Base-free selective oxidation of glycerol with 3% H2O 2 catalyzed by sulphonato-salen-chromium(III) intercalated LDH

Article abstract of DOI:10.1016/j.catcom.2012.08.014

A MgAl layered-double hydroxides (LDH) intercalated by sulphonato-salen- chromium(III) complex was used to the selective oxidation of glycerol (GLY) using 3% H₂O₂ as oxidant. The results revealed that the LDH hosted chromium complex was effective heterogeneous catalyst. And the main product was the C₃ oxygenated products of secondary alcohol-dihydroxyacetone (DHA). Under the optimal reaction conditions, the highest conversion of GLY reached 73.1% with 43.5% of the selectivity to DHA. Moreover, the catalytic performance remained after being recycled 6 times. In addition, the reaction probably involved an enzyme mimetic mechanism.

Full text of DOI:10.1016/j.catcom.2012.08.014

Catalysis Communications 28 (2012) 73–76
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Base-free selective oxidation of glycerol with 3% H O catalyzed by
2
2
sulphonato-salen-chromium(III) intercalated LDH
a
a,
b
a
a
a
a
Xiaoli Wang , Gongde Wu ⁎, Fang Wang , Keqiang Ding , Fang Zhang , Xianfeng Liu , Yunbo Xue
a
Department of Environment and Technology, Nanjing Institute of Technology, Nanjing, 211167, PR China
College of Sciences, Nanjing University of Technology, Nanjing 210009, Jiangsu, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2012
Received in revised form 13 August 2012
Accepted 13 August 2012
Available online 23 August 2012
A Mg\Al layered-double hydroxides (LDH) intercalated by sulphonato-salen-chromium(III) complex was used
to the selective oxidation of glycerol (GLY) using 3% H as oxidant. The results revealed that the LDH hosted
chromium complex was effective heterogeneous catalyst. And the main product was the C oxygenated products
of secondary alcohol‐dihydroxyacetone (DHA). Under the optimal reaction conditions, the highest conversion of
GLY reached 73.1% with 43.5% of the selectivity to DHA. Moreover, the catalytic performance remained after
being recycled 6 times. In addition, the reaction probably involved an enzyme mimetic mechanism.
2 2
O
3
Keywords:
Layered-double hydroxide
Schiff base
©
2012 Elsevier B.V. All rights reserved.
Selective oxidation
Glycerol
Dihydroxyacetone
1
. Introduction
Therefore, in recent years, much effort has been paid to the selective
catalytic oxidation of GLY to high-value DHA.
GLY is a co-product of triglyceride transesterification in the pro-
Most previous selective oxidation of GLY mainly used supported
noble metals (Pd, Pt and Au) as catalysts [5–12]. However, noble
metal catalysts were not only expensive, but also suffered catalytic
deactivation with increasing reaction time. Therefore, in recent
years the research had been focusing on the design of effective
low-cost transition metal catalysts for selective oxidation of GLY.
Unfortunately, up to now only a few of relevant reports were
found. McMorn et al. reported that the transition metal-containing
silicates and aluminophosphate catalysts could oxidize GLY in the
duction of fatty acid esters employed as biodiesel. For every 9 kg of
biodiesel produced, about 1 kg of a crude GLY by-product is formed.
With the increase of biodiesel production, the price of GLY will
decrease sharply. GLY is expected to become a major platform chem-
ical, and has been recently identified as an important building block
for future biorefineries by the US Department of Energy (DOE) [1–3].
Therefore, GLY should find new outlets to optimize the economy of
biodiesel production, and to synthesize the value-added chemicals.
Various valuable conversion of GLY has been studied, including oxida-
tion, reduction, halogenation and eterification. Among them, oxida-
tion is one of the most intensively studied pathways. Because GLY is
a highly functionalized molecule in comparison with hydrocarbons,
the oxidation of GLY often shows a wild product distribution: DHA,
glyceraldehyde (GLAD), glyceric acid (GLYAC), hydroxypyruvic acid
2 2
presence of H O , but the main products were the low-value formic
acid and a mono-formate ester of GLY [13]. Zhou et al. used
Cu-containing layered double hydroxide (LDH) to the selective
oxidation of GLY by O
Shul'pin et al. reported the oxidation of GLY in the homogeneous
manganese complex-H -oxalic acid-acetonitrile system, whereas
2
, and the main product was glyceric acid [3].
