Controlled synthesis and catalytic properties of mesoporous nickel-silica core-shell microspheres with tunable chamber structures

Article abstract of DOI:10.1016/j.materresbull.2012.05.022

In 550°C and H₂ current, the mesoporous nickel-silica composite core-shell microspheres with tunable chamber structures have been successfully prepared by reduction of Ni₃Si₂O ₅(OH)₄ microspheres, which are synthesized by the reaction between Ni(Ac)₂·4H₂O and SiO₂ microspheres via a self-template approach. The chamber (SiO₂ core sizes) and shell thickness (40-150 nm) of the nickel-silica microspheres can be controlled by adjusting the synthetic parameters of Ni₃Si ₂O₅(OH)₄, such as the reaction time. After reduction, these microspheres still have the same sizes, morphologies, and core-shell structures with porous shell as before. These mesoporous nickel-silica microspheres with large BET surface area, exhibit good catalytic activity in m-dinitrobenzene (m-DNB) and high selectivity of m-phenylenediamine (m-PDA) after 3.5 h, but different selectivity of m-PDA in the progress, showing good potential in the catalyst industry.

Full text of DOI:10.1016/j.materresbull.2012.05.022

Materials Research Bulletin 47 (2012) 2344–2348
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Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Controlled synthesis and catalytic properties of mesoporous nickel–silica
core–shell microspheres with tunable chamber structures
*
Dawei Chen, Zhiyan Guo, Tao Sun, Fanglin Du
Key Laboratory of Nanostructured Materials, College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao, 266042, China
A R T I C L E I N F O
A B S T R A C T
Article history:
In 550 8C and H2 current, the mesoporous nickel–silica composite core–shell microspheres with tunable
chamber structures have been successfully prepared by reduction of Ni3Si2O5(OH)4 microspheres, which
are synthesized by the reaction between Ni(Ac)2ꢀ4H2O and SiO2 microspheres via a self-template
approach. The chamber (SiO2 core sizes) and shell thickness (40–150 nm) of the nickel–silica
microspheres can be controlled by adjusting the synthetic parameters of Ni3Si2O5(OH)4, such as the
reaction time. After reduction, these microspheres still have the same sizes, morphologies, and core–shell
structures with porous shell as before. These mesoporous nickel–silica microspheres with large BET
surface area, exhibit good catalytic activity in m-dinitrobenzene (m-DNB) and high selectivity of m-
phenylenediamine (m-PDA) after 3.5 h, but different selectivity of m-PDA in the progress, showing good
potential in the catalyst industry.
Received 8 October 2011
Received in revised form 29 February 2012
Accepted 21 May 2012
Available online 30 May 2012
Keywords:
A. Composites
A. Microporous materials
A. Nanostructures
B. Chemical synthesis
D. Catalytic properties
ß 2012 Elsevier Ltd. All rights reserved.
1. Introduction
In this paper, we reported a process for synthesizing mesoporous
nickel–silica core–shell microspheres by reduction of Ni3Si2O5(OH)4,
In the past decade, the spherical materials with core–shell
structures have attracted considerable attention in many fields
owing to their specific structures and interesting properties,
including catalysis, batteries, gas sensors, water treatment
agents, luminescent, separation of proteins, drug delivery, and
materials science [1–8]. In particular, silicate materials with such
core–shell structures have been extensively studied in diverse
field of catalysis support, ion exchange, and molecular adsorp-
tion because of their high surface area, well-defined and tunable
pore sizes, uniform porous structure, and rich surface properties
[9–12]. Various methods have been developed for preparing
silicate materials with hollow structure. The common route for
preparing hollow microspheres is to coat nanocrystals on the
surfaces of templates followed by removing the templates
through etching or calcinations [13–15]. For example, nickel–
silica and copper–silicate composite hollow microspheres have
been synthesized through such method [5,15]. However, the
traditional physical template synthesis have several shortcom-
ings, for example, the core is not directly participate in the
formation of the shell wall and must be removed in the end of
the reaction, complicating the whole process. Our group had
successfully developed a one-step self-template approach to
fabricating mesoporous SiO2/Ni3Si2O5(OH)4 core–shell micro-
spheres with tunable chamber structures [16].
which were synthesized by the above self-template approach. The
chamber and shell thickness of the nickel–silica microspheres can be
increased by adjusting the synthetic parameters of Ni3Si2O5(OH)4,
such as prolonging reaction time. Obviously, the structures and
nickel content would be varied with the changes of chamber and
shellthickness. Recently, thesilica-supportednickelhas been used in
the hydrogenation of m-dinitrobenzene (m-DNB) [17–19]. So the
catalytic activities of the mesoporous nickel–silica microspheres
were studied by m-dinitrobenzene hydrogenation reaction.
