Monitoring the catalytic synthesis of glycerol carbonate by real-time attenuated total reflection FTIR spectroscopy

Article abstract of DOI:10.1016/j.apcata.2011.09.036

In situ Attenuated Total Reflectance FTIR spectroscopy was used to study the carbonylation of glycerol with urea. Cobalt oxide nanoparticles, Co ₃O₄, hierarchically dispersed on zinc oxide microparticles, ZnO, were used as catalysts. The present work demonstrates that in situ real-time attenuated total reflection ATR-FTIR spectroscopy is a valuable tool for monitoring reaction progress and analyzing the reaction mechanism of the synthesis of glycerol carbonate. ATR-FTIR spectroscopy during the carbonylation reaction of glycerol with urea reveals differences in reactivity of various Co₃O₄/ZnO catalysts, and in particular demonstrates that the first (fast) step in the conversion of glycerol with urea is the formation of glycerol urethane, whereas the consecutive conversion to glycerol carbonate is relatively slow. In addition, possible interactions of the catalytically active sites with in particular the product glycerol carbonate were also evaluated. Interactions of the 2-hydroxyethyl chain of the product with the surface of the catalysts were identified, suggesting product inhibition might be of relevance to the reaction kinetics.

Full text of DOI:10.1016/j.apcata.2011.09.036

Applied Catalysis A: General 409–410 (2011) 106–112
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Monitoring the catalytic synthesis of glycerol carbonate by real-time attenuated
total reflection FTIR spectroscopy
V. Calvino-Casildaa,b,∗, G. Mulb, J.F. Fernándezc, F. Rubio-Marcosc,1, M.A. Ban˜aresa
a Catalytic Spectroscopy Laboratory, Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, 28049 Madrid, Spain
b Photocatalytic Synthesis Group, Faculty of Science & Technology, University of Twente, Enschede, The Netherlands
c Electroceramic Department, Instituto de Cerámica y Vidrio, CSIC, Kelsen 5, 28049 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
In situ Attenuated Total Reflectance FTIR spectroscopy was used to study the carbonylation of glycerol
with urea. Cobalt oxide nanoparticles, Co3O4, hierarchically dispersed on zinc oxide microparticles, ZnO,
were used as catalysts. The present work demonstrates that in situ real-time attenuated total reflection
ATR-FTIR spectroscopy is a valuable tool for monitoring reaction progress and analyzing the reaction
mechanism of the synthesis of glycerol carbonate. ATR-FTIR spectroscopy during the carbonylation reac-
tion of glycerol with urea reveals differences in reactivity of various Co3O4/ZnO catalysts, and in particular
demonstrates that the first (fast) step in the conversion of glycerol with urea is the formation of glycerol
urethane, whereas the consecutive conversion to glycerol carbonate is relatively slow. In addition, pos-
sible interactions of the catalytically active sites with in particular the product glycerol carbonate were
also evaluated. Interactions of the 2-hydroxyethyl chain of the product with the surface of the catalysts
were identified, suggesting product inhibition might be of relevance to the reaction kinetics.
© 2011 Elsevier B.V. All rights reserved.
Received 15 July 2011
Received in revised form
25 September 2011
Accepted 28 September 2011
Available online 5 October 2011
Keywords:
Glycerol
Urea
Glycerol carbonate
Biomass
ATR-FTIR spectroscopy
1. Introduction
good yields under moderate reaction conditions [8,9]. Further, hier-
archical nanoscaled materials dispersed on microscaled particles
Glycerol is a renewable and inexpensive raw chemical, which
use depends on its efficient conversion to value-added materials.
