Nickel nanoparticles highly dispersed in silica pillared clay as an efficient catalyst for chlorobenzene dechlorination

Article abstract of DOI:10.1039/c5ra05926g

A series of highly dispersed nickel nanoparticles supported by silica pillared clay (SPC) have been synthesized with a facile process. The synthesized samples were characterized by XRD, HRTEM, SEM, IPC-ES, FTIR, N₂ adsorption-desorption isother

Full text of DOI:10.1039/c5ra05926g

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DOI: 10.1039/C5RA05926G
A series of highly dispersed nickel nanoparticles (with a uniform size about 4.7 nm) between the
lamellae of silica pillared clay has been synthesized with a facile process. The nickel catalysts
exhibit high catalytic performance on the hydrodechlorination of chlorobenzene, about 97.8% at 6%
Ni-content, and better reusability.

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Journal Name
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ARTICLE
Nickel nanoparticles highly dispersed in the silica
pillared clay as an efficient catalyst for chlorobenzene
dechlorination
Cite this: DOI: 10.1039/x0xx00000x
Zhiming Ren,1 Fei Zhang,3 Liwen Yue,*2 Xuan Li,4 Yu Tao,4 Ge Zhang,4 Kai Wu,5 Cong
Wang,6 Baoshan Li*1
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
A series of highly dispersed nickel nanoparticles supported by silica pillared clay (SPC) have
been synthesized with a facile process. The synthesized samples were characterized by XRD,
HRTEM, SEM, IPCꢀES, FTIR, N2 adsorption–desorption isotherm and XPS techniques. The
results suggest that the materials possess highly ordered mesoporous structure and the highly
dispersed nickel nanoparticles with a uniform size about 4.7 nm are in an ordered configuration
in the silica pillared clay’s pores. Moreover, the nickel catalysts exhibit high catalytic
performance on the hydrodechlorination of chlorobenzene, about 97.8% at 6 wt.% Niꢀcontent,
and better reusability.
www.rsc.org/
materials exhibit ordered mesoporous structure and large
1. Introduction
surface areas, even more than 1000m2/g. Moreover, the pore
size of SPC is controllable by using different molecular length
of surfactants. Furthermore, the synthesized condition is easy
for industry. The application of pillared clays is then expanded
to more different fields. If the Ni nanoparticles can be
intercalated into the SPC, they would be much more stable,
because the resultant composite structure can stabilize Ni
nanoparticles and protect them from agglomeration,
consequently, the catalytic efficiency of Ni nanoparticles can be
elaborated. The weak points of Ni nanoparticles can be
overcome. And the synthesized material will be cheap and easy
to be industrialized.
Metal nanoparticles, such as Ni, Pd, Pt, Au, and Rh, have
received increasing attention due to their fascinating physical
and chemical characteristics[1ꢀ6]
.
Compared with the
conventional materials, nanoparticles exhibit smaller size,
higher surface area and better activity etc[7,8]
Nickel
.
nanoparticles, as a kind of metal nanoparticle, in recent years,
have attracted more and more interesting, due to diverse
promising applications in the fields of chemical catalysis for
hydrogenation of nitrobenzene and nitrophenol, oxygen
reduction, oxidation of olefins and hydrodechlorination of
chlorobenzene[9].
In this research, we induced the Ni nanoparticles into the
interlaminar of SPC by a two steps method and produce a kind
of metal nanoꢀmaterial with the Ni nanoparticles highly
dispersed in the mesoporous. The cost of the sample is cheap
Although, Ni nanoparticles have so many strong points, they
have the same weak points as nanoparticles, such as the
aggregation[10ꢀ11]. Therefore, many methods have been taken
forward to protect the Ni nanoparticles from aggregation,
keeping them in high activity, such as impregnating the Ni
and the process of synthesis is easy to control, even if under the
Ⅱ
metal precursors into the zeolite[12], coating with SiO2 around industry condition. In the first step, we synthesized the Ni ꢀ
the Ni nanoparticles[13] , modified with polymers[14ꢀ19] and
SPC, in which the nickel atoms were doped into the framework
of SPC uniformly[32,35]. In the second step, the nickel atoms
loading Ni nanoparticles on the surface of some metal
oxides[20,21]. But the application of these methods in catalysts
industry is very limited, because the preparation processes are
complicated, expensive, and the size of the Niꢀnanoparticles are
hard to be controlled in a low level under those processes.
were reduced from the NiIIꢀSPC precursor in hydrogen flow at a
moderate temperature without destroying the structure of SPC.
