Lewis-acid-promoted catalytic cascade conversion of glycerol to lactic acid by polyoxometalates

Article abstract of DOI:10.1039/c5cc10262f

The polyoxometalates AlPMo₁₂O₄₀ and CrPMo₁₂O₄₀ show high activity and reusablility for cascade conversion of glycerol directly to lactic acid under mild conditions without the addition of base, and can be reused more than 12 times with 90.5% selectivity at 93.7% conversion. AlPMo₁₂O₄₀ is tolerant to crude glycerol from biodiesel production.

Full text of DOI:10.1039/c5cc10262f

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Dear editor,
Please find attached our manuscript “Lewis-acid-promoted catalytic cascade conversion of
glycerol to lactic acid by polyoxometalates”.
Lactic acid (LA) is a very promising platform compound for production of polylactic acid and
chemicals, which is generally produced by fermentation of sugars under severe conditions.
Chemical synthesis of LA from glycerol is a potential alternative to meet the expected demand for
limited sugar feedstocks, because glycerol is an abundant waste of biodiesel production. By now,
high efficiency of glycerol conversion to LA was achieved under hydrothermal conditions (severe
temperature and pressure) requiring large excess of inorganic hydroxides without any recycles.
Due to drawbacks of such process, economic profitability and environmental sustainability of new
value processes would be extremely desired for LA production. Because of the limitation and
difficulty of LA production under base, there were only three reports on conversion of glycerol to
LA without adding any base over noble metal as catalysts combined with Lewis acid. However,
the efficiency was not higher enough for satisfactory even at high temperature or using long
reaction time. In this respect, designation and evaluation of new catalysts is particularly important
under base free.
In this paper, we synthesized two Keggin polyoxometalate catalysts MPMo12O40 (M = Al2 and
Cr2 ) both showed high activity and reusablility for cascade conversion of glycerol direct to lactic
acid (LA) under mild conditions without adding any base. These bifunctional catalysts not only
have advantages in promoting the oxidation of glycerol to some useful products, but also can be
assistance during the transformation from intermediates to the target products we wanted. More
importantly, AlPMo12O40 exhibited almost the highest activity (93.7 %) and the highest selectivity
(90.5 %) to LA under 60 °C within 5 h among reported heterogeneous catalysts under base free. In
addition, the MPMo12O40 catalysts demonstrated nearly no leaching and stable catalytic
performance in more than 12 catalytic runs. Very high potential of AlPMo12O40 as a catalyst for
LA synthesis can be highlighted to convert crude glycerol (LA yield 82.7 % under optimized
conditions) as well as neat glycerol (LA yield 49.3 % under optimized conditions for 24 h), which
made it more economic to sound environmental benign.
Another contribution of this work is to find firstly the promoting effect of Lewis metal ions on
the redox potentials for POMs, which opens the alternative way to further optimization of these

Page 3 of 26
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DOI: 10.1039/C5CC10262F
and related catalysts by Lewis ions modification to increase their catalytic ability in redox
reactions. This also provides guidance for POM application in cascade reactions for this or other
biomass-related transformations.
We are convinced that this study is of high relevance and interesting for the broad readership
of Chem. Commun. We hope that you and the referees come to the same conclusion.
Sincerely yours
Dr Xiaohong Wang

ChemComm
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Dear editor:
Thank you for your useful comments and suggestions on our manuscript. After having seen those
comments, we considered carefully each point raised by the referees and the changes are listed
numerically below:
Referee: 1
Comments to the Author
In the revised manuscript, the authors have answered most of the questions raised by two
reviewers. Only one question they should clarify: Referee 2, Question 1, the authors should
provide BET surface area values rather than N2 sorption isotherms (shown in Fig. S10).
Afterwards, this work can be accepted for publication in ChemComm..
Answer: We have added the BET surface area values in Fig. S10 as you suggested.
The manuscript has been resubmitted to your journal. We look forward to your positive response.
Sincerely yours
Dr. Xiaohong Wang

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COMMUNICATION
Lewis-acid-promoted catalytic cascade conversion of glycerol to
lactic acid by polyoxometalates
Received 00th January 20xx,
Accepted 00th January 20xx
Meilin. Tao,a Dan. Zhang,a Xi. Deng,a Xiangyu. Li,b Junyou. Shib* and Xiaohong. Wang a
*
DOI: 10.1039/x0xx00000x
www.rsc.org/
air, using high glycerol concentrations and crude glycerol as a
feedstock.
