Catalytic performance of Ni/La2O3 materials in glycerol valorization for acetol and syngas production

Article abstract of DOI:10.1016/j.apcata.2015.03.045

The current global tendency is to increase the use of biofuels. This tendency has generated an oversupply of glycerol, which is the primary byproduct that is formed during the production of biodiesel. An alternative use for glycerol is based on chemical transformation to high-added-value derivatives at the industrial and/or energy level. During the decomposition of gaseous glycerol, polymers, alcohols and other oxygenated compounds can be generated with a selectivity that depends on the characteristics of the catalyst used. Accordingly, in this work, the acid and base characteristics of the catalyst support and the nickel in the Ni/La₂O₃ were investigated, as well as their influence on selectivity toward acetol at 400 °C and syngas at 700 °C. Generally, it was determined that the use of a basic catalyst support favors glycerol dehydration with respect to the formation of acetol. Moreover, it was found that the nickel particles present in the catalyst increased yield gas fraction at high reaction temperatures with a high selectivity to the syngas.

Full text of DOI:10.1016/j.apcata.2015.03.045

Applied Catalysis A: General 499 (2015) 13–18
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Catalytic performance of Ni/La2O3 materials in glycerol valorization
for acetol and syngas production
Diana Hernández, Diana López, Jhon J. Fernández∗
Grupo Química de Recursos Energéticos y Medio Ambiente, Instituto de Química, Facultad de Ciencias Exactas y Naturales,
Universidad de Antioquia (UdeA), Calle 70 No. 52-21, Medellín, Colombia
a r t i c l e i n f o
a b s t r a c t
Article history:
The current global tendency is to increase the use of biofuels. This tendency has generated an oversup-
ply of glycerol, which is the primary byproduct that is formed during the production of biodiesel. An
alternative use for glycerol is based on chemical transformation to high-added-value derivatives at the
industrial and/or energy level. During the decomposition of gaseous glycerol, polymers, alcohols and
other oxygenated compounds can be generated with a selectivity that depends on the characteristics of
the catalyst used. Accordingly, in this work, the acid and base characteristics of the catalyst support and
the nickel in the Ni/La2O3 were investigated, as well as their influence on selectivity toward acetol at
400 ◦C and syngas at 700 ◦C. Generally, it was determined that the use of a basic catalyst support favors
glycerol dehydration with respect to the formation of acetol. Moreover, it was found that the nickel
particles present in the catalyst increased yield gas fraction at high reaction temperatures with a high
selectivity to the syngas.
Received 1 December 2014
Received in revised form 28 March 2015
Accepted 30 March 2015
Available online 7 April 2015
Keywords:
Glycerol
Conversion
Ni/La2O3
Acetol
Syngas
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
(conversions above 80% have been reported for La2O3) [9–11].
This has been attributed to the basic character of the catalyst (the
Currently, due to the increase in the price of petroleum, the
limited resources of fossil fuels and the environmental implica-
tions related to their use, there exists a clear tendency toward the
increase in the use of alternative fuels; among these, the production
of biodiesel has increased significantly in recent years [1]. As a con-
sequence, this has brought about the oversupply of glycerol, which
is the primary sub-product generated during biodiesel production.
One alternative use of glycerol involves its chemical transformation
into derivatives of high added value at the industrial scale [2–6]. For
example, a recent comparison for a fossil- and renewable-based
route for 1,2-propanediol production showed that the renewable-
based routes can provide a viable alternative to the petrochemical
route and both approaches must therefore be considered in a global
process [7].
In this type of process, catalysis is of great importance, given that
the reaction selectivity increases with respect to certain products,
depending on the catalyst characteristics [8]. In this sense, basic
catalysts, such as rare-earth oxides (La2O3, Pr6O11, Nd2O3), among
others, have shown high catalytic activity toward the dehydration
of alcohols, such as 1,3-butanediol, 1,4-butanediol and glycerol;
strength and quantity of the active sites); accordingly, it can expect
that the use of light rare-earth oxides (REOS) could favor the forma-
tion of glycerol-dehydration products due to their strong basicity
[12].
