Sulfur and iron co-doped titanoniobate nanosheets: A novel efficient solid acid catalyst for alcoholysis of styrene epoxide at room temperature

Article abstract of DOI:10.1039/c3cc42951b

Sulfur and iron co-doped titanoniobate nanosheets were prepared and evaluated in alcoholysis of styrene epoxide. The resultant co-doped catalyst exhibited excellent catalytic performance (yield of 99% with methanol as the nucleophile in only 1 h at room temperature) and may act as a promising candidate in many acid-catalyzed reactions.

Full text of DOI:10.1039/c3cc42951b

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Sulfur and iron co-doped titanoniobate nanosheets:
a novel efficient solid acid catalyst for alcoholysis of
styrene epoxide at room temperature†
Cite this: Chem. Commun., 2013,
4
9, 7507
Received 21st April 2013,
Accepted 21st June 2013
a
a
a
a
a
Lihong Zhang, Chenhui Hu, Junfeng Zhang, Liyuan Cheng, Zheng Zhai,
b
a
a
Jing Chen, Weiping Ding and Wenhua Hou*
DOI: 10.1039/c3cc42951b
www.rsc.org/chemcomm
Sulfur and iron co-doped titanoniobate nanosheets were prepared and their thermal stability is insufficient. As a result, much
and evaluated in alcoholysis of styrene epoxide. The resultant attention has been focused on the modification of nanosheets
5
6
co-doped catalyst exhibited excellent catalytic performance (yield by metals or nonmetals. The hybridization of layered metal
of 99% with methanol as the nucleophile in only 1 h at room oxides with other metal oxides can provide a valuable strategy
temperature) and may act as a promising candidate in many acid- to create novel functionality via an exfoliation–reassembling
catalyzed reactions.
method, in which a large amount of guest species is highly
dispersed on the 2D nanosheet and thus mesoporous 3D
b-Alkoxyalcohols, which are synthesized through alcoholysis of nanohybrid materials can be obtained with a significantly
epoxides with corresponding alcohols, are important organic improved specific surface area. On the other hand, nonmetal
1
compounds and precursors widely used for pharmaceuticals.
doping of layered metal oxides may be helpful for stabilizing
To accomplish this transformation from epoxides to b-alkoxy- layered structures to some extent.
alcohols, various homogeneous catalysts have been employed, In this work, sulfur and iron were successfully co-doped into
HTiNbO nanosheets (SFTN-400) through an exfoliation–
2
such as InCl
3
, Cu(BF
4
)
2
, TiCl
3
(OTf), Er(OTf)
3
and Fe(ClO
4
)
3
.
5
Obviously, many homogeneous catalytic systems have the flocculation–calcination process using thiourea as the sulfur
inherent disadvantage of the separation of the product and source and iron oxide colloids as the iron source. By compari-
the reuse of the catalyst. In turn, heterogeneous catalysts have son, single-doped catalysts were also obtained under the same
received much attention, such as amberlyst-15, aluminosilicate, conditions. The detailed preparation process is shown in the
CuO–SiO2 and silica-supported iron(III), polymer-supported ESI† (Fig. S1).
iron and ruthenium complexes or Cu and Fe metal–organic
XRD results display a typical layered structure of HTiNbO5
3
frameworks. Unfortunately, in spite of their respective merits, and the full collapse of a periodic layered structure of undoped
the available methods for the synthesis of b-alkoxyalcohols still and single-doped catalysts (HTNNS-400, STN-400 and FTN-400),
have certain limitations including high reaction temperature, while the S, Fe co-doped catalyst maintains a layered structure
long reaction time and unsatisfactory yields. Hence, it remains to some extent, revealing a high thermostability of SFTN-400
a great challenge to develop novel efficient heterogeneous (Fig. S2, ESI†).
catalysts for the alcoholysis of epoxide under mild reaction
conditions.
Fig. 1 shows that pristine HTiNbO presents a well-ordered
layered structure and SFTN-400 has a visible lamellar structure
5
Nanosheets, obtained from the delamination of cation- with a relatively disordered restacking. However, the resultant
exchangeable layered metal oxides, are considered to be pro- HTNNS-400, STN-400 and FTN-400 display a rather loose structure
mising nanomaterials because they overcome the inherent (Fig. S3, ESI†). Moreover, the HRTEM image further confirms
disadvantage of original layered metal oxides which cannot the existence of the layered structure of SFTN-400. In addition,
be intercalated by bulky molecules due to the high charge the EDXS spectrum and the mapping spectrum also confirm the
4
À
density of layers. However, the specific surface areas of the successful co-doping of S and Fe in [TiNbO
5
] nanosheets with a
+
H -flocculated nanosheets are still limited for many reactants, high dispersion.
The surface area and porosity analysis results indicate that the
four catalysts are mesoporous with a relatively narrow range of
pore size distribution except for STN-400 (Fig. S4, ESI†). Besides,
a
Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210093, P R China.
E-mail: whou@nju.edu.cn; Fax: +86-25-83317761; Tel: +86-25-83686001
Department of Applied Chemistry, College of Science,
b
5
compared with the original HTiNbO , the surface area and pore
volume of the resulted catalysts are drastically increased (Table S1,
Nanjing University of Technology, Nanjing 210009, P R China
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/c3cc42951b ESI†), which may be helpful for the catalytic performance.
This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 7507--7509 7507

