Continuous Synthesis of Glycerol Carbonate by Transesterification of Glycerol with Dimethyl Carbonate Over Fe–La Mixed Oxide Catalysts

Article abstract of DOI:10.1007/s10562-020-03397-4

Abstract: Transesterification of glycerol with dimethyl carbonate to produce glycerol carbonate was studied under continuous reaction over Fe–La mixed oxide catalysts. A series of Fe–La oxide catalysts with different molar compositions were synthesized by co-precipitation method. Surface and structural investigations of the catalysts were carried using N₂ physisorption, powder X-ray diffraction, temperature-programmed desorption, X-ray photoelectron spectroscopy, FT-infra red spectroscopy, scanning electron microscopy and Laser Raman spectroscopy. Glycerol carbonate yield was influenced by the molar ratios of Fe/La and catalyst calcination temperature, which are responsible for the variation in acid–base properties of the catalysts. The catalyst with a molar ratio of 1:1 calcined at 550?°C exhibited superior activity with 71% yield of glycerol carbonate. The synergistic effect between Fe–La oxides and the formation of LaFeO₃ perovskite structure are responsible for the high activity of the catalyst. The catalyst exhibited unprecedented stability over 100?h during the time on stream analysis. Graphic Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-020-03397-4

Catalysis Letters
https://doi.org/10.1007/s10562-020-03397-4
Continuous Synthesis of Glycerol Carbonate by Transesterifcation
of Glycerol with Dimethyl Carbonate Over Fe–La Mixed Oxide Catalysts
Piyusa P. Pattanaik1,2 · P. Mahesh Kumar1,2 · N. Raju1 · N. Lingaiah1,2
Received: 16 June 2020 / Accepted: 17 September 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Transesterifcation of glycerol with dimethyl carbonate to produce glycerol carbonate was studied under continuous reaction
over Fe–La mixed oxide catalysts. A series of Fe–La oxide catalysts with diferent molar compositions were synthesized by
co-precipitation method. Surface and structural investigations of the catalysts were carried using N2 physisorption, powder
X-ray difraction, temperature-programmed desorption, X-ray photoelectron spectroscopy, FT-infra red spectroscopy, scan-
ning electron microscopy and Laser Raman spectroscopy. Glycerol carbonate yield was infuenced by the molar ratios of
Fe/La and catalyst calcination temperature, which are responsible for the variation in acid–base properties of the catalysts.
The catalyst with a molar ratio of 1:1 calcined at 550 °C exhibited superior activity with 71% yield of glycerol carbonate.
The synergistic efect between Fe–La oxides and the formation of LaFeO3 perovskite structure are responsible for the high
activity of the catalyst. The catalyst exhibited unprecedented stability over 100 h during the time on stream analysis.
Graphic Abstract
Keywords Glycerol · Dimethyl carbonate · Glycerol carbonate · Fe–La mixed oxides · Transesterifcation
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1 3

P. P. Pattanaik et al.
the limitations associated with the batch process. The prepa-
ration of GLC by continuous transesterifcation reaction will
be more advantageous compared to the batch process. In the
batch process, the formation of consecutive products like
glycidol is possible at high glycerol conversion. The con-
tinuous reaction for GLC preparation will lead to selective
formation of the desired product with high throughput.
In recent times few studies reported for the synthesis of
glycerol carbonate in continuous mode [19–23]. Lari et al.
reported hydrotalcite mixed oxide catalysts using urea as
the source of carbonylation where the highest 60% yield of
GLC obtained using the aprotic solvent and catalytic binder.
The catalytic deactivation found after 10–15 h and the yield
lowered to 20% at the end of the reaction [24]. Wang et al.
recently reported modifed organocatalyst P2–tBu/PS as the
heterogeneous catalyst using DMC as the source of car-
bonylation under continuous reaction. It has been found a
gradual decrease in catalytic activity after 3 h and dropped
to 15% less in conversion by the end of 33 h of the reaction
[22]. Even though few researchers attempted continuous
reaction for the preparation of GLC, the overall activity and
stability are limited. The main drawback glycerol carbonate
synthesis during continuous operation is the stability of the
base catalysts. Development of stable catalyst is essential for
the preparation of glycerol carbonate from glycerol transes-
terifcation under environmentally benign continuous pro-
cess in place of existing batch process. It has been reported
that lanthanum oxide containing mixed oxides showed better
catalytic performance in transesterifcation of glycerol [25,
26]. La in combination with other metal oxide like Mg, Zn
are explored as base catalysts for transesterifcation reaction
with high stability [27]. It is thought the addition of La to Fe
oxide may improve the basicity and stability of the catalyst
towards the transesterifcation of glycerol with DMC.