Moreover, some studies have shown that metallic catalysts are
a good alternative for glycerol decomposition via reforming, show-
ing high selectivity toward the formation of hydrogen [13–15].
In this case, although various authors have suggested that nickel
catalysts maximize hydrogen production from glycerol, their use
has been equally associated with the formation of carbonaceous
residues that cause catalyst deactivation [16–18]. One of the alter-
natives for counteracting this effect is the use of mixed oxides as
catalytic precursors; for example, the perovskite LaNiO3. Ni/La2O3
catalysts composed of metallic nanoparticles highly dispersed on
the surface of the support have been generated from this material.
This type of catalyst has shown high activity and stability during
methane reforming reactions, which could be extended to glycerol
reforming reactions [19,20].
Hernandez et al. [21] reported that the basic catalysts La2O3 and
Ni/La2O3 can both be used to produce added value products such
as acetol by glycerol dehydration. In the present work, the objec-
tive was to establish the acid–base properties of Ni/La2O3 and its
effect in the catalytic activity of the glycerol decomposition reac-
tion at 400 ◦C. The acid–base properties of La2O3 and its catalytic
∗
Corresponding author. Tel.: +57 4 2196611; fax: +57 4 2191073.
E-mail address: john.fernandez@udea.edu.co (J.J. Fernández).
http://dx.doi.org/10.1016/j.apcata.2015.03.045
0926-860X/© 2015 Elsevier B.V. All rights reserved.

14
D. Hernández et al. / Applied Catalysis A: General 499 (2015) 13–18
effect were determined, in comparison to a commercial catalyst,
i.e., ␥-alumina, which displays a predominantly acidic character
even though it possess both acidic and basic sites [22,23].
infrared spectroscopy technique. The experiments were carried out
in a Nexus Nicolet spectrometer equipped with a high tempera-
ture transmission cell and a DTGS detector, spectra were recorded
with a resolution of 4 cm−1 and 64 scans. The oxide powder was
pressed into self-supported wafer (2 cm diameter) mounted into
the cell and degassed overnight at 700 ◦C under vacuum. Then pyri-
dine vapor was adsorbed by the sample at room temperature, after
that the excess of pyridine was eliminated from the system using
vacuum. FTIR spectra were recorded after pyridine desorption at
different temperatures.
2. Experimental
2.1. Preparation of the catalysts
Lanthanum oxide (La2O3) and the perovskite LaNiO3 were pre-
pared by the auto-combustion method, following the procedure
reported in previous works from our research group [19,20]. Fol-
lowing this method, an equimolar solution was prepared from
metal nitrates and glycine (H2NCH2CO2H) was used as an ignition
promoter, at a ratio of NO3−/NH2 = 1, in which water was evapo-
rated at 90 ◦C until the formation of a gel. Subsequently, this gel
was taken to the temperature at which auto-combustion occurs
(approximately 250 ◦C), which is an exothermic process and is
responsible for the combustion of carbonaceous material and the
formation of a metal oxide. To eliminate the fraction of carbona-
ceous compounds that remain in the metal oxide, calcination was
carried out at 700 ◦C in an oxidizing atmosphere for 6 h with the
goal of removing the carbon present in the solid and forming the
perovskite-type crystalline phase, LaNiO3 (the nickel nominal con-
tent was 23.8% by weight). The Ni/La2O3 catalyst was obtained by
in situ reduction of the LaNiO3 perovskite at 700 ◦C prior to the start
of the reaction.
2.3. Catalytic tests
The decomposition of pure glycerol was carried out in a fixed bed
reactor at atmospheric pressure, which can be seen in Fig. 1. During
the reaction, a continuous flow of pure glycerol (99.9%) was passed
through the vaporizer before the reactor. The vaporizer was hold
at 290 ◦C and the reactor temperature varied between 400 ◦C and
700 ◦C. The glycerol/argon ratio was 20/80 during all experiments.
