Novel hierarchical Co3O4/ZnO mixtures by dry nanodispersion and their catalytic application in the carbonylation of glycerol

Article abstract of DOI:10.1016/j.jcat.2010.08.009

Cobalt oxide nanoparticles (40-50 nm) were hierarchically dispersed on ZnO microparticles (0.2-1 μm) using a low-energy dry mixing method, resulting in a zinc-cobalt interaction that stabilizes Co²⁺ sites. Raman spectroscopy is used to evidence the nature of the interphase reaction between ZnO and Co₃O₄ particles. The system evolves toward the formation of the spinel phase, ZnCo₂O₄, with further temperature thermal treatment at 400 °C. The catalytic activity of these materials was tested in the transformation of renewable materials via the carbonylation of glycerol by urea. Room-temperature-prepared Co ₃O₄/ZnO systems exhibit catalytic behavior in the production of glycerol carbonate reaching conversions up to 69% in 4 h with close to 100% selectivity.

Full text of DOI:10.1016/j.jcat.2010.08.009

Journal of Catalysis 275 (2010) 288–293
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Novel hierarchical Co3O4/ZnO mixtures by dry nanodispersion
and their catalytic application in the carbonylation of glycerol
c
c
b
F. Rubio-Marcos a,b, , V. Calvino-Casilda , M.A. Bañares , J.F. Fernandez
⇑
a Departamento de Física de Materiales, UCM, 28040 Madrid, Spain
b Electroceramic Department, Instituto de Cerámica y Vidrio, CSIC, Kelsen 5, 28049 Madrid, Spain
c Catalytic Spectroscopic Laboratory, Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, 28049 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 July 2010
Revised 16 August 2010
Accepted 19 August 2010
Available online 21 September 2010
Cobalt oxide nanoparticles (40–50 nm) were hierarchically dispersed on ZnO microparticles (0.2–1 lm)
using a low-energy dry mixing method, resulting in a zinc–cobalt interaction that stabilizes Co2+ sites.
Raman spectroscopy is used to evidence the nature of the interphase reaction between ZnO and Co3O4
particles. The system evolves toward the formation of the spinel phase, ZnCo2O4, with further tempera-
ture thermal treatment at 400 °C. The catalytic activity of these materials was tested in the transforma-
tion of renewable materials via the carbonylation of glycerol by urea. Room-temperature-prepared
Co3O4/ZnO systems exhibit catalytic behavior in the production of glycerol carbonate reaching conver-
sions up to 69% in 4 h with close to 100% selectivity.
Keywords:
Heterogeneous catalysis
Biomass
Glycerol carbonate
Urea
Ó 2010 Elsevier Inc. All rights reserved.
Cobalt oxide
Zinc oxide
Nanoparticles
1. Introduction
agent; Mouloungui et al. [15] patented the synthesis of glycerol
carbonate by carbonylation of glycerol with urea over heteroge-
Glycerol is a renewable strategic raw chemical, which use de-
pends on its efficient conversion to value-added products. How-
ever, glycerol exhibits a too versatile chemistry, resulting in a
broad distribution of products that typically hampers its applica-
tion [1–4]. The use of co-reactants to narrow product distribution
is a particularly successful approach; for instance, the use of
ammonia to make acrylonitrile, both in the vapor phase and in
the liquid phase, results in yield values to acrylonitrile of 40% with
nearly 90% selectivity [5–7]. Like acrylonitrile, glycerol carbonate is
also a valuable chemical. Glycerol carbonate is one of the glycerol
derivatives that attract more scientific and industrial interest due
to its potential end uses. The search for successful routes to effi-
ciently produce glycerol carbonate from renewable raw materials
is a key subject for different manufacturing areas since these
may compete and replace petroleum-derived materials [8–10].
