Ultrasmall Particle Sizes of Walnut-Like Mesoporous Silica Nanospheres with Unique Large Pores and Tunable Acidity for Hydrogenating Reaction

Article abstract of DOI:10.1002/smll.202002091

The large particle sizes, inert frameworks, and small pore sizes of mesoporous silica nanoparticles greatly restrict their application in the acidic catalysis. The research reports a simple and versatile approach to synthesize walnut-like mesoporous silica nanospheres (WMSNs) with large tunable pores and small particle sizes by assembling with Beta seeds. The as-synthesized Beta-WMSNs composite materials possess ultrasmall particulate sizes (70 nm), large radial mesopores (≈30 nm), and excellent acidities (221.6 mmol g^?1). Ni₂P active phase is supported on the surface of Beta-WMSNs composite materials, and it is found that the obtained composite spherical materials can reduce the Ni₂P particle sizes from 8.4 to 4.8 nm with the increasing amount of Beta seeds, which can provide high accessibilities of reactants to the active sites. Furthermore, the unique large pores and ultrasmall particle sizes of Beta-WMSNs samples facilitate the reduction of the diffusion resistance of reactants due to the short transporting length, thus the corresponding Ni₂P/Beta-WMSNs composite catalysts show the excellent hydrogenating activity compared to the pure Ni₂P/WMSNs catalyst.

Full text of DOI:10.1002/smll.202002091

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Ultrasmall Particle Sizes of Walnut-Like Mesoporous Silica
Nanospheres with Unique Large Pores and Tunable Acidity
for Hydrogenating Reaction
Di Hu, Huiping Li, Jinlin Mei, Cong Liu, Qian Meng, Chengkun Xiao, Gang Wang, Yu Shi,
and Aijun Duan*
and stabilities due to their low cost, nontox-
icity, and like noble metal structures.[11–13]
Oyama[14] found that Ni2P/SiO2-based
catalyst showed higher activity than other
tradition metal phosphides catalysts for
hydrodesulfurization (HDS) and hydroden-
itrogenation (HDN). The superior activity
of Ni2P/SiO2 catalyst was attributed to the
higher electron density in Ni2P, which
could facilitate the dissociation of H2.[15,16]
Ni2P supported catalysts have shown high
hydrogenating activity in the application of
HDS,[8,17,18] HDN,[19,20] and HDO.[21–23] The
hydrogenation of aromatic compound is in
urgent need of this highly active catalysts
to produce deep hydrogenation products
and further ring-opening products. And the
higher electron density in Ni2P can enhance
the adsorption of the aromatic hydrocar-
bons on the Ni2P active sites. Therefore, we
choose Ni2P as the active species to prepare
The large particle sizes, inert frameworks, and small pore sizes of mesoporous
silica nanoparticles greatly restrict their application in the acidic catalysis. The
research reports a simple and versatile approach to synthesize walnut-like
mesoporous silica nanospheres (WMSNs) with large tunable pores and small
particle sizes by assembling with Beta seeds. The as-synthesized Beta-WMSNs
composite materials possess ultrasmall particulate sizes (70 nm), large radial
mesopores (≈30 nm), and excellent acidities (221.6 mmol g−1). Ni2P active
phase is supported on the surface of Beta-WMSNs composite materials, and it
is found that the obtained composite spherical materials can reduce the Ni2P
particle sizes from 8.4 to 4.8 nm with the increasing amount of Beta seeds,
which can provide high accessibilities of reactants to the active sites. Further-
more, the unique large pores and ultrasmall particle sizes of Beta-WMSNs
samples facilitate the reduction of the diffusion resistance of reactants due
to the short transporting length, thus the corresponding Ni2P/Beta-WMSNs
composite catalysts show the excellent hydrogenating activity compared to the
pure Ni2P/WMSNs catalyst.
the supported catalysts for aromatic hydrogenation.
