Silica/chitosan core-shell hybrid-microsphere-supported CuI catalyst for terminal alkyne homocoupling reaction

Article abstract of DOI:10.1016/j.apcata.2015.06.016

A new microfluidic approach to prepare silica/chitosan core-shell hybrid microspheres was developed. The hybrid microspheres exhibit improved mechanics and adsorption properties. In addition, the silica/chitosan-supported CuI is an outstanding catalyst fo

Full text of DOI:10.1016/j.apcata.2015.06.016

Accepted Manuscript
Title: Silica/chitosan core-shell hybrid-microsphere-supported
CuI catalyst for terminal alkyne homocoupling reaction
Author: Hong Zhao Jianhong Xu Tao Wang
PII:
S0926-860X(15)30031-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.06.016
APCATA 15428
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
10-3-2015
10-6-2015
15-6-2015
Please cite this article as: Hong Zhao, Jianhong Xu, Tao Wang, Silica/chitosan core-shell
hybrid-microsphere-supported CuI catalyst for terminal alkyne homocoupling reaction,
Applied Catalysis A, General http://dx.doi.org/10.1016/j.apcata.2015.06.016
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Silica/chitosan core-shell hybrid-microsphere-
supported CuI catalyst for terminal alkyne
homocoupling reaction
Hong Zhao, Jianhong Xu, Tao Wang
The State Key Lab of Chemical Engineering, Department of Chemical Engineering, Tsinghua
University, Beijing 100084, China
Corresponding author: J. H. Xu, Ph. D, Associate Prof.(xujianhong@tsinghua.edu.cn); Tel: 86-10-
62773017; Fax: 86-10-62773017.
Graphical abstract
Highlights
1






Silica/chitosan core-shell hybrid microspheres were prepared in microchannel.
These hybrid microspheres have controlled structure and component distribution.
As catalyst support for fast reaction, they could reduce mass transfer resistance.
The reaction could complete within 10min without solvent at room temperature.
It’s easy to recover and reuse the supported catalyst with high catalytic activity.
Abstract: A new microfluidic approach to prepare silica/chitosan core-shell hybrid microspheres
was developed. The hybrid microspheres exhibit improved mechanics and adsorption properties.
In addition, the silica/chitosan-supported CuI is an outstanding catalyst for terminal alkyne
homocoupling reaction. Because there is chitosan with a large amount of –NH2, which has a strong
force with metal ions, on the shell of the microspheres, the chitosan can effectively reduce mass
transfer resistance. Meantime, the chitosan can adsorb reactants and subsequently increase the
reactant concentration around the catalyst. These two reasons make this solvent-free reaction
complete within 10 min at room temperature. It is easy to recover the catalyst simply through
sedimentation by centrifuge. Furthermore, the silica/chitosan-supported catalyst can be reused
many times with high catalytic activity.
Keywords: silica-chitosan hybrid microspheres; core-shell; supported catalyst; Glaser coupling;
microfluidic
2

1. Introduction
With the increasing consciousness of environmental protection, it is increasingly important to
perform chemical reactions under benign conditions with recyclable catalysts. Catalysts are
usually immobilized on a solid, green support for easy separation and reuse. To a large extent,
catalytic activities depend on the properties of the supports; therefore, the development of better
catalyst supports is necessary. To date, different support materials have been reported, including
inorganic materials (e.g., SiO2, [1, 2] Al2O3, [3] zeolites [4]) and organic materials (e.g.,
polystyrenes, polysaccharides). It has been demonstrated that support properties, which include
the material itself and the structure, play an important role in the catalyst’s performance. Ji et al.
[3] found apparent differences in the decomposition and reduction processes between unsupported
and Al2O3-supported metal compounds only because of their different existing states. In Bouilhac’s
work, [5] the catalyst that was bound to a star-like polystyrene composed of a microgel core with
functionalized arms showed high catalytic activities, and this special support structure contributed
to the polystyrene’s monomodal molar mass distribution. It is essential to choose suitable support
materials with optimized structures for specific chemical reactions.
1,3-Diyne derivatives, which are intermediates, play an important role in the preparation of various
structural entities, particularly macrocyclic annulenes, organic conductors, supramolecular
switches and carbon-rich materials. Terminal alkyne homocoupling reactions, which are also
known as Glaser coupling, are notably important in the preparation of 1,3-diynes. [6-10] The
reaction is usually performed with Cu or Pd as the catalyst and organic base under heated condition
in organic solvents, which are not environmentally friendly. [11-15] An environmentally friendly,
efficient and solvent-free method for the terminal alkyne homocoupling reaction was reported in
2010. [7] The terminal alkyne can be totally transformed at 60℃ after 6 h with catalytic amounts
3