CO2 has been used as a carbonylating agent under supercritical
conditions [11]; but its experimental conditions are highly
demanding. Other carbonylating agents like dimethyl carbonate
[12,13], dialkyl carbonates [14] or urea [15] allow for milder reac-
tion conditions. Urea is a particularly attractive carbonylating
neous zinc catalysts such as zinc sulfate, zinc organosulfate and
zinc ion exchange resins. Calcined ZnSO4 affords the best results
by reaction with urea (glycerol carbonate yields 86% in 2 h) at
150 °C and 40 mbar; the ammonia formed is removed during reac-
tion. However, ZnSO4 salt is soluble in glycerol; thus, this is a
homogeneous catalysis reaction, where the catalyst is partially
recovered after reaction. There is a strong strategic and environ-
mental benefit in developing a heterogeneous catalyst for this
process. Heterogeneous catalysts are particularly efficient for cab-
onylation of glycerol with urea [16,17] affording good yield values
under more moderate reaction conditions. Climent et al. [17] have
recently reported the carbonylation of glycerol (glycerol carbonate
yield 72% in 5 h) with urea at 145 °C over heterogeneous catalysts
such as basic oxides (MgO and CaO) and mixed oxides (Al/Mg and
Al/Li) derived from hydrotalcites with adequate acid–base pairs
[17].
The reactions described above have a significant environmental
and sustainable value; the development of environmental friendly
catalytic process requires heterogeneous catalysts. The preparation
stage is a key component in the environmental value of a catalyst.
We have reported a residue-free and solvent-free preparation meth-
od to make hierarchical nanoscaled catalysts dispersed on micro-
scaled particles [18,19]. This nanodispersion method opens up
opportunities to obtain hierarchical nanoparticles–microparticles
⇑
Corresponding author at: Electroceramic Department, Instituto de Cerámica
y Vidrio, CSIC, Kelsen 5, 28049 Madrid, Spain. Fax: +34 91 735 584.
E-mail address: frmarcos@icv.csic.es (F. Rubio-Marcos).
0021-9517/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2010.08.009

F. Rubio-Marcos et al. / Journal of Catalysis 275 (2010) 288–293
289
systems with unusual properties by mixing oxides of dissimilar
materials. The interfaces created after the partial reaction of two
oxides exhibits new and interesting properties due to proximity
and diffusion phenomena [20,21], which become relevant at the
nanoscale range. We have demonstrated that interface-related
properties lead to the appearance of ferrimagnetism in mixtures
of ZnO and Co3O4 despite the constituting oxides present diamag-
netic and paramagnetic characters at room temperature, respec-
tively [22,23].
amount of glycerol. After the reaction was completed, water was
added and the catalyst was removed by filtration. The catalyst
was washed with acetone several times and dried at room temper-
ature for 24 h to be used in a new cycle of reaction. The reactions
were followed by gas chromatography using a HP5890 gas chro-
matograph (GC) equipped with a 50-m-long Ultra2–5% Phenyl
methyl siloxane capillary column and a flame ionization detector
(FID) (Accuracy <5% relative).
The effects in the preparation procedure of Co3O4/ZnO mixtures
obtained by dry nanodispersion is presented and discussed. In
addition, the effects on the phase structure and morphology of
Co3O4/ZnO mixtures are evaluated. It is shown that Co3O4/ZnO
interface properties are modified producing changes in the cata-
lytic properties of the mixtures as it was tested in the carbonyl-
ation reaction of glycerol with urea.
3. Results and discussion
3.1. Morphology of the Co3O4/ZnO mixtures
Fig. 1a and b shows the morphology of pure ZnO and Co3O4 raw
materials. The FE-SEM micrograph, Fig. 1a, shows the typical ZnO
morphology, consisting mainly of elongated prismatic particles
and nearly cubical particles, with sizes of 0.2–1.0
age particle size 0.5 m. The morphology of Co3O4 particles is that
of small spherical particles with sizes of 40–50 nm (see insert
Fig. 1b) which form globular agglomerates ranged from 0.5 m to
m, Fig. 1b. On the other hand, the FE-SEM image of the mixture
lm and an aver-
2. Experimental details
l
2.1. Nanodispersion procedure of Co3O4/ZnO mixtures
l
4
l
The compositions with 0.5, 1, 5 and 10 wt.% of Co3O4 nanopar-
ticles (hereafter, named as ZCo0.5-Nps, ZCo1-Nps, ZCo5-Nps and
ZCo10-Nps respectively) were prepared by incorporating the
appropriate amounts of Co3O4 nanoparticles and ZnO microparti-
cles by a previously described dry nanodispersion procedure [18].
