Hydrodechlorination of chlorophenols catalyzed by SiO2/Pd@m-SiO2 core-shell structured catalyst

Article abstract of DOI:10.1016/j.molcata.2015.05.016

Palladium metal nanoparticles have been applied to hydrodechlorination of chlorophenols in contaminated water using H₂ as a clean and sustainable reductant. However, there are two major challenges to widespread technology adoption which are the activity loss caused by nanoparticle aggregation and the difficulty of nanoparticle recovery. In this study, a synthesis of a core-shell structured catalyst with encapsulated Pd nanoparticles has been given and whose catalytic activity has been tested in hydrodechlorination of chlorophenols under 1 atm H₂ at room temperature. The catalyst material consists of a nonporous silica core decorated with Pd nanoparticles that are further encapsulated within an ordered mesoporous silica shell. Well-defined mesopores (2.4 nm) provide a physical barrier to prevent Pd nanoparticle (～10 nm) movement, aggregation and detachment from the support into water. Compared with some supported Pd catalysts such as Pd/AC and Pd/Al₂O_3, SiO₂/Pd@m-SiO₂ exhibits higher catalytic performance. After 5 times of recycling, catalytic activity of SiO₂/Pd@m-SiO₂ reduces slightly and this result confirms the good recyclability of SiO₂/Pd@m-SiO₂. The function of the mesoporous shell, preventing aggregation of active nanoparticles, suggests a promising general strategy of using metal nanoparticle catalysts for water purification and related aqueous-phase applications.

Full text of DOI:10.1016/j.molcata.2015.05.016

Accepted Manuscript
Title: Hydrodechlorination of chlorophenols catalyzed by
SiO2/Pd@m-SiO2 core-shell structured catalyst
Author: Yansheng Liu Bo Qiao Xinlin Li Xuanduong Le Wei
Zhang Jiantai Ma
PII:
S1381-1169(15)00200-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.05.016
MOLCAA 9502
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
1-3-2015
21-5-2015
23-5-2015
Please cite this article as: Yansheng Liu, Bo Qiao, Xinlin Li, Xuanduong Le, Wei
Zhang, Jiantai Ma, Hydrodechlorination of chlorophenols catalyzed by SiO2/Pd@m-
SiO2 core-shell structured catalyst, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2015.05.016
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Hydrodechlorination of chlorophenols catalyzed by SiO2/Pd@m-SiO2 core-shell
structured catalyst
Yansheng Liu, Bo Qiao, Xinlin Li, Xuanduong Le,Wei Zhang and Jiantai
Ma*majiantai@lzu.edu.cn
Gansu Provincial Engineering Laboratory for Chemical Catalysis, College of
Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR
China.
 Corresponding author. Tel.: +86 0931 891 2577; fax.: +86 0931 891 2582
1

Graphical abstract
Highlight
1. SiO2/Pd@m-SiO2 catalyst with encapsulated Pd nanoparticles has been synthesis.
2. Which good catalytic activity has been establish in HDC of 4-CP
3. The mesoporous shell can solve two major challenges to widespread technology
adoption.
4. SiO2/Pd@m-SiO2 catalyst exhibited good recycle character.
2

Abstract
Palladium metal nanoparticles have been applied to hydrodechlorination of
chlorophenols in contaminated water using H2 as a clean and sustainable reductant.
However, there are two major challenges to widespread technology adoption which
are the activity loss caused by nanoparticle aggregation and the difficulty of
nanoparticle recovery. In this study, a synthesis of a core-shell structured catalyst with
encapsulated Pd nanoparticles has been given and whose catalytic activity has been
tested in hydrodechlorination of chlorophenols under 1 atm H2 at room temperature.
The catalyst material consists of a nonporous silica core decorated with Pd
nanoparticles that are further encapsulated within an ordered mesoporous silica shell.
Well-defined mesopores (2.4 nm) provide a physical barrier to prevent Pd
nanoparticle (∼10 nm) movement, aggregation and detachment from the support into
water. Compared with some supported Pd catalysts such as Pd/AC and Pd/Al2O3,
SiO2/Pd@m-SiO2 exhibits higher catalytic performance. After 5 times of recycling,
catalytic activity of SiO2/Pd@m-SiO2 reduces slightly and this result confirms the
good recyclability of SiO2/Pd@m-SiO2. The function of the mesoporous shell,
preventing aggregation of active nanoparticles, suggests a promising general strategy
3

