Molybdenum arsenate crystal: A highly efficient and recyclable catalyst for hydrolysis of ethylene carbonate

Article abstract of DOI:10.1016/j.apcata.2013.11.028

A simple one-step hydrothermal reaction was employed to synthesize the molybdenum arsenate crystallite catalyst, [{Cu(imi)₂} ₃As₃Mo₃O₁₅]·H₂O (1) (imi = imidazole). The catalyst was characterized using X-ray crystallographic analyses, FT-IR, TGA, XRD, ICP-AES, NH₃-TPD and BET techniques. Moreover, we performed evaluation on its catalytic activity towards the hydrolysis of ethylene carbonate to produce ethylene glycol. Interestingly, the conversion of this reaction reaches 96.5% and the selectivity is close to 100% at optimum conditions. No polyoxometalate leaching or framework decomposition was observed and the catalyst can be recovered and reused with slight loss of reactivity under identical reaction conditions.

Full text of DOI:10.1016/j.apcata.2013.11.028

Applied Catalysis A: General 471 (2014) 50–55
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Molybdenum arsenate crystal: A highly efficient and recyclable
catalyst for hydrolysis of ethylene carbonate
Zhifeng Zhaob,∗, Yuanzhu Dingb, Jiancong Bib, Zhanhua Sua,∗∗, Qinghai Caia,
Limin Gaob, Baibin Zhoua
a Key Laboratory of Synthesis of Functional Materials and Green Catalysis, Colleges of Heilongjiang Province, Harbin Normal University, Harbin 150025,
PR China
b College of Materials Science and Engineering, University of Science and Technology Heilongjiang, Harbin 150022, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple one-step hydrothermal reaction was employed to synthesize the molybdenum arsenate crys-
tallite catalyst, [{Cu(imi)2}3As3Mo3O15]·H2O (1) (imi = imidazole). The catalyst was characterized using
X-ray crystallographic analyses, FT-IR, TGA, XRD, ICP-AES, NH3-TPD and BET techniques. Moreover, we
performed evaluation on its catalytic activity towards the hydrolysis of ethylene carbonate to produce
ethylene glycol. Interestingly, the conversion of this reaction reaches 96.5% and the selectivity is close to
100% at optimum conditions. No polyoxometalate leaching or framework decomposition was observed
and the catalyst can be recovered and reused with slight loss of reactivity under identical reaction
conditions.
Received 13 August 2013
Received in revised form
14 November 2013
Accepted 23 November 2013
Available online 1 December 2013
Keywords:
POMs crystal
Heterogeneous catalysis
Hydrolysis
© 2013 Elsevier B.V. All rights reserved.
Ethylene glycol
1. Introduction
an efficient heterogeneous system with active, selective, environ-
mentally benign, and recyclable POMs catalyst without additives.
Polyoxometalates (POMs) chemistry continues to be an interest-
ing subject due to their diverse structures and unique properties
[1–5]. The POMs with strong Brønsted acidity have shown great
potentiality in catalysis [6–8], such as in water splitting [9,10],
epoxidation of alkenes and alkenols [11–14], hydration of alkenes,
esterification, alkylation [15–19], bromination of alkenes, alkynes
and aromatics [20,21], and biphasic oxidations with hydrogen per-
oxide [22]. However, catalyst separation and reuse have imposed
great limitations for the applications of POMs for catalyzing most
of homogeneous reactions. Moreover, many reported heteroge-
neous POM catalysts supported on silica [23–27], activated carbon
[28,29] and mesoporous molecular sieves [30–33], always suf-
fer from slow reaction rates, leaching of the active species, low
loading, deactivation of acid sites, conglomeration or very com-
plex preparation process, which are also not conductive to their
applications as solid catalysts. Therefore, it is desirable to develop
The POMs crystal has a suitable solid matrix and framework with
integrity and stability, which can overcome the above-mentioned
drawbacks and possess appropriate openings allowing for the diffu-
sion of reactants and products. Thus, the POMs crystal is a promising
material towards the challenging goal of catalysis.