The current work discloses the preparation of Fe and La
mixed oxide catalysts for the selective transesterifcation of
glycerol with DMC under continuous reaction conditions.
Mixed oxides of Fe and La were prepared with diferent
molar ratios and assessed for continuous transesterifcation
of glycerol under moderate reaction conditions. The reaction
was studied at diferent conditions to optimize the maximum
yield. The establishment of the stability of the catalysts is
one of the aims of the present study.
1 Introduction
The increasing worldwide demand for biofuels could retard
the harmful efect on the environment like greenhouse gas
emissions occurring from the burning of fossil fuels [1–3].
Among the biofuels, biodiesel is a green and sustainable
fuel in place of petroleum diesel [4]. The high production of
biodiesel could obviously resolve the future energy crisis in
society. The preparation of biodiesel from vegetable oils by
transesterifcation led to generate about ten percent of glyc-
erol as a by-product. Glycerol, a highly functional molecule
is a useful platform chemical to prepare diferent value-added
products. It can be converted into various useful chemicals by
diferent chemical transformation reactions such as hydrog-
enolysis, esterifcation, oxidation, carbonylation, etc.to syn-
thesize chemicals like 1,2-propanediol, acrolein, esters of
glycerol and glycerol carbonate (GLC) etc. [5–7].
Among the diferent possible products from glycerol,
GLC is one of the important molecules as it has extensive
applications in the preparation of polymers like polyes-
ters, polycarbonates, polyurethanes, surfactants, coatings,
adhesives, and lubricants [8–10]. It is widely used also as a
green solvent due to its low volatility and nontoxic nature.
Various routes for the synthesis of GLC from glyc-
erol were practiced. Synthesis of GLC largely carried by
phosgene and oxidative carbonylation routes. These routes
are having strong limitations due to the toxic nature of
the reactants [11]. Another method for the preparation of
GLC is direct carbonylation of glycerol with CO2. This
approach is not gained importance because of low yield
and requires supercritical conditions [12, 13]. Alcoholy-
sis of urea for GLC synthesis by fxing CO2 during urea
preparation may be an efective way but have a fair limita-
tion since the reaction should carry under reduced pressure
conditions for removing ammonia continuously.
A productive and promised pathway for synthesis of GLC
is the transesterifcation of glycerol with dimethyl carbonate
(DMC) [14, 15]. The synthesis of GLC by transesterifcation
was mainly achieved using base catalysts. Several base catalysts
like NaOH, KOH and K2CO3, etc.were studied under homoge-
neous conditions. The separation and reusability of the catalysts
are the major drawbacks for these catalysts even though the
activity is very high [16]. On the other hand, heterogeneous
solid base catalysts that overcome all these limitations are stud-
ied extensively. Diferent catalytic systems such as alkali and
alkaline earth metal oxides, hydrotalcite, mixed base oxides
have been studied for the preparation of GLC from glycerol
and DMC [17, 18]. Most of these catalysts showed reasonable
activity and these reactions are carried in batch process. Some
of these catalysts showed limited activity upon reuse.
2 Experimental
2.1 Materials
Glycerol (GLY:≥99% pure) was procured from Fisher Sci-
entifc, India. The metal precursors, La(NO3)3·6H2O and
Fe(NO3)3·9H2O obtained from Merck Chemicals, India.
Nowadays the continuous process is gaining importance
in the synthesis of fne chemicals as this approach overcomes
1 3

Continuous Synthesis of Glycerol Carbonate by Transesterifcation of Glycerol with Dimethyl…
Dimethyl carbonate was purchased from Finar Chemicals
Ltd. All chemicals were used without further purifcation.
desorption of CO2 was carried by increasing the temperature
up to 800 °C with a temperature ramp of 10 ºC/min and the
desorbed CO2 was estimated. Similarly, the acidic sites and
strength of the catalysts were measured from the temperature
desorption of NH3 where the aforementioned pre-treatment
and analysis conditions were similar except the adsorption
of 5% NH3 balance He gas at 100 ºC as the probe molecule
in place of CO2.