of using metal nanoparticle catalysts for water purification and related aqueous-phase
applications.
Keywords
SiO2/Pd@m-SiO2 nanocatalyst, metal nanoparticles , HDC reaction, 4-CP
4

1. Introduction
Nowadays, the environmental pollution caused by organic wastes has become an
un-ignorable issue. With the staggering growth of industrialization, large numbers of
organic compounds, such as the aryl chlorides, have been produced and employed.
During the application of aryl chlorides severe environmental pollutions have been
produced. Among the most harmful organic contaminants, aryl chlorides are
considered as hazardous pollutants because of their acute toxicity and strong potential
bioaccumulation.1 Special attentions have been paid to chlorophenols (CPs) for their
widespread availability in important industrial processes, such as the production of
germicides, algaecides, fungicides, herbicides, dyes, wood protectors and plant
growth regulators.2 So how to deal with pollutions caused by CPs has become
increasingly important and has no time to delay. Up to now, many reported traditional
4
methods including thermal combustion, reduction dechlorination,3,
oxidation
dechlorination,5 biodegradation and photocatalytic degradation have been employed
in disposing the wastewater containing CPs. Among the treatment methods mentioned
above, thermal combustion and chemical oxidation have been largely employed in the
treatment of CPs. Although there are some advantages, it must be noticed that these
methods cannot decompose 4-CP completely into simple inorganic compounds such
as CO2, H2O and HCl. In addition, toxic chlorinated chemicals such as dioxins,
phosgene and chlorine could generate in these treatments processes.6 These
5

accompanied chemicals can result in secondary pollutions and especially do harm to
the health of human beings and atmospheric ecosystem. Therefore, removal of these
compounds through a cost-effective and environmentally-friendly way has attracted
many researchers’ attentions. Compared with traditional treatments of 4-CP
mentioned above, hydrodechlorination (HDC) possesses some advantages. By using
efficient catalysts, the reaction can be run under a mild condition and the energy
consumption can be reduced. In addition, it can reduce the formation of by-products
and can be suitable for the treatment of a wide range of chlorinated compounds.7 Both
from the economic point of view and for achieving the greatest degradation of 4-CP,
catalytic HDC can be considered as an effective and promising method.
In the 1960s, the study of HDC of CPs was initiated, however the first
comprehensive report of the liquid phase exhaustive HDC of CPs to phenol over Pd/C
only appeared in 1992.8 From that moment on, the liquid phase catalytic HDC has
been studied by many researchers.7, 9, 10 Many influence factors of 4-CP HDC have
been studied, such as active phase, supports, sources of hydrogen and reaction
media.11, 12 By summarizing the experiences of pioneers, the HDC treatment of CPs
using noble metal as activity phase and molecular hydrogen as hydrogen source has
been proved to be an efficient method.13 Till now, large numbers of catalysts using
metal nanoparticles (NPs) like Pd12, 14-17, Pt18, 19, Rh20 and Ni15 as active phases have
been researched greatly. Among them, Pd based catalysts show an excellent catalytic
activity for the treatment of CPs at room temperature and atmospheric pressure.
6