of Cu(II) salt and base. The catalyst can also be recycled. However, the relatively high temperature
and long reaction time must be improved. He et al. [16] developed a benign, solvent-free method
to transform terminal alkyne to 1,3-diynes at room temperature by loading the copper catalyst on
Amberlyst A-21. However, considerably more attention has been paid to the support material
properties and less to the structural properties, which are also important to the catalyst’s
performance. For example, the catalyst inside the support cannot be efficiently used. Thus, the
core-shell supported catalyst with the catalyst on the shell is beneficial to take full advantage of
the catalyst and obtain high yield in a short time. [5] Lin et al. [17] prepared the Pd/SiO2@ZIF-8
core-shell catalyst and used it in the hydrogenations of alkenes. This core-shell catalyst exhibits
selective, antipoisoning and antileaching properties. Therefore, it is important to develop a simple
method to prepare the support with a core-shell structure to investigate the effect of the support
structure on terminal alkyne homocoupling reactions.
Chitosan, which is the only basic polysaccharide in nature, is abundant. Chitosan has outstanding
properties, such as nontoxicity, biocompatibility, biodegradability and low cost. Chitosan has a
large amount of amino and hydroxyl groups, which have strong chelating characteristics with
metal ions and organics. [18] Furthermore, chitosan’s good formability enables convenient
structure regulation. However, the poor mechanical property restricts its practical applications.
Recently, chitosan was composited with inorganic materials because the obtained hybrid material
showed improved catalytic, thermal and mechanical properties through synergistic effects. [19-22]
Therefore, hybrid materials have been applied in diverse fields, such as catalysis, separation
techniques, smart coating, and immobilization of enzymes.
It has been demonstrated that silica-chitosan hybrid materials exhibit an enhanced mechanical
property compared with other hybrid materials. [19, 20] In addition, silica has superior
4

biocompatibility, insolubility, mechanical stability and adsorption properties. Thus, the
silica/chitosan hybrid material is a good candidate for catalyst support. The primary preparation
approach of core-shell hybrid microspheres is the layer-by-layer technique using electrostatic
force. [23, 24] Although obtaining core-shell hybrid microspheres is relatively easy, regulating the
structure and repeating the process are difficult. Therefore, an easy approach to prepare
silica/chitosan core-shell hybrid microspheres with controllable structures and better repeatability
is essential.
In the past decade, microfluidic technology has rapidly developed and shows great advantages in
synthesizing monodispersed microspheres with different structures. [25-27] Many microfluidic
devices have been developed for high-throughput production. [28] In our previous work,
chitosan/silica core-shell hybrid microspheres with silica shell and chitosan core were prepared as
a catalyst support with most catalysts in the core for a slow reaction. Compared with other
microspheres, chitosan/silica core-shell hybrid microspheres have higher catalyst load efficiency;
therefore, a higher yield was obtained in mild condition in the azide-alkyne cycloaddition reaction,
which was controlled by a reaction instead of mass transfer. However, this approach could not
satisfy the demands of fast reactions because the mass transfer path was too long. To develop a
suitable catalyst support for a fast reaction that is controlled by reaction itself, we developed a
facile microfluidic approach to prepare silica/chitosan core-shell hybrid microspheres with silica
core and chitosan shell in this work. Silica/chitosan-supported CuI was used as a green catalyst for
the terminal alkyne homocoupling reaction without any solvent at room temperature. The
silica/chitosan core-shell hybrid support can decrease the mass transfer resistance and effectively
adsorb terminal alkyne, which leads to a short reaction time. Furthermore, the supported catalyst
has good stability and is recyclable.
5