2.2 Catalysts Preparation
Fe and La mixed oxide catalysts were prepared by co-precip-
itation method with varying their molar ratios. In a typical
procedure, the required calculated amount of Fe(NO3)3 and
La(NO3)3 were dissolved in deionized water. The solution
was precipitated by adding a dilute ammonia solution drop
by drop while stirring. The addition of ammonia solution
continued until the pH of the solution reaches 10. Further,
the stirring was continued for 30 min. After that, the slurry
was kept for aging at 60 °C over a period of 6 h with vigor-
ous stirring. Then the solution was washed thoroughly with
distilled water and then the residue was dried overnight at
100 °C in an air oven. The obtained solid mass was ther-
mally calcined in static air at 450–850 °C for 4 h with a
ramping rate of 5 °C/min to obtain Fe–La catalysts. Fe–La
mixed oxide catalysts with molar ratios of 1:1, 1:2, 1:3, 2:1
and 3:1 were prepared and labelled as FL-11, FL-12, FL-13,
FL-21, and FL-31 catalysts. The F and L correspond to Fe
and La and the numbers indicate the respective molar ratio.
The elemental composition of the catalysts quantifed
by X-ray fluorescence spectroscopy (XRF) operated at
35 kV using the Rh source. The catalysts were character-
ized by Raman spectroscopy (Horiba Jobin–Yvon Lab Ram
HR, Japan) using 633 nm He–Ne laser. The spectra were
recorded by spreading about 10 mg of solid sample over a
glass slide kept under microscope.
The oxidation state and presence of anionic vacancies of
the catalysts were acquired from the binding energy of the
element using the XPS analysis. The spectra were obtained
using the AXIS Nova spectrometer. The quantitative paral-
lel imaging of the catalysts was recorded with a 165 mm
radius hemispherical analyser and a spherical mirror ana-
lyzer coupled with a Delay-line detector. The non-mono-
chromatic Mg Kα X-ray using a dual anode of Mg and Al
(1486.6 eV) which was controlled by 12.5 kV and 16 mA.
Prior to analysis, the sample was degassed at 100 ºC under
vacuum (1×10–7 Torr) for 3 h for cleaning catalyst surface.
The instrument was calibrated by using Au as standard and
the energy calibration was made by C (1s) photoelectron
using the binding energy of 284.6 eV. Also, the charge neu-
tralization of 2 eV balanced to charge up the sample.
2.3 Catalyst Characterization
The structural characteristics of the catalysts were deter-
mined using an X-ray difractometer which operated at a
specifc tube voltage of 40 kV and tube current of 30 mA
equipped with Ni-fltered CuKα source. The difractograms
were recorded at a 2-theta range of 10°–80° with angular
steps of 0.0450° and step time of 0.7 s.
2.4 Continuous Transesterifcation of Glycerol
The surface area of the catalysts was estimated using the
N2 physisorption method over BELSORP II (BEL Japan.
Inc.) instrument. Prior to analysis about 0.2 g of the sample
was subjected to vacuum to outgas the surface at 200 °C
for 2 h. The N2 adsorption isotherm was measured and the
surface area was calculated using the BET equation. FT-IR
analyses of the samples were obtained on a DIGILAB Bio-
rad spectrometer using KBr disc at a resolution of 1 cm−1.
Scanning electron microscopy analysis were performed
using JEOL FE-SEM-7610F microscope to elucidate the
morphology. Thermo gravimetric analysis (TGA) was per-
formed on TGA Q500 V20.13 Build 39 instrument.
The continuous transesterifcation of glycerol with DMC
was carried in a fxed bed downfow reactor at atmospheric
pressure. In this procedure, about 1 g of catalyst diluted with
equal amount of quartz particles and was suspended in the
reactor under isothermal zone with the help of two quartz
wool plugs. The catalyst was pre-treated under N2 gas atmos-
phere at 450 ºC for 1 h. After that, the temperature of the
catalyst bed was brought to the required reaction tempera-
ture. The reaction was conducted by passing the reactants
glycerol and DMC with two dosing pumps along with N2 as
the carrier gas. The reaction was carried in the temperature
range of 200–260 ºC. The products coming out of the reac-
tor were collected in a trap kept undercooling. The products
were quantifed by analysing gas chromatography (Shimadzu
2010 plus, Japan) equipped with fame ionization detector by
separating the products over a capillary column (Innowax,
diameter: 0.25 mm, length: 30 m). The yield of the product
was estimated by using the following equation.
The basicity and basic site strength of the catalysts were
estimated by temperature-programmed desorption of CO2.