According to the studies of L. Calvo21 and F. J. Urbano1,22 it seems that HDC may
be a structure-sensitive reaction. The effect factors of supports in HDC reactions had
been extensively studied. Recent researches have demonstrated that the supports are
significant influences on the dispersion and electronic properties of the NPs. Many
26
supports, such as activated carbon (AC),23-25 Al2O3 or zeolites27, 28 have been
employed to prepare catalysts for HDC of 4-CP. The studies show that Al2O3 as
support can improve the stability of active species of the catalyst. Nevertheless, this
metal oxide support is more sensitive to HCl produced during the HDC process.
Compared with Al2O3, AC seems more suitable as a support because of its large
surface area and particular physical and chemical properties.13 However, the strong
adsorption properties based on surface area, pore size distribution, and surface
composition limit the applications of AC. During the HDC process, bare NPs can be
directly connected with the reactant molecules which can accelerate reaction velocity.
However, the bare NPs can easily drop off the support and result in a loss of noble
metal. This situation can reduce the recycling value and catalytic activity of catalyst.
In this study, active phase focuses on Pd NPs because of the excellent catalytic
activity of Pd NPs in HDC of 4-CP. Based on the considerations of catalytic activity
affected by surface area, large size SiO2 with ~500 nm is used as a core that can make
Pd NPs well dispersed. In order to solve the noble metal loss problem, a
sandwich-like structure with large size of NPs and small size of pore has been
7

designed in this research and its catalytic performance for HDC of CPs has also been
studied.
2. Experimental
2.1 Materials
Tetraethoxysilane (TOES), Pd(II) acetate, (3-aminopropyl)triethoxysilane (APTES)
and Hexadecyl trimethyl ammonium Bromide (CTAB) are purchased from Aladdin
Chemical Co., Ltd. 4-Chlorphenol (4-CP), 2-Chlorphenol (2-CP) , 2,4-Dichlorophenol
(2,4-DCP) and concentrated ammonia aqueous solution are purchased from Lanzhou
Aihua Chemical Company. NaBH4 is supplied by Sinophrm Chemical Reagent Co.,
Ltd. Oganic solvents used are of analytical grade and do not require further
purification.
2.2 Preparation of SiO2 microsphere
The Silica nanospheres is synthesized by a modified Stöber protocol.29 In a typical
synthesis, 2.7 mL of TEOS is added dropwise into a mixture solution of 180 mL of
ethanol, 30 mL of concentrated ammonia aqueous solution and 9 mL of distilled water
by stirring it at room temperature. After additional stirring for 12 h, the SiO2
microspheres are collected by centrifugation (8000 rpm, 3 min) and washed with
distilled water and ethanol for several times. Then the collected microspheres are
dried at 40 °C in a vacuum drying oven over night for further use.
2.3 Preparation of APTES modified SiO2 microsphere
8

300 mg of SiO2 microspheres are added in 30 mL of methylbenzene under
ultrasonic dispersion for 15 min. Then 150 mg of APTES is added and refluxed at 90
°C for 12 h. The modified SiO2 microspheres are collected by centrifugation (8000
rpm, 3 min) and washed with distilled water and ethanol for several times. Then the
collected nanospheres are dried at 40 °C in a vacuum drying oven over night for
further use.
2.4 Preparation of SiO2/Pd NPs
300 mg of APTES modified SiO2 is added in 30 mL of distilled water under
ultrasonic dispersion for 15 min. Then 60 mL of Pd acetate acetonitrile solution (2.11
mg mL-1) is added under strong stirring for 12 h. After this step, 30 mL of 0.3 M
NaBH4 aqueous solution is added in the solution drop by drop. The products are
collected by centrifugation (8000 rpm, 3 min) and washed with distilled water and
ethanol for several times. Then the collected nanospheres are dried at 40 °C in a
vacuum drying oven over night for further use.
2.5 Preparation of SiO2/Pd@mesoporous-SiO2
To grow a mesoporous silica shell on the SiO2@Pd microspheres, the as-made
SiO2/Pd nanosphere (300 mg) is redispersed in a mixed solution containing CTAB
(0.45 g, 1.2 mmol), distilled water (100 mL), concentrated ammonia solution (2.0 mL,
28 wt %), and ethanol (150 mL). The resultant mixed solution is ultrasonic dispersed
for 5 min and then stirred for 30 min to form a uniform dispersion. Subsequently, 0.8
mL of TEOS is added drop-wise to the dispersion under continuous stirring. After
9

