture (1:3) of concentrated nitric acid and hydrochloric acid
was prepared and Pd@Hal-CCD (0.02 g) was digested in the
aforementioned acidic solution through constant stirring for
4
2
2
. Experimental
2.1. Materials and instruments
The chemicals used for the synthesis of the catalyst and per-
forming the catalytic experiments included nitrobenzene, 1-
nitronaphthalene, hydrogen gas, EtOH, toluene, Pd(OAC) , NaBH
-nitroacetophenone, Hal, b-CD and deionized water, all purchased
2
4 h. Subsequently, the resulting extract was analyzed by ICP-
AES. The Pd content of the catalyst was measured to be about
.28 wt%.
2
4
,
4
0
from Sigma-Aldrich and used as received without further
purification.
Catalyst characterization was carried out by applying various
techniques, including XRD, BET, TGA, FTIR, TEM, SEM and ICP-
AES. XRD patterns of CCD, Hal and Pd@Hal-CCD were obtained
2.2.4. Synthesis of control samples
To shed light to the roles of CCD and Hal in the catalysis, two
control samples, Pd@Hal and Pd@CCD were prepared via the
reported procedure for preparing the catalyst, except, Hal and
CCD were applied as supports respectively. To investigate the
effect of ratio of Hal:CD, apart from the main catalyst (Pd@Hal-
CCD (1:2)), two other samples with different ratios of Hal:CCD,
Pd@Hal-CCD (1:1) and Pd@Hal-CCD (2:1), were fabricated with a
similar method, except with use of Hal:CCD ratios of 1:1 and 2:1
respectively.
by using a Siemens, D5000. Cu K
a radiation from a sealed tube.
The BET analyses of the final catalyst and pristine Hal were per-
formed using BELSORP Mini II instrument. To perform the BET
analysis, the required amount of the samples were pre-heated at
1
50 °C for 2 h. To study the thermal stability of the catalyst and
some prepared compounds, METTLER TOLEDO thermogravimetric
analysis apparatus was employed. The thermograms of the sam-
ples were recorded under N
2
atmosphere. The used heating range
À1
and rate were 50–800 °C and 10 °C min respectively. The FTIR
spectra of Pd@Hal-CCD and other samples were recorded by
employing PERKIN-ELMER Spectrum 65 instrument. The metal
loading of Pd@Hal-CCD as well as its leaching in the course of recy-
cling were estimated by using ICP analyzer (Varian, Vista-pro).
FESEM/EDS images were obtained by applying a Tescan instru-
ment, using Au-coated samples and acceleration voltage of 20 kV.
Transmission electron microscope (TEM) images of Pd@Hal-CCD
were recorded with a CM30300Kv field emission transmission
electron microscope.
2.3. Hydrogenation of nitroarene
In a typical reaction, Pd@Hal-CCD catalyst (1 wt%) and nitroar-
ene compound (1 mmol) in deionized water as solvent (2 mL) were
placed in the reaction vessel. Then, hydrogen (1 bar) as reducing
agent was purged into the stirring reaction mixture at room tem-
perature for 1.5 h. Upon completion of the reaction (monitored
by TLC), the reaction was held and Pd@Hal-CCD was separated
from the reaction mixture and the corresponding aniline was iso-
lated by evaporation of water. To recycle Pd@Hal-CCD, the recov-
ered catalyst was washed with water and EtOH several times,
then dried in oven at 80 °C for 8 h. All the obtained products were
known and their formation was verified by using FTIR, GC-Mass
and comparing their melting/boiling points with that of authentic
samples, see ‘‘Supporting Information”.
2
2
.2. Catalyst preparation
.2.1. Synthesis of CCD
The CCD nanospheres were synthesized by a facile hydrother-
mal process followed by a two-step heat treatment [33]. Typically,
0.0 g b-CD in aqueous solution was placed into 150 mL Teflon
sealed autoclave and maintained at 200 °C for 12 h and then cooled
to the room temperature. Subsequently, the precipitate was fil-
tered off and washed with distilled water several times and dried
in oven at 80 °C for 12 h. Then, the collected precursor was car-
1
3
. Results and discussion
First, the formation of CCD was confirmed by recording its
specific surface area, FESEM images, XRD pattern and FTIR spec-
trum, Fig. 2. The FESEM images, Fig. 2 A and B, showed the spher-
ical morphology of the prepared CCD. In the FTIR spectrum of CCD,
Fig. 2 D, several characteristic bands, including the bands at
2
bonized at 800 °C for 2 h under N atmosphere. Finally, the
obtained product was further annealed at 400 °C for 1.5 h in air
for activation.