The dry dispersion process consisted on shaking Co3O4/ZnO mix-
tures 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 were produced by the mixing
process. The raw materials used in this study are cobalt oxide
(Co3O4, 99.99%) and ZnO (99.99%). Analytical grade powders were
dried at 110 °C for 2 h before dry mixing.
of ZnO with 10 wt.% of Co3O4 nanoparticles prepared by dry nanod-
ispersion method is shown in Fig. 1c. The micrographs show that
most of the Co3O4 agglomerates disappear and the individual
nanoparticles are adhered to the ZnO surfaces Fig. 1d. The disper-
sion and great adherence of nanoparticles could indicate the
appearance of Co3O4/ZnO interfaces at room temperature between
these materials, due to the high initial reactivity of the Co3O4 and
ZnO. All individual nanoparticles are dispersed below 10 wt.%
Co3O4, but some agglomerates become apparent at higher Co3O4
loadings. This means that a dispersion limit of Co3O4 nanoparticles
on ZnO microparticles has been reached. It is worth to mention
that ZnO particles morphology is kept invariant, as a result of the
low energy of the mixture process. The TEM micrograph in
Fig. 1d confirms the presence of interfaces between ZnOꢀCo3O4
after the dry mixing process.
2.2. Morphology characterization
The particle size and morphology of the powders were evalu-
ated using secondary electrons images of Field Emission-Scanning
Electron Microscopy, FE-SEM (Hitachi S-4700) and Transmission
Electron Microscopy (TEM, Hitachi H-7100 175) with an accelerat-
ing voltage of 120 kV. For TEM investigations, powders were
suspended in isopropanol, and a drop of this suspension was
deposited on a holey carbon-coated film supported on a 400 mesh
copper grid.
3.2. Structural characterization of Co3O4/ZnO system
The X-ray diffraction patterns of the raw materials and the
Co3O4/ZnO mixtures, displayed in Fig. 2, can be indexed on the ba-
sis of a phase mixture constituted by a majority of ZnO and a
minority of Co3O4. As expected, the intensity of the diffraction
peaks of Co3O4 phase becomes increasingly stronger with Co3O4
loading.
In order to check the effect of the thermal treatment tempera-
ture on the phase structure, the mixtures were thermally treated
at 500 °C for 36 h. No changes are observed in the XRD pattern
after such thermal treatment, Fig. 2.
2.3. Structural characterization
The crystalline structure was determined by X-ray diffraction
analysis (XRD, Siemens D5000, Munich, Germany, Cu K
a radia-
No evidence of metallic Co, CoO or any additional phases differ-
ent than ZnO, Co3O4 were found in any sample, within the XRD res-
olution. The expected reaction between Co3O4 and ZnO is the
formation of a Zn1ꢀxCoxO wurtzite-type solid solution, which pos-
sesses the same lattice parameters than ZnO. This would explain
the fact that only the diffraction peaks of ZnO are observed at
500 °C. There is little difference between the ionic radii of Co2+
(0.058 nm) and Zn2+ (0.060 nm) and, therefore, small changes in
the c-axis value due to Co substitution in ZnO can be expected.
At higher temperatures, the formation of the spinel phase ZnCo2O4
is possible but this phase is isostructural with Co3O4 and X-ray dif-
fraction patterns cannot determine whether the spinel forms.