2 2
O
(
HYPAC), mesooxalic acid (MESAC), tartronic acid (TARAC), etc.
the yield of DHA did not surpass 15% [14]. Thus, there is still an
urgent need to develop effective catalysts for selective oxidation of
GLY to DHA.
Here we reported the efficient selective oxidation of GLY to DHA
2 2
with 3% H O catalyzed by sulphonato-salen-chromium(III) complex
intercalated LDH. The catalytic performance of LDH hosting complex
was compared with that of LDH, homogeneous complex and the
immobilized complex on mesoporous MCM-41, and an in-depth
study on the differences in their catalytic performance was carried
out. Moreover, the roles of reaction conditions in the catalytic
These products are valuable chemical intermediates; particularly
DHA was economically the most interesting one due to its applications
in cosmetics. At present the commercially available DHA is generally
produced in a fermentation process due to the quality requirements
by good manufacturing practice regulation in cosmetics industry [4].
⁎
Corresponding author. Tel. /fax: +86 25 86118960.
E-mail address: wugongde@njit.edu.cn (G. Wu).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.08.014

74
X. Wang et al. / Catalysis Communications 28 (2012) 73–76
performance of catalyst, the stability of catalyst as well as the reaction
mechanism were also discussed in detail.
chromium complex present in the catalytic system, the amounts of
different catalysts was determined according to their elemental com-
position. Under the conditions used herein, only five products DHA,
GLYAC, TARAC, formic acid and oxalic acid were detected. Other prod-
ucts, if any, present as minor constituents could not be detected.
2
. Experimental
2
.1. Catalyst preparation and characterization
When O
tion did not take place under the present non-alkaline conditions (see
Table 1). This indicated that when 3% H was used as oxidant, the
disproportionation decomposition of H to O was unproductive
for GLY oxidation. Obviously, if a catalyst was inactive to dispropor-
tionately decompose H , namely showed high H efficiency, it
would exhibit high catalytic activity. This could explain the almost
identical profiles of H O efficiency and GLY conversion over different
2 2
catalysts in Table 1.
The results in Table 1 also showed no significant amount of GLY
was oxidized without catalyst or with MCM-41 as catalyst. In contrast,
the GLY conversion was 6.4% over parent LDH, but the overoxidation
product of formic acid was found to be the main dominant product
2
was used as oxidant, it was noted that the oxidation reac-
The homogeneous sulphonato-salen-chromium complex was pre-
2 2
O
pared, and then was intercalated into LDH, The so-obtained homogeneous
complex and intercalated complex were denoted as Cr(SO -salen) and
LDH-[Cr(SO -salen)], respectively. The synthetic and characterization
procedures had been described in our previous report [15].
For comparison, Cr(SO -salen) was also immobilized on mesoporous
MCM-41 by a similar procedure [16], except Cr(SO -salen) was used in
place of Cr(salen). The so-obtained immobilized complex [abbreviated
as Cr(SO -salen)-MCM-41] was characterized by various physico-
2
O
2
2
3
3
2
O
2
2 2
O
3
3
3
2
chemical measurements such as FT-IR, UV–vis, XRD, N sorption
and elemental analysis (see supplementary information).
(
Sel. 92.6%). In the presence of homogeneous Cr(SO
3
-salen), the GLY
oxygen-
2
.2. Catalytic test
The catalytic glycerol oxidation experiments were carried out
conversion reached 36.1%. Simultaneously, a small amount C
3
ated products of DHA and GLAD was detected (Sel. 9.5 and 13.7%, re-
spectively); though formic acid was still the main product (Sel.