The production of ethylene glycol from ethylene carbonate by
hydrolysis is a well-known process. However, low ethylene gly-
col selectivity and use of large excess amount of water would
cause high energy expenditure, making this process economi-
cally unattractive [34–37]. Hence, extensive efforts have been
paid to explore the suitable catalyst for catalytic hydrolysis of
ethylene carbonate. Here, we present a POM crystalline catalyst,
[{Cu(imi)2}3As3Mo3O15]·H2O (1), whose crystal structure has been
reported previously by our group [38]. The catalyst 1 was also
characterized by X-ray crystallographic analyses, FT-IR, TGA, XRD,
ICP-AES, NH3-TPD and BET. In addition, the dependence of the
conversion of hydrolysis on the reactions variables such as the
large excess water, the amount of catalysts used, reaction temper-
atures, reaction time, reusability were also appraised. To the best
of our knowledge, catalyst 1 represents the first example of effi-
cient heterogeneous catalyst for preparation of ethylene glycol via
hydrolysis of ethylene carbonate.
∗
Corresponding author. Tel.: +86 451 88036690.
Corresponding author.
∗∗
E-mail addresses: zhifengzhao1980@163.com (Z. Zhao), su zhan hua@163.com
(Z. Su).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.11.028

Z. Zhao et al. / Applied Catalysis A: General 471 (2014) 50–55
51
Table 1
Catalytic performance of various catalysts for hydrolysis of ethylene carbonate.a
Entry
Catalyst
Solubility
Conversionb [%]
Selectivityc [%]
1
2
3
4
5
6
7
[Ni6(imi)6(B-␣-H3AsW9O33)2]·2H2O
Insoluble
Insoluble
Insoluble
Part of soluble
Insoluble
0
0
0
–
–
–
[Zn6(imi)6(B-␣-H3AsW9O33)2]·2H2O
[Mn6(imi)6(B-␣-H3AsW9O33)2]·4H2O
[Cu4(phen)4(HPO4)2(H2O)2(OH)2]·[HPMo12O40]·H2O
[(CuO6)(As3O3)2Mo6O18][imi]2
0
–
90.7
27.2
94.5
>99
92
>99
(en)6{Cu(H2O)Na[(Mo6O12)(OH)3(PO4)(H2PO4)(HPO4)2][(Mo6O12)·(OH)3(H2PO4)2·(HPO4)2]}·5H3O
Part of soluble
Insoluble
[{Cu(imi)2}3As3Mo3O15]·H2O
a
Reaction conditions: catalyst (0.05 mmol), ethylene carbonate (22.67 mmol), H2O (30 mL), 95 ◦C, 4 h.
Conversion of ethylene carbonate.
Selectivity for the ethylene glycol product; by-products: diethylene glycol.
b
c
2. Experimental
filtration and subjected to a recycling experiment. The liquid was
analyzed with the gas chromatograph.
2.1. Reagents and catalyst characterization
3. Results and discussion
All reagents and solvents were purchased from commercial
sources and were used as received. The IR spectra were obtained on
Alpha Centauri Fourier transform IR (FT-IR) spectrometer with KBr
pellet in the 400–4000 cm−1 region. The crystal data were collected
on a Bruker SMART APEX II CCD diffractometer using Mo-Ka radia-
3.1. Screening of catalyst
Catalytic performance of POMs crystal for hydrolysis of ethylene
carbonate is listed in Table 1. POMs crystals (entries 1–4) do not
show catalytic activity for hydrolysis of ethylene carbonate. The
POMs crystal (entry 7) was insoluble in the reaction and thus led
to a liquid–solid heterogeneous system, exhibiting close to 100%
selectivity with a high conversion of 94.5%. Moreover, POMs crystal
(entry 5) also caused similar heterogeneous reactions and close to
100% selectivity with high conversions of 90.7%, indicating highly
catalytic activity and selectivity of molybdenum arsenate crystal.
In contrast molybdenum phosphate crystal (entry 6) was inactive
and showed a low conversion of 27.2%.
˚
tion (0.71073 A) at 273 K. Thermal gravimetric analyses (TGA) were
performed on a PerkinElmer TGA7 instrument in flowing N2 with
a heating rate of 10 ◦C/min. The acidity of the catalyst was stud-
ied by temperature programmed desorption using NH3 as probe
molecule. NH3–TPD experiment was performed using a Thermo
Finnigan TPDRO 1100 apparatus equipped with a thermal conduc-
tivity detector. The catalyst 1 (0.1 g) was placed in the reactor,
treated under 200 ◦C for 15 min in N2 (20 mL/min). 10% NH3 in
helium gas was ramped at 1 ◦C/min for 60 min. The purging with
N2 was done at room temperature for 45 min to remove NH3 in
the gas phase. The analysis of NH3 desorption was then carried out
between 100 and 700 ◦C under helium flow (15 ◦C/min, 20 mL/min)
and detected by thermal conductivity detector. Elemental anal-
ysis was performed on ICP-AES spectrometer (Thermo Scientific
iCAP 6000 series). Surface area measurement (by BET method) was
carried out on Micromeritics Gemini at −196 ◦C using nitrogen
adsorption isotherms. The products of the catalytic hydrolysis reac-
tion were analyzed using a gas chromatograph (Shimadzu, GC-14)
equipped, with a FID detector and Agilent DB-1 column.