Finally, the Ni atoms are anchored to the framework of SPC,
which ensures the nanoparticles be stable in the framework of
SPC, preventing them from agglomeration. The catalytic
performance of the result samples were examined by the
reaction of HDC of CB. The significance of the work is that Ni
nanoparticles can be highly dispersed in the structure of SPC
with an ordered distribution and the result materials possess the
advantages of SPC and Ni nanoparticles for catalysis,
simultaneously.
On the other hand, montmorillonite (MMT), as a kind of clay,
is widely distributed in the entire world. It is cheap and easy to
get. MMT possess layered structure, large surface area and high
cation exchange capacity (CEC)[22,23]. Therefore, MMT is
always used as the raw material for some valuable production,
like organic clays[24], pillared clays[25,26], clay nanocrystalline
composites, and clayꢀpolymer composites[27]. It is worth to talk
about the pillared clays. The pillared clays always arise from
the combination of clays with metal and metal oxide materials,
with micropores less than 2nm[28], which limited the application
of the pillared clays very much. However, in the past several
years, Mao [29ꢀ34] and his workers have developed the synthesis
method of silica pillared clay (SPC). The synthesized SPC
2. Experimental Section
2.1 Materials
The natural montmorillonite clay (MMT) with a cation
exchange capacity (CEC) of 91 meq/100 g was obtained from
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Inner Mongolia and was used without any further purification (HRTEM) images were obtained by
a JEMꢀ3010 with an
or cationicꢀexchange process. Tetraethoxysilane (TEOS, A.R.) accelerating voltage of 200kV. The crystal morphology was studied
was purchased from West Long Chemical Co, Ltd., using a Hitachi Sꢀ4700 scanning electron microscope (SEM). The
Guangdong, China. Dehydrated alcohol (A.R.), ammonia nitrogen adsorptionꢀdesorption isotherms were measured at the
solution (25%) and was purchased from Beijing Chemical liquid nitrogen temperature with a Quantachrome Autosorbꢀ1
Plant, Beijing, China. Cetyltrimethylammonium bromide volumetric adsorption analyser. Prior to measurement, the samples
(CTAB, A.R.) and Nickel nitrate (Ni(NO3)2·6H2O, AR) were were degassed at 300 °C for 16 h. The pore size distribution curves
purchased from Beijing Yili Fine Chemical Product Limited were calculated from the desorption branch of nitrogen adsorptionꢀ
Company, China.
desorption isotherms. The Xꢀray photoelectron spectroscopy (XPS)
analyses were conducted on an ESCALAB 250 spectrometer
equipped with an Al Kα Xꢀray source. The carbon 1s peak at 284.6
eV was used as the reference for binding energies. Elemental
analysis for Ni was performed using a Shimadzu ICPSꢀ75000
inductively coupled plasma emission spectrometer (ICPꢀES), an
Elementar Vario EL elemental analyzer, and a PANalytical Axios
Advanced wavelength dispersive Xꢀray fluorescence (WDXRF)
spectrometer.
Ⅱ
2.2 Synthesis of Ni -SPC
0.5g of MMT was first dispersed in 20 mL deꢀionized water,
to which a certain amount of Ni(NO3)2·6H2O was added and
stirred for 30 min. At the same time, 0.5g of CTAB was
dissolved in 2ml ethanol and 20ml deꢀionized water, to which
3.7ml tetraethoxysilane (TEOS) was added and ultrasonic for
0.5 h to get emulsion. The emulsion was dropped into the clay
dispersion slowly and stirred vigorously for 1.5h. Then
deceleration stirred for 4.5h. Subsequently, 2ml of ammonia
solution (25%) was added to it and continue stirring for 2h. The
product was recovered by filtration and washed three times
with deꢀionized water. Finally the product was dried overnight
2.7 Catalytic performance test
The catalytic performance of the samples was tested through
the reaction of HDC of CB. The experiments were carried out
in a 250 mL stainless steel autoclave with ethanol as the solvent
at the H2 partial pressure of 1.5 MPa and with the reaction
Ⅱ
Ⅱ
at 105 °C. The samples were named Ni ꢀSPCꢀ6, Ni ꢀSPCꢀ3
Ⅱ
temperature of 100
℃ for 1h. The percentage of reactant in the
and Ni ꢀSPCꢀ2, according to the amount of nickel added in this
reaction system was 10 wt. %, and the catalyst dosage was 1.0
wt. %. The reactants and the products were analyzed by GC
with a flame ionization detector online. And the conversion was
calculated by the formula:
process were 6%, 3% and 2%, respectively.