The Co3O4/ZnO mixtures prepared by nanodispersion method
and thermally treated at 500 °C have also been investigated by Ra-
man spectroscopy, and the resulting spectra are depicted in Fig. 3a.
ZnO has a wurtzite structure, with two formulae per primitive cell
tion). The Raman spectra were measured in air atmosphere at
room temperature, using the 514 nm excitation line from an Ar+ la-
ser operating at 10 mW. The signal was collected by a microscope
Raman spectrometer (Renishaw Micro-Raman System 1000) in the
100 cmꢀ1ꢀ1100 cmꢀ1 range.
2.4. Reaction procedure in the carbonylation of glycerol with urea
In a typical experiment, an equimolecular mixture of glycerol
and urea were placed in a 10 mL round-bottom flask in a batch
reactor for 5 min before the catalyst was added. The reaction was
heated in an oil bath at 140–145 °C and stirred at 300 rpm. Reac-
tions were run in the absence of a solvent at atmospheric pressure
removing ammonia from the system by air passing through the
reactor. The amount of catalyst used was 6% by weight of the initial

290
F. Rubio-Marcos et al. / Journal of Catalysis 275 (2010) 288–293
a
b
d
c
Fig. 1. Field emission-scanning electron microscopy micrograph of the initial materials: (a) ZnO microparticles and (b) Co3O4 nanoparticles agglomerates. The insert shows a
detail of Co3O4 spherical nanoparticles by Transmission Electron Microscopy. FE-SEM micrograph of ZnO particles covered by Co3O4 nanoparticles adhered to the surface after
low-energy mixing. (c) Mixture of ZnO with 10 wt.% of Co3O4 nanoparticles. (d) TEM micrograph detail of the Co3O4 nanoparticles dispersed over ZnO elongated prismatic
particles observed in the mixtures with Co3O4 contains higher than 5 wt.%.
Fd3m (Oh7) space group, one should theoretically expect five
Raman active modes (A1g + Eg + 3F2g). Pure cobalt oxide exhibits
the five expected Raman active modes in this spectral range: A1g
(689 cmꢀ1); F2g (619, 521 and 191 cmꢀ1) and Eg (481 cmꢀ1). The
high-frequency peak, A1g, has been assigned to vibrations involving
the motion of oxygen atoms inside the octahedral unit (e.g. CoO6 in
Co3O4). Their breadth is related to the cation–anion bond lengths
and polyhedral distortion occurring in the spinel lattice [26]
whereas F2g and Eg modes combine the vibration of tetrahedral
(e.g. CoO4 in Co3O4) and octahedral sites [27]. The Raman spectra
of the ZnO and Co3O4 as raw materials and the Co3O4/ZnO mix-
tures, displayed in Fig. 3a, can be indexed on the basis of a phase
mixture constituted by both phases. After annealing the Co3O4/
ZnO mixtures at 500 °C, the cobalt oxide Raman bands present
changes. The possible insertion of Zn2+ into the lattice of spinel
slightly alters the observed vibrations frequencies as shown in
Fig. 3b. Raman bands are substantially blueshifted. The Raman
peak associated with the motion of oxygen atoms inside the octa-
hedral unit, A1g, in the Co3O4 is the most intense for any annealing
time. Moreover, the nanodispersion of Co3O4 produces a slight
broadening of the A1g Raman peak and the appearance of a double
peak upon treatments at ꢁ500 °C. The second peak could be attrib-
Fig. 2. XRD patterns corresponding to the raw materials, the Co3O4/ZnO mixtures
and thermally treated at 500 °C during 36 h as a function of the Co3O4 content.
uted to the appearance of the spinel phase ZnCo2O4 at ꢁ714 cmꢀ1
which emerges concomitantly, Fig. 3b. Actually, at Co3O4 concen-
tration as low as 0.5 wt.%, the formation of the ZnCo2O4 spinel is
clearly observed. The formation of the spinel requires a large diffu-
sion of Zn atoms (not only those at the particle surface) and there-
fore is more favored by the longer annealing time. Recently, the
formation of the spinel phase at low temperature, ꢁ400 °C, was re-
ported for this system [28], which could be related to zinc cations
diffusion.
