Sulfonated hollow sphere carbon as an efficient catalyst for acetalisation of glycerol

Article abstract of DOI:10.1039/c3ta10956a

Sulfonated hollow sphere carbon (HSC-SO₃H) was synthesized from carbonization of a SiO₂-polymer core-shell structure, followed by removal of the SiO₂ core and sulfonation with chlorosulfonic acid. HSC-SO₃H shows superior performances in acetalisation of glycerol, which is related to the hollow sphere carbon shell with rich microporosity for good mass transfer in the reaction.

Full text of DOI:10.1039/c3ta10956a

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Materials Chemistry A
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Sulfonated hollow sphere carbon as an efficient catalyst
for acetalisation of glycerol†
Cite this: J. Mater. Chem. A, 2013, 1,
9422
Liang Wang,ab Jian Zhang,a Shuang Yang,c Qi Sun,a Longfeng Zhu,b Qinming Wu,a
Haiyan Zhang, Xiangju Meng and Feng-Shou Xiao
b
a
a
*
Received 6th March 2013
Accepted 26th April 2013
DOI: 10.1039/c3ta10956a
www.rsc.org/MaterialsA
Sulfonated hollow sphere carbon (HSC-SO3H) was synthesized from heterogeneous solid acids.9 However, the small micropores of
carbonization of a SiO2–polymer core–shell structure, followed by aluminosilicate zeolites strongly limit their use in the conver-
removal of the SiO2 core and sulfonation with chlorosulfonic acid. sion of bulky molecules,9a while the sulfonated resins with
HSC-SO3H shows superior performances in acetalisation of glycerol, relatively low thermal stability are usually used at relatively low
which is related to the hollow sphere carbon shell with rich micro- reaction temperatures.9c
porosity for good mass transfer in the reaction.
To overcome the low thermal stability of sulfonated resins,
preparation of sulfonated carbons with relatively high thermal
stability has been developed.2b,10,11 For example, Suganuma et al.
reported that sulfonated amorphous carbon is catalytically active
for hydrolysis of cellulose;11a,b Wang et al. found that sulfated
carbon could catalyze dehydration of fructose to 5-hydroxy-
methylfurfural (HMF).11c Notably, mostof thesulfatedcarbonshave
low surface areas due to the absence of porosity, which strongly
limits the interaction between the acidic sites and substrates.
Herein, we demonstrate a successful synthesis of sulfonatedhollow
sphere carbon (HSC-SO3H) with a large surface area due to the
hollow sphere structure with rich microporosity. As a typical model
for glycerol conversion, catalytic tests in acetalisation of glycerol
show that HSC-SO3H exhibits high catalytic activity and excellent
recyclability, compared with conventional solid acids. To the best of
our knowledge, this is the rst time that the acetalisation of glycerol
is performed on porous carbon-based acids.
Biodiesel, which is regarded as a renewable fuel and has clear
benets relative to diesel fuel, has been widely produced from
vegetable oils and animal fat.1–4 In the production of biodiesel,
glycerol is formed as a by-product in a large amount.1–4 For
example, 1.2 million tons of glycerol was formed in 2010, mostly
coming from the production of biodiesel.4 Therefore, the
conversion of glycerol into valuable chemicals has attracted much
attention in recent years.5–7 Many routes have been developed to
transform glycerol, such as hydrogenation, dehydration, dehy-
drogenation, esterication and oxidation.5,6 Particularly, acetali-
sation of glycerol with ketones or aldehydes is an efficient way to
transform glycerol into important ne chemicals.7 For example,
the acetalisation of glycerol with acetone could yield solketal (2,2-
dimethyl-1,3-dioxolane-4-methanol, Scheme S1†), which could be
directly applied as a fuel additive and surfactant.3b,7
Normally, liquid acids and metal complexes show high
catalytic activities in this kind of reaction, but these homoge-
neous catalysts have difficulty in separation and regeneration
from the reaction system. Recently, the replacement of liquid
acids by solid acids in acid-catalyzed reactions became a hot
topic, due to the obvious advantages of heterogeneous catalysts
including good stability and regenerability.8 Typically, alumi-
nosilicate zeolites and sulfonated resins are two kinds of
For the synthesis of HSC-SO3H, resorcinol–formaldehdye
resin and SiO2 nanocomposites (SiO2@resin) with a core–shell
structure was synthesized under Stober conditions at rst.12 Aer
¨
carbonization at 650 ꢀC for 2 h, carbon and SiO2 nanocomposites
(SiO2@HSC) were obtained. Aer washing with hydrouoric
acid, SiO2 was removed and pure hollow sphere carbon (HSC)
was obtained. Then, the HSC was treated with chlorosulfonic
acid for 12 h at 0 ꢀC, forming HSC-SO3H (Scheme 1).
