H3PW12O40/mpg-C3N4 as an efficient and reusable bifunctional catalyst in one-pot oxidation-Knoevenagel condensation tandem reaction

Article abstract of DOI:10.1039/c6cy01669c

A single-site bifunctional catalyst for the oxidation-Knoevenagel condensation tandem reaction was prepared by the immobilization of phosphotungstic acid (HPW) on mesoporous graphitic carbon nitride (mpg-C₃N₄) via electrostatic interaction (HPW/mpg-C₃N₄). The results of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), solid-state ³¹P nuclear magnetic resonance (solid-state ³¹P NMR), zeta potentials, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) demonstrated that HPW was successfully immobilized on the protonated mpg-C₃N₄ by electrostatic interaction. The acid amounts of the catalysts were determined by NH₃ temperature programmed desorption (NH₃-TPD). The textural properties and morphology of HPW/mpg-C₃N₄ were characterized by N₂ adsorption-desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 30% HPW/mpg-C₃N₄ shows the best catalytic performance in the tandem reaction with 98.4% benzyl alcohol conversion and 96.2% selectivity to benzylidene malononitrile. The excellent catalytic performance of 30% HPW/mpg-C₃N₄ in the tandem reaction is due to the good catalytic performance of HPW in the oxidation and Knoevenagel condensation, respectively. Furthermore, protonated mpg-C₃N₄ not only acts as a support to facilitate good dispersion of HPW but also promotes the Knoevenagel condensation reaction effectively. Moreover, the HPW/mpg-C₃N₄ catalyst could be recycled easily without significant loss of catalytic activity.