magnetic stirring for 6 h, the product is collected by centrifugation (8000 rpm, 3 min)
and washed with distilled water and ethanol for several times. Finally, the purified
microsphere is re-dispersed in 100 mL of ethanol and 1 mL of concentrated
hydrochloric acid at room temperature for 24 h to remove the template CTAB. The
as-prepared catalyst is dried at 40 °C in a vacuum drying oven over night.
2.6 General procedures for the hydrodechlorination of CPs
HDC experiments are performed in a three-necked jacketed glass reactor connected
with hydrogen balloon by a three-way valve. Firstly, a certain quantity/amount of
catalyst is placed into the mixed solution of 30 mL of solvent (H2O, ethyl acetate, ethyl
alcohol), 1 mmol of reactant and 1mmol base (Na2CO3, NaAc, triethyl amine, Na2OH).
Secondly, use a circulating water vacuum pump to extract the air in the reactor for 5 –
10 sconds. Then open the three-way valve and make the hydrogen get into reactor.
Repeating the gases replacement process three times and starting the clock. The reaction
maintains for 2 h under vigorous stirring at room temperature. The results of the
experiments are analysed by gas chromatograph-mass spectrometer (GC-MS).
2.6 Reusability experiment
The reusability experiments are performed in a centrifuge tube (in order to
reduce catalyst losing) with supplied H2. The catalyst is recovered by centrifugation
and simple decantation of liquid products. The catalyst is then washed with deionized
water and used directly for the next cycle of the reaction without further purification.
10

2.7 General methods
Transmission electron microscopy (TEM) images are obtained on a Tecnai G2 F30,
FEI, USA. The Brunauer–Emmett–Teller (BET) surface area and pore-size distribution
are obtained by measuring N2 adsorption isotherms at 77 K with using a TriStar 3020
(Micromeritics). Powder x-ray diffraction (XRD) spectra are obtained by a Rigaku
D/max-2400 diffractometer with using Cu-K radiation in the 2 range of 0°-80°.
X-ray photoelectron spectroscopy (XPS) is recorded on a PHI-5702 and the C1S line at
284.6 eV is used as the binding energy reference. The reaction conversion is estimated
by using GC-MS (P.E. AutoSystem XL).
3. Results and Discussion
3.1 Characterization
Figure 1 shows the FT-IR spectra of the SiO2 sphere and SiO2/Pd@m-SiO2
nanocatalyst. The FTIR bands at 1091 cm−1 and 804 cm−1, corresponding to the
antisymmetric and symmetric stretching vibration of Si–O–Si bond in oxygen-silica
tetrahedron, respectively. The bands at 461 correspond to Si–O stretching. The band
at 3420 cm−1 shows the large number of Si–OH groups which are proved to be
advantageous to the modification of APTES on the SiO2 surface by hydrogen bonds.
The band at 2923 cm−1 corresponds to -CH stretching. In the FT-IR spectrum of
SiO2/Pd@m-SiO2, the band around 3400 cm−1 represents the adsorption of –OH and
11

