Fabrication of propylsulfonic acid functionalized SiO2 core/PMO shell structured PrSO3H-SiO2@Si(R)Si nanospheres for the effective conversion of D-fructose into ethyl levulinate

Article abstract of DOI:10.1016/j.apcata.2017.08.004

Propylsulfonic acid functionalized SiO₂ core/alkyl- or phenyl-bridged organosilica shell structured PrSO₃H-SiO₂@Si(R)Si (R = –C₂H₄–, –C₆H₄– or –C₆H₄–C₆H₄–) nanospheres are facilely prepared by a CTAB-directed one-pot two-step condensation strategy. The morphological characteristics, textural properties, Br?nsted acid nature and structure of the PrSO₃H-SiO₂@Si(R)Si nanospheres are well characterized. The materials are successfully applied in the catalytic transformation of D-fructose into the important organic chemical, ethyl levulinate, in the presence of ethanol as both reactant and solvent. The catalytic activity of the PrSO₃H-SiO₂@Si(R)Si nanospheres outperform commercially available Amberlyst-15, HY zeolite and HCl, mainly attributing to their strong Br?nsted acid nature; additionally, unique core-shell structure with excellent porosity properties and well-adjusted hydrophilicity/hydrophobicity also give the positive influence on the ethanolysis activity, which can improve the accessibility of the reactants to the PrSO₃H sites and facilitate the multi-step ethanolysis reaction proceeding to the formation of the final product. The PrSO₃H-SiO₂@Si(R)Si nanospheres can be reused three times without obvious activity loss, contributed from covalent bonding of the PrSO₃H groups with the silica and organosilica framework as well as hydrophobic PrSO₃H-functionalized organosilica shell.

Full text of DOI:10.1016/j.apcata.2017.08.004

Accepted Manuscript
Title: Fabrication of propylsulfonic acid functionalized SiO2
core/PMO shell structured PrSO H-SiO @Si(R)Si
3
2
nanospheres for the effective conversion of D-fructose into
ethyl levulinate
Authors: Daiyu Song, Yingnan Sun, Qingqing Zhang, Panpan
Zhang, Yihang Guo, Jiyan Leng
PII:
S0926-860X(17)30374-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2017.08.004
APCATA 16359
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
2-5-2017
19-7-2017
2-8-2017
Please cite this article as: Daiyu Song, Yingnan Sun, Qingqing Zhang, Panpan
Zhang, Yihang Guo, Jiyan Leng, Fabrication of propylsulfonic acid functionalized
SiO2 core/PMO shell structured PrSO3H-SiO2@Si(R)Si nanospheres for the
effective conversion of D-fructose into ethyl levulinate, Applied Catalysis A,
Generalhttp://dx.doi.org/10.1016/j.apcata.2017.08.004
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Fabrication of propylsulfonic acid functionalized SiO
structured PrSO H-SiO @Si(R)Si nanospheres for the effective conversion of
D-fructose into ethyl levulinate
2
core/PMO shell
3
2
a
a
a
a
a,*
b,*
Daiyu Song , Yingnan Sun , Qingqing Zhang , Panpan Zhang , Yihang Guo Jiyan Leng
a
School of Environment, Northeast Normal University, Changchun 130117, P.R. China
b
First Hospital of Jilin University, Jilin University, Changchun 130021, PR China
*Corresponding authors.
Tel./fax: +86 431 89165626. E-mail: guoyh@nenu.edu.cn (Y. Guo)
Graphic Abstract
Propylsulfonic acid functionalized SiO
2
core/alkyl- or phenyl-bridged organosilica shell structured
– or –C –C –) nanospheres exhibit excellent
PrSO H-SiO @Si(R)Si (R = –C –, –C
3
2
2
H
4
6
H
4
6
H
4
6
H
4
catalytic activity and stability for the ethanolysis of D-fructose to ethyl levulinate.
1

Highlights





Propylsulfonic acid functionalized SiO
2
core/PMO shell nanospheres are prepared.
PrSO H-SiO @Si(R)Si exhibit excellent catalytic activity in D-fructose ethanolysis.
3
2
Strong Brønsted acid nature of as-prepared catalysts plays key role to the activity.
Unique hydrophilicity core/hydrophobicity shell positively influences the activity.
PrSO
3
H-SiO @Si(R)Si can be reused at least 3 times without loss of activity.
2
Abstract
Propylsulfonic acid functionalized SiO
structured PrSO H-SiO @Si(R)Si (R = –C
facilely prepared by a CTAB-directed one-pot two-step condensation strategy. The morphological
characteristics, textural properties, Brønsted acid nature and structure of the PrSO H-
SiO @Si(R)Si nanospheres are well characterized. The materials are successfully applied in the
catalytic transformation of D-fructose into the important organic chemical, ethyl levulinate, in the
presence of ethanol as both reactant and solvent. The catalytic activity of the PrSO H-
SiO @Si(R)Si nanospheres outperform commercially available Amberlyst-15, HY zeolite and
2
core/alkyl- or phenyl-bridged organosilica shell
3
2
2
H
4
–, –C – or –C –C –) nanospheres are
6
H
4
6
H
4
6
H
4
3
2
3
2
HCl, mainly attributing to their strong Brønsted acid nature; additionally, unique core-shell
structure with excellent porosity properties and well-adjusted hydrophilicity/hydrophobicity also
give the positive influence on the ethanolysis activity, which can improve the accessibility of the
reactants to the PrSO
3
H sites and facilitate the multi-step ethanolysis reaction proceeding to the
H-SiO @Si(R)Si nanospheres can be reused three times
formation of the final product. The PrSO
3
2
2

without obvious activity loss, contributed from covalent bonding of the PrSO
3
H groups with the
silica and organosilica framework as well as hydrophobic PrSO
3
H-functionalized organosilica
shell.
Keywords: Solid acid, Biomass-derived platform molecule, Biofuel, D-fructose, Ethyl levulinate
1
. Introduction
The utilization of abundant, naturally available and renewable biomass/derivatives for the
sustainable production of fuels and chemicals is of great current interest due to growing concerns
over the depletion of fossil resources and associated environmental issues [1-3]. In this research
field, catalytic transformation of carbohydrates (monosaccharides or polysaccharides) such as D-
fructose, glucose, sucrose and cellulose into the important chemical building blocks like 5-
hydroxymethylfurfural (5-HMF), 5-ethoxymethylfurfural (5-EMF), levulinic acid (LA) and alkyl
levulinate (AL) have attracted particular attention since the feedstocks can be derived from
lignocellulosic biomass [4-7]. Among the aforementioned chemical building blocks, ALs such as
methyl, ethyl and n-butyl levulinate have strong potential to be applied in the perfume and flavor
industries and as blending agents for diesel fuel formulation [8-10]; moreover, ethyl levulinate
(EL) is the most suitable fuel blend which can be directly used in diesel engines [11]. EL can be
synthesized from the acid-catalyzed esterification of levulinic acid with ethanol [12], however,
high price of levulinic acid makes the processes uneconomical [13]. More economically alternative
EL production process is the acid-catalyzed ethanolysis of various feedstocks such as furfuryl
alcohol, monosaccharides or polysaccharides, and particularly, efficient conversion of
3