Full text of DOI:10.1039/c6cy01669c

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DOI: 10.1039/C6CY01669C
Catalysis Science & Technology
PAPER
H3PW12O40/mpg-C3N4 as efficient and reusable bifunctional
catalyst in one-pot oxidation-Knoevenagel condensation tandem
reaction
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Hefang Wang, Cunyue Wang, Yongfang Yang*, Meng Zhao, Yanji Wang*
www.rsc.org/
A singleꢀsite bifunctional catalyst for the oxidationꢀKnoevenagel condensation tandem
reaction was prepared by the immobilization of phosphotungstic acid (HPW) on mesoporous
graphitic carbon nitride (mpgꢀC3N4) via electrostatic interaction (HPW/mpgꢀC3N4). The results
of Fourier transform infrared spectroscopy (FTꢀIR), Xꢀray diffraction (XRD), solidꢀstate 31P
nuclear magnetic resonance (solidꢀstate 31P NMR), zeta potentials, Xꢀray photoelectron
spectroscopy (XPS) and thermo gravimetric analysis (TGA) demonstrated that HPW was
successfully immobilized on the protonated mpgꢀC3N4 by electrostatic interaction. The acid
amounts of the catalysts were determined by ammonia temperature programmed desorption of
NH3 (NH3ꢀTPD). The textural and morphology of HPW/mpgꢀC3N4 were characterized by N2
adsorptionꢀdesorption, scanning electronic micrograph (SEM) and transmission electron
microscope (TEM). 30%HPW/mpgꢀC3N4 shows the best catalytic performance in the tandem
reaction with 98.4% benzyl alcohol conversion and 96.2% selectivity to benzylidene
malononitrile. The excellent catalytic performance of 30%HPW/mpgꢀC3N4 in the tandem
reaction is due to the good catalytic performance of HPW in the oxidation and Knoevenagel
condensation, respectively. Furthermore, protonated mpgꢀC3N4 not only acts as support to
facilitate good dispersion of HPW but also promotes the Knoevenagel condensation reaction
effectively. Moreover, the HPW/mpgꢀC3N4 catalyst could be recycled easily without
significant loss of catalytic activity.
facile and versatile route to the formation of carbonꢀ
1. Introduction
carbon bond with numerous applications in the synthesis
of fine chemicals as well as heterocyclic compounds of
biological significance.1,2 Various catalysts, such as
graphitic carbon nitride,3,4 metalꢀorganic framework
(MILꢀ100(Al), UiOꢀ66 and ZIFꢀ8),5,6 polyoxometalate
intercalated layered double hydroxide composite
materials,7 amine functionalized K10 montmorillonite,8
amineꢀfunctionalized mesoporous zirconia,9 nanocrystallꢀ
The Knoevenagel condensation of aldehydes with
compounds containing activated methylene groups is a
School of Chemical Engineering and Technology, Hebei University of Technology,
Tianjin 300130, China
E-mail address: wuyuyang123456@163.com (Y. Yang), yjwang@hebut.edu.cn (Y.
Wang)
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ine CexZr1ꢀxO2,10 showed high catalytic activity towards
Knoevenagel condensation reactions at mild conditions.
In general, Knoevenagel condensation reactions are
promoted not only by base catalysts but also by acid
catalysts.10 Among these catalysts, the acidicꢀbase
bifunctional catalysts, such as polyoxometalate
intercalated layered double hydroxide composite
More recently, Au/NH2ꢀUiOꢀ66 was used as catalyst
in oxidationꢀKnoevenagel condensation reaction with
tertꢀbutyl hydroperoxide (TBHP) as oxidant, whereas
noble metal Au and a long reaction time (34 h) were
required.29 Thus, it is urgent to design noble metalꢀfree
and more efficient catalyst to develop a green and mild
oneꢀpot oxidationꢀKnoevenagel condensation reaction
system. The catalytic oxidation of alcohols with hydrogen
peroxide as oxidant over heterogeneous catalyst has
received considerable attention from the viewpoint of
green chemistry.30,31 Hydrogen peroxide as a green
oxidant is attractive and competitive for oxidation
reactions,32 which can provide abundant active oxygen
species with water as the only byproduct. Hydrogen
peroxide is much cheaper and safer than organic
peroxides and peracids.31,33,34
materials,7 amine functionalized K10 montmorillonite8
10
and nanocrystalline CexZr1ꢀxO2
were considerable
attractive for their high catalytic efficiency. The
synergistic effect between the acidic and basic sites is
crucial in the catalytic process.
Tandem reactions, which enable multistep reactions in
one pot, increase the economic competitiveness in the
production of target compounds and the greenness of the
whole process by reducing capital investment, being
effective in the minimization of wastes and energy
consumption and optimizing the use of solvents.11,12 Thus
oneꢀpot synthesis of benzylidene malononitrile has raised
extensive interest as an attractive synthetic concept for
improving overall process efficiency.13,14 Benzylidene
malononitrile was reported to be obtained by tandem
deacetalizationꢀKnoevenagel condensation reaction or
oxidationꢀKnoevenagel condensation reaction. Several
acidꢀbase bifunctional catalysts were used in oneꢀpot
deacetalizationꢀKnoevenagel condensation reaction with
good yields, which were reported by Shiju,15 Zhong,16
Lu,17 Xu,18 Goyal,19 Gianotti1 and Zhang20. However, the
preparation of multifunctional catalysts with both acids
and bases active sites is complicated, due to the
incompatible nature of active sites.1
Polyoxometalates
(POMs),
especially
phosphotungstic acid (H3PW12O40, HPW), due to its
controllable redox and acidic properties, have been used
as effective catalysts in oxidation35,36 and Knoevenagel
condensation reaction37,38. However, HPW has low
specific surface area and usually cannot be recovered for
its solubility in many polar solvents, causing the difficulty
in separation and recycling, which limits its
utilization.39,40 Therefore, it is imperative to develop
recyclable POMs based catalysts for practical application.
Various strategies for immobilization of HPW on supports
have been developed including embedding HPW into
metalꢀorganic framework,41,42 adsorption on actived
carbon,43,44 electrostatic attachment to quanternary
ammonium functionalized chloromethylated polystyrene
(DMA16/CMPS),45 amineꢀgrafted graphene oxide,46
exfoliated montmorillonite47 and carbon nitride
materials,48,49 covalently grafted POM on mesoporous
hybrid silicas50 and SBAꢀ1551. The most developed and
widely used technique is electrostatic attachment of HPW
to positively charged supports.52 More recently, Song
prepared a series of POM intercalatedꢀlayered double
hydroxides (POMꢀLDHs) catalysts by facile ion exchange
method, which showed excellent activity (99%) and
selectivity (≥ 99%) in oxidationꢀKnoevenagel
condensation reactions.53 This is the first case for the
efficient utilization of POMꢀLDH as biꢀfunctional
heterogeneous catalysts for the promotion of tandem reaꢀ
21
Recently, ZrꢀMOFꢀNH2 and NH2ꢀMILꢀ101(Fe)22
were used for oneꢀpot sequential photocatalytic aerobic
oxidationꢀKnoevenagel condensation reaction by light
irradiation. However, excess malononitrile was required
in the reaction, owing to the decrease of reaction rate of
Knoevenagel condensation under UVꢀlight irradiation.
Moreover, unstability is one of the major drawbacks of
MOFs based catalysts.11,23 Furthermore, aerobic
oxidationꢀKnoevenagel condensation reaction has been
also reported by a series of researchers including Qi,24
Chen,25 Ang,26 Sarmah,27 Horiuchi28 and so on. During
the aerobic oxidation reaction, noble metals were used as
catalysts with molecular oxygen as oxidant.
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ctions.
were obtained on a BioꢀRad FTS 6000 system using
diffuse reflectance sampling accessories. Powder Xꢀray
diffraction (XRD) patterns were obtained using Xꢀray
diffraction (XRD, D/maxꢀ2500 with Cu Kα radiation,
λ=1.5406 Å). Solidꢀstate 31P nuclear magnetic resonance
was performed on Varian Infinityplus 300. 31P nuclear
magnetic resonance (31P NMR) was obtained on Avavce
400. Thermal properties of the composites were measured
by thermo gravimetric analysis (TGA). The samples were
heated to 800 °C at a heating rate of 10 °C·minꢀ1 under air
atmosphere on a SDT Q600. The content of W was
determined by inductively coupled plasmaꢀatomic
emission spectrometry (ICPꢀAES) on Opfima 7300V. The
morphology of the composites was observed by scanning
electronic micrograph (SEM, JEOL JSMꢀ5600) and
transmission electron microscope (TEM, JEMꢀ100CX).
BrunauerꢀEmmettꢀTeller (BET) surface area analysis was
performed using the nitrogen adsorption isotherms at 77
K using a Micromeritics Model ASAP 2020 instrument.
All samples were degassed at 423 K under vacuum for 6
h. The average pore diameter and pore volume were
calculated based on the BarrettꢀJoynerꢀHalenda (BJH)
method. Zeta potential measurements were performed
using the Zetasizer Nano ZS (Malvern Instruments) based
on the dynamic lightꢀscattering analysis. Xꢀray
photoelectron spectroscopy (XPS) measurement was
performed on PHIꢀ5000 Versaprobe spectrometer
equipped with a monochromatic Al Kα Xꢀray source.
Ammonia temperature programmed desorption of NH3
Graphitic carbon nitride (gꢀC3N4) is composed of a
large number of nitrogen with potential base functionality
(terminal amino groups ꢀNH2 and bridging N atoms ꢀNꢀ).
Except for large surface area and abundant mesopores,
mesoporous graphitic carbon nitride (mpgꢀC3N4) has
more nitrogen as active sites, which can be as anchors for
HPW54 and show good catalytic performance in
Knoevenagel condensations as active sites55,56
.
Herein, HPW was immobilized on protonated mpgꢀ