Polyoxometalates AlPMo12O40 and CrPMo12O40 show high activity
and reusablility for cascade conversion of glycerol directly to lactic
acid under mild conditions without adding base, which can be
Polyoxometalates (POMs) are well known acid and redox
reused more than 12 times with 90.5 % selectivity at 93.7 % catalysts for various organic reactions.6 For cascade conversion
of glycerol to LA under base free, the bifunctional catalysts
containing Lewis acidity and redox ability are needed.7 In this
concept, POMs are good candidates and could be designed to
own redox and Lewis centers in one unit. In general, the Lewis
conversion. AlPMo12O40 is tolerant to crude glycerol from of
biodiesel production.
With the requirements of sustainable development, the acidic sites were introduced to Brønsted acidic POMs through
production of fuel and chemicals from waste materials has exchanging protons by Lewis metal ions, which were under
been paid more attention.1 Glycerol is an easily available deep investigation.8 To the best of our knowledge, there is no
feedstock from biodiesel production, which can be converted study on the introduction of Lewis centers to redox POMs and
into several value-added chemicals.2 Among these, oxidation then investigation of the influence of these Lewis metals on
of glycerol to lactic acid is the most important due to its their redox potentials, especially for their oxidative catalysis.
extensive application in food, pharmaceutical and chemical
The conversion of glycerol to LA reportedly is atom-
industries as platform chemicals and green solvents.3 Apart
economic but requires both redox conversion and
from fermentation route,1,4 an alternative production of LA
dehydration/rehydration steps in the presence of noble metals
combined with Lewis acidic additive such as AlCl3.9 And CrCl3 is
from glycerol has been developed, which generally requires
a common used Lewis acid catalyst in biomass conversion.10
oxidation and dehydration/rehydration steps under reductive
During these reactions, the hydration of Al3+ and the toxicity of
or inert conditions, or with oxidants or electrochemicals. Such
Cr3+ or Cl- often influence their application. Modifying Al or Cr
conversion needs bifunctional cascade catalysts, generally
using noble metals Pt, Ir, Au, and Pd plus alkaline, or Au, Pt
combined with Lewis centers Sn, AlCl3 or TiO2 (Table S1).3,5
Under base conditions, Ir (Ⅰ) bis-carbonyl complex was the
with POMs might escape such disadvantages and could also
fabricate double catalytic sites, i.e. redox center and Lewis acid
sites for developing new application in wild organic synthesis.
In this paper, we reported POM catalytic system
MPMo12O40 (abbreviated as MPMo, M = Al and Cr )
most active homogeneous catalyst giving 96 % selectivity and
94% conversion at 130 ° C for 24 h. Because of the side effect
of bases and harsh reaction conditions under bases,
elimination of bases while maintaining high activity and
selectivity for aerobic oxidation of glycerol to LA needs to be
developed. By now, under base free, Pt/Sn-MFI was the best
heterogeneous catalyst giving 89.8 % conversion of glycerol
and 80.5 % selectivity at 100 °C for 24 h with TOF 1.95, while
long reaction time, high temperature and noble metals were
needed to achieve a high yield of LA. It is therefore highly
desirable to develop new heterogeneous catalytic system to
escape side reactions to attain high efficiency and high
selectivity under more mild conditions, no solvent, reaction in
a
Ⅲ
Ⅲ
―the
redox center PMo12O40, in combination of Lewis acid sites Al3+
or Cr3+, for the green production of LA from glycerol. In this
reaction, PMo12O40 catalyzed oxidation of glycerol to
glyceraldehydes (GCA) and dihydroxyacetone (DHA), and then
the produced intermediates GCA and DHA dehydrated to
pyruvaldehyde (PLA) over Al or Cr to generate the target
product LA (Scheme 1).
In a typical reaction protocol, 0.5 g of glycerol was mixed
with 5 mL of water in a Parr reactor, then 0.023 mmol of
MPMo was added as the catalyst. The Parr reactor was stirred
at 60 °C for a specified time.
Conversion of glycerol to LA with high efficiency was
achieved by MPMo heterogeneous catalysts. Table 1 showed
the catalytic performance of a range of acids including AlCl3,
CrCl3, K3PMo12O40 (KPMo), CrPMo and CrPMo. The range of
a.Key Lab of Polyoxometalate Science of Ministry of Education, Northeast Normal
University, Changchun 130024, P. R. China. E-mail: wangxh665@nenu.edu.cn,
Fax: 0086-431-85099759
b.Wood Material Science and Engineering Key laboratory of Jilin Province, Beihua
University, Jilin, 132013, P. R. China
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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Journal Name
OH
KPMo, AlPMo and CrPMo have the same redox center
PMo12O403-, but the difference in conversion efficiency was
firstly due to the influence of Lewis metal ions on their original
redox potentials (Fig. S1). It can be seen that the order of the
redox potentials of the MPMo was AlPMo (0.78 V) > CrPMo
(0.62 V) > KPMo (0.20 V same as H3PMo12O40), respectively. To
our surprise, it was found for the first time that the Lewis
metal ions had significant influence on the redox potentials for
POMs. Compared to their parent H3PMo12O40, the redox
potentials shifted 0.58 and 0.42 V to the positive direction
corresponding to Cr and Al, respectively, while K did not have
such effect. This result showed that the addition of Lewis
metal ions could help to increase oxidation-reduction
performance for POMs. The reason was the interaction
O
O
O
+
H2O
-
H2O
O
HO
OH
Lewis acid
(fast)
pyruvaldehyde
lactic aOcHid
dihydroxyacetone
(High selectivity)
O2
OH
O2
(slow)
HO
OH
OH
glycerol
OH
O2
O
O2
OH
HO
OH
acetic acid
O
HO
O
glyceraldehyde
glyceric acid
Scheme 1 Proposed tandem reaction pathways for the
selective oxidation of glycerol to lactic acid over the MPMo
catalyst.