2.3 Synthesis of Ni0 -SPC
Ⅱ
The synthesis of Ni0
precursor was carried out as follow. Ni
quartz tube and then heated in hydrogen flow from room
-
SPC by reduction of the Ni
-
SPC
Ⅱ
-
SPC was put into a
c
- c
C6H5Cl i
C6H5Cl 0
conver si on( %) =
× 100
o
o
temperature to 650 C at a heating rate of 5 C/min and kept
c
C6H5Cl 0
o
650 C for 1 h. Then, it was cooled naturally in hydrogen flow
to the room temperature. The resulting sample was designated
cC6H5Cl0 and cC6H5Cli denotes the molar concentration of CB
before and after reaction, respectively.
as Ni0
-
SPC.
To determine the turnover frequency (TOF), additional
reactions with low chlorobenzene conversion (<15%) were
tested. TOFs of catalysts at 70 °C are calculated as follows:
2.4 Synthesis of SPC
Ⅱ
The synthesis process of SPC was similar to that of Ni ꢀSPC,
and the only difference being that the Ni(NO3)2·6H2O was not
added to the MMT solution. After the product was dried
overnight, the organic part was entirely removed from the
material by calcination in air flow in a tubular furnace at 600 °C
for 6 h with a temperature ramp of 1 °C min–1. The product is
denoted SPC.
rate of chlorobenzene consumption
[36]
TOF=
.
No. of exposed Ni sites on catalyst
The No. of exposed Ni sites on catalyst is calculated using the
formula:
No. of exposed Ni sites on catalyst=
W
catalyst
×
Percentage of Ni content
×
D
, where Wcatalyst is the weight of catalyst used in the catalytic
reaction. And D is dispersion of Ni, which is calculated using
the formula described by J. R. Anderson[37]
2.5 Synthesis of Ni0/SPC
The nickel loading silicaꢀpillared clay was synthesized as
follows. The dry SPC was impregnated with nickel nitrate
solution with a certain amount of nickel loading (40 mL of
:
Ni surface
Ni total
π
r2
π
r3
3V
2
1
1
D=
= (4 ) / (4/3 ) =
r 2
V
π
r 2 r
nickel nitrate solution to 1 g of SPC). Then the as prepared
π
Ⅱ
2
2
2 1
samples were reduced with a process as the Ni - -
SPC to Ni0
SPC. The samples were named Ni0/SPCꢀ6, Ni0/SPCꢀ3 and
Ni0/SPCꢀ2, according to the amount of nickel added in this
process were 6%, 3% and 2%, respectively.
r1: radius of one nickel particle, r2: radius of one nickel atom,
V2: volume of one nickel atom.
The nickel leaching analysis is also carried out as follows:
the catalytic reaction is carried out for 1h, then the catalyst is
separated by centrifugation. The solution without the catalyst is
further stirred for 1h and the products in this solution and the
products in this solution are determined. If the conversion of
chlorobenzene is further improved without the presence of the
catalyst, the nickel leaching is existence.
2.6 Characterization
Xꢀray powder diffraction (XRD) patterns were taken with a
philips X’Pert diffractometer equiped with a rotating anode, using
CuꢀKα radiation (λ = 0.1541 nm) in the 2θ range 5ꢀ70° with a scan
speed of 10° min−1 and in the 2θ range 0.5ꢀ10° with a scan speed of
2° min−1. Highꢀresolution transmission electron microscopy
3. Results and discussion
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Ni0/SPCs would be much bigger with an average diameter of
26.4 nm (measured on the basis of 200 particles) comparing
with the Ni0ꢀSPCs. From Fig.2A to Fig.2B and to Fig.2C, the
number of metal nickel particles presented the law of
diminishing, which is corresponding to the ICPꢀES results that
were given in Table 1. Furthermore, highꢀresolution
transmission electron microscopy (HRTEM) provides more
morphological information for nickel nanoparticles, as shown
in Fig. 2B. The aligned lattice fringes of the nickel
nanoparticles are clearly illustrated in the image with adjacent
fringe spacing of about 0.20 nm, which is corresponding with
the (1 1 1) diffraction we have observed at 2θ 44.5° of XRD.