1. Introduction
Mesoporous silica nanoparticles (MSNs) have received con-
siderable attraction owing to their advantageous structural
properties.[24] It is well-known that the uniform mesopores
and various morphologies of MSNs have great influence on
their physical properties.[25–27] Compared to the conventional
mesoporous silica supports (e.g., mesoporous crystalline mate-
rial and Santa Barbara amorphous material series mesoporous
materials), MSNs with hierarchically pore channels exhibit
good biocompatibilities and high loading capacities as car-
riers for biomedicine and catalysis.[28–30] Especially, MSNs pos-
sess adjustable external and internal textural properties, such as
relatively high specific surface areas and pore volumes, which
contribute to the high accessibility of active sites.[31,32] Moreover,
the multiple combination of micropore–mesopore–macropore
in hierarchical channels facilitates the diffusion of reactants
in various molecular sizes.[31,33] However, most of the reported
particle sizes of MSNs are still in very large sizes (regularly
>100 nm),[34–36] resulting in the low utilization efficiency of the
active sites and in the high diffusion resistance to large aromatic
hydrocarbons, which might restrict the relative applications sig-
nificantly. Moreover, the acidity of catalysts plays an important
role in hydrogenation, isomerization (ISO) and ring opening
activity of naphthalene.[37] The intrinsic defects of weak acidity,
low metal–support interaction, and poor hydrothermal stability
With the continual increase of energy consumption, more strin-
gent environmental protection laws and regulations require the
petroleum industry to produce more environmental-friendly
transportation fuels for the economic development. Aromatics
in diesel are prone to produce hydrocarbon (HC) emission
and particle matter (PM).[1] In order to protect the environ-
ment, hydrogenation of aromatic hydrocarbon in fuel would be
one of the main approaches to decrease the toxic contents of
aromatics. As a typical bicyclic aromatic species, naphthalene is
usually taken as a probe molecule in the study of deep hydro-
genation of aromatic hydrocarbons.[2,3]
It is reported that transition metal phosphides, such as MoP,[4]
FeP,[5,6] CoP,[7] and Ni2P,[8–10] displayed higher catalytic activities
Dr. D. Hu, Dr. H. Li, Dr. J. Mei, Dr. C. Liu, Dr. Q. Meng, Dr. C. Xiao,
Dr. G. Wang, Dr. Y. Shi, Prof. A. Duan
State Key Laboratory of Heavy Oil Processing
China University of Petroleum-Beijing
18 Fuxue Road, Beijing 102249, P. R. China
E-mail: duanaijun@cup.edu.cn
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.202002091.
DOI: 10.1002/smll.202002091
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Figure 1. Wide angle XRD patterns of A) Beta seeds obtained at different crystallization times and B) BW series composite supports with different
SiO2/Al2O3 molar ratios.
from pure mesoporous silicas should be avoided to benefit their
extensive usages in different processes.[38] Previous studies[38–40]
proved that in situ assembling of zeolites (Beta, ZSM-5, and Y-zeo-
lites) into the framework of mesoporous silicas could not only
improve the acidity and hydrothermal stability of MSNs materials,
but also enhance the metal–support interaction, which would be
conducive to the formation of high-dispersive Ni2P active phases.
Compared with the commercial zeolites of Y and ZSM-5, Beta
type zeolite has good structural selectivity, modulated acidity, and
hydrothermal stability due to its unique 3D 12-ring pore system
and the wide range of SiO2/Al2O3 ratio from tens to hundreds,
which make it widely used in catalytic hydrogenation process.[41–43]
Nowadays, the synthesis of spherical mesoporous materials
with ultrasmall particle sizes, uniform morphology, and large
tunable pores, especially with the pore diameter larger than
20 nm, is significant in scientific research.[13] Moreover, it is
a great challenge for coordinating the pore structure and acid
property of spherical silica nanoparticles to achieve a good bal-
ance. In this research, we report an effective simple approach to
fabricate walnut-like mesoporous silica nanospheres (WMSNs)
with large tunable pores by combining with Beta zeolites. And,
the Beta microcrystallines were added before TEOS to synthe-
size the Beta-WMSNs composites. This method can not only
guarantee the complete combination of Beta and WMSNs mate-
rials, but also easily control the structure and morphology of the
synthesized samples. Nickel phosphide is used as active species
to evaluate the catalytic performance of naphthalene hydrogena-
tion. Meanwhile, the acidity of Beta-WMSNs supported catalysts
could be easily controlled by adjusting the amount of Beta addi-
tion. The influence of synthesis parameters on the typical phys-
icochemical properties of walnut-like mesoporous silicas and
the corresponding catalytic activity is investigated.
the relationship between the growth of Beta zeolites and
crystallization time, the growth of Beta zeolites at different
crystallization times was investigated at the temperature of
120 °C. It can be seen from Figure 1A that there is no char-
acteristic diffraction peak of Beta phase within 0–18 h, indi-
cating solid phase is mainly amorphous during this period.
