One-pot synthesis of a hierarchical microporous-mesoporous phosphotungstic acid-HKUST-1 catalyst and its application in the selective oxidation of cyclopentene to glutaraldehyde

Article abstract of DOI:10.1016/S1872-2067(15)60972-X

A hierarchical microporous-mesoporous metal-organic framework of HKUST-1(Cu)-encapsulated phosphotungstic acid (HPW) material, referred to as HPWs@Meso-HKUST-1, is prepared by a one-pot synthesis method using cetyltrimethylammonium bromide as the supramolecular template. The addition of HPWs to the synthesis mixture of hierarchical porous HKUST-1 results in the direct encapsulation of HPWs inside the mesopores of the HKUST-1 structure, with a homogeneous distribution over the HKUST-1 crystals, which is confirmed by XRD, FT-IR, N₂ adsorption, UV-Vis DRS, and TEM. FT-IR-CO adsorption experiments indicated that additional Lewis acid sites were present in the HPWs@Meso-HKUST-1 sample. The novel heterogeneous catalyst demonstrates excellent catalytic performance for the selective oxidation of cyclopentene (CPE) to glutaraldehyde (GA) using tert-butyl hydroperoxide and acetonitrile (MeCN) as the oxidant and solvent, respectively. The high activity of the catalyst is attributed to the mesostructure of the catalyst and the nature and appropriate abundance of the HPWs - being highly dispersed with the addition of Lewis sites. After a reaction for 36 h, the 30% wt% HPWs@Meso-HKUST-1 catalyst exhibits a CPE conversion of 92.5% and a high GA yield of 73%. Furthermore, the HPWs@Meso-HKUST-1 material is sufficiently stable to prevent the leaching of HPWs, and behaves as a true heterogeneous catalyst that can be repeatedly recycled without sustaining a loss of activity and selectivity in the selective oxidation of CPE.

Full text of DOI:10.1016/S1872-2067(15)60972-X

Chinese Journal of Catalysis 36 (2015) 1875–1885
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
One‐pot synthesis of a hierarchical microporous‐mesoporous
phosphotungstic acid‐HKUST‐1 catalyst and its application in the
selective oxidation of cyclopentene to glutaraldehyde
Xinli Yang a,#, Liming Qiao a, Weilin Dai b,*
a School of Chemistry & Chemical Engineering, Henan University of Technology, Zhengzhou 450001, Henan, China
b Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A hierarchical microporous‐mesoporous metal‐organic framework of HKUST‐1(Cu)‐encapsulated
phosphotungstic acid (HPW) material, referred to as HPWs@Meso‐HKUST‐1, is prepared by a
one‐pot synthesis method using cetyltrimethylammonium bromide as the supramolecular template.
The addition of HPWs to the synthesis mixture of hierarchical porous HKUST‐1 results in the direct
encapsulation of HPWs inside the mesopores of the HKUST‐1 structure, with a homogeneous dis‐
tribution over the HKUST‐1 crystals, which is confirmed by XRD, FT‐IR, N2 adsorption, UV‐Vis DRS,
and TEM. FT‐IR‐CO adsorption experiments indicated that additional Lewis acid sites were present
in the HPWs@Meso‐HKUST‐1 sample. The novel heterogeneous catalyst demonstrates excellent
catalytic performance for the selective oxidation of cyclopentene (CPE) to glutaraldehyde (GA)
using tert‐butyl hydroperoxide and acetonitrile (MeCN) as the oxidant and solvent, respectively.
The high activity of the catalyst is attributed to the mesostructure of the catalyst and the nature and
appropriate abundance of the HPWs—being highly dispersed with the addition of Lewis sites. After
a reaction for 36 h, the 30% wt% HPWs@Meso‐HKUST‐1 catalyst exhibits a CPE conversion of
92.5% and a high GA yield of 73%. Furthermore, the HPWs@Meso‐HKUST‐1 material is sufficiently
stable to prevent the leaching of HPWs, and behaves as a true heterogeneous catalyst that can be
repeatedly recycled without sustaining a loss of activity and selectivity in the selective oxidation of
CPE.
Received 15 July 2015
Accepted 10 September 2015
Published 20 November 2015
Keywords:
Metal‐organic frameworks
HKUST‐1
Phosphotungstic acids
Cyclopentene
Glutaraldehyde
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
sis. HPAs have been extensively used as acid and oxidation
catalysts in many reactions since their acid‐base and redox
Heteropolyacids (HPAs), as a unique class of anionic met‐
al‐oxygen clusters of early transition metals, possess many
properties that make them candidates for application in cataly‐
properties can be tuned easily by changing the polyanion
chemical composition [1]. Phosphotungstic acid (HPW) with
the strongest Brönsted acidity in the HPAs series has promise
* Corresponding author. Tel: +86‐21‐55664678; Fax: +86‐21‐55665701; E‐mail: wldai@fudan.edu.cn
# Corresponding author. Tel: +86‐371‐67756718; Fax: +86‐371‐67756718; E‐mail: xlyang@haut.edu.cn
This work was supported by the Plan of Nature Science Fundamental Research in Henan University of Technology (2013JCYJ09), the Fundamental
Research Funds for the Henan Provincial Colleges and Universities (2014YWQQ13), and the National Natural Science Foundation of China
(20903035, 21373054).
DOI: 10.1016/S1872‐2067(15)60972‐X | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 11, November 2015

1876
Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
as a heterogenous catalyst for many organic reactions, such as
esterification, alkylation, hydrolysis, and oxidation [1,2]. How‐
ever, the pure bulk HPAs present relatively small surface areas
(< 10 m2/g) that hinder accessibility to the active sites. There‐
fore, the applications of HPAs as solid catalysts are limited.
Thus, various high‐surface‐area supports, such as silica [3,4],
activated carbon [5,6], ion‐exchange resin [7], and mesoporous
molecular sieves [8–10], have been used for HPA dispersion.
Additionally, the supported HPA catalysts usually display low
activities because of low HPA loading, HPA leaching, the con‐
glomeration and non‐uniformity of HPA particles and the deac‐
tivation of acid sites by water. Therefore, the immobilization of
HPAs in a suitable solid matrix, which can overcome these
drawbacks, is a step toward the challenging goal of catalysis.
Metal‐organic frameworks (MOFs), the newest generation of
porous materials, can be used as host matrices to encapsulate
HPAs and form a series of unique, tunable catalysts.
considerable efforts have been made to expand the pore widths
of MOFs to the mesoporous regime, including the use of elon‐
gated organic ligands, post‐synthetic modification, a combina‐
tion of mixed ligands, the use of surfactants as struc‐
ture‐directing agents, and using specially designed spacers
with hierarchical functional groups, among others. Recently,
Fang et al. [28], Xuan et al. [29], and Sun et al. [30] have inde‐
pendently reported important reviews on mesoporous MOFs.
The presence of mesopores in MOFs markedly expands their
use as hosts to accommodate large bulky molecules, allowing
their reaction or transformation without the limitations of dif‐
fusion in a confined space. However, in practice, the heat of
adsorption is somewhat reduced. Despite this reduction,
large‐pore MOFs generally outperform small‐pore MOFs;
hence, their synthesis and characterization are thoroughly in‐
vestigated and targeted for a wide range of applications.