Table 1 Comparison between representative catalysts from literature and as-prepared MPMo for glycerol oxidation to LA
T
CON
(%)
Selectivity
to LA(%)
Glycerol
concentration
Time
(h)
Molar ratio of
gly. to cat.
Catalysts
Substrate
Addition
Ref
(°C)
[3b]
[3c]
[5b]
[5c]
[6a]
Cp*Ir
Glycerol
Glycerol
Glycerol
Glycerol
KOH
none
AlCl3
Neat
0.2 M
15
24
2
115
100
160
100
142.8
2.2
8.4
89.8
29.7
99
> 95
80.5
58.5
80
Pt/Sn-MFI
AuPd/TiO2
Au–Pt/nCeO2
0.005 M
25.0
6.8
NaOH
0.17 M
0.5
Au/CeO2
AlCl3
Glycerol
Glycerol
Glycerol
Glycerol
Glycerol
Glycerol
DHA
NaOH
none
none
none
none
none
none
none
none
none
none
none
none
none
-
48
5
5
5
5
5
3
3
2
3
3
2
3
3
90
60
60
60
60
60
60
60
60
60
60
60
60
60
1.1
2.4
2.4
2.4
2.4
2.4
2.4
2.4
2.4
2.4
2.4
2.4
2.4
2.4
98
7.6
5.2
93.7
88.0
77.1
64
83
0.6
0.5
90.5
85.3
73
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
0.1 M
This report
This report
This report
This report
This report
This report
This report
This report
This report
This report
This report
This report
This report
CrCl3
AlPMo
CrPMo
KPMo
AlPMo
AlPMo
AlPMo
CrPMo
CrPMo
CrPMo
KPMo
KPMo
74
GCA
50
42
LA
2.2
60
DHA
69.0
38.0
GCA
46
LA
2.0
48.6
40.3
DHA
35.1
16.0
GCA
glycerol conversion is AlPMo (93.7 %) > CrPMo (88.0 %) >
KPMo (77.1 %) > AlCl3 (7.6 %) > CrCl3 (5.2 %). Here, AlPMo
showed a superior performance compared to other catalysts,
AlPMo gave a higher yield of LA than pure redox KPMo and
pure Lewis acid AlCl3, which can be concluded that the redox
between Mo = O ••••••••Al, which was mainly contributed to
the acceleration of electron transferring in oxidation.11 This
linkage was supported by IR spectra (Fig. S2a), in which νas
Mo=O blue shifted to 940 cm-1 compared to that of HPMo.
Stronger Lewis acidity is, higher redox potential exhibits, which
ability of a catalyst is essential for glycerol conversion to LA.
2 | J. Name., 2012, 00, 1-3
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is correlated to their Lewis acid strength (Z/r values for Al and CrPMo was also attributed to the slow oxidation of LA to
Cr are 7.69 and 4.84, respectively). From this point, it was further acetic acid. The last reason for higher efficiency of
helpful to tailor the redox potentials for POMs through
introduction of Lewis metal cations for specialized oxidation
reaction. Therefore, the conversion of glycerol was improved
over AlPMo and CrPMo compared to KPMo.
(a)
For LA yields within 2 h, AlPMo and CrPMo presented
increasing LA yield from 4.5 % over KPMo to 33.8 % and 25.8
%, respectively (Fig. 1). And TOF was enhanced significantly
from 5.4 to 41.5 and 31.7 h-1, 8 and 6 times higher than KPMo,
respectively. The enhanced TOF over MPMo was also
contributed to the effect of Lewis acidity on LA production in
comparison to KPMo (Table S1). KPMo shows a litter Lewis
acidity with 0.03 mmol/g, while the Lewis acidity is 0.60 and
0.40 mmol/g corresponding to AlPMo and CrPMo,
respectively.
