Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured Promoted SnO2 Catalysts

Article abstract of DOI:10.1007/s10562-020-03241-9

Abstract: In this study nanostructured MoO₃ and WO₃ promoted SnO₂ solid acid catalysts were explored for the production of glycerol carbonate via carbonylation of bioglycerol with urea. The investigated reference SnO₂ and promoted catalysts were synthesized by fusion and wet-impregnation methods, respectively. The physicochemical properties of the prepared catalysts were thoroughly analyzed by XRD, Raman, BET surface area, TEM, FTIR, pyridine adsorbed FTIR, NH₃-TPD, and XPS techniques. It was found from the characterization studies that integration of SnO₂ with MoO₃ and WO₃ promoters leads to remarkable structural, textural, and acidic properties. Especially, a high quantity of acidic sites were observed over the MoO₃/SnO₂ catalyst (~ 81.45?μmol?g^?1) followed by WO₃/SnO₂ (61.81?μmol?g^?1) and pure SnO₂ (46.47?μmol?g^?1), which played a key role in the carbonylation of bioglycerol with urea. The BET specific surface area and oxygen vacancies of SnO₂ were significantly enhanced after the addition of MoO₃ and WO₃ promoters. TEM images revealed the formation of nanosized particles with a diameter of around 5–25?nm for the synthesized catalysts. The MoO₃/SnO₂ catalyst exhibited a high conversion and selectivity towards glycerol carbonate in comparison to other catalysts. The observed better performance is attributed to unique properties of MoO₃/SnO₂ catalyst including smaller crystallite size, high specific surface area, abundant oxygen vacancies, and more number of acidic sites. This catalyst also exhibited remarkable stability with no significant loss of activity in the recycling experiments. Graphic Abstract: Nanostructured MoO₃/SnO₂ solid acid catalyst exhibited an excellent catalytic activity and a high selectivity to glycerol carbonate in the carbonylation of bioglycerol with urea under solvent-free and mild conditions.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-020-03241-9

Catalysis Letters
https://doi.org/10.1007/s10562-020-03241-9
Solvent‑Free Production of Glycerol Carbonate from Bioglycerol
with Urea Over Nanostructured Promoted SnO2 Catalysts
Baithy Mallesham1,2 · Agolu Rangaswamy1 · Bolla Govinda Rao1 · Tumula Venkateshwar Rao1 ·
Benjaram M. Reddy1
Received: 25 March 2020 / Accepted: 26 April 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
In this study nanostructured MoO3 and WO3 promoted SnO2 solid acid catalysts were explored for the production of glyc-
erol carbonate via carbonylation of bioglycerol with urea. The investigated reference SnO2 and promoted catalysts were
synthesized by fusion and wet-impregnation methods, respectively. The physicochemical properties of the prepared catalysts
were thoroughly analyzed by XRD, Raman, BET surface area, TEM, FTIR, pyridine adsorbed FTIR, NH3-TPD, and XPS
techniques. It was found from the characterization studies that integration of SnO2 with MoO3 and WO3 promoters leads
to remarkable structural, textural, and acidic properties. Especially, a high quantity of acidic sites were observed over the
MoO3/SnO2 catalyst (~81.45 μmol g−1) followed by WO3/SnO2 (61.81 μmol g−1) and pure SnO2 (46.47 μmol g−1), which
played a key role in the carbonylation of bioglycerol with urea. The BET specifc surface area and oxygen vacancies of SnO2
were signifcantly enhanced after the addition of MoO3 and WO3 promoters. TEM images revealed the formation of nano-
sized particles with a diameter of around 5–25 nm for the synthesized catalysts. The MoO3/SnO2 catalyst exhibited a high
conversion and selectivity towards glycerol carbonate in comparison to other catalysts. The observed better performance is
attributed to unique properties of MoO3/SnO2 catalyst including smaller crystallite size, high specifc surface area, abundant
oxygen vacancies, and more number of acidic sites. This catalyst also exhibited remarkable stability with no signifcant loss
of activity in the recycling experiments.
Graphic Abstract
Nanostructured MoO3/SnO2 solid acid catalyst exhibited an excellent catalytic activity and a high selectivity to glycerol
carbonate in the carbonylation of bioglycerol with urea under solvent-free and mild conditions.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-020-03241-9) contains
supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
Vol.:(0123456789)
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B. Mallesham et al.
Keywords Bioglycerol · Urea · Glycerol carbonate · Acidic sites · SnO2 · MoO3/SnO2
of catalytic systems have been reported for the production
of glycerol carbonate via carbonylation of glycerol with
urea [21–24]. Although homogeneous catalysts are found
to be efective for glycerol carbonylation reaction, the use of
toxic and expensive reagents, difculty of catalyst separation
from the reaction mixture, tedious work-up procedure, and
generation of large amounts of waste have restricted their
application in the chemical industry. On the other hand, vari-
ous heterogeneous catalysts, such as promoted metal oxides,
hydrotalacites, rare earth metal oxides, zeolites, and metal
oxide supported noble and/or non-noble metal catalysts have
been reported for this reaction [25–31]. Among them, the
promoted metal oxides exhibit quite attractive physicochem-
ical and acidic properties and played a critical role in the
stability and higher catalytic activity for the carbonylation of
glycerol with urea [30, 31]. Particularly, SnO2 is an impor-
tant metal oxide due to its favorable structural, textural, and
acidic properties owing to multiple oxidation states of Sn
(Sn4+/Sn2+) and the presence of sufcient oxygen vacancy
defects [4]. It is therefore anticipated that addition of MoO3
and WO3 promoters to the SnO2 may lead to remarkable
enhancement in the defect sites and acidic properties which
could play a favorable role in the carbonylation of glycerol
with urea.
1 Introduction
It is now widely recognized that abundant, safe, and renew-
able sources of energy alternative to fossil fuels are desirable
to ensure long-term economic and social stability [1, 2]. As
known, the excessive consumption of fossil fuels leads to
increased levels of greenhouse gas emissions, resulting in
amplifed global average temperatures [3–5]. At the same
time, the demand for fossil fuel-based products is continu-
ously increasing, which could further worsen the environ-
mental pollution [6, 7]. In order to overcome the negative
impacts of fossil fuels, signifcant eforts have been under-
taken for the synthesis of platform chemicals towards a sus-
tainable society and the economy [8–10]. Glycerol is one of
the most abundant platform chemicals that can be obtained
largely in the biodiesel production (~10% of glycerol) pro-
cess i.e. the transesterifcation of vegetable oils or fats with
methanol [4]. Therefore, considerable research eforts are
going on for efcient transformation of surplus glycerol into
valuable products.
A number of reaction procedures for the conversion of
glycerol to high-value products have been reported in the
literature, including oxidation, esterifcation, transesterif-
cation, dehydration, hydrogenolysis, etherifcation, acetali-
sation, polymerization, pyrolysis, carbonylation, and steam
reforming [3–10]. Among them, the carbonylation of glyc-
erol is considered as one of the promising processes for the
synthesis of green and commercially important chemicals,
such as glycerol carbonate. Particularly, glycerol carbonate
is a versatile and renewable building block for organic syn-
thesis. For example, glycerol carbonate can be converted
into epichlorohydrin, surfactants, polymers and other, which
have a wide range of industrial applications [11–13]. Owing
to high boiling point, high fash point and low volatility
characteristics, glycerol carbonate and its esters are used as
solvents alternative to hazardous organic solvents for many
applications [14–16]. More importantly, glycerol carbonate
has a tremendous potential to become a key intermediate in
the polymers production industry [17].
The present investigation was undertaken against the
aforesaid background. Accordingly, the main aim of this
work was to synthesize glycerol carbonate more efciently
via carbonylation of glycerol with urea employing promoted
SnO2-based catalysts. In this study, MoO3 and WO3 pro-
moted SnO2 catalysts were prepared and explored for the
title reaction. The physicochemical properties of the pre-
pared catalysts were intensely investigated by employing
various characterization techniques, namely, X-ray difrac-
tion (XRD), BET surface area, Raman spectroscopy, Fourier
transform infrared spectroscopy (FTIR), pyridine adsorbed
FTIR (Py-FTIR), NH3-temperature programmed desorption
(NH3-TPD), and X-ray photoelectron spectroscopy (XPS).
Attempts were made to correlate the structural properties
of the prepared catalysts with their catalytic performance.
Diferent carbonyl sources, such as phosgene, CO2, alkyl
carbonate (dimethyl carbonate, ethylene carbonate, and pro-
pylene carbonate), and urea have been used for the produc-
tion of glycerol carbonate from glycerol [18–27]. Among
them, the utilization of urea has received signifcant atten-
tion because urea is a readily available, safe, clean, and
cheaper chemical. Further, urea has also drawn unequivocal
attention due to the signifcance of indirect CO2 chemical
utilization. To remove the NH3 formed during the reac-
tion, two diferent modes are normally employed namely,
reduced pressure or purging gas [13, 14, 25–27]. A number
2 Experimental Section
2.1 Materials
Various chemicals employed for the preparation of inves-
tigated catalysts were procured from commercial vendors
which include, glycerol (SRL, anhydrous extra pure AR
grade), crude glycerol (obtained during biodiesel syn-
thesis within the institute), urea, ammonium molybdate
1 3

Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured…
tetrahydrate ((NH4)6Mo7O24·4H2O) (Aldrich, AR grade),
ammonium metatungstate hydrate ((NH4)6H2W12O40·xH2O)
(Aldrich, AR grade), SnCl2·2H2O (Aldrich, AR grade), and
NaNO3 (Aldrich, AR grade). All these chemicals were used
without further purifcation. The crude glycerol contained
80–85% of glycerol, 15–20% of impurities such as water,
phospholipids, NaCl, FAMEs, soaps, MeOH, monoglycer-
ides, NaOH, and other.
The specifc surface areas were measured by BET analy-
sis on a SMART SORB‐92/93 instrument at liquid N2 tem-
perature. Prior to the experiment, catalysts were degassed
at 393 K for 2 h to remove surface adsorbed residual mois-
ture. Surface areas were obtained using the desorption data.
NH3-temperature programmed desorption (NH3-TPD) anal-
ysis was carried out on a Micromeritics AutoChem 2910
instrument. A thermal conductivity detector was used for
continuous monitoring of the desorbed NH3. The chem-
isorbed amount of ammonia was analysed in fowing He
gas with a fow rate of 20 mL/min from 323 to 1073 K at a
heating rate of 10 K/min. The amount of desorbed NH3 was
calculated from the peak area of the TCD signal.
2.2 Catalyst Preparation
A simple fusion procedure was employed for the synthesis
of pure SnO2 by using SnCl2·2H2O (Aldrich, AR grade) and
NaNO3 (Aldrich, AR grade) as the precursors. In a typi-
cal procedure, the desired amounts of both precursors were
dissolved in deionised water under mild stirring conditions
for 1 h at room temperature (NaNO3:SnCl2·2H2O=∼1:5).
The successive evaporation of excess water from the solu-
tion at 383 K resulted in a porous and foam-like solid mate-
rial. Subsequently, the reaction temperature was raised to
∼ 523 K and continued at the same temperature until the
formation of tin oxide powder. The resulting material was
washed with deionized water and dried at 373 K for 12 h and
calcined at 923 K for 5 h in the presence of atmospheric air.
The promoted 10 wt% MO3/SnO2 (M=Mo and W) cat-
alysts were prepared by incipient wetness impregnation
method. In a typical procedure, the desired quantities
of respective metal precursors (NH4)6Mo7O24·4H2O or
(NH4)6H2W12O40·xH2O were dissolved in double distilled
water followed by the addition of fnely powdered tin oxide
with stirring. The reaction mixture was placed on a hot plate
(383 K) and the excess water was evaporated under vigor-
ous stirring. The resulting materials were dried at 393 K for
12 h and fnally calcined at 923 K for 5 h in atmospheric air.
X-ray photoelectron spectra were recorded on a Shi-
madzu (ESCA 3400) spectrometer. The X-ray source uti-
lized was Mg Kα (1253.6 eV) radiation. Analysis was done
at room temperature, and the samples were mounted using
double-sided adhesive tape and the binding energies were
referenced to C (1 s) binding energy of adventitious carbon
contamination which was taken to be 284.7 eV. The TEM
studies were carried out on a JEM-2010 (JEOL) instrument
equipped with a slow-scan CCD camera at an accelerating
voltage of the electron beam 200 kV. The preparation of
samples for TEM analysis involved crushing of the materials
in an agate mortar and ultrasonically dispersing in ethanol
for 15–20 min followed by deposition on a copper grid. The
specimen was dried under vacuum at room temperature.
The elemental analysis of the prepared catalysts was car-
ried out by ICP-OES technique (Thermo Jarrel Ash model
IRIS Intrepid II XDL, USA) following sample dissolution
using acid digestion procedure.
The FTIR spectra were recorded on a Nicolet 740 FTIR
spectrometer at ambient conditions using KBr disks with a
nominal resolution of 4 cm−1 and averaging 100 spectra. For
FTIR analysis of adsorbed pyridine, the sample was oven
dried at 373 K for 1 h. The oven dried sample (∼ 50 mg),
in a sample cup, was contacted with pyridine (∼ 0.1 cm3)
directly. The sample cup was then kept in a vacuum oven
at 393 K for 1 h to remove the physisorbed pyridine. After
cooling to room temperature, the spectrum was recorded
with a nominal resolution of 4 cm−1 in the spectral range of
1400–1900 cm−1 using KBr background.
2.3 Catalyst Characterization
Powder XRD patterns were recorded on a Rigaku Multi-
fex instrument with a nickel-fltered CuKα radiation source
(1.5406 Å) and a scintillation counter detector. The intensity
data were collected over a 2θ range of 20° to 80° with scan-
ning at 0.01° step size and a counting time of 1 s per each
point. Raman spectra were recorded at ambient temperature
using a LabRam HR800UV Raman spectrometer (Horiba
Jobin–Yvon) equipped with a liquid-nitrogen cooled charge
coupled device (CCD) detector. The spectra were recorded
in the range of 100–1300 cm−1 and at a spectral resolution
of 2 cm−1 using the 632.81 nm excitation line from an argon
ion laser. The Ar+ laser was focused on the sample under a
microscope with the diameter of the analyzed spot being
∼1 μm. The acquisition time was adjusted in relation to the
intensity of Raman scattering.
2.4 Activity Measurements
The catalytic evaluation experiments were conducted in a
standard 25 mL two necked round bottom fask ftted with
refex condenser. The dry N2 gas was purged through the
second neck to remove the ammonia formed during the reac-
tion. In a typical experiment, the catalytic runs were per-
formed using 5.43 mmol of glycerol and 16.25 mmol of urea
with 50 mg of catalyst at 423 K and 4 h of reaction time with
constant stirring (800 rpm) under solvent-free conditions.
1 3