C3N4 via electrostatic interaction and used as a singleꢀsite
bifunctional heterogeneous catalyst in the oxidationꢀ
Knoevenagel condensation tandem reaction. Due to its
controllable redox and acidic properties, HPW can
efficiently catalyze oxidation and Knoevenagel
condensation reaction. Moreover, mpgꢀC3N4 not only acts
as support but also promotes the Knoevenagel
condensation
effectively.
HPW/mpgꢀC3N4
as
heterogeneous catalysts can be easily recovered and
reused without obvious deterioration of their structural
integrity and activity.
2. Experimental
2.1 Materials
All the reagents were analytical purity and were used as
received.
Poly(ethyleneglycol)ꢀblockꢀpoly(propylene
glycol)ꢀblockꢀpoly(ethylene glycol) (Pluronic P123) was
purchased from SigmaꢀAldrich. Dicyandiamide (DCDA),
phosphotungstic acid hydrate (H3PW12O40·6H2O), ethyl
acetate, ethyl cyanocaetate and diethyl malonate were
obtained from Tianjin Guangfu Fine Chemical Research
Institute. 30wt% H2O2 and benzyl alcohol were purchased
from Tianjin Bodi Chemical Co. Ltd. Malononitrile,
(NH3ꢀTPD) measurements were performed on
a
Micromeritics AutoChem 2920 instrument. The sample
(100 mg) was pretreated at 300 °C in N2 flow (30 mL/min)
for 2 h and then cooled down to 50 °C. Introducing NH3
in the sample tube for 30 min, saturated adsorption of
NH3 on the sample was obtained. Then the physically
adsorbed NH3 was removed by flushing the sample tube
with an argon flow. TPD measurements were carried out
in the range 50ꢀ550 °C at a heating rate of 10 °C/min.
cinnamyl
alcohol,
4ꢀmethylbenzyl
alcohol,
4ꢀ
methoxybenzyl alcohol, 4ꢀfluorobenzyl alcohol, 3ꢀ
fluorobenzyl alcohol, 2ꢀfluorobenzyl alcohol and 2ꢀ
pyridinemethanol were purchased from Energy Chemical
Co. Ltd.
2.3 Catalysts preparation
2.3.1 Preparation of mpg-C3N4. MpgꢀC3N4 was
obtained by selfꢀcondensation of DCDA with elimination
of ammonia according to the previous method.57 In a typiꢀ
2.2 Characterization
Fourier transform infrared spectroscopy (FTꢀIR) spectra
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cal synthesis, P123 (7.0 g) as the soft template was firstly
dissolved in 60 mL of water, and then DCDA (10 g) was
added into the solution and stirred vigorously for 4 h, and
subsequently dried at 100 °C in air. Then the mixture was
transferred into a 50 mL crucible with a cover. The
crucible was heated stepwise in muffle furnace, first 0.5 h
at 250 °C, then 0.5 h at 350 °C with a heating rate of
1.7 °C·minꢀ1. Finally it was heated to 550 °C at a rate of
3.3 °C·minꢀ1 and kept for 4 h at 550 °C. The mpgꢀC3N4
was obtained simultaneously with the remove of soft
template during the calcination.
and then dried for 12 h in a vacuum oven (60 °C, ꢀ0.1
MPa). The catalysts were reused for the above tandem
reaction.
3. Results and discussion
3.1 Catalyst characterization
3.1.1 Compositional and structural information of
HPW/mpg-C3N4. The FTꢀIR spectra of mpgꢀC3N4, HPW
and HPW/mpgꢀC3N4 are shown in Fig. 1. The
characteristic band of the mpgꢀC3N4 shows a framework
band at 806 cmꢀ1, which corresponds to the characteristic
mode of the triazine units.54,58 The band at 1637 cmꢀ1 is
associated with C=N stretching vibration mode, and the
bands at 1245, 1319 and 1403 cmꢀ1 are ascribed to
aromatic CꢀN stretching.54,59,60 The band at 3414 cmꢀ1
may be related to NH stretching mode in the aromatic
ring.61 The spectrum of the HPW with Keggin structure at
1079 cmꢀ1 is assigned to the asymmetric vibrations of the
PꢀO of tetrahedral PO4, and the bands at 984, 890 and 805
cm−1 are attributed to the stretching modes of the terminal
W=O, edge sharing of WꢀObꢀW and corner sharing of Wꢀ
OcꢀW units, respectively.40,62ꢀ65 These characteristic bands
of Keggin structure are obviously observed in the FTꢀIR
spectrum of HPW/mpgꢀC3N4. Furthermore, the
characteristic bands of HPW in the FTꢀIR spectrum of
HPW/mpgꢀC3N4 have a slightly redꢀshift (1079 to 1075
cmꢀ1, 890 to 884 cmꢀ1) compared with those of HPW,
indicating a strong interaction between [PW12O40]3ꢀ and
mpgꢀC3N4.49,63 The results of FTꢀIR suggest that HPW
could be immobilized on mpgꢀC3N4.
2.3.2 Preparation of HPW/mpg-C3N4. The
HPW/mpgꢀC3N4 catalysts were prepared by a method of
incipient wetness. A typical process was as follows: 1.0 g
of mpgꢀC3N4 was added to 5.0 mL of aqueous solution
containing a certain amount of HPW under vigorous
stirring at 25 °C for 12 h. The mixture was then dried for
12 h in a vacuum oven (60 °C, ꢀ0.1 MPa). The obtained
samples are referred to as X wt%HPW/mpgꢀC3N4 (where
‘X wt%’ represents the weight of percent of HPW in the
sample).
2.4 Catalytic one-pot tandem reaction
The oneꢀpot synthesis of α,βꢀunsaturated compounds was
carried out in a 25 mL threeꢀnecked round flask equipped
with a magnetic stirrer and a reflux condenser. In a
typical run, 3 mmol of benzyl alcohol, 150 mg of catalyst,
9 mmol of 30% H2O2 and 3 mL of deionized water were
added into the flask. The mixture was vigorously stirred
at 90 °C for 3 h. Subsequently, malononitrile (6 mmol)
was added into the mixture rapidly, and then the reaction
mixture was further stirred for 4 h at the same
temperature. The reaction mixture was extracted with
ethyl acetate and the catalyst was separated by
centrifugation after reaction. The organic phase was
analyzed by a SPꢀ3420A gas chromatograph (Beijing
BeifenꢀRuili analytical instrument Co. Ltd) equipped with
a KBꢀWax column (30 m, 0.32 mm id, 0.25 ꢁm film
thickness) with toluene as internal standard and products
Fig. 2 shows the XRD patterns of mpgꢀC3N4, bulk gꢀ
C3N4, HPW and HPW/mpgꢀC3N4 with different HPW
loading (20ꢀ40%). For mpgꢀC3N4, the strong peak located
at 27.3° (d = 0.326 nm) is attributed to the interlayer
stacking (002) peak of aromatic segments of the carbon
nitride sheets.54,66 An lowꢀangle reflection at 13.2° (d =
0.670 nm) is connected to the (100) plane,67 which is
smaller inꢀplanar distance than one triꢀsꢀtriazine unit
(0.713 nm), presumably originated from the inꢀplanar triꢀ
sꢀtriazine units with a small tilt angularity to the main
layers.68 However compared with those of gꢀC3N4, the
(002) and (100) peaks of the XRD pattern of mpgꢀC3N4
were confirmed by
a Thermo Trace DSQ gas
chromatographꢀmass spectrometer. The recovered
catalysts were washed with ethanol and deionized water
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broadened with low intensity, suggesting the effect of the
geometric confinement in the nanosized pore walls.69 The
diffraction peaks at 2θ (in degree) = 8ꢀ11°, 18ꢀ22°, 24ꢀ30°
and 33ꢀ40° are characteristic of HPW with Keggin
structure.70 In the XRD patterns of HPW/mpgꢀC3N4, the
intensity of mpgꢀC3N4 characteristic peak at 27.5°
gradually weakens and the intensity of the HPWꢀrelated
peak at 26.4° gradually increases with increase loading of
HPW (20%ꢀ40%). The typical peaks of HPW in the XRD
patterns of HPW/mpgꢀC3N4 indicated that HPW was
successfully immobilized onto the mpgꢀC3N4 and its
structure was well preserved.
Fig. 3A shows the solidꢀstate 31P MAS NMR spectra
of HPW and 30%HPW/mpgꢀC3N4. The spectrum of HPW
shows one signal at ꢀ15.7 ppm, which is attributed to the
tetrahedral coordination of PO4 in the Keggin unit.71 For
the solidꢀstate 31P NMR spectrum of 30%HPW/mpgꢀ
C3N4, a similar signal at ꢀ15.5 ppm can be observed,
indicating that the HPW have been successfully
immobilized into the mpgꢀC3N4 and the primary structure
of HPW is well preserved. The results are consistent with
the results of FTꢀIR and XRD.
in the WꢀO bond configuration and W6+ in HPW.53,74
The C 1s spectrum can be deconvoluted into three
peaks at 284.4, 285.2 and 288.2 eV, corresponding to the
pure graphitic sites in the CN matrix (CꢀC), sp2ꢀbonded to
N inside the sꢀtriazine units (N=CꢀN) and sp2 C atoms
bonded to aliphatic amine in the aromatic rings (N=C(ꢀ
N)ꢀN), respectively.75,76 Additionally, the N 1s spectrum
displays four deconvoluted peaks with binding energies
of 398.3, 399.9, 401.3 and 403.8 eV, indicating four types
of N with different bonding states on the surface of mpgꢀ
C3N4. Among them, the three peaks of 398.3, 399.9 and
401.3 eV are ascribed to the sp2ꢀbonded aromatic N in the
triazine units (CꢀN=C), the bridging N bonding to carbon
atoms (Nꢀ(C)3 or CꢀN(ꢀH)ꢀC) and the terminal amino
groups (C–NH2) due to incomplete condensation,
respectively.73,76,77 The peak at 403.8 eV is attributed to
the positive charge effect in the heterocycles due to a
small amount of protonated N of mpgꢀC3N4, which is
consistent with the results of zeta potentials.72,73,76 The
results of XPS indicate the structural integrity of HPW
after the immobilization onto mpgꢀC3N4 by electrostatic
interaction, which are in good agreement with the results
obtained from FTꢀIR, XRD and solidꢀstate 31P NMR
spectra.
In order to investigate the interaction between HPW
and mpgꢀC3N4, HPW was substituted by HCl with the
same molar of H+ to obtain protonated mpgꢀC3N4 (mpgꢀ
C3N4ꢀH+) during the preparation of 30%HPW/mpgꢀC3N4.
As shown in Fig. 3B and Fig. S1, the zeta potential of
mpgꢀC3N4 is ꢀ22.0 mV under neutral conditions whereas
the protonated mpgꢀC3N4 is ꢀ14.8 mV, suggesting partial
protonation of N (C=N, CꢀN and CꢀN(H) of mpgꢀ
C3N4)72,73. More negative charges on the surfaces of
HPW/mpgꢀC3N4 were observed with increase of HPW
loading from 20% to 40%. This result demonstrated that
HPW was successfully immobilized by electrostatic
interaction with mpgꢀC3N4ꢀH+.
Fig. 5 shows the TGA curves of HPW, HPW/mpgꢀ