(b)
Fig. 1 Oxidation of glycerol catalyzed by different POMs.
Reaction conditions: 2.3×10-5 mol of catalyst, 1.1 M of glycerol
(5 mL), 60 ºC, 2 h, 10 bar. TOF = (concentration of formed LA,
Fig. 2 Time course of glycerol and the products. (a) for CrPMo,
(b) for AlPMo, Reaction conditions: 5 mL, 1.1 M of glycerol,
mol L-1)/((amount used HPA, mol L-1)×(reaction time, h)
The representative product distributions verse reaction time 2.3×10-5 mol of MPMo, 10 bar O2, 800 rpm.
catalyzed by AlPMo and CrPMo was given in Fig. 2. It can be
seen that oxidation of glycerol to LA through three steps
S4). AlPMo or CrPMo are insoluble in water due to being
including glycerol oxidation to DHA and GCA, dehydration of
DHA and GDA to PLA, then benzylic acid rearrangement-like
their solubility was affected by the calcination temperatures.
transformation of PAL to LA. POMs with bifunctional sites such
AlPMo or CrPMo was that their hydrophobic properties (Fig.
treated at 250 ºC under calcinations (Table S2, Fig. S5) and
Insoluble MPMo salts are highly water-tolerant and capable of
as Lewis acidity and redox potential were contributed to these
rapidly releasing of generated water from their secondary
three steps―oxidation needs redox sites and chemselectivity
structure to promote the dehydration of DHA to PAL. AlPMo,
to DHA by Lewis acid sites; dehydration requires Lewis acid
being strong water-tolerance, presented the fast speed of
sites; and transformation of PAL to LA needs Lewis acid sites.
generation of LA.
The faster transformation of DHA and GCA to LA catalyzed
Therefore, the formation of LA over AlPMo was monitored
by AlPMo and CrPMo than by KPMo was determined by the
by different amount of catalyst (0.007-0.039 mmol),
compared experiment (Table 1, Fig. S3), showing the effect of
concentration of glycerol (0.5-2.2 M), reaction times (2 - 5 h),
Lewis acidic sites. Meanwhile, the different Lewis acidic
strength gave different conversion rate for DHA and GCA
(Fig. S6). The 93.7 % conversion of glycerol and 84.8 % of LA
dehydration, while stronger Lewis acidity resulted in their
faster conversion to LA. AlPMo exhibited higher activity for
h, 60 °C, and 10 bar.
DAH and GCA conversion compared to CrPMo. Therefore, the
formation of LA mainly depended on Lewis acidity through
temperatures (40-70 °C) and amount of oxygen (2.5-12.5 bar)
yield were found at 0.023 mmol of catalyst, 1.1 M of glycerol, 5
The reusability of AlPMo or CrPMo is the essential factor for
industrial application. To determine the nature of AlPMo in
dehydration and rearrangement reaction. In addition, the fast
transformation of DHA and GCA might further impel the
glycerol oxidation, the leaching test was done.12 AlPMo was
filtered after reaction 1 h (ca. 36.2 % conversion and 10.6 % LA
glycerol conversion. The higher LA yield over AlPMo and
yield) and the filtrate allowed reacting over further 1 h at the
same temperature. The conversion of glycerol was only 37.0 %
This journal is © The Royal Society of Chemistry 20xx
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with slight increase, which showed that AlPMo could only MPMo, the surface acidity, structure characterization, typical
leach
a
little into the mixture and it could act as
a
procedures for glycerol oxidation), and figures S1-10.
heterogeneous catalyst in such reactions. Fig. S7 showed
reusability and the leaching of AlPMo and CrPMo during 12
time cycles. AlPMo and CrPMo could be recycled more than 12
times without significant loss. The exceptional reusability
contributed to their stability under reaction conditions, and
little leaching of the active sites during 12 time cycles. The
leaching amount of AlPMo was only 5.2 wt % of initial amount
after 12 cycles. Therefore, MPMo (M = Al, Cr) are rather stable
catalysts in glycerol conversion.
Notes and references
1
2
J. J. Bozell and G. R. Petersen, Green Chem, 2010, 12, 539.
(a) S. H. Chai, H. P. Wang, Y. Liang and B. Q. Xu, Appl. Catal. A
Gen, 2009, 353, 213; (b) J. M. Clomburg and R. Gonzalez,
Trends Biotechnol, 2013, 31, 20.
(a) B. Sarkar, C. Pendem, L. N. S. Konathala, R. Tiwari, T.
Sasaki and R. Bal, Chem. Commun, 2014, 50, 9707. (b) J. Xu,
H. Zhang, Y. Zhao, B. Yu, S. Chen, Y. Li, L. Hao and Z. Liu,
Green Chem, 2013, 15, 1520; (c) L. S. Sharninghausen1, J.