Qiu et al. [31] have successfully applied
a surfac‐
MOFs are hybrid inorganic‐organic crystalline solids formed
by the linkage of single metal ions or metal clusters with tuna‐
ble oligotrophic organic ligands. Over the last few decades,
MOFs have attracted considerable attention because of their
unique ensemble of properties, such as high surface area, crys‐
talline open structure, tunable pore size, and functionality.
These materials have demonstrated immense potential in ap‐
plication of luminescence, magnetism, separation, gas storage,
drug delivery, and heterogeneous catalysis [11–13]. The cop‐
per‐based MOF, HKUST‐1 (Cu‐BTC or MOF‐199), with a struc‐
tural formula of Cu3(BTC)2 (BTC = 1,3,5‐benzenetricarbox‐
ylate), is one of the most intensively investigated and charac‐
terized structures in the field of MOFs [14]. This material was
first reported by Chui et al. [15] in 1999, and its crystalline
structure consists of a so‐called copper paddle wheel, with a
Cu–Cu distance of 0.263 nm, where each copper atom is octa‐
hedrally coordinated by four oxygen atoms of the BTC linkers
and by one water molecule (solvent). The water molecules can
be easily removed by heating under vacuum, which leaves un‐
saturated Cu sites available for adsorption and catalytic trans‐
formation (material activation). Additionally, benzene rings are
bonded to three dimeric cupric tetracarboxylate units.
MOF‐based catalysts have to exhibit sufficient stability under
the applied reaction conditions, including thermal stability and
chemical resistance, in addition to the presence of accessible
active catalytic sites. Cu‐BTC exhibits all prerequisite proper‐
ties; hence, the material has been used as the active catalyst
itself in the cyanosilylation of carbonyl compounds [16], the
isomerization of α‐pinene oxide, the cyclization of citronellal
[17], and oxidation or epoxidation [18–21]. As a well‐known
MOF, Cu‐BTC has also been used as a stable host to encapsulate
various Keggin‐type HPAs, whose attractive catalytic perfor‐
mance can be endowed by the HPAs@Cu‐BTC [22–26].
tant‐templated route for synthesizing hierarchically micro‐ and
mesoporous HKUST‐1 with tailored porosities. Phosphotung‐
stic acid (HPW) has been proven to be an efficiently homoge‐
neous catalyst for the selective oxidation of cyclopentene (CPE)
to glutaraldehyde (GA) [32], which is extensively used for dis‐
infection and sterilization. The selective oxidation of CPE is an
important method for producing GA, as significant quantities of
CPE can be easily obtained by the selective hydrogenation of
cyclopentadiene, which is easily obtained from the decomposi‐
tion of dicyclopentadiene; dicyclopentadiene is the main
by‐product from the C‐5 fraction in the petrochemical or coking
industry [33,34]. The work herein investigates if the catalytic
activity of the HPW catalyst is enhanced when encapsulated in
the hierarchically porous HKUST‐1 support, compared with
HPW alone in the selective oxidation of CPE to GA.
Herein, the novel HPWs@Meso‐HKUST‐1 catalyst was syn‐
2+ and BTC as
thesized by a one‐pot synthesis method using Cu
the framework building block, cetyltrimethylammonium bro‐
mide (CTAB) as the structure‐directing agent, and HPW as the
active component. Analysis revealed that HPWs were uniformly
encapsulated in the disordered nanoscale mesopores of
HKUST‐1, leading to an improvement in GA yield for the selec‐
tive oxidation of CPE to GA.
2. Experimental
2.1. Catalyst preparation
HKUST‐1 was synthesized according to the hydrothermal
method described in Ref. [15].
The encapsulation of HPWs in microporous HKUST‐1 fol‐
lowed the same procedure as described in Ref. [15,35] with
respect to the synthesis mixture and cleaning. However, the
HPWs were added in situ to the Teflon container with the rest
of the mixture. The as‐prepared material was denoted as
HPWs@HKUST‐1.
The encapsulation of HPWs in the hierarchical mi‐
croporous‐mesoporous HKUST‐1(Cu) was synthesized by a
one‐pot synthesis method. In a typical synthesis, 0.70 g of
H3BTC and 0.12 g of CTAB were dissolved in 16 mL of absolute
However, hitherto, most of the MOFs reported are still re‐
stricted to the microporous regime, which hinders fast molec‐
ular diffusion and mass transfer. In addition, micropores are
seldom accessible for anchoring molecular catalysts or im‐
pregnating catalyst precursors or voluminous drug molecules,
thereby limiting their applications in fine chemical transfor‐
mation, nanoparticle formation, or drug delivery [27]. Thus,

Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
1877
ethanol.
A
separate solution containing 1.45
g
of
by means of GC‐MS. Details can be found elsewhere [37,38].
Cu(NO3)2·3H2O dissolved in 12 mL of distilled water was pre‐
pared. Both solutions were combined and mixed under vigor‐
ous stirring for approximately 30 min. Thereafter, the mixtures
were transferred into a Teflon‐lined autoclave and HPWs were
added to the Teflon container. Finally, the obtained mixtures
were isolated in the autoclave and subjected to crystallization
temperatures at 393 K for 12 h in an oven under static condi‐
tions. After the desired time, the synthesis mixture was natu‐
rally cooled to room temperature. The solid product was fil‐
tered and washed with water and ethanol. To remove CTAB, a
solvothermal treatment was performed using absolute ethanol
under reflux at 351 K for 3 h and repeated three times. The
as‐prepared catalyst was dried at 423 K for 10 h before catalyt‐
ic testing. The resulting material was referred to as
HPWs@Meso‐HKUST‐1.
3. Results and discussion
3.1. Catalyst characterization
Figure 1(a) shows the N2 adsorption‐desorption isotherms.
Table 1 shows the textural properties of the obtained Me‐
so‐HKUST‐1 and HPWs@Meso‐HKUST‐1 samples acquired
from low‐temperature N2 adsorption measurements. Fig. 1(b)
shows the pore size distributions for each sample. In relation to
the pure Meso‐HKUST‐1 sample, the very unique style of the N2
adsorption‐desorption isotherm is attributed to the combina‐
tion of type I, which is characteristic of microporous materials
at low relative pressure, and type IV, which is characteristic of
mesoporous materials with type H2 hysteresis at higher rela‐
tive pressure. These results, in combination with the pro‐
nounced hysteresis in the N2 isotherm, provide evidence for a
porous structure constructed from both mesopores and mi‐
cropores [31,39,40]. The BET surface area is given to be 611
m2/g with a mesopore volume of 0.25 cm3/g. In addition to the
mesopores with a diameter of 3.9 nm (Fig. 1(b)), the sample
contained micropores with a diameter of 0.82 nm, which is in
agreement with the micropore diameter (0.85 nm) estimated
from the crystallographic data for microporous HKUST‐1 [15].
These results are in agreement with those reported by Qiu et al.