Particularly, glycerol carbonate and its derivatives have received
increasing attention during the last years due to their potential
end use as solvent and for plastics. Since renewable raw chemicals
may compete with, and replace petroleum-derived ones [1–3], the
need for successful routes to efficiently produce glycerol carbonate
is evident. This reaction is typically run with carbonylating agents;
glycerol carbonate is formed by reaction of glycerol with CO2 under
supercritical conditions, or with dimethyl carbonate [4,5], or dialkyl
carbonates [6] or urea [7] under milder reaction conditions. Among
these, urea is a particularly attractive carbonylating agent due to
the mild reaction conditions and high selectivity. Therefore, devel-
oping a heterogeneous catalyst for this process has strategic and
environmental benefits.
have been recently reported as successful catalysts for the syn-
thesis of glycerol carbonate, affording very high yield [10]. These
hierarchically dispersed materials raise additional environmental
value since their synthesis is particularly clean. They are pre-
pared by mixing oxides of different materials using a residue-free
and solvent-free nanodispersion method that leads to hierarchi-
cal nano–microparticle systems [10–12]. It has been proven that
after the partial reaction of two oxides, the creation of interfaces
at the nanoscale range endow the catalysts with new properties
that range from magnetic or optic to catalytic [10,12–15], due to
proximity and diffusion phenomena.
Consistent with previous studies [7,9,10], urea reacts with glyc-
erol when heated in the presence of a catalyst. The reaction
mechanism follows four possible steps; carbamoylation of glycerol
to glycerol urethane, carbonylation of glycerol urethane to glyc-
erol carbonate with abstraction of ammonia, or carbonylation of
glycerol urethane to 5-(hydroxymethyl)oxazolidin-2-one without
abstraction of the ammonia. Finally glycerol carbonate can react
with another molecule of urea to obtain (2-oxo-1,3-dioxolan-4-
yl)-methyl carbamate, which would decrease glycerol carbonate
selectivity [9,10]. Hierarchical Co3O4/ZnO systems are catalytically
active in the synthesis of glycerol carbonate, which performance
depends on the degree of interaction at the interface that is directly
related to temperature treatment [10]. The nanodispersion method
of preparation yields Co3O4 active sites dispersed in the Co3O4/ZnO
It has been demonstrated that heterogeneous catalysts are par-
ticularly efficient for cabonylating glycerol with urea affording
∗
Corresponding author at: Catalytic Spectroscopy Laboratory, Instituto de Catáli-
sis y Petroleoquímica, CSIC, Marie Curie 2, 28049 Madrid, Spain. Tel.: +34 915854879.
E-mail addresses: vcalvino@icp.csic.es (V. Calvino-Casilda), banares@icp.csic.es
(M.A. Ban˜ares).
1
Current address: Laboratoire de Science des Procédés Céramiques et de Traite-
ments de Surface, Université de Limoges, France.
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.09.036

V. Calvino-Casilda et al. / Applied Catalysis A: General 409–410 (2011) 106–112
107
HO
HO
HO
O
OH
HO
O
HO
+ NH3
+ NH3
O
+
NH2-CO-NH2
O
O
B
H2N
A
Scheme 1. Reaction mechanism between glycerol and urea over Co3O4/ZnO cat-
alytic systems. Reaction products: (A) Glycerol urethane (intermediate); (B) Glycerol
carbonate (main product).
system. The Co3O4/ZnO systems prepared by dry nanodispersion at
room temperature showed the best results (Co3O4 10 wt.%: up to
69% conversion, 96% selectivity to glycerol carbonate) compared
to Co3O4/ZnO systems preheated at 500 ◦C (ZnCo2O4 spinel inac-
tive species were formed) [10]. A further increase in the amount of
cobalt oxide (from 1 to 10 wt.%) led to an increase in catalytic activ-
ity, which is less significant for calcined samples since the spinel is
the main phase present in the system [10]. Therefore, systems with
a given chemical composition provide a collection of catalysts with
very different catalytic performance, which can be used to study the
reaction mechanism by comparison of the performance of a high-
and a low-performing catalyst.
Fig. 1. ATR-FTIR spectra of reactants; glycerol (G) and urea (U), and the product;
glycerol carbonate (P).