Campos1, M. G. Manas1 and R. H. Crabtree, Nat. Commun,
3
An interesting finding is that AlPMo was also available for
the conversion of neat glycerol and crude glycerol from
biodiesel production, which was more important for the
industrial applications. AlPMo could successfully catalyze neat
glycerol convert to LA under the optimized reaction conditions
(5 mL neat glycerol, 0.023 mmol of AlPMo, 10 bar O2, 800 rpm,
60 °C) with 64.0 % yield at 77.2 % conversion for 24 h.
Conversion of crude glycerol is another challenging due to the
negative influence by the impurities.13 Here used crude
glycerol was obtained from biodiesel production without any
purification comprising 71 wt% of glycerol, 28 wt % of
methanol and other minor organic admixtures. Surprisingly,
AlPMo displayed a good activity in converting crude glycerol to
LA with almost the same conversion (94.2 %) and selectivity
(88.3 %) under mild conditions (10 wt.% aqueous solution of
crude glycerol, 0.023 mmol of AlPMo, 10 bar O2, 800 rpm, 60
°C, 5 h). This result suggested AlPMo to be a methanol-tolerant
catalyst capable of converting crude glycerol.
2014,
(a) M. Dusselier, P. Van Wouwe, A. Dewaele, E. Makshina
and B. F. Sels, Energy Environ. Sci, 2013, , 1415; (b) P. Mäki-
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Arvela, I. L. Simakova, T. Salmi and D. Y. Murzin, Chem. Rev,
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Uparea, N. T. Le, Y. K. Hwang, D. W. Hwang, U. H. Lee, H. R.
Kim and J. S. Chang, Appl Catal A: Gen, 2013, 468, 260.
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(a) T. Okuhara, Chem Rev, 2002, 102, 3641; (b) I.V.
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7
8
In summary, we have synethsized the first heterogeneous
POM catalsyts for one-pot preparation of LA from glycerol
under extremely mild conditions without adding any base.
AlPMo exhibited almost the highest activity (93.7% of
conversion and 90.5% of LA selectivity) among the reported
catalysts Pt/Sn-MFI (89.8 % conversion and 80.5 % selectivity
at 100 ºC for 24 h) and AuPd/TiO2 (29.7 % conversion and 58.5
% selectivity at 160 ºC for 2 h) under base free. More
importantly, production of LA from glycerol was achieved
under mild conditions (60 ºC, 5h), catalyst concentration as
low as 0.023 mmol, without adding solvent, reusability of
AlPMo, and tolerant to crude feedstocks, which fulfill the
“green chemistry” concept. Very high potential of AlPMo as a
catalyst for LA synthesis can be highlighted to convert crude
glycerol (LA yield 83.1 % under optimized conditions) as well as
neat glycerol (LA yield 49.3 % under optimized conditions for
24 h), which made it more economic to sound environment.
Another contribution of this work is to find the promoting
effect of Lewis metal ions on the redox potentials for POMs,
which opens an alternative way to further optimization of
catalysts by Lewis ions modification to increase their catalytic
ability in redox reactions. This also provides guidance for POM
application in cascade reactions for this or other biomass-
related transformations.
9
10 J. Song, B. Zhang, J. Shi, H. Fan, J. Ma, Y. Yang and B. Han,
RSC Adv, 2013, , 20085.
3
11 L. Dong, Y. Wang, Y. Lv, Z. Chen, F. Mei, H. Xiong and G. Yin,
Inorg. Chem, 2013, 52, 5418.
12 R. Sheldon, M. Wallau, I. Arends, U. Schuchardt, Acc. Chem.
Res, 1998, 31, 485.
13 (a) E. Skrzyńska, A. W. Grabowska, M. Capron, F. Dumeignil,
Appl.Catal. A Gen, 2014, 482, 245; (b) F. Yang, M. Hanna, R.
Sun, Biotechnol. Biofuels, 2012, 5, 12.
This work was supported by the National Natural Science
Foundation of China (No. 51578119), the major projects of Jilin
Provincial
Science
and
Technology
Department
(20140204085GX), the National public welfare special
(201504502), and the Changbai Mountain scholars program
(2013076).
Electronic
Experimental Methods (general information, preparation of
Supplementary
Information
Available:
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
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lactic acid
+[H2O]
pyruvaldehyde
-[H2O]
dihydroxyacetone
glycerol
glycerol
[O2]

ChemComm
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Supporting information
Lewis - acid- promoted catalytic cascade conversion of glycerol to lactic acid by
polyoxometalates
Meilin Tao1, Dan Zhang1, Xi Deng1, Xiangyu Li2, Junyou Shi2,*, Xiaohong Wang 1,*
Key Lab of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry,
Northeast Normal University
Page
S1
Contents
Table of Contents
Experimental Methods and some explanation
S2-4
Table S1. Acid strength distribution of of MPMo
S5
S6
Table S2 The solubility and catalytic performance of MPMo catalysts calcined at
different temperatures.