B. Mallesham et al.
After completion of the reaction, methanol was added to
the reaction mixture and the catalyst was separated by fl-
tration. The obtained products were identifed by GC–MS
equipped with a DB-5 capillary column. Samples were taken
periodically and analyzed by GC equipped with a BP-20
(wax) capillary column and fame ionization detector. The
GC analyses were usually repeated three times in order to
decrease the experimental error and reproducibility. In this
study, each experiment was performed under the kinetically
controlled region (Fig. S1, Supporting Information). The
conversion and product selectivity were calculated as per
the established procedures [4]. In this study, the calculated
carbon balance of all the catalytic runs was always greater
than 93%.
values compared to that of pure SnO2. As well, no charac-
teristic difraction peaks corresponding to MoO3 and WO3
were noticed in the XRD patterns of the impregnated SnO2
samples. This unusual observation could be either due to
the incorporation of Mo and W cations into the SnO2 lattice
or the amorphous nature of the MoOx and WOx species.
To understand this, we estimated the lattice parameters ‘a’
and ‘c’ by using the most intense lines of the XRD patterns
and the calculated values are presented in Table 1. These
observations, such as peak shift, diference in the lattice
parameters, and absence of peaks due to MoO3 and WO3
noticeably confrm the formation of metal ion-doped SnO2
solid solutions. The average crystallite sizes of all the sam-
ples were calculated using Debye–Scherrer formula and the
obtained values are summarized in Table 1. It was found that
the crystallite size of SnO2 noticeably decreases after the
addition of MoO3 and WO3, indicating the benefcial role of
the promoters towards inhibition of crystal growth against
the higher calcination temperatures.
3 Results and Discussion
3.1 Catalyst Characterization
Raman spectroscopy measurements were carried out
to know the phases of the oxides as well as structural
defects in the prepared catalysts (Fig. S2, Supporting
Information). The pure SnO2 sample exhibits primarily
three fundamental Raman bands at around 474, 632, and
774 cm−1, which are attributed to vibrational modes of Eg,
A1g, and B2g, respectively [32, 33]. Interestingly, the WO3
and MoO3 promoted SnO2 samples also showed the char-
acteristic vibration modes of pure SnO2. A closer obser-
vation of Fig. S2 reveals that Raman band (A1g) of the
Powder X-ray difraction patterns of pure and promoted
SnO2 samples are shown in Fig. 1. All the difraction peaks
can be readily indexed to the tetragonal structure of SnO2
with lattice constants of a=4.75 Å and c=3.19 Å, which are
well in agreement with the reported values (PDF #880287).
It can be clearly noted from Fig. 1 that the intensity of SnO2
peaks decreased with the incorporation of promoters into
the SnO2 lattice. It is obvious from Fig. 1 that the promoted
SnO2 samples exhibit broad peaks and shifted to higher 2θ
Fig. 1 Powder X–ray difrac-
tion patterns of (a) SnO2, (b)
*
*
WO3/SnO2, and (c) MoO3/SnO2
samples. (*, Characteristic XRD
lines of SnO2)
*
*
*
*
*
*
(c)
*
*
*
*
(b)
(a)
20
30
40
50
60
70
80
2 Theta (o)
1 3

Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured…
Table 1 Crystallite size (D),
Surface area (S), Pore volume
(V), Acidic sites (T), and
Lattice parameter (A) of SnO2,
WO3/SnO2, and MoO3/SnO2
catalysts
Catalyst
Da (nm) Db (nm)
Sc (m2/g) Vc cm3/g) Td (μmol/g) Loading
(wt%)e
Aa (Å)
a
MoO3 WO3
c
SnO2
WO3/SnO2
MoO3/SnO2
13.47
8.76
6.06
17.8 0.4 11
12.2 0.3 32
10.1 0.2 56
0.0739
0.0637
0.0679
46.47
61.81
81.45
–
–
9.51
–
4.75 3.19
9.49 4.71 3.17
– 4.69 3.16
aFrom XRD analysis
bFrom TEM
cFrom BET and BJH analysis
dFrom NH3-TPD
eFrom ICP-OES technique
promoted SnO2 samples is shifted to lower wavenumbers
compared to that of pure SnO2. This is due to the doping
of smaller W6+ and Mo6+ cations into the SnO2 lattice
and the consequent lattice contraction of SnO2 as well as
metal–oxygen vibration frequency that may cause a shift
in the A1g peak position. On the other hand, the observed
Eg peak represents the presence of oxygen vacancies in the
SnO2-based materials. It can be clearly noted from Raman
studies that the Mo6+ and W6+ doped SnO2 samples exhibit
higher quantities of oxygen vacancies than the pure SnO2.
Oxygen vacancy defects are a special class of point defects
in many oxide materials, which could play an important
role in heterogeneous catalysis [34]. As well, the observed
Raman band at around 200–360 cm−1 can be assigned to
the contributions from intrinsic lattice defects, resulting
from the substitution of Sn4+ with smaller sized promoter
metal ions.
Figure 2a presents the N2 adsorption–desorption iso-
therms of SnO2-based materials, which can be classifed as
Type IV isotherms with H1-type hysteresis loop. These iso-
therms are characteristic of mesoporous nature of the synthe-
sized materials [35]. The appearance of a H1 hysteresis loop
usually suggests improved pore size and pore connectivity of
prepared samples with uniform distribution [35, 36]. It can
be expected that pure SnO2 undergoes agglomeration and
sintering at higher temperatures, resulting in larger crystal-
lite sizes and smaller surface area. On the contrary, the pro-
moted SnO2 samples exhibit signifcant resistance towards
agglomeration and sintering during high temperature treat-
ment, which is due to the cooperative nature of the cations of
both the oxides. Therefore, the MoO3 and WO3-doped SnO2
samples exhibited a high specifc surface area compared to
that of pure SnO2. The obtained specifc surface area values
of SnO2, WO3/SnO2 and MoO3/SnO2 samples were ~ 11,
50
(A)
(B)
MoO3/SnO2
WO3/SnO2
SnO2
40
30
20
10
0
MoO3/SnO2
4
6
8
10
12
12
WO3/SnO2
4
6
8
10
SnO2
20
40
60
80
100
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/Po)
Pore diameter (nm)
Fig. 2 N2 adsorption–desorption isotherms (a) and pore size distribution (b) of SnO2, MoO3/SnO2, and WO3/SnO2 catalysts
1 3

B. Mallesham et al.
32 and 56 m2 g−1, respectively (Table 1). Figure 2b shows
the BJH pore size distribution analysis of the prepared sam-
ples. It is observed that SnO2 and MoO3/SnO2 materials
exhibit a unimodal pore size distribution, while the WO3/
SnO2 material shows a bimodal pore size distribution. The
pore volume of the SnO2 sample was also increased after
the addition of MoO3 and WO3 species. Fig. S3 (Supporting
Information) shows NH3-TPD profles of various catalysts.
From NH3-TPD profles, we have calculated total amount of
acidic sites of the catalysts and the results are presented in
Table 1. Higher numbers of acidic sites were observed for
MoO3/SnO2 sample (~81.45 μmol g−1) followed by WO3/
SnO2 (61.81 μmol g−1), and pure SnO2 (46.47 μmol g−1).
It is therefore obvious that the addition of MoO3 and WO3
species to the SnO2 enhances its acidic properties with BET
specifc surface area (Table 1).
Raman results. Figure 3b illustrates the O 1s XP spectra
of SnO2, WO3/SnO2, and MoO3/SnO2 catalysts. The O 1s
spectra were ftted with two Gaussian functions, indicating
the presence of two oxygen environments in the synthesized
samples. The observed major peak at lower binding energy
side (~530.2 eV) can be assigned to the presence of oxygen
species in the SnO2 lattice [39–42]. Another peak identi-
fed at higher binding energy side (~ 532.2 eV) reveals the
adsorbed oxygen species (− OH, CO, CO32−, etc.) on the
catalyst surface [39–41]. Fig. S4 (Supporting Information)
shows Mo 3d and W 4f spectra of the Mo- and W-promoted
SnO2 catalysts. The observed bands at ~232.7 (3d5/2) and
236.2 eV (3d3/2) in the Mo 3d spectrum indicates the pres-
ence of Mo6+ oxidation state [43, 44]. On the other hand,
the binding energies observed at ~35.6 and 37.8 eV can be
assigned to spin–orbit splitting of W 4f7/2 and W 4f5/2 com-
ponents, respectively, confrming the existence of W6+ ions
in WO3/SnO2 sample [45].
Figure 3a shows the Sn 3d core level XP spectra of the
prepared catalysts. The binding energy (BE) of the peaks
observed at around 487.4 and 495.8 eV correspond to Sn
3d5/2 and Sn 3d3/2, respectively. The BE diference between
the Sn 3d5/2 and Sn 3d3/2 is equal to 8.5 eV, which is a strong
evidence to identify the oxidation state of the Sn species in
the sample. Appearance of these peaks indicated that the
Sn is present in +4 oxidation state in the prepared materi-
als [37–39]. Interestingly, the Sn 3d peak position of the
promoted samples is shifted to higher binding energies
relative to pure SnO2. This observation indicates the pres-
ence of Mo(W)–Sn interactions, in line with the XRD and
The morphology of SnO2, WO3/SnO2, and MoO3/SnO2
catalysts were investigated by TEM analysis (Fig. 4). The
presence of irregular, non-uniform, and highly agglomer-
ated nanoparticles are observed for pure SnO2 sample.
In contrast, quite uniform sized particles were found for
the promoted SnO2 samples, which reveal the existence
of strong interactions between the promoter and SnO2.
The estimated average particle sizes for SnO2, WO3- and
MoO3-promoted SnO2 samples are ~17.8 0.4, 12.2 0.3
and 10.1 0.2 nm, respectively. The obtained FTIR spectra
Sn 3d
(A)
3d3/2
(B)
O 1s
3d5/2
(c)
(c)
(b)
(a)
(b)
(a)
528
530
532
534
536
538
480
485
490
495
500
Binding energy (eV)
Binding energy (eV)
Fig. 3 Sn 3d XP spectra (a) and O 1s XP spectra (b) of pure SnO2, MoO3/SnO2, and WO3/SnO2 samples
1 3

Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured…
Fig. 4 TEM images of SnO2, WO3/SnO2, and MoO3/SnO2 samples
represent the structural features of the catalysts as shown in
Fig. S5 (Supporting Information). The observed major FTIR
bands at ~680, 623 and 553 cm−1 can be assigned to difer-
ent vibration modes of O–Sn–O bridging bond and Sn–O–Sn
terminal bonds [44, 46]. The bands at ~1628 and 3410 cm−1
are attributed to O–H stretching and the deformation bend-
ing vibration modes of weakly bonded water molecules,
respectively. Two FTIR bands at ∼947 and 860 cm−1 were
1 3

B. Mallesham et al.
found for the promoted SnO2 samples due to the stretching
modes of the terminal M–O bonds with a certain amount of
double bond character and typical Sn–O–M modes (where
M=Mo and/or W), respectively [47, 48].
As shown in Scheme 1, various products are possible in
the catalytic carbonylation of glycerol with urea, such as
4-(hydroxymethyl)-1,3-dioxolan-2-one (glycerol carbon-
ate), 2,3-dihydroxypropyl carbamate (glycerol urethane),
and (2-oxo-1,3-dioxolan-4-yl)methyl carbamate. The cata-
lytic experiments were carried out at 423 K under solvent-
free conditions for 4 h under refux conditions. Very low
glycerol conversion (5.1%) and selectivity of glycerol car-
bonate (52.7%) were obtained in the absence of catalyst.
The conversion of pure glycerol over MoO3/SnO2, WO3/
SnO2 and SnO2 catalysts was observed to be ~69.2, 59.7 and
34.4% with glycerol carbonate selectivities of ~97.1, 95.1
and 79.2%, respectively. On the other hand, the achieved
crude glycerol conversions of MoO3/SnO2, WO3/SnO2 and
SnO2 catalysts were ~ 65.6, 57.5 and 31.3% with glycerol
carbonate selectivities of 95.3, 91.1 and 74.7%, respectively.
It was obvious that similar results were found in the case
of both crude glycerol and pure glycerol with urea for all
the catalysts (Table 2). This observation indicates that the
wide applicability of the prepared solid acid catalysts for
the production of glycerol carbonate from carbonylation of
glycerol with urea. Another interesting observation to be
noted is that incorporation of Mo- and W-species into the
SnO2 lattice drastically improved the catalytic efciency in
both the cases of pure and crude glycerol. The calculated
TOF values of SnO2, WO3/SnO2, and MoO3/SnO2 catalysts
were found to be 5.6, 10.0, and 11.2 h−1, respectively. The
The pyridine absorbed FTIR spectroscopy analysis is
used to understand the nature of the acidity of catalysts
(Fig. 5). Pyridine is a basic probe molecule employed to
examine the surface acidity of solid materials and also gives
the possibility to diferentiate the Lewis acidic sites from
the Brønsted acid sites [49]. Various bands were found in
the range of 1400–1700 cm−1. All the samples show pyri-
dine absorption bands at 1550 cm−1 followed by a peak at
around 1639 cm−1 which can be assigned to the presence of
Brønsted acid sites. The bands at ~1450 and 1610 cm−1 indi-
cate Lewis acidic sites (L). An additional band was found at
1455 cm−1 which can be attributed to pyridine adsorbed on
the Lewis acidic sites [50, 51]. On the other hand, the band
observed at around 1490 cm−1 is due to the combination of
both Lewis and Brønsted acid sites [4, 52]. It is evident from
the fgure that all the samples contain a higher amount of
Brønsted acid sites compared to Lewis acid sites.
3.2 Catalytic Activity
The carbonylation of pure and crude glycerol with urea
was conducted using MoO3/SnO2, WO3/SnO2, and
SnO2 catalysts and the results are presented in Table 2.
Fig. 5 Pyridine absorption
FTIR spectra of (a) SnO2, (b)
5
0
5
9
WO3/SnO2, and (c) MoO3/SnO2
catalysts. B Brønsted, L Lewis
acidic sites
4
(c)
4
1
1
0
5
5
1
(b)
9
3
6
1
(a)
L
B&L
1500
B
B
1400
1600
1700
1800
1900
Wavenumber (cm-1)
1 3

Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured…
Table 2 Catalytic activity of SnO2, WO3/SnO2, and MoO3/SnO2 solid acids in carbonylation of pure and crude glycerol with urea
Catalysts
XGly (%)
Selectivity of products (%)
TOF (h−1 a
)
C.B. (%)
3
4
5
Blank
SnO2
5.1
34.4
59.7
69.2
31.3
57.5
65.6
47.3
20.8
4.6
1.8
25.3
8.7
52.7
79.2
95.1
97.1
74.7
91.1
95.3
0
0
0.3
1.1
0
0.2
0.8
–
100.2
98.7
97.1
98.3
93.4
94.1
95.7
5.6
10.0
11.2
5.0
9.7
10.6
WO3/SnO2
MoO3/SnO2
b
SnO2
b
WO3/SnO2
MoO3/SnO2
b
3.9
Reaction conditions:1:3 molar ratios of glycerol (5.43 mmol) to urea (16.25 mmol), 423 K reaction temperature, 50 mg of catalyst, 4 h of reac-
tion time, and stirring speed=800 rpm
C.B. carbon balance
aTOF (h–1) mole of glycerol converted per hour/mole of catalyst used
bIndicates the crude glycerol activity
promoted catalysts were found to be most efcient with a
nearly two times higher activity than that of SnO2 (5.6 h−1)
sample. This result reveals the benefcial role of promoter
(Mo and W) in the enhancement of catalytic activity of SnO2
for carbonylation of glycerol with urea. Among all the cata-
lysts, the MoO3/SnO2 exhibited remarkable catalytic activity
and selectivity. It could be explained on the basis of unique
properties of MoO3/SnO2 catalyst including smaller crystal-
lite size, more crystal defects, high specifc surface area, and
more number of acidic sites.
urea is shown in Scheme 2. Various theories on the reaction
mechanism of carbonylation of bioglycerol with urea can be
found in the literature [13, 28, 53, 54]. The catalytic reaction
proceeds through adsorption, surface reaction and desorption
on M–O–Sn (M=Mo and W) catalyst surface. As shown in
Scheme 2, the glycerol and urea get adsorbed on the cata-
lyst surface via hydrogen bonding and Lewis acid–base
interactions. It is expected that Lewis acid sites of metal
ion activates the carbonyl oxygen of urea. Subsequently,
the activated urea can react with primary –OH group of the
glycerol to produce the terminal glycerol urethane with the
release of NH3 [25]. Now, there are two possible pathways:
The plausible reaction mechanism for the production of
glycerol carbonate from carbonylation of bioglycerol with
Scheme 1 Plausible reaction products for reaction between glycerol
(1) and urea (2), various products such as glycerol urethane (2,3-dihy-
droxypropyl carbamate) (3), 4-(hydroxymethyl)-1,3-dioxolan-2-one
(glycerol carbonate) (4), and (2-oxo-1,3-dioxolan-4-yl)methyl carba-
mate (glycerol carbamate) (5)
1 3

B. Mallesham et al.
Scheme 2 Plausible reaction
mechanism for carbonylation
of glycerol with urea over
SnO2-based solid acids
Fig. 6 Efect of reaction temperature on carbonylation of pure glyc-
erol (a) and crude glycerol (b) with urea over MoO3/SnO2 catalyst.
Reaction conditions: stirring speed=800 rpm; molar ratio of bioglyc-
erol to urea=1:3; reaction time=4 h; catalyst amount=50 mg. Sel. 3
selectivity of glycerol urethane (3), Sel. 4 selectivity of glycerol car-
bonate (4), Sel. 5 selectivity of glycerol carbamate (5)
(i) the –NH2 group of the intermediate can again react with
the glycerol carbamate to produce the product (5-hydroxym-
ethyl-2-oxazolidinone) with the removal of water molecule.
However, 5-hydroxymethyl-2-oxazolidinone product was not
observed in this study. Hence, this reaction follows another
pathway i.e., the secondary –OH group of the glycerol ure-
thane reacts with carbonyl carbon of the same urea molecule
to form the glycerol carbonate with the release of another
molecule of ammonia [23, 25]. In addition, the produced
glycerol carbonate further reacts with second molecule of
urea to form (2-oxo-1,3-dioxolan-4-yl)methyl carbamate (5).
It is therefore clear that the presence of more acidic sites and
higher surface area could play a key role in the carbonylation
of glycerol with urea to produce glycerol carbonate.
1 3

Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured…
To understand the effect of reaction temperature
(383–443 K) on the carbonylation of pure and crude glycerol
with urea, the reaction was performed over the MoO3/SnO2
catalyst and the obtained results are presented in Fig. 6a,
b. Very low glycerol conversions (~21.3 and 18.1%) were
noticed at 383 K for both the cases (crude and pure glycerol).
Afterwards, the glycerol conversions rapidly increased with
increasing of reaction temperature up to 423 K, and further
increase of temperature slightly increased the conversion
up to 443 K. This could be explained by low activation of
reactant molecules at 383 K, hence less number of reactant
molecules interacted with the catalyst and a low glycerol
conversion was achieved. At lower reaction temperature, low
selectivity of glycerol carbonate was found along with the
formation of glycerol urethane as intermediate product. With
rising of temperature the selectivity of glycerol carbonate
(97.1%) gradually increased with the expense of glycerol
urethane product up to 423 K and afterwards the selectiv-
ity was slowly decreased to 88.4% at 443 K. The glycerol
carbonate easily reacts further with another urea molecule
to produce (2-oxo-1,3-dioxolan-4-yl)methyl carbamate (5),
hence decreased selectivity of glycerol carbonate at higher
reaction temperatures.
conditions were kept same as shown in Table 2. The glyc-
erol conversion was drastically increased with increasing
of reaction time up to 4 h, and after that slowly increased
to 92.1% with the reaction time up to 8 h. At the initial
reaction time, the selectivities towards glycerol urethane
and glycerol carbonate were found to be 35.8 and 64.2%,
respectively. With increasing reaction time (up to 4 h) the
glycerol urethane was rapidly converted into glycerol car-
bonate and its selectivity reached to 97.1%. Subsequently,
there is a considerable decrease in the selectivity of glycerol
carbonate (87.3%) after 8 h of reaction time. The selectivity
of glycerol carbonate decreased with further time because
glycerol carbonate reacts with excess urea to yield the by-
product (5) (Scheme 1). The best glycerol conversion and
highest selectivity of glycerol carbonate achieved at 4 h of
reaction time were 69.2 and 97.1% respectively.
Figure 8 shows the infuence of glycerol to urea molar
ratios on the carbonylation of glycerol with urea over the
MoO3/SnO2 catalyst. The experiments were carried out by
varying the glycerol to urea molar ratio from 1:1 to 1:5 at
423 K reaction temperature, 4 h of reaction time, 800 rpm
of stirring speed and 10 wt% of catalyst with respect to glyc-
erol. At 1:1 molar ratio of glycerol to urea, 35.6% of glyc-
erol conversion and 72.2% of glycerol carbonate selectivity
along with 27.8% of glycerol urethane intermediate product
were obtained. It was found that the glycerol conversion
signifcantly enhanced with increasing of glycerol to urea
molar ratio up to 1:3 and the highest selectivity of glycerol
The infuence of reaction time was examined for the opti-
mization of glycerol carbonate production over the MoO3/
SnO2 catalyst and the achieved results are shown in Fig. 7.
These catalytic experiments were conducted at diferent
time intervals from 1 to 8 h and the remaining experimental
Fig. 7 Infuence of reac-
tion time on carbonylation
of bioglycerol with urea over
MoO3/SnO2 catalyst. Reac-
tion conditions: reaction
temperature=423 K; stirring
speed=800 rpm; molar ratio
of bioglycerol to urea=1:3;
catalyst amount=50 mg. Sel. 3
selectivity of glycerol urethane
(3), Sel. 4 selectivity of glycerol
carbonate (4), Sel. 5 selectivity
of glycerol carbamate (5)
1 3

B. Mallesham et al.
Fig. 8 Infuence of molar ratio
on carbonylation of bioglycerol
with urea over MoO3/SnO2
catalyst. Reaction condi-
tions: temperature=423 K;
stirring speed=800 rpm;
reaction time=4 h; catalyst
amount=50 mg. Sel. 3 selectiv-
ity of glycerol urethane (3),
Sel. 4 selectivity of glycerol
carbonate (4), Sel. 5 selectivity
of glycerol carbamate (5)
Fig. 9 Infuence of catalyst
amount on carbonylation of
bioglycerol with urea over
MoO3/SnO2 catalyst. Reac-
tion conditions: reaction
temperature=423 K; stirring
speed=800 rpm; reaction
time=4 h; molar ratio of
bioglycerol to urea=1:3. Sel. 3
selectivity of glycerol urethane
(3), Sel. 4 selectivity of glycerol
carbonate (4), Sel. 5 selectivity
of glycerol carbamate (5)
carbonate (97.1%) was achieved at 1:3 molar ratio. Subse-
quently, the selectivity of glycerol carbonate decreased with
rising of glycerol to urea molar ratios from 1:3 to 1:5. This
is primarily due to the reaction of glycerol carbonate with
excess urea to produce 2-oxo-1,3-dioxolan-4-yl)methyl car-
bamate as the by-product at higher molar ratios of glycerol
1 3

Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured…
to urea. The glycerol conversions achieved were ~35.6, 56.3,
69.2, 74.9, and 79.2% at molar ratios of 1:1, 1:2, 1:3, 1:4,
and 1:5, respectively. These observations are in line with
earlier reported results [14].
be ~20 and 64.2% at 10 mg of catalyst amount, respectively.
It can be observed from Fig. 9 that glycerol conversion rap-
idly increases with rising of catalyst amount up to 70 mg,
and there after not much variation in the glycerol conversion.
However, there is a remarkable change in the selectivity of
glycerol carbonate with the variation of catalyst amount up
to 50 mg. Then, the selectivity of glycerol carbonate slowly
decreased from 97.1 to 87.3%. These results suggest that
more amount of catalyst favor the conversion of glycerol as
well as glycerol carbonate due to the availability of more
number of active sites on the catalyst surface. Therefore, fur-
ther increase in the catalyst amount could favor the forma-
tion of 2-oxo-1,3-dioxolan-4-yl)methyl carbamate (12.3%),
We have investigated the efect of catalyst amount on the
glycerol conversion and the selectivity of the products over
the MoO3/SnO2 catalyst and the obtained results are pre-
sented in Fig. 9. The catalytic experiments were conducted
by varying the catalyst amount from 10 to 100 mg, and
keeping other experimental conditions same as described in
Table 2. The MoO3/SnO2 sample exhibited superior glycerol
conversion even at a low catalyst amount. The glycerol con-
version and selectivity of glycerol carbonate were found to
Fig. 10 Reusability on car-
bonylation of pure glycerol (a)
and crude glycerol (b) with
urea over MoO3/SnO2 catalyst.
Reaction conditions: reaction
temperature=423 K; stirring
speed=800 rpm; molar ratio of
bioglycerol to urea=1:3; cata-
lyst amount=50 mg; reaction
time=4 h. Sel. 4 selectivity of
glycerol carbonate (4)
1 3

