Fibrous nano-silica supported palladium nanoparticles: An efficient catalyst for the reduction of 4-nitrophenol and hydrodechlorination of 4-chlorophenol under mild conditions

Article abstract of DOI:10.1016/j.catcom.2014.09.029

The Pd/KCC-1 catalyst with low cost is easy to prepare.Pd NPs were well-dispersed on the fibers of the KCC-1 without aggregation.The catalyst with easy accessible area attributed to its fibers and not pores.The catalyst showed high activity for the reduction of 4-NP and HDC of 4-CP.

Full text of DOI:10.1016/j.catcom.2014.09.029

Catalysis Communications 59 (2015) 21–25
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Fibrous nano-silica supported palladium nanoparticles: An efficient
catalyst for the reduction of 4-nitrophenol and hydrodechlorination of
4-chlorophenol under mild conditions
a
a
b
a,
Xuanduong Le a, Zhengping Dong a, , Xinlin Li , Wei Zhang , Minhdong Le , Jiantai Ma
⁎
⁎
a
Gansu Provincial Engineering Laboratory for Chemical Catalysis, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China
Faculty of Physic-Chemical Engineering, Le Quy Don Technical University, Hanoi, Viet Nam
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 June 2014
Received in revised form 2 September 2014
Accepted 17 September 2014
Available online 28 September 2014
In this study, a fibrous nano-silica supported palladium nanocatalyst (Pd/KCC-1), which features with easy
accessibility of active sites and high catalytic activity, was synthesized by a simple, cost-effective procedure.
The Pd/KCC-1 nanocatalyst exhibited excellent catalytic activity in the reduction of 4-nitrophenol and
hydrodechlorination of 4-chlorophenol in aqueous solution under mild condition. The unique dendritic fibrous
morphology of the support led to the poor aggregation of the Pd nanoparticles and dramatically increased its ac-
cessibility. The easy accessibility and excellent catalytic activity demonstrated by the Pd/KCC-1 nanocatalyst
make it a promising candidate for various Pd-based catalytic applications.
Keywords:
Palladium nanocatalyst
Accessibility
© 2014 Elsevier B.V. All rights reserved.
Hydrodechlorination
Fibrous nano-silica
1. Introduction
both the reduction of 4-NP and the HDC of 4-CP and to transfer them
into reusable products.
Recently, the transformation of harmful organic wastes into reusable
compounds with low toxicity in aqueous solutions under mild condi-
tions has become an extremely important area of study for chemists.
In this aspect, the disposal of nitrophenol and chlorophenol is one
area of intensive research. As is well known, 4-nitrophenol (4-NP) and
4-chlorophenol (4-CP) are among the most used chemicals in the chem-
ical industry today. 4-NP and 4-CP can be used for the synthesis of phar-
maceutical products, dyes, and explosives [1]. However, a significant
drawback associated with the use of 4-NP and 4-CP is the tendency of
these chemicals to cause both soil and water pollution due to their
high toxicity [2]. Because of this, the disposal of 4-NP and 4-CP has be-
come a major environmental concern. The handling methods for 4-NP
and 4-CP contamination mainly include: adsorption [3], microbial
degradation [4], incineration [5], photocatalytic degradation [6], catalyt-
ic chemical oxidation [7], nitro group reduction [8], and catalytic
hydrodechlorination (HDC) [9]. Among these methods mentioned
above, the reduction of the nitro group was commonly used for 4-NP,
while HDC was often used for 4-CP. These methods have the following
advantages: mild reaction conditions, simple reaction treatment, and
environment-friendly characteristics [10]. Furthermore, the reduction
product (aminophenol) and the HDC product (phenol) can be reused.
