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Research Article
acssuschemeng.8b02933
pubs.acs.org/journal/ascecg

Cite This: ACS Sustainable Chem. Eng. 2018, 6, 16169−16178

A Coupled Density Functional Theory−Microkinetic Modeling for
the Hydrodeoxygenation of Glycerol to Propylene on MoO3
Marcos Rellán-Piñeiro and Núria López*
Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, Avinguda Països Catalans
16, 43007 Tarragona, Spain

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S
* Supporting Information

ABSTRACT: The production of propylene from renewable resources might be
relevant to provide this compound in a scenario of scarcity due to the use of shale
gas as a raw material. In the present, work we provide a full density functional
theory description of the reaction network that drives the hydrodeoxygenation of
glycerol on molybdenum oxide. From these results, a microkinetic model is built
that allows the analysis of the most common routes and the potential bottlenecks
compromising the activity and selectivity of the process. With this integrated
scheme, we have found that the reaction proceeds mainly through the formation
of hydroxypropanal, propanal, and 1-propanol, and the reaction order for
hydrogen is close to 1. Our work paves the way toward the evaluation of complex
reaction networks for the study of biomass compounds.
KEYWORDS: Density functional theory, Hydrodeoxygenation, Molybdenum oxide, Selectivity, Propylene

■

produced per 100 tonnes of biodiesel.26 Thus, as a side
product in biodiesel synthesis, glycerol is an abundant
compound,27 and finding new efficient and environmentally
friendly routes to upgrade it is a challenging industrial
target.28−33 Therefore, it was included as one of the top 12
building blocks by the DOE.34,35 The deoxygenation of
glycerol can be a source for propanediols and propanols and
more interestingly propylene, the starting compound for the
production of polypropylene, acrylonitrile, propylene oxide,
oxo alcohols, cumene, isopropyl alcohol, and others.36 The
current propylene production is around 90 million tonnes, and
it is forecasted to grow up to 130 million tonnes worldwide by
2023.37 Nowadays, it is mainly obtained as a byproduct in
naphtha steam cracking