About 0.1 g of the solid sample was taken in the quartz sam-
ple tube and pre-treated at 300 °C for 60 min in inert condi-
tion to remove impurities over the catalyst surface. Then the
sample was cooled and allowed for adsorption of 10% CO2
balance He at room temperature. Then the surface of the
catalyst was made free from the physisorbed CO2 through
purging with He gas over the catalyst surface. After that
1 3

P. P. Pattanaik et al.
Yield(%) =
all the catalysts as a major phase. FL-11 catalyst exhibited
peaks at 32.34°, 39.86°, 46.36°, 52.08°, 57.61°, 67.62°, and
76.70° are attributed to LaFeO3 phase (JCPDS 88-0641). At
the equimolar content of Fe and La, the insertion of Fe2O3
into the lattice of La2O3 might take place to form a predomi-
nantly LaFeO3 phase [30]. Upon increasing the Fe content
(FL-21 catalyst) signifcant formation of La2O2CO3 occurred
while further increase in Fe (FL-31 catalyst) diminished
La2O2CO3 species in the mixed oxides due to enhanced
cationic mobility of Fe3+ ions [31].
Conversion of Glycerol × Selectivity of Glycerol Carbonate
100
Yield of Glycerol carbonate × Feed Rate (mmol∕s)
RateGLY
=
gm of catalyst (gcat)
3 Results and Discussion
3.1 Catalysts Characterization
The elemental composition and surface properties of the
Fe–La mixed oxide catalysts are shown in Table 1. It has
been found that the FL-11 catalyst exhibited a surface area
of 16.4 m2/g. Further increase in La content (FL-12 and
FL-13 catalysts) surface area increased marginally. On the
other hand, increasing the Fe content (FL-21 and FL-31
catalysts) the surface area increased substantially up to 53.8
m2/g. However, further, increase in Fe content (FL-31 cata-
lyst) a marginal decrease in surface area to 45.4 m2/g was
noticed. Thus, it has been inferred that the incorporation of
Fe resulted in improvement in the surface area to a higher
value [28].
The results indicate that variation in the content of Fe
or La afected the surface area of the Fe–La mixed oxide
catalysts.
Fe–La oxide catalysts are characterized by X-ray difrac-
tion and the patterns are shown in Fig. 1. The difraction
peaks of La2O3 (JCPDS 74-2430) found in bulk La2O3 and
Fe–La mixed oxides at difraction angles of 26.02° 29.72°
and 55.25° which corresponding to the hexagonal phase
of La2O3 having lattice planes of (100), (101) and (200)
respectively. The absence of Fe2O3 difraction peaks in
Fe–La mixed oxides might be due to good interaction of the
host oxide. Apart from these, difraction peaks related to
La2O2CO3 (JCPDS 84-1964) and La(OH)3 (JCPDS 83-2034)
phases were observed for bulk La2O3 [25, 29]. The mixed
oxide catalysts showed the presence of LaFeO3 phase in
Fig. 1 Powder XRD patterns of Fe–La mixed oxide catalysts.
La2O3 (flled circle), La(OH)3 (inverted triangle), Fe2O3 (asterisk),
La2O2CO3 (open diamond) and LaFeO3 (theta)
Table 1 Composition and surface properties of Fe–La mixed oxide
catalysts
S. no.
Catalyst
Fe contenta
La contenta
Surface
area
(m2/g)
1
2
3
4
5
FL11
FL12
FL13
FL21
FL31
0.97
0.89
1.06
1.92
3.04
1.03
2.11
2.94
1.08
0.96
16.4
17.9
22.4
53.8
45.3
aMolar content measured from XRF analysis.
Fig. 2 Raman spectra of Fe–La mixed oxide catalysts
1 3

Continuous Synthesis of Glycerol Carbonate by Transesterifcation of Glycerol with Dimethyl…
Raman spectra of Fe–La mixed oxide catalysts are shown
in Fig. 2. Pure La2O3 catalyst showed the characteristic
Raman bands at 363.6, 394.5 and 1090 cm−1. Fe2O3 catalyst
exhibited bands at 225, 292.6, 409, 496.08, 609.7, 656.07,
and 1314.8 cm−1 which are due to the presence of α-Fe2O3
in hematite phase [32, 33]. The mixed oxide FL catalysts
showed the major band at 630 cm−1 related to the LaFeO3
phase. This phase is observed in the catalysts with an equal
or high molar ratio of La (FL-11, 12 and 13 catalysts). These
catalysts did not show the bands related to individual oxides.
These results indicate that the mixed oxide phase is pre-
dominant in these catalysts. The catalysts with high Fe con-
tent (FL-21 and 31) showed the Raman bands related to the
Fe2O3 phase apart from LaFeO3 mixed oxide. The presence
of the hematite phase is responsible for lowering the forma-
tion of La2O2CO3 species by the mobility of Fe3+ over the
catalyst surface [30].