monosaccharides or polysaccharides to EL is the ultimate process for the production of biofuels
and chemical buildings directly from lignocellulosic biomass [14]. Homogeneous liquid acids such
as HCl, H
2
SO or p-toluenesulfonic acid can catalyze the conversion of monosaccharides or
4
polysaccharides into ALs effectively due to their strong acidity and high acid site density.
However, the employment of them in industry often faces problems of waste generation,
equipment corrosion and recycling difficulty [15,16]. Heterogeneous acid catalysts such as
sulfated metal oxides [9,17], acidic zeolites [18], sulfonic acid silicas [18] and resin sulfonic acids
[
17] have therefore received considerable attentions and applied in the above process. However,
the applications of the reported solid acids are limited owing to the disadvantages of low surface
area, worse accessibility to the acid sites, poor mechanical or thermal stability as well as inferior
durability and reusability. Thus, the development of novel, robust and recyclable strong solid acid
catalysts for direct synthesis of ALs from lignocellulosic biomass-derived carbohydrate remains a
challenge [17].
Silicas (SiO
the advantages of tunable porosity properties, morphological characteristics and surface
hydrophilicity/hydrophobicity as well as easy functionalization. SiO or PMO nanopores,
2
) or periodic mesoporous organosilicas (PMOs) are the ideal catalyst supports with
2
nanospheres, nanorods, nanofibers and nanotubes have been successfully constructed [19].
Functionalization of these supports with sulfonic acid groups can significantly improve the
catalytic activity of SO H-based solid acids because the aforementioned properties can influence
3
the accessibility to the acid sites [20-24]. In the search for novel solid acid catalysts for the
transformation of D-fructose (FOS) into EL, herein, propylsulfonic acid functionalized silica
core/alkyl- or phenyl-bridged organosilica shell structured nanospheres, PrSO
3
H-SiO @Si(R)Si,
2
(R = –C
2
H
4
–, –C
6
H
4
– or –C
6
H
4
–C
6
H
4
–), with interesting micro/mesoporous bimodal structure are
4

facilely prepared by a CTAB-directed one-pot two-step condensation strategy. In the PrSO
SiO @Si(R)Si nanospheres, PrSO H functionalized SiO core is more hydrophilic owing to the
presence of abundant hydroxyl groups in the silica framework, while PrSO H functionalized PMO
3
H-
2
3
2
3
shell is more hydrophobic because of the presence of alkyl or phenyl moieties within PMO
framework. Core-shell structured nanospheres with interior core and outer shell exhibit unique
properties including accessible pore channels, low density, large surface area, high permeability
and excellent loading capacity; meanwhile, their shell thickness can be well-adjusted, and both the
cores and shells can be functionalized. Therefore, as-prepared PrSO
are expected to exhibit excellent catalytic activity and reusability in direct ethanolysis of FOS to
EL. During the PrSO H-SiO @Si(R)Si nanospheres-catalyzed FOS ethanolysis process, the
influence of the shell thickness and core/shell compositions on the catalytic activity are studied.
Subsequently, the mechanism of EL production from the PrSO H-SiO @Si(R)Si-catalyzed
ethanolysis of FOS is reasonably put forward based on the identified intermediates. The excellent
ethanolysis activity of the PrSO H-SiO @Si(R)Si nanospheres is explained in terms of the strong
Brønsted acid nature, well-adjusted hydrophilicity/hydrophobicity and unique porosity and
morphological properties. Finally, the reusability of the PrSO H-SiO @Si(R)Si is investigated.
3
H-SiO
2
@Si(R)Si nanospheres
3
2
3
2
3
2
3
2
2
. Experimental
2
.1. Materials
,2-Bis(trimethoxysilyl)ethane (BTMSE, 97%), 1,4-bis-(triethoxysilyl)benzene (BTESB,
6%), 4,4′-bis(triethoxysilyl)-1,1′-biphenyl (BTESBP, 95%) and 3-
1
9
mercaptopropyltrimethoxysilane (MPTMS, 95%) were purchased from Sigma-Aldrich.
Tetraethoxysilane (TEOS, 98%) and D-fructose (FOS, 98%) was purchased from Sinopharm
5

Chemical Reagent Co. Ltd.. Cetyltrimethylammonium bromide (CTAB, 99%) was purchased from
Beijing Fine Chemical Co.. Ethyl levulinate (EL, > 98.0%) was purchased from TCI. Commercial
available Amberlyst-15 and HY zeolite was purchased from Alfa Aesar. The above reagents were
used without further purification.
2
2
.2. Catalyst preparation
.2.1. PrSO
3
H-SiO @Si(Ph)Si nanospheres
2
Typically, CTAB (0.16 g) was dissolved in 30 mL ethanol and 75 mL water solution containing
o
1
mL 25% ammonia at 35 C under stirring for 1 h. Then, TEOS (1.2 mmol) and MPTMS (0.212
o
mmol) were simultaneously added to the above clear solution. After stirring for 24 h at 35 C, a
mixture of BTESB (0.45, 0.6 or 0.75 mmol) and MPTMS (0.212 mmol) were rapidly added to the
o
above suspension, and the resultant white suspension was stirred at 35 C for 24 h. The final
chemical composition of the precursor solution was 0.439CTAB: 1.2TEOS: (0.45, 0.6 or
0
.75)BTESB: 0.424MPTMS: 6.5NH
4
OH: 514C
2
H
5
OH: 4167H
2
O: 100H
2
O
2
(molar ratio).
Subsequently, the white product was collected by centrifugation and washed with ethanol and
dispersed in aqueous solution. The suspension was transferred to an autoclave and heated at 120
o
o
−1
C with a heating rate of 2 C min for additional 5 h. The resulting white solid powder was
collected by centrifugation and washed with boiling ethanol containing concentrated HCl (240 µL,
7%) for three times to remove CTAB in the product. The obtained product was washed with
ethanol three times and then dispersed in 10 mL H aqueous solution at room temperature under
3
2
O
2
stirring for 24 h. The product was washed with deionized water to remove residual H
2
O
2
aqueous
H-
@Si(Ph)Si-3, respectively,
o
solution and then air-dried at 60 C for 12 h. The corresponding product is denoted as PrSO
3
SiO
2
@Si(Ph)Si-1, PrSO
3
H-SiO
2
@Si(Ph)Si-2 and PrSO
3
H-SiO
2
representing different contents of phenyl-bridged organosilica in the product.
6