The catalytic tests were carried out using 20 mg of catalyst.
During the reaction time (2.5 h), the gases were identified on-
line, using a quadrupole mass analyzer (Pfeiffer QMS 200) in which
the evolution of syngas was evaluated. In the case of liquid-phase
products, the condensates were recovered in a water-ice trap
during the reaction. Product separation and quantification were
performed using an Agilent 6890 gas chromatograph equipped
with a DB-FFAP column (60 m × 0.25 mm × 0.25 ␮m) and FID detec-
tor. For product quantification, butanol was used as the internal
standard. Generally, all of the runs carried out in GC to identify and
quantify the compounds were performed by triplicate. In the case
of the catalytic tests, the reactions were performed by duplicate in
order to guarantee the reproducibility of the results.
2.2. Characterization of the catalysts
The La2O3 and Ni/La2O3 catalysts were characterized by X-ray
diffraction (XRD) using a Panalytical X’PERT PRO MPD powder X-ray
˚
diffractometer equipped with a copper anode (Cu K␣1 = 1.5406 A).
Conversion of glycerol and product selectivity in the liquid phase
was calculated according to the following equations:
The equipment was operated at 45 kV and 40 mA, and data acquisi-
tion was carried out for an angle 2ꢀ between 10 and 90◦, with a step
size of 0.01◦ and an acquisition time of 1 s/step. The mesh param-
eters were determined with a step size of 0.01◦ and an acquisition
time of 2 s/step. The experimental diffractograms were compared
with the Power Diffraction File (PDF) database.
The determination of the number of acidic and basic sites in
the Ni/La2O3, La2O3, and ␥-Al2O3 catalysts was carried out via
the temperature programmed desorption (TPD) of NH3 and CO2,
respectively, these experiments were carried out in a Micromerit-
ics Autochem II using a thermal conductivity detector (TCD). Before
carrying out the TPD experiments, the catalysts were first subjected
to a pre-treatment in helium at 400 ◦C for 1 h.
In the case of the TPD experiments with NH3 (TPD NH3), after
cooling the system to 50 ◦C, each catalyst was subjected to an NH3
flow (0.3% in helium) for 90 min; after purging the system in helium
for 30 min, a thermal treatment in helium from 50 ◦C to 1000 ◦C was
performed, using a ramp rate of 10 ◦C/min and then holding at this
temperature for 30 min. The adsorption of CO2 was performed at
50 ◦C, for which each catalyst was subjected to a pure CO2 flow for
90 min. Subsequently, the system was purged under He flow for
30 min. The desorption of CO2 was performed under He flow while
increasing the temperature from 50 ◦C to 850 ◦C, using a ramp rate
of 10 ◦C/min; at this temperature, an isothermal hold was carried
out for 1 h.
weight of glycerol reacted
weight of glycerol in the feed
Glycerol conversion (%) =
Product i Selectivity (%) =
3. Results and discussion
× 100
weight of i product
weight of liquid fraction
× 100
3.1. Properties of the catalysts
The presence of the metallic nickel and lanthanum oxide phases
in the structure of the Ni/La2O3 catalyst prepared by reduction
of LaNiO3 perovskite at 700 ◦C was corroborated by XRD (Fig. 2),
which is in agreement with previous studies, where the experimen-
tal conditions for achieving the reduction (under H2 atmosphere at
700 ◦C) ensured the complete destruction of the perovskite struc-
ture [20–24]. Meanwhile, the measurement of nickel oxidation
state using XPS analysis, reported in our recent paper, indicates
that the reduction of LaNiO3 perovskite at 700 ◦C allows to obtain
only metallic nickel (100% Ni0 on the catalyst surface) [21].