under atmospheric pressure in a three neck flask (100 mL) equipped
with a heat-gathering style magnetism mixer (DF-II). For each reactor,
75.8%). This indicated that Cr(SO
tributed to the oxidation of secondary alcohol in GLY. When
Cr(SO -salen)-MCM-41 was used as catalyst, compared to the catalytic
performance of homogeneous complex, only the GLY conversion was
slightly increased to 45.9%, no significantly enhanced selectivity to
DHA was found. Interestingly, when the reaction was performed over
LDH-[Cr(SO -salen)], the GLY conversion was remarkably increased to
3
71.3%, while the main product was DHA (Sel. 43.5%) instead of
GLAD (Sel. 20.9%) and formic acid (Sel. 35.2%). Considering the sim-
3
-salen) Schiff base complex con-
0
.2 g of catalyst was suspended in 50 mL aqueous solution of glycerol
3
−
1
(
0.2 mol L ). Once the required temperature reached, 3% H
2
O
2
was
introduced into the reactor. After reaction, catalyst was filtered off,
and the aqueous solution was analyzed using an Agilent 1200 series
high-performance liquid chromatography (HPLC) equipped with re-
fractive index detector and UV–vis detectors. Product separation in
the HPLC was carried out using an Aminex HPX-87 H column
(
Bio-Rad) operating at 333 K with 0.01 mol/L H
at 0.5 mL/min. An injection volume of 10 μL and a measure time of
0 min were adjusted. The retention times and calibration curves
2
SO
4
as eluent flowing
ilar content of active Cr(SO
3 3
-salen) complex in LDH-[Cr(SO -salen)]
and Cr(SO -salen)-MCM-41, the differences in their catalytic perfor-
3
3
mance could be related to their different supports. It was known that
−
were found using known concentrations of products. During the oxi-
dation reaction, gas in the effluent was collected and analyzed by a
BALZERS OMNISTAR QMS200 mass spectrometer. H
was determined after the reactions by iodometric titration.
the weak base LDH host (OH ) benefited the cleavage of peroxide
2 2
O
due to the formation of H-bonding between the OH−
bond in H
and the hydrogen atom of H
the oxidation capacity of H
2
O
2
consumption
2
O
2
, which could significantly improve
2
O
2
[15]. On the other hand, the weak
base environment could also enhance the catalytic performance by fa-
cilitating the formation of intermediate product alkoxide [5]. Therefore,
the synergistic effect of chromium Schiff base complex and the weak
3
. Results and discussion
3
.1. Catalytic performance
base LDH host made LDH-[Cr(SO
selective oxidation of GLY to DHA with 3% H
It is known that, when O was used as oxidant, basic environment
can significantly enhance both the catalytic activity and the selectivity
3
-salen)] an effective catalyst for the
2 2
O .
Without any organic solvent, phase transfer catalyst or additive,
2
the so-obtained catalysts were used to the selective oxidation of
GLY. In order to ensure the identical concentration of active
to C
3
oxidation products of primary alcohol — GLYAC [1,5,11], while
Table 1
a
Catalytic performance of samples in GLY oxidation.
Catalysts
Cr wt.%
Amounts of
catalysts (g)
GLY Con.
(mol %)
Sel. (mol %)
DHA
2 2
H O Efficiency
(mol %)
GLAD
TARAC
Formic acid
Oxalic acid
Blank
MCM-41
LDH
Cr(SO
Cr(SO
LDH-[Cr(SO
LDH-[Cr(SO
LDH-[Cr(SO
LDH-[Cr(SO
LDH-[Cr(SO
……
……
……
11.50
2.20
6.36
6.36
6.36
6.36
6.36
……
0.58
0.20
0.11
0.58
0.20
0.20
0.20
0.20
0.20
0
0
6.4
36.1
45.9
71.3
71.2
72.0
70.5
0
0
0
0
9.5
9.7
43.5
43.0
42.7
43.5
0
0
0
1.6
13.7
13.5
20.9
21.5
21.2
19.8
0
0
0
0.2
0.8
0
0
0
0.2
0
0
0
0
0
0
0
0
9.7
40.2
52.0
77.5
77.0
78.5
76.2
0
92.6
75.8
76.7
35.2
33.0
34.1
35.4
0
5.6
0.2
0.1
0.4
2.5
1.6
1.3
0
3
-salen)
3
-salen)-MCM-41
3
3
3
3
3
-salen)]
-salen)]
-salen)]
-salen)]
b
c
d
-salen)]e
a
Reaction conditions: GLY (10 mmol), 3% H
Adding pyrocatechol (20 mmol).
Adding resorcinol (20 mmol).