Fig. S1. CVꢀpotential curves of MPMo catalysts.
S7
S8
Fig. S2. FTIR spectra (a) and XRD patterns (b) of MPMo catalysts.
Fig. S3. HPLC spectra of the products after reaction for 1 h catalyzed by CrPMo.
Fig. S4. The CA of the two surfaces of the KPMo (a), CrPMo (b) and AlPMo.
Fig. S5. UvꢀVis spectrum of MPMo after being calcined over different temperature.
S9
S10
S11
S12
S13
S14
S15
S16
Fig. S6. The conversion and selectivity of oxidation of glycerol with various process
parameters.
Fig. S7. Reusability test catalyzed by MPMo in oxidation of glycerol.
Fig. S8. FTIR spectra of pyridine adsorption of bulk MPMo catalysts.
Fig. S9. SEM micrographs and EDX of (a) CrPMo, and (b) AlPMo.
Fig. S10. N2 sorption isotherms of CrPMo (a) and AlPMo (b) and BET of CrPMo (c) and
AlPMo (d)
S1

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Experimental Methods
General Information
All solvents and chemicals were used as obtained from commercial supplies. Elemental analysis
was carried out using a Leeman Plasma Spec (I) ICPꢀES. IR spectra (4000 ꢀ 500 cmꢀ1) was recorded
in KBr discs on a Nicolet Magna 560 IR spectrometer. Xꢀray diffraction (XRD) patterns of the sample
were collected on a Japan Rigaku Dmax 2000 Xꢀray diffractometer with Cu Kα radiation (λ=
0.154178 nm). The measurements were obtained in the step of 0.04º with account time of 0.5 s and in
the 2θ rang of 5ꢀ90 º. Raman spectroscopy was obtained on a RenishawꢀUVꢀvis Raman System 1000
equipped with a CCD detector at room temperature. The airꢀcooled frequency doubled NdꢀYag laser
operating at 532 nm was employed as the exciting source with a power of 30 MW. SEM micrographs
were recorded on a scan electron microscope (XL30 ESEM FEG 25kV). EDX spectra were obtained
using 20 kV primary electron voltages to determine the composition of the samples. The redox
potential were tested on a CS Corrtest electrochemical workstation equipped with glassy carbon as
both working and counter electrodes and saturated calomel as reference electrode. Electrochemical
measurements were performed with 0.1 M sulfuric acid solution as the supporting electrolyte. Surface
areas were calculated using the BET equation on a Micromeritics ASAP2010 micropore analyzer.
Preparation of MPMo
The MPMo catalysts were synthesized by an ionꢀexchanged method. 9.125 g (0.005 M) of
H3PMo12O40 was dissolved in 20 mL of deionized water at room temperature under vigorous stirring.
Then, the appropriate amount of metal salts aqueous solution (5 mmol) (nitrates for Cr and sulfate for
Al) was added dropwise to the former solution with continuous stirring. Then the mixture was dried in
nitrogen to produce the desired HPA catalyst. The remaining powder was dried at 80 ºC overnight and
then calcined at 250 ºC in static air for 4 h. The formation of MPMo reaction undergoes based on the
following equations:
M3+ + H3PMo12O40 → 3H++MPMo12O40 (M=Al, Cr)
MPMo catalysts were calcined at different temperatures ranging from 150 to 250 °C. These
catalysts are denoted as MPMo ꢀ150 to 250. The number indicates the calcination temperature. The
resulting AlPMo12O40 was obtained with yield 78.6 %. IR (1% KBr pellet, 4000 ꢀ 400 cmꢀ1): 1050 (sh,
νas PꢀOa, internal oxygen connecting P and Mo), 956 (s, νas MoꢀOd, terminal oxygen bonding to Mo
atom), 882 (m, νas MoꢀOb, edgeꢀsharing oxygen connecting Mo), 763 cmꢀ1 (s, νas MoꢀOc, cornerꢀ
sharing oxygen connecting Mo3O13 units). Anal. Calcd for AlPMo12O40: Mo, 62.72; Al, 1.69; P, 1.70
S2

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%. Found: Mo, 62.26; Al, 1.46; P, 1.68 %. The EDX analysis of the catalyst: Al, 0.02; Mo, 0.23 ; P,
0.02 (At%). The EDX measurement results showed that the approximate ratio of atomic percentage of
Al, Mo and P was 1: 11.5: 1. The resulting CrPMo12O40 was obtained with yield 78.6 %. IR (1% KBr
pellet, 4000 ꢀ 400 cmꢀ1): 1054 (sh, νas PꢀOa, internal oxygen connecting P and Mo), 944 (s, νas
MoꢀOd, terminal oxygen bonding to Mo atom), 861 (m, νas MoꢀOb, edgeꢀsharing oxygen connecting
Mo), 747 cmꢀ1 (s, νas MoꢀOc, cornerꢀ sharing oxygen connecting Mo3O13 units). Anal. Calcd for
CrPMo12O40: Mo, 62.11; Cr, 2.14; P, 1.61 %. Found: Mo, 61.43; Cr, 2.77; P, 1.65 %. The EDX
analysis of the catalyst: Cr, 0.02; Mo, 0.25; P, 0.02 (At%). The EDX measurement results showed that
the approximate ratio of atomic percentage of Cr, Mo and P was 1: 12.5: 1.