The ATR-FTIR technique is used in a wide range of applications
and, recently, has been proven to be a useful tool for real-time mon-
itoring and in situ studies of liquid phase reactions under working
conditions (“operando”) [16–21]. Both reaction intermediates and
species adsorbed on/or interacting with the catalyst surface can be
detected. These advantages make this technique very suitable for
both kinetic and mechanistic studies of heterogeneous catalyzed
liquid phase reactions. This work studies both the evolution of the
reaction mixture and interaction of reactants and products with
the Co3O4/ZnO catalyst. Thus, we could study the mechanism of
the formation of the glycerol urethane intermediate and that of the
glycerol carbonate product (Scheme 1A and B). The surplus value
of the in situ technique was illustrated by the fact that interactions
with catalyst particles could be observed in the reaction.
In addition, this accessory also offers a high pressure, wide spectral
range and heated crystal plate.
The coating of the catalyst was carried out by suspension of the
catalyst in water using a concentration of 6 wt.% of the respective
Co3O4/ZnO mixture. The catalyst was spread on the diamond crys-
tal and dried at 70 ◦C in vacuum for 30 min. Prior to the reaction,
adsorption of the reactants glycerol and urea (1:1) on the coating
was monitored from room temperature to 145 ◦C taking spectra
during heating (heating ramp 10 ◦C/min). The FTIR spectra were
registered on a Bruker Vertex 70, equipped with a liquid nitrogen
cooled MCT detector. All measurements had a 4 cm−1 resolution.
When the reaction reached 145 ◦C, spectra were registered every
10 min for a period of 4 h. The reaction temperature was continu-
ously monitored by a thermocouple during experiments.
2. Experimental
3. Results and discussion
2.1. Preparation of the Co3O4/ZnO catalysts
Fig. 1 shows the ATR-FTIR spectra at room temperature of reac-
tants, glycerol (G) and urea (U), the corresponding product, glycerol
carbonate (P) and the mixture of reactants and product (G + U + P).
The main characteristic bands of glycerol carbonate can be found
at 3280, 3402 and 1400 cm−1 due to O–H vibrations of the 2-
hydroxyethyl chain of the product; 2900, 2972 and 2987 cm−1 due
to CH2 and CH vibrations of the O-methylene and O-methylidyne
groups of the cyclic carbonate, 1791 cm−1 due to C O stretching of
the 5-membered cyclic carbonate; and finally 1167 and 1045 cm−1
due to C–C, and C–O stretching respectively of the 2-hydroxyethyl
chain of the product. To study the reaction, we followed the deple-
Catalysts containing 1 and 10 wt.% of Co3O4 nanoparticles on
ZnO microparticles were prepared by a well-defined dry nanodis-
persion procedure [10,11]. The dry dispersion process consisted on
shaking Co3O4/ZnO mixtures and 1 mm ZrO2 balls in a 60 cm3 nylon
container for 5 min at 50 rpm using a tubular-type mixer. Pure ZnO
and Co3O4 powders were also subject to the same mixing process to
ensure that no structural disorder contributions occur by the mix-
ing process. Then, ZnO and Co3O4 powders were dried at 110 ◦C for
2 h before dry mixing. The resulting materials were used as pre-
pared (room-temperature), denoted as RT-10CoZn, and calcined at
increasing temperatures, up to 500 ◦C, denoted as 500C–10CoZn.
The characterization of these catalysts is reported and discussed
elsewhere [10], including particle size and morphology (FE-SEM
and TEM) and structural features (XRD and Raman spectroscopy)
of the powders.
tion of the bands corresponding to urea at 1664 and 1626 cm−1
,
which show the most well-defined changes in the spectra dur-
ing reaction, besides the formation of new bands corresponding
to glycerol urethane intermediate and glycerol carbonate product.
The results corresponding to the real-time ATR monitoring of
the carbonylation reaction of glycerol with urea are shown below.
Fig. 2 illustrates the results of the reaction of glycerol with urea
at 145 ◦C over room-temperature synthesized 10%Co3O4/ZnO (RT-
10CoZn) catalysts. This is the most active and selective catalyst
in this series for formation of glycerol carbonate, delivering 69%
conversion and 96% selectivity [10]. As the reaction temperature
increases from room temperature to 145 ◦C with a heating ramp of
10 ◦C/min (Fig. 2, top), new IR bands corresponding to O-methylene
2.2. ATR-FTIR experiments
ATR-FTIR experiments were performed using a Pike accessory
equipped with a diamond ATR crystal coupled to a 1 mL cell con-
taining a quartz window on the top plate. The operation conditions
of the Co3O4/ZnO catalysts are suitable for the high-temperature
ATR cell (145 ◦C reaction temperature, and urea-glycerol mixture).