2. Experimental
2.1 Materials and chemicals
Chitosan (0.20 g, deacetylation degree below 95%, Sinopharm chemical reagent Co., Ltd., Beijing,
P.R. China) aqueous solution with acetic acid (0.20 g, VAS Chemical Co., Ltd., Tianjin, P.R.
China) was used as the middle fluid. A certain amount (1.0 ~ 4.0 g) of tetraethoxysilane (TEOS)
was dissolved in the acetic acid (0.20 g) aqueous solution and stirred overnight to prepare a silica
sol (10.0 g), which was used as the inner fluid. N-octanol (VAS Chemical Co., Ltd., Tianjin, P.R.
China) served as the continuous phase. N-octane (10.0 g) with cross-linking reagent,
glutaraldehyde, (0.040 g) and surfactant, Span 80, (0.20 g, VAS Chemical Co., Ltd., Tianjin, P.R.
China) was used as the solidification bath. N-butylamine (0.5 mmol, VAS Chemical Co., Ltd.,
Tianjin, P.R. China), CuI and phenyl acetylene (1.0 mmol, Alfa Aesar, Tianjin, P.R. China) were
used in the catalysis reaction.
2.2 Microfluidic device
The microfluidic device was described in details in our previous work. [29] A circular glass
capillary (0.3 mm × 0.6 mm) is tapered to approximately 20 m using a micropipet puller (P-97,
SUTTER Co. Ltd., USA) for the inner fluid. This device is inserted into a second glass capillary
(1.05 mm × 1.5 mm), the orifice of which is tapered to approximately 150 m for the middle
fluid. Next, the orifices of those two compound capillaries are inserted into a Teflon tube with 0.5
mm inner diameter, as shown in Fig. 1. The Teflon tube is inserted as the continuous phase inlet
and the multiphase flow’s channel to form the co-axial structure. [29] These fluids are pumped
into the microchannel through three microsyringe pumps and four gastight microsyringes. The
droplets are collected with a solidification bath, which is placed on a shaker.
6

2.3 Preparation of monodispersed silica/chitosan core-shell hybrid microspheres with
different structures
To prepare silica/chitosan core-shell hybrid microspheres, the inner and middle fluids were
injected into the microchannel and broken into monodispersed droplets by the shearing force of
the continuous flow at the intersection. The droplets were collected in the solidification bath, where
the Schiff’s base reaction between glutaraldehyde and chitosan and the extraction of water out of
droplets using n-octanol were used to pre-solidify the droplets. The microspheres’ structure
depends on the pre-solidification time, which could be controlled by adjusting the residence time
in the solidification bath. Then, the microspheres were washed with and submerged in n-octane
for 24 h to ensure the silica gelation. Finally, the spheres were dried by freeze-drying.
The silica-chitosan hybrid microspheres with uniform component distribution, which are called
homogeneous hybrid microspheres in the following text, were also prepared as the control group.
The operation was described in details in our previous work. [20] The amount of TEOS and
chitosan in the homogeneous hybrid microspheres were identical to that in the core-shell hybrid
microspheres.
2.4 Adsorption kinetics experiments of Cu(II)
First, 0.030 g microspheres were added into a conical flask, which was placed in a water-bath
shaker at 30℃ and 130 rpm with 25 ml aqueous solution of 100 ppm Cu(II). A Raman atomic
absorption spectrophotometer (Type Z-5000, Hitachi, Japan) was used to analyze the Cu(II)
concentration of the sample solution, which was taken out at fixed time intervals. Based on the
mass balance equation, the amount of adsorbed Cu(II) per unit weight of the microspheres at time
ti, which is denoted by q(ti) (mg/g), was calculated as:
7

C V  i1CiV Ci[V0  (i 1)V ]
1
0
0
q(ti ) 
m
where C0 (mg/l) is the initial Cu(II) concentration, Ci is the concentration at time t, V is the volume
of the remaining solution at time ti (samples that were taken out were not added back to the beaker),
and m is the weight of the microspheres in the beaker.
2.5 Preparation of hybrid-microsphere-supported copper catalyst
In a nitrogen atmosphere, a conical flask with different amounts of hybrid microspheres, CuI (0.20
g) and CH3CN (10 ml) was put into a water-bath shaker at room temperature for 24 h. Next, the
resulting microspheres were separated, washed with CH3CN and CH2Cl2, and dried in vacuum
overnight.
2.6 Catalysis of the terminal alkyne homocoupling reaction
A certain amount of the supported catalyst, phenylacetylene and n-butylamine was added into a
conical flask. The reaction was performed at room temperature for 10~35 min. Finally, the product
of 1,4-diphenylbutadiyne was separated by dissolving in CH2Cl2 and purified by recrystallization
or column chromatography. Dividing the weight of obtained product by the weight calculated in
theory, the yield can be obtained. Dividing the weight of phenylacetylene converted to product by
its initial weight, the conversion can be obtained. The space-time yield (STY) was defined as the
weight of product obtained per gram of supported catalyst in one hour. Normalized yield was used
in the reactant ratio optimization experiment. Divide the yield obtained under different reactant
ratio by the maximum yield, then the normalized yield could be obtained. The ratio of
phenylacetylene to n-butylamine was abbreviated as alkyne : amine. The catalyst was simply
separated by sedimentation and subsequently reused after dried.
8