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FTN-400 and STN-400. It indicates that the Fe and S species in
SFTN-400 show a rather good synergetic effect, resulting in the
strongest surface acidity. Moreover, the acid type of the resulted
catalysts is Lewis acid (Fig. S5, ESI†).
The environments and chemical states of S, Fe, Ti and Nb in
corresponding catalysts were determined by XPS (Fig. S6, ESI†).
2
À
The results show that SO
4
ions in SFTN-400 and STN-400
are directly anchored on iron species and titaniumniobate
sheets respectively and no signals from sulfide and elemental
sulfur are observed. In addition, the surface iron species are
3
+
trivalent and two different chemical environments of Fe ions
exist in FTN-400 arising from the presence of Fe–O–Ti and
Fe–O–Ti(Nb).
By comparison, for SFTN-400, a positive shift of all Fe 2p
main peaks is caused by the strong interaction between the iron
and sulfate species, which may then lead to stronger Lewis acid
2
4
À
sites. Moreover, Ti 2p spectra of SFTN-400 indicate that SO
ions are tightly anchored on the surface of Fe species which
ultimately gives rise to a much lower outer electron density
of Ti and thus the binding energy of Ti 2p increases. Nb 3d
spectra imply the presence of interaction between S (or Fe) and
À
[TiNbO
5
]
nanosheets.
IR further suggests that sulfate was coordinated to different
surface metals, and S–O–Fe and Fe–O–Ti (or Ti and Nb) bonding
were formed in SFTN-400 (Fig. S7, ESI†).
5
Fig. 1 SEM images of (a) HTiNbO and (b) SFTN-400, HRTEM image (c), EDXS (d)
and mapping (e) of SFTN-400.
Fig. 3 shows the catalytic performance of the resulted
catalysts for the alcoholysis of styrene oxide with methanol as
a nucleophilic reagent at room temperature. The alcoholysis
of styrene oxide with MeOH did not occur in the absence of
catalyst within 24 h. Among these four catalysts, SFTN-400
demonstrated the best performance with a yield of >99% and
the alcoholysis reaction could be accomplished within 1 h.
This performance is much better than those reported in the
3
literature.
By comparison, STN-400, FTN-400 and HTNNS-400 show a
relatively poor yield of 80%, 55% and 50% in 5 h, respectively.
Hence, the order of the catalytic activity can be listed as follows:
SFTN-400 > STN-400 > FTN-400 > HTNNS-400. It reveals that the
co-doping of S and Fe is superior to the single-doping or non-doping.
3
Fig. 2 Microcalorimetric adsorption of NH at 423 K.
The surface acidity and type of the resulted catalysts were
determined by ammonia adsorption calorimetry and IR spectro-
scopy of adsorbed pyridine, respectively. The corresponding
results are provided in Fig. 2 and Fig. S5 (ESI†).
As shown in Fig. 2, HTNNS-400 exhibits the lowest initial
À1
adsorption heat of 104 kJ mol and the smallest saturation
À1
coverage of 307 mmol g , revealing the weakest surface acidity.
FTN-400 and STN-400 have the same initial adsorption heat of
À1
1
15 kJ mol , but the saturation coverage of STN-400 is slightly
larger than that of FTN-400. Interestingly, among four catalysts,
À1
SFTN-400 displays the largest saturation coverage of 576 mmol g
,
although it has nearly the same initial heat of adsorption as Fig. 3 The alcoholysis of styrene epoxide with methanol by different catalysts.