3.1 Wide angle XRD patterns of the catalyst after reduction
In order to detect the phase of samples, wide angle XRD test
was taken for all samples (Ni0ꢀSPCs) and the compared
samples (Ni0/SPCs).
Fig.1 Wide angle XRD patterns of Ni0/SPC-6, Ni0/SPC-3,
Ni0/SPC-2, Ni0-SPC-6, Ni0-SPC-3 and Ni0-SPC-2.
Fig.1 shows the wide angle XRD patterns of Ni0/SPCꢀ6,
Ni0/SPCꢀ3, Ni0/SPCꢀ2, Ni0ꢀSPCꢀ6, Ni0ꢀSPCꢀ3 and Ni0ꢀSPCꢀ2.
In these patterns, all of samples are observed the typical peaks
of MMT of its subgroup of 2:1 phyllosilicates, at 20°, 29°, and
35° and one weak broad feature at 62° 2θ[32]. This suggests that
the MMT’s structure of all of samples is not affected any more.
The wide angle XRD pattern of natural MMT can be found in
Fig.1S (ESI). However, there are some difference between
Ni0/SPCs and Ni0ꢀSPCs. At wide angle XRD patterns of
Ni0/SPCs, the two sharp peaks at 44.5°and 51.5° (asterisks
marked) can be clearly seen. This indicates that the Ni0 is
[38ꢀ40]
present in the form of bulk Ni metal particles
.
Correspondingly, for the Ni0ꢀSPCs, only one wide peak at
about 44.5° can be seen and the peak at 51.5° is disappeared.
The peak at 44.5° is characteristic of bulk nickel metal particles
(1 1 1), which indicates that the nickel is still in the form of Ni
metal particles. But the wide peak at 44.5° and the disappeared
peak at 51.5° is the result of that the size of Ni metal particles
Fig.2 TEM images of samples with different nickel contents: (A)
Ni0-SPC-6, (B) Ni0-SPC-3, (C) Ni0-SPC-2 and (D) Ni0/SPC-6, (E)
Ni0/SPC-3, (F) Ni0/SPC-2.
are at the nanoꢀscale [41]
.
3.2 TEM images of samples
3.3 Low angle XRD patterns of the catalyst after reduction
In order to study the size of metal nickel particles and their
distribution in Ni0–SPCs and Ni0
/
SPCs, the TEM of Ni0
–
SPCs
The pattern of an ordered lamellar clay material sample
would usually exhibit one main peak (0 0 1) when recorded
with a regular powder XRD. The order of (0 0 1) Xꢀray
reflection, indicating layered structures, is observed for Ni0ꢀ
SPCꢀ2, Ni0ꢀSPCꢀ3 and Ni0ꢀSPCꢀ6 with a basal spacing of 4.8
nm, 5.0 nm and 5.2 nm, and the gallery height of 3.8 nm, 4.0
nm and 4.2 nm after deducting the MMT layer thickness 0.96
nm respectively. The gallery height of Ni0ꢀSPCs is
corresponding of that of NiIIꢀSPCs, which can be seen in Fig.
2S (ESI). This indicates that the NiꢀSPCs still possess the
lamellar structure. But the strength of peak is a little weaker and
and Ni0
/SPCs with different nickel contents were employed.
These results are shown in Fig.2.
The internal pore structures and nickel particle distributions
of the asꢀprepared samples were observed by means of TEM.
As is observed in Fig.2, the interlayer gallery pore structure is
clearly evident. In the images, the clay layers are discernible as
solid dark lines are the interlamellar pillars and the pores appear
in lighter contrast between the layers[34,42]. For the Ni0ꢀSPCs,
the metal nickel particles between the MMT layers which with
an average diameter of 4.7 nm (measured on the basis of 200
particles) were distributed evenly around the silicon pillars in
TEM images. However, the size of metal nickel particles in the
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Table 1. ICP-ES results and textural properties of Ni0-SPCs and Ni0/SPCs.
Ni content tested by ICPꢀES
Sample
Si/Ni
BET (m2g–1)
Total pore volume (cm3g–1) Mesopore diameter (nm)
(wt. %)
5.68
2.75
1.83
5.89
2.91
1.90
Ni0ꢀSPCꢀ6
Ni0ꢀSPCꢀ3
Ni0ꢀSPCꢀ2
Ni0/SPCꢀ6
Ni0/SPCꢀ3
Ni0/SPCꢀ2
10
20
30
10
20
30
476
471
451
520
517
490
0.496
0.421
0.380
0.460
0.452
0.458
3.81
3.43
3.27
3.25
3.18
3.17
addition of too much nickel would affect the regularity of the
Ni0ꢀSPC material.