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V. Calvino-Casilda et al. / Applied Catalysis A: General 409–410 (2011) 106–112
2,0
1,6
1,2
0,8
0,4
0,0
Urea (U)_1664cm-1
Glycerol urethane (I)_2843cm-1
Glycerol carbonate (P)_1791cm-1
0
50
100
150
200
250
Fig. 3. Evolution of the intensity of representative peaks corresponding to urea
(reactant), intermediate (glycerol urethane) and glycerol carbonate (product) at
145 ◦C on RT-10CoZn catalyst.
Fig. 3 plots the evolution during reaction at 145 ◦C of the most
representative bands of urea (reactant) at 1664 cm−1, glycerol ure-
thane (reaction intermediate) at 2843 cm−1 and glycerol carbonate
(product) at 1791 cm−1, using the RT-10CoZn catalyst. The charac-
teristic band of urea decreases initially rapidly with reaction time,
reflecting its consumption; concomitantly the band corresponding
to glycerol carbonate increases with time, evidencing the forma-
tion of this reaction product. During ca. the first hour of reaction
time, the characteristic band of the reaction intermediate (glycerol
urethane) follows a trend similar to that corresponding to the prod-
uct; thus the glycerol urethane forms quickly and then is converted
rather slowly into the glycerol carbonate product. This confirms
that the urethane is an intermediate in the formation of the car-
bonate and agrees with the mechanism suggested for this reaction
[7,9]; the fast step of the reaction is the conversion of glycerol to
glycerol urethane and the slow step of the reaction is the conversion
of glycerol urethane to glycerol carbonate. Glycerol urethane inten-
sity passes through a maximum with reaction time; while glycerol
carbonate signal keeps on increasing with reaction time. Further
insight is illustrated in Fig. 4 where the evolution of the bands
Fig. 2. ATR-FTIR spectra during heating from 25 to 145 ◦C (top) (heating ramp
10 ◦C/min) and time-resolved ATR-FTIR spectra of carbonylation of glycerol with
urea at 145 ◦C during 4 h (spectra taken every 10 min) over RT-10CoZn systems (bot-
tom). “//” symbol indicates a spectrum omitted due to interferences caused by the
formation of ammonia bubbles.
vibrations associated with the glycerol urethane reaction inter-
mediate, (Scheme 1A) become apparent at 2843, 1716, 1352 and
644 cm−1. The formation of some characteristic bands of the glyc-
erol carbonate product (Scheme 1B) also becomes apparent. One
of the most prominent changes during the heating of the mix-
ture were observed in the range 3700–3000 cm−1 corresponding
to hydroxyl vibrations in the glycerol molecule, reaction interme-
diate and final product. As we can observe in Fig. 2, the interaction
between hydroxyl groups and cobalt active sites slightly shifts char-
acteristic bands of hydroxyls to higher frequencies, when heating
the mixture from 25 to 145 ◦C.
U- Urea
P- Product (glycerol carbonate)
I- Intermediate (glycerol urethane)
2,0
isosbestic
point
1,5
1,0
0,5
0,0
U
U
P
I
The urea bands at 1626 and 1664 cm−1 decrease while the mix-
ture is kept at 145 ◦C for 4 h (Fig. 2, bottom). The formation of
glycerol carbonate product is also apparent, but its IR bands are
less pronounced as compared to those due to glycerol urethane
intermediate. Intensity changes in the 2900–2700 cm−1 range due
to CH2 and CH vibrations, might also be affected by detachment
of some catalyst particles from the diamond. This will result in
changes in reflective index of the catalyst/reactant mixture at the
diamond interface, and hence in the effective path for absorption
[22–24]. Detachment should not affect catalysis: interactions of
the catalyst particles and the diamond crystal are small, and mass
transfer limitations to the catalyst coating not expected as a result
of the low reaction rate.