[31] and further demonstrate that, by using a supramolecular
2.2. Characterization
Powder X‐ray diffraction (XRD) patterns were recorded on a
Rigaku D/max‐rB spectrometer with Cu Kα radiation, which
was operated at 60 mA and 40 kV. The FT‐IR measurements
were performed using an IR Prestige‐21 spectrometer
(SHIMADZU) using the KBr pellet technique. Nitrogen adsorp‐
tion and desorption isotherms were measured at 77 K using a
Micromeritics ASAP 2020 instrument after the samples were
degassed (1.33 × 10–2 Pa) at 423 K overnight. The Langmuir
surface area was estimated from the adsorption branch ac‐
cording to the Langmuir equation [36]. The BET surface area
was calculated using adsorption data within the relative pres‐
sure range 0.05 to 0.25. The mesopore pore volume was ob‐
tained from the BJH cumulative specific adsorption volume
according to the literature [31]. The mesopore size distribu‐
tions were calculated from the BJH model. Micrographs ob‐
tained from transmission electron microscopy (TEM) were
from a Philips Tecnai F20 transmission electron microscope.
The samples were supported on carbon‐coated copper grids
prior to observation. The HPW contents were determined by
means of inductively coupled plasma optical emission spec‐
troscopy (Thermo ICP‐OES 6500). UV‐Vis DR spectra were
collected on a Shimadzu UV‐2540 spectrometer using BaSO4 as
a reference. The in situ FT‐IR spectra using CO as a probe mol‐
ecule were collected on a BRUKER (Tensor 27) spectropho‐
tometer equipped with a DTGS detector at 4 cm–1 resolution on
a thin self‐supported wafer. The sample was activated in a
home‐made cell under high vacuum (residual pressure 1×10–2
Pa) at 473 K for 2 h. CO gas (p = 6.7 kPa) was dosed on the
sample for 20 min at RT.
240
(a)
230
(1)
220
210
200
190
180
170
160
(2)
(3)
c
(4)
(5)
Adsorption
Desorption
(6)
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(b)
(1)
(2)
(3)
(4)
(5)
(6)
2.3. Activity test
The activity test was performed at 303 K for 36 h with
magnetic stirring in a closed 100‐mL regular glass reactor using
t‐butylhydroperoxide (TBHP) as the oxygen‐donor and ace‐
tonitrile (MeCN) as the solvent. Quantitative analysis of the
reaction products was performed by GC and the identification
of different products in the reaction mixture was determined
0
5
10
15
20
Pore width (nm)
Fig. 1. (a) Nitrogen adsorption‐desorption isotherms and (b) pore size
distributions for (1) Meso‐HKUST‐1; (2) 8 wt%; (3) 18 wt%; (4) 25
wt%; (5) 30 wt%; (6) 33 wt% HPWs@Meso‐HKUST‐1.

1878
Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
Table 1
Physicochemical parameters of Meso‐HKUST‐1 as a function of HPW
loading.
(9)
(8)
(7)
Mesopore Mesopore
diameter volume
SLangmuir SBET
Sample
(m2/g) (m2/g)
(nm)
3.9
3.8
3.8
3.6
3.6
3.5
(cm3/g)
0.25
0.23
0.21
0.20
Meso‐HKUST‐1
863 611
557 426
559 401
480 379
452 347
432 315
(6)
8 wt% HPWs@Meso‐HKUST‐1
18 wt% HPWs@Meso‐HKUST‐1
25 wt% HPWs@Meso‐HKUST‐1
30 wt% HPWs@Meso‐HKUST‐1
33 wt% HPWs@Meso‐HKUST‐1
(5)
(4)
(3)
(2)
0.19
0.15
template such as CTAB, mesoporous HKUST‐1 with a hierar‐
chical structure was successfully fabricated, in which the mes‐
opore walls consisted of microporous frameworks [39]. After
the introduction of HPW to the synthetic system, the N2 ad‐
sorption desorption isotherms for the HPWs@Meso‐HKUST‐1
samples maintained the same shape as that for the Me‐
so‐HKUST‐1 sample; however, a reduction in the uptake capac‐
ity was observed. These results clearly demonstrate that hier‐
archically micro‐ and mesoporous HKUST‐1‐encapsulated HPW
samples can be obtained by a supramolecular template strategy
via a one‐pot synthesis method. As shown in Fig. 1(a), a no‐
ticeable shrinkage of the hysteresis loop was observed as a
function of increasing HPW content, which in turn affected the
meso‐textural properties of the HPWs@Meso‐HKUST‐1 sam‐
ples. The BET surface area, mesopore diameter, and volume of
these samples significantly decreased because of the incorpo‐
ration of HPWs into the mesoporous cages of the Me‐
so‐HKUST‐1 support (Fig. 1 and Table 1).
(1)
5
10 15 20 25 30 35 40 45 50 55 60
2/(o )
Fig. 2. XRD patterns of various samples. (1) HKUST‐1, simulated from
X‐ray data of HKUST‐1 single crystal [15]; (2) Meso‐HKUST‐1; (3) 8
wt%; (4) 18 wt%; (5) 25 wt%; (6) 30 wt%; (7) 33 wt%
HPWs@Meso‐HKUST‐1; (8) 30 wt% after the third reaction cycle; (9)
HPW.
ture‐directing agent for preparing the mesostructured
HKUST‐1 MOF. Weak and broad diffraction peaks indicate that
Meso‐HKUST‐1 is composed of small nanoscale crystals, which
are approximately 24 nm, as calculated by the application of
the Scherrer formula on the (222) diffraction peak. Further‐
more, the small‐angle XRD (SXRD) pattern of Meso‐HKUST‐1
exhibited a single low‐angle diffraction peak at 2θ = 1.38 (not
shown), suggesting
a disordered mesostructure without
long‐range order in the arrangement of the mesopores [31,42].
Meanwhile, regarding the HPWs@Meso‐HKUST‐1 samples,
there was no observable difference in the small‐angle XRD pat‐
terns when compared with the bare sample of Meso‐HKUST‐1,
indicating that the HPWs@Meso‐HKUST‐1 samples also exhibit
a disordered mesostructure without long‐range order. Addi‐
Notably, Wee et al. [41] fabricated a hierarchical variant of
microporous cubic HKUST‐1 by a dual‐templating approach at
room temperature involving HPW and CTAB as the struc‐
ture‐directing agents, which has strictly repetitive mesopores
having a width of 5 nm separated by uniform microporous
walls. The MOF framework of this new material, termed
COK‐15, is stabilized by HPW being systematically occluded in
the cavities constituting the walls between the mesopores. The
group postulated that HPW, when added to the hydrothermal
synthesis, was observed in the cavities of MOFs; however, at
room temperature, a strong interaction was observed between
Cu(II) and the Keggin‐type HPW. Thus, in the presence of CTAB
and under mild conditions, the Keggin ions served as a molecu‐
lar template for the structural motif of the MOF, while CTAB
directed these units in an ordered mesoporous structure. Ac‐
cording to the above discussion, it is clear that the HPW mole‐
cules of HPWs@Meso‐HKUST‐1 samples, synthesized via a
one‐pot hydrothermal synthesis herein, are encapsulated in the
mesopore cages of the Meso‐HKUST‐1 MOF.