When the crystallization time extends to 20 h, the charac-
teristic peaks of Beta at 2θ = 7. 7 ° and 22.3° are detected.[44]
During this period, Beta zeolites undergo a short nucleation
induction period and a relatively rapid crystal growth period.
After 20 h crystallization, there is no obvious change in crys-
tallinity, indicating that the growth of the crystallization of
Beta zeolites was relatively complete. Therefore, Beta zeo-
lite obtained in 20 h crystallization time are chosen to be the
optimal seeds to compound with WMSNs. Figure 1B shows
the XRD patterns of BW series composite supports. All the
BW composite supports display the characteristic peaks of
Beta seeds compared with single WMSNs samples and the
peak intensities increase with more amount of Beta, indi-
cating that as-synthesized BW composite materials possess
both Beta and WMSNs structures.
2.1.2. N2 Adsorption–Desorption Characterization
Figure 2A,B displays the N2 adsorption–desorption isotherms
and the pore size distributions of BW series supports, respec-
tively. The N2 adsorption–desorption isotherms reveal that
all the supports possess the type-IV isotherms. The step of
the near-saturation adsorption at a high relative pressure of
P/Po > 0.8 become more sharper, and the H4 type of hyster-
esis loop gradually transforms to H3 type as adding more
amount of Beta seeds, indicating the appearances of large
mesoporous structures. When the ratios of SiO2/Al2O3 decrease
to 100, the corresponding specific surface areas increase from
340.2 to 542.5 m2 g−1, and the pore volumes enlarge from
0.47 to 1.47 cm3 g−1 (Table 1). It can be found from Figure 2B
that a narrow peak at 3.5 nm is shown on all the series sup-
ports, which belongs to pure WMSNs sample. Moreover, a wide
peak appears as Beta seeds are added, which indicates that the
pore sizes of corresponding samples are enlarged as the Beta
seeds penetrate into the WMSNs framework.
2. Results
2.1. Characterization Results of Supports
2.1.1. X-Ray Diffraction (XRD) Characterization
Crystallization time has a very important impact on the crys-
tallinity and the growth of Beta zeolites. In order to explore
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Figure 2. A) N2 adsorption–desorption patterns and B) pore diameter distribution patterns of BW series supports.
 
membered rings of Si O Al bond due to the addition of zeolite
2.1.3. Scanning Electron Microscopy (SEM) and Transmission
Electron Microscopy (TEM) Characterizations
Beta.[39,40] Moreover, the peak intensity of Si O Al bond in BW
 
series composite becomes stronger when more amount of Beta
seeds is added into the WMSNs, manifesting that WMSNs and
The changes of particle sizes of BW supports can be clearly
observed from SEM images in Figure 3. After adding Beta seeds,
the particle sizes of spherical silica materials directly decrease
from 200 nm of pure WMSNs support to 120 nm of BW-120
composite support, and continue to shrink down to 70 nm of
BW-100 as the addition of Beta increases. As seen from TEM
images in Figure 4, the pore sizes of BW materials can also be
gradually enlarged at the same time. The largest diameters of
the opening pores on the surface almost reach 30 nm as the
ratios of SiO2/Al2O3 reach 100, which is beneficial for the mass
transportation of reactants by reducing the diffusion barriers.
In order to trace the location of Beta seeds, the energy-
dispersive X-ray spectroscopy (EDS) elemental mapping was
performed and the results of Al, Si, and O species on BW-160
support are shown in Figure 5. It can be found that when only a
small amount of Beta seeds is added, the Al species are already
uniformly distributed in the silica pore channels, which con-
firms that the Beta seeds have been successfully assembled into
the WMSNs framework.
 
Beta seeds are composited via Si O Al bonds.