with C3 symmetry. For this structure, the group theory predicts
t
the following Raman active modes A1 + E1 + 2E2 [24,25]. These dis-
tinct Raman active modes of ZnO can be observed in Table 1 along
with their proposed assignment. Moreover, Table 1 also identifies
the main Raman modes of Co3O4, which Raman spectra can be ob-
served in Fig. 3a. Considering that spinel structures belong to the

F. Rubio-Marcos et al. / Journal of Catalysis 275 (2010) 288–293
291
Fig. 3. (a) The Raman spectra of raw materials, Co3O4/ZnO mixtures and thermally treated at 500 °C during 36 h as a function of the Co3O4 content. (b) Magnified Raman
spectra in the wavenumber ranges from 640 to 760 cmꢀ1 of the Co3O4/ZnO mixtures thermally treated and Lorentzian fits of the individual peak of the Raman mode
associated with the appearance of the spinel phase (ZnCo2O4).
Table 1
carbonate
(4-hydroxymethyl-1,3-dioxolan-2-one)
(B)
with
Main Raman modes observed on ZnO and Co3O4 phases. The intensity of the peaks is
marked from very low to very intense. (l: low; m: medium; s: strong; v: very).
abstraction of the ammonia or (III) carbonylation of glycerol ure-
thane to 5-(hydroxymethyl)oxazolidin-2-one (C) without abstrac-
tion of the ammonia and (IV) glycerol carbonate can react with
another molecule of urea to obtain (2-oxo-1,3-dioxolan-4-yl)-
methyl carbamate (D), which would decrease glycerol carbonate
selectivity [15,17], see Scheme 1.
Raw materials
ZnO
Raman shift (cmꢀ1)/process
Intensity (a.u)
References
[24,25,29]
203 (2TA; 2El2ow
)
l
333ðEh2igh ꢀ El2ow
Þ
m
378 (A1TO)
m
l
Fig. 4 shows the activity results obtained during carbonylation
of glycerol over the constituting oxides and the Co3O4/ZnO cata-
lytic systems prepared by dry nanodispersion at room temperature
and those further calcined at 500 °C. ZnO is hardly more active
than the blank test, in line with literature data [30]. Co3O4 is more
active and selective. The combination of both oxides exhibits a cat-
alytic activity that depends on the specific preparation procedure
and treatment temperature. Cobalt oxide loading in Co3O4/ZnO in-
creases the activity dramatically for the room-temperature series
but it exhibits a moderate increase for the series calcined at
500 °C (Fig. 4). Thus, the catalytic activity is hampered upon calci-
nation. The room-temperature series with 1%wt Co3O4 exhibits
100% selectivity to glycerol carbonate, but it is only slightly more
active than the blank test; at higher loading (10 wt.% Co3O4), con-
version reaches 69% with 97% selectivity to glycerol carbonate. The
performance of this series is unlike those reported earlier [17],
where total conversion is attained with selectivity values near
75%. For the Co3O4/ZnO series, calcination at 500 °C has a deleteri-
ous effect on both conversion and selectivity.