Fig. 1 shows TEM images of various samples. SiO2@resin
shows a typical core–shell structure (Fig. 1a). Aer carboniza-
tion, the sample morphology is still spherical (Fig. 1b). Aer
removal of the silica core, a hollow sphere structure is clearly
shown (Fig. 1c). The thickness of the carbon shell is about 10–13
nm, and the size of the hollow sphere is about 180–340 nm
(Fig. 1d). In addition, a large scale SEM image indicates high
purity of HSC (Fig. S1†).
aKey Lab of Applied Chemistry of Zhejiang Province, Zhejiang University, Hangzhou
310028, China. E-mail: fsxiao@zju.edu.cn
bState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin
University, Changchun 130012, China
cDepartment of Chemistry, Jilin University, Changchun 130012, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3ta10956a
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Fig. 2 (A) The nitrogen sorption isotherms of (a) SiO2@resin and (b) HSC-SO3H;
(B) enlarged isotherms with a relative pressure of 10ꢁ6 to 0.01; (C) DFT micropore
size distribution of HSC-SO3H.
Scheme 1 Synthesis scheme of HSC-SO3H ( ¼ resin, ¼ carbon, ¼ –SO3H).
related to the hollow sphere structure. Very interestingly, the
BET surface area of HSC-SO3H is estimated at 419 m2 gꢁ1. The
large surface area of the sample is very helpful for catalytic
conversion of glycerol because catalysis is
phenomenon.
a
surface
Fig. 3 shows IR spectra of HSC and HSC-SO3H. Compared
with HSC, HSC-SO3H shows obvious bands at 1031, 1119, and
1385 cmꢁ1. The band at 1031 cmꢁ1 is assigned to the presence
of the C–S bond,14 while the bands at 1119 and 1385 cmꢁ1 are
associated with the asymmetric and symmetric stretching
signals of O]S]O bonds of a sulfonic group.14 These results
indicate the successful introduction of sulfonic groups in the
HSC-SO3H sample.
Fig. 4 shows X-ray photoelectron spectra (XPS) of HSC-SO3H.
The survey spectrum gives signals mainly associated with C1s,
O1s, and S2p species, indicating that HSC-SO3H mainly consists
of C, O, and S elements. Furthermore, the C1s XPS spectrum
Fig. 1 TEM images of (a) SiO2@resin, (b) SiO2@HSC, and (c) HSC-SO3H; (d)
hollow size distribution of HSC-SO3H.
Fig. 2A shows nitrogen sorption isotherms of SiO2@resin
and HSC-SO3H. The SiO2@resin sample exhibits low adsorption
capacity for nitrogen and a very low surface area at 30 m2 gꢁ1
.
However, HSC-SO3H shows sorption isotherms of type IV plus
type I. A steep increase occurs in the curve at a relative pressure
of 10ꢁ6 < P/P0 < 0.01, which is due to the lling of micropores
(Fig. 2B).13 Density Functional Theory (DFT) micropore size
distribution is estimated at 0.64 nm (Fig. 2C). The formation of
micropores in the HSC-SO3H is possibly attributed to the resin
framework during the carbonization process. Another step can
be identied in the curve at 0.85 < P/P0 < 0.95, which is due to
the presence of large pores.13 In this work, this feature should be Fig. 3 IR spectra of (a) HSC and (b) HSC-SO3H.
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strength.15 In addition, acid–base titration tests show that HSC-
SO3H has a relatively high acidic concentration at 1.9 mmol gꢁ1
.
Fig. S3† shows TG curves of HSC-SO3H and Amberlyst-15.