2.1.5. Synthesis Mechanism of the BW Supports
In order to investigate the formation mechanism of BW com-
posite support, the ratio of Al2O3:TEAOH has changed in the
formation of Beta seeds. The SEM images in Figure S2 in the
Supporting Information show that the pore sizes of BF com-
posite supports continue to enlarge when increasing the ratio
of Al2O3:TEAOH amount, which confirms that Beta framework
with more aluminum species can penetrate into the as-formed
 
CTAB micelles easily via Si O Al bonds, as seen in Figure 7A.
Moreover, the addition amount of TEOS at the final step has also
been investigated. As seen in Figure 7B and Figure S3a in the
Supporting Information, both WMSNs support and BW com-
posite material cannot be synthesized without the addition of
TEOS. As the amount of TEOS increasing to 10 mL, part of Beta
seeds can insert into the CTAB micelles to form the BW com-
posite materials successfully, whereas singe Beta seeds can still be
seen in Figure 7B and Figure S3b in the Supporting Information.
It can be seen from Figure 7B and Figure S3c in the Supporting
Information and that all the Beta seeds are embedded within the
framework of WMSNs when 20 mL TEOS are dropped into the
final solution, and the as-synthesized BW composite nanoparti-
cles are evenly dispersed. Therefore, it can be found that Beta
seeds can penetrate into CTAB micelles through bonding with
the surface silicon source. As the increasing amount of Beta
2.1.4. FT-IR Characterization
Fourier transform infrared spectroscopy (FT-IR) spectra of the
series BW composites are shown in Figure 6. The characteristic
peaks at 803, 964, and 1094 cm−1 are attributed to the Si O Si
 
bond of pure mesoporous silica nanoparticles.[45] The distinct
absorption peak of BW composite at 570 cm−1 is appeared com-
pared to the pure WMSNs, which is attributed to six- or five-
 
combining with the TEOS through Si O Al bonds, the large
pore sizes of BW composites tend to form small-sized nanopar-
Table 1. Textural properties of the supports.
ticles in order to maintain the stability of spherical particles.[46]
Samples
WMSNs
BW-160
BW-140
BW-120
BW-100
DBJHc) [nm]
SBETa) [m2 g−1
340.2
]
Vtb) [cm3 g−1
0.47
]
5.1
6.0
7.3
2.2. Characterization Results of Catalysts
400.7
0.54
2.2.1. XRD Characterization
413.9
0.60
528.0
1.15
11.2
13.7
Figure 8 exhibits the XRD pattern of the synthesized series
catalysts, which show the typical peaks at 40.7°, 44.8°, and
47.5° of Ni2P phase over all the Ni2P supported catalysts.[10]
Furthermore, it is apparent that the corresponding peaks of
542.5
1.47
a)Surface area obtained by BET method; b)Total pore volume obtained by BET
method; c)Pore diameter collected from the adsorption isotherm by BJH method.
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Figure 3. SEM images of the series supports. A) WMSNs; B) BW-160; C) BW-140; D) BW-120; E) BW-100; F) Beta zeolites.
Ni2P over BW catalysts are weakened and broadened compared
to those over Ni2P/WMSNs pure siliceous catalysts without the
addition of Beta. According to Scherrer equation, the sizes of
Ni2P crystallites decrease from 10.7 to 3.5 nm as the addition of
Beta seeds (Table 2).[47]
Figure 9. It can be found that some Ni2P particles are aggregated
over Ni2P supported pure WMSNs catalyst, due to its low surface
areas and small pore sizes. The size distributions of Ni2P parti-
cles calculated by statistic method are displayed in Figure S4 in
the Supporting Information. The size distribution of Ni2P parti-
cles over the Ni2P/WMSNs pure catalyst is much wider compared
to the Ni2P/BW composite catalysts, ranging from 2 to 20 nm.
As the addition amount of Beta increases, the size distribution of
Ni2P become more concentrated and the corresponding average
sizes of Ni2P particles calculated from TEM images decrease
from 8.4 to 4.8 nm (Table 2), which agrees with the XRD analysis.
2.2.2. TEM Characterization
In order to further investigate the size change of Ni2P particles,
TEM images of Ni2P supported series catalysts are shown in
Figure 4. TEM images of the series supports. A) WMSNs; B) BW-160; C) BW-140; D) BW-120; E) BW-100.