–NH2 groups. The nitrogen, hydrogen, and carbon contents are 0.9%, 1.65%, and
3.92%, which are measured by the elementary analysis, respectively. The FT-IR
spectra and elementary analysis results reveal that the APTES is successfully grafted
on the surface of SiO2 30, thus enabling them to act as robust anchors for metal NPs.31,
32
The synthesis procedures of SiO2/Pd@m-SiO2 nanaocatalyst are represented in
Scheme 1 and described in detail in the experimental section. TEM and SEM images
of SiO2/Pd@m-SiO2 with 7.0% metal loading which calculated by inductive coupled
measurement are shown in Figure 2. Figure 2b shows a typical SEM image of
prepared SiO2/Pd@m-SiO2 core-shell structured NPs. From Figure 2a and Figure 2d,
it can be seen that mesoporous SiO2 is capped on the surface of SiO2/Pd and it also
can be measured that average diameter of SiO2 core, the thicknesses of m-SiO2 shell
and pore size of m-SiO2 shell are about ~500 nm, 100 nm and 2.35 nm, respectively.
From figure 2c, it can be clearly seen that the Pd NPs with a dimater of 10 nm are
located between the SiO2 core and m-SiO2 shell. This core-shell structure matches our
original intention.
N2 adsorption-desorption isotherms for the SiO2/Pd@m-SiO2 are given in Figure 3.
According to the IUPAC classification, the curves of as-prepared sample is type IV
isotherms with a very sharp capillary condensation step at P/P0 = 0.10–0.30 and H4-type
12

hysteresis loop characterizing small-pore mesoporous materials. The pore size of
as-prepared catalyst derived from the BJH analysis on the desorption branch is 2.4 nm.
The calculated BET surface area and pore volume of SiO2/Pd@m-SiO2 are 560 m2 g−1
and 0.34 cm3 g−1, respectively.
The small-angle and wide-angle XRD patterns of nanaocatalyst are obtained in Figure 4.
There is an intense characteristic peak at 2 = 2.3°, which corresponds to the plane (211)
of mesoporous material. From the Figure 3b, SiO2/Pd@m-SiO2 possesses three peaks,
which correspond to planes (111), (200), (220) of Pd. Within the approximation of the
Scherrer equation, one would expect a FWHM of 2. 3° 2theta for the (111) reflection of
Pd with an average crystal size of 9.8 nm that matches with the particles size of Pd NPs
calculated by using TEM images.
The electronic state of Pd species on the SiO2/Pd@m-SiO2 is measured with XPS. The
pattern of SiO2/Pd@m-SiO2 catalyst is exhibited in Figure 5. The Pd3d peaks in XPS
spectra show that the binding energy values of 335.8 eV and 341.2 eV are attributed to
the 3d5/2 and 3d3/2 peaks of Pd. Because the Pd NPs is encapsulated within an ordered
mesoporous silica shell, the intensity of XPS peak of Pd is weak. In addition, no
evidence proves the presence of palladium oxide, which indicates that Pd(OAc) 2 is
completely reduced to Pd NPs.
3.2 HDC of 4-CP
13

The catalytic activity of nanocatalyst is established in the HDC of CPs at room
temperature and atmospheric pressure. The HDC of 4-CP is negligible without catalyst
at the same conditions, which shows that the presence of metal NPs is indispensable for
high catalytic activity. In some researchers’ studies, three products such as phenol,
cyclohexanol and cyclohexanone are generated in the process of HDC of 4-CP.22
Compared with the reactant 4-CP, the three products are detected of low toxicity and
useful as intermediates in the production of high value-added chemicals. The low
selectivity of HDC of 4-CP performs in fixed bed reactor33, 34 or under a high H2
pressure condition.18 In the study of L. Calvo, the conversion of 93% and the selectivity
of 85% are reported by using Pd/C as catalyst and formic acid as hydrogen source in
continuous stirred-tank reactor.2 Pd/Al2O3 as HDC catalyst are also studied by E.
Diaz.33 in fixed bed reactor with the conversion of 87% and the selectivity of 62%,
respectively.33 However, only high selective product phenol is detected as product and
less than 0.1% of CYC is detected after 120 min reaction in presente reaction syetem.
These differences may be caused by using different reaction systems. Also this result
agrees with the study that uses the same reaction system in which phenol as major
product is detected.13, 32, 35-38
The HDC reaction pathway is described as below: H2 adsorbed on the active site of
the nanocatalyst is activated in two hydrogen atoms, in which 4-CP is also adsorbed on
the surface of the Pd NPs. The C-Cl bond of 4-CP is attacked by the active hydrogen
atoms to form phenol.36 Simultaneously, in the process of HDC of 4-CP, HCl formes as
14