1900
1800
1700
1600
1500
Wavenumber (cm-1)
Fig. 4. Isosbestic point in the synthesis of glycerol carbonate from glycerol and urea
at 145 ◦C with on RT-10CoZn catalyst. Arrows pointing up indicate increasing bands,
and arrows pointing down, decreasing bands (spectra are taken every 10 min).

V. Calvino-Casilda et al. / Applied Catalysis A: General 409–410 (2011) 106–112
109
2,5
G = glycerol
U = urea
i = intermediate (o-methylene vib.)
P = glycerol carbonate
2,0
25ºC
1,5
1,0
0,5
0,0
Urea (U)_1664cm-1
Glycerol urethane (I)_2843cm-1
Glycerol carbonate (P)_1791cm-1
145ºC
G
0
50
100
150
200
250
U
U
G G
G
G
G
G
G
Time (min)
4000
3500
3000
2500 1800 1500 1200
Wavenumber (cm-1)
900
600
Fig. 6. Evolution of the intensity of representative peaks corresponding to urea
(reactant), glycerol urethane (intermediate) and glycerol carbonate (product) during
reaction at 145 ◦C on using the 500C–10CoZn catalyst.
145ºC
apparent; only those corresponding to glycerol and urea reactants
are present, indicating that no reaction occurs. New bands corre-
sponding to the reaction intermediate (glycerol urethane) and the
glycerol carbonate product appear when the temperature was kept
at 145 ◦C during 4 h (Fig. 5, bottom). With reaction time, most bands
grow sharper, again the result of detachment of the particles from
the crystal. Fig. 6 illustrates the evolution of representative peaks
corresponding to urea (reactant), glycerol urethane (intermediate)
and glycerol carbonate (product) using the 500C–10CoZn catalyst.
The intensity of the representative band of urea decreases more
rapidly during the first 80 min of reaction and levels off. The charac-
teristic band of the urethane intermediate grows quickly and quite
in parallel to that of the carbonate product, which means that glyc-
erol urethane is formed and fully converted into the product. Unlike
on RT-10CoZn, urethane signal does not decrease and that of the
carbonate does not grow with reaction time. The IR bands corre-
sponding of hydroxyl groups are significantly less shifted to higher
frequencies on 500C–10CoZn than on RT-10CoZn; this is indicative
of a weaker interaction of these groups with the catalytic surface.
Glycerol carbonate synthesis on Co3O4/ZnO depends on cobalt
oxide loading. Low loading catalyst, 1%Co3O4/ZnO, prepared at
room temperature (RT-1CoZn) is half as active as the one con-
taining 10%Co3O4/ZnO (RT-10CoZn), but it is highly selective to
glycerol carbonate (35% conversion, nearly 100% selectivity) [10].
Figure 7 shows the ATR-FTIR results during reaction on RT-1CoZn.
New bands due to O-methylene vibrations corresponding to glyc-
erol urethane (Scheme 1A) and to glycerol carbonate (Scheme 1B)
develop when the reaction temperature increases from room tem-
perature to 145 ◦C (Fig. 7, top) shows the rapid formation of new
bands corresponding to O-methylene vibrations of glycerol ure-
thane (Scheme 1A) and also the formation of some characteristic
bands of the product glycerol carbonate formation (Scheme 1B).
The sharpening of several bands in the spectra suggests the forma-
tion of a reactants–products–catalyst suspension. Fig. 7 illustrates
that the hydroxyl vibrations frequency shifts to higher frequen-
cies. The lower the amount of Co3O4 used in the preparation of the
catalysts, the lower the number of cobalt active sites in its structure.