Fig.3 Low angle XRD patterns of Ni0/SPC-6, Ni0/SPC-3, Ni0/SPC-2,
Ni0-SPC-6, Ni0-SPC-3 and Ni0-SPC-2.
the width become wider, which infers that the structure of the
interlamellar pillars has been changed during the reduction
process. The order of (0 0 1) Xꢀray reflection is also observed
for Ni0/SPCꢀ2, Ni0/SPCꢀ3 and Ni0/SPCꢀ6 with a basal spacing
about 4.4 nm and the gallery height of 3.4 nm after deducting
the MMT layer thickness 0.96 nm. Compared with the change
between NiIIꢀSPCs and Ni0ꢀSPCs, it infers that the silica pillar
in the Ni0/SPCs is not affected any more.
Fig. 4 SEM images of (A) Ni0-SPC-6, (B) Ni0-SPC-3, (C) Ni0-SPC-2.
3.5 N2 adsorption-desorption analysis of the samples
Fig.5 shows the nitrogen adsorptionꢀdesorption isotherms
and the pore size distribution curves (calculated from the
desorption branch) of Ni0ꢀSPCs and Ni0/SPCs. For all of these
materials, the uptake of nitrogen increased linearly with
pressure between 0.03 and 0.8, and a jump of nitrogen uptake
was observed above 0.8. The curve is categorized as the type
IV isotherm according to the BDDT (Brunauer ꢀDeming ꢀ
Deming ꢀ Teller) classification with a hysteresis loop, whose
features correspond to the type B in Boer’s five types
representing the presence of open slitꢀshaped pores formed in
gallery regions. The adsorption isotherm and the hysteresis loop
are contributed by mesopores and slitꢀshaped spacing in gallery
cooperatively. The Ni0/SPCs have BET specific areas of 490ꢀ
520 m2/g and pore volumes of 0.452ꢀ0.460 cm3g–1. However,
the BET specific areas of Ni0ꢀSPCs were a little smaller
compared with that of Ni0/SPCs, being 451ꢀ476 m2/g. And the
pore volumes of Ni0ꢀSPCs were 0.380ꢀ0.496 cm3g–1.
3.4 SEM images of samples
The morphologies of the asꢀprepared samples were observed
by means of SEM. It is observed that except for the detailed
roughness of surfaces, the overall morphology of the MMT
layer was well retained when the Ni0 ꢀSPC samples were just
completed. As it is shown in Fig.4C, for the Ni content was in a
very low condition, the morphology of the asꢀprepared sample
was very similar to that of SPC (Fig.3S in ESI). With the
increase of nickel content in the Ni0 ꢀSPC, the surface of clay
sheets became rougher (Fig.4B). When the nickel content was
in a highest condition (Fig.4A), there was even little amorphous
SiO2 particles can be observed on the surface of clay sheets in
Ni0ꢀSPC sample. This phenomenon may be due to the fact that
most of the TEOS hydrolysis occurred in the gallery regions of
MMT under such intercalation condition. However, the
The pore size distribution curve of Ni0ꢀSPCꢀ2 shows that the
narrow pore size distribution is similar with MCMꢀ41, which
possess mesopores produced by surfactant micelles. This
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oxidation state of Ni0 and Ni2+, maybe due to the
electronegative of montmorillonite lamellar and the interaction
between Ni atom and silica of SPC interlamellar.
At the same time, the BE value of the Si2p and O1S decrease
to 103.2 and 532.0 eV, respectively, compared with the
reported oxidation state of silica and SPC[43]. This might be due
to the NiꢀOꢀSi bonds between the Ni atom of nickel
nanoparticles and the framework of SPC, which causes a
decrease of the density of the lining electron cloud of the
oxygen and silicon atoms.[44]
indicates that the samples were wellꢀordered mesostructure
materials and probably produced by surfactant micelles.