by-product which can poison catalysts. In order to reduce the inhibition of generated
HCl, four kinds of bases have been studied. By comparing the HDC results, it can be
easiliy summarized that NaOH is the best choice.36 With the addition of base, catalyst
deactivation is largely governed by HCl solubility/transport and the nature of the basic
species in the catalyst matrix have reported higher HDC rates and enhanced catalyst
stability.39 In addtion, organic and inorganc solvent are also tested and water could be
consider as the best choice. The results of HDC of 2-CP, 3-CP, 4-CP and 2,4-DCP
using SiO2/Pd@m-SiO2 catalyst are carried out and exhbited in Table 1. At the same
catalyst dosage (15 mg), after 90 min of reaction, 4-CP completely convertes and the
convertion of 3-CP and 2-CP are 89.4% and 81.6%, respectively.
The concentration of H2 can be considered constant since all the reactions are carried
out with a high excess H2. Therefore, the reaction follows pseudo-first-order reaction
kinetics:
dC4CP
R4-CP

 r  kC4CP
(1)
dt
ct
t
 c1

dct  k dt
(2)
t
co '
0
Ct
ln
 kt
(3)
(5)
(6)
(7)
C0'
Ct
Xt 
(4)
C0'  C0 C1
C0'
Ct
ln
Ct
C0 C1
C
 ln Xt  ln(1 1 )  kt
C0
 ln
C0'
C1
)
ln Xt  kt  ln(1
C0
15

In the practical experiments process, nearly 30s required to make the system stable.
So the at the time zero point, some amount of reactant has been converted and the
initial concentration changes from C0 to C0’ which make the fitted curve do not cross
original point.
According to the concentration value related to the reaction time, and the plotted
logarithm of 4-CP concentration versus reaction time, the linear fittings are drew in
Figure 6. The average reaction rate constant per unit mass k′= k/MPd is calculated
to be 39.2 min−1 g−1. The kinetic reaction rate of HDC catalyzed by Pd/Al2O3,
Pd/pillared clays, Pd/MCM-48 catalyst are 3.33 min−1 g−1, 7.6 min−1 g−1 and 42.9 min
min−1 g−1, respectively.18 34 35 Compared with these Pd based catalysts which had been
reported, the catalyst activity of SiO2/Pd@m-SiO2 is at a middle position. On one
hand, the catalyst of SiO2/Pd@m-SiO2 performs higher than low surface area catalyst
Pd/Al2O3 and Pd/pillared clays. On the other hand, catalytic activity of
SiO2/Pd@m-SiO2 is smaller than Pd/MCM-48 catalyst which Pd NPs is bare. This
indicates that the m-SiO2 shell can restrain the combination between the reactant
molecules and activity phase, which results in the activity reduction of
SiO2/Pd@m-SiO2.
The recoverability and reusability are investigated by the HDC reaction of 4-CP
and the results are summarized in Figure 7. After 5 times of recycling, the metal
loading of catalyst is 6.9% instead of 7.0% and catalytic activity of SiO2/Pd@m-SiO2
16