C3N4 (20%ꢀ40%) and mpgꢀC3N4. The TGA curve of
HPW shows three weight loss steps. The first weight loss
(8.3%) between 25 °C and 100 °C is due to the weight
loss of physically absorbed water. The second weight loss
(3.3%) between 100 °C and 250 °C is due to the weight
loss of structural water. The third weight loss (0.7%) up
to 600 °C results from the loss of acidic protons and the
decomposition of the Keggin structure.78,79 For mpgꢀC3N4,
a weight loss of 7.4% up to 200 °C is due to the removal
of adsorbed water, and the weight loss of 92.4% between
500 °C and 730 °C is due to the direct thermal
decomposition of mpgꢀC3N4.80 The TGA curves also
show that HPW/mpgꢀC3N4 (20%, 30% and 40%) have
excellent chemical stability from 25 to 500 °C. According
to the above results, the actual HPW loading in
HPW/mpgꢀC3N4 are about 19.5%, 28.0% and 38.6%
respectively, which are similar to the corresponding
theoretical value of 20%, 30% and 40%. Additionally, the
HPW loading of the catalysts was also determined by
XPS were performed to investigate the composition
and chemical states of the elements in the
30%HPW/mpgꢀC3N4 (Fig. 4). The XPS wide scan
spectrum shows that 30%HPW/mpgꢀC3N4 is composed of
P, W, O, C and N. The P 2p spectrum exhibits a broad
signal peak at about 133.8 eV, indicating the existence of
P5+ in the oxidation state.66 The W 4f spectrum is
deconvoluted into two peaks at 35.1 eV (4f5/2) and 37.3
eV (4f7/2) respectively, which are typically ascribed to W
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analysis of P by ICPꢀAES. The HPW loading are about
18.8%, 27.6% and 38.1% respectively, which are similar
to those of TGA.
30%HPW/mpgꢀC3N4 (9.71 nm for 20%HPW/mpgꢀC3N4),
which indicates the mesoporous structure of mpgꢀC3N4
can be preserved even after immobilization of HPW. Thus,
due to its larger surface area and porosity, HPW/mpgꢀ
C3N4 is expected to show good catalytic performance in
the tandem reaction.
NH3ꢀTPD was performed to investigate the acid
amounts
of
HPW,
20%HPW/mpgꢀC3N4
and
30%HPW/mpgꢀC3N4 (Fig. S2). The detailed explanation
is shown in ESI.
Fig. 7 shows the morphology of mpgꢀC3N4 and
30%HPW/mpgꢀC3N4. The SEM image of mpgꢀC3N4
exhibits the tortile flakeꢀlike texture of mpgꢀC3N4. Fig.
7B shows SEM image of 30%HPW/mpgꢀC3N4, in which
the mpgꢀC3N4 sheets are shaggy with lots of wrinkles,
which may be due to that the changes of the morphology
of mpgꢀC3N4 by protonation. Furthermore, there is no
HPW aggregation on the mpgꢀC3N4 surface. Fig. 7C and
D show typical TEM images of 30%HPW/mpgꢀC3N4, in
which the nanosheet morphology and porous texture are
clearly observed. However HPW cannot be observed
obviously in the TEM images of 30%HPW/mpgꢀC3N4,
possibly due to HPW in the form of [PW12O40]3ꢀ anion
immobilized onto mpgꢀC3N4 and well dispersed on mpgꢀ
C3N4. The similar results was also obtained by Zhu54.
3.1.2 Morphology and textural property of
HPW/mpg-C3N4.
The
N2
adsorptionꢀdesorption
isotherms and the corresponding pore size distribution
curves (PSD curves) of gꢀC3N4, mpgꢀC3N4,
20%HPW/mpgꢀC3N4 and 30%HPW/mpgꢀC3N4 are shown
in Fig. 6. The N2 adsorptionꢀdesorption of mpgꢀC3N4
shows a type IV isotherm pattern with a H3 hysteresis
loop and two capillary condensation steps at a low
relative pressure and a high relative pressure region
respectively, which is characteristics of highly ordered
mesoporous materials with bimodal pores.81 The
corresponding PSD curve of mpgꢀC3N4 (Fig. 6 inset) also
shows that the sample has two distributions with small
mesopores and large mesopores. The small mesopores
(the pore distribution centered at 3.89 nm) originate from
the decomposition of P123 template,61 while the large
mesopores with a broad distribution (10.0ꢀ40.0 nm) may
be assigned to either the aggregates (loose assemblages)
of plateꢀlike particles of the carbon nitride61 or the
coalescence of the mesopores due to the decomposition of
the lower molecular weight CN polymers during the
carbonization process82. For bulk gꢀC3N4, there is also a
small hysteresis loop starting at p/p0 = 0.8, indicating
poor porosity of bulk gꢀC3N4 compared with mpgꢀC3N4.
The detailed textural parameters are summarized in Table
1. MpgꢀC3N4 has higher surface area (146 m2·g−1) and
larger pore volume (0.206 cm3·g−1) than bulk gꢀC3N4
(12.2 m2·g−1 and 0.0627 cm3·g−1). This result confirms
that the introduction of the template favorably generation
of mesospores. Compared with that of mpgꢀC3N4 and
20%HPW/mpgꢀC3N4, the N2 adsorptionꢀdesorption
isotherm and PSD curve of 30%HPW/mpgꢀC3N4 have no
significant changes, however, a slight decrease in BET
surface area (SBET) and pore volume (Table 1) is observed,
which is due to partial blockage of the pores by HPW on
mpgꢀC3N4.54 After the impregnation, the average pore
size of mpgꢀC3N4 decreases from 9.98 nm to 9.67 nm for
3.2 Catalytic Activity
HPW/mpgꢀC3N4 was used as the catalyst for oneꢀpot
synthesis of benzylidene malononitrile (Scheme 1). The
tandem reaction involves two separate steps: 1) oxidation
of benzyl alcohol (A1) to benzaldehyde (B1) with H2O2
and 2) Knoevenagel condensation between benzaldehyde
and malononitrile to produce benzylidene malononitrile
(C1). The oxidations of A1 catalyzed by 30%HPW/mpgꢀ
C3N4 with different molar ratio of H2O2/A1 were
investigated (Fig. S3). With the increase of the molar
ratio of H2O2/A1 from 2.0 to 3.0, the conversion of A1
increased sharply from 48.7% to 98.4%. While the molar
ratio of H2O2/A1 further increased to 3.5, the conversion
of A1 almost unchanged, but the selectivity to B1
decreased obviously. Increase of the amount of H2O2
enhanced conversion of A1 to B1. However the excess of
oxidant lead to the deep oxidation with more benzoic acid
formed. Considering the conversion and selectivity of the
oxidation reaction, the optimized molar ratio of H2O2/A1
was 3.0.
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The first oxidation step could be very important for
the oxidationꢀKnoevenagel condensation tandem reaction.
HPW, mpgꢀC3N4, 30%HPW/gꢀC3N4 and 30%HPW/mpgꢀ
C3N4 were used as catalysts in oxidation (Fig. 8A). No B1
was formed in the presence of mpgꢀC3N4. The HPWꢀ
containing catalysts (HPW, 30%HPW/gꢀC3N4 and
30%HPW/mpgꢀC3N4) presented high catalytic activities
for A1 oxidation. High conversion of A1 (98.7%) and low
selectivity to B1 (74.8%) were obtained over HPW.
Moreover, HPW completely dissolved in reaction
medium, leading to difficulty of catalyst recovery and
recycling. 30%HPW/mpgꢀC3N4 afforded a selectivity of
95.8% to B1 with A1 conversion of 98.4%. Compared
with 30%HPW/mpgꢀC3N4, 30%HPW/gꢀC3N4 afforded a
low selectivity to B1 and low conversion of A1. As
observed from the N2 adsorptionꢀdesorption isotherms
and PSD carves, the large surface area and porosity for
mpgꢀC3N4 can make it more favorable for the dispersion
of HPW than bulk gꢀC3N4, which is beneficial to the
excellent catalytic activity.
time 3+1 h (oxidation for 3 h and Knoevenagel
condensation for 1 h), temperature at 90 °C and catalyst
amount of 150 mg. Then under the optimized conditions,
the oneꢀpot synthesis of C1 over HPW/mpgꢀC3N4
catalysts in water was investigated (Fig. 9). As expected,
HPW was able to catalyze the oxidationꢀKnoevenagel
tandem reaction with 96.7% conversion of A1. However,
the selectivity to C1 was poor with high selectivity to
benzoic acid (23.7%), which was the over oxidation
product of A1. 30%HPW/mpgꢀC3N4 and 40%HPW/mpgꢀ
C3N4 catalysts showed high A1 conversion (98.4% and
98.8% respectively) compared with that of
20%HPW/mpgꢀC3N4 catalyst (80.0%). However, the
selectivity to C1 decreased over 40%HPW/mpgꢀC3N4
compared with that of 30%HPW/mpgꢀC3N4, which was
due to the deep oxidation of B1 to benzoic acid over
excess acidic active sites. The similar results were also
obtained with A1 oxidation over VO@gꢀC3N4 catalyst,83
and epoxidation of cyclohexene over QAPPESKꢀPMo84.
30%HPW/mpgꢀC3N4 showed the best catalytic activity in
the tandem reaction with 98.4% A1 conversion and 96.2%
selectivity to C1. The activity of the 30%HPW/gꢀC3N4 is
lower than that of the 30%HPW/mpgꢀC3N4, which is
consistent with the results of separate A1 oxidation and
Knoevenagel condensation reaction. This is due to good
dispersion of HPW and the cooperative effects of HPW
and mpgꢀC3N4 for the Knoevenagel condensation. A
physical mixture of HPW and mpgꢀC3N4 also promoted
the tandem reaction, but it was not as efficient as the
30%HPW/mpgꢀC3N4 catalyst likely due to increased
diffusion limitations. The high efficient catalytic
performance of 30%HPW/mpgꢀC3N4 in the tandem
reaction benefits from the good catalytic performance of
HPW in the oxidation and Knoevenagel condensation
respectively. Moreover, protonated mpgꢀC3N4 facilitates
good dispersion of HPW as support, which also attributes
to high catalytic performance.
Generally, Knoevenagel condensation reactions are
promoted not only by base catalysts but also by acid
catalysts. Due to its redox and acidic properties, HPW as
a singleꢀsite bifunctional catalyst was able to efficiently
catalyze the A1 oxidation (Fig. 8A) and Knoevenagel
condensation reaction respectively (Fig. 8B). Furthermore,
mpgꢀC3N4 shows excellent catalyst activity with 97.5%
conversion of B1 and 98.9% selectivity to C1 for the
Knoevenagel condensation reaction compared with gꢀ
C3N4, which is in agreement with the obtained results by
Su.56 Moreover, 30%HPW/mpgꢀC3N4 exhibits a better B1