2. Experimental procedure
2.1. Synthesis of mesoporous nickel–silica microspheres
2.1.1. Synthesis of Ni3Si2O5(OH)4
In a typical synthesis, SiO2 (0.12 g) and Ni(Ac)2ꢀ4H2O (4 m mol)
were dispersed in 70 ml deionized water. The solutions were
transferred to Teflon-line stainless steel autoclaves and main-
tained at 180 8C for 6, 12 and 24 h, respectively. The green products
were collected by centrifugation and washed with distilled water
several times.
2.1.2. Synthesis of nickel–silica microspheres
After being dried in a vacuum stove, 0.3 g of the green products
were placed in a ceramic boat in the middle of a horizontal tube
furnace. The green products were reduced in H2 current at 550 8C
for 3 h and the products were kept until the temperature decreased
* Corresponding author. Tel.: +86 532 84022870; fax: +86 532 84022870.
E-mail address: dufanglin@qust.edu.cn (F. Du).
0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2012.05.022

D. Chen et al. / Materials Research Bulletin 47 (2012) 2344–2348
2345
˚
to room temperature. Black powder was obtained in the ceramic
boat.
a = b = c = 3.524 A, which is in good agreement with the JCPDS
file for Ni (JCPDS 65-2865).
The process for the formation of mesoporous Ni3Si2O5(OH)4 and
the reduction of nickel–silica composites may be summarized by
the following reactions:
2.2. Catalytic hydrogenation of m-DNB
The liquid phase hydrogenation of m-DNB was carried out in a
1000 ml stainless steel autoclave reactor, which was filled with m-
DNB (13.4 g) and the catalyst (1.1 g) in ethanol (500 ml, as solvent).
Firstly, air was flushed out of the reactor with N2 at room
temperature, and H2 was then filled into the reactor. After replacing
N2 with H2, the reactor was heated to 373 K and filled with H2 to
3.0 MPa, and the reaction was then carried out with stirring at
500 rpm. During the reaction, seven samples were obtained in 4 h
and every sample was withdrawn every half an hour.
2SiO2 þ 3NiðACÞ2 þ 5H2O ¼¼¼ Ni3Si2O5ðOHÞ4 þ 6HAC
Ni3Si2O5ðOHÞ4 þ 3H2 ¼¼¼ 2SiO2 þ 3Ni þ 5H2O
Fig. 2(a) shows the SEM image of one of the precursors with
hollow structure used in the process of reduction, which are about
500 nm in outer diameter and the broken shells confirm that the
thickness of the shell is about up to about 150 nm.
2.3. Characterization
The chamber and the shell thickness of the mesoporous SiO2/
Ni3Si2O5(OH)4 core–shell microspheres can be controlled by the
reaction parameters, such as the mesoporous SiO2/Ni3Si2O5(OH)4
core–shell microspheres with different shell thicknesses of from
40 nm to 150 nm were obtained by increasing the reaction time
from 3 h to 24 h using a molar ratio of Si and Ni of 1:2. As shown in
Fig. 3(a), (b) and (c), TEM images of the Ni3Si2O5(OH)4 at reaction
times of 6, 12 and 24 h, the diameters of SiO2 core are about 200,
The chemical composition of the nickel–silica composite was
characterized by X-ray power diffraction (XRD, D/MAX-500 X-ray
˚
power diffractometer with Cu Ka radiation, g = 1.5418 A at 40 kV
and 70 mA). The morphologies and sizes of the nickel–silica
composites were determined by field-emission scanning electron
microscope (FE-SEM, JSM 6700F) and transmission electron
microscope (TEM, JEM-2000EX), respectively. N2 adsorption
desorption isotherms were measured on a TriStar 3000 apparatus
at 77 K. The surface areas were calculated by the Brunauer–
Emmett–Teller (BET) method, and the pore size distribution was
calculated from the adsorption branch using the Barett–Joyner–
Halenda (BJH) theory. The chemical composition of the liquid was
analyzed on a VARIAN CP-3800 gas chromatography equipped
with a FID detector and a DB-5 packed column. The temperature of
column oven was controlled at 533 K.