The surface acidity of MPMo
Titration was used to evaluate the total acid content of the solids. 0.05 g MPMo suspended in 45 mL
acetonitrile and then the mixture was stirred for 3 h. The density of acid sites in the catalysts was
measured by titration with a solution of nꢀbutylamine in acetonitrile (0.05 M) using the indicator
anthraquinone (pKa = ꢀ8.2). The IR spectra of adsorbed pyridine (PyꢀIR) helped to measure the acid
content and distinguish the properties of acid sites (Lewis or Brønsted). The samples were exposed to
the pyridine vapor for 12 h under vacuum (10ꢀ3 Pa) at 60 ºC. The quantification of acidity was
calculated by Lambert–Beer equation:
where A is the absorbance (area in cmꢀ1), ε is the extinction coefficient (m2/mol), W the sample
weight (kg), c the concentration of acid (mol/kg or mmol/g) and S is the sample disk area (m2). The
amount of Brønsted and Lewis acid sites was estimated from the integrated area of the adsorption
bands at ca. 1540 and 1450 cmꢀ1, respectively, using the extinction coefficient values based on the
previous report (Fig. S8).
The morphology, BET surface area, and solubility of MPMo
A representative selection of SEM images of CrPMo and AlPMo samples were presented in
Fig. S9. It can be found that these asꢀsynthesized materials displayed wellꢀshaped crystalline
particles. Furthermore, EDX was examined to determine the elemental compositions of these
samples, which determined the analytic results.
And from BET (Fig. S10) it can be seen that MPMo formed mesopore structure and the pore
sizes were 4.32 and 4.36 nm corresponding to CrPMo and AlPMo, respectively. In addition, the
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surface areas were 9.16, and 12 m2/g corresponding to CrPMo and AlPMo, respectively. The
difference of surface area and pore sizes for these two compounds was not high enough to
influence the conversion of glycerol. The absorption of glycerol by these two different catalysts
showed no difference.
MPMo catalysts were calcined at different temperatures in the range of 150ꢀ250 °C. The
solubility of MPMo was given in Table S2. It can be seen that with the increase in calcination
temperature from 150 to 250 °C, the solubility of the MPMo decreased. This determined that
calcinations of MPMo could give insoluble samples in water. Meanwhile, the total acidity of
MPMo catalysts being calcinated or not also gave us useful information that is the acid content
increased to some extent being treated by calcinations(Table S1).
Typical procedure for glycerol oxidation
Glycerol oxidation was performed in a highꢀpressure batch autoclave of stainless steel with a
polytetrafluoroethylene inlet (10 mL). The autoclave was equipped with gas supply system and a
magnetic stirrer. A catalyst was suspended in 5 mL aqueous glycerol, and the mixture was heated up
to 60 °C. During the reaction, oxygen pressure was maintained at 10 bar. After the experiment, the
reaction mixture was diluted 10 times with distilled water and analyzed by high performance liquid
chromatography (HPLC) using a Shimadzu LC10AꢀVP chromatograph equipped with a SPBꢀ10A
Variable UV (210 nm) and a RIDꢀ10A R.I. detector. Prevail TM C18 column (4.6 mm ×250 mm) was
used with a solution of H2SO4 (0.1% w/w) in H2O/acetonitrile (1/2 v/v)(1.0 mL minꢀ1) as the eluent at
50 ºC. External standard method was used to test the yields of intermediates including DHA, GCA,
GlyA and AcA, a serious of different concentrations of standard solutions were prepared and analyzed
by HPLC, then the corresponding yield of different intermediates was obtained clearly.