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Figure 5. A) TEM, B) STEM images, and C–E) EDS patterns of BW-160 sample.
2.2.3. Py-IR Characterization
The acidity of the series Ni2P/BW catalysts are measured by
Py-IR at 200 and 350 °C, respectively (Figure S5, Supporting
Information), and the corresponding quantifications are sum-
marized in Table 3. According to Table 3, the total acid amounts
of BW supports are increased due to the introduction of Beta
seeds into the silica skeleton structures, from 37.8 mmol g−1 for
pure Ni2P/WMSNs catalyst to 221.6 mmol g−1 for Ni2P/BW-100
catalyst. Moreover, the Lewis acid sites increase greatly as the
amount of Beta addition changes, indicating that the addition
of Beta seeds can adjust the ratio of Lewis acid and Bronsted
acid in the supported Ni2P catalysts.
Figure 7. A) Schematic of the formation mechanism of BW materials
by incorporating Beta seeds into CTAB micelles. B) The key role of silicon
source TEOS in the synthesis process of BW composite materials.
and 800 °C, which belong to the reductions of Ni and P species,

respectively. Since the P O bond energy is extremely high, the
2.2.4. H2-Temperature-Programmed Reduction (H2-TPR)
Characterization
reduction of P precursor is the key step in the formation of Ni2P.
It can be seen from the H2-TPR patterns that the reduction peaks
of Ni and P species over the series catalysts all move to the high
temperature region, among which the reduction peak of the P
species shifts to a higher temperature from 800 to 820 °C. These
H2-TPR patterns of Ni2P/BW series catalysts, as shown
in Figure 10, exhibit two major reduction peaks at around 420
Figure 6. FT-IR spectra of series supports. A) WMSNs; B) BW-160;
C) BW-140; D) BW-120; E) BW-100.
Figure 8. The XRD patterns of Ni2P/BW series catalysts. A) Ni2P/WMSNs;
B) Ni2P/BW-160; C) Ni2P/BW-140; D) Ni2P/BW-120; E) Ni2P/BW-100.
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Table 2. Textural properties of the series catalysts.
indicating that a higher addition of Beta in our research scope
can contributes to the formation of Ni2P active phases.
Samples
Dc [nm]a)
10.7
7.9
Daver [nm]b)
Ni2P WMSNs
Ni2P/BW-160
Ni2P/BW-140
Ni2P/BW-120
Ni2P/BW-100
8.4
6.5
6.2
5.5
4.8
2.3. The Results of Naphthalene Selective Hydrogenation
5.0
Naphthalene is a kind of representative aromatic compound,
which is widely used to evaluate the performance of aromatic
hydrogenation catalysis. The results of naphthalene hydro-
genating conversion are presented in Figure 11A. During the
temperature range from 300 to 380 °C, the hydrogenating
conversion rate of naphthalene over Ni2P/BW catalysts are all
higher than that over pure WMSNs supported Ni2P catalyst.
When the temperature continues to increase, the naphthalene
conversions over Ni2P/WMSNs, Ni2P/BW-160, and Ni2P/BW-140
decrease to some extent, especially for the pure Ni2P/WMSNs
catalyst, which can be ascribed to the exothermic reaction con-
trolled by kinetical constrain at high temperature.
4.1
3.5
a)The particle size of Ni2P determined by Scherrer equation: Dc = Kλ/βcos(θ),
where K is a constant taken as 0.9, λ is the wavelength of the X-ray radiation, β is
the width of the peak at half maximum, and 2θ is the Bragg angle[52] b)The average
;
size of Ni2P obtained by statistical analyses based on TEM images from 200 to
300 Ni2P particles.
results confirm that the interaction between Ni2P precursor and
BW support become stronger as the increase amount of Beta addi-
tion, which can reduce the aggregation of Ni2P particles and be
conducive to the formation of high-dispersive Ni2P active phases.
In order to investigate the reaction route of naphthalene hydro-
genation, the products distribution is illustrated in Figure 11B.