À1
À1
3
438 cm (AOH), 1656 cm (AC@O) can be observed, indicating
that CCD contained oxygenated functionalities. The XRD pattern of
CCD, Fig. 2C, exhibited a broad band at 2h = 25° and a sharp band at
2
.2.2. Synthesis of Hal-CCD
To prepare Hal-CCD nanocomposite, Hal and CCD with weight
2h = 36°. This pattern is in a good agreement with the previous
ratio of 1:2 were mixed in distilled water and then transferred into
a 150 mL Teflon-lined stainless steel autoclave. The reactor was
sealed and maintained at 220 °C for 48 h. After hydrothermal treat-
ment, the nanocomposite was filtered off and after washing with
distilled water dried in oven at 60 °C in 24 h.
report, in which these bands were attributed to the (0 0 2) and
(
[
1 0 0) reflections of the graphitic framework, JCPDSno.04-0850
33]. Using BET, the specific surface area of CCD was calculated
2
À1
to be 561 m g
.
Following the successful fabrication of CCD, it was studied
whether CCD in its free form has any catalytic activity for promot-
ing hydrogenation reaction of nitrobenzene. To this purpose, the
2.2.3. Synthesis of Pd@Hal-CCD
Immobilization of Pd nanoparticles on Hal-CCD nanocompos-
hydrogenation reaction in water as solvent, in the presence of H
2
ites, was accomplished by wet impregnation method. Briefly, a
solution of 0.02 g Pd(OAc) in toluene was added to the suspension
of 1 g Hal-CCD dispersed in dry toluene (17 mL). The mixture was
gas (1 bar) and CCD (1 wt%) as catalyst was performed at room
temperature. The result confirmed that even after passing 1.5 h
no desired product, aniline, was furnished, confirming that bare
2

S. Sadjadi et al. / Polyhedron 175 (2020) 114210
3
Fig. 1. The schematic protocol for the synthesis of Pd@Hal-CCD.
Fig. 2. A and B, the FESEM images, C, the XRD pattern and D the FTIR spectrum of the prepared CCD.
CCD was not catalytically active for this reaction. Next, CCD was
palladated (Experimental section) and applied as a catalyst under
similar reaction condition. The result, Table 1, confirmed that
Pd@CCD showed slight catalytic activity and led to 30% aniline.
Considering the promising results of our previous studies on the
catalytic activity of Hal-carbon nanocomposites [12], it was inves-
tigated whether incorporation of Hal could improve the catalytic
activity of CCD. In this line, hybrid of Hal-CCD (1:2) was prepared
and then palladated (Experimental section). The prepared catalyst
was first characterized via XRD, FTIR, BET, TGA and TEM
techniques.
In Fig. 3 the FTIR spectrum of Pd@Hal-CCD (1:2) is depicted and
compared with that of Hal and CCD (the FTIR spectrum of CCD is
discussed previously and provided here for comparison). As shown
the FTIR spectrum of the catalyst is very similar to that of CCD and
À1
showed the characteristic bands of CCD at 3463 and 1656 cm
.
Comparing the FTIR spectrum of Pd@Hal-CCD (1:2) with that of
pristine Hal, it can be concluded that in the FTIR spectrum of the

4
S. Sadjadi et al. / Polyhedron 175 (2020) 114210
Table 1
This issue confirmed the fact that the tubes of Hal are preserved
in the Pd@Hal-CCD (1:2). On the other hand, the two characteristic
peaks of CCD, Fig. 2 C, overlapped with those of Hal. Hence, the
presence of CCD can be confirmed by other analyses such as TGA
(vide infra). The characteristic peaks of Pd in Pd@Hal-CCD (1:2)
was not observed. This issue can be justified by small particle size
of well-dispersed Pd nanoparticles (see the TEM images).