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Table S1 Acid strength distribution of of MPMo
Catalyst
cTotal acidity
(mmol/g)
aBrønsted acidity
(mmol/g)
aLewis acidity
(mmol/g)
aTotal acidity
(mmol/g)
bTotal acidity
(mmol/g)
H3PMo12O40
CrPMo12O40
AlPMo12O40
1.01
0.14
0.19
0.03
0.40
0.60
1.04
0.54
0.79
1.12
0.59
0.82
0.95
0.50
0.69
aThe B, L acidity and total acidity were valued by the IR spectra of adsorbed pyridine and calculated by LambertꢀBeer
equation.
bThe total acidity was measured by titration and the catalysts were calcined at 250 °C.
cThe total acidity was measured by titration and the catalysts were not calcined.
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Table S2 The solubility and catalytic performance of MPMo catalysts calcined at different
temperatures.
catalytic activity
Entry
Catalysts
Solubility (g/L)
Conversion (%)
Sel. to LA (%)
76.0
1
2
3
4
5
6
CrPMoꢀ150
CrPMoꢀ200
CrPMoꢀ250
AlPMoꢀ150
AlPMoꢀ200
AlPMoꢀ250
0.512
0.309
0.106
0.329
0.206
0.084
78.2
84.8
88.0
86.6
90.2
93.7
81.6
85.3
79.0
86.8
90.5
Reaction conditions: 5 mL, 1.1 M of glycerol, 2.3×10ꢀ5 mol of MPMo, 10 bar O2, 800 rpm, 5 h.
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Fig. S1. CVꢀpotential curves of MPMo catalysts.
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(a)
(b)
AlPMo
CrPMo
HPMo
Fig. S2. FTIR spectra (a) and XRD patterns (b) of MPMo catalysts.
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0.03
0.02
0.01
0.00
0.03
0.02
0.01
Detector A (210nm)
test
Ganyou20140618-4-2
1
Retention Time
Pk #
Area
4
2
3
6
5
0.00
12
0
1
2
3
4
5
6
7
8
9
10
11
Minutes
Fig. S3. HPLC spectra of the products after reaction for 1 h catalyzed by CrPMo:
1) Dihydroxyacetone (DHA); 2) Glyceraldehydes (GCA);
3) Pyruvaldehyde (PLA); 4) Lactic acid (LA); 5) Glyceric acid (GLA); 6) Acitic acid (AcA).
S9

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(a)
(b)
(c)
93.1±0.4
°
86.3±0.5
°
95.3±0.5
°
Fig. S4. The CA of the two surfaces of the KPMo (a), CrPMo (b) and AlPMo.
S10

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Fig. S5. UvꢀVis spectrum of MPMo after being calcined over different temperature.
S11

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100
80
100
80
(a)
(b)
CON
CON
Sel.to LA
Sel.to LA
60
60
)
(
)
%
40
%
(
40
20
0
20
0
0.007 0.015 0.023 0.031 0.039
The amount of catalyst (mmol)
0.5
0.9
1.1
1.6
2.2
concentration of glycerol (M)
100
80
100
(c)
(d)
CON
Sel.toLA
CON
80
60
Sel.toLA
60
)
(
)
%
40
%
(
40
20
0
20
0
2
3
4
5
40
50
60
70
Reactiontime(h)
ReactionTemperature(°C)
100
80
(e)
CON
Sel.toLA
60
)
%
40
(
20
0
2.5
5
7.5
10
12.5
Theamountofoxygen(bar)
Fig. S6. The conversion and selectivity of oxidation of glycerol with various process parameters:
(a) Amount of catalyst (AlPMo, 1.1 M of glycerol, 60 ºC, 5 h, 10 bar);
(b) Concentration of glycerol (2.3×10ꢀ5 mol of AlPMo, 60 ºC, 5 h, 10 bar);
(c) Reaction time (2.3×10ꢀ5 mol g of AlPMo,1.1 M of glycerol, 60 ºC, 10 bar);
(d) Reaction temperature (2.3×10ꢀ5 mol of AlPMo, 1.1 M of glycerol, 5 h, 10 bar).
(e) Amount of oxygen (2.3×10ꢀ5 mol of AlPMo, 1.1 M of glycerol, 5 h, 60 ºC).
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CrPMo
AlPMo
Fig. S7. Reusability test catalyzed by MPMo in oxidation of glycerol.
Reaction conditions: 2.3×10ꢀ5 mol of catalyst, 1.1 M of glycerol (5 mL), 60 ºC, 5 h, 10 bar.
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Fig. S8. FTIR spectra of pyridine adsorption of bulk MPMo catalysts.
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(a)
(b)
Fig. S9. SEM micrographs and EDX of (a) CrPMo, and (b) AlPMo.
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(a)
(b)
(c)
(d)
Fig. S10. N2 sorption isotherms of CrPMo (a) and AlPMo (b) and BET of CrPMo (c) and AlPMo (d)
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S17