The FL catalysts are characterized by FT-IR spectros-
copy and the spectra are depicted in Fig. S1 (Supplementary
information). The FL catalysts with 1:1, 1:2, 1:3 molar ratio
showed a peak around 595 cm−1. This was attributed to the
stretching mode vibration involving internal motion during
change in the length of Fe–O or Fe–O–Fe bond. This is the
characteristic band of octahedral FeO6 group in LaFeO3
structure [34]. The absorption bands appeared at 1644
and 1360 cm−1 were assigned to the interaction between
atmospheric CO2 and LaFeO3 phase, which suggested the
formation of La–carbonate species on the LaFeO3 surface
[35]. The broad absorption peaks observed in the range of
1400–1500 cm−1 belonging to the absorption peaks of water/
surface hydroxyl on the LaFeO3 crystal surface. The FT-IR
results are in in support of the observations made from
Raman spectroscopy about the presence of LaFeO3 phase
in Fe2O3–La2O3 mixed oxide catalysts.
The representative FL-11 catalyst is characterized by
XPS. The XPS spectra of Fe, La, and O2 of FL-11 catalyst
are shown in Fig. 3. It showed the B.E values related to Fe
2p3/2 and 2p1/2 at 710 and 723 eV along with satellite peaks
at 718 and 732 eV respectively [32]. It has been reported
that the presence of satellite peaks is usually observed right
after~8 eV of parent peak which confrms the existence of
Fe in + 3 oxidation state [33, 36, 37]. The binding energy
at 833.5 and 837 eV are ascribed to La 3d5/2 and the bind-
ing energy at 850 and 854 eV corresponds to La 3d3/2 with
the splitting of about 4.5 eV corresponds to La2O3 with
La in + 3 oxidation state [38]. The existence of Fe–O and
La–O bond confrmed by the availability of core oxygen
Fig. 3 XPS spectrum of FL-11catalyst a Fe 2p, b La 3d and c O 1s
at a binding energy of 530 eV which is related to lattice
oxygen (OL) in anionic vacancy and possible to form mixed
oxide (Fe–La–O) structure of the catalyst [38]. The binding
energy at 538 eV was observed which is attributed to the
physisorbed molecular oxygen (OM) [39].
The basicity of Fe–La mixed oxide catalysts was analysed
by TPD of CO2 and the results are shown in Table 2. All
the catalysts showed a desorption peak at high temperature
centred at around 750 °C related to strong basic sites as
1 3

P. P. Pattanaik et al.
Table 2 Acid–base properties of Fe–La mixed oxide catalysts
noticed. However, the catalytic activity marginally increased
upon increasing the Fe molar composition (FL-21 and FL-31
catalysts). The catalytic activity of the catalysts are as fol-
lows: FL-11>FL-13>FL-12>FL-21>FL-31. Thus, it is
evident that the equimolar composition of La2O3 and Fe2O3
(FL-11 catalyst) in the catalyst resulted in the enhanced
activity. The variation of the FL catalysts activity can be cor-
related with their surface-structural and acid–base proper-
ties. The FL-11 catalyst showed the presence of both strong
basic and acid sites. This catalyst also contains the mixed
oxide LaFeO3 perovskite phase which account for the pres-
ence of La3+ and Fe3+ in the cationic lattice and O2− anionic
lattice as revealed from XPS analysis. Raman spectra of the
FL-11 catalyst also indicated the existence of the LaFeO3
phase.
S. no.
Catalyst
Basicity
Acidity (mmol/g)
(mmol/g)
1
2
3
4
5
FL11-550
FL12-550
FL13-550
FL21-550
FL31-550
1.41
0.382
0.350
0.845
0.634
0.161
0.315
0.755
0.737
0.228
shown in Fig. S2 (Supplementary information). Among all
the FL-11 catalyst showed high basicity of 1.41 mmol/g.
The high basicity of the FL-11 catalyst might be due to the
presence of mixed oxide LaFeO3 phase.
FL catalysts acidity was determined by TPD of NH3 and
the results are presented in the same Table along with basic-
ity. The patterns suggest that the catalysts are possessing
strong acidic sites apart from few moderate acidic sites as
shown in Fig. S3 (Supplementary information). The total
acidity of the catalysts is estimated by calculating the area of
the desorption peaks. The results indicate that an increase in
La content in the catalysts enhanced the total acidity. How-
ever, increasing Fe content in the catalysts resulted in lower
acidity. The TPD of both CO2 and NH3 results directly con-
frms that the FL catalysts are posing both acid and base
properties.