conversion (98.6%) and selectivity to C1 (99.4%) than
that of 30%HPW/gꢀC3N4. The better Knoevenagel
condensation activity of 30%HPW/mpgꢀC3N4 was due to
the mesoporous structure and abundant nitrogen of mpgꢀ
C3N4, which facilitated good dispersion of HPW and with
more basic sites for the condensation reaction. Therefore,
the above results suggest that the HPW/mpgꢀC3N4 could
be used as the desired catalyst to combine both oxidation
and Knoevenagel condensation reaction in a oneꢀpot
reactor.
A possible mechanism for oxidationꢀKnoevenagel
tandem reaction of A1 and malononitrile over
30%HPW/mpgꢀC3N4 is proposed (Fig. S5). The detailed
explanation is also included in ESI.
The effects of reaction conditions such as reaction
time, temperature and catalyst amount were investigated
(Fig. S4). The optimized reaction conditions are reaction
To describe directly the reaction process, the oneꢀpot
tandem synthesis of C1 from A1 was carried out at
different reaction time. As shown in Fig. 10A, the A1 conꢀ
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version and B1 yield gradually increased to the maximum
values within 3 h. After adding malononitrile into the
reaction solution, the intermediate B1 yield decreased
rapidly, whereas the C1 yield increased sharply within 0.5
h. The results indicate that the oneꢀpot synthesis occurred
in a consecutive manner, and the oxidation was the rateꢀ
controlling step. The similar results were also obtained
with Pd/LSꢀATꢀOHꢀ for the aerobic oxidationꢀ
Knoevenagel condensation reaction18. Then the kinetic
study for A1 conversion over 30%HPW/mpgꢀC3N4 has
been shown in Fig. 10B. The A1 conversion and ln(Ct/C0)
are plotted against reaction time, in which C0 and Ct are
initial A1 concentration and the concentration at time t,
respectively. The linear fit of the data indicates that the
catalytic reaction follows pseudoꢀfirstꢀorder kinetics for
A1 conversion (R2=0.9947). According to the Equations
(1) and (2), the rate constant k of A1 conversion can be
determined to be 1.0448 hꢀ1. The similar results were also
obtained with oxidationꢀKnoevenagel condensation of
benzyl alcohol and ethyl cyanoacetate catalyzed by
polyoxometalate intercalatedꢀlayered double hydroxides
(POMꢀLDHs)53.
can be attributed to the electron withdrawing effect and
increased steric hindrance. Moreover, the heterocyclic
alcohol (2ꢀpyridinemethanol) could also be converted to
corresponding products under the optimal conditions
(Table 2, entry 8). When the condensation reactant
malononitrile is substituted by ethyl cyanocaetate or
diethyl malonate, the yield for C decreases moderately
(Table 2, entries 9 and 10), which is due to the fact that
malononitrile is the most active methylene compound
than other used condensation substrates.18 No C was
formed in the presence of mpgꢀC3N4 due to no active sites
for A oxidation. For various benzyl alcohol derivatives,
30%HPW/mpgꢀC3N4 shows good catalyst activity
compared with that of HPW and physical mixture of
HPW and mpgꢀC3N4. Thus 30%HPW/mpgꢀC3N4 exhibits
the general applicability and high efficiency for the
oxidationꢀKnoevenagel tandem reaction.
Table 3 summarizes the catalytic performance of
various catalysts previously reported in oneꢀpot tandem
synthesis of C1 from A1. 30%HPW/mpgꢀC3N4 exhibits
good catalytic activity with H2O2 as oxidant under mild
reaction condition compared with other previously
reported catalysts (Table 3, entries 1ꢀ8). And
30%HPW/mpgꢀC3N4 shows comparative catalytic
activity compared with TrisꢀLDHꢀZn4(PW9)2 for the
oxidationꢀKnoevenagel condensation reaction (Table 3,
entries 9 and 10). Due to the properties of easy
preparation, noble metalꢀfree, stability and regeneration,
30%HPW/mpgꢀC3N4 is a good and efficient catalyst for
oxidationꢀKnoevenagel tandem reaction.
ꢀdCt/dt = kCt
(1)
(2)
ln(Ct/C0) = ꢀkt
In order to test the general applicability and efficiency
of the 30%HPW/mpgꢀC3N4, physical mixture of HPW
and mpgꢀC3N4, HPW and mpgꢀC3N4 in the tandem
reactions with different substrates, various benzyl alcohol
derivatives (A) and active methylene compounds were
investigated (Table 2). For 30%HPW/mpgꢀC3N4, benzyl
alcohol and cinnamyl alcohol are efficiently converted to
the corresponding target products (C) with malononitrile
under the same reaction conditions (Table 2, entries 1 and
2). Introducing electron donor groups at the paraꢀposition
of the benzyl alcohol has no effect on the high activities
with appropriate prolonged reaction time (Table 2, entries
3 and 4). However, when the electron withdrawing group
substituted at the paraꢀposition, the decrease in
conversion of A is observed (Table 2, entry 5), which
indicates that the electron withdrawing group impedes the
oxidation process.24,53 Furthermore, 30%HPW/mpgꢀC3N4
has different catalytic performance for aromatic alcohols
with a fluorine group substituted at orthoꢀ, metaꢀ and
paraꢀposition respectively (Table 2, entries 5ꢀ7), which
3.3 Catalyst recycling
An important issue associated with the performance of a
heterogeneous catalyst is its recovery and reusability. The
HPW/mpgꢀC3N4 catalyst could be easily separated by
centrifugation after reaction. To investigate the
recyclability of the 30%HPW/mpgꢀC3N4 catalyst, the
catalyst was recycled eight times. As summarized in Fig.
11A, the catalyst exhibits no obvious decline of the
conversion of benzyl alcohol and the selectivity to
benzylidene malononitrile during the eighth run. In order
to confirm that the active species are not the HPW
leaking from 30%HPW/mpgꢀC3N4 catalyst in the tandem
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reaction, hot filtration experiment was carried out. After 1
h reaction time, the catalyst was filtered, and reaction
solution was kept on stirring under the same experimental
conditions. The conversion of benzyl alcohol almost
remained unchanged during the investigated reaction
(from 1 h to 4 h) after the hot filtration experiment (Fig.
11B). Additionally, no P was detected in the filtrate
according to the 31P NMR data, indicating that the
catalytic activity originated from 30%HPW/mpgꢀC3N4
other than from the dissolved HPW from the leak of
catalyst. The FTꢀIR spectra (Fig. 1e) and XRD pattern
(Fig. 2g) of the recovered 30%HPW/mpgꢀC3N4 catalyst
showed no significant differences compared with the
fresh catalyst, indicating the good reusability of the
catalyst in the tandem reaction. Combined with the results
of catalytic performance of the reused catalyst, leaking
test, FTꢀIR and XRD, the 30%HPW/mpgꢀC3N4 catalyst is
recoverable and recyclable.
Acknowledgements
This work was financially supported by the National
Natural Sciences Foundation of China (Nos.2090618 and
21236001), the Natural Sciences Foundation of Hebei
province (No. B2010000027, B2015202262), Tianjin
Municipal Natural Science Foundation (15JCYBJC21000)
and Foundation of Education Bureau of Hebei Province
(QN2016152). We thank to Prof. J. Zhao for helpful
comments.
References
1 E. Gianotti, U. Diaz, A. Veltya and A. Corma, Catal.
Sci. Technol., 2013, 3, 2677ꢀ2688.
2 U. P. N. Tran, K. K. A. Le and N. T. S. Phan, ACS
Catal., 2011, 1, 120ꢀ127.
3 J. Xu, Y. Wang, J. K. Shang, Q. Jiang and Y. X. Li,
Catal. Sci. Technol., 2016, 6, 4192ꢀ4200.
4 J. Xu, K. Shen, B. Xue and Y. X. Li, J. Mol. Catal. A:
Chem., 2013, 372, 105ꢀ113.
4. Conclusions
A singleꢀsite bifunctional HPW/mpgꢀC3N4 with different
HPW loading was prepared by a facile impregnation
method via electrostatic interaction between HPW and
protonated mpgꢀC3N4. According to the results of NH3ꢀ
TPD, the total acid amounts of 20%HPW/mpgꢀC3N4 and
30%HPW/mpgꢀC3N4 are 0.385 and 0.467 mmol·gꢀ1,
respectively. 30%HPW/mpgꢀC3N4 has good catalytic
performance in the oxidationꢀKnoevenagel condensation
tandem reaction for various substituted benzyl alcohol.
The high catalytic performance of 30%HPW/mpgꢀC3N4
(98.4% benzyl alcohol conversion and 96.2% selectivity
to benzylidene malononitrile) is attributed to good
catalytic performance of HPW in the oxidation and
Knoevenagel condensation, respectively. Simultaneously,
the excellent catalytic performance is also attributed to
good dispersion of HPW over mpgꢀC3N4 and the
cooperative effects of HPW and mpgꢀC3N4 for the
Knoevenagel condensation. The present approach
provides a promising and universal strategy for the
construction of hybrid catalysts based on HPW and
mesoporous materials for tandem reaction.
5 V. N. Panchenko, M. M. Matrosova, J. Jeon, J. W. Jun,
M. N. Timofeeva and S. H. Jhung, J. Catal., 2014,
316, 251ꢀ259.
6 F. Pang, M. Y. He and J. P. Ge, Chem. Eur. J., 2015, 21,
1ꢀ10.
7 Y. Q. Jia, Y. J. Fang, Y. K. Zhang, H. N. Miras and Y. F.
Song, Chem. Eur. J., 2015, 21, 14862ꢀ14870.
8 G. B. B. Varadwaj, S. Rana and K. M. Parida, Dalton
Trans., 2013, 42, 5122ꢀ5129.
9 K. M. Parida, S. Mallick, P. C. Sahoo and S. K. Rana,
Appl. Catal. A: Gen., 2010, 381, 226ꢀ232.
10 G. Postole, B. Chowdhury, B. Karmakar, K. Pinki, J.
Banerji and A. Auroux, J. Catal., 2010, 269, 110ꢀ121.
11 A. Dhakshinamoorthy and H. Garcia, ChemSusChem.,
2014, 7, 2392ꢀ2410.
12 L. L. Chng, N. Erathodiyil and J. Y. Ying, Acc. Chem.
Res., 2013, 46, 1825ꢀ1837.
13 J. M. Lee, Y. Na, H. Han and S. Chang, Chem. Soc.
Rev., 2004, 33, 302ꢀ312.
14 J. C. Wasilke, S. J. Obrey, R. T. Baker and G. C. Bazan,
Chem. Rev., 2005, 105, 1001ꢀ1020.
This journal is © The Royal Society of Chemistry 20xx
Catal. Sci. Technol., 2016, 00, 1-11 | 9
Please do not adjust margins