3. Results and discussion
In the process of preparing mesoporous Ni3Si2O5(OH)4 core–
shell and hollow microspheres, the SiO2 with diameters of about
400 nm played two roles both as templates and source of silicate
ions. The pattern (a) in Fig. 1 shows the XRD pattern of the
Ni3Si2O5(OH)4 hollow microspheres. The pattern (b) shows a
typical XRD pattern of the nickel–silica composite reduced at
550 8C in H2 current. The peaks for (1 1 1) and (2 0 0) in this pattern
(b) can be well-indexed to a pure regular tetrahedron phase of Ni
(space group: Fm-3 m) with calculated lattice constants
Fig. 2. SEM images of (a) Ni3Si2O5(OH)4 hollow microspheres and (b) nickel–silica
Fig. 1. XRD patterns of (a) the Ni3Si2O5(OH)4 and (b) the nickel–silica composites.
composites.

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D. Chen et al. / Materials Research Bulletin 47 (2012) 2344–2348
Fig. 3. TEM images of as-synthesized Ni3Si2O5(OH)4 core–shell microspheres: experiments were performed for a molar ratio of Si and Ni of 1:2. (a), (b) and (c) Correspond to
reaction times of 6, 12 and 24 h, respectively, (d) is the TEM image of (b) after removing silica.
Fig. 4. TEM images of (a), (b) and (c) mesoporous Ni3Si2O5(OH)4 with different shell thickness by reduction at 550 8C in H2 current; (d) is prepared by reduction after removing
silica cores of (b).

D. Chen et al. / Materials Research Bulletin 47 (2012) 2344–2348
2347
100 and 0 nm, and the shell thickness are about 60, 80 and 150 nm,
respectively.
After mesoporous SiO2/Ni3Si2O5(OH)4 core–shell spheres are
reduced at 550 8C in H2 current for 3 h, the mesoporous Ni/SiO2
core–shell microspheres catalysts with different shell thicknesses
about from 40 nm to 150 nm have been successfully prepared. As
shown TEM images in Fig. 4(a), (b) and (c), the microspheres after
reduction still have the similar surface morphologies and
diameters as before. The bright areas inside the microspheres
indicate that nickel ions were in situ reduced to form nickel
particles and the original porous structures were reserved after
reduction, which might be due to the magnetic interaction
between nickel nanoparticles.
The dissolving property of silica spheres in alkaline conditions
enlightens us to prepare mesoporous nickel–silica hollow micro-
spheres with different shell thicknesses of about from 40 nm to
150 nm. Fig. 3(d) is the TEM image of the mesoporous
Ni3Si2O5(OH)4 hollow spheres with the shell thickness of 80 nm,
which is the SiO2/Ni3Si2O5(OH)4 core–shell microspheres im-
mersed in NaOH solution for two days. After reduction, mesopor-
ous nickel hollow spheres with shell thickness of about 80 nm
were obtained, as shown in Fig. 4(d). It is explored the possibility of
synthesizing mesoporous nickel–silica hollow microspheres with
different shell thicknesses of from 40 nm to 150 nm. It was
reported that the nickel content obviously affected the physico-
chemical and reductive properties of the catalyst [20] and the
catalytic activity was concerned with the chamber size of the
catalysts [21]. Apparently, due to such different core–shell and
hollow structures, the nickel–silica catalysts will show the
different catalytic activity, which is critical for hydrogenation
reaction and other applications in the catalysis.