410 (E1TO)
438 ðEh2igh
Þ
vs
483 (2LA)
vl
l
536 (2Bl1ow; 2LA)
574 (A1LO)
590 (E1LO)
vl
l
Co3O4
481 (Eg)
m
m
l
[26,27]
521 (F2g
619 (F2g
)
)
689 (A1g
)
vs
In summary, Raman spectroscopy uncovers a progressive inter-
face reaction in ZnO–Co3O4 mixtures, which is produced by the dry
dispersion method in which cobalt oxide nanoparticles are effec-
tively dispersed onto ZnO microparticles. Longer annealing treat-
ments at low temperature allow Zn cations to diffuse and form
the spinel phase, ZnCo2O4. Zn cations are active at temperatures
near 400 °C due to the thermal desorption of interstitial Zinc
(Znþ) and the formation of oxygen vacancies (Vo)s. This behavior
i
When Co3O4 nanoparticles disperse on ZnO microparticles, the
Co3O4/ZnO systems were catalytically active since the nanodisper-
sion method of preparation leaves the Co3O4 active sites dispersed
in the Co3O4/ZnO system. After calcination of the Co3O4/ZnO sys-
tems, the phenomenon can be explained as follows: ZnO may
interact with Co3O4 and form inactive species such as ZnCo2O4 spi-
nel, as confirmed by Raman spectroscopy, decreasing the number
of free active sites Co3O4 in the system. The zinc–cobalt oxide spi-
nel has very little activity, because of the restriction of the active
species of cobalt in the tetrahedral sites. A further increase in the
amount of cobalt oxide (from 1 to 10 wt.%) leads to an increase
in the catalytic activity, which is less significant for calcined
facilitates Zn cations volatilization from the wurtzite crystal lattice
and the zinc diffusion in nearest particles of dissimilar materials,
thus promoting the solid-state reaction during the thermal treat-
ment [22,29].
3.3. Catalytic activity of the Co3O4/ZnO system
According to previous works, urea reacts with glycerol when
heated in the presence of a catalyst; the reaction mechanism fol-
lows four possible steps: (I) carbamylation of glycerol to glycerol
urethane (A), (II) carbamylation of glycerol urethane to glycerol

292
F. Rubio-Marcos et al. / Journal of Catalysis 275 (2010) 288–293
HO
HO
HO
O
OH
HO
O
HO
+ NH3
+ NH3
O
+
NH2-CO-NH2
O
O
B
H2N
+ NH2-CO-NH2
A
O
O
NH2
O
O
O
O
OH
O
D
N
H
C
Scheme 1. Reaction mechanism between glycerol and urea. Reaction products: (A) Glycerol urethane; (B) Glycerol Carbonate; (C) 5-(hydroxymethyl)oxazolidin-2-one;
(D) (2-oxo-1,3-dioxolan-4-yl)methyl carbamate.
recoverable and reusable at least three times without any loss in
activity and selectivity during the carbonylation of glycerol.
To conclude the Co3O4/ZnO systems prepared by dry nanodi-
spersion at room temperature showed the best results compared
with raw materials and those other Co3O4/ZnO systems preheated
at 500 °C. Particularly, the samples containing more Co3O4 (10
wt.%) exhibited better activity (up to 69% conversion, 97% selectiv-
ity to glycerol carbonate) demonstrating that a good dispersion of
the Co3O4 catalytically active sites in the interface of the system
that play a crucial role during reaction. The results shown high-
lighting the importance of the synthesis method used in the prep-
aration of this heterogeneous catalytic system.
The phenomenology described here can be interpreted as a sim-
ple model based on the formation of Co3O4/ZnO interfaces at room
temperature and the formation of new crystalline phases, ZnCo2O4,
at low thermal treatment, see Fig. 5. Fig. 5a and b shows a sche-
Fig. 4. Catalytic performance of Co3O4/ZnO catalytic systems for the synthesis of
glycerol carbonate at 145 °C during 4 h.
matic representation of an individual ZnO particles hierarchically
coated with Co3O4 nanoparticles by the dry nanodispersion meth-
od. The dispersion and great adherence of nanoparticles may indi-
cate that a spontaneous reaction occurs at room temperature
between these materials, due to the high initial reactivity of the
samples since the spinel is the main phase present in the system.
Finally, the Co3O4/ZnO catalytic system was found to be completely
a
c
d
b
Fig. 5. Schematic of the attachment of nanoparticles to the outer surface of an individual ZnO microparticle obtained by dry nanodispersion method, (a) Co3O4/ZnO mixtures
before and (b) after of the dry nanodispersion process. (c) Magnified ZnO surface cover Co3O4 nanoparticles hierarchically dispersed, where it can be observed Co3O4ꢀZnO
interfaces. (d) Schematic representation of the spinel phase formed after thermal treated at 500 °C/36 h.