As can be seen from Figure 11B, the tetralin selectivity gradually
decreases from 56.69% over Ni2P/WMSNs to 2.84% over Ni2P/
BW-100, while the contents of decalin increased from 33.62% to
65.78%. These trends indicate that more tetralin hydrogenates
further to produce decalin and a higher hydrogenating conver-
sion is achieved over BW composite catalysts compared to the
pure WMSNSs supported catalyst. Moreover, besides the hydro-
genation products, the ISO products of both tetralin and decalin
are also detected over Ni2P/BW-120 and Ni2P/BW-100 catalysts.
Those isomerization products are prepared for further ring
opening reactions, which can be seen that some ring opening
(OP) products are detected over Ni2P/BW-100 catalyst. Among all
the catalysts, the Ni2P/BW-100 catalyst exhibit higher hydrogena-
tion conversion as well as ISO and OP activities. The reaction
route of naphthalene hydrogenation can be proposed based on
the product distribution. As shown in Figure 12, naphthalene
first undergoes hydrogenation reaction to produce tetralin and
decalin, followed by isomerization and ring opening reactions.
Thus, the hydrogenation products of tetralin and decalin have a
significant effect on the ISO and OP products.
2.2.5. XPS Characterization
For further investigating the states of Ni and P species over the
series Ni2P supported catalysts, X-ray photoelectron spectro-
scopy (XPS) spectra of different catalysts were exhibited in
Figures S6 and S7 in the Supporting Information. As seen from
Figure S6 in the Supporting Information, two main Ni 2p peaks
with the bonding energy of around 857 and 853 eV are shown
on all the catalysts, which are assigned to Ni2+ and Ni2P phase,
respectively. Moreover, a small signal with the corresponding
peak at about 861 eV corresponds to the divalent species.[48]
According to Figure S7 in the Supporting Information, the
binding energy of p2p at around 134 and 133 eV are assigned
−
to the PO43− and H2PO3 , respectively.[49] In addition, the broad
peak detected at ≈129 eV corresponds to the Pδ− (0 < δ < 1) spe-
cies, which represents the Ni species in the Ni2P phase.
The atom percentages over different Ni2P supported catalysts
are calculated in Table 4. The atom percentages of Niδ+ and
Pδ− species in the Ni2P phase increase after adding Beta seeds,
3. Discussion
Combined with the systematical characterization and assess-
ment results, the series Ni2P/BW composite samples exhibit
outstanding hydrogenating activity than the pure Ni2P/WMSNs
silica materials. The superiorities of BW materials are closely
related to its unique nanostructure and chemical properties,
which could be described from the following aspects:
First, the unique structure properties of BW composite
materials contribute a lot to the diffusion of large aromatic
molecules. Through incorporating Beta seeds into WMSNs
frameworks, the pore sizes of series BW supports enlarged
from 5 nm of pure WMSNs to 30 nm of BW-100 composite.
Moreover, the particle sizes of spherical silica supports directly
decrease from 200 nm of pure WMSNs support to 70 nm of
BW-100 support, which are beneficial to Ni2P loading due to
its high specific surface areas. In addition, the short diffusion
Figure 9. TEM patterns of Ni2P/BW series catalysts. A) Ni2P/WMSNs;
B) Ni2P/BW-160; C) Ni2P/BW-140; D) Ni2P/BW-120; E) Ni2P/BW-100.
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Table 3. Acid site amounts calculated from Py-IR.
Acid amount (200 °C) [mmol g−1
]
Acid amount (350 °C) [mmol g−1]
Catalysts
B
L
B/L
0.09
0.06
0.03
0.01
0.03
B
L
B/L
0.79
0.12
0.13
0.07
0.03
L+B
37.8
L+B
11.9
Ni2P/WMSNs
Ni2P/BW-160
Ni2P/BW-140
Ni2P/BW-120
Ni2P/BW-100
3.1
3.0
2.7
2.1
7.3
34.7
44.7
87.8
167.6
214.3
5.3
3.2
4.3
3.6
3.5
6.6
47.7
26.4
32.1
49.0
103.7
29.6
36.4
52.6
107.2
90.5
169.7
221.6
paths of ultrasmall particle sizes are also better for adsorption
and desorption of reactants inside the hierarchical pore chan-
nels, which can largely reduce the diffusion resistance of large
reactants.