Comparison of catalyst activity of various catalysts developed in this study for THE
hydrogenation of nitrobenzene.a
Entry
Catalyst
Yield (%)b
1
2
3
4
5
6
7
CCD
Pd@CCD
Pd@Hal
Pd@Hal-CCD (1:1)
Pd@ Hal-CCD (2:1)
Pd@ Hal-CCD (1:2)
Hal/Pd@CCD
0
30
20
80
60
100
30
The measurement of the specific surface area of Pd@Hal-CCD
(
1:2) was accomplished using BET method. This value was esti-
3
À1
mated to be 109.15 cm
Pd@Hal-CCD (1:2) was higher than that of pristine Hal (~52 cm -
g
g . Notably, the specific surface area of
3
a
Reaction condition: Benzyl alcohol (1 mmol), catalyst (1 w%), H
2
O (2 mL), H
2
À1
3
À1
) and lower than that of CCD (561.3 cm g ).
The morphology of Pd@Hal-CCD (1:2) was studied by recording
(
1 bar), agitation (400 rpm) at r.t in 1.5 h.
Isolated yields.
b
its TEM images, Fig. 5. The TEM images showed the tubes of Hal,
indicating that Hal maintained its structure in the course of
hydrothermal treatment with CCD. This issue was previously
reported the literature [35]. The tiny black spots in the TEM are
representative of Pd nanoparticles (mean particle diameter of
4
nm). The potential of Pd species for coordination on the surface
of the support is reported previously [36]. As shown, the Pd
nanoparticles were well dispersed and no aggregation was
observed. The TEM images also showed that Hal tubes are covered
to some extend with CCD. However, in the recorded TEM images,
the spherical morphology of CCD was not no longer detectable.
The thermograms derived from TG analysis of Pd@ Hal-CCD
(
1:2) and pristine Hal are illustrated in Fig. 6. As shown, the pris-
tine Hal mass losses occurred at ~150 °C (loss of water) and
500 °C (dehydroxylation) [37,38]. The thermogram of Pd@Hal-
~
CCD (1:2) showed an additional loss step due to the presence of
CCD, the loss goes from 540 °C to 800 °C showing a 13% of weight
loss.
Fig. 3. FTIR spectra of CCD, Hal and Pd@ Hal-CCD (1:2).
Confirming the formation of Pd@Hal-CCD (1:2), its catalytic
activity for the hydrogenation of nitrobenzene was studied. First,
the effects of reaction variables, including reaction temperature,
solvent and catalyst amount were investigated, Table S1. In the
first try, the reaction was performed in water as environmentally
benign solvent at room temperature and in the presence of very
low amount of the catalyst (1 wt%). Gratifyingly, the catalytic tests
showed Pd@Hal-CCD (1:2) led to 100% aniline after 1.5 h. To inves-
tigate whether increase of the reaction time could accelerate the
reaction, the model hydrogenation reaction was repeated at
catalyst the characteristic bands of Hal can be observed, i.e. the
À1
À1
bands at 580 cm (Al-O-Si vibration), 1035 cm (SiAO stretch-
À1
ing), 3695 and 3622 cm (internal AOH). However, their intensi-
ties significantly reduced in the hybrid system.
In Fig. 4 the XRD patterns Hal and Pd@Hal-CCD (1:2) are illus-
trated. According to the literature, the Hal distinctive peaks are
appeared at 2h = 12.3°, 20.6°, 25.2°, 36.7°, 39.0°, 56.3° and 62.5°
(
JCPDS No. 29-1487, labeled as *) [34]. Comparing the XRD pattern
5
0 °C. Tracing the reaction at short time intervals, it was found
of the Pd@Hal-CCD (1:2) with that of Hal, it was found that in the
XRD pattern of the catalyst the Hal peaks are present. However, the
intensities of those peaks remarkably reduced. It is worth mention-
ing that in the XRD pattern of Pd@Hal-CCD (1:2), the Hal peaks
were in the same position of pristine Hal with no displacement.
out that increase of temperature accelerated the reaction and the
reaction reached to 80% conversion and yield after 1 h. However,
the reaction kinetic slowed down and after 1.5 h quantitative yield
and conversion were achieved. Therefore, the optimum reaction
temperature was found to be ambient temperature. Regarding cat-
alyst amount, examining the reaction using higher catalyst amount
showed that increase of the catalyst had no effect on the time and
yield of the reaction, while use of lower catalyst loading led to
lower yield and conversion. Although water as solvent proved to
be efficient, the efficiencies of some other conventional solvents,
3 2
including EtOH, CH CN, H O:EtOH (1:1), THF and toluene were also
examined. The results confirmed that water resulted in the best
catalytic performance. Noteworthy, the disperse ability of the cat-
alyst in water was better than other solvents. Hence, it was
selected as an environmentally benign solvent for the reaction.