The shape of the N2 adsorption/desorption isotherm and pore
diameter distribution of Ni3Si2O5(OH)4 microspheres and nickel–
silica microspheres further reveals the characteristic of their
porosity, as shown in Fig. 5. All of the N2 adsorption/desorption
isotherm exhibited a type IV isotherm with a clear hysteresis loop,
demonstrating these samples with the mesoporous character-
istics. The BET surface areas of the Ni3Si2O5(OH)4 microspheres
corresponding to reaction times of 6, 12, and 24 h are about 212.8,
213.2 and 160.0 m2 gꢁ1, while the nickel–silica core–shell micro-
spheres corresponding to reaction times of 6, 12, and 24 h are
about 211.1, 201.5 and 158.4 m2 gꢁ1, respectively, which are
larger than that of Raney Ni (95 m2 gꢁ1) [22]. The pore volume of
the Ni3Si2O5(OH)4 microspheres corresponding to reaction times
of 6, 12, and 24 h are about 0.324, 0.400 and 0.323 cm3 gꢁ1, while
the pore volume of nickel–silica microspheres corresponding to
reaction times of 6, 12, and 24 h are about 0.395, 0.391 and
0.305 cm3 gꢁ1, respectively. A majority of the pores for the
Ni3Si2O5(OH)4 microspheres corresponding to reaction times of 6,
12, and 24 h have diameters about 3.8, 3.7, and 3.8 nm, while the
pore diameters of the nickel–silica microspheres are about 3.8, 3.7
and 3.8 nm, respectively. It was found that the specific surface
area of SiO2/Ni3Si2O5(OH)4 core–shell microspheres was much
similar, and the specific surface area of Ni3Si2O5(OH)4 hollow
microspheres decreased to 160.0 m2 gꢁ1. And meanwhile, the
pore diameters of the Ni3Si2O5(OH)4 microspheres remain
unchanged with increasing the reaction time. However, the pore
size and specific surface area of as-synthesized nickel–silica
composites were much the same as before reduction. The
mesoporous structure provides efficient transport pathways to
their interior voids, which is critical for catalysis and other
applications.
Fig. 5. N2 adsorption/desorption isotherm and pore diameter distribution the
nickel–silica composites: (A), (C) and (E) N2 adsorption/desorption isotherm of the
nickel–silica composites corresponding to reaction times of 6, 12, and 24 h,
respectively; (B), (D) and (F) pore diameter distribution of the nickel–silica
composites corresponding to reaction time of 6, 12, and 24 h, respectively.
The catalytic activity of these nickel–silica composites catalysts
was also evaluated by the m-dinitrobenzene hydrogenation
reaction at 373 K and 3.0 MPa [21,23]. Fig. 6 shows the effect of
the catalysts on hydrogenation of m-dinitrobenzene (m-DNB) and
selectivity of m-phenylenediamine (m-PDA). (a), (b) and (c) were
related to the nickel–silica catalysts corresponding to reaction
times of 6, 12 and 24 h, respectively. Within 1 h, the conversion
rates of m-DNB corresponding to the catalysts a, b, c reach up to

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D. Chen et al. / Materials Research Bulletin 47 (2012) 2344–2348
Fig. 6. Effects of the time on the hydrogenation of m-DNB in ethanol. (A) Conversion of m-DNB (B) selectivity of m-PDA. (a), (b) and (c) With the nickel–silica composites
corresponding to reaction times of 6, 12 and 24 h, respectively.
90.0%, 90.1%, and 93.6%, respectively. The conversion rates of m-
DNB were all increased to 100% after 3.5 h. It can be seen that the
difference of these three kind of nickel–silica catalysts on
conversion rates of m-DNB was not obvious. The catalysts a, b, c
had a notable influence on selectivity of m-PDA with increasing the
reduction time, as shown in Fig. 6(B). In the range of 1–4 h, the
selectivity of m-PDA corresponding to the catalysts a, c increased
from 3.8% and 21% to 91.2% and 92.4%, respectively. However,
catalyst c exhibited relatively high selectivity and the selectivity
was over 93.9%. These catalysts exhibited very high catalytic
activity and different selectivity for m-PDA, which may be
explained for these catalysts had different shell thickness and
diameter of SiO2 core, suggesting that these kind of catalysts were
promising catalysts for the synthesis of m-PDA.
Acknowledgements
This work was supported by the Higher School Specialized
Research Fund for the Doctoral Program Funding Issue of China
(20093719110003) and Qingdao Science Bureau (10-3-4-4-9-jch).