The reaction was also performed with the unsupported CuI in an identical procedure as above,
except that the catalyst was separated by centrifuge.
2.7 Adsorption of phenylacetylene
An n-octanol solution of phenylacetylene with an initial concentration of 402.6 mg/ml was
obtained by mixing a certain amount of phenylacetylene with n-octanol. Next, 0.30 g microspheres
were added into 10 ml solution and placed in a water-bath shaker at 30℃ and 130 rpm. A fixed
volume of the solution was taken out after 10 min and 20 min and analyzed with gas
chromatography-mass spectrum (GC-MS, ISQ) to obtain the concentration of phenylacetylene to
find the phenylacetylene adsorption capacity of the hybrid microspheres.
2.8 Analysis and characterization
The preparation process and overall morphology of the droplets and microspheres were observed
using an optical microscope (Type BX-61, Olympus, Japan) and an on-line CCD (Pixelink,
Canada). The detailed structure of the microspheres and element analysis were obtained with
scanning electron microscopy (SEM, type TM3000 and F6301, Hitachi, Japan). The element
valence of the catalyst was obtained using x-ray photoelectron spectroscopy (XPS) in a PHI
Quantera SXM system (ULVAC-PHI Inc., Kanagawa, Japan) with a monochromatic Al KR source
and a charge neutralizer. The product was analyzed by Fourier transform infrared spectroscopy
(Type Tensor27, Bruker, Germany) and gas chromatography-mass spectrum (GC-MS, ISQ).
9

3. Results and Discussion
3.1 Formation and characterization of the silica/chitosan core-shell hybrid microspheres
The inner and middle fluids broke up into droplets because of the shearing force of the continuous
phase at the intersection of the microchannel, as shown in Fig. 1. In the solidification bath, the
droplets were pre-solidified through Schiff’s base reaction between chitosan and glutaraldehyde
and the extraction of water from the droplets by n-octanol. After the 24 h gelation in n-octane,
silica/chitosan core-shell hybrid microspheres were obtained. The pre-solidification time and
gelation time depend on the residence time of the microspheres in the solidification bath and n-
octane.
The typical silica/chitosan core-shell hybrid microspheres (2.0 wt. % TEOS in the inner fluid and
2.0 wt. % chitosan in the middle fluid, pre-solidified for 20 min and gelated for 24 h) were used to
characterize the component distribution and core-shell structures. It was observed that the droplets
had good sphericity and a uniform size distribution in Fig. 2 a. The energy spectrum results in Fig.
2 b demonstrate that the silica was successfully composited in the microspheres. Next, to ensure
the core-shell structure of the hybrid microspheres, the spheres that were calcinated at 800℃ or
washed in the alkaline solution were compared to the original ones, as shown in Figs. 2 c, d and e.
The diameter of the microspheres after calcination significantly decreased because of the loss of
the chitosan shell. The microspheres that were washed in the alkaline solution had only the shell
and a nearly hollow core because of the loss of silica. This result proves that the hybrid
microspheres have a core-shell structure with a silica core and a chitosan shell. It should be noted
that the usual core-shell microspheres are composed of two immiscible materials. Then, there is a
clear dividing line between the core and the shell. In this work, the inner fluid (silica sol) and the
middle fluid (chitosan aqueous solution) are miscible. Although they are injected through different
10