Catalysis Science & Technology
Page 10 of 28
View Article Online
DOI: 10.1039/C6CY01669C
Journal Name ARTICLE
15 N. R. Shiju, A. H. Alberts, S. Khalid, D. R. Brown and
G. Rothenberg, Angew. Chem., 2011, 123, 9789ꢀ9793.
16 L. Zhong, C. Anand, K. S. Lakhi, G. Lawrence and A.
Vinu, Sci. Rep., 2015, 5, 12901.1ꢀ12901.8.
17 L. C. Lee, J. Lu, M. Weck and C. W. Jones, ACS
Catal., 2016, 6, 784ꢀ787.
and H. Vali, Tetrahedron, 2014, 70, 6114ꢀ6119.
35 Y. Leng, J. Wang, D. Zhu, M. Zhang, P. Zhao, Z. Long
and J. Huang, Green Chem., 2011, 13, 1636ꢀ1639.
36 Y. Leng, P. P. Zhao, M. J. Zhang and J. Wang, J. Mol.
Catal. A: Chem., 2012, 358, 67ꢀ72.
37 H. A. Oskooie, M. M. Heravi, F. Derikvand and M.
Khorasani, Synthetic Commun., 2006, 36, 2819ꢀ2823.
38 B. Viswanadham, P. Jhansi, K. V. R. Chary, H. B.
Friedrich and S. Singh, Catal Lett, 2016, 146, 364ꢀ
372.
18 L. Xu, C. G. Li, K. Zhang and P. Wu, ACS Catal.,
2014, 4, 2959ꢀ2968.
19 R. Goyal, B. Sarkar, N. Lucus and A. Bordoloi,
ChemCatChem, 2014, 6, 3091ꢀ3095.
20 F. Zhang, H. Y. Jiang, X. Y. Li, X. T. Wu and H. X. Li,
ACS Catal., 2014, 4, 394ꢀ401.
39 Y. J. Chen, R. Tan, W. G. Zheng, Y. Y. Zhang, G. W.
Zhao and D. H. Yin, Catal. Sci. Technol., 2014, 4,
4084ꢀ4092.
21 T. Toyao, M. Saito, Y. Horiuchi and M. Matsuoka,
Catal. Sci. Technol., 2014, 4, 625ꢀ628.
40 B. L. Li, J. Li, X. M. Wang, Z. X. Wan and L. C. Wang,
Kinet. Catal., 2013, 54, 69ꢀ75.
22 D. K. Wang and Z. H. Li, Catal. Sci. Technol., 2015, 5,
1623ꢀ1628.
41 X. L. Yang, L. M. Qiao and W. L. Dai, Micropor.
Mesopor. Mat., 2015, 211, 73ꢀ81.
23 D. Jagadeesan, Appl. Catal. A: Gen., 2016, 511, 59ꢀ77.
24 Y. Qi, Y. Luan, X. Peng, M. Yang, J. Y. Hou and G.
Wang, Eur. J. Inorg. Chem., 2015, 2015, 5099ꢀ5105.
25 C. Chen, H. M. Yang, J. Z. Chen, R. Zhang, L. Guo, H.
M. Gan, B. N. Song, W. W. Zhu, L. Hua and Z. S.
Hou, Catal. Commun., 2014, 47, 49ꢀ53.
42 F. M. Zhang, Y. Jin, J. Shi, Y. J. Zhong, W. D. Zhu and
M. S. ElꢀShall, Chem. Eng. J., 2015, 269, 236ꢀ244.
43 L. Y. Liu, Y. Zhang and W. Tan, Ultrason. Sonochem.,
2014, 21, 970ꢀ974.
44 L. Y. Liu, Y. Zhang and W. Tan, Front. Chem. Sci.
Eng., 2013, 7, 422ꢀ427.
26 W. J. Ang, Y. S. Chng and Y. L. Lam, RSC Adv., 2015,
5, 81415ꢀ81428.
45 H. F. Wang, L. P. Fang, Y. F. Yang, R. B. Hu and Y. J.
Wang, Appl. Catal. A: Gen., 2016, 520, 35ꢀ43.
46 W. F. Zhang, Q. S. Zhao, T. Liu, Y. Gao, Y. Li, G. L.
Zhang, F. B. Zhang and X. B. Fan, Ind. Eng. Chem.
Res., 2014, 53, 1437ꢀ1441.
27 B. Sarmah, R. Srivastava, P. Manjunathan and G. V.
Shanbhag, ACS Sustainable Chem. Eng., 2015, 3,
2933ꢀ2943.
28 Y. Horiuchi, D. D. Van, Y. Yonezawa, M. Saito, S.
Dohshi, T. H. Kim and M. Matsuoka, RSC Adv., 2015,
5, 72653ꢀ72658.
47 H. F. Wang, L. Zhang, Y. F. Yang, L. P. Fang and Y. J.
Wang, Catal. Commun., 2016, 87, 27ꢀ31.
29 C. S. Hinde, W. R. Webb, B. K. J. Chew, H. R. Tan, W.
H. Zhang, T. S. A. Horbd and R. Raja, Chem.
Commun., 2016, 52, 6557ꢀ6560.
48 J. J. He, H. Q. Sun, S. Indrawirawan, X. G. Duan, M.
O. Tade and S. B. Wang, J. Colloid Interf. Sci., 2015,
456, 15ꢀ21.
30 M. R. Farsani, E. Assady, F. Jalilian, B. Yadollahi and
H. A. Rudbari, J. Iran. Chem. Soc., 2015, 12, 1207ꢀ
1212.
49 K. X. Li, L. S. Yan, Z. X. Zeng, S. L. Luo, X. B. Luo,
X. M. Liu, H. Q. Guo and Y. H. Guo, Appl. Catal. B:
Environ., 2014, 156-157, 141ꢀ152.
31 W. Zhao, Y. S. Zhang, B. C. Ma, Y. Ding and W. Y.
Qiu, Catal. Commun., 2010, 11, 527ꢀ531.
32 Y. Ding, W. Zhao, H. Hua and B. C. Ma, Green Chem.,
2008, 10, 910ꢀ913.
50 X. J. Luo and C. Yang, Phys. Chem. Chem. Phys.,
2011, 13, 7892ꢀ7902.
51 E. Grinenval, J. M. Basset and F. Lefebvre, J. Inorg.
Chem., 2013, 2013, 1ꢀ8.
33 C. Ragupathi, J. J. Vijaya, S. Narayanan, S. K.
Jesudoss and L. J. Kennedy, Ceram. Int., 2015, 41,
2069ꢀ2080.
52 C. L. Hill, O. A. Kholdeeva, in: M. G. Clerici, in
Liquid Phase Oxidation via Heterogeneous Catalysis:
Organic Synthesis and Industrial Applications, ed. O.
A. Kholdeeva, John Wiley & Sons, Inc. Hoboken,
34 B. Karimi, F. B. Rostami, M. Khorasani, D. Elhamifar
This journal is © The Royal Society of Chemistry 20xx
Catal. Sci. Technol., 2016, 00, 1-11 | 10
Please do not adjust margins