Fig. 8 shows the evolution during reaction of the representa-
tive urea, glycerol urethane intermediate and glycerol carbonate
product bands. It seems that the formation of the product occurs
gradually but not as fast as in the case of RT-10CoZn catalysts due to
a lower number of active sites. This is consistent with lower activ-
ity recorded by off-line gas chromatography analyses. The urethane
P
G
P
i
U U
i
P
i
G
i
P
G
P
P
i
4000
3500
3000
2500
1800 1600 1400 1200 1000 800 600
Wavenumber (cm-1)
Fig. 5. ATR-FTIR spectra during heating from 25 to 145 ◦C (top) (heating ramp
10 ◦C/min) and time-resolved ATR-FTIR spectra during reaction of glycerol with urea
on 500C–10CoZn at 145 ◦C for 4 h (spectra taken every 10 min) (bottom). “//” sym-
bol indicates a spectrum omitted due to interferences caused by the formation of
ammonia bubbles.
at 1716 cm−1 (glycerol urethane intermediate) and at 1664 cm−1
(urea reactant) defines an isosbestic point at 1690 cm−1. Such an
isosbestic point underlines that the conversion of urea to glycerol
urethane is direct, with no other reaction intermediate during this
first step of reaction [10]. At 115 min time-of-reaction glycerol ure-
thane (intermediate) begins to be fully converted into the product,
however, the signal of glycerol urethane remains constant. It is an
equilibrium-limited reaction due to the fast reversible conversion
of glycerol and urea to glycerol urethane [25]; glycerol urethane
will be present (and monitored) as long as ammonia remains in
solution. Thus, a combination of NH3-limiting conditions and of a
slow second reaction step to form the carbonate would account for
the presence of glycerol urethane intermediate for such a prolonged
period after the initial rapid concentration changes.
Fig. 5 shows ATR-IR spectra during the reaction of glycerol with
urea over high-temperature calcined, 500C-10ZnCo, catalysts. We
have reported that this catalyst is less active, but very selective,
(37% conversion, 98% selectivity) for the reaction due to the forma-
tion of spinel inactive species ZnCo2O4 [10], which decreases the
number of active sites. When the reaction temperature increases
from room temperature to 145 ◦C (Fig. 5, top) no new bands become

110
V. Calvino-Casilda et al. / Applied Catalysis A: General 409–410 (2011) 106–112
Fig. 7. Time-resolved ATR-FTIR spectra of the reaction of glycerol with urea on
RT-1CoZn during: (top), heating from 25 to 145 ◦C (heating ramp 10 ◦C/min); and
(bottom), time-resolved ATR-FTIR spectra at 145 ◦C for 4 h (spectra taken every
10 min). “//” symbol indicates a spectrum omitted due to interferences caused by
the formation of ammonia bubbles.
Fig. 9. ATR-FTIR spectra during heating from 25 to 145 ◦C (top) (heating ramp
10 ◦C/min) and time-resolved ATR-FTIR spectra during reaction of glycerol with urea
on 500C–1CoZn at 145 ◦C for 4 h (spectra taken every 10 min) (bottom). “//” sym-
bol indicates a spectrum omitted due to interferences caused by the formation of
ammonia bubbles.
intermediate develops at 5 min reaction time, and then follows the
same trend than for urea in a similar way as for RT-10CoZn.
Fig. 9 shows the performance of the 500C–1CoZn, which pos-
sess the ZnCo2O4 spinel phase and exhibits low performance (26.8%
conversion, 82.8% selectivity). This plot shows that most of the
bands are sharper, this would be indicative of the formation of a sus-
pension of 500C–1CoZn particles. Comparison of Fig. 2 (up), Fig. 5
(up), Fig. 7 (up) and Fig. 9 (up) shows that during heating of the mix-
ture with the catalysts prepared at room temperature (RT-10CoZn
and RT-1CoZn), the product appears quickly. In case of catalysts cal-
cined at 500 ◦C, this is less intense. In addition, hydroxyl vibrations
in the 3700–3000 cm−1 range shows that their interaction with the
active sites clearly depends on the catalyst used.
Glycerol urethane slowly forms during the first hour of reac-
tion at 145 ◦C (Fig. 10), then increases quickly and levels off after
100 min of reaction time. During these 100 min of reaction, glyc-
erol urethane is slowly converted into the product remaining in
the solution, which would explain the lowest selectivity obtained
by off-line gas chromatography analyses. The remarkable change
observed in the glycerol urethane band trend is related to the low
interaction of reactants with the surface of the catalyst, due to the
presence of the spinel phase.