The acid–base sites play an important role in the trans-
esterifcation reaction of glycerol with DMC. The hydroxyl
groups of glycerol are adsorbed on basic sites of the cata-
lysts by hydrogen bonding. The other reactant DMC is acti-
vated on acidic sites of the catalyst. The activated hydroxyl
group undergoes nucleophilic attack on the carbonyl group
of DMC leading to the formation of glycerol-DMC adduct
by the elimination of methanol. Then the active hydroxyl
groups and carbonyl groups of the adduct undergoes an
intramolecular nucleophilic substitution with the elimina-
tion of another methanol molecule to give glycerol carbonate
[40]. The high activity of the FL-11 catalyst might be due to
the presence of high amount of both basic and acidic sites.
3.2 Glycerol Transesterifcation Activity
3.3 Infuence of Catalyst Calcination Temperature
The continuous transesterifcation of glycerol with DMC
was carried over FL mixed oxide catalysts and the results
are illustrated in Table 3. The activity results of the bulk
La2O3 and Fe2O3 catalysts were included for the sake of
comparison. The catalysts showed near complete selectiv-
ity to glycerol carbonate. The bulk La2O3 and Fe2O3 cata-
lysts exhibited 49% and 53% yield of GLC respectively. The
FL-11 catalyst exhibited the highest GLC yield of 71%.
On increasing the La composition in the catalyst (FL-
12 and FL-13 catalysts), a gradual decrease in activity was
on Transesterifcation Activity
Along with the metal oxide content in the catalyst, the cal-
cination temperature has a strong infuence over the surface
and structural properties of the catalysts. The active FL-11
catalyst was calcined at diferent calcination temperatures
in the range of 450–750 °C and evaluated for their activ-
ity towards glycerol carbonate preparation. The activity of
the catalyst is shown in Table 4. The GC yield increased
from 56 to 71% with enhancement in calcination tempera-
ture from 450 to 550 °C. Further increasing the calcination
Table 3 Activity data of the Fe–La mixed oxide catalysts during con-
tinuous glycerol transesterifcation
Table 4 Glycerol transesterifcation activity of FL-11 catalyst cal-
cined at diferent temperatures
Sl. no.
Catalysts
GLC yield (%)
S. no.
Catalyst
Calcination tempera- GLC
1
2
3
4
5
6
7
Fe2O3
La2O3
FL-11
FL-12
FL-13
FL-21
FL-31
53
49
71
53
60
51
48
ture (°C)
Yield
(%)
1
2
3
4
FL11-450
FL11-550
FL11-650
FL11-750
450
550
650
750
56
71
61
60
1 3

Continuous Synthesis of Glycerol Carbonate by Transesterifcation of Glycerol with Dimethyl…
temperature to 650 °C a decrease in yield to 61% was
noticed. Still further increase in calcination temperature
to 750 °C a marginal decrease in the yield of GLC was
observed. So as to understand the diference in activity with
the change in the calcination temperature the catalysts were
further characterized.
3.4 Characterization of Catalysts Calcined
at Diferent Temperatures
The XRD pattern of FL-11 catalyst calcined at diferent
temperatures in the range of 450–750 °C is illustrated in
Fig. 4. The difraction pattern showed major refections at
32.3° due to the presence of the LaFeO3 phase. The FL-11
catalysts calcined at 450 °C showed a broad peak at 13.10°
ascribed to the presence of La(OH)3 phase. The predominant
phase observed at all calcination temperature is LaFeO3. The
intensity of LaFeO3 peak increased with raising in calcina-
tion temperature.
Fig. 5 Raman spectra of FL-11 catalyst calcined at (a) 450 °C, (b)
550 °C, (c) 650 °C and (d) 750 °C temperatures
Raman spectra of the FL-11 catalysts calcined at difer-
ent calcination temperatures are shown in Fig. 5. The cata-
lyst calcined at 450–650 °C showed a broad Raman band
at 630 cm−1 is attributed to the presence of LaFeO3 phase
[31, 41]. However, at higher calcination temperature of
750 °C, the band position located at 154 and 179.3 cm−1
are attributed to the presence of one phonon scattering that
confrms the presence of La in the cationic lattice [38, 39,
42]. There are two sharp intense Raman bands observed at
222.8 cm−1 (A1g mode) and 291.6 cm−1 (Eg mode) which
are ascribed to Fe (+3) oxide phase resembles to α-Fe2O3
(hematite) structure [31, 32]. In addition, the broad Raman
band observed at 1312.8 cm−1 due to second-order scatter-
ing where IR active LO mode appeared due to combination
of both Raman bands at 630 and 490 cm−1 respectively [31,
43]. Thus, it is evident that upon increasing the calcination
temperature of the catalyst the Raman peaks are broadened
without much shifting and thus generated defects in the lat-
tice. These defects in cationic and anionic lattice confrmed
the presence of the LaFeO3 phase which is also well agreed
with XPS and XRD studies.