Page 11 of 28
Journal Name ARTICLE
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C6CY01669C
2013, cha. 6, pp. 263ꢀ319.
Wang, Catal. Commun., 2015, 70, 6ꢀ11.
53 K. Liu, Y. Q. Xu, Z. X. Yao, H. N. Miras and Y. F.
Song, ChemCatChem, 2016, 92, 112ꢀ117.
71 R. Liu, X. N. Xia, X. Z. Niu, G. Z. Zhang, Y. B. Lu, R.
F. Jiang and S. L. He, Appl. Clay Sci., 2015, 105-106,
71ꢀ77.
54 Y. F. Zhu, M. Y. Zhu, L. H. Kang, F. Yu and B. Dai,
Ind. Eng. Chem. Res., 2015, 54, 2040ꢀ2047.
55 M. B. Ansari, H. Jin, M. N. Parvin and S. E. Park,
Catal. Today, 2012, 185, 211ꢀ216.
72 T. Y. Ma, Y. H. Tang, S. Dai and S. Z. Qiao, Small,
2014, 10, 2382ꢀ2389.
73 W. J. Ong, L. L. Tan, S. P. Chai, S. T. Yong and A. R.
Mohamed, Nano Energy, 2015, 13, 757ꢀ770.
74 E. V. RamosꢀFernandez, C. Pieters, B. V. D. Linden, J.
JuanꢀAlcañiz, P. SerraꢀCrespo, M. W. G. M.
Verhoeven, H. Niemantsverdriet, J. Gascon and F.
Kapteijn, J. Catal., 2012, 289, 42ꢀ52.
56 F. Z. Su, M. Antoniettia and X. C. Wang, Catal. Sci.
Technol., 2012, 2, 1005ꢀ1009.
57 Y. Wang, X. C. Wang, M. Antonietti and Y. J. Zhang,
ChemSusChem, 2010, 3, 435ꢀ439.
58 J. Xu, F. Wu, Q. Jiang and Y. X. Li, Catal. Sci.
Technol., 2014, 5, 447ꢀ454.
75 J. Xu, F. Wu, H. T. Wu, B. Xue, Y. X. Li and Y. Cao,
Micropor. Mesopor. Mat., 2014, 198, 223ꢀ229.
76 W. J. Ong, L. K. Putri, L. L. Tan, S. P. Chai and S. T.
Yong, Appl. Catal. B: Environ., 2016, 180, 530ꢀ543.
77 Q. Su, J. Sun, J. Q. Wang, Z. F. Yang, W. G. Cheng
and S. J. Zhang, Catal. Sci. Technol., 2014, 4, 1556ꢀ
1562.
59 J. A. Singh, S. H. Overbury, N. J. Dudney, M. J. Li and
G. M. Veith, ACS Catal., 2012, 2, 1138ꢀ1146.
60 S. Kumar, T. Surendar, B. Kumar, A. Baruah and V.
Shanker, J. Phys. Chem. C, 2013, 117, 26135ꢀ26143.
61 W. Z. Shen, L. W. Ren, H. Zhou, S. C. Zhang and W.
B. Fan, J. Mater. Chem., 2011, 21, 3890ꢀ3894.
62 J. Liu, Y. Liu, W. Yang, H. Guo, F. Fang and Z. H.
Tang, J. Mol. Catal. A: Chem., 2014, 393, 1ꢀ7.
63 G. Q. Luo, L. H. Kang, M. Y. Zhu and B. Dai, Fuel
Process. Technol., 2014, 118, 20ꢀ27.
78 L. Zhang, H. Q. He, R. K. A. Rasheed, W. J. Zhou, Y.
H. Xue, O. L. Ding and S. H. Chan, J. Power Sources,
2013, 221, 318ꢀ327.
79 R. Liu, X. Z. Niu, X. N. Xia, Z. B. Zeng, G. Z. Zhang
and Y. B. Lu, RSC Adv., 2015, 5, 62394ꢀ62401.
64 B. S. Li, Z. X. Liu, C. Y. Han, W. Ma and S. J. Zhao, J.
Colloid Interface Sci., 2012, 377, 334ꢀ341.
80 J. J. Zhu, P. Xiao, H. L. Li and S. A. C. Carabineiro ,
́
65 L. Chen and B. Bai, Int. J. Photoenergy, 2013, 2013,
6687ꢀ6692.
ACS Appl. Mater. Inter., 2014, 6, 16449ꢀ16465.
81 Z. K. Zhao, Y. T. Dai, J. H. Lin and G. R. Wang, Chem.
Mater., 2014, 26, 3151ꢀ3161.
66 Z. S. Li, S. Y. Yang, J. M. Zhou, D. H. Li, X. F. Zhou,
C. Y. Ge and Y. P. Fang, Chem. Eng. J., 2014, 241,
344ꢀ351.
82 S. N. Talapaneni, S. Anandan, G. P. Mane, C. Anand,
D. S. Dhawale, S. Varghese, A. Mano, T. Moricd and
A. Vinu, J. Mater. Chem., 2012, 22, 9831ꢀ9840.
83 S. Verma, R. B. N. Baig, M. N. Nadagouda and R. S.
Varma, ACS Sustainable Chem. Eng., 2016, 4, 1094ꢀ
1098.
67 D. A. Giannakoudakis, M. Seredych, E. R. Castellón
and T. J. Bandosz, ChemNanoMat, 2016, 79, 187ꢀ209.
68 S. X. Min and G. X. Lu, J. Phys. Chem. C, 2012, 116,
19644ꢀ19652.
69 F. Goettmann, A. Fischer, M. Antonietti and A.
Thomas, Angew. Chem. Int. Ed., 2006, 45, 4467ꢀ4471.
70 H. F. Wang, R. B. Hu, Y. F. Yang, M. D. Gao and Y. J.
84 Z. H. Weng, J. Y. Wang, S. H. Zhang, C. Yan and X. G.
Jian, Appl. Catal. A: Gen., 2008, 339, 145ꢀ150.
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Fig. 1 FTꢀIR spectra (A) and partial enlarged detail (B) of mpgꢀC3N4 (a), 20%HPW/mpgꢀC3N4 (b), 30%HPW/mpgꢀC3N4 (c),
40%HPW/mpgꢀC3N4 (d), Rꢀ30%HPW/mpgꢀC3N4 (e) and HPW (f).