channels, there will be mass transfer when they form the droplets and contact each other.
Furthermore, the distribution of chitosan and silica in different types of hybrid microspheres can
be calculated according to the energy spectrum results because there is C only in chitosan and Si
Siout
Siin
Cout
Cin
in silica, and the results are shown in Table 1. If the value of
is closer to 1, the distribution
of silica and chitosan in the microspheres is much more uniform. If the value is far from 1, there
is less silica in the shell of the microspheres, and the silica core and chitosan shell are formed. In
table 1, 0.499 is the value in this work and 0.908 is the value for homogeneous hybrid
microspheres. The results show that silica and chitosan are non-uniformly distributed in the
microspheres with most silica in the core and chitosan in the shell, and they subsequently form a
core-shell structure.
The hybrid microspheres show a core-shell structure in terms of component distribution at
the micro-scale. The macro-scale structures of the hybrid microspheres can also be adjusted by
changing the pre-solidification time for the identical gelation time of 24 h, as shown in Fig. 3. The
structure changed from completely porous to a compact shell and a porous core and subsequently
to completely compact with the increase in pre-solidification time, as shown in Figs. 3 a-j. The
diffusion of glutaraldehyde from outside to inside the microspheres made the microspheres
gradually become compact from the outside. Simultaneously, the water inside microspheres was
extracted outside by n-octanol, which also contributed to the compact structure.
3.2 Adsorption and catalytic properties of the core-shell hybrid microspheres as support
Because the load efficiency of the catalyst on the support significantly affects the catalytic activity,
the adsorption properties of the hybrid microspheres were studied. Fig. 4 a shows the adsorption
of Cu(II) by the microspheres with different amounts of pre-solidification time. A larger adsorption
11

amount could be obtained with shorter pre-solidification time because the free –NH2 amount
determines the adsorption amount. Longer pre-solidification time implies that much more –NH2 is
consumed in the Schiff’s base reaction. The effect of the TEOS-to-chitosan ratio on adsorption
was also studied for the identical pre-solidification time of 20 min, as shown in Fig. 4 b. In the
experimental range, the adsorption amount slightly decreased with the increasing ratio possibly
because more silica hindered the exposure of –NH2. However, the effect was small, and a larger
amount of silica increased the mechanical intensity, which indicates that it could withstand a
considerably larger force. Therefore, 2% TEOS was used in the experiment. Then, the adsorption
amount can change in a larger range by preparing silica/chitosan core-shell microspheres.
However, as the catalyst support, whether there is an optimized catalyst-loading amount for the
reaction requires further study, as shown in Fig. 5. The space-time yield and yield in 30 min both
increased at first and subsequently decreased when the load ratio increased, but they did not
simultaneously reach the maximum. The optimized load ratio of the yield was larger than that of
the space-time yield because when the load ratio was small, they would increase with the catalytic
site increasing. However, when the load ratio reached a certain value, although the yield continued
to increase, the space-time yield began to decrease because of the inhibition effect among the
catalytic sites. Not all catalytic sites could participate when the load ratio was too large; thus, they
both decreased. For a better catalytic effect, the load ratio of the highest yield was used in the
catalytic reaction.
Compared with homogeneous hybrid microspheres, we must investigate whether core-shell
hybrid microspheres as the support have advantages in the catalysis of fast reactions, such as the
terminal alkyne homocoupling reaction. The two types of microspheres were compared with each
other under the same experiment conditions. To study the reaction clearly, a less supported catalyst
12

was used to slow the reaction, and the results are shown in Fig. 6. The kinetic equations for core-
shell hybrid microspheres and homogeneous hybrid microspheres are equations (1) and (2),
respectively.
y=-0.0012x2+0.0752x-0.2832
y=0.0198x+0.1157
(1)
(2)
Higher yield was obtained for the identical reaction time using the core-shell-microsphere-
supported catalyst. According to the equation
dCA

 kCA
dt
（3）


where is the reaction order for the reactant, the two curves were calculated, and was 1.56 and
0 for the core-shell hybrid microspheres and homogeneous ones, respectively. Thus, the reaction
was controlled by mass transferwhen homogeneous hybrid microspheres were used as the support.
When core-shell hybrid microspheres were used as the support, the mass transfer resistance was
reduced because the catalyst was distributed on the microsphere surface, and a higher yield was
consequently obtained in a shorter time. Therefore, as the catalyst support, the silica/chitosan core-
shell hybrid microspheres are beneficial for the solvent-free terminal alkyne homocoupling
reaction.
Next, the catalytic performance of silica/chitosan core-shell hybrid-microsphere-supported
catalyst was further optimized. The effect of the catalyst amount on the yield was studied at the
fixed reaction time of 10 min and fixed reactant amounts (0.450 mmol alkyne and 0.225 mmol
amine without any solvent), as shown in Fig. 7. The relationship between the yield and supported
catalyst weight is as follows:
13