XRD patterns of the synthesized materials shown in Fig. 2
are compared with that of HPW, in addition to a simulated dif‐
fractogram using the crystallographic data of HKUST‐1 [15].
The pattern of the as‐made Meso‐HKUST‐1 was in perfect
agreement with the simulated pattern of microporous
HKUST‐1, confirming the phase purity of the synthesized Me‐
so‐HKUST‐1. The results demonstrate that the crystal structure
of HKUST‐1 is well maintained using CTAB as the struc‐
tionally,
the
wide‐angle
XRD
patterns
of
the
HPWs@Meso‐HKUST‐1 samples were in good agreement with
those of Meso‐HKUST‐1 and the reported microporous
HKUST‐1, demonstrating that the crystal structure appears to
be unchanged after the encapsulation of HPWs into Me‐
so‐HKUST‐1. Nonetheless, some deviation was observed with
respect to the relative intensity at 2θ between 5.0 and 10.0.
By comparing the intensity ratio of I
(111)/I(200) for the pristine
Meso‐HKUST‐1 sample with that of the HPWs@Meso‐HKUST‐1
samples, the ratio significantly increased and then gradually
decreased as a function of increasing HPW. Another noticeable
deviation is the intensity of the I(220) reflection (~9°). However,
in this case an opposite trend to the I(111)/I(200) ratio is ob‐
served—that is, the I(220) intensity decreases and then increases
as a function in increasing HPW content. Such differences in the
diffractograms are thought to result from the introduction of
HPW into the cavities of the Meso‐HKUST‐1 material, which is
consistent with the results reported by Férey et al. [43]. HPW
peak reflections in the XRD patterns are weakly detected at 2θ
between 5.0 and 10.0 and between 21.0 and 25.0, and the
other peaks of HPW cannot be obtained from the XRD patterns

Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
1879
of Meso‐HKUST‐1‐encapsulated HPWs, which implies the even
distribution of HPWs and the absence of large HPW crystals on
the outer surface of Meso‐HKUST‐1. Fig. 2 also shows the XRD
pattern of the 30 wt% HPWs@Meso‐HKUST‐1 sample after the
third reaction cycle; the pattern was almost identical to that of
the freshly prepared catalyst, demonstrating that the Me‐
so‐HKUST‐1 crystal structure is highly stable for the selective
oxidation of CPE using TBHP and MeCN as the oxidant and sol‐
vent, respectively.
TEM is an important technique for mesostructured charac‐
terization. Fig. 3 shows several representative TEM micro‐
graphs of Meso‐HKUST‐1, freshly prepared 30 wt%
HPWs@Meso‐HKUST‐1, and the catalyst after three catalytic
cycles. It is difficult to obtain high‐quality TEM micrographs
because the HPWs@Meso‐HKUST‐1 samples have small meso‐
pore diameters and pore volumes, in addition to the
beam‐sensitive properties of MOFs. The TEM micrographs of
(6)
982
820
(5)
(4)
(3)
(2)
(1)
1084
898
400
600
800 1000 1200 1400 1600 1800
Wavenumber (cm1)
the
synthesized
Meso‐HKUST‐1,
30
wt%
Fig. 4. FT‐IR spectra of various samples. (1) Meso‐HKUST‐1; (2) 18
wt%; (3) 25 wt%; (4) 30 wt%; (5) 33 wt% HPWs@Meso‐HKUST‐1; (6)
30 wt% HPWs@Meso‐HKUST‐1 after the third reaction cycle.
HPWs@Meso‐HKUST‐1, and the catalyst after three cycles ex‐
hibited disordered worm‐hole mesopore structure, which cor‐
roborates well with the results obtained from SXRD and N2
adsorption measurements, confirming the mesoporosity of the
samples. Furthermore, the bright areas in the TEM micro‐
graphs indicate the positions of the mesopore openings. As the
mesopores had worm‐like channels and were not parallel to
other channels, the orientation of the channels varied, resulting
in the various sizes observed for the mesopore openings. On
comparing the TEM micrographs of the three samples shown in
Fig. 3, no significant change was observed in the morphology
for the Meso‐HKUST‐1 and 30 wt% HPWs@Meso‐HKUST‐1
materials, indicating that HPWs encapsulated in Me‐
so‐HKUST‐1 do not alter the Meso‐HKUST‐1 structure. Re‐
garding the catalyst after the three catalytic cycles, the degree
of disorder in the worm‐hole structure increased, which may
have resulted from the liquid‐phase reaction processes. How‐
ever, their crystal structure remained unchanged according to
the XRD results.
tetrahedron), 985 (terminal bands for W=O in the exterior WO6
octahedron), 889 and 808 cm−1 (bands for the W–Ob–W and
W–Oc–W bridges, respectively) [44,45]. The spectra of the
HPWs@Meso‐HKUST‐1 samples contained not only typical IR
bands corresponding to Meso‐HKUST‐1 but also typical IR
bands belonging to HPW with Keggin structure, revealing that
the HPW structure remains intact even when encapsulated in
the mesopores of Meso‐HKUST‐1. However, the characteristic
bands at 889 and 808 cm−1 shifted to higher wavenumbers,
probably because of confinement effects of the pores within the
Meso‐HKUST‐1 matrix for the guest HPW molecules. The same
phenomenon was also observed for MIL‐101 reported by
Zhang et al. [46]. For the 30 wt% HPWs@Meso‐HKUST‐1 sam‐
ple, the FT‐IR spectra were the same after the third catalytic
cycle, indicating that the HPWs@Meso‐HKUST‐1 material has a
highly stable structure in the selective oxidation reaction sys‐
tem, which is in agreement with the XRD result.
FT‐IR measurements were performed to determine whether
the Meso‐HKUST‐1 and HPW structure were preserved in the
composite materials. Fig. 4 shows the FT‐IR spectra of different
materials in the skeletal mode region. The HPWs possessing
Keggin structures exhibited several strong and typical FT‐IR
bands at 1084 (stretching frequency of P–O in the central PO4
CO adsorption followed by in situ infrared spectroscopy was
employed to investigate the nature of the acid sites residing on
the surface of Meso‐HKUST‐1 and HPWs‐encapsulated Me‐
so‐HKUST‐1 materials (30 wt% HPWs@Meso‐HKUST‐1). Fig. 5
shows the FT‐IR spectra of the samples recorded after outgas‐
Fig. 3. TEM micrographs of various samples. (a) Meso‐HKUST‐1; (b) 30 wt% HPWs@Meso‐HKUST‐1; (c) 30 wt% HPWs@Meso‐HKUST‐1 after the
third reaction cycle.

1880
Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
HPWs@Meso‐HKUST‐1 sample, in addition to the two 2170
and 2190 cm−1 bands in common with the Meso‐HKUST‐1 sam‐
ple, a third band centered at 2206 cm−1 was observed (Fig.
5(c)). The assignment is not straightforward; however, one
hypothesis is the presence of secondary Lewis acid sites, dif‐
fering from the Cu2+ environment present in the Me‐
so‐HKUST‐1 sample. The newly formed Lewis acid sites are
possibly formed by two new species: (i) a series of defects form
during the encapsulation of the polyanion forming new Lewis
acid sites, or (ii) Cu2+ sites possessing varying acidity because
of the presence of HPWs [47]. This is in agreement with obser‐
vations on Cr‐MIL‐101 encapsulated HPWs, an active nano‐
material for catalyzing the alcoholysis of styrene oxide [47].