2
.2.2. PrSO
3
H-SiO
2
@Si(Ph-Ph)Si or PrSO
3
H-SiO
2
@Si(Et)Si nanospheres
@Si(Ph)Si nanospheres, however, BTESB
The procedure is similar to that of the PrSO
3
H-SiO
2
was replaced by BTESBP (precursor of biphenyl-bridged organosilica) or BTMSE (precursor of
ethyl-bridged organosilica). The final chemical composition of the precursor solution was
0
4
.439CTAB: 1.2TEOS: 0.6BTESBP (or BTMSE): 0.424MPTMS: 6.5NH
167H O: 100H (molar ratio).
4
OH: 514C
2
5
H OH:
2
2
O
2
2
.2.3. PrSO
The procedure is similar to that of the PrSO
TEOS was successively added to the preparation system. The final chemical composition of the
precursor solution was 0.439CTAB: 1.2TEOS: 0.6BTMSE: 0.424MPTMS: 6.5NH OH:
3
H-Si(Et)Si@SiO
2
nanospheres
3
H-SiO @Si(Et)Si nanospheres, but BTMSE and
2
4
5
14C
2
H
5
OH: 4167H
2
O: 100H
2
2
O (molar ratio).
2
.2.4. PrSO
The procedure is similar to that of the PrSO
not added in the preparation system. The final chemical composition of the precursor solution was
3
H-SiO
2
nanospheres
3
H-SiO @Si(Ph)Si nanospheres, but BTESB was
2
0
.439CTAB:1.2TEOS:0.2MPTMS:6.5NH
4
OH:514C
2
H
5
OH:4167H
2
O:100H
2
2
O (molar ratio).
2
.2.5. PrSO
The procedure is similar to that of the PrSO
by BTESB. The final chemical composition of the precursor solution was
3
H-Si(Ph)Si nanospheres
3
H-SiO nanospheres, however, TEOS was replaced
2
0
.439CTAB:0.6BTESB:0.2MPTMS:6.5NH
4
OH:514C
2
H
5
OH:4167H
2
O:100H
2
2
O (molar ratio).
2
.3. Catalyst characterization
7

Transmission electron microscope (TEM) observations were performed on a JEM-2100F high
resolution transmission electron microscope at an accelerating voltage of 200 kV. Scanning
electron microscopy (SEM) images were taken on a XL-30 ESEM FEG field emission scanning
electron microscope. Nitrogen porosimetry measurement was performed on a Micromeritics
ASAP 2020M surface area and porosity analyzer after the samples were outgassed under vacuum
at 363 K for 1 h and 373 K for 12 h. The surface area (SBET) was calculated using the Brunauer-
Emmett-Teller equation, pore diameters (D
p
) was calculated using Barrett-Joyner-Halenda
2
9
desorption branch of the isotherms, and pore volume (V
p
) was accumulated up to P/P = 0.99. Si
0
1
3
magic angle spinning (MAS) NMR and C cross polarization-magic angle spinning (CP-MAS)
NMR spectra were recorded on a Bruker AVANCE III 400 WB spectrometer equipped with a 4
mm standard bore CP MAS probe head. The dried and finely powdered samples were packed in
2
9
the ZrO
MAS NMR and C CP-MAS NMR spectra were referenced to the signal of 3-(trimethylsilyl)-1-
propanesulfonic acid sodium salt standard (δ = 0.0) and C10 16 standard (δCH = 38.5),
respectively. The Brønsted acid-site density (Atitration, μeq(H ) g ) was determined by titration with
2
rotor closed with a Ke-F cap which was spun at 12 kHz rate. Chemical shifts for Si
1
3
H
2
+
−1
−
1
NaOH solution (0.0045 mol L ), and the detailed procedures were followed by the literature work
[
25].
2
.4. Catalytic test
o
The catalysts were dried for 2 h at 120 C in a vacuum before the catalytic tests.
Ethanolysis of FOS was carried out in an autoclave with a Teflon lining under the conditions of
o
1
40 C, ethanol (68.95 mmol) to FOS (0.278 mmol) molar ratio of 248 and the ratio FOS/catalyst
of 1 wt/wt, and stirring was applied throughout the reaction. The concentration of the produced
EL was determined periodically on a Shimadzu 2014C gas chromatograph fitted with a HP-
8

INNOWAX capillary column and flame ionization detector. The injection port temperature was
o
o
o
2
50 C, the oven temperature was maintained at 60 C for 5 min, and then raised to 180 C for 10
o
−1
o
min at a heating rate of 8 C min . The GC injector temperature was 250 C. Ethyl laurate was
applied as an internal standard. The catalytic activity of the catalyst was evaluated quantitatively
−
1
by the yield of EL (Y, %) and turnover frequency (TOF, h ), respectively. Herein, Y (%) =
(M
D
/M ) × 100, where M and M is the number of moles of EL produced and expected. TOF
T
D
T
values were determined from the linear portion of the initial reaction rate profile for the yield of
EL, which were normalized to the acid site density measured by acid-base titration. The
intermediates produced during the catalytic process were identified by a mass spectrometry
coupled with gas chromatography (HP6890GC-5973MSD) and a high-resolution electrospray
ionization time-of-flight mass spectrometry equipped with high performance liquid
chromatography (Agilent1200HPLC-micrOTOFESI-TOF-MS).
3
. Results and discussion
3
.1. Preparation of the PrSO
3
H-SiO @Si(R)Si nanospheres
2
The PrSO
directed one-pot two-step condensation strategy followed by H
shown in Scheme 1, the PrSO H-SiO core is obtained by a CTAB-directed
hydrolysis/condensation of tetraethoxysilane (TEOS) with 3-mercaptopropyltrimethoxysilane
MPTMS) under ammonia environment. Specifically, when TEOS and MPTMS are mixed with
3
H-SiO
2
@Si(R)Si nanospheres are facilely and repeatedly prepared by a CTAB-
2
O
2
post-oxidation process. As
3
2
(
aqueous ethanol solution containing CTAB and ammonia, they gradually hydrolyze to give the
hydroxyl group-containing hydrolyzed precursors. Subsequently, the hydrolyzed precursors co-
+
assembly with spherical CTAB cation micelles (CTA ) via electrostatic interaction and condense
9

to form spherical propylthiol (SH) group-functionalized SiO core. In the next step, spherical SH
2
group-functionalized PMO shell is fabricated around the core after further adding bissilylated
organic precursors (e.g. BTESB, BTESBP or BTMSE) and MPTMS into the reaction system with
a time interval of 24 h. The successive growth of the core and shell is further facilitated under
o
hydrothermal condition (120 C, 5 h), leading to the formation of perfect spherical morphology
with porous core and shell (see Fig. 1). Moreover, the shell thickness can be modulated by
changing the starting amount of the bissilylated organic precursors, and the hydrophobicity of the
shell can be adjusted by the introduction of different alkyl or phenyl moieties within the
silica/carbon framework. Finally, propylsulfonic acid functionalized silica core/PMO shell
nanospheres are obtained after removing CTAB by acidic boiling ethanol washing and oxidation
of –SH groups by H
2
2
O .
3
3
.2. Catalyst characterization
.2.1. Morphological characteristics and porosity properties
Morphological characteristics of as-prepared PrSO H-SiO
) and SEM observations (Fig. 2). The images shown in Fig. 1a and b indicate that the PrSO
or PrSO H-Si(Ph)Si prepared by a CTAB-directed hydrolysis/condensation of TEOS or
BTESB with MPTMS exhibit solid and monodispersed spherical morphology with porous
structure and well-distributed particle size, and the estimated outer diameter of the PrSO H-SiO
and PrSO H-Si(Ph)Si particles are 155 and 140 nm (Table 1). After the formation of the PrSO H-
SiO @Si(R)Si particles, their porous core-shell structure can be visibly observed (Fig. 1c-g), and
the average core diameter is closed to the outer diameter of the PrSO H-SiO or PrSO H-Si(Ph)Si
nanospheres (Table 1). From the result shown in Fig. 1c, f and g it is found that the PrSO H-
SiO @Si(R)Si nanospheres prepared at the same bissilylated organic precursor (BTESB, BTESBP
3
2
@Si(R)Si are revealed by TEM (Fig.
H-
1
3
SiO
2
3
3
2
3
3
2
3
2
3
3
2
1
0