3.2. Structure of catalyst 1
The structure of 1, shown in Fig. 1, consists of a new molyb-
denum arsenate fragment [As3Mo3O15]
3−, decorated with three
[Cu(imi)2] complexes. The molybdenum arsenate fragment is con-
structed from three MoO6 octahedras and three AsO3 trigonal
pyramids. The three MoO6 octahedra are joined to each other by
edge-sharing. The As3O7 group consists of three AsO3 pyramids
linked in a triangular arrangement by sharing corners and bonded
to three MoO6 octahedra via bridging oxygen atoms. In compound
1, the N atoms of organic ligands and the O atoms of polyanions
are linked to each other by means of hydrogen bonds, which make
the crystal structure of compound 1 more stable (Fig.S1). Important
atomic distances and bond angles are listed in Table S1.
2.2. Preparation of catalyst 1
The POM crystal was prepared and characterized according
to the literature. The detailed procedure is as follows: a mix-
ture of (NH4)6Mo7O24·4H2O (0.72 g, 0.58 mmol), NaAsO2 (0.40 g,
2.96 mmol), CuCl2·2H2O (0.35 g, 2.05 mmol), imidazole (0.27 g,
4.01 mmol) and H2O (22 mL) was stirred for 60 min in air. The
resulting gel was then transferred to a 30 mL Teflon-lined autoclave
and kept at 160 ◦C for 6 days. After the mixture was slowly cooled to
room temperature, light-yellow block crystals were isolated (yield
ca. 42% based on Mo).
2.3. Typical procedure for hydrolysis of ethylene
carbonate
In a typical experiment, ethylene carbonate (22.67 mmol), cat-
alyst 1 (0.02 mmol) and H2O (2 mL) were added to a 3-neck Pyrex
flask (ca. 20 mL) equipped with a refluxing condenser, sampling
tube and thermometer. Then the reaction mixture was stirred for
8 h under refluxing conditions and vigorous stirring, at a temper-
ature of about 95 ◦C. After reaction, the catalyst was separated by
Fig. 1. Molecular structure of catalyst 1.

52
Z. Zhao et al. / Applied Catalysis A: General 471 (2014) 50–55
Fig. 2. The IR spectra of catalyst 1 before and after heated at 200 ◦C.
Fig. 3. NH3-TPD of catalyst 1.
3.3. Charaterization of catalyst 1
3.4. Catalytic performance
An essential property of solid catalyst is the stability of the active
component with respect to leaching and other transformations, and
toleration for thermal or acid–base conditions. Catalyst 1 was sta-
ble for months under air atmosphere, and no efflorescence was
observed. After rinsing in 0.02 M sodium hydroxide solution, or
0.02 M hydrochloric solution, or one of common organic solvents
(methanol, ethanol, acetonitrile, acetone, chloroform, and DMF)
under stirring at 80 ◦C for 10 h, no compound dissolution or frame-
work decomposition occurs on catalyst 1, or POM leaching from it,
as evidenced by the single-crystal X-ray diffraction analysis. More-
over, after heated at 200 ◦C for 10 h, leading to the loss of isolated
water molecule, catalyst 1 showed no evidence of POM framework
decomposition in IR spectra (Fig. 2), confirming the maintenance
of crystalline framework and indicating its high thermal stability.
The TGA curve shows a three-step weight-loss process (Fig.S2).
The first step in the temperature range 160–193 ◦C corresponds to
the loss of isolated water molecule. The second step occurs between
200 and 350 ◦C and corresponds to the loss of two imi ligands. The
third step in the temperature range 370–436 ◦C is probably due to
the loss of organic components and As2O3. The result of TG analysis
basically agrees with that of the structure determination, reflecting
that POMs have highly stable framework.
NH3-TPD measurements were carried out to determine the acid
strength and amounts of acid sites on the catalyst surface using
ammonia as an adsorbate. The NH3-TPD profile showed that the
catalyst 1 had four desorption peaks (Fig. 3). Two peaks from 240
to 340 ◦C and the other two from 350 to 700 ◦C that were assigned
to two types of acid site. These peaks corresponded to medium and
strong acid sites with total acid density of about 2.1 mmol/g. The
acid sites may be Brønsted acidity because imidazole ligands can
give proton [39,40]. Surface area (BET method) for catalyst 1 was
found to be 10.4 m2/g.