Therefore, it is extremely important to develop effective catalysts for
Previously, palladium-based catalysts has been confirmed the most
effective catalysts for both the reduction of 4-NP and the HDC of 4-CP
[11,12]. Palladium nanoparticles (Pd NPs) are of particular importance
among the noble metals, owing to their superior catalytic performances
[13]. Pd NP nanocatalysts are now receiving more and more attention
for their catalytic activity in the treatment of wastewaters containing
4-NP or 4-CP pollutants [14,15]. However, the surface energy of NPs in-
creases as their particle size decreases, which makes them unstable and
increases the tendency for inter-particle aggregation [16]. Thus, various
support materials have been employed to prevent Pd NP aggregation,
including SBA-15 [17], PPy nanocapsules [18], activated carbon [19],
and Al2O3 [20]. However, none of these supported catalysts were ideal
for mass transport. Therefore, in order to enhance mass transfer effects
and avoid Pd NP aggregation, catalytic supports with high surface areas
and easy accessibility are required.
Fibrous nano-silica (KCC-1), which features a high surface area and
easy accessibility through its fibers (as opposed to the traditional use
of pores), is reported by Polshettiwar et al. [21]. This would be an
ideal catalyst support candidate for the fabrication of noble metal-
based catalysts that exhibit high accessibility of active sites and excel-
lent catalytic activity.
Inspired by the abovementioned considerations, in this study, the fi-
brous nano-silica supported palladium nanocatalyst (Pd/KCC-1) was
synthesized (Scheme 1) and used for the reduction of 4-NP and HDC
of 4-CP. This catalytic system has three major advantages: first, the
⁎
Corresponding authors. Tel.: +86 931 891 2311; fax: +86 931 891 2582.
E-mail addresses: dongzhp@lzu.edu.cn (Z. Dong), majiantai@lzu.edu.cn (J. Ma).
http://dx.doi.org/10.1016/j.catcom.2014.09.029
1566-7367/© 2014 Elsevier B.V. All rights reserved.

22
X. Le et al. / Catalysis Communications 59 (2015) 21–25
Scheme 1. Preparation of the Pd/KCC-1 catalyst.
preparation of the Pd/KCC-1 nanocatalyst is simple and cost effective;
second, the Pd/KCC-1 nanocatalyst exhibits high accessibility and excel-
lent catalytic activity; and third, the as-prepared catalyst exhibits long-
life and high reusability in the reduction of 4-NP and HDC of 4-CP. The
Pd/KCC-1 nanocatalyst is a promising candidate for various Pd-based
catalytic applications.
hydrothermal reactor and heated 120 °C for 5 h. The silica formed was
isolated by centrifugation, washed with deionized water and acetone,
and dried in a drying oven. This material was then calcined at 550 °C
for 5 h in air.
2.3. Preparation of Pd/KCC-1 nanocatalyst
2. Experimental section
KCC-1 supported palladium catalyst was reported by Fihri et al. [23].
In this work, we used a simple and energy saving method (Scheme 1).
Firstly, KCC-1 was functionalized with APTES to obtain KCC-1-NH2
nanocomposite. Secondly, a 100 mL round-bottom flask was charged
with 0.5 g of KCC-1-NH2 nanocomposite, 0.1 g of Pd(OAc)2 and 50 mL
of acetonitrile, after which it was ultrasonically dispersed for 30 min.
Subsequently, the fresh NaBH4 solution (0.2 M, 10 mL) was added
dropwise into the abovementioned suspension. The product was isolat-
ed by centrifugation, washed repeatedly with deionized water and eth-
anol, and dried in a vacuum.
2.1. Material
Tetraethoxysilane (TOES), 3-aminopropyltriethoxysilane (APTES)
and Pd(II) acetate were purchased from Aladdin Chemical Co., Ltd.
4-CP, 4-NP, 1-pentanol and urea were purchased from Lanzhou
Aihua Chemical Company. Organic solvents used were of analytical
grade and did not require further purification.