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Fig. 2 XRD patterns of bulk gꢀC3N4 (a), mpgꢀC3N4 (b), HPW (c), 20%HPW/mpgꢀC3N4 (d), 30%HPW/mpgꢀC3N4 (e), 40%HPW/mpgꢀC3N4 (f)
and Rꢀ30%HPW/mpgꢀC3N4 (g).

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Fig. 3 Solidꢀstate 31P NMR spectra (A) and zeta potential (B).

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Fig. 4 XPS wide scan spectra of 30%HPW/mpgꢀC3N4 (A) and P 2p, W 4f, C 1s and N 1s XPS spectrum of 30%HPW/mpgꢀC3N4 (B–E).

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Fig. 5 TGA analysis of HPW (a), 40%HPW/mpgꢀC3N4 (b), 30%HPW/mpgꢀC3N4 (c), 20%HPW/mpgꢀC3N4 (d) and mpgꢀC3N4 (e).

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Fig. 6 N2 adsorptionꢀdesorption isotherms of mpgꢀC3N4 (a), 20%HPW/mpgꢀC3N4 (b), 30%HPW/mpgꢀC3N4 (c) and gꢀC3N4 (d) and the
corresponding PSD curves (inset).

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Fig. 7 SEM images of mpgꢀC3N4 (A) and 30%HPW/mpgꢀC3N4 (B) and TEM of 30%HPW/mpgꢀC3N4 (C, D).

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Fig. 8 Benzyl alcohol oxidation (A) and Knoevenagel condensation reaction (B) using different catalysts, conversion of A1 (black),
selectivity to B1 (red), selectivity to benzoic acid (green), conversion of B1 (blue) and selectivity to C1 (pink). Reaction conditions: (A) A1 (3
mmol), H2O2/A1 = 3 : 1 (molar ratio), H2O (3 mL), 90 °C, 3 h; (B) B1 (3 mmol), B1/malononitrile = 1 : 2 (molar ratio), H2O (3 mL), 90 °C, 4
h for gꢀC3N4 and mpgꢀC3N4, 1 h for others.

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Fig. 9 Oneꢀpot oxidationꢀKnoevenagel tandem reaction, conversion of A1 (black), selectivity to C1 (pink), selectivity to B1 (red) and
selectivity to benzoic acid (green). Reaction conditions: A1 (3 mmol), H2O (3 mL), 90 °C, 3 + 1 h, H2O2/A1/malononitrile = 3 : 1 : 2 (molar
ratio), catalyst: a) catalyst 150 mg, b) HPW 40 mg, c) physical mixture of HPW 40 mg and mpgꢀC3N4 110 mg.

Page 21 of 28
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Fig. 10 (A) Reaction profile of oxidationꢀKnoevenagel condensation of A1 and malononitrile, (a) A1, (b) B1 and (c) C1. (B) Kinetic study for
conversion of A1 over 30%HPW/mpgꢀC3N4. Reaction conditions: A1 (3 mmol), H2O (3 mL), 30%HPW/mpgꢀC3N4 (150 mg),
H2O2/A1/malononitrile = 3 : 1 : 2 (molar ratio), 90 °C, 3 + 1 h.

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Fig. 11 (A) Recyclability test of 30%HPW/mpgꢀC3N4 catalyst; (B) Hot filtration experiments: (a) with the presence of 30%HPW/mpgꢀC3N4;
(b) 30%HPW/mpgꢀC3N4 was hot filtrated at 1 h.

Page 23 of 28
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Table 1 Textural parameters of gꢀC3N4, mpgꢀC3N4, 20%HPW/mpgꢀC3N4 and 30%HPW/mpgꢀC3N4
sample
gꢀC3N4
Pore volume (cm3·gꢀ1)
SBET ( m2·gꢀ1)
Average pore sizea (nm)
0.0627
0.206
12.2
146
124
107
21.3
9.98
9.71
9.67
mpgꢀC3N4
20%HPW/mpgꢀC3N4
30%HPW/mpgꢀC3N4
0.0814
0.0562
a) Average pore size determined by the desorption branch of isotherms.

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Table 2 OxidationꢀKnoevenagel tandem reactions with different substrates
R2
R3
R2
R3
HPW/mpg-C3N4
R1
OH
R1
O
R1
H2O2
H2O
B
A
C
Selectivity (%)
Entry
A
R2
R3 Time (h)
Catalyst
Conversion A (%)
C
B
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
98.4
86.2
96.7
97.6
88.5
97.1
98.9
87.3
98.4
95.3
85.3
96.2
84.4
76.8
86.0
61.9
57.6
63.4
53.7
51.9
60.4
87.6
85.2
89.8
96.2
82.8
74.8
98.4
85.2
77.3
96.8
81.6
75.2
96.2
83.7
74.3
95.6
82.1
70.9
96.9
84.3
71.9
97.1
87.1
70.8
95.3
87.7
74.3
0.421
0.346
1.53
OH
1
CN CN
CN CN
CN CN
CN CN
CN CN
CN CN
CN CN
CN CN
3+1
3+1
3+1
5+1
5+1
5+1
5+1
7+1
OH
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
2.39
2
3
4
5
6
7
8
2.21
3.67
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
0.343
0.374
1.83
OH
H3C
H3CO
F
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
1.42
OH
0.415
2.32
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
0.563
0.392
2.84
OH
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
0.421
0.418
3.04
OH
F
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
0.371
0.336
3.27
OH
F
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
0.430
0.371
1.89
OH
N

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Table 2 (continued) OxidationꢀKnoevenagel tandem reactions with different substrates
Selectivity (%)
Entry
A
R2
R3
Time (h)
Catalyst
Conversion A (%)
C
B
30%HPW/mpgꢀC3N4
HPW+mpgꢀC3N4
HPW
98.6
86.8
96.9
98.4
91.6
79.8
67.1
82.7
5.36
4.36
8.24
13.1
OH
OH
9
CN
COOEt
3+4
30%HPW/mpgꢀC3N4
10
COOEt COOEt
3+4
HPW+mpgꢀC3N4
HPW
86.5
96.6
71.6
57.9
12.3
15.8
Reaction conditions: A (3 mmol), H2O (3 mL), 90 °C, H2O2/A/active methylene compound = 3 : 1 : 2 (molar ratio), catalyst:
(a) 30%HPW/mpgꢀC3N4 150 mg, (b) physical mixture of HPW 40 mg and mpgꢀC3N4 110 mg and (c) HPW 40 mg.

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Table 3 Comparison of catalytic activity between 30%HPW/mpgꢀC3N4 and reported catalysts
Temperature
Time
(h)
48
40
13
11
2.5
7
Conversion Selectivity to C1
Entry
Catalyst
Oxidant
Ref.
(°C)
90
(%)
100
88
(%)
91
1a
2a
3
ZrꢀMOFꢀNH2
NH2ꢀMILꢀ101(Fe)
Au@MILꢀ53(NH2)
Pd/LSꢀATꢀOH−
Pd1–Au1/LDH
O2
O2
21
25
72
22
O2
100
85
99
99
24
4
O2
89.6
99
88.3
98.0
79 (86)
84.5
88.9
99
18
5
O2
80
25
6
Bispidineꢀcopper
OMSꢀ2ꢀSF
O2
40
ꢀ
26
7
O2
85/70
85/70
80
9.5
9.5
4
99.5
91.6
99
27
27
8
OMSꢀ2ꢀU
O2
9
TrisꢀLDHꢀZn4(PW9)2
30%HPW/mpgꢀC3N4
H2O2
H2O2
53
10
90
4
98.4
96.2
This study
a Photocatalytic aerobic oxidationꢀKnoevenagel condensation reaction by light irradiation.

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DOI: 10.1039/C6CY01669C
CN
CHO
NC
CN
HPW/mpg-C3N4
OH
CN
H2O2
H2O
A1
B1
C1
Scheme 1 OxidationꢀKnoevenagel tandem reaction over HPW/mpgꢀC3N4.

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Table of contents entry
A single-site bifunctional catalyst for oxidation-Knoevenagel condensation tandem reaction was
prepared by immobilizing H3PW12O40 on mpg-C3N4 via electrostatic interaction.