To explore the optimum conditions for hydrolysis reaction on
catalyst 1, we studied effects of difference reaction conditions
including temperature, time, the amount of catalyst and large
excess water for hydrolysis of ethylene carbonate. Firstly, the effect
of temperature on hydrolysis reaction was investigated at 45–95 ◦C
(Fig. 4a). At 95 ◦C, 100% selectivity to ethylene glycol was achieved
at a conversion closes to 80%. As expected, the conversion increased
steadily as the temperature was raised from 45 to 95 ◦C. Based on
the obtained results, the optimum catalytic performance (highest
yield of ethylene glycol) was achieved at 95 ◦C. Secondly, the effect
of reaction time on the catalytic performance is shown in Fig. 4b.
When the time was less than 1 h, catalytic activity was almost
unchanged. However, the activity increased remarkably when the
time was over 6 h, and ethylene carbonate conversion exceeded
70%, when the reaction time reached 10 h. Thirdly, the catalytic per-
formance is also influenced by the catalyst amount. In the present
study, the catalyst amount was varied within the 0.005–0.02 mmol
range and the reactant conversion increased remarkably with the
catalyst amount, as shown in Fig. 4c. This can be explained by an
increase in the number of acid sites. Beyond 0.02 mmol, the cat-
alytic conversion curve was found to be almost flat. Finally, ethylene
carbonate conversion reaches the highest value of 96.46% with 2 mL
water (Fig. 4d), which shows that large excess water is adversely for
the reaction. The experimental results show that 96.5% conversion
and close to 100% selectivity could be achieved under the optimum
conditions (catalyst (0.02 mmol), ethylene carbonate (22.67 mmol),
H2O (2 mL), temperature (95 ◦C) and time (8 h)).
We examined the hydrolysis of ethylene carbonate catalyzed
by two molybdenum arsenate crystals (Table 2). Among them, cat-
alyst 1 shows the highest activity, and a 96.5% conversion and
close to 100% selectivity could be achieved after 8 h of reaction,
Table 2
The hydrolysis of ethylene carbonate catalyzed by molybdenum arsenate crystals.a
Entry
Catalyst
Time [h]
Conversionb [%]
Selectivityc [%]
1
2
3
4
5
[{Cu(imi)2}3As3Mo3O15]·H2O
[{Cu(imi)2}3As3Mo3O15]·H2O
[{Cu(imi)2}3As3Mo3O15]·H2O
[{Cu(imi)2}3As3Mo3O15]·H2O
[(CuO6)(As3O3)2Mo6O18][imi]2
2
4
6
8
8
56.91
90.36
91.81
96.46
90.06
>99
>99
>99
>99
>99
a
Reaction conditions: catalyst (0.02 mmol), ethylene carbonate (22.67 mmol), H2O (2 mL), 95 ◦C.
Conversion of ethylene carbonate.
Selectivity for the ethylene glycol product; by-products: diethylene glycol.
b
c

Z. Zhao et al. / Applied Catalysis A: General 471 (2014) 50–55
53
Fig. 4. Dependence of catalytic performance on (a) temperature, (b) time, (c) the amount of catalyst, (d) solvent (H2O).
in comparison, catalyst [(CuO6)(As3O3)2Mo6O18][imi]2 [41] shows
a conversions of 90.1% at the same reaction condition.
3.5. Activity change after repeating of the reaction
The catalyst recycling is an important step as it minimizes the
cost of the process. In order to test the reusability, the catalyst
1 was recycled and used for five times at same reaction condi-
tions (Fig. 5). The slight drop in the activity was detected after five
recycles indicating the efficiency of the catalyst. Elemental analy-
sis performed by ICP-AES for filtrate shows Cu = 0.043%, As = 0.037%
and Mo = 0.163%. The leaching amounts are negligible and the reac-
tion completely stops after the removal of catalyst at the reaction
temperature, which indicated the heterogeneous nature of the cat-
alyst. The recovery of the present crystalline catalyst is explicitly
more convenient than the previous homogeneous organic POM salt
catalyst. Furthermore, not only can our new POM crystalline cata-
lyst be comparable to the other classic POM catalysts in conversion,
selectivity and reusability, but also is the preparation of the present
catalyst much simpler, i.e., there is no need to strictly control the
complex multiple-steps. Comparing the IR spectra (Fig. 6) of cata-
lyst 1 before and after the reactions, it was found that there was
almost no difference. Fig. 7 shows the XRD patterns of catalyst 1
before and after the reactions, exhibiting strong diffraction peaks
Fig. 5. Changes of catalytic activity of catalyst 1 for hydrolysis of ethylene carbonate
with repeating the reactions (reaction conditions: catalyst (0.02 mmol), ethylene
carbonate (22.67 mmol), H2O (2 mL), time (4 h); temperature (95 ◦C)).