2,0
1,5
1,0
0,5
Urea (U)_1664cm-1
Glycerol urethane (I)_2843cm-1
Glycerol carbonate (P)_1791cm-1
0,0
0
50
100
150
200
250
Time (min)
Fig. 8. Evolution of the intensity of representative peaks corresponding to urea
(reactant), glycerol urethane (intermediate) and glycerol carbonate (product) using
RT-1CoZn during reaction at 145 ◦C.

V. Calvino-Casilda et al. / Applied Catalysis A: General 409–410 (2011) 106–112
111
ATR-FTIR spectra during carbonylation of glycerol with urea
suggest a possible interaction between the cobalt active sites and
glycerol molecules. It seems that glycerol interacts first with the
catalyst surface and then urea reacts with glycerol. Fig. 11 stud-
ies the possible interaction between glycerol carbonate product
and the catalyst surface during heating from room temperature
to 145 ◦C. This plot suggests that the band corresponding to OH
vibrations shifts to higher frequencies due to interactions of the 2-
hydroxyethyl chain of the product with the surface of the catalysts.
Besides the aforementioned reasons for the observed trends in con-
centration profiles, additionally product inhibition of the reaction,
induced by the relatively strong interaction of glycerol carbonate
with the surface, might contribute to relatively slow conversion
rates after the initial high rate of reaction. Detailed kinetic mod-
elling is necessary to further reveal the kinetically relevant steps in
the process, which is beyond the scope of the present study.
These results show that ATR-FTIR spectroscopy is a convenient
technique to monitor chemical reactions, like the synthesis of glyc-
erol carbonate and that ATR-FTIR spectroscopy may also provide
real-time feedback for process control.
Fig. 10. Evolution of the intensity of the most representative peaks corresponding to
urea (reactant), glycerol urethane (intermediate) and glycerol carbonate (product)
during reaction on 500C–1CoZn at 145 ◦C.
4. Conclusions
In situ attenuated total reflectance FTIR spectroscopy was used
to investigate the reaction pathway of glycerol to glycerol car-
bonate via carbonylation of glycerol urethane. To carry out these
experiments hierarchical Co3O4/ZnO catalysts were deposited on a
diamond internal reflection element incorporated in a heated base
plate, and the reaction carried out in a home made liquid cell. The
present work demonstrates that ATR-FTIR spectroscopy is a pow-
erful tool for assessing the reaction progress and to investigate the
reaction mechanism, while the technique is non-invasive.
25ºC
Real-time ATR-FTIR monitoring during reaction provides thor-
ough molecular information on the reaction mechanism and
possible intermediates and formation of co-products. It is possible
to see progressive dry media reaction of glycerol with urea. This
methodology can be applied to an unlimited number of processes.
Thus, this methodology is critical to understand reaction mech-
anisms of any organic reaction and provides a tool for real-time
reaction monitoring and reaction control.
145ºC
145ºC(10min)
145ºC(20min)
1%Co_coating_room T
4000
3500
3000
2500
1500
1000
500
Wavenumber (cm-1)
Acknowledgements
*spectra each 1min
Dr. V. Calvino-Casilda is indebted to CSIC for a JAE-DOC fellow-
ship. COST Action D36 is acknowledged for the STSM mission of VCC
at the University of Twente. Dr. F. Rubio-Marcos is indebted to the
“Conseil Regional du Limousin” for post-doctoral fellowship. This
work was funded by the Spanish Ministry of Science and Innovation
(CTQ2008-04261/PPQ) and MAT2010-21088-C03-01.
25ºC
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.apcata.2011.09.036.
145ºC
145ºC(10min)
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145ºC(20min)
10%Co_coating_room T
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4000
3500
3000
2500
1500
1000
500
Wavenumber (cm-1)
*spectra each 1min
Fig. 11. Time-resolved ATR-FTIR spectra of glycerol carbonate supported on Co–ZnO
systems during heating from 25 to 145 ◦C on RT-1CoZn (top) and RT-10CoZn (bot-
tom).

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