F. Rubio-Marcos et al. / Journal of Catalysis 275 (2010) 288–293
293
[2] R.R. Soares, D.A. Simonetti, J.A. Dumesic, Angew. Chem. Int. Ed. 45 (2006) 3982.
[3] M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, C. Della Pina, Eur. J. Lipid Sci.
Technol. 111 (2009) 788.
[4] M. O Guerrero-Pérez, J.M. Rosas, J. Bedia, J. Rodríguez-Mirasol, T. Cordero,
Recent Patents Chem. Eng. 2 (2009) 11.
[5] M.O. Guerrero-Pérez, M.A. Bañares, ChemSusChem. 1 (2008) 511, doi:10.1002/
cssc.200800023.
[6] V. Calvino-Casilda, M.O. Guerrero-Pérez, M.A. Bañares, Green Chem. 11 (2009)
939.
[7] V. Calvino-Casilda, M.O. Guerrero- Pérez, M.A. Bañares, Appl. Catal. B: Environ.
95 (2010) 192.
[8] J.H. Teles, N. Rieber, W. Harder, US Patent 5 359 094, 1994.
[9] J.R. Ochoa-Gómez, O. Gómez-Jiménez-Aberasturi, B. Maestro-Madurga, A.
Pesquera-Rodríguez, C. Ramírez-López, L. Lorenzo-Ibarreta, J. Torrecilla-Soria,
M.C. Villarán-Velasco, App. Catal. A: Gen. 366 (2009).
[10] C. Vieville, J.W. Yoo, S. Pelet, Z. Mouloungui, Catal. Lett. 56 (1998) 245.
[11] M. Aresta, A. Dibenedetto, F. Nocito, C. Pastore, J. Mol. Catal. A: Chem. 257
(2006) 149.
[12] J. Ochoa-Gómez, Olga Gómez-Jiménez-Aberasturi, B. Maestro-Madurga, A.
Pesquera-Rodríguez, C. Ramírez-López, L. Lorenzo-Ibarreta, J. Torrecilla-Soria,
M.C. Villarán-Velasco, Appl. Catal. A: Gen. 366 (2009) 315.
[13] Z. Herseczki, T. Varga, G. Marton, Int. J. Chem. Reactor Eng. 7 (2009) A87.
[14] A. Takagaki, K. Iwatani, S. Nishimura, K. Ebitani, Green Chem. 12 (2010) 578.
[15] S. Claude, Z. Mouloungui, J.-W. Yoo, A. Gaset, US Patent 6025504, 2000.
[16] M. Aresta, A. Dibenedetto, F. Nocito, C. Ferragina, J. Catal. 268 (2009) 106.
[17] M.J. Climent, A. Corma, P. de Frutos, S. Iborra, M. Noy, A. Velty, P. Concepción, J.
Catal. 269 (2010) 140.
[18] J.F. Fernández, I. Lorite, F. Rubio-Marcos, J.J. Romero, M.A. García, A. Quesada,
M.S. Martín-González, J.L. Costa-Krämer, Patent Numbers WO2010010220-A1;
ES2332079-A1, 2010, to Consejo Superior de Investigaciones Científicas, CSIC.
[19] M.S. Martín-González, M.A. García, I. Lorite, J.L. Costa-Krämer, F. Rubio-Marcos,
N. Carmona, J.F. Fernández, J. Electrochem. Soc. 157 (2010) E31–E35.
[20] A. Brinkman, M. Huijben, M. Van Zalk, J. Huijben, U. Zeitler, J.C. Maan, W.G. Van
der Wiel, G. Rijnders, D.H.A. Blank, H. Hilgenkamp, Nature Mater. 6 (2007) 493.