or BTMSE) adding amount possess the similar shell thickness (21, 23 and 23 nm), regardless of
the structure of the incorporated functional organic moieties (R).
The core-shell structured PrSO
3
H-SiO @Si(R)Si particles with opened porous structure favor
2
the diffusion of the reactants and intermediates into the interior of the spheres, which can improve
the accessibility of the active sites to the substrates. Moreover, the shell thickness is also one of
the factors that influence the diffusion of the reactants and products. In order to evaluate the
influence of the shell thickness on the catalytic activity of the PrSO
the shell thickness of the representative PrSO H-SiO @Si(Ph)Si is modulated by changing the
starting amount of BTESB, which gives rise to the PrSO H-SiO @Si(Ph)Si-1, PrSO H-
SiO @Si(Ph)Si-2 and PrSO H-SiO @Si(Ph)Si-3 nanospheres with the estimated shell thickness
of 21, 25 and 30 nm, respectively (Fig. 1c–e and Table 1).
As for the PrSO H-functionalized ethyl-bridged organosilica core/SiO
PrSO H-Si(Et)Si@SiO nanoparticles, its porous core-shell structure is also fabricated. The
3
H-SiO
2
@Si(R)Si nanospheres,
3
2
3
2
3
2
3
2
3
2
shell structured
3
2
estimated core diameter and shell thickness are 165 and 21 nm, respectively (Fig. 1h).
From the SEM images shown in Fig. 2a and b it is found that the representative samples,
PrSO
3
H-SiO
2
@Si(Ph)Si-2 (outer diameter of 205 nm) and PrSO
3
H-SiO @Si(Ph-Ph)Si (outer
2
diameter of 206 nm), exhibit uniform and monodispersed spherical morphology; however, their
core-shell structure is hardly observed by this method.
The results of nitrogen gas porosimetry measurement support the above TEM and SEM
observations. From the nitrogen gas adsorption/desorption isotherms of three PrSO
SiO @Si(Ph)Si nanospheres with different shell thicknesses it is found that the samples exhibit
interesting micro/mesoporosity with the characteristics of a rapid increasing nitrogen gas adsorbed
amount at relative pressure (P/P ) lower than 0.1 (Type I isotherm) and Type IV isotherm with a
3
H-
2
0
1
1

large H1-type hysteresis loop at P/P
SiO @Si(Ph)Si nanospheres possess regular mesopores without interconnecting channels,
regardless of the shell thickness. The pore size distribution curves indicate that the mesopores of
three PrSO H-SiO @Si(Ph)Si nanospheres are well-distributed (Fig. 3b), and the average pore
diameter is 3.8 (PrSO H-SiO @Si(Ph)Si-1), 3.8 (PrSO H-SiO @Si(Ph)Si-2) and 4.2 nm (PrSO H-
SiO @Si(Ph)Si-3), respectively. From the determined textural parameters summarized in Table 1
it can be seen that three PrSO H-SiO @Si(Ph)Si nanospheres exhibit excellent porosity properties
with extremely large BET surface area (866, 810 and 815 m g ) and high pore volume (0.77, 0.73
0
= 0.41.0 (Fig. 3a). The result signifies that the PrSO H-
3
2
3
2
3
2
3
2
3
2
3
2
2
–1
3
–1
and 0.62 cm g ), and the shell thickness of the nanospheres has little influence on their BET
surface area. However, the pore volume is affected by the shell thickness in some extent, and the
nanospheres with thicker shell thickness possesse lower pore volume. The extremely large BET
surface area of the PrSO
surface of both the core and the shell as well as open porous structure of the nanospheres.
Similarly, the PrSO H-SiO @Si(Ph-Ph)Si and PrSO H-SiO @Si(Et)Si nanospheres also show
the micro/mesoporosity properties to those of the PrSO H-SiO @Si(Ph)Si nanospheres, and their
nitrogen gas adsorption/desorption isotherms display a rapid increasing nitrogen gas adsorbed
amount at P/P lower than 0.1 (Type I isotherm) and H2- or H4-type hysteresis loop at P/P
.400.85 (Fig. 3c). Therefore, it is inferred that the PrSO H-SiO @Si(Ph-Ph)Si and PrSO
@Si(Et)Si nanospheres possess narrow mouth shaped mesopores. These two samples show
3
H-SiO @Si(Ph)Si nanospheres is contributed from the outer and inner
2
3
2
3
2
3
2
0
0
=
0
3
2
3
H-
SiO
2
very sharp pore size distribution curves, implying that they have uniform mesopores (Fig. 3d). The
determined average pore diameter of them is 3.8 nm, and they still possess large BET surface area,
2
–1
i.e., 696 and 790 m g for the PrSO
3
H-SiO
2
@Si(Ph-Ph)Si and PrSO
3
H-SiO @Si(Et)Si,
2
respectively (Table 1).
1
2

As for the PrSO
3
H-Si(Et)Si@SiO
2
nanospheres composed of PrSO H-functionalized ethyl-
3
bridged organosilica core and silica shell, it still exhibits micro/mesoporosity with very small
hysteresis loop (Fig. 3c); meanwhile, its pore size distribution curve becomes wider, together with
2
–1
low pore volume (Fig. 3d). However, its BET surface area (777 m g , Table 1) is still large. The
individual PrSO H-SiO and PrSO H-Si(Ph)Si nanospheres also show micro/mesoporosity
3
2
3
properties, evidenced by the nitrogen gas adsorption/desorption isotherms and pore size
distribution curves presented in Fig. 3e and f; additionally, both of them possess extremely small
hysteresis loop. Owing to having plentiful pores within the nanospheres, the PrSO
3
H-SiO
2
has
2
–1
2
–1
extremely larger BET surface area (1060 m g ) than that of the PrSO
3
H-Si(Ph)Si (757 m g ),
but their pore diameter is the same (3.9 nm, Table 1). As expected, after the formation of the core-
2
–1
shell structured PrSO
3
H-SiO
2
@Si(Ph)Si-1 nanospheres, its BET surface area (866 m g ) is larger
than that of PrSO H-Si(Ph)Si but smaller than PrSO
3
3
H-SiO
2
.
3
.2.2 Composition and structure
The formation of the inorganic-organic silica framework and the incorporation of PrSO
3
H
2
9
groups within the framework of the PrSO
3
H-SiO @Si(R)Si nanospheres were studied by Si
2
1
3
MAS NMR (Fig. 4a) and C CP-MAS NMR spectra (Fig. 4b-d).
2
9
In the Si MAS NMR spectrum of the representative sample, PrSO
3
H-SiO @Si(Ph)Si-2, three
2
characteristic resonances are found at –56, –60 and –69 ppm, respectively, which are originated
1
2
3
from the organosiloxane species including T [C–Si(OSi)(OH)
Si(OSi) ] within the carbon/silica framework of the shell [26,27]; additionally, the other four
characteristic resonances detected at –80, –94, –102 and –111 ppm are assigned to the inorganic
2
], T [C–Si(OSi) (OH)] and T [C–
2
3
1
2
], Q [Si(OSi)
(OH)] and Q4
3
silica species including Q [Si(OSi)(OH)
3
], Q [Si(OSi)
2
(OH)
2
3
[
Si(OSi) ] from the core of nanospheres, respectively [27]. The result indicates that the silica core
4
1
3