2 2
O (25 mL), 60 °C, 4 h.
b
c
d
e
Adding hydroquinone (20 mmol).
Reaction conditions: GLY (10 mmol), O
2
60 mL min−1, 60 °C, 4 h.

X. Wang et al. / Catalysis Communications 28 (2012) 73–76
75
In order to obtain the best catalytic results, the effect of condition
parameters on the catalytic performance of LDH-[Cr(SO -salen)] was
3
investigated. It was found that the amount of oxidant and catalyst, the
reaction time and temperature all significantly influenced the catalyt-
ic performance of this intercalated complex (see Fig. 2). When the re-
action run for 4 h at 60 °C over 0.2 g catalyst with 25 mL 3% H O , the
2 2
best GLY conversion of 71.3% with 43.5% of the selectivity to DHA
were achieved.
The mechanistic probe for the selective oxidation of alcohols with
H
2
O
2
by oxometal complexes was attracting continuous interests, and
the prevailing accepted ones were the enzyme mimetic mechanism
the heterolytic bond cleavage of peroxide) and the free-radical
(
mechanism (the homolytic bond cleavage of peroxide) [17,18]. To
check the presence of radicals, the inhibition experiments were
designed by the use of three radical scavengers (pyrocatechol, resor-
cinol and hydroquinone). No significant lowering of the conversion of
GLY was observed (see Table 1), suggesting the involvement of
enzyme mimetic mechanism.
Fig. 1. Effect of pH value on the catalytic performance of LDH-[Cr(SO
3
-salen)].
3
In addition, a further study on the stability of LDH-[Cr(SO -salen)]
the acidic environment assisted the formation of the C
3
oxidation
was also carried out. After the first catalytic run, the catalyst was sep-
arated from the reaction solution, washed several times with water to
remove any physisorbed molecules, dried and then reused in another
five catalytic runs. The results in Fig. 3 revealed that the catalyst was
still active until being reused for six times. Chemical analysis revealed
that the recovered catalyst after six times held almost the same chro-
mium content (Cr wt%: 6.35) as the fresh catalyst, indicating that the
chromium leaching was negligible. The nature of the above recovered
catalyst had also been followed by FTIR spectrum (see Fig. 4), and no
significant change was observed. This further indicated that the
obtained LDH hosted chromium complex was stable in the present
reaction conditions. Therefore, the significantly decreasing catalytic
performance over the recovered catalyst after the sixth runs might
product of secondary alcohol – DHA [1,6]. Here, we also investigated
the role of pH value in the catalytic performance of LDH-[Cr(SO -salen)]
in the selective oxidation of GLY with 3% H . Basic and acidic environ-
ment was provided by adding NaOH and NaHSO at the beginning of the
3
2 2
O
3
reaction, respectively. The results in Fig. 1 revealed that both acidic and
basic environments were not conducive to the oxidation reaction. It had
been prevailing accepted that Schiff base complex was susceptible to be
inactive due to oxidative degradation under acidic environment. In con-
trast, basic environment promoted the invalid decomposition of H
2 2
O
to O though the catalyst was stable. Therefore, in the present catalytic
2
oxidation system, neutral environment favored the selective oxidation
of GLY.
3
Fig. 2. Effect of condition parameters on the catalytic performance of LDH-[Cr(SO -salen)].

76
X. Wang et al. / Catalysis Communications 28 (2012) 73–76
Fig. 3. Reusability of LDH-[Cr(SO
3
-salen)]. Reaction conditions: GLY (10 mmol), 3%
H
2
O
2
(25 mL), catalyst (0.2 g), 60 °C, 4 h.
Fig. 4. FTIR spectra of LDH-[Cr(SO3-salen)]: (a) as prepared, (b)used six times.
Appendix A. Supplementary data
be related to the increasing residual adsorbed molecules which
prevented the reactants from accessing the active sites.
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2012.08.014.
References
4
. Conclusions
[
1] Ch.H. Zhou, J.N. Beltramini, Y.X. Fan, G.Q. Lu, Chemical Society Reviews 37 (2008)
527–549.
LDH hosted sulphonato-salen-chromium(III) complex was
a
[
[
2] L. Prati, P. Spontoni, A. Gaiassi, Topics in Catalysis 52 (2009) 288–296.