y=0.0603x-0.1332
（4）
Higher yield could be obtained with the increase in amount of the supported catalyst, and they
were linearly related, which indicates that the reaction order for the catalyst was 1. When the
catalyst amount was 17.0 mg, the reaction finished within 10 min.
The reactant ratio should also be optimized after optimizing the effect of the amount of
supported catalyst on the reaction to avoid pollution and waste caused by excess reactants for this
solvent-free reaction. The amount of added n-butylamine should be considered because it was
required in the reaction. The yields of product under different reactant ratios were obtained.
Normalized yield was used here. And normalized yield means yields obtained under different
reactant ratio divides by the maximum yield. The highest yield was obtained when the alkyne-to-
amine (phenylacetylene : n-butylamine) ratio was 0.4, as shown in Fig. 8, because low
concentrations of phenylacetylene and n-butylamine decrease the reaction rate. Therefore, there is
an optimal ratio.
The experimental conditions were optimized, and the reaction completed within 10 min under
the optimized conditions, which was relatively faster. Table S2 shows that the hybrid microspheres
can effectively adsorb phenylacetylene because large amounts of –NH2 and –OH, which are strong
electron donors, can have relatively strong interactions with phenylacetylene, which is an electron
acceptor. Thus, the concentration of phenylacetylene around the supported catalyst increases, and
the reaction rate increases, which is another reason for the better catalytic performance.
3.3 Study of the catalytic stability of silica/chitosan core-shell hybrid microspheres as catalyst
supports
14

Based on the optimized catalyst amount and experimental conditions, the catalytic stability of
silica/chitosan core-shell hybrid-microsphere-supported catalyst was also studied. The supported
catalyst was recycled, and the results are shown in Table 2. High yield was obtained in a short
time, and the supported catalyst could be reused for more than 5 times. Due to 1,4-
diphenylbutadiyne is the only product in this condition, therefore the conversion of reactant is
equal to yield. The catalyst had good stability and maintained good catalysis performance even
after a few days. CuI is relatively stable in dry condition, but it becomes inactive when it contacts
water in the reaction process because the reaction is exposed in the air, and a small amount of
water enters with the reactants. The results were compared with other works and exhibit good
catalytic performance, as shown in Table S3. However, the performance certainly decreased after
5 times of usage, and the reason was investigated. The reason is not the loss of Cu but the
conversion of CuI to Cu2O, CuO and Cu(OH)2, as shown in Tables 3 and S1. It could be found that
the supported catalysts could keep the valance of Cu as well as the unsupported ones. However,
the unsupported catalysts couldn’t be collected and recycled effectively and most were lost and
became pollutant. The XPS results in Fig. S1 show that the inactive catalyst had two peaks, which
implies that a part of Cu(I) was converted to other formations, whereas the fresh catalyst had only
one peak. Thus, the silica/chitosan core-shell microspheres had a strong interaction with the
catalyst and could avoid the loss of catalyst. In addition, the support enabled the catalyst’s easy
recycling and prevented its agglomeration.
4. Conclusions
Silica/chitosan core-shell hybrid microspheres with different structures and component
distributions were prepared using a facile microfluidic method. The hybrid microspheres exhibit
good adsorption property of heavy metal ions, such as Cu(II). The effects of the pre-solidification
15

time and TEOS content in the inner fluid on the structure and adsorption performance of the hybrid
microspheres were systematically studied. The optimized experimental conditions for the porous
core-shell hybrid microspheres are 2.0% chitosan in the middle fluid, 2.0% TEOS in the inner fluid
and pre-solidification time of 20 min. The hybrid-microsphere-supported CuI also shows
outstanding catalytic activity in the solvent-free terminal alkyne homocoupling reaction.
Compared with homogeneous hybrid microspheres, the silica/chitosan core-shell hybrid-
microsphere-supported catalyst can effectively decrease the mass transfer resistance; meanwhile,
the silica/chitosan hybrid microspheres can adsorb terminal alkyne, which leads to a higher
reactant concentration around the catalyst and consequently increases the catalytic reaction speed.
The reaction order of the supported catalyst is 1, and with a suitable amount of catalyst, the reaction
can finish within 10 min at room temperature without any solvent. The entire process is relatively
green. Furthermore, the supported catalyst has good stability with relatively high catalytic
performance for more than 5 times without losing its activity.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the supports of the National Natural Science Foundation of
China (21322604, 21136006) and the National Basic Research Program of China
(2012CBA01203).
16