and organosilica shell of the PrSO
preparation route.
3
H-SiO @Si(R)Si nanospheres are fabricated by using current
2
1
3
In the C CP-MAS NMR spectrum of the PrSO
3
H-SiO @Si(Ph)Si-2 nanospheres (Fig. 4b), the
2
1
3
detected three signals at 11, 17 and 53 ppm belong to the C –C species of the PrSO
3
H groups,
implying that the PrSO
3
H groups are successfully introduced within the silicon/carbon framework
[
28]. Additionally, the other predominant signal found at 132 ppm is due to the carbon species (C4)
of phenyl-bridged silsesquioxane framework of the shell [17,24,29].
13
Similarly, in the C CP-MAS NMR spectra of the PrSO
3
H-SiO
@Si(Et)Si nanospheres (Fig. 4d), three characteristic resonances originated from
H groups can also be found at 11, 17 and53 ppm. As for the other four strong signals found
2
@Si(Ph-Ph)Si (Fig. 4c) and
PrSO
3
3
H-SiO
2
PrSO
4
7
at 143.0, 134.6, 130.3 and 126.2 ppm in Fig. 4c, they are assigned to C –C species of biphenyl-
bridged silsesquioxane framework of the shell [24], while the strongest signal detected at 5.1 ppm
4
in Fig. 4d attributes to C species of ethyl-bridged silsesquioxane framework of the shell [28,30].
As for the signal found at 58.2 ppm in Fig. 4b, c and d, it is assigned to the residual carbon species
of the ethoxy groups, which are formed during the boiling ethanol washing step [12,21,31].
2
9
13
Combination of the Si MAS NMRand C CP-MAS NMR spectra it is concluded that PrSO
group-functionalized silica core/alkyl- or phenyl-bridged organosilica shell are created in the
PrSO H-SiO @Si(R)Si nanospheres by using CTAB-directed one-pot two steps sol-gel process,
and its core and shell are composed of covalently bonded –Si–O1.5–Si–PrSO H and O1.5–Si–R–Si–
1.5–Si–PrSO H (R = –C –/–C –C –/–C –) framework, respectively (Scheme 1).
3
H
3
2
3
O
3
6
H
4
6
H
4
6
H
4
H
2 4
3
.2.3. Brønsted acid site density
The Brønsted acid site density (Atitration, μeq g ) of as-prepared PrSO
nanospheres is determined by titration with dilute NaOH solution. As shown in Table 1, three
–
1
3
H-SiO @Si(R)Si
2
1
4

–
PrSO
3
H-SiO
2
@Si(Ph)Si nanospheres possess similar Brønsted acid-site density (522540 μeq g
H-SiO @Si(Ph-
@Si(Et)Si (571 μeq g ) nanospheres, their Brønsted acid-
site density is similar to that of the PrSO H-SiO @Si(Ph)Si-1 nanospheres. The PrSO H-
Si(Et)Si@SiO nanospheres has the highest Brønsted acid-site density (621 μeq g ) among all
tested PrSO H-based nanospheres. Additionally, the soilid PrSO H-Si(Ph)Si and PrSO H-SiO
nanospheres have somewhat higher Brønsted acid-site density (585 and 603 μeq g ) than that of
the PrSO H-SiO @Si(R)Si nanospheres.
1)
, and the shell thickness has a slight influence on this value. As for the PrSO
3
2
–
1
–1
Ph)Si (508 μeq g ) and PrSO
3
H-SiO
2
3
2
3
–
1
2
3
3
3
2
–
1
3
2
3
.3. Catalytic performance
The catalytic performance including activity, reaction mechanism and reusability of the
PrSO H-SiO @Si(R)Si nanospheres is studied in the synthesis of EL from ethanolysis of FOS
3
2
under the conditions of ethanol-to-FOS molar ratio of 248, the ratio FOS/catalyst of 1 wt/wt and
o
1
40 C.
3
.3.1. Catalytic activity
Firstly, influence of ethanol-to-FOS molar ratio on the ethanolysis activity of the PrSO H-
3
SiO
2
@Si(Ph)Si is studied by selecting the PrSO
3
H-SiO @Si(Ph)Si-2 as the representative catalyst,
2
and the result is presented in Fig. 5a. It shows that after the reaction proceeds for 4 h, the yield of
EL increases from 24.9, 32.4 to 35.6% as increasing ethanol-to-FOS molar ratio from 124, 186 to
2
48. In the PrSO
3
H-SiO @Si(Ph)Si-catalysed FOS ethanolysis reaction, ethanol is used as both
2
the reactant and solvent, and higher ethanol-to-FOS molar ratio (e.g. 248) can facilitate the
conversion process of FOS5-HMF5-EMFEL, giving rise to higher EL yield. Otherwise, at
lower ethanol-to-FOS molar ratio (e.g. 124), more oligomeric byproducts may be produced owing
1
5

to self-polymerization of some intermediates (e.g. 5-HMF), accompanying with the decreased EL
yield. Much higher ethanol-to-FOS molar ratio (higher than 248) may dilute the substrate and
thereby decreasing the yield of EL; meanwhile, excessive ethanol may lead to the above process
uneconomic. Therefore, in the subsequent catalytic test, ethanol-to-FOS molar ratio is set at 248.
Subsequently, influence of the shell thickness on the ethanolysis activity is studied by selecting
the PrSO
Fig. 5b it can be seen that the yield of EL has a slight decrease with increasing the shell thickness
from 21, 25 to 30 nm, and it is 62.5 (PrSO H-SiO @Si(Ph)Si-1), 60.6 (PrSO H-SiO @Si(Ph)Si-
) and 58.8% (PrSO H-SiO @Si(Ph)Si-3) after the reaction carried out for 12 h. As for the core-
free PrSO H-Si(Ph)Si and shell-free PrSO H-SiO nanospheres, their ethanolysis activity are
lower than that of the core-shell structured PrSO H-SiO @Si(Ph)Si. Under the same conditions,
the yield of EL is 50.8 and 47.7%, respectively, for the PrSO H-Si(Ph)Si- and PrSO H-SiO
catalyzed FOS ethanolysis reaction. The result suggests that permeable and porous hydrophilic
silica core/hydrophobic PMO shell structure of the PrSO H-SiO @Si(R)Si nanospheres play an
important role in the enhancement of the ethanolysis activity.
Next, the catalytic activity of the PrSO H-SiO @Si(Ph)Si nanospheres with different R moieties
within the shell framework is tested. From the result shown in Fig. 6a it is found that the tested
catalysts follow the ethanolysis activity order of PrSO H-SiO @Si(Ph-Ph)Si > PrSO H-
SiO @Si(Ph)Si-2 > PrSO H-SiO @Si(Et)Si > PrSO H-Si(Et)Si@SiO . After the ethanolysis
reaction proceeded for 12 h, the yield of EL reaches 62.6, 60.6, 59.3 and 53.9%, respectively, for
the PrSO H-SiO @Si(Ph-Ph)Si-, PrSO H-SiO @Si(Ph)Si-2-, PrSO H-SiO @Si(Et)Si- and
PrSO H-Si(Et)Si@SiO -catalyzed ethanolysis reaction.
3
H-SiO
2
@Si(Ph)Si nanospheres as the representative catalysts. From the result shown in
3
2
3
2
2
3
2
3
3
2
3
2
3
3
2
-
3
2
3
2
3
2
3
2
3
2
3
2
3
2
3
2
3
2
3
2
1
6