3] Ch.H. Zhou, J.N. Beltramini, Ch.X. Lin, Zh.P. Xu, G.Q. Lu, A. Tanksale, Catalysis
Reviews: Science and Technology 1 (2011) 111–122.
promising catalyst for the selective oxidation of GLY to DHA with 3%
. This could be attributed to the synergistic effect between chro-
2 2
H O
mium Schiff base complex and the weak base LDH host. The chromium
Schiff base complex contributed to the oxidation of secondary alcohol
in GLY, while the weak base LDH host could improve H O efficiency,
2 2
and could also facilitate the formation of intermediate product alkox-
ide. The highest GLY conversion reached 73.1%, with 43.5% of the
selectivity to DHA, when the reaction ran at 60 °C for 4 h over 0.2 g
[4] B. Katryniok, J. Kimura, E. Skrzyńska, J.-S. Girardon, P. Fongarland, M. Capron, R.
Ducoulombier, N. Mimura, S. Paul, F. Dumeignil, Green Chemistry 13 (2011)
1960–1979.
[
[
[
5] L. Prati, A. Villa, C.E. Chan-Thaw, R. Arrigo, D. Wang, D.S. Su, Faraday Discussions
152 (2011) 253–365.
6] H. Kimura, K. Tsuto, T. Wakisaka, Y. Kazumi, Y. Inaya, Applied Catalysis A: General
96 (1993) 217–228.
7] A. Tsuji, K.T.V. Rao, Sh. Nishimura, A. Takagaki, K. Ebitani, ChemSusChem 4 (2011)
542–548.
2 2
catalyst with 25 mL 3% H O . Moreover, the catalytic performance
[
[
8] A. Villa, G.M. Veith, L. Prati, Angewandte Chemie 122 (2010) 4601–4604.
9] A. Villa, G.M. Veith, L. Prati, Angewandte Chemie International Edition 49 (2010)
remained after being recycled 6 times. We believe that the more effi-
cient intercalated catalysts for the selective oxidation of GLY can be
prepared by modifying the structure and composition of Schiff base
complex and LDH host, which will exhibit more wildly application
prospect. This work will be of significance for high effective heteroge-
neous catalyst design.
4499–4502.
[10] G.L. Brett, Q. He, C. Hammond, P.J. Miedziak, N. Dimitratos, M. Sankar, A.A.
Herzing, M. Conte, J.A. Lopez-Sanchez, Ch.J. Kiely, D.W. Knight, S.H. Taylor, G.J.
Hutchings, Angewandte Chemie International Edition 50 (2011) 1–4.
11] B.N. Zope, D.D. Hibbitts, M. Neurock, R.J. Davis, Science 330 (2010) 74–77.
12] M. Sankar, N. Dimitratos, D.W. Knight, A.F. Carley, R. Tiruvalam, Ch.J. Kiely, D.
Thomas, G.J. Hutchings, ChemSusChem 2 (2009) 1145–1151.
[
[
[
[
13] P. McMorn, G. Roberts, G.J. Hutchings, Catalysis Letters 63 (1999) 193–197.
14] G.B. Shul'pin, Y.N. Kozlow, L.S. Shul'pina, T.V. Strelkova, D. Mandelli, Catalysis
Letters 138 (2010) 193–204.
Acknowledgements
[
15] G. Wu, X.L. Wang, J.P. Li, N. Zhao, W. Wei, Y.H. Sun, Catalysis Today 131 (2008)
4
02–407.
16] X.L. Wang, G.D. Wu, W. Wei, Y.H. Sun, Transition Metal Chemistry 35 (2010)
13–220.
[17] L. Roecker, T.J. Meyer, Journal of the American Chemical Society 109 (1987)
46–754.
18] B.-H. Éva, S. Gábor, Journal of Molecular Catalysis A: Chemical 230 (2005) 79–83.
The authors acknowledge the financial supports from the National
Natural Science Foundation of China (21003073, 21203093), the Program
to Cultivate Outstanding Young Key Teachers of Colleges and Universities
of Jiangsu Province and the Innovation Technology Funding Project of
Nanjing Institute of Technology (CKJ2010012).
[
2
7
[