Meanwhile, for Ni0ꢀSPCs, with the nickel content increasing,
the pore size, pore volume and the surface area are increasing
(Table 1). This is because with the increase of nickel content in
the samples, the content of metallic nickel particles between the
MMT layers increases, so that the spacing of MMT layer
enlarges, and more space is formed, which is corresponding
with the lowꢀangle XRD results of Ni0ꢀSPCs. However, the
pore size distribution curves of Ni0/SPCs were very similar,
with a pore size distribution of 3.17ꢀ3.25 nm, indicating that the
pore structure of SPC was not changed after nickel was loaded.
3.7 FTIR patterns of as-prepared samples
Fig. 6 XPS spectrum of Ni0-SPC-6 (Asterisks indicate Ni 2p peaks
and arrows are the peak positions of Ni0 and Ni2+ satellite peaks).
Fig.7 FTIR patterns of Ni0-SPC-6, Ni0-SPC-3 and Ni0-SPC-2.
Fig. 7 shows the FTIR spectra of the products in the range of
4000ꢀ450 cmꢀ1. The strong and wide bands around 1200ꢀ1000
cmꢀ1 are associated to the asymmetric Si–O stretching modes.
Fig.5 N2 adsorption-desorption and pore size distributions of
Ni0/SPC-6, Ni0/SPC-3, Ni0/SPC-2, Ni0-SPC-6, Ni0-SPC-3 and Ni0-
SPC-2.
The intensity of the band at 1385 cmꢀ1 (Ni
–O–Si bond) has
3.6 XPS test of the samples
become much weaker comparing with the band of NiIIꢀSPCs at
1385 cmꢀ1(Fig.4S in ESI). Moreover, the characteristic bands in
806 cmꢀ1 could be observed for all the samples, which is a
slight blueꢀshift comparing with the shift of NiIIꢀSPCs in 803
cmꢀ1. This can be contributed to the fact that as most of the Ni
atoms were reduced from the framework of SPC, the NiꢀOꢀSi
In order to explore the state of Ni material, the XPS spectrum
is employed. The results are shown in the Fig. 6.
As shown in Fig. 6, the two strong peaks at 856.2 and 874.6
eV are correspond to Ni02p3/2 and Ni02p1/2, respectively. And
the peaks appeared at 863.6 and 881.0 eV are attributed to the
Ni2+2p3/2 and Ni2+2p1/2, respectively. The peaks of Ni0 2p and
Ni2+ 2p are shift to higher energies compared with the reported
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bonds were destroyed[43,45]. However, the reduction process is
not complete, leading to a small part of the Ni Si bonds
–O–
exist in the samples, which is the reason that nickel particles
were fixed between the interlayer of Ni0ꢀSPCs.
3.8 Catalytic performance test
The reaction of HDC of CB was carried out using the Ni0ꢀ
SPCs and the Ni0/SPCs as catalysts under the same conditions.
Normally, HDC of CB results in the production of three
products: benzene, cyclohexane, and chlorocyclohexane. But in
this catalytic performance test, by using the Ni0ꢀSPCs as
catalyst, the only detected product is benzene and there are not
cyclohexane and chlorocyclohexane at all. The reason to lead
this result can be attributed not only to the lower reaction
temperature than that of the previous reports, but also to the
high ordered pore structure of SPC. The catalytic performances
are shown in Fig.8.
Fig.8 shows the conversion of chlorobenzene to benzene
with different nickel contents of Ni0ꢀSPCs and Ni0/SPCs. It can
be observed that the Ni0ꢀSPCs show better conversion of
chlorobenzene to benzene in this catalytic reaction than the
Ni0/SPCs did. The conversions of CB increase from 74.1% to
83.6% and finally to 97.8% as the nickel contents of the Ni0ꢀ
SPCꢀi increase from 2% to 3% and to 6%. And this is much
better than 57.2%, 62.1%, 70.1% over the corresponding
sample Ni0/SPCꢀi (i=2, 3, 6), respectively. The Ni0ꢀSPCꢀi
samples exhibited much higher catalytic activity than the
Ni0/SPCꢀi samples, which can be attributed to the much smaller
nickel nanoparticles with high dispersion in an ordered
distribution manner in the high ordered pore structure of SPC.
Fig.9 Reusability of Ni0-SPC-6 and Ni0/SPC-6.
TOF, as the intrinsic activity of the reaction, is calculated at 70 °C
and is expressed as the rate of chlorobenzene consumption per
number of exposed Ni sites on the catalyst. The TOF value of Ni0ꢀ
SPCꢀ6 (0.0897sꢀ1) is comparable to that of Ni0/SPCꢀ6 (0.1278sꢀ1)
under similar reaction conditions, but do vary somewhat with the
nickel dispersion. This indicates that the highly dispersion of Ni in
Ni0ꢀSPCꢀ6 leading to the good catalytic activity of chlorobenzene to
benzene.