Since the tested PrSO
3
H-SiO @Si(Ph)Si nanospheres possess different Brønsted acid site
2
densities, their ethanolysis activity is further compared in terms of TOF values determined from
the linear portion of the initial reaction rate profile for the yield of EL, which are normalized by
the acid site density. As displayed in Fig. 6b, the catalysts follow the TOF value order of PrSO
3
H-
–1
–1
SiO
2
@Si(Ph-Ph)Si (0.86 h ) > PrSO
3
H-SiO
2
@Si(Ph)Si-2 (0.81 h ) > PrSO
3
H-SiO
2
@Si(Et)Si
–
1
–1
(
0.68 h ) > PrSO
Fig. 6b).
Finally, the catalytic activity of the PrSO
3
H-Si(Et)Si@SiO
2
(0.62 h ), in line with the activity revealed by the yield of EL
(
3
H-SiO @Si(Ph)Si-2 is further compared with some
2
reference acid catalysts including HCl, HY zeolite and Amberlyst-15. Fig. 7a displays the
ethanolysis activity of the tested catalysts revealed by the yield of EL, showing that they follow
the activity order of Amberlyst-15 > PrSO
Amberlyst-15-, PrSO H-SiO @Si(Ph)Si-2-, HCl- and HY zeolite-catalyzed ethanolysis reaction,
the yield of EL reached 75.5, 60.6, 53.4 and 30.9%, respectively, after the reaction proceeded for
2 h. Considering the difference of Brønsted acid site density among the tested acid catalysts, the
corresponding TOF values are determined and presentated in Fig. 7b, showing that they follow the
3
H-SiO
2
@Si(Ph)Si-2 > HCl > HY zeolite. For the
3
2
1
–1
–1
TOF order of PrSO
3
H-SiO
2
@Si(Ph)Si-2 (0.81 h ) > HY zeolite (0.31 h ) > Amberlyst-15 (0.14
–
1
–1
h ) > HCl (0.02 h ). Therefore, the ethanolysis activity of the PrSO
3
H-SiO @Si(Ph)Si-2
2
nanosphere outferforms these commerical acid catalysts, attributing to its unique hydrophilic
core/hydrophobic shell structure and excellent porosity properties such as large BET surface area
2
–1
3
–1
(
810 m g ) and high pore volum (0.73 cm g ). In the case of Amberlyst-15 and HCl, they have
high EL yield but low TOF value, which is due to their high Brønsted acid site density. Moreover,
o
the mechanical stability of Amberlyst-15 is poor at higher temperature (e.g. 140 C), leading to it
difficultly being recycled. Homogeneous HCl suffers from disadvantages such as corrosion,
1
7

difficulty in separation and acid-waste generation, resulting in it uncompetitive with respect to
heterogeneous acid catalysts. The lowest ethanolysis activity of microporous HY zeolite is due to
its small micropore, leading to poor accessibility of the reactants to the acid sites.
3
.3.2. Possible reaction mechanism
During the process of ethanolysis of FOS to EL catalyzed by the PrSO
3
H-SiO @Si(R)Si
2
nanospheres, the intermediates including ethyl fructoside (Compound 1), 5-HMF (Compound 2),
-EMF (Compound 3), 5-hydroxymethylfurfural diethylacetal (Compound 4) and 5-
5
ethoxymethylfurfural diethylacetal (Compound 5) are identified through GC-MS and LC-MS
analysis (Scheme 2). Based on the identified intermediates and the relevant literature work, the
reaction mechanism of the PrSO
tentatively proposed and illustrated in Scheme 2 [32,33]. Firstly, FOS molecules are activated by
the PrSO H sites of the PrSO H-SiO @Si(R)Si nanospheres, and the activated FOS molecules are
3
H-SiO
2
@Si(R)Si-catalyzed ethanolysis of FOS to EL is
3
3
2
attacked by ethanol molecules to form ethyl fructoside, accompanying with the release of water.
Further release of both water and ethanol molecules from the activated ethyl fructoside gives rise
to 5-HMF. 5-HMF molecules are activated by the PrSO H sites, and the activated 5-HMF
3
molecules are attacked by ethanol molecules to form 5-EMF or 5-hydroxymethylfurfural
diethylacetal and water. 5-EMF may also be yielded directly from the release of water from the
activated FOS molecule. Next, 5-EMF or 5-hydroxymethylfurfural diethylacetal are further
attacked by ethanol molecules to form 5-ethoxymethylfurfural diethylacetal and water (Step I). In
the other parallel pathway, the activated FOS molecules are isomerized by ethanol followed by the
release of water to form 5-HMF (Step II). During the above FOS5-HMF5-EMF dehydration
stage, permeable hydrophobic shell of the PrSO
3
H-SiO @Si(R)Si nanospheres is favorable to
2
1
8

selectively create an unsuitable environment for water, leading to it easy desorption from the
catalyst surface. As a consequence, the formation of 5-HMF and 5-EMF is facilitated.
Subsequently, the formation of EL (Compound 6) may undergo the following three possible
approaches: (i) protonation of epoxy groups of 5-EMF by the PrSO H sites gives rise to cyclic
3
oxonium of 5-EMF, and the latter suffers from the ring-opening reaction under the attack of water
and ethanol molecules to produce EL; (ii) the activated 5-hydroxymethylfurfural diethylacetal is
attacked by water molecules, and EL is formed via the ring-opening reaction; and (iii) under the
attack of water molecules, the activated 5-ethoxymethylfurfural diethylacetal suffers from the ring-
opening reaction to form EL. During the above 5-EMFEL stage, water yielded from the
dehydration of FOS participates in the ring-opening reaction of the intermediates, and therefore,
in order to increase the accessibility of the intermediates to the acid sites, core of the PrSO
SiO @Si(R)Si nanospheres should be more hydrophilic than its shell, which can provide a more
suitable environment for the rehydration of hydrophilic intermediates.
3
H-
2
3
.3.3. Discussion
The excellent ethanolysis activity of the PrSO
3
H-SiO @Si(R)Si nanospheres is attributed to
2
their strong Brønsted acid nature, unique core-shell structure with excellent porosity properties
and well-adjusted hydrophilicity/hydrophobicity.
The strong Brønsted acid nature of the PrSO
to the synthesis of EL from FOS based on the above reaction mechanism discussion. Moreover, in
the PrSO H-SiO @Si(R)Si nanospheres, both the core and shell are functionalized by the PrSO H
3
H-SiO
2
@Si(R)Si nanospheres plays the key role
3
2
3
groups, which can provide more acid sites for the ethanolysis reaction. This is another reason that
ensures the target reaction proceeds at a fast rate.
1
9