The above analysis show that by adjusting the addition
amount of Beta seeds, the acidity and pore structure of BW
supports can be collaborative optimization, which contrib-
utes to the well-dispersion of Ni2P active sites. The evaluation
results show that the high hydrogenation activity is correlated
with the acidity of BW support and the particle sizes of Ni2P
active sites, among which the isomerization reaction is closely
related to the acidity.
Secondly, the acidity exerts a positive effect upon the ISO
and OP activities for naphthalene. According to the Py-IR
results, the amount of total (B+L) acids and medium-strong
acids increase from 37.8 and 11.9 mmol g−1 of Ni2P/WMSNs
to 221.6 and 107.2 mmol g−1 of Ni2P/BW-100, confirming that
the addition of Beta seeds contributes to the optimal acidity.
Moreover, Ni2P/BW-100 catalyst with the largest acidity exhibits
high hydrogenating conversion as well as some isomeriza-
tion products and ring opening products, while the pure Ni2P/
WMSNs with the minimal acidity produces only hydrogenating
products. Thus, the increased acidity plays a significant role
in promoting the isomerization and ring opening reaction of
naphthalene hydrogenation.
Thirdly, the Ni2P active sites have profound consequence for
high hydrogenation activity. According to the statistical analysis
from TEM images, the size distributions of Ni2P particles over
BW composite supports are much concentrated than those over
pure silica WMSNs support, which can attribute to the high
specific surface areas and big pore volumes of BW supports.
Among all the synthesized catalysts, Ni2P/BW-100 catalyst has
smaller Ni2P average particle sizes, leading to high accessi-
bility of active sites in the pore channel. It is achieved from the
product distribution in Figure 11B, more hydrogenation prod-
ucts of decalin are produced over Ni2P/BW-100 catalysts due to
its improved utilization rate of Ni2P active sites.
4. Conclusions
In this research, walnut-like mesoporous silica nanoparticles
with ultrasmall particle sizes and large radial pores were suc-
cessful synthesized through the introduction of Beta seeds.
The obtained BW composite materials exhibited high loading
capacity, which enhanced the dispersity of Ni2P active phases.
Meanwhile, the acidities of Ni2P/BW series materials could be
easily adjusted through tuning the amounts of Beta addition,
which consequently achieved the superior hydrogenation ability
and isomerization activity. The results showed that the series
Ni2P/BW catalysts exhibit higher hydrogenation activity than
pure Ni2P/WMSNs catalysts. We believed that this combined
synthesis of mesoporous silica nanoparticles provides a new
insight into the catalytic materials for the widely potential appli-
cation in the industry processes.
5. Experimental Section
Synthesis of Beta Precursor Seeds: First, NaAlO2, TEOS, TEAOH, NaOH,
and deionized water were mixed with the Al2O3:SiO2:TEAOH:NAOH:H2O
molar ratio of 1:45:100:2:50. After stirring for 18 h, the precursor powders
of Beta seeds were collected by filtration and desiccation.
Support Preparation: The pure WMSNs support was synthesized by
the same method as mentioned in the previous papers.[50,51] Typically,
5 g CTAB, 3 g urea, 7.5 mL n-butyl alcohol, 150 mL deionized water, and
150 mL cyclohexane were agitated together. Then, TEOS was added
dropwise to the above solution. After stirring for 30 min, the solution
temperature was adjusted to 70 °C and stirring was continued for
24 h. Finally, the WMSNs product was obtained after filtering, dried, and
calcinated at 550 °C for 6 h.
Beta-WMSNs support was prepared using the similar method by
dissolving Beta precursor powder in the mixture solution of 5 g CTAB,
3 g urea, 7.5 mL n-butyl alcohol, 150 mL deionized water, and 150 mL
cyclohexane. Then, TEOS was added dropwise into the above solution.
The following steps were the same as the above synthetic method of
pure WMSNs support. Through adjusting the amount of Beta precursor
powders, Beta-WMSNs composites with different SiO2/Al2O3 molar
Figure 10. H2-TPR patterns of Ni2P/BW series catalysts. A) Ni2P/WMSNs;
B) Ni2P/BW-160; C) Ni2P/BW-140; D) Ni2P/BW-120; E) Ni2P/BW-100.
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Table 4. The XPS analysis results of Ni2P supported catalysts.