The CO probing study reveals that an additional Lewis acid site
is noted for the 30 wt% HPWs@Meso‐HKUST‐1 sample, which
is essential to catalyze the selective oxidation of CPE to GA.
Figure 6 shows a comparison of the UV‐Vis diffuse reflec‐
tance spectra of the different HPW‐encapsulated samples with
those of the bare Meso‐HKUST‐1 and bulk HPWs. Two main
absorptions were observed in the HPW spectrum: the first was
centered at 255 nm, which is attributed to the oxygen‐tungsten
charge‐transfer absorption band for Keggin anions; the second
broad absorption in HPW was centered at 360 nm [49,50].
Furthermore, two broad absorptions were also observed at
300 and 600 nm, respectively, in the spectra of the bare Me‐
so‐HKUST‐1 sample, which may be attributed to the oxy‐
gen‐copper charge‐transfer absorption bands in Me‐
so‐HKUST‐1. On the addition of HPW, in addition to the bands
of the Meso‐HKUST‐1 support, HPWs@Meso‐HKUST‐1 samples
displayed the bands of HPW at 255 and 360 nm. These results
provide clear evidence of the presence of HPW, further indi‐
cating that the Keggin molecules are intact after direct inclusion
in the porous structure.
(a)
2170
2118
(2)
(1)
(b)
2190
(c)
2206
2250
2200
2150
Wavenumber (cm1)
2100
2050
3.2. Catalytic activity tests for the selective oxidation of CPE to
GA
Fig. 5. (a) FT‐IR spectra of (1) Meso‐HKUST‐1 and (2) 30 wt%
HPWs@Meso‐HKUST‐1 recorded after outgassing at 473 K for 2 h, after
adsorption of CO at room temperature; (b) and (c) peak‐fitting FT‐IR
spectra of Meso‐HKUST‐1 and 30 wt% HPWs@Meso‐HKUST‐1, respec‐
tively.
The catalytic performance of the new HPWs@Meso‐
sing at 473 K for 2 h, after adsorption of CO at room tempera‐
ture. Both samples display two intense and broad bands posi‐
tioned at 2118 and 2170 cm−1 (Fig. 5(a)). The former corre‐
sponds to CO physisorbed species [47,48]. The latter band has
been reported to relate to the heterogeneity of the Lewis acid
sites in Meso‐HKUST‐1 [48]. After HPWs were incorporated
into Meso‐HKUST‐1, the band at 2170 cm−1 increased in inten‐
sity and became broader. To establish the difference between
the two samples, a curve‐fitting procedure was adopted to an‐
alyze the broad band centered at 2170 cm−1 according to pre‐
vious works investigating Lewis sites in MIL‐100 materials
reported by Daturi’s group [48]. Peak‐fitting results of the
FT‐IR spectra corresponding to the two samples are summa‐
rized in Fig. 5(b) and 5(c). For the Meso‐HKUST‐1 sample, two
main ν(CO) bands are obtained (2170 and 2190 cm−1, Fig.
5(b)), which are assigned to CO coordinated on Lewis acid
sites; that is, coordinative Cu sites. However, for the 30 wt%
(7)
(6)
(5)
(4)
(3)
(2)
(1)
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 6. UV‐Vis diffuse reflectance spectra of various samples. (1) HPW;
(2) Meso‐HKUST‐1; (3) 8 wt%; (4) 18 wt%; (5) 25 wt%; (6) 30 wt%
HPWs@Meso‐HKUST‐1; (7) 33 wt% HPWs@Meso‐HKUST‐1.

Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
1881
HKUST‐1 materials was assessed for the selective oxidation of
CPE to GA with TBHP in MeCN. Aqueous H2O2 and tert‐butyl
alcohol were also chosen as the oxidant and solvent, respec‐
tively. However, H2O2 rapidly decomposed and released a sig‐
timum catalyst. However, increasing the HPW content to
greater than 30 wt% results in a noticeable CPE conversion
decrease (73.9%), and a significantly lower yield (54.2%) of GA
was obtained. The results are likely to be attributed to the fact
that an excess of HPWs inevitably affects the meso‐textural
properties of the HPWs@Meso‐HKUST‐1 samples. As com‐
pared with those of pure Meso‐HKUST‐1, the BET surface area,
mesopore diameter, and volume of the HPWs@Meso‐HKUST‐1
sample significantly decreased (Table 1), thus hindering the
mass transfer of the reactants to the active centers. The intri‐
guing difference in the catalytic performance of these
HPWs@Meso‐HKUST‐1 samples prompted the further investi‐
gation of the influence of the mesostructure on the catalytic
performance, and Table 2 lists the catalytic result undergoing
the selective oxidation reaction over 30 wt% HPWs@HKUST‐1
material containing microporosity only. The 30 wt%
HPWs@HKUST‐1 catalyst exhibited moderate activity for the
selective oxidation of CPE with TBHP; however, the CPE con‐
version only reached 76.4%, with a GA selectivity of 20.1%,
thus leading to a low GA yield. The reduced catalytic efficiency
may be related to the fact that the microporous structure of 30
wt% HPWs@HKUST‐1 is not suitable for the formation of the
larger bulky GA molecule, but rather is beneficial for the for‐
mation of the comparatively smaller molecules of cyclopente‐
none. The significant differences in the catalytic performance
among the HPWs@Meso‐HKUST‐1 catalysts indicate that the
HPW content affects the textural properties of the Me‐
so‐HKUST‐1 MOF in the HPWs@Meso‐HKUST‐1 catalysts, thus
leading to varying degrees of catalytic performance, and the
presence of the highly dispersed HPWs in the MOF matrices
having a mesostructure is necessary for the selective oxidation
of CPE to GA using TBHP as the oxidant.
To optimize the product yield and selectivity, 30 wt%
HPWs@Meso‐HKUST‐1 was selected as the catalyst (Table 3)
for investigating the effects of varying reaction parameters (i.e.,
reaction temperature, reaction solvent, reaction time, catalyst
loading, and TBHP concentration) on the selective oxidation of
CPE to GA using TBHP as the oxidant. Table 3 lists the results of
these observations. In general, the nature of the solvent plays
an important role in catalytic reactions performed in the liquid
phase. As the 30 wt% HPWs@Meso‐HKUST‐1 catalyst is com‐
pletely insoluble in organic solvents such as ethanol, tert‐butyl
alcohol, acetone, and MeCN, the oxidation reaction using 30
wt% HPWs@Meso‐HKUST‐1 as the catalyst was performed at
303 K in the presence of these organic solvents. As shown in
entries 1–4, the conversion (and yield) for the selective oxida‐
tion of CPE to GA was 47.3% (27.4%), 61.2% (48.8%), 75.6%
(60.5%), and 92.5% (73.0%), respectively. The results indicate
that aprotic solvents are beneficial to the reaction, and MeCN is
the best solvent for the reaction using TBHP as the oxidant.