With the purpose to evaluate the acid–base properties of the
La2O3 and Ni/La2O3 catalysts, Table 1 shows the TPD results for the
The moles of desorbed NH3 and CO2 were calculated via the
integration of the thermogram signals and then were related to the
areas obtained for known volumes of each gas analyzed at standard
conditions, for which the deconvolution of the areas was carried
out by assuming a Gaussian distribution (with a correlation index
of 99%). The results obtained were normalized per gram of catalyst.
Additionally, the surface acidic sites of the supports were char-
acterized by pyridine adsorption–desorption experiment using
Table 1
The acid–base properties of the different catalysts.
a
Al2O3
La2O3
Ni/La2O3
BET area (m2/g)
Total number of acidic sites (␮moles NH3/g)
Total number of basic sites (␮moles CO2/g)
80
609
289
10
115
511
12
69
342
a
␥ Al2O3 Alfa Aesar, 99.97%.

D. Hernández et al. / Applied Catalysis A: General 499 (2015) 13–18
15
Mass flow
controllers
Vaporizer
290°C
H
Ar
2
Syringe
Pump
Glycerol
supply
Catalytic
bed
Vent
Reactor
400 °C - 700 °C
QMS
Analyzer
Water / ice
trap
Fig. 1. The experimental set-up.
NH3 and CO2 test molecules on these materials, and the compar-
ison with a commercial catalyst (␥-Alumina Alfa – Aesar) whose
acid–base characteristics are known [22,23]. The results indicate
the highly basic character of La2O3 and Ni/La2O3 prepared from the
perovskite LaNiO3 and the strongly acidic character of the alumina.
The distribution of basic sites in the catalysts was evaluated
based on the desorption profiles (TPD CO2), as is shown in Fig. 3,
and it was found that both Ni/La2O3 and La2O3 displayed significant
heterogeneity in basic sites, showing only a single desorption at
temperatures below 450 ◦C (with a maximum at 373 ◦C) for La2O3.
In contrast, for Ni/La2O3, two desorption peaks were observed (with
maxima at 401 ◦C and 419 ◦C, respectively). However, the relative
proportion of species in the catalysts, associated with the forma-
tion of bicarbonates in weak OH− and O2− species, is greater in
La2O3 with respect to Ni/La2O3 (Table 1). Additionally, the peaks
at temperatures above 450 ◦C observed in both catalyst correspond
to CO2 desorption, which is associated with the presence of mon-
odentate and polydentate carbonates species [12,25], though the
type of species and amount are different on La2O3 with respect to
Ni/La2O3 as observed for adsorption sites at lower temperatures;
suggesting that the Ni–La2O3 interactions significantly modified
the surface properties of the support. In the case of ␥-Al2O3 (no
showed), only one desorption peak of weak species is present in
relation to La2O3 and Ni/La2O3, which is consistent with previous
reports in the literature [23].
Regarding the acidic properties, Fig. 4 shows the NH3 TPD
with the distribution of acidic sites in the tested catalysts. In this
figure it is important to highlight in the case of ␥-alumina (Fig. 4c),
the NH3 desorption behavior at low and moderate temperatures,
which can be attributed to the presence of acidic sites of weak
and moderate character (with maxima at 142 ◦C and 380 ◦C) in
agreement with the literature reports. These results demonstrate
the prevailing acidic character of this material. Concerning La2O3
(Fig. 4b), two NH3 desorption peaks with maxima at 317 ◦C and
436 ◦C (moderately acidic sites) are observed, which indicates two
types of sites with different acidic strength. It is important to high-
light that the presence of Ni caused the formation of new weakly
acidic sites (with a maximum at 142 ◦C), in addition to the forma-
tion of a unique type of moderately acidic site (with a maximum
at 420 ◦C). This result could be related to interactions between the
support and the active phase that can occur in this catalyst as could
Fig. 2. XRD of the LaNiO3 and Ni/La2O3 catalyst after in situ reduction of LaNiO3
at 700 ◦C (•) LaNiO3 (PDF 00-88-0633), (ꢀ) La2O3 (PDF 01-083-1349), (ꢁ) Ni0 (PDF
00-045-1027).