Catalysts
Ni 2p3/2 (binding energy)a)
P 2p3/2 (binding energy)a)
3−
−
Ni2+
PO4
H2PO3
Ni2P
Ni2P
Ni2P/WMSNs
Ni2P/BW-160
Ni2P/BW-140
Ni2P/BW-120
Ni2P/BW-100
857.0 (56.9)
857.0 (54.6)
856.8 (53.2)
856.9 (50.0)
857.0 (48.3)
853.6 (43.1)
853.6 (45.4)
853.5 (46.8)
853.5 (50.0)
853.6 (51.7)
134.1 (84.8)
134.1 (64.4)
134.1 (74.2)
134.3 (49.3)
134.2 (61.0)
133.0 (4.4)
133.3 (16.5)
133.3 (3.5)
133.4 (24.9)
133.4 (11.6)
129.7 (10.8)
129.8 (19.1)
129.9 (22.3)
129.9 (25.8)
129.8 (27.4)
a)The data in parentheses are atom percentages.
Figure 11. A) Naphthalene conversion over Ni2P supported catalysts and B) products distribution for Ni2P supported catalysts under the temperature
of 360 °C.
ratios (100/120/140/160) were synthesized and denoted as BW-X, where
X represents the mass ratios of SiO2/Al2O3 molar ratios.
Measurement and Characterization: Wide-angle XRD patterns of supports
and catalysts were measured on a Japan Shimadzu X-6000 diffractometer
with Cu Kα radiation (40 kV, 30 mA, λ = 0.1540598 nm). Nitrogen
adsorption–desorption isotherms were collected using Micromeritics
Tristar 3020 at 77 K. The specific surface areas were calculated by
Brunauer–Emmett–Teller (BET) method. The acidity of the series catalysts
was tested by Pyridine adsorption infrared spectroscopy (Py-FTIR) using a
Digilab FT-IR infrared spectrometer from Bole Pacific Company. TEM was
utilized through a JEM 2100 transmission electron microscope from Japan
JEOL Corporation at the operating voltage of 200 kV. SEM measurements
were conducted on a Hitachi SU-8010 instrument operating at 5.0 kV. The
morphologies of the series supports and the dispersion of Ni2P phases
were obtained by TEM images using a microscope grid in a Philips Tecnai
G2 F20 S-TWIN microscope at an accelerating voltage of 300 kV. The size
distributions of Ni2P phases were counted by more than 300 Ni2P particles
from different regions in TEM images. The average Ni2P particles were
calculated according to Equation (1)
Catalyst Preparation: The Ni2P/BW catalysts were obtained after
temperature-programmed reduction. The supported Ni2P catalyst
precursors were prepared by impregnating with nickel nitrate
(Ni(NO3)2·6H2O) and ammonium hypophosphite (NH4H2PO4) with an
initial Ni/P molar ratio of 1/1. After drying and calcinating at 550 °C for
3 h, the oxidic precursors were placed in a fixed bed reactor at continued
H2 flow rate of 150 mL min−1 and temperature of 120 °C. Then, the
temperature was gradually heated to 440 °C and kept for 1 h, and then
rising to 550 °C at a rate of 1 °C min−1 was kept for another 3 h. The nickel
phosphides were collected after cooling down to the room temperature.
n
i=1di
ni
∑
(1)
Daver
=
where di represents the size of each Ni2P particle and ni is the total
number of Ni2P particles.
Catalytic Activity Measurements: After temperature-programmed
reduction, 1.0 g samples of Ni2P supported catalysts were loaded
in the middle of a fixed bed reactor, with both ends filled with mesh
quartz sands. The hydrogenation activity of aromatic hydrocarbons
was assessed by using 5% naphthalene in cyclohexane as a model
compound. The naphthalene hydrogenation reaction was carried out
under the condition of 4 MPa, H2/oil volumetric ratio of 500 (v/v),
liquid hourly space velocity (WHSV) of 10 h−1, and temperature in the
range of 300–380 °C. The reaction products were analyzed using gas
chromatography-mass spectrometry (GC-MS).
Figure 12. Proposed reaction routes for the main products of naphtha-
lene over Ni2P/BW catalysts. ISO: isomerization; RO: ring opening.
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The conversion of naphthalene can be expressed by Equation (2)
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Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
This research was financially supported by the National Natural Science
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