7
508 Chem. Commun., 2013, 49, 7507--7509
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Table 1 The alcoholysis of styrene epoxide with different alcohols
phenyl group through conjugation. Therefore, nucleophiles
(
i.e., alcohols) would mainly attack the most stable benzyl
Entry
Alcohol
Time (h)
Yield (%)
carbocation, giving rise to b-alkoxyalcohols (Fig. 4).
1
2
3
4
5
6
7
8
MeOH
1
2
3
4
1
2
3
4
99
98
98
98
99
99
90
99
À
In conclusion, sulfur and iron co-doped [TiNbO5] nano-
sheets were successfully prepared and evaluated as a novel solid
acid catalyst in alcoholysis of styrene oxide at room tempera-
ture. A variety of alcohols were used as nucleophilic reagents
and methanol was incredibly easy to accomplish. Compared
with undoped and single-doped catalysts, the co-doped catalyst
exhibited excellent catalytic performance (99% yield in only 1 h
with methanol as nucleophile). After recycling for 3 times, the
yield was still up to 98%. These behaviors could be due to the
high dispersion of iron species, appropriate Lewis acid strength
from the strong interaction between the sulfur group and iron,
high thermalstability and moderate surface area. The avail-
ability and nontoxicity of iron as well as the mild synthetic and
reaction conditions involved make the synthetic process
appealing from an environmental point of view. In addition,
the new catalyst may act as a promising candidate in many
acid-catalyzed reactions and the present work may provide a
new approach for the design and fabrication of novel hetero-
geneous catalysts.
MeOH, 1st recycle
MeOH, 2nd recycle
MeOH, 3rd recycle
EtOH
n-PrOH
i-PrOH
n-BuOH
Reaction conditions: styrene epoxide (1 mmol), alcohol (2 mL), catalyst
SFTN-400, 50 mg), room temperature.
(
This work was supported by the National Natural Science
Foundation of China (Grant No. 21073084 and 20773065),
Natural Science Foundation of Jiangsu Province (Grant
No. BK2011438), 973 Project (Grant No. 2009CB623504) and
Modern Analysis Center of Nanjing University. We also thank
Fig. 4 The proposed catalytic mechanism for the alcoholysis of styrene epoxide
with alcohols by SFTN-400.
The observed catalytic performance agrees well with the above- Professor Jianyi Shen and Professor Weijie Ji for their help
mentioned surface acidity analysis results. in ammonia adsorption calorimetry and IR spectroscopy of
Table 1 lists the catalytic performance of SFTN-400 for the adsorbed pyridine.
alcoholysis of styrene oxide with different alcohols. All reac-
Notes and references
tions could occur readily at room temperature and the corre-
sponding b-alkoxyalcohols were obtained in a high yield (>90%).
Specifically, for the alcoholysis of styrene oxide with primary
alcohols such as methanol, ethanol, n-propyl alcohol and n-butyl
alcohol (entries 1, 5, 6 and 8), the reaction could be complete.
Nevertheless, a relatively longer time is required for alcohols
with a higher molecular weight. In contrast, for the alcoholysis
of styrene oxide with isopropyl alcohol, the reaction was slow
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This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 7507--7509 7509