Since MeCN is the optimal solvent for the reaction, the effect of
reaction temperatures on the title reaction was investigated in
the presence of MeCN. As shown in entries 4–7, CPE conversion
first increased linearly and then slightly decreased in the tem‐
perature range from 298 to 313 K. However, GA selectivity
observably changed, leading to an optimum GA yield at 303 K.
The lower GA yield at 313 K may be attributed to the higher
nificant
amount
of
bubbles
upon
adding
the
HPWs@Meso‐HKUST‐1 catalyst to the reaction system, which
may be caused by the Meso‐HKUST‐1 material.
Table 2 shows the results of the selective oxidation of CPE to
GA over several HPWs@Meso‐HKUST‐1 catalysts, along with
experiments performed in the presence of pristine Me‐
so‐HKUST‐1 and the corresponding homogeneous HPW. For
the purpose of comparison, the catalysts used in these experi‐
ments contained the equivalent amounts of HPWs. As shown in
Table 2, the HPW catalyst exhibited excellent activity for oxida‐
tion. However, further recycling of the homogeneous catalytic
system was restricted as a result of separation difficulties and
reuse of the homogeneous catalyst. The pristine Meso‐HKUST‐1
exhibited marginal activity for the selective oxidation of CPE to
GA, whereas the samples with HPWs well dispersed on the
Meso‐HKUST‐1 support exhibited substantial activity and se‐
lectivity for the cleavage reaction. This result indicates that the
HPWs incorporated in the 3D framework of the Meso‐HKUST‐1
material serve as active centers for the selective oxidation of
CPE. The in situ FT‐IR spectra demonstrated that HPWs encap‐
sulated in the Meso‐HKUST‐1 materials can provide additional
Lewis acid sites, which are different from those of the Me‐
so‐HKUST‐1 supports and essential to catalyze the selective
oxidation of CPE to GA. Although Meso‐HKUST‐1 shows a de‐
gree of catalytic performance for the reaction under study
herein, the CPE conversion is very low and the Lewis acid sites
are more suitable to generate cyclopentenone. For the
HPWs@Meso‐HKUST‐1 catalysts, HPWs are the active centers
and Meso‐HKUST‐1 materials are the supports, which provide
high surface area and mesoporous cages to encapsulate HPWs.
Thus, the catalyst can provide a large concentration of accessi‐
ble, highly dispersed, and structurally well‐confined active sites
for the selective oxidation of CPE. Furthermore, CPE conversion
is strongly dependent on the content of HPWs in the
HPWs@Meso‐HKUST‐1 catalysts; this result reveals that the
optimum catalyst possesses 30 wt% HPW. CPE conversion
reached 92.5%, and the GA yield reached 73.0% using the op‐
Table 2
Catalytic performance in the selective oxidation of CPE over various
samples.
Selectivity (%)
CPE conver‐ GA yield
Sample
sion (%)
(%)
GA
CLPO
79.6
43.7
25.0
26.4
26.7
21.1
26.7
79.9
Meso‐HKUST‐1
HPWs
27.6
5.6
20.4
56.3
75.0
73.6
73.3
78.9
73.3
20.1
100.0
47.6
51.5
73.3
92.5
56.3
30.4
37.9
53.7
73.0
54.2
15.4
8 wt% HPWs@Meso‐HKUST‐1
18 wt% HPWs@Meso‐HKUST‐1
25 wt% HPWs@Meso‐HKUST‐1
30 wt% HPWs@Meso‐HKUST‐1
33 wt% HPWs@Meso‐HKUST‐1
30 wt% HPWs@HKUST‐1*
73.9
76.4
Reaction conditions: The molar ratio of CPE:TBHP:HPWs = 1000:2500:
3, the volume ratio of MeCN/CPE = 10, reaction time 36 h, reaction
temperature 303 K; CLPO, cyclopentenone.
*Prepared by a one‐pot synthesis method with microporosity only.

1882
Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
structural integrity of the catalyst under the reaction condi‐
Table 3
tions. To investigate the stability and duration of the active
HPW components in the 30 wt% HPWs@Meso‐HKUST‐1 cata‐
lyst, a three‐consecutive‐cycle experiment was performed in
the selective oxidation of CPE, and the HPWs remaining in the
catalyst were determined by inductively coupled plasma anal‐
yses after the final cycle (Table 4). Approximately 3%(w) HPWs
leached from the catalyst after three consecutive cycles. How‐
ever, such a loss of HPWs did not result in the appreciable de‐
crease in CPE conversion. The CPE conversion decreased from
92.5% to 90.3%, and the GA yield decreased from 73.0% to
70.1% under the same experimental conditions after three
consecutive cycles. The XRD pattern and FT‐IR spectrum of the
30 wt% HPWs@Meso‐HKUST‐1 catalyst after three cycles of
the selective oxidation of CPE revealed the principal peaks and
bands of HPW and Meso‐HKUST‐1. Hence, we suppose that
Meso‐HKUST‐1 and HPW supported on Meso‐HKUST‐1 main‐
tain structural integrity during the three reaction cycles. Hill’s
group [51] has reported that the deactivation of homogeneous
HPW is mainly caused by the reaction product. The
HPWs‐MIL‐101 catalyst was also reported to be poisoned by
the leaching of small amounts of HPW species and oxidized
products [52]. To explain the reasons for the decrease of the
catalytic performance, the catalysts were washed with ethanol
and DMF to remove the adsorbed organic substances after the
three‐consecutive‐cycle reactions. Thereafter, the catalytic ac‐
tivity was tested and the results are listed in Table 4 (entry 4).
The catalytic activity compared with the third reaction cycle
slightly increased; however, the degree of activity was below
that of the fresh activity. Therefore, we believe that the slight
decrease in the observed catalytic activity was caused by the
leaching of small quantities of HPW species together with the
adsorption of oxidized products on the catalyst. Thus, the 30
wt% HPWs@Meso‐HKUST‐1 catalyst exhibits high stability and
catalytic activity for the selective oxidation of CPE to GA.
Catalytic performance in the selective oxidation of CPE over 30 wt%
HPWs@Meso‐HKUST‐1.