The Koros−Nowak test is an effective method to identify heat or
mass transfer limitations in the measurement of catalytic rates[46,47]
.
If the observed TOFs of catalysts with different metal loadings are
the same, this means that there are no heat or mass transfer
limitations under the tested conditions. Therefore, a Koros−Nowak
test was carried out on catalysts with similar dispersion but different
nickel contents at 70 °C. As shown in Figure 10, the values of TOF
remain almost unchanged under the same reaction conditions when
altering the nickel contents, demonstrating that there are no heat or
mass transfer limitations under this condition.
Fig.8 Conversion of chlorobenzene to benzene with Ni0-SPC-i or
Ni0/SPC-i as catalyst (i=2, 3, 6).
The reusability of Ni0ꢀSPCꢀ6 and Ni0/SPCꢀ6 were also
examined under the same conditions, and the results are shown
in Fig.9.
Fig.9 shows the reusability of Ni0ꢀSPCꢀ6 and Ni0/SPCꢀ6. It
can be observed that after five times of catalytic reaction, the
conversion of CB with Ni0/SPCꢀ6 as catalyst was still 94.1%,
which is only 3.7% lower corresponding with the first time.
However, the catalytic performance of Ni0/SPCꢀ6 had
significant decrease after four runs, and the conversion of CB
was only 46.6% in the fifth time. These data significantly
indicate that the reusability of Ni0ꢀSPCꢀ6 was much better than
that of Ni0/SPCꢀ6.
Fig. 10 TOFs of Ni0-SPC-i o and Ni0/SPC-i (i=2, 3, 6).
The nickel leaching analysis of Ni0ꢀSPCꢀ6 and Ni0/SPCꢀ6 were
carried out after their fifth times of catalytic reaction. The result
shows that after another hour of reaction, conversion of
chlorobenzene in the Ni0ꢀSPCꢀ6 reaction system did not further
improve, indicating no nickel leaching of Ni0ꢀSPCꢀ6. However, the
conversion of chlorobenzene in the Ni0/SPCꢀ6 was improved after
another hour of reaction without catalyst. This indicates that after
five times of reaction, the nickel of Ni0/SPCꢀ6 was leached out. The
6 | J. Name., 2012, 00, 1-3
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Journal Name
DOI: 10.1039/C5RA05926G
samples were also analysed by ICPꢀES, showing that the nickel interlayer space of MMT. After liquid crystal assembling of the
content of Ni0ꢀSPCꢀ6 after the five times of reaction was 5.63%, gels, when ammonium was added into the gel mixture, there
nearly the same as that before reaction (5.68%), however, the nickel were two important processes occurs in the clay interlayer
content of Ni0/SPCꢀ6 after five times of reaction was 4.27%, much space. (1) The nickelꢀammonia complex was formed
lower compared with that before reaction (5.89%).
immediately and adsorbed into the interlayer space by cationic
In order to investigate the distribution of nickel particles after five surfactant. (2) The hydrolysis of the TEOS occurs rapidly
times of catalytic reaction, the Ni0ꢀSPCꢀ6 and Ni0/SPCꢀ6 were around the molecular micelles which the CTA+ forms. During
analysed by TEM, and the results are shown in Fig. 5S. As is the hydrolysis process, nickelꢀammonia complex was
observed in Fig.5S, for Ni0ꢀSPCꢀ6, the metal nickel particles with an incorporated into SiO2 frame and formed the nickel doped
average diameter of 5.4 nm (measured on the basis of 200 particles) pillars of NiIIꢀSPC.
were distributed evenly between the MMT layers. The average
Finally, the mesoporous material with unify pore structure
diameter of nickel particles was increased 0.7 nm after five times of was successfully synthesized through a direct synthesis method
catalytic reaction (the average diameter of nickel particles of Ni0ꢀ and all the Ni(II) ions were uniformly dispersed in the silica
SPCꢀ6 before catalytic reaction was 4.7 nm, which can be found in framework. After the Ni(II) species were reduced to Ni(0), the
Fig.2). The largest particles we have observed were about 13 nm, metallic Ni(0) atoms would transfer along with the channel to
which was increased 4 nm after five times of catalytic reaction. form nickel atom clusters and then become nickel particles.