54
Z. Zhao et al. / Applied Catalysis A: General 471 (2014) 50–55
of ethylene glycol from ethylene carbonate because it has more acid
sites and higher acid density.
4. Conclusions
The
molybdenum
arsenate
crystalline
catalyst,
[{Cu(imi)2}3As3Mo3O15]·H2O, could be fabricated using the
hydrothermal method. The catalyst 1 possesses 2.1 mmol/g acid
density and high thermal stability, which exhibited better catalytic
performance towards the hydrolysis of ethylene carbonate to
produce ethylene glycol under optimum conditions. The mild and
simple synthesis conditions of POM crystalline catalyst permit the
one-step framework construction with integrity and stability. The
new catalyst leads to the liquid solid heterogeneous hydrolysis of
ethylene carbonate with green features of convenient recovery,
steady reusability, high conversion and selectivity. Further studies
directed to analogous reactions and their mechanistic understand-
ings are underway. Our work may provide a useful guidance for
further fabricate molybdenum-based catalysts.
Fig. 6. The IR spectra of catalyst 1 before and after reaction.
Acknowledgements
This work is supported by Technological Innovation Talent Spe-
cial Foundation of Harbin Science and Technology Bureau (Grant
No. 2011RFQXG024), the Project of Heilongjiang Provincial Depart-
ment of Education (Grant No. 12521481) and the National Science
Foundation of China (Grant No. 21271056).
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
2013.11.028.
References
[1] T. Ozeki, T. Yamase, H. Naruke, Y. Sasaki, Inorg. Chem. 33 (1994) 409–410.
[2] C.L. Hill, Chem. Rev. 98 (1998) 1–389.
[3] D.L. Long, C. Streb, Y.F. Song, S. Mitchell, L. Cronin, J. Am. Chem. Soc. 130 (2008)
1830–1832.
[4] S.T. Zheng, J. Zhang, G.Y. Yang, Angew. Chem. Int. Ed. 47 (2008) 3909–3913.
[5] H.Y. Lü, J.B. Gao, Z.X. Jiang, F. Jing, Y.X. Yang, G. Wang, C. Li, J. Catal. 239 (2006)
369–375.
Fig. 7. XRD patterns of catalyst 1 before and after reaction.
[6] M.T. Pope, A. Müller, Angew. Chem. Int. Ed. Engl. 30 (1991) 34–48.
[7] N. Mizuno, K. Kamata, Coord. Chem. Rev. 255 (2011) 2358–2370.
[8] D.L. Long, R. Tsunashima, L. Cronin, Angew. Chem. Int. Ed. 49 (2010) 1736–1758.
[9] Q. Yin, J.M. Tan, C. Besson, Y.V. Geletii, D.G. Musaev, A.E. Kuznetsov, Z. Luo, K.I.
Hardcastle, C.L. Hill, Science 328 (2010) 342–345.
[10] F.M. Toma, A. Sartorel, M. Lurlo, M. Carraro, P. Parisse, C. Maccato, S. Rapino,
B.R. Gonzalez, H. Amenitsch, T. Da Ros, L. Casalis, A. Goldoni, M. Marcaccio,
G. Scorrano, G. Scoles, F. Paolucci, M. Prato, M. Bonchio, Nat. Chem. 2 (2010)
826–831.
[11] R. Neumann, M. Dahan, Nature 388 (1997) 353–355.
[12] Y. Nakagawa, K. Kamata, M. Kotani, K. Yamaguchi, N. Mizuno, Angew. Chem.
Int. Ed. 44 (2005) 5136–5141.
[13] K. Kamata, K. Sugahara, K. Yonehara, R. Ishimoto, N. Mizuno, Chem. Eur. J. 17
(2011) 7549–7559.
[14] Y. Leng, J. Wang, D.R. Zhu, M.J. Zhang, P.P. Zhao, Z.Y. Long, J. Huang, Green Chem.
13 (2011) 1636–1639.