Fig. 3. The CO2 TPD profiles for Ni/La2O3 (a), La2O3 (b).

16
D. Hernández et al. / Applied Catalysis A: General 499 (2015) 13–18
Table 2
The identified products generated during the glycerol decomposition reaction.
Fraction
Identified products
Liquid fraction
CH3OH (methanol), C2H5OH (ethanol),
HOCH2(OH)CHCH3 (1,2-propanediol),
HO(CH2)3OH (1,3-propanediol), CH3CHO
(acetaldehyde), CH2 CHCHO (acrolein),
CH3COOH (acetic acid), C2H5COOH (propionic
acid), CH3C(O)CH3 (acetone), CH3C(O)CH2OH
(hydroxyacetone).
Gaseous fraction
Solid fraction
H2 (hydrogen), CO (carbon monoxide), CO2
(carbon dioxide), CH4 (methane), C2H4
(ethylene), C2H6 (ethane)
Carbonaceous material (coke)
Fig. 4. The NH3 TPD profiles for Ni/La2O3 (a), La2O3 (b) and Al2O3 (c).
could indicate the presence of Bronsted acidic sites on La2O3 surface
to protonate pyridine.
be seen in the case of basic sites evaluated via TPD of CO2, sug-
gesting in addition that such interaction occurs selectively, that is,
the Ni interacts with La2O3 through acidic sites of intermediate
strength.
In Fig. 5b, the amount of adsorbed pyridine was estimated
by integrating the absorption band at ∼1452 cm−1 (ꢁ19b) using
its molar coefficient (εꢁ19b = 1.3 cm ␮mol−1) [28,29,32]. This fig-
ure shows that the amount of acidic Lewis sites in the ␥-Al2O3 is
largely superior to the amount obtained for La2O3. ␥-Al2O3 exhibits
LAS sufficiently strong for retaining pyridine adsorbed at elevated
temperatures.
Taking into account all of the above, it is possible to conclude
that the basic character of the studied catalysts (as a function
of the number of basic sites evaluated) followed the trend ␥-
Al2O3 < Ni/La2O3 < La2O3, for which the number of basic sites in
the catalyst Ni/La2O3 decreased with respect to La2O3, possibly
because of the strong interaction between nickel and the La2O3.
Regarding the acidic character of the evaluated catalysts, the trend
of Ni/La2O3 < La2O3 < ␥ Al2O3 was found, which corroborated the
strong effect of the metal–support interaction on the acid–base
characteristics of the catalyst. It is important to highlight that, in
the case of alumina, although the catalyst showed a high NH3 des-
orption, indicating a strongly acidic character, it equally exhibits a
significant number of basic sites, given that the amount of desorbed
CO2 is comparable to that of the catalyst Ni/La2O3 and more than
half of the value obtained for La2O3.
The surface acidic properties for the supports were further
evaluated by FTIR analyses of adsorbed pyridine. Upon pyridine
adsorption at room temperature, the FTIR spectra were collected
after desorption at different temperatures. Fig. 5 shows the differ-
ence spectra of the samples in the pyridine ring vibration region.
In Fig. 5a characteristics absorption bands of pyridine at
1623/1618, 1577, 1493 and 1452 cm−1 on ␥-Al2O3 sample were
observed [26–30]; indicating the presence of different types of
Lewis acidic sites with different strength [31]. For La2O3, absorp-
tion bands of pyridine were also observed at 1603, 1582, 1545,
1479/1474, 1439 cm−1; the absorption band centered at 1545 cm−1
3.2. Identification of the reaction products
During the catalytic decomposition reaction of glycerol at
400 ◦C, various products distributed in different fractions were
obtained, including a liquid fraction, primarily comprising con-
densable oxygenated compounds, a gaseous fraction, and a solid
fraction, composed of carbonaceous material generated during the
reaction. The products that were identified are shown in Table 2.