B. Mallesham et al.
Table 3 Comparison of
performance of MoO3/SnO2
solid acid catalyst with reported
catalysts for carbonylation of
glycerol
Catalysts
Temperature Time (h)
(K)
XG (%)
XGC (%)
YGC (%)
Refs
MoO3/SnO2
Sn-beta zeolite
Au/Fe2O3
423
418
423
423
418
413
418
418
418
423
4
5
4
4
4
6
3
3
5
7
69
70
80
66
60
72
66
60
73
71
97
37
48
32
100
84
68
89
98
92
67
26
38
21
60
60
45
53
71
65
This work
[52]
[13]
[13]
[29]
[14]
[55]
[55]
[55]
Au/Nb2O5
Co3O4/ZnO
PS-(Im)2ZnI2
Cu/MCM-41
Ni/MCM-41
Zn/MCM-41
ZMG
[57]
hence decreased selectivity of the glycerol carbonate at
higher catalyst amounts.
be due to the agglomeration of smaller crystals to form
larger crystals after repeated cycles. As well, it was found
from BET and NH3-TPD results that the spent MoO3/SnO2
sample exhibits signifcantly decreased specifc surface
area with lower pore volume and small amounts of acidic
sites compared to that of fresh catalyst (Table ST1). The
obtained physicochemical properties of the spent cata-
lyst of crude glycerol reveal more deactivation than with
the spent catalyst of pure glycerol. It is primarily due to
easy deactivation of the catalyst surface in the presence
of more impurities in the crude glycerol. As mentioned in
the experiment section the crude glycerol contains vari-
ous impurities that include both organic and inorganic
compounds. The inorganic residues remained in the crude
glycerol are expected to play a critical role in the deactiva-
tion of the catalyst. Based on the above results, it can be
concluded that changes in the physicochemical properties
of MoO3/SnO2 catalyst are the major reason for its deac-
tivation in the recycling tests.
The stability of MoO3/SnO2 catalyst was evaluated by
recycling experiments for both pure and crude glycerol.
For each run, the catalytic experiments were performed at
423 K of reaction temperature under solvent-free condi-
tions with a 1:3 molar ratio of glycerol to urea, 800 rpm
of stirring speed and 50 mg of catalyst for 4 h of reaction
time. After completion of each cycle, the catalyst was sep-
arated by simple centrifugation, washed with de-ionized
water and methanol to remove the products adhering on
the surface of the catalyst. The resulting sample was dried
at 373 K for 12 h, and then reused directly for the next run.
The obtained results are shown in Fig. 10a,b. The obtained
pure glycerol conversions were ~ 69.2, 68.1, 67.4, 66.1,
and 56.6% for 1st, 2nd, 3rd, 4th, and 5th cycles, respec-
tively. These results indicate that there was no considera-
ble change in the performance of the catalyst up to 4th run,
and then the glycerol conversion and selectivity of glycerol
carbonate were slightly reduced. As well, the crude glyc-
erol conversions were found to be 65.6, 64.4, 63.2, 53.7,
and 48.3% for 1st, 2nd, 3rd, 4th, and 5th runs, respec-
tively. After 3rd run, the glycerol conversion and selectiv-
ity of glycerol carbonate were signifcantly decreased. To
determine the reasons for the decreased catalytic efciency
of MoO3/SnO2 catalyst after fourth and third cycles, we
performed various characterization studies namely, XRD,
BET SA, and NH3-TPD over the used MoO3/SnO2 catalyst
(4th and 3rd cycle) and the obtained results are presented
in Table ST1 (Supporting Information). The XRD profles
of the fresh and spent catalysts are shown in Fig. S6 (Sup-
porting Information). Similar characteristic difraction
peaks were found for both spent and fresh catalysts. The
estimated crystallite size of fresh and spent catalysts was
found to be ~ 6.06 and 10.14 (pure glycerol), 13.25 nm
(crude glycerol), respectively (Table ST1). It was clear
that the spent catalyst shows relatively larger crystallite
size compared to that of the fresh catalyst, which could
3.3 Comparison of MoO3/SnO2 with Reported
Catalysts
Finally, we have made an efort to compare the catalytic
activity results of MoO3/SnO2 solid acid with the reported
catalysts (Table 3). It can be noted that MoO3/SnO2 cata-
lyst shows comparable activity with the literature reported
works. However, we must understand that the reaction con-
ditions used in the present study are signifcantly diferent
with respect to the literature reports. Among the various
reported catalysts, the Au/Fe2O3 and Au/Nb2O5 samples
exhibited a high glycerol conversion with very low yield of
glycerol carbonate [13]. Copper, nickel, and zinc supported
on MCM-41 materials exhibited higher glycerol conver-
sions at low reaction times (3 h). However, the selectivity
of desired glycerol carbonate product was very low [55]. In
the case of PS-(Im)2ZnI2 and ZMG catalysts, higher glyc-
erol conversions and reasonable selectivity towards glycerol
1 3

Solvent-Free Production of Glycerol Carbonate from Bioglycerol with Urea Over Nanostructured…
carbonate were found, but longer reaction times are required
[14, 56, 57]. As well, Co3O4/ZnO catalyst shows lower glyc-
erol conversion with higher selectivity of glycerol carbonate
[29]. The Sn-β zeolite exhibited 70% of glycerol conversion
at lower reaction times [45]. In comparison to the literature
reports, it can be stated that the MoO3/SnO2 is a promising
catalyst for the carbonylation of glycerol with urea.
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Afliations
Baithy Mallesham1,2 · Agolu Rangaswamy1 · Bolla Govinda Rao1 · Tumula Venkateshwar Rao1 ·
Benjaram M. Reddy1
1
* Baithy Mallesham
Catalysis and Fine Chemicals Department, CSIR-
Indian Institute of Chemical Technology, Uppal Road,
Hyderabad 500 007, India
baithy.m@gmail.com
* Benjaram M. Reddy
2
bmreddy@iict.res.in
Chemical Engineering Department, Indian Institute
of Technology Hyderabad, Sangareddy, Kandi 502285, India
1 3