[15] F. Lefebvre, F.X. Liu-Cai, A. Auroux, J. Mater. Chem. 4 (1994) 125–133.
[16] M. Misono, Catal. Rev. Sci. Eng. 30 (1988) 339–340.
[17] I.V. Kozhevnikov, Chem. Rev. 98 (1998) 171–198.
Scheme 1. Proposed mechanism of hydrolysis catalyzed by catalyst 1.
3−
and weak peaks that
that correspond to fragment [As3Mo3O15
]
[18] T. Okuhara, N. Mizuno, M. Misono, Adv. Catal. 41 (1996) 113–252.
[19] K. Kamata, K. Yonehara, Y. Nakagawa, K. Uehara, N. Mizuno, Nat. Chem. 2 (2010)
478–483.
correspond to [Cu(imi)2] complexes. These results indicate a rather
durable catalyst structure that accounts for the steady reusability.
[20] S. Mallik, K.M. Parida, S.S. Dash, J. Mol. Catal. A: Chem. 261 (2007) 172–179.
[21] K. Yonehara, K. Kamata, K. Yamaguchi, N. Mizuno, Chem. Commun. 47 (2011)
1692–1694.
3.6. Proposed mechanism
[22] M. Craven, R. Yahya, E. Kozhevnikova, R. Boomishankar, C.M. Robertson, A.
Steiner, I. Kozhevnikov, Chem. Commun. 49 (2013) 349–351.
[23] F. Lefebvre, J. Chem. Soc., Chem. Commun. (1992) 756–757.
[24] G. Peng, Y.H. Wang, C.W. Hu, E.B. Wang, S.H. Feng, Y.C. Zhou, H. Ding, Y.H. Liu,
Appl. Catal. A 218 (2001) 91–99.
Scheme 1 shows the proposed mechanism of hydrolysis of eth-
ylene carbonate. The ethylene carbonate and water in liquid phase
penetrate and react in between in the lattice of catalyst 1. The cata-
lyst 1 would be expected to have a higher activity for the production
[25] D.C. Phillips, S.J. Sawhill, R. Self, M.E. Bussell, J. Catal. 207 (2002) 266–273.

Z. Zhao et al. / Applied Catalysis A: General 471 (2014) 50–55
55
[26] Y.H. Guo, Y.H. Wang, C.W. Hu, Y.H. Wang, E.B. Wang, Y.C. Zhou, S.H. Feng, Chem.
Mater. 12 (2000) 3501–3508.
[27] H. Guo, C.W. Hu, J. Mol. Catal. A 262 (2007) 136–148.
[28] R.D. Gall, C.L. Hill, J.E. Walker, Chem. Mater. 8 (1996) 2523–2527.
[29] B.A. Watson, M.A. Barteau, L. Haggerty, A.M. Lenhoff, R.S. Weber, Langmuir 8
(1992) 1145–1148.
[34] V. Kruchten, WO Patent 9,719,043 (1997).
[35] Y.C. Li, B. Yue, S.R. Yan, W.M. Yang, Z.K. Xie, Q.L. Chen, H.Y. He, Catal. Lett. 95
(2004) 163–166.
[36] T. Masuda, K. Asano, N. Hori, S. Ando, Eur. Patent 226,799 (1992).
[37] Q.S. Lin, S.M. Li, B. Zhou, Z.H. Zhou, Y.R. Zhang, Y.B. Zhang, X.P. Wang, X.C. Zhou,
Y.H. Wang, G. Chen, CN Patent 1,237,481 (1999).
[30] T. Blasco, A. Corma, A. Martinez, P. Martinez-Escolano, J. Catal. 177 (1998)
306–313.
[38] Z.F. Zhao, B.B. Zhou, Z.H. Su, H.Y. Ma, C.X. Li, Inorg. Chem. Commun. 11 (2008)
648–651.
[31] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D. Stucky,
Science 279 (1998) 548–552.
[39] R. Kore, R. Srivastava, J. Mol. Catal. A: Chem. 345 (2011) 117–126.
[40] D.S. Zhao, M.S. Liu, J. Zhang, J.P. Li, P.B. Ren, Chem. Eng. J. 221 (2013) 99–104.
[32] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992)
710–712.
[41] M.D. Liu, Z.H. Su, Y.C. Shang, Acta Crystallogr. Sect.
m1308–m1309.
E 66 (2010)
[33] I.V. Kozhevnikov, A. Sinnema, R.J.J. Jansen, K. Pamin, H. Van Bekkum, Catal. Lett.
30 (1995) 241–252.