Because of the strong interaction between the nickel particles and the Because of the strong restrictive effect of the framework of
SPC supporter, the nickel particles were prevented from aggregation, SPC, the nickel particle diameters were restricted and hard to
leading to a good reusability in the catalytic reaction. For Ni0/SPCꢀ6, form big nickel particles under the experimental conditions.
the average diameter of metal nickel particles was 31.2 nm Meanwhile, those Ni metal particles is almost anchored on the
(measured on the basis of 200 particles) after five times of catalytic framework of SPC, because there may be trace of Ni atoms on
reaction, which was increased 4.8 nm than that before the catalytic the Ni metal particles that they are not reduced to the Ni0 and
reaction (the average diameter of nickel particles of Ni0/SPCꢀ6 they are still related with the silica pillar.
before catalytic reaction was 26.4 nm, which can be found in Fig.2).
The biggest particles we have observed were more than 50 nm,
which was increased 10 nm after five times of catalytic reaction. The
4. Conclusion
In summary, a series of highly dispersed nickel nanoparticles
between the lamellae of silica pillared clay have been
synthesized with a facile process. The high degree of NiII
dispersion in the NiIIꢀSPC precursor induces a good distribution
of Ni nanoparticles and prevents their aggregation by anchoring
on the framework. The highly dispersed nickel nanoparticles
with a uniform size about 4.7 nm and narrow size distribution
are in an ordered configuration between the lamellae of silica
pillared clay. Moreover, the materials possess highly ordered
mesoporous structure with high specific surface area and large
pore volume. And the nickel catalysts exhibit high catalytic
performance and good reusability on the hydrodechlorination of
chlorobenzene.
increase of diameter of nickel particles indicates that the nickel
particles of Ni0/SPCꢀ6 were aggregated after five times of catalytic
reaction, which is in accordance with some other support catalysts
published previous[48,49]
.
Above all, the enhanced stability of the Ni0ꢀSPCꢀi samples is
consistent with the smaller crystallite size, higher nickel
dispersion, higher ordered distribution of the nickel
nanoparticles, and the stronger interaction between the nickel
species and the SPC supporter.
3.9The formation mechanism of Ni0-SPC
According to the aforementioned observations, we propose a
mechanism (Scheme 1) to explain the formation of Ni0ꢀSPCs.
Notes and references
1
State Key Laboratory of Chemical Resource Engineering, Beijing
University of Chemical Technology, No. 15 Beiꢀsanhuan East Road,
Beijing 100029, P. R. China.
2
Zhengzhou University of Light Industry, No. 5 Dongfeng Road,
Zhengzhou, Henan Province 450002,P. R. China.
3 Beijing Institute of Aerospace Testing Technology.
4 No. 153 Central Hospital of Chinese PLA, Zhengzhou, Henan Province
450007, P. R. China.
5 Yanshan branch of Beijing Research Institute of Chemical Industry, No.
15 Fenghuangting Road, Beijing 102500, P. R. China.
6
Henan Radio&Television University, No. 124 Huanghe Road,
Zhengzhou, Henan Province 450000, P. R. China.
Electronic Supplementary Information (ESI) available: [Wide angle XRD
Scheme 1. The formation mechanism of Ni0-SPC.
Ⅱ
The mixture of the MMT, Ni2+, CTA+, and TEOS resulted in
swollen gel, allowing the formation of intercalation compound
in which Ni2+, CTA+ and TEOS are simultaneously intercalated
into the interlayer space of MMT. Here, Ni2+ and CTA+ are
intercalated into clay interlayers by ion exchange and TEOS is
introduced into clay interlayered space by solvation. The
intercalation process also results in the expansion of the
patterns of SPC and MMT; TEM images of MMT, SPC and Ni ꢀSPCꢀ6;
Low angle XRD patterns of NiIIꢀSPCs; SEM images of SPC, Ni0/SPCꢀ6,
Ni0/SPCꢀ3, and Ni0/SPCꢀ2; FTIR patterns of NiIIꢀSPCꢀ6, NiIIꢀSPCꢀ3, NiIIꢀ
SPCꢀ2, SPC and MMT.] See DOI: 10.1039/b000000x/
1
Y. Mei, G. Sharma, Y. Lu and M. Ballauff, Langmuir, 2005, 21,
12229ꢀ12234.
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VJieowuArrtnicalelONnlainme e
DOI: 10.1039/C5RA05926G
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