Then, the catalytic activity of the catalyst was compared with
that of Pd@Hal and Pd@CCD. It is worth noting that Hal in its indi-
vidual form was not a suitable support for Pd nanoparticles and the
catalytic activity of Pd@Hal was very low (20%). Notably, the dis-
perse ability of Pd@Hal was lower compared to that of the catalyst.
To shed light to the origin of high catalytic activity of Pd@Hal-
CCD, the Pd loading and specific surface area of Pd@Hal and
Pd@CCD were obtained and compared with those of the catalyst.
The specific surface area of these samples decreased in the order
Fig. 4. XRD patterns of Hal and Pd@ Hal-CCD (1:2).

S. Sadjadi et al. / Polyhedron 175 (2020) 114210
5
Fig. 5. The TEM images of Pd@Hal-CCD (1:2).
Finding the best catalytic nanocomposite, it was investigated
whether Pd@Hal-CCD (1:2) could catalyze the reaction of other
nitroarenes. First, hydrogenation of 4-nitroacetophenone was
examined to see whether the presence of competing functional
group (here AC@O) could intervene the hydrogenation of nitro
group. The result showed that the catalyst was 100% selective
towards hydrogenation of nitro group and AC@O functionality
was not hydrogenated under the reaction condition and the only
product was 4-aminoacetophenone. However, the conversion for
this catalyst was lower and reached to 70%. The second substrate
was 1-nitronaphthalene that was steric compared to nitrobenzene.
The result, Table 2, confirmed that the catalyst could successfully
promote the hydrogenation of sterically demanding substrates.
Then, to confirm the generality of the developed protocol, the
hydrogenation of some other nitroarenes with electron withdraw-
ing and electron donating functional groups was examined. As tab-
ulated, nitroarenes with different electron densities could tolerate
the hydrogenation reaction under Pd@Hal-CCD catalysis to furnish
the corresponding products in good to excellent yields. However,
the substrates with electron withdrawing groups were more active
and led to higher reaction yields.
Fig. 6. The thermogram of Pd@Hal-CCD (1:2) and pristine Hal.
2
À1
2
À1
of Pd@CCD (~450 m g ) > Pd@Hal-CCD (~109 m g ) > Pd@Hal
2
À1
(
~40 m g ). The order of decrease of loading of Pd was as follow:
Pd@Hal-CCD (0.28 wt%) > Pd@Hal (0.22 wt%) > Pd@CCD (0.19 wt%).
According to the literature, pristine Hal cannot effectively stabi-
lize Pd nanoparticles [11] and led to the immobilization of Pd
nanoparticles with high average particle sizes. Moreover, low
In the following to elucidate whether the efficiency of Pd@Hal-
CCD is comparable with the previously reported catalysts, the reac-
tion condition and performance of Pd@Hal-CCD for the hydrogena-
tion of nitrobenzene were compared with some of the reported
procedures and catalysts, Table 3. As depicted, hydrogenation of
nitrobenzene was reported in the presence of various catalysts
and reducing agents. Among various reducing agents, hydrogen
gas is more appealing compared to chemical reducing agents in
2
À1
specific surface area of this sample (~40 m g ) can contribute
to this observation. The low catalytic activity of Pd@CCD can be
attributed to its lower Pd loading. Moreover, low disperse ability
of this sample in aqueous media can justify its low catalytic activ-
ity. Regarding Pd@Hal-CCD, higher loading of Pd nanoparticles as
well as its improved wet ability and water disperse ability can
rationalize its higher catalytic activity. Considering the previous
reports, the synergism between Hal and carbon material can be
expected in the case of Pd@Hal-CCD [39].
Encouraged by the positive effect of hybridization of Hal and
CCD, the role of Hal:CCD ratio in the catalytic activity of the final
catalyst was elucidated by comparing the catalytic activity of
Pd@Hal-CCD (1:2) with that of Pd@Hal-CCD (1:1) and Pd@Hal-
CCD (2:1), Table 1. As tabulated, decreasing the content of CCD
Table 2
a
Hydrogenation of nitro compound by Pd@Hal-CCD.
Yield (%)b
Entry
Substrate
1
2
3
4
5
6
7
8
9
10
Nitrobenzene
100
90
70
85
92
93
95
96
89
85
1-Nitronaphthalene
4-Nitroacetophenone
4-Nitroaniline
(
confirmed by TG analysis) had a detrimental effect on the catalytic
activity of the catalyst, indicating the contribution of CCD to the
catalysis and importance of use of optimum ratio of Hal:CCD.