References
[1] J.C. Park, H.J. Lee, J.Y. Kim, K.H. Park, H. Song, J. Phys. Chem. C 114 (2010) 6381.
[2] R. Rengarajan, P. Jiang, V.L. Colvin, D. Mittleman, Appl. Phys. Lett 77 (2000) 3517.
[3] J.B. Fei, Y.H. Cui, W. Qi, Y. Yang, K.W. Wang, Q. He, J.B. Li, Adv. Mater. 20 (2008) 452.
[4] Y.Q. Wang, C.J. Tang, Q. Deng, C.H. Liang, D.H.L. Ng, F.L. Kwong, H.Q. Wang, W.P.
Cai, L.D. Zhang, G.Z. Wang, Langmuir 26 (2010) 18.
[5] S. Dembski, M. Milde, M. Dyrba, S. Schweizer, C. Gellermann, T. Klockenbring,
Langmuir 27 (2011) 14025.
[6] M.F. Shao, F.Y. Ning, J.W. Zhao, M. Wei, D.G. Evans, X. Duan, J. Am. Chem. Soc. 10
(2012) 1021.
4. Conclusions
[7] Y.F. Zhu, Y. Fang, S. Kaskel, J. Phys. Chem. C 114 (2010) 16382.
[8] J.Y. Sun, Z.K. Wang, H.S. Lim, S.C. Ng, M.H. Kuok, T.T. Tran, X.M. Lu, ACS Nano 4
(2010) 7692.
In summary, we have successfully demonstrated a route for
controlled synthesis of mesoporous nickel–silica composite core–
shell and hollow microspheres catalyst with tunable chamber,
which is critical for hydrogenation reaction and other applications
in the catalysis. After reduction, these microspheres still retained
the same sizes, morphologies, hollow structures and BET surface
area as before. At 373 K and 3.0 MPa, all of these mesoporous
nickel–silica composites catalysts, which have different shell
thickness and diameter of SiO2 core, exhibit 100% conversion of m-
dinitrobenzene (m-DNB) and more than 91% selectivity of m-PDA
in the end, but different selectivity of m-PDA in the progress,
showing potential applications as catalysts being used in the
synthesis of m-PDA.
[9] S. Ahmed, S. Chughtai, M.A. Keane, Sep. Purif. Technol. 13 (1998) 57.
[10] N. Bektas, B.A. Agim, S.J. Kara, Hazard. Mater. 112 (2004) 115.
[11] A. Corma, Chem. Rev. 97 (1997) 2373.
[12] I.I. Slowing, B.G. Trewyn, S. Giri, V.S. Lin, Adv. Funct. Mater. 17 (2007) 1225.
[13] P. Jiang, J.F. Bertone, V.L. Colvin, Science 291 (2001) 453.
[14] C.N. Lin, M.H. Huang, J. Phys. Chem. C 113 (2009) 925.
[15] N. Ren, B. Wang, Y.H. Yang, Y.H. Zhang, W.L. Yang, Y.H. Yue, Z. Gao, Tang, Chem.
Mater. 17 (2005) 2582.
[16] Z.Y. Guo, F.L. Du, G.C. Li, Z.L. Cui, Chem. Commun. (2008) 2911.
[17] M.M. Telkar, J.X. Nadgeri, C.V. Chaudhari, Appl. Catal. A 23 (2005) 259.
[18] Y.X. Liu, J.X. Chen, J.Y. Zhang, Chin. J. Catal. 24 (2003) 224.
[19] L. Zhao, J.X. Chen, J.Y. Zhang, J. Mol. Catal. A 246 (2006) 140.
[20] Y.X. Liu, Z.J. Wei, J.Y. Zhang, Korean J. Chem. Eng. 23 (2006) 902.
[21] H. Li, Z. Bian, J. Zhu, D. Zhang, G. Li, Y. Lu, J. Am. Chem. Soc. 129 (2007) 8406.
[22] J. Shim, H.K. Lee, Mater. Chem. Phys. 69 (2001) 72.
[23] J.X. Chen, J.X. Zhang, J.Y. Zhang, React. Kinet. Catal. Lett. 93 (2008) 2359.