CPE conversion GA yield
Entry Solvent
T/K t/h TBHP/CPE
(%)
47.3
61.2
75.6
92.5
84.9
99.0
98.9
42.6
52.8
92.3
54.9
68.6
87.3
74.3
90.3
84.1
(%)
27.4
48.8
60.5
73.0
66.7
55.9
55.4
38.8
46.9
71.6
49.7
60.9
52.4
58.0
67.0
60.1
1
2
3
4
5
6
7
8
C2H5OH
(CH3)3COH 303 36
CH3COCH3 303 36
303 36
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
1.5
2.0
3.0
2.5
2.5
2.5
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
303 36
298 36
308 36
313 36
303 12
303 24
303 48
303 36
303 36
303 36
303 36
303 36
303 36
9
10
11
12
13
14 a
15 b
16 c
Reaction conditions: The molar ratio of CPE:HPWs = 1000:3, the vol‐
a
ume ratio of solvent/CPE = 10. The molar ratio of CPE:HPWs =
1000:2.5, the volume ratio of MeCN/CPE = 10; b The molar ratio of
CPE:HPWs = 1000:3.5, the volume ratio of MeCN/CPE = 10;c The molar
ratio of CPE:HPWs = 1000:4, the volume ratio of MeCN/CPE = 10.
temperature, which results in further oxidation of GA to form
over‐oxidized by‐products. On extending the reaction time
from 6 to 36 h (entries 4 and 8–10), both CPE conversion and
GA yield linearly increased and reached saturation after 36 h of
reaction. Furthermore, on further increasing the reaction time,
the CPE conversion and GA yield slightly decreased. Hence, the
optimum reaction time is 36 h. The effect of the TBHP amount
on the selective oxidation of CPE to GA is shown in entries 4
and 11–13. By varying the molar ratio of TBHP to CPE from
1.5:1 to 2.5:1, both CPE conversion and GA yield increased, and
TBHP was not detected in the reaction mixture (entries
4,11,12). However, the conversion of CPE to GA decreased
when the ratio of TBHP to CPE was increased to 3:1 (entry 13),
thus suggesting that the optimum ratio of TBHP to CPE for the
conversion of CPE to GA is 2.5:1. The effect of catalyst loading
on the selective oxidation of CPE is shown in entries 4 and
14–16. Additionally, with increasing catalyst loading, the GA
yield increased and reached a maximum of 73.0% when the
molar ratio of HPWs to CPE reached 0.3%. However, the CPE
conversion and GA yield significantly decreased when the cata‐
lyst loading was increased to 0.4%, which may be ascribed to
the increased diffusion limitations of mass transfer during the
reaction. This result suggests that the optimum molar ratio of
HPW to CPE for the selective oxidation of CPE to GA is 0.3%.
According to the above results, it can be concluded that the 30
wt% HPWs@Meso‐HKUST‐1 catalyst exhibits the best catalytic
performance for the selective oxidation of CPE to GA using
TBHP and MeCN as the oxidant and solvent, respectively, with a
reaction temperature of 303 K, a reaction time of 36 h, and a
molar ratio of HPW:TBHP:CPE of 3:2500:1000.
Additionally, the nature of the catalyst is a significant factor
in liquid‐phase processes. After the reaction was subjected to
12 h over the 30 wt% HPWs@Meso‐HKUST‐1 catalyst, the cat‐
alyst was removed from the experiment while under test con‐
ditions to verify the heterogeneity of the HPWs@Meso‐
HKUST‐1 catalyst in the reaction. No detectable increase was
observed in the GA yield and CPE conversion after the catalysts
were removed, indicating that the selective oxidation process is
truly heterogeneous and occurs on the catalyst surface rather
Table 4
Re‐usability of 30 wt% HPWs@Meso‐HKUST‐1.
Selectivity (%)
Recycle CPE conversion
Yield HPW loading
entry
(%)
92.5
91.6
90.3
91.2
(%)
73.0
71.7
70.1
71.6
(wt%)
GA
CLPO
21.1
21.7
22.4
21.5
1
2
3
4*
78.9
78.3
77.6
78.5
30
28
27
—
Reaction conditions: The molar ratio of CPE:TBHP:HPWs = 1000:2500:
3, the volume ratio of MeCN/CPE = 10, reaction time 36 h, reaction
temperature 303 K; CLPO = cyclopentenone.
* The catalyst was washed with ethanol and DMF to remove the ad‐
sorbed organic substances.
While studying liquid‐phase processes over solid catalysts,
it is extremely important to address the issue of the stability of
the active component with respect to leaching and maintaining

Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
1883
than in the solution. Even if trace quantities of the HPW species
leached from the catalyst during selective oxidation, the ob‐
served catalytic activity was not attributed to these species
alone.
sites may account for the high catalytic properties of HPWs@
Meso‐HKUST‐1. The developed HPWs@ Meso‐HKUST‐1 has the
potential to be used as an industrial catalyst.
From the results of the catalytic activity tests and catalyst
characterization, it can be concluded that the hierarchically
micro‐ and mesoporous HKUST‐1‐encapsulated HPW sample
(HPWs@Meso‐HKUST‐1) can be prepared by employing a su‐
pramolecular template strategy via a one‐pot synthesis meth‐
od. It is conceivable that the design of the mesoporous struc‐
ture of Meso‐HKUST‐1—possessing high porosity and high
surface area, in conjunction with microporous frameworks—is
more suitable to encapsulate and confine HPWs into the mes‐
oporous cages, and prevent leaching of active HPWs. Further‐
more, the incorporation of HPWs into the mesoporous cages of
hierarchical Meso‐HKUST‐1 enhances molecular diffusion and
mass transfer, and further provides the catalysts with tailored
properties, such as a large concentration of accessible, highly
dispersed, additional Lewis acid sites, and structurally
well‐confined active sites for the selective cleavage of CPE.
Hence, the HPWs@Meso‐HKUST‐1 catalysts exhibit high cata‐
lytic performance for the selective oxidation of CPE to GA.
References
[1] Kozhevnikov I V. Chem Rev, 1998, 98: 171
[2] Inumaru K, Ishihara T, Kamiya Y, Okuhara T, Yamanaka S. Angew
Chem Int Ed, 2007, 46: 7625
[3] Bigi F, Corradini A, Quarantelli C, Sartori G. J Catal, 2007, 250: 222
[4] Khder A E R S. Appl Catal A, 2008, 343: 109
[5] Schwegler M A, Vinke P, van der Eijk M, van Bekkum H. Appl Catal
A, 1992, 80: 41
[6] Dupont P, Védrine J C, Paumard E, Hecquet G, Lefebvre F. Appl
Catal A, 1995, 129 : 217
[7] Nomiya K, Murasaki H, Miwa M. Polyhedron, 1986, 5: 1031