is reduced slightly. These results confirm the good recyclability of the Pd NPs in
SiO2/Pd@m-SiO2 catalyst.
4. Conclusion
In summary, SiO2/Pd@m-SiO2 core–shell structured nanocatalyst has been
synthesised successfully and the catalytic property is investigated in HDC process in
which 4-CP is used as target compound under the condition of sodium hydroxide
aqueous solution and at atmospheric H2 pressure, fairly mild conditions. According to
the characters of SiO2/Pd@m-SiO2, large size of Pd NPs are located between SiO2
core and m-SiO2 shell. The SiO2 layer is used as a barrier to prevent the shedding of
Pd NPs from support and the small pores in mesoporous SiO2 allow the molecules to
pass through. This structure can reduce the metal losing and increase utilization of
catalyst. By analysing the HDC result, SiO2/Pd@m-SiO2 nanocatalyst shows a good
catalytic activity for HDC of 4-CP, with the reaction rate constant per unit mass k′ =
k/MPd is 39.2 min−1 g−1. The SiO2/Pd@m-SiO2 nanocatalyst can be recycled for at
least five times in the corresponding reactions without significant deactivation and
metal loss. In this study, SiO2/Pd@m-SiO2 nanocatalyst acts as a relatively mild,
economical, and environmental friendly catalyst, and could be regarded as a
promising candidate for various Pd based catalytic applications.
17

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21

Scheme and Figure captions
Scheme 1. The schematic synthesis of the SiO2/Pd@m-SiO2 catalyst
Figure 1. FT-IR spectra of SiO2 and SiO2/Pd@m-SiO2
Figure 2. TEM image(a), SEM image(b) and partial enlarged drawing (c,d) of
SiO2/Pd@m-SiO2
Figure 3. Nitrogen adsorption–desorption isotherms and pore size distribution (inset)
of SiO2/Pd@m-SiO2
Figure 4. Small-angle (a) and Wide-angle (b) XRD patterns of SiO2/Pd@m-SiO2
Figure 5. XPS spectra of SiO2/Pd@m-SiO2 (inset: high resolution spectrum of Pd 3d)
Figure 6. Fitted kinetic rate constants of HDC 4-CP to phenol under the catalyst
dosage of 10mg (a), 15mg (b), 20mg (c)
Figure 7. The reusability SiO2/Pd@m-SiO2 of nanocatalyst for the HDC of 4-CP
22

Tables
Table 1. The yield of HDC of 4-CP catalysed by SiO2/Pd@m-SiO2
SiO2/Pd@m-SiO2
OH
OH
X
catalyst
dosage
15mg
reactant
Base
Solvent
Time(min)/Yield%
a4-CP
a4-CP
Na2CO3
NaAc
H2O
H2O
90/82%
90/72%
15mg
triethyl
amine
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
a4-CP
H2O
15mg
90/47%
a4-CP
a4-CP
a4-CP
a4-CP
a4-CP
a2-CP
a3-CP
b2,4-DCP
ethyl acetate
ethyl alcohol
H2O
15mg
15mg
15mg
20mg
10mg
15mg
15mg
15mg
90/5%
90/4%
90/100%
50/100%
120/90%
90/82%
90/89%
90/50%
H2O
H2O
H2O
H2O
H2O
Reaction conditions: solvent (30 mL), CPs (0.5 mmol); a 0.5 mmol base, b 1 mmol base
23

Figures
Scheme 1. The schematic synthesis of the SiO2/Pd@m-SiO2 catalyst
Figure 1. FT-IR spectra of SiO2 and SiO2/Pd@m-SiO2
24

Figure 2. TEM image(a), SEM image(b) and partial enlarged drawing (c,d) of
SiO2/Pd@m-SiO2
25

Figure 3. Nitrogen adsorption–desorption isotherms and pore size distribution (inset)
of SiO2/Pd@m-SiO2
Figure 4. Small-angle (a) and Wide-angle (b) XRD patterns of SiO2/Pd@m-SiO2
Figure 5. XPS spectra of SiO2/Pd@m-SiO2 (inset: high resolution spectrum of Pd 3d)
26

Figure 6. Fitted kinetic rate constants of HDC 4-CP to phenol under the catalyst dosage of 10mg
(a), 15mg (b), 20mg (c)
Figure 7. The reusability SiO2/Pd@m-SiO2 of nanocatalyst for the HDC of 4-CP
27