These results are in agreement with Eq. (1), which shows the
general glycerol decomposition reaction [33].
C3H8O3(l) → CxHyOz(l,g) + (H2, CO, CO2, CH4, . . .)(g) + C(s)
(1)
3.3. Effects of metallic Ni and the acid–base properties of the
catalyst
In order to study the effects of metallic nickel and the acid–base
properties of the Ni/La2O3, on its catalytic activity during glyc-
erol decomposition at 400 ◦C, the results of a catalytic test were
compared to the results obtained for La2O3, whose character is pre-
dominantly basic, and for the alumina, which, although it displayed
moderately basic sites, showed a prevailing acidic character.
Fig. 5. (a) FTIR spectra of pyridine adsorbed on ␥-Al2O3 and La2O3 after desorption at 150 ◦C, (b) amount of Lewis acidic sites (LAS) on ␥-Al2O3 and La2O3.

D. Hernández et al. / Applied Catalysis A: General 499 (2015) 13–18
17
Analyzing the products identified via this route, it was possible
to establish the primary presence of highly oxygenated polymers,
such as glycerol- and acetol-based oligomers. However, it was
found that acetol formation decreased by utilizing Ni/La2O3 as a
catalyst, and at the same time, the amount of oxygenated light com-
pounds present in the liquid phase and the amount of polymers
generated from these compounds increased.
The use of alumina (Al2O3) as catalyst showed a significant
decrease in the formation of acetol. In turn, the formation of poly-
mers and the presence of water in the liquid phase increased
significantly, which can be related to the greater formation of
acrolein as the intermediate product [8]. Acrolein reacted to cause
the formation of polymers via condensation reactions, which could
explain the simultaneous increase in the production of water. In
this case, in addition to the polymers generated from acrolein, poly-
mers generated from glycerol and acetol also were identified in the
liquid phase.
Fig. 6. Effect of the nature of the catalyst on glycerol conversion toward different
fractions during glycerol decomposition at 400 ◦C.
Based on the above mentioned discussion and considering the
results found in the literature, which suggest that catalysts with
acidic characteristics favor the glycerol dehydration route toward
the formation of acrolein [8,36,37], in this study, it is suggested
that the formation of acetol from glycerol dehydration is directly
related to the acid–base properties of the catalyst support. Although
the presence of Bronsted sites has been associated in the liter-
ature with a greater selectivity toward the dehydration product
(acrolein) [38,39], in La2O3 the negligible amount of acidic sites
observed in Fig. 5b explains the absence of acrolein in the liq-
uid phase using this catalyst. Instead, high selectivity to acetol is
achieved which has been associated with the basic character of
La2O3 catalyst support. For the case of catalysts such as alumina,
which has potentially catalytic acidic and basic sites in its struc-
ture, it has been found that the dehydration mechanisms occur by
means of a concerted reaction on the basic sites and on Lewis-acid
sites present in the structure [23].
For catalysts with a strongly basic character, such as La2O3, it is
proposed that the glycerol dehydration reaction occurs via the E1cB
mechanism, which involves the formation of a carbanion. Accord-
ingly, it was found that this type of catalyst promotes the formation
of products through Hoffman elimination, possibly because in this
case, the primary hydroxyl groups are the least impeded and thus
the most reactive [12].
Concerning the formation of acetol from glycerol, previous
reports have suggested that glycerol hydrogenolysis occurs prior
to the dehydration mechanism, generating glyceraldehyde as an
intermediate product. These dehydrogenation–dehydration and
hydrogenation mechanisms are both justified by the presence of
a catalyst with a strongly basic character, as is the case of La2O3
[40].