[8] Kozhevnikov I V, Kloetstra K R, Sinnema A, Zandbergen H W, van
Bekkum H. J Mol Catal A, 1996, 114: 287
[9] Yuan C Y, Chen J. Chin J Catal, 2011, 32: 1191
[10] Khder A E R S, Khder, Hassan H M A, El‐Shall M S. Appl Catal A,
2012, 411‐412: 77
[11] Ferey G. Chem Soc Rev, 2008, 37: 191
[12] Long J R, Yaghi O M. Chem Soc Rev, 2009, 38: 1213
[13] Dhakshinamoorthy A, Garcia H. Chem Soc Rev, 2012, 41: 5262
[14] Prestipino C, Regli L, Vitillo J G, Bonino F, Damin A, Lamberti C,
Zecchina A, Solari P L, Kongshaug K O, Bordiga S. Chem Mater,
2006, 18: 1337
4. Conclusions
In summary, a novel mesoporous MOF HKUST‐1 with a hi‐
erarchical‐structure‐encapsulated HPW material (HPWs@
Meso‐HKUST‐1) was successfully prepared for the first time by
a simple one‐pot hydrothermal synthesis method using CTAB
as the supramolecular template. The resulting material exhib‐
ited high activity and excellent re‐usability in the selective oxi‐
dation of CPE to GA, behaving as a truly heterogenous oxidative
catalyst without significant leaching of HPWs during reuse; the
product maintains structural integrity of HKUST‐1 with hier‐
archical micro‐ and mesopores. The unique textural properties
of Meso‐HKUST‐1 and the well‐dispersed HPWs confined in the
mesoporous cages of the Meso‐HKUST‐1 matrix together with
an appropriate HPW loading providing additional Lewis acid
[15] Chui S S Y, Lo S M F, Charmant J P H, Orpen A G, Williams I D. Sci‐
ence, 1999, 283: 1148
[16] Schlichte K, Kratzke T, Kaskel S. Microporous Mesoporous Mater,
2004, 73: 81
[17] Alaerts L, Séguin E, Poelman H, Thibault‐Starzyk F, Jacobs P A, De
Vos D E. Chem Eur J, 2006, 12: 7353
[18] Dhakshinamoorthy A, Alvaro M, Garcia H. J Catal, 2009, 267: 1
[19] Wu Y, Qiu L G, Wang W, Li Z Q, Xu T, Wu Z Y, Jiang X. Trans Met
Chem, 2009, 34: 263
[20] Brown K, Zolezzi S, Aguirre P, Venegas‐Yazigi D, Paredes‐Garcia V,
Baggio R, Novak M A, Spodine E. Dalton Trans, 2009: 1422
[21] Marx S, Kleist W, Baiker A. J Catal, 2011, 281: 76
[22] Sun C Y, Liu S X, Liang D D, Shao K Z, Ren Y H, Su Z M. J Am Chem
Soc, 2009, 131: 1883
Graphical Abstract
Chin. J. Catal., 2015, 36: 1875–1885 doi: 10.1016/S1872‐2067(15)60972‐X
One‐pot synthesis of a hierarchical microporous‐mesoporous
phosphotungstic acid‐HKUST‐1 catalyst and its application in
the selective oxidation of cyclopentene to glutaraldehyde
Xinli Yang *, Liming Qiao, Weilin Dai *
Henan University of Technology; Fudan University
A hierarchical microporous‐mesoporous MOF of HKUST‐1(Cu)‐encapsulated
phosphotungstic acid (HPW) material, referred to as HPWs@Meso‐HKUST‐1,
was prepared by a one‐pot synthesis method using cetyltrimethylammonium
bromide as the supramolecular template for the selective oxidation of cyclo‐
pentene to glutaraldehyde.

1884
Xinli Yang et al. / Chinese Journal of Catalysis 36 (2015) 1875–1885
[23] Janssens N, Wee L H, Bajpe S, Breynaert E, Kirschhock C E A,
Martens J A. Chem Sci, 2012, 3: 1847
[24] Song J, Luo Z, Britt D K, Furukawa H, Yaghi O M, Hardcastle K I, Hill
C L. J Am Chem Soc, 2011, 133: 16839
[40] Sun L B, Li J R, Park J, Zhou H C. J Am Chem Soc, 2012, 134: 126
[41] Wee L H, Wiktor C, Turner S, Vanderlinden W, Janssens N, Bajpe S
R, Houthoofd K, Van Tendeloo G, De Feyter S, Kirschhock C E A,
Martens J A. J Am Chem Soc, 2012, 134: 10911
[25] Yang H, Li J, Wang L Y, Dai W, Lü Y, Gao S. Catal Commun, 2013, 35:
101
[42] Pauly T R, Liu Y, Pinnavaia T J, Billinge S J L, Rieker T P. J Am Chem
Soc, 1999, 121: 8835
[26] Wee L H, Janssens N, Bajpe S R, Kirschhock C E A, Martens J A.
Catal Today, 2011, 171: 275
[43] Férey G, Mellot‐Draznieks C, Serre C, Millange F, Dutour J, Surblé S,
Margiolaki I. Science, 2005, 309: 2040
[27] Klein N, Senkovska I, Gedrich K, Stoeck U, Henschel A, Mueller U,
Kaskel S. Angew Chem Int Ed, 2009, 48: 9954
[44] Rao K M, Gobetto R, Iannibello A, Zecchina A. J Catal, 1989, 119:
512
[28] Fang Q R, Makal T A, Young M D, Zhou H C. Comments Inorg Chem,
2010, 31: 165
[45] Damyanova S, Dimitrov L, Mariscal R, Fierro J L G, Petrov L,
Sobrados I. Appl Catal A, 2003, 256: 183
[29] Xuan W M, Zhu C F, Liu Y, Cui Y. Chem Soc Rev, 2012, 41: 1677
[30] Song L F, Zhang J, Sun L X, Xu F, Li F, Zhang H Z, Si X L, Jiao C L, Li Z
B, Liu S, Liu Y L, Zhou H Y, Sun D L, Du Y, Cao Z, Gabelica Z. Energy
Environ Sci, 2012, 5: 7508
[46] Zang Y D, Shi J, Zhao X M, Kong L C, Zhang F M, Zhong Y J. Reac
Kinet Mech Catal, 2013, 109: 77
[47] Wee L H, Bonino F, Lamberti C, Bordiga S, Martens J A. Green
Chem, 2014, 16: 1351
[31] Qiu L G, Xu T, Li Z Q, Wang W, Wu Y, Jiang X, Tian X Y, Zhang L D.
Angew Chem Int Ed, 2008, 47: 9487
[32] Furukawa H, Nakamura T, Inagaki H, Nishikawa E, Imai C, Misono
M. Chem Lett, 1988: 877
[48] Vimont A, Goupil J M, Lavalley J C, Daturi M, Surblé S, Serre C,
Millange F, Férey G, Audebrand N. J Am Chem Soc, 2006, 128: 3218
[49] Youn M H, Kim H, Jung J C, Song I K, Barteau K P, Barteau M A. J
Mol Catal A, 2005, 241: 227
[33] Furukawa H, Nishikawa E, Koyama T. JP Patent 62029546. 1987
[34] Deng J F, Xu X H, Chen H Y, Jiang A R. Tetrahedron, 1992, 48:
3503
[35] Schlichte K, Kratzke T, Kaskel S. Microporous Mesoporous Mater,
2004, 73: 81
[36] Yuan D Q, Lu W G, Zhao D, Zhou H C. Adv Mater, 2011, 23: 3723
[37] Chen H, Dai W L, Deng J F, Fan K N. Catal Lett, 2002, 81: 131
[38] Dai W L, Chen H, Cao Y, Li H X, Xie S H, Fan K N. Chem Commun,
2003: 892
[39] Gregg S J, Sing K S W. Adsorption, Surface Area and Porosity. Lon‐
don: Academic Press, 1997. 111
[50] Juan‐Alcañiz J, Ramos‐Fernandez E V, Lafont U, Gascon J, Kapteijn
F. J Catal, 2010, 269: 229
[51] Duncan D C, Chambers R C, Hecht E, Hill C L. J Am Chem Soc, 1995,
117: 681
[52] Hu X F, Lu Y K, Dai F N, Liu C G, Liu Y Q. Microporous Mesoporous
Mater, 2013, 170: 36
Page numbers refer to the contents in the print version, which include
both the English version and extended Chinese abstract of the paper. The
online version only has the English version. The pages with the extended
Chinese abstract are only available in the print version.