In the following, it was investigated whether hybridization of
palladated CCD (Pd@CCD) with Hal (Hal/Pd@CCD) will result in a
similar effect. Interestingly, it was found that the catalytic activity
of Hal/Pd@CCD was similar to that of Pd@CCD and far lower than
that of Pd@Hal-CCD (1:2). This issue can be attributed to the lower
Pd loading of this sample (confirmed by ICP) compared to that of
Pd@Hal-CCD.
1-Bromo-2-nitrobenzene
1-Bromo-4-nitrobenzene
1-Chloro-2-nitrobenzene
1-Chloro-4-nitrobenzene
4-Nitrotoluene
2-Nitrotoluene
a
Reaction condition: Substrate (1 mmol), catalyst (1 wt%), H
2
O (2 mL), agitation
(
400 rpm) at r.t and H
Isolated yields.
2
pressure of 1 bar in 1.5 h
b

6
S. Sadjadi et al. / Polyhedron 175 (2020) 114210
Table 3
The comparison of the catalytic activity of Pd@Hal-CCD for the hydrogenation of nitrobenzene with that of some the catalysts in the literature.
Entry
Catalyst
Time
Solvent
Temperature (°C)
Reducing agent
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
Pd@Hal-CCD (1.wt.%)
1.5 h
1 h
3 h
10 min
1.5 h
2 h
1.5 h
1.5 h
1 h
H
EtOH
THF
2
O
r.t.
40
r.t.
r.t.
50
r.t.
50
50
50
H
H
H
2
2
2
/1 atm
/10 bar
/1 atm
100
99
100
99
98
100
91
This work
[40]
[41]
[42]
[43]
À4
Pd/PPh
PdNP(0.5%)/Al
Pd-(CH NHBH
3
@FDU-12 (8.33 Â 10 mmol Pd)
2
O
3
(0.3 g)
)
3 2
3
(6 mol%)
H
H
2
O/MeOH
O/EtOH
(CH
NaBH
/40 atm
3
)
2
NHBH
3
PdCu/graphene (2 mol% Pd)
2
4
APSNPa (1 mol%)
EtOH
H
2
[44]
[43]
Pd/graphene
H
2
H
2
H
2
O/EtOH
O/EtOH
O
NaBH
NaBH
4
PdCu/C (2 mol% Pd)
4
85
100
[43]
[45]
b
40
Pd@Hal/di-urea (1.5 wt%)
H
2
/1 bar
a
activated palladium sucrose nanoparticles.
Pd immobilized on functionalized Hal.
b
method and applied as a heterogeneous catalyst for promoting
hydrogenation of nitroarenes. The results confirmed high catalytic
activity, selectivity and recyclability of the catalyst. To elucidate
the role of CCD and Hal in the catalysis, two control catalysts,
Pd@Hal and Pd@CCD were prepared and their catalytic activities
were compared with that of the catalyst. The result confirmed
the higher catalytic activity of the latter, which was attributed to
the higher Pd loading and water disperse ability of the catalyst.
The investigation of the ratio of Hal:CCD confirmed that this was
an effective parameter on the catalytic activity and the best perfor-
mance was observed with the ratio of 1:2.
Acknowledgments
The authors appreciate the partial supports from Iran Polymer
and Petrochemical Institute and Alzahra University and INSF.
Appendix A. Supplementary data
Fig. 7. The recyclability of Pd@ Hal-CCD for hydrogenation of nitrobenzene under
optimized reaction condition.
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.poly.2019.114210.
terms of green chemistry criteria. Moreover, the protocols that pro-
ceed using low hydrogen pressure are safer and more cost effec-
tive. On the other hand, use of non-toxic solvents is very
environmentally friendly and more interesting comparing to use
of hazardous solvents such as THF. Regarding the reaction temper-
ature, the protocols that could proceed at low temperature could
be less expensive. Hence, it can be concluded that Pd@Hal-CCD
that led to the desired product in relatively short reaction time
and in aqueous media at ambient temperature can be considered
as an efficient catalyst. Apart from high efficiency of Pd@Hal-
CCD, use of naturally occurring biocompatible raw materials for
the synthesis of the catalyst as well as simple preparation method
rendered Pd@Hal-CCD a good candidate for catalysis.
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