Additionally, the unique core-shell structure of the PrSO
positive influence on their ethanolysis activity. On the one hand, the PrSO
nanospheres exhibit interesting micro/mesoporous bimodal structure, leading to them excellent
porosity properties and better dispersion of the PrSO H sites throughout the core and shell. The
large BET surface area and high pore volume can increase the population of the PrSO H sites,
while the opened porous structure can reduce the diffusion limit of the reactants to the interior of
the spheres, leading to the increased accessibility of FOS molecules to the PrSO H sites throughout
3
H-SiO
2
@Si(R)Si nanospheres gives a
3
H-SiO @Si(R)Si
2
3
3
3
the core and shell. Both of the advantages can improve the catalytic activity of multi-step
ethanolysis reaction. For the reference acid catalyst Amberlyst-15, although it has extremely high
Brønsted acid site density, its TOF value is lower than the PrSO
3
H-SiO @Si(Ph)Si nanosphere,
2
2
–1
which is attributed to its smaller BET surface area (50 m g ) or less exposed acid sites. In the
case of HY zeolite, its microporous structure limits the accessibility of the acid sites to the bulky
FOS molecules, leading to severe diffusion limit and thereby poor ethanolysis activity. The above
results further confirm that the porosity properties of the solid acids influence their catalytic
activity except for the Brønsted acid nature.
The another contribution of the core-shell structured PrSO
ethanolysis activity is that they have permeable shell, which can facilitate mass transfer of the
reactants. The PrSO H-SiO @Si(Ph)Si-1 nanosphere with the thinnest shell among three PrSO H-
SiO @Si(Ph)Si nanospheres exhibits the highest ethanolysis activity, attributing to the shortest
3
H-SiO
2
@Si(R)Si nanospheres to the
3
2
3
2
mass transfer distance and thereby the increased accessibility of the PrSO
3
H groups to the
reactants.
Finally, the PrSO
3
H-SiO
2
@Si(R)Si nanospheres with more hydrophilic PrSO
3
H-functionalized
silica core and more hydrophobic PrSO
3
H-functionalized organosilica shell have a considerable
2
0

influence on the ethanolysis activity. The conversion of FOS into EL in the presence of ethanol is
a continuous process of multi-step reaction. In the first stage, FOS dehydration or etherification
produces 5-HMF or ethyl fructoside, and then 5-EMF, 5-hydroxymethylfurfural diethylacetal and
5
-ethyloxymethylfurfural diethylacetal are obtained. The process accompanies with the release of
water and formation of some hydrophilic oligomeric byproducts such as diethyl ether and 5,5′-
oxybis(methylene)bis-2-furfural (identified by GC-MS and LC-MS). In the next stage, EL is
formed via the ring opening reactions of the aforementioned intermediates with the help of the
yielded water in the first stage. Well-adjusted hydrophilicity/hydrophobicity of the PrSO
SiO @Si(R)Si nanospheres can match the above reaction process. In the first stage, the
hydrophobic PrSO H-functionalized organosilica shell may avoid the adsorption of water and
hydrophilic oligomeric byproducts on the catalyst surface, which can further facilitate the mass
transfer of the intermediates to the interior of hydrophilic PrSO H-functionalized silica core
3
H-
2
3
3
besides the shell. Accordingly, the ring opening reactions of the intermediates with the assistance
of water proceed effectively on the hydrophilic core, leading to considerably higher EL yield with
respect to shell-free PrSO
core) nanospheres. The lower catalytic activity of the PrSO
strong interaction of the PrSO H sites with water and hydrophilic oligomeric byproducts, which is
confirmed by the following recycling test (Fig. 8). Additionally, slight activity difference among
three PrSO H-SiO @Si(R)Si nanospheres with different bridging organic groups (e.g. ethyl,
phenyl and biphenyl) within the shell framework is mainly due to their different hydrophobicity.
The PrSO H-SiO @Si(Ph-Ph)Si nanosphere with the highest hydrophobicity exhibits the highest
ethanolysis activity although its BET surface area and acid site density are the lowest.
3
H-SiO
2
and PrSO
3
H-Si(Et)Si@SiO
2
(hydrophilic shell and hydrophobic
3
H-SiO nanospheres is due to the
2
3
3
2
3
2
3
.3.4. Regeneration and reusability
2
1

The reusability of the supported catalysts is one of the important properties that determines their
practical applications. To explore the catalytic stability of the incorporated PrSO H groups and the
reusability of as-prepared PrSO H-SiO @Si(R)Si nanospheres, the PrSO H-SiO @Si(Ph)Si-2
nanosphere is selected and reused for three times in ethanolysis of FOS. As a comparison, the
reusability of shell-free PrSO H-SiO nanosphere is also investigated under the same conditions.
As shown in Fig. 8a, the PrSO H-SiO nanosphere exhibits an obvious activity loss during three
consecutive cycles, and the yield of EL decreased from 47.7% (the first cycle) to 29.9% (the third
cycle). In the case of the PrSO H-SiO @Si(Ph)Si-2 nanosphere, it shows excellent catalytic
stability, and the yield of EL is 60.6 (1st cycle), 58.5 (2nd cycle) and 58.8% (3rd cycle),
respectively, under the same conditions. The result implies that the reusability of the PrSO H-
SiO @Si(R)Si nanosphere is superior to the shell-free PrSO H-SiO nanosphere. The excellent
reusability of the PrSO H-SiO @Si(R)Si nanosphere is firstly due to the covalent bonding between
the PrSO H groups with silica or PMO framework, which can avoid the leakage of the PrSO
groups during the catalytic recycle process. Additionally, the hydrophobic PrSO H-Si(R)Si shell
can prevent the adsorption of the hydrophilic oligomeric byproducts on the catalyst surface and
maintain high accessibility of the reactants and intermediates to the PrSO H sites of the core, and
3
3
2
3
2
3
2
3
2
3
2
3
2
3
2
3
2
3
3
H
3
3
therefore the deactivation of the catalyst hardly occurred in current catalytic system. However, the
hydrophilic oligomeric byproducts can be easily adsorbed on the surface of hydrophobic shell-free
PrSO
TEM image (Fig. 8b) and C CP-MAS NMR spectrum (Fig. 8c) of the third used PrSO
SiO @Si(Ph)Si-2 catalyst are presented, showing that both the morphology and chemical structure
3
H-SiO nanopheres, leading to it poor reusiability. To further support the above explanation,
2
1
3
3
H-
2
of the catalyst remain intact. The result also implies that the catalyst possesses excellent
mechanical stability under vigorous stirring and solvothermal conditions. Importantly, the
2
2

adsorption of the oligomeric byproducts on the catalyst surface and obvious block of the
micro/mesoporous channel are hardly observed. Therefore, the PrSO H-SiO @Si(R)Si
3
2
nanospheres can work effectively as the recyclable solid acid catalysts in the conversion of FOS
to EL.
4
. Conclusions
The CTAB-directed one-pot two-step co-condensation strategy was designed for the preparation
of propylsulfonic acid functionalized silica core/PMO shell structured nanospheres. The shell
thickness of the PrSO H-SiO @Si(R)Si nanospheres can be regulated by changing the starting
3
2
amount of the bissilylated organic precursors, while the hydrophobicity of the shell can be adjusted
by the introduction of different alkyl or phenyl moieties within the silica/carbon framework. The
PrSO
EL from ethanolysis of FOS, which is mainly attributed to the strong Brønsted acid nature;
additionally, the unique core-shell structure of the PrSO H-SiO @Si(R)Si nanospheres with
micro/mesoporosity and permeable shell gives a positive influence on their catalytic activity,
which can improve the accessibility of to the PrSO H sites throughout the core and shell; finally,
well-adjusted surface hydrophilicity/hydrophobicity of the PrSO H-SiO @Si(R)Si nanospheres
can avoid the adsorption of water and hydrophilic oligomeric byproducts on the shell, which can
further facilitate the mass transfer of the intermediates to the interior of hydrophilic PrSO H-
functionalized silica core and thereby ensuring the formation of EL with considerably high yield.
As-prepared PrSO H-SiO @Si(R)Si nanospheres also show excellent catalytic stability in the
target reaction, which is due to the covalent bonding the PrSO H groups with the silica or
3
H-SiO
2
@Si(R)Si nanospheres exhibited excellent acid catalytic activity in the synthesis of
3
2
3
3
2
3
3
2
3
2
3