2.2. Synthesis of KCC-1
In this study, KCC-1 was successfully synthesized by a traditional hy-
drothermal method [22]. TEOS (2.5 g) was dissolved in a solution of cy-
clohexane (30 mL) and 1-pentanol (1.5 mL). A stirred solution of
cetylpyridinium bromide (CPB 1 g) and urea (0.6 g) in water (30 mL)
was then added. The resulting mixture was continually stirred for
45 min at room temperature and then placed in a teflon-sealed
2.4. Characterization, reduction of 4-NP and HDC of 4-CP
The characterization of the samples and the detailed experimental
procedures for the reduction of 4-NP and HDC of 4-CP could be found
in the supporting information.
Fig. 1. TEM images of (a) KCC-1, (b) Pd/KCC-1, inset pictures HRTEM image of the Pd NPs crystal structure in detail on KCC-1.

X. Le et al. / Catalysis Communications 59 (2015) 21–25
23
Fig. 2. (a) The wide-angle XRD of Pd/KCC-1 and KCC-1 (b) XPS spectrum of the Pd/KCC-1 (inset: high resolution spectrum of Pd 3d).
3. Results and discussion
3.1. Catalyst preparation and characterization
As can be seen in Scheme 1, the aminopropyl groups can be acted as
adsorption centers for Pd2+. When the NaBH4 was added to the solu-
tion, the Pd2+ ions were reduced and immobilized on the fibers of
KCC-1.
The properties of KCC-1 and KCC-1-NH2, including results of FT-IR
(Fig. S1), TGA (Fig. S2) were provided in the supporting information.
The FT-IR (Fig. S1) spectra reveal that the APTES was successfully
grafted on the KCC-1 surface. The total weight loss of the organic part
was determined to be 8.254% (Fig. S2). A large amount of successfully
modified aminopropyl groups on the KCC-1 surface proves to be advan-
tageous for the absorption Pd2+ and immobilized Pd NPs. The weight
percentage of Pd in the Pd/KCC-1 catalyst, as determined by atomic ab-
sorption spectroscopic analysis, was 7.8 wt.%.
Fig. 1 shows the morphologies and structural features of the KCC-1
and Pd/KCC-1 nanocatalyst. As is illustrated in Fig. 1a, KCC-1 silica
nano-spheres indicate the presence of fibers, which are ordered den-
dritic fibers coming out from the center of the particle and are distribut-
ed uniformly in all directions. Moreover, the image indicates that the
KCC-1 particle size is approximately 280 nm, and the distance between
the two fibers is about 20.5 nm. This catalyst revealed that the fibrous
nano-silica KCC-1 was loaded with well-dispersed Pd NPs (Fig. 1b),
and the Pd NP diameters were approximately 3 nm. From the inset pic-
ture of Fig. 1b, it can be seen that the resolved lattice fringes of Pd(111)
planes (d = 0.225 nm) detected in the HRTEM image were attributed to
Pd nanocrystals.
XRD patterns of KCC-1 and Pd/KCC-1 samples were displayed in
Fig. 2a. The broad peak between 20–30° corresponds to amorphous sil-
ica [24]. The XRD patterns of Pd NPs show four characteristic diffraction
peaks at 2θ = 40.1°, 46.5°, 68°, and 82° corresponding to (111), (200),
(220), and (311), respectively. The XRD pattern of the Pd/KCC-1 catalyst
reveals that the Pd NPs were successfully grafted on the KCC-1 surface.
Fig. 2b presents XPS elemental survey scans of the surface of the Pd/
KCC-1 catalyst. Peaks corresponding to oxygen, silica, carbon, nitrogen,
and palladium were clearly observed. In the inset figure, Pd(0) binding
energy of KCC-1/Pd exhibits two sharp peaks centered at 335 and
340 eV, which are assigned to Pd 3d5/2 and Pd 3d3/2
.
3.2. Reduction of 4-NP by Pd/KCC-1 nanocatalyst
The reduction of 4-NP by NaBH4 at room temperature was used as a
model reaction to characterize the catalytic performance of Pd/KCC-1.