Both curves show obvious weight loss at 40–165 ꢀC, which is
attributed to the desorption of water.16 Amberlyst-15 exhibits
two weight losses centered at 309 and 455 ꢀC, which are
attributed to the decomposition of sulfonic groups and the
Amberlyst-15 framework, respectively.16 In contrast, HSC-SO3H
requires a much higher temperature for the decomposition of
ꢀ
sulfonic groups and the carbon framework at 388 and 512 C,
respectively. These results conrm that HSC-SO3H has much
better thermal stability than Amberlyst-15, which is very favor-
able for catalyst recycling.
Table 1 presents the catalytic data of various catalysts in
acetalisation of glycerol. Solketal selectivity is greater than 98%
in most of the cases. Notably, HSC without acidic groups results
in very low conversion of glycerol (3.7%). However, aer intro-
duction of acidic sulfonic groups, HSC-SO3H is very active,
resulting in a conversion of 79.1% (entry 1, Table 1). This value
is much higher than that of the homogeneous catalyst
H3PO40W12 (14.2%, entry 2, Table 1), heterogeneous catalysts
SBA-15-SO3H (44.5%, entry 3, Table 1), Amberlyst-15 (66.5%,
entry 7, Table 1), H-USY zeolite (39.2%, entry 4, Table 1), and
H-ZSM-5 zeolite (24.0%, entry 5, Table 1), and even comparable
with that of liquid H2SO4 (82.8%, entry 8, Table 1).
Considering that Amberlyst-15 has a much higher acidic
concentration than HSC-SO3H and SBA-15-SO3H has a much
higher surface area than HSC-SO3H, much higher activity over
HSC-SO3H than those over Amberlyst-15 and SBA-15-SO3H
should be related to the unique structure of hollow sphere
carbon with rich microporosity. Possibly, the thin carbon shell
Fig. 4 (a) Survey and (b) C1s XPS spectra of HSC-SO3H.
shows obvious signals at 286.3 and 287.9 eV, which are associ- (10–13 nm) with micropores is very favorable for mass transfer
ated with C–S/C–O and C]O species. These results conrm the in acetalisation of glycerol. Therefore, most of the sulfonic
presence of sulfonic groups on HSC-SO3H, which is in good groups inside and outside the hollow sphere carbon could be
agreement with those of IR spectra. Moreover, HSC-SO3H gives exposed to the reactants.17 In contrast, SBA-15-SO3H and
an S2p peak at 169.1 eV (Fig. S2†), which is very similar to that of Amberlyst-15 have relatively long channels, resulting in rela-
Amberlyst-15 (168.9 eV), suggesting that HSC-SO3H and tively slow mass transfer.10b As a consequence, some of the
Amberlyst-15 have similar acidic strength of sulfonic groups, sulfonic groups on these porous catalysts might not be acces-
because the binding energy of S2p is sensitive to the acidic sible to reactants.
Table 1 The textural, acidic parameters, and catalytic performances in acetalisation of glycerol and acetone to solketal over various acid catalystsa
S content
Acid density
Entry
Catalysts
(mmol gꢁ1
)
(mmol gꢁ1
)
SBET (m2 gꢁ1
)
Dpb (nm)
Conversionc (%)
1
2
3
4
5
6
7
8
HSC-SO3H
H3PO40W12
SBA-15-SO3H
H-USYd
2.2
1.2
1.9
1.0
1.1
2.0
0.4
0.3f
4.3
20.4
1.8
3.8
418
<5
0.64
79.1 (78.5)
14.2 (8.0)
815
610
360
622
46
7.3
0.72
0.52
2.8
44.5 (44.0)
39.2 (39.0)
24.0 (23.7)
42.1 (42.0)
66.5 (66.5)g
82.8 (82.2)g
78.0 (78.0)
57.4 (57.0)
H-ZSM-5e
Sn-MCM-41
Amberlyst-15
H2SO4
HSC-SO3H
Amberlyst-15
4.0
10.2
2.2
39.5
9h
10h
411
37
0.64
42.2
3.8
a
Reaction conditions: 10 mmol of glycerol, 10 mmol of acetone, 4 g of t-BuOH, and 50 mg of catalyst with the temperature of oil bath at 80 ꢀC for 6 h.
b
c
Average pore size distribution estimated from the DFT model for HSC-SO3H and BJH model for other catalysts. Glycerol conversion
d
e
f
g
(solketal yield). Ratio of Si/Al at 7.5. Ratio of Si/Al at 40. Sn density, ratio of Si/Sn at 50. The same number of acidic sites as that of
HSC-SO3H in the reaction system. h Recycled for four times.