silica/carbon framework; meanwhile, the hydrophobic PrSO H-Si(R)Si shell can prevent the
3
catalyst deactivation originating from the adsorption of the hydrophilic oligomeric byproducts.
Acknowledgements
This work is supported by the Natural Science Fund Council of China (21573038).
2
4

References
[
[
[
[
[
1]
2]
3]
4]
5]
C. Chatterjee, F. Pong, A. Sen, Green Chem. 17 (2015) 40-71.
E. Ahmad, M.I. Alam, K.K. Pant, M.A. Haider, Green Chem. 18 (2016) 4804-4823.
F. Liu, C. Liu, W. Kong, C. Qi, A. Zheng, S. Dai, Green Chem. 18 (2016) 6536-6544.
A. Corma, S. Iborra, A. Velty, Chem. Rev. 107 (2007) 2411-2502.
J.-P. Lange, R. Price, P.M. Ayoub, J. Louis, L. Petrus, L. Clarke, H. Gosselink, Angew.
Chem. Int. Ed. 49 (2010) 4479-4483.
6] P. Lanzafame, D.M. Temi, S. Perathoner, G. Centi, A. Macario, A. Aloise, G. Giordano,
Catal. Today 175 (2011) 435-441.
[
[
[
[
[
[
(
[
[
[
[
7]
8]
9]
S. Saravanamurugan, O. NguyenVanBuu, A. Riisager, ChemSusChem 4 (2011) 723-726.
D.J. Hayes, Catal. Today 145 (2009) 138-151.
L. Peng, L. Lin, H. Li, Q. Yang, Appl. Energ. 88 (2011) 4590-4596.
10] A. Démolis, N. Essayem, F. Rataboul, ACS Sustain. Chem. Eng. 2 (2014) 1338-1352.
11] B.C. Windom, T.M. Lovestead, M. Mascal, E.B. Nikitin, T.J. Bruno, Energ. Fuel. 25
2011) 1878-1890.
12] F. Su, L. Ma, D. Song, X. Zhang, Y. Guo, Green Chem. 15 (2013) 885-890.
13] G.F. Wang, Z. Zhang, L. Song, Green Chem. 16 (2014) 1436-1443.
14] E. Ahmad, M.I. Alam, K.K. Pant, M.A. Haider, Green Chem. 18 (2016) 4804-4823.
15] M. Karaki, A. Karout, J. Toufaily, F. Rataboul, N. Essayem, B. Lebeau, J. Catal. 305 (2013)
2
04-216.
[
16] X. Zhang, Y. Zhao, Q. Yang, J. Catal. 320 (2014) 180-188.
2
5

[
17] C.-H. Kuo, A.S. Poyraz, L. Jin, Y. Meng, L. Pahalagedara, S.-Y. Chen, D.A. Kriz, C. Guild,
A. Gudz, S.L. Suib, Green Chem. 16 (2014) 785-791.
[
[
(
[
18] S. Saravanamurugan, A. Riisager, Catal. Commun. 17 (2012) 71-75.
19] J.G. Croissant, X. Cattoen, M. Wong Chi Man, J.-O. Durand, N.M. Khashab, Nanoscale 7
2015) 20318-20334.
20] X. Zhang, F. Su, D. Song, S. An, B. Lu, Y. Guo, Appl. Catal. B: Environ. 163 (2015) 50-
6
2.
[
[
[
[
[
21] J. Liu, S. Bai, H. Zhong, C. Li, Q. Yang, J. Phys. Chem. C 114 (2010) 953-961.
22] L. Wang, F.-S. Xiao, Green Chem. 17 (2015) 24-39.
23] F. Su, Y. Guo, Green Chem. 16 (2014) 2934-2957.
24] S. An, Y. Sun, D. Song, Q. Zhang, Y. Guo, Q. Shang, J. Catal. 342 (2016) 40-54.
25] J.A. Melero, G.D. Stucky, R. van Grieken, G. Morales, J. Mater. Chem. 12 (2002) 1664-
1
670.
26] Y. Chen, P. Xu, H. Chen, Y. Li, W. Bu, Z. Shu, Y. Li, J. Zhang, L. Zhang, L. Pan, X. Cui,
Z. Hua, J. Wang, L. Zhang, J. Shi, Adv. Mater. 25 (2013) 3100-3105.
27] Z. Teng, X. Su, Y. Zheng, J. Zhang, Y. Liu, S. Wang, J. Wu, G. Chen, J. Wang, D. Zhao,
G. Lu, J. Am. Chem. Soc. 137 (2015) 7935-7944.
[
[
[
[
[
28] S. An, D. Song, B. Lu, X. Yang, Y.H. Guo, Chem. Eur. J. 21 (2015) 10786-10798.
29] Y. Goto, S. Inagaki, Chem. Commun. (2002) 2410-2411.
30] M.H. Tucker, A.J. Crisci, B.N. Wigington, N. Phadke, R. Alamillo, J. Zhang, S.L. Scott,
J.A. Dumesic, ACS Catal. 2 (2012) 1865-1876.
[
[
31] D. Song, S. An, Y. Sun, Y. Guo, J. Catal. 333 (2016) 184-199.
32] J. Chen, G. Zhao, L. Chen, RSC Adv. 4 (2014) 4194-4202.
2
6

[
[
[
33] T. Flannelly, S. Dooley, J.J. Leahy, Energ. Fuel. 29 (2015) 7554-7565.
34] Y.-B. Huang, Y. Fu, Green Chem. 15 (2013) 1095-1111.
35] Z. Zhang, Z.K. Zhao, Carbohyd. Res. 344 (2009) 2069-2072.
2
7

Fig. 1 TEM images of the PrSO
3
H-SiO
@Si(Ph)Si-2 (d), PrSO H-SiO
@Si(Et)Si (g) and PrSO H-Si(Et)Si@SiO
2
(a), PrSO
@Si(Ph)Si-3 (e), PrSO
nanospheres (h).
3
H-Si(Ph)Si (b), PrSO
3
H-SiO
2
@Si(Ph)Si-1 (c),
PrSO
3
3
H-SiO
H-SiO
2
2
3
2
3
H-SiO
2
@Si(Ph-Ph)Si (f),
PrSO
3
2
2
8

Fig. 2 SEM images of the PrSO
3
H-SiO
2
@Si(Ph)Si-2 (a) and PrSO
3
H-SiO @Si(Ph-Ph)Si
2
nanospheres (b).
2
9