The reduction process was monitored by UV–Vis absorption spectrosco-
py. An aqueous solution of 4-NP has an absorbance peak at about
317 nm, which shifts to 400 nm in the presence of alkali because of
Fig. 3. (a) UV–Vis spectra of 4-NP before and after adding NaBH4 solution, (b) successive
UV–Vis spectra for the reduction reaction of 4-NP by NaBH4 with Pd/KCC-1 as catalyst, and
(c) kinetic curve for the reduction of 4-NP catalyzed by Pd/KCC-1 (Ct and C0 are 4-NP con-
centrations at time t and 0, respectively).

24
X. Le et al. / Catalysis Communications 59 (2015) 21–25
Fig. 4. (a) Comparison of the HDC of 4-CP in water and in organic solvents, (b) comparison of the HDC of 4-CP in different bases.
the formation of 4-nitrophenolate ions (Fig. 3a) [25]. The reduction re-
action proceeded when the catalyst Pd/KCC-1 was added in solution;
the absorption of 4-nitrophenolate at 400 nm quickly decreased while
a new adsorption peak of 4-AP at 300 nm appeared accordingly
(Fig. 3b). Fig. 3c shows the ln(Ct/C0) versus reaction time for the reduc-
tion of 4-NP, where Ct and C0 are the concentrations of the 4-NP at inter-
vals and the initial stage, respectively. Since the concentration of NaBH4
was very high compared with that of 4-NP, the reaction followed
pseudo-first-order reaction kinetics [26]. Thus, pseudo-first-order
kinetics could be applied to evaluate the kinetic rate constant (k) of
the current reaction [Eq. (1)], where A0 and At are absorbance values
of 4-NP initially and at time t, respectively.
catalytic activity of Pd/KCC-1 nanocatalyst is higher than that of the Pd/
SBA-15 catalyst.
3.3. HDC of 4-CP by Pd/KCC-1 nanocatalyst
The above investigation revealed that Pd/KCC-1 nanocatalyst exhib-
ited excellent activity for the reduction of 4-NP. We then further ex-
plored the catalytic activity of Pd/KCC-1 for the HDC of 4-CP.
To evaluate the catalyst activity under green conditions, reaction
conditions were established at room temperature and atmospheric
pressure, the H2 flow rate of 60 mL min−1 and a stirring speed of
600 rpm were set. We compared the HDC reaction in water and organic
solvents. The effects of different solvents on the HDC of 4-CP were
shown in Fig. 4a, where it can be seen that the Pd/KCC-1 nanocatalyst
showed very high activity in water. When the reaction was carried out
in ethanol and n-hexane under the same reaction conditions, the con-
version of 4-CP was only about 40% and 10% within 90 min (Fig. 4a), re-
spectively. The HDC reaction pathway was described below: firstly, H2
was adsorbed on the surface of the Pd/KCC-1 nanocatalyst and was dis-
sociated into two active hydrogen atoms: secondly, 4-CP was also
adsorbed on the surface of the Pd/KCC-1 nanocatalyst. Therefore, the
C\Cl bond of 4-CP was attacked by the active hydrogen atoms to
from phenol [28]. Simultaneously, in the catalytic HDC of 4-CP, HCl,
formed as a byproduct, results in poisoning the catalyst. In order to pre-
vent the catalyst from being poisoned by HCl, certain bases are usually
used in the HDC reactions [29]. In this paper, NaOH was used within
the reaction systems. Therefore, NaCl was generated by the neutraliza-
tion of HCl and NaOH. NaCl deposits on the surface of Pd/KCC-1 blocked
the pores of KCC-1 support, thereby inhibiting adsorption and
dCt=dt ¼ −kt; or ln ðCt=C0Þ ¼ ln ðAt=A0Þ ¼ −kt:
ð1Þ
The expected linear relationship between ln(C /C0) and reaction
t
time (t) was confirmed through pseudo-first-order kinetics. The corre-
sponding pseudo-first-order rate constant was 0.008 s−1. For a quanti-
tative comparison, the activity parameter k′ = k/M was introduced, and
defined as the ratio of the rate constant k to the weight of the catalyst
added, where M is the total mass of the catalyst added in the reaction
mixture [27]. Thus, the reaction rate constant per unit mass (MPd) was
calculated to be 1025.64 s−1 g−1
.