[21] F.Y. Bruno, J. Garcia-Barriocal, M. Torija, A. Rivera, Z. Sefrioui, C. Leighton, C.
Leon, J. Santamaria, Appl. Phys. Lett. 92 (2008) 082106.
Co3O4 and ZnO [19]. Fig. 5c shows the magnification of the ZnO
surface, which illustrates the formation of new interfaces between
ZnO microparticles and Co3O4 nanoparticles. The dry nanodisper-
sion process performed to mix ZnO and Co3O4 creates new reactive
surfaces (as evidenced by FE-SEM and TEM) that must favor the
catalytic activity. This novel way to de-agglomerate nanoparticles
has been applied in the carbonylation reaction of glycerol with
urea producing novel properties at the interfaces with a high activ-
ity and selectivity catalytic. The high reactivity of ZnO may pro-
mote a higher availability of Zn cations to diffuse into Co3O4
nanoparticles, and thus the stable spinel phase is rapidly formed
when the Co3O4/ZnO were thermally treated at 500 °C during
36 h as it can be observed in Fig. 5d. The thermal treatment pro-
vokes the formation of inactive species such as ZnCo2O4 spinel
decreasing the number of free active sites Co3O4 in the system
and therefore presented a lower catalytic activity.
4. Conclusions
This work presents the preparation of hierarchical nanoscaled
Co3O4/ZnO catalytic systems using a very fast, easy and eco-
friendly (no solvent, no surfactant, no residue) dry nanodispersion
method of synthesis. This room-temperature preparation method
results in a clear interaction between Co3O4 and ZnO oxides,
endowing them with high activity (69% conversion and near
100% selectivity) for the transformation of renewable materials
as the carbonylation of glycerol by urea at moderate reaction con-
ditions (140 °C/4 h). The methodology here proposed offers invalu-
able insight into catalysts design and for their mass production due
its simplicity.
[22] A. Quesada, M.A. García, M. Andrés, A. Hernando, J.F. Fernández, A.C. Caballero,
M.S. Martín-González, F. Briones, J. Appl. Phys. 100 (2006) 113909.
[23] M.S. Martín-González, J.F. Fernández, F. Rubio-Marcos, I. Lorite, J.L. Costa-
Krämer, A. Quesada, M.A. Bañares, J.L.G. Fierro, J. Appl. Phys. 103 (2008)
083905.
[24] R. Cuscó, E. Alarcón-Lladó, J. Ibáñez, L. Artús, J. Jiménez, B. Wang, M.J. Callahan,
Phys Rev. B 75 (2007) 165202.
Acknowledgments
[25] C.A. Arguello, D.L. Rousseau, S.P.S. Porto, Phys. Rev. 181 (1969) 1351.
[26] S.Z.V. Marinkovic, N. Romecevic, Sci. Direct 27 (2007) 903.
[27] C.F. Windisch, G.J. Exarhos, K.F. Ferris, M.H. Engelhard, D.C. Stewart, Thin Solid
Films 45 (2001) 398.
[28] M. Peiteado, S. Sturm, A.C. Caballero, D. Makovec, J. Ceram. Soc. Jpn. 118 (2010)
337.
The authors express their thanks to the MICINN (Spain) projects
MAT 2010-21088-C03-01 and CTQ2008-02461/PPQ for their finan-
cial support. Dr. V. Calvino-Casilda is indebted to CSIC for a JAE-
DOC fellowship.
[29] F. Rubio-Marcos, A. Quesada, M.A. García, M.A. Bañares, J.L. García Fierro, M.S.
Martín-González, J.L. Costa-Krämer, J.F. Fernández, J. Solid State Chem. 182
(2009) 1211.
References
[30] W.M. Shaheen, M.M. Selim, Int. J. Inorg. Mater. 3 (2001) 417.
[1] M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, C. Della Pina, Angew. Chem. Int.
Ed. 46 (2007) 4434.