The acidic and basic properties of the catalysts calcined
at diferent temperatures are estimated by TPD of NH3
and CO2 respectively and the results are shown in Table 5.
The TPD of CO2 and NH3 patterns are presented in Figs.
S4 and S5 respectively (Supplementary information).
The catalysts calcined at 450 °C exhibited low amount
of basicity and it is increased with increase in calcina-
tion temperature up to 550 °C. Further enhancement in
temperature resulted in gradual decrease in the number
of basic sites. In the case of acidity, the FL-11 catalyst
calcined at 450 °C showed low acidity consists of weak
Table 5 Acidity and basicity of FL-11 catalysts calcined at diferent
temperatures
S. no.
Catalysts
Basicity
Acidity (mmol/g)
(mmol/g)
1
2
3
4
FL11-450
FL11-550
FL11-650
FL11-750
0.305
1.413
6.758
4.158
0.152
0.382
0.089
0.421
Fig. 4 X-Ray difraction of FL-11 catalyst calcined at diferent cal-
cination temperatures. La2O3 (flled circle), La(OH)3 (inverted trian-
gle), La2O2CO3 (asterisk) and LaFeO3 (open diamond)
1 3

P. P. Pattanaik et al.
Fig. 7 The efect of glycerol to DMC ratio on glycerol transesterifca-
Fig. 6 The infuence of reaction temperature on glycerol transesterif-
tion over FL-11 catalyst
cation over FL-11catalyst
due to the more availability of the carbonating agents to
glycerol. The increase in DMC concentration subsequently
excels in the higher yield of GLC and reduces the forma-
tion of glycidol and at the same time inhibits the formation
of other by-products [45]. It is observed that an additional
increase in DMC to glycerol mole ratio to 5, the reaction rate
is decreased. This might be related to blocking of active sites
mostly by DMC and the number of available sites to glycerol
might decrease thus lead to a decrease in overall activity.
and moderate acidic sites. The catalyst calcined at 550 °C
exhibited higher amount acidity mainly associated with
strong acidic sites. Further increase in the calcination tem-
perature led to decrease in the total acidity. The catalysts
calcined at above 650 °C showed the presence of both
moderate and strong acidic sites.
3.5 Efect of Reaction Temperature
The infuence of reaction temperature for the transesterif-
cation of glycerol over the active FL-11 catalyst calcined at
550 °C is shown in Fig. 6. The yield of GLC increased with
increasing the reaction temperature from 200 to 240 °C. The
highest yield of 71% of GLC achieved at the reaction tem-
perature of 240 °C. When the reaction temperature increased
from 240 to 260 °C, the amount of yield decreased to 58%.
The decrease in the yield of GC at high reaction temperature
is due to further conversion of GC to glycidol [44]. It is con-
cluded that the reaction temperature of 240 °C is favourable
over the FL-11 catalyst.
3.7 Plausible Reaction Mechanism
Based on the nature of base and acidic sites of the catalyst
and the product distribution during glycerol transesterifca-
tion with DMC, a plausible reaction mechanism is proposed
as shown in Scheme 1. In the reaction mechanism glycerol
molecule acidic proton of hydroxyl group interacted with
the Lewis basic site of the Fe–La catalyst. The other reactant
DMC might adsorb on the acidic sites the catalysts associ-
ated with Fe. Then it is followed by the attack of oxygen
of the of glycerol hydroxyl group on the carbonyl carbon
of DMC. This is followed by an elimination of the meth-
oxy group in the form of methanol. Then, the oxygen of the
secondary hydroxyl of glycerol attacks the DMC carbonyl
carbon. This led to elimination of methanol followed by for-
mation of glycerol carbonate.