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17

Figure captions
Fig. 1. The schematic diagram of microfluidic device [29]
Fig. 2. (a) Optical micrographs of silica/chitosan hybrid microspheres; (b) Results of the energy
spectrum of silica/chitosan hybrid microspheres; (c) SEM images of silica/chitosan hybrid
microspheres without any treatment (the scale bar is 200 μm); (d) SEM images of silica/chitosan
hybrid microspheres after calcination under 800℃ (the scale bar is 100 μm); (e) SEM images of
silica/chitosan hybrid microspheres that were washed by an alkaline solution (the scale bar is 200
μm).
Fig. 3. SEM images of the surface and inner region of the hybrid microspheres with different pre-
solidification time of 20, 30 and 40min. (a), (c), (e), (g) and (i) are the images of integral
microspheres with pre-solidification time of 10 min, 20 min, 45 min, 60 min and 90 min,
respectively. (b), (d), (f), (h) and (j) are the images of broken microspheres with pre-solidification
time of 10 min, 20 min, 45 min, 60 min and 90 min, respectively.
Fig. 4. Adsorption properties. (a) Adsorption kinetic curves of Cu by hybrid microspheres with
different pre-solidification time; (b) Effect of the TEOS ratio in the dispersed phase on the
equilibrium adsorption amount of Cu by hybrid microspheres (initial concentration of Cu is
100ppm, pre-solidified for 20 min).
Fig. 5. Relationship between load ratio of Cu on support and yield or space-time yield (STY).
Reaction conditions: phenylacetylene (1.0 mmol); n-butylamine (0.5 mmol); room temperature in
air; reaction time (30 min)
18

Fig. 6. Catalytic performance of silica-chitosan core-shell or homogeneous hybrid microspheres
supported CuI. (Reaction conditions: phenylacetylene (1.0 mmol); n-butylamine (0.4 mmol); Cat.
(2.2 mol% of the copper content); room temperature in air).
Fig. 7. Effect of weight of supported catalyst (hybrid microspheres loaded with CuI) on the
reaction yield. (Reaction conditions: phenylacetylene (0.450 mmol); n-butylamine (0.225 mmol);
room temperature in air; reaction time (10 min)).
Fig. 8. Effect of the alkyne-to-amine ratio on the reaction yield (the yield here represents the yield
of 1,4-diphenylbutadiyne). (Reaction conditions: phenylacetylene (1.0 mmol); Cat. (5.7 mol% of
the copper content); room temperature in air; reaction time (10 min)).
Tables
Table 1. Element ratios inside and outside the microspheres
Components
Siout
Siin
Cout
Cin
Core-shell hybrid microspheres
0.499
0.908
Homogeneous hybrid
microspheres
19

Table 2. Recycling of the catalyst
No of cycles
Yield
Conversion
1
>96% (10 min)
>95% (10 min)
>95% (10 min)
>92% (10 min)
>90% (10 min)
>86% (30 min)
>64% (10 min)
>86% (30 min)
>61% (10 min)
>85% (30 min)
>56% (10 min)
>96%
>95%
>95%
>92%
>90%
>86%
>64%
>86%
>61%
>85%
>56%
2
3
4
5
6 (2nd day)
7 (3rd day)
8 (4th day)
Table 3. XPS results of the supported and non-supported catalysts
Times of use
Cu2p (supported) Cu2p (non-supported)
0
2
6
932.47
932.46
932.32
932.6
932.43
932.32
20

Figure 1
21

a
b
d
c
e
Figure2
22

b
g
c
a
d
e
f
h
i
j
Figure 3
23

80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
b
a
20min
30min
40min
0
5
10
15
20
1
2
3
adsorption time / h
TEOS %
Figure 4
24

0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
120
100
80
60
STY
yield
40
0.02
0.04
0.06
0.08
0.10
0.12
loadrateofCuonsupportg/g
Figure 5
25

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
core-shell
homogeneous
5
10
15
20
25
30
35
40
reaction time / min
Figure 6
26

1.2
1
y = 0.0603x - 0.1332
R² = 0.9656
0.8
0.6
0.4
0.2
0
0
5
10
15
20
supported catalyst weight / mg
Figure 7
27

1.2
1
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
alkyne:amine
Figure 8
28