9424 | J. Mater. Chem. A, 2013, 1, 9422–9426
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To investigate the mass transfer over the HSC-SO3H catalyst,
In summary, we have successfully prepared sulfonic groups
we performed the acetalisation reactions over HSC-SO3H functionalized hollow sphere carbon (HSC-SO3H), which shows
poisoned by pyridine and 4,40,400-tris(2-methyl-2-propyl)- high activity and excellent recyclability in acetalisation of glyc-
2,20:60,200-terpyridine (tri-pyridine, Scheme S2†). When pyridine erol, compared with conventional solid acid catalysts. The
was added to the reaction system, HSC-SO3H lost nearly all of superior catalytic performance is strongly related to the unique
its activity, because the small pyridine molecules could enter structure of sulfonated hollow sphere carbon with rich micro-
the hollow sphere carbon from the micropores, poisoning all porosity, which is favorable for mass transfer in the reaction.
acidic sites in and out of the hollow sphere carbon (Table S1, These features should be potentially important for the future
Scheme S2†). In contrast, when tri-pyridine was added to the design and synthesis of novel efficient catalysts for conversion
reaction system, the poisoned HSC-SO3H could still catalyze of glycerol produced from biomass transformation.
the acetalisation reaction, giving a glycerol conversion of
76.0% (Table S1†). This phenomenon is interpreted by the fact
that the bulky tri-pyridine molecules could only poison the
Acknowledgements
acidic sites on the outside surface of HSC-SO3H due to the pore This work is supported by the National Natural Science Foun-
size limitation of the micropores (0.64 nm) on the carbon shell dation of China (21273197, and U1162201), State Basic
for the entrance of tri-pyridine. In this case, only acidic sites Research Project of China (2009CB623501), National High-Tech
inside of the poisoned HSC-SO3H could catalyze the acetali- Research and Development Program of China (2013AA065301),
sation reaction. Furthermore, we performed the synthesis of and Fundamental Research Funds for the Central Universities
the bulky molecule (2-(2-methoxyphenyl)-1,3-dioxolan-4-yl)- (2013XZZX001).
methanol by acetalisation of glycerol and 2-methoxy-
benzaldehyde (Scheme S3†). When pyridine or tri-pyridine was
added to the reaction system, the HSC-SO3H catalyst was
Notes and references
nearly inactive (Table S2†), which is very different from the fact
that only pyridine could make HSC-SO3H lose all the activity in
the acetalisation of glycerol and acetone (Table S1†). This
phenomenon is due to the fact that the acetalisation of glycerol
and 2-methoxybenzaldehyde only occurs on the external
surface of HSC-SO3H, because the micropores in HSC-SO3H
limit the transfer of the bulky molecule, the product (2-(2-
methoxyphenyl)-1,3-dioxolan-4-yl)methanol (Scheme S4†).
These observations, in particular the low activity in acetalisa-
tion of glycerol and 2-methoxybenzaldehyde over tri-pyridine-
poisoned HSC-SO3H, suggested that tri-pyridine almost
completely poisoned all the acid sites on the external surface of
HSC-SO3H. Even if there were some acid sites which were not
poisoned, they made almost no contribution to the catalytic
acetalisation. Very interestingly, the conversion over the tri-
pyridine poisoned HSC-SO3H (76.0%, 100 mg catalyst) is very
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(Table S1†). These results suggest that there is almost no
limitation for mass transfer from the outside to inside of
hollow sphere carbon. Additionally, these experiments also
demonstrate that the pore size distribution of micropores in
the hollow sphere carbon shell is ranged at kinetic diameters
between pyridine and tri-pyridine because pyridine easily
passes through the micropores and tri-pyridine is completely
blocked by these micropores.
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