Due to the strongly basic character found for the Ni/La2O3 cat-
alyst, it is possible to infer that glycerol dehydration with this
catalyst occurs via the E1cB mechanism, which explains the high
selectivity toward acetol formation. However, it is also proposed
that the presence of the nickel metallic sites favored, to a certain
degree, the cracking of both glycerol and some dehydration inter-
mediaries into smaller molecules, which accounts for the increase
in the selectivity toward lighter oxygenated compounds. Such com-
pounds can be polymerized easily due to the basic characteristics
of the catalyst, as has already been reported in some publications
[41,42]. This effect becomes more evident upon increasing the reac-
tion temperature, as shown in Fig. 7. It can be seen that at 700 ◦C, the
conversion to gaseous products exceeds 80%, with hydrogen and
carbon monoxide being the primary products that are generated in
this fraction.
Regarding glycerol conversion, Fig. 6 shows that, independently
of the type of catalyst used during the reaction, there is a high
selectivity toward products pertaining to the liquid fraction (above
96% in all cases) in addition to the low formation of gases and
carbonaceous material because the reactions of dehydration and
partial decomposition of glycerol are primarily favored at 400 ◦C.
In turn, the increase in glycerol conversion when using the catalyst
with nickel confirmed that the presence of this metal favors crack-
ing of the glycerol molecule, as has been reported in the literature
[34].
Moreover, due to the large quantity of products in the liq-
uid fraction that were obtained at 400 ◦C, the selectivity toward
specific products from this fraction was evaluated at this tem-
perature (as shown in Table 3). Generally, it was found that the
selectivity toward acetol is influenced by the basic characteris-
tics of the catalyst, according to the trend Al2O3 < Ni/La2O3 < La2O3.
Additionally, Table 3 shows that the formation of polymers has an
inverse trend, That is, the formation of polymers was influenced
by the acidic properties of the catalyst and followed the trend of
Al2O3 > Ni/La2O3 > La2O3.
From the analysis of these results, it is possible to infer that the
use of lanthanum oxide as a catalyst favored the route of partial
glycerol decomposition toward the formation of acetol and, conse-
quently, toward the formation of 1,2-propanediol; this compound
can be produced through a two-step process, where glycerol is
first dehydrated to acetol which is subsequently hydrogenated to
1,2-Propanediol. The solid catalysts active for the reaction usually
are composed of bi-functional metal–acid catalysts, which combine
acid sites for dehydration reactions (like ZnO, C, Rh, SiO2, Al2O3) and
metal sites for hydrogenation reactions (such as Cu, Pd, Rh, Ni). Best
results are obtained by using noble metals, because their presence
promotes the subsequent hydrogenation of acetol [7,21,35].
Table 3
Products composition of the liquid fraction obtained during the catalytic decompo-
sition of glycerol at 400 ◦C.
Catalyst
XL (%)
Selectivity to products in the liquid phase (%)
Water
Acetola
1,2-Propb
Polymc
Othersd
La2O3
Al2O3
Ni/La2O3
97.2
97.5
96.8
10.3
16.8
6.0
59.6
30.9
39.9
7.9
4.2
7.0
18.5
46.5
35.9
3.7
1.6
11.2
a
Acetol
1,2-Propanediol.
b
With regard to the composition of the syngas as a function
of temperature, it was found that by increasing the temperature,
the formation of CO was favored. Meanwhile, the ratio of H2/CO
c
Polymers of glycerol.
Others: acetaldehyde, acetone, acrolein, methanol, ethanol, acetic acid,
d
propanoic acid.

18
D. Hernández et al. / Applied Catalysis A: General 499 (2015) 13–18
for financial support. Diana Hernández thanks COLCIENCIAS for the
doctoral scholarship.
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The authors thank the Ministry of Agriculture and Rural Devel-
opment of Colombia (MADR project 20X07D3347-498) and the
Universidad de Antioquia (Programa de Sostenibilidad 2014–2015)