In the reduction of 4-NP, our results showed that the reaction rate
constant per total weight of Pd for Pd/KCC-1 was higher than the Pd/
SBA-15 (750 s−1 g−1) that was reported in the reported literature
[17]. Because SBA-15 is a mesoporous structure, it is difficult to access
the active sites of Pd NPs. KCC-1, however, has dendritic fibrous
morphology that enables easy accessibility of the active sites. Therefore,
Fig. 5. (a) Time evolution of 4-CP and phenol with a Pd/KCC-1 catalyst, (b) kinetic curve for the HDC of 4-CP catalyzed by Pd/KCC-1 (Ct and C0 are 4-CP concentrations at time t and 0,
respectively).

X. Le et al. / Catalysis Communications 59 (2015) 21–25
25
Table 1
4. Conclusions
The recycling experiments of the catalyst Pd/KCC-1 in the reduction of 4-NP and HDC
of 4-CP.
In conclusion, in this study, the Pd/KCC-1 nanocatalyst was synthe-
sized by a simple, cost-effective procedure. The Pd/KCC-1 nanocatalyst
exhibited excellent catalytic activity in its reduction of 4-NP and HDC
of 4-CP because of the unique dendritic fibrous morphology of the sup-
port, which dramatically increased the accessibility and low amount of
aggregation of the Pd NPs on the KCC-1 support. Therefore, factors in-
cluding its chemical stability, eco-friendly nature, unique dendritic fi-
brous morphology of the support and ease of use make the Pd/KCC-1
nanocatalyst a promising candidate for potential applications in indus-
trial synthesis.
Run
Yield (%) (1)
Yield (%) (2)
1
2
3
4
5
100
100
100
99
98
96
95
93
90
99
Acknowledgments
The authors acknowledge financial support from the NSFC (Grants
activation. The solubility of NaCl is 26.5 g/100 g in water and 0.055 g/
100 g in ethanol at 25 °C, respectively. In hexane, NaCl is almost unsolv-
able at room temperature [30]. However, in water, NaCl is completely
dissociated into Na+ and Cl−, and does not inhibit the activity of the cat-
alyst. Thus, the catalytic activity of Pd/KCC-1 was the highest in water,
while it was much lower in ethanol and hexane solvent, because of
very low solubility of NaCl in two organic solvents [31].
21301082).
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.doi.
org/10.1016/j.catcom.2014.09.029. These data include MOL files and
InChiKeys of the most important compounds described in this article.
In the catalytic HDC of 4-CP, HCl was played an important inhibiting
effect on the activity of the catalyst. In order to observe and evaluate the
HDC in water, the effects of a series of bases were investigated in the
HDC of 4-CP in water. Fig. 4b exhibits the effect on the HDC using a stoi-
chiometric amount of NaOH, K2CO3 and triethylamine under the same
reaction conditions. NaOH was far superior to K2CO3 and triethylamine
in water.
After optimizing the reaction conditions, the catalytic activity of Pd/
KCC-1 for HDC of 4-CP reaction was completed in 75 min. When the re-
action continued for 90 and 180 min, 0.6% and 1.5% of cyclohexanone
were also produced by the HDC of 4-CP. When the catalyst dosage is in-
creased to 50 and 100 mg, and the reaction times continued for 90 and
180 min, the yield of cyclohexanone increased accordingly. The results
were shown in Table S2.
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3.4. Reusability of the Pd/KCC-1 nanocatalyst
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further investigated. The catalyst was recycled in the reduction of 4-NP
with NaBH4 and HDC of 4-CP. The reduction of 4-NP catalytic process
was carried out within 6 min under each cycle, and HDC of the 4-NP cat-
alytic process was achieved within 90 min under each cycle. After the
reaction was finished, the catalyst was recovered by centrifugation. As
illustrated in Table 1, the recovered catalyst was added each time to
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