3.6 Efect of Glycerol to Dimethyl Carbonate Molar
Ratio
In the preparation of GLC, the mole ratio of DMC to glyc-
erol plays an important role in the transesterifcation reac-
tion. The infuence of the mole ratio of DMC to glycerol was
studied and the results are presented in Fig. 7. As the DMC
to glycerol ratio increase the rate of the reaction increased
up to a mole ratio of 4. Further increase in the ratio led to a
marginal decrease in the overall reaction rate. The increase
in the reaction rate with more amount of DMC might be
3.8 Comparison of the Activity with Reported
Catalysts
The transesterifcation of glycerol with DMC activity of
the present FL-11 catalyst was compared with the reported
catalysts. The compassion of activity results of the difer-
ent reported catalytic systems are presented in Table 6. The
1 3

Continuous Synthesis of Glycerol Carbonate by Transesterifcation of Glycerol with Dimethyl…
Scheme 1. Plausible reaction
mechanism for glycerol transes-
terifcation with DMC
Table 6 Comparison of FL-11 catalyst activity with reported catalysts
Catalysts
Mode of operation
DMC/Glycerol Reaction
GLC yield (%) GLC sel. (%) TOS (h) Reference
(Molar ratio)
tempera-
ture (°C)
Ambersep 900 Flow reactor; with solvent
4:1
140
135
90
78
63
90
71
82
84
93
–
[20]
[22]
[23]
Present work
PS-P2-t-Bu
CaO–ZrO2
Fe–La–O
Flow reactor with homogeneous catalyst 3:1
Fixed bed continuous reaction
Fixed bed continuous reaction
80
15
100
3:1
4:1
240
100
reported continuous reactions are carried with fow reactor
using both homogeneous and heterogeneous catalysts. The
Ambersep-900 catalyst gave about 78% yield of GLC and
the details about the catalyst stability is not reported. The
other reaction used homogeneous catalyst under fow condi-
tions with 63% conversion. Fixed bed continuous reaction is
reported using CaO–ZrO2 catalyst which showed 90% yield
with limited stability up to 15 h. The present catalyst showed
71% GLC yield with a high stability of 100 h. These results
indicate the superior activity and stability of FL-11 catalysts
for the synthesis of GLC.
3.9 Time on Stream Analysis
The stability of the FL-11 catalyst unveiled by conducting
time on stream analysis and the obtained results are shown
in Fig. 8. Interestingly, it is found that the catalytic activity
Fig. 8 Time on stream analysis of FL-11 catalyst during transesterif-
cation of glycerol with DMC
1 3

P. P. Pattanaik et al.
2. Schubert C (2006) Can biofuels fnally take center stage? Nat
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remains unchanged up to 40 h of reaction time with 71%
GLC yield. Interestingly, on further progress, the yield of
GLC increased marginally with TOS and continued to show
a stable yield up to 100 h. It is noteworthy to mention that
the FL-11 catalyst retained high stability over a period of
100 h. In comparison with the reported literature, this is the
highly stable catalyst for the continuous preparation of GLC
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In order to know the details about the stability of the
FL-11catalyst, the spent catalyst was characterized by SEM
EDAX and TGA. The details of the characterization of
FL-11 fresh and used catalysts are shown in Fig. S6 and 7
(Supplementary information). The SEM images (Fig. S6)
suggests that there was no distinguishable diference in the
morphology of the spent catalyst after 100 h of reaction.
The EDAX analysis also showed similar patterns as that of
virgin catalyst. The TGA profles (Fig. S7) of the fresh and
used catalysts suggests that the diference in the weight loss
of fresh and used catalysts is marginal. This indicates that
there was no absorption of any organic species and coke
in the used catalyst. These results suggest that the FL-11
catalyst is highly stable and active for the preparation of
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In summary, Fe–La mixed oxide catalysts were prepared
by co-precipitation method and evaluated for the synthesis
of glycerol carbonate by continuous transesterifcation of
glycerol with DMC. Fe–La mixed oxide catalyst with molar
ratio of 1:1 exhibited the highest 71% yield of GLC. The
higher activity of the catalyst is due to the presence of Fe
and La mixed oxides in LaFeO3 phase. The formation of
mixed oxide phase created a greater number of strong acidic
and basic sites. The catalyst surface and structural properties
and there by the yield of glycerol carbonate also afected
with catalyst calcination temperature. The yield of glycerol
carbonate during glycerol transesterifcation also depends on
the reaction parameters. The FL catalysts are highly stable
and showed 100 h of stability with constant yield.
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Acknowledgements The authors thanks CSIR, New Delhi for the
fnancial support in the form of Mission Mode project HCP-0009. We
thank Director, CSIR-IICT for permitting to publish our results (IICT
Communication No: IICT/Pubs./2020-127)
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Afliations
Piyusa P. Pattanaik1,2 · P. Mahesh Kumar1,2 · N. Raju1 · N. Lingaiah1,2
2
* N. Lingaiah
nakkalingaiah@iict.res.in
Academy of Scientifc and Innovative Research (AcSIR),
Ghaziabad-201002, India
1
Department of Catalysis & Fine Chemicals, CSIR-Indian
Institute of Chemical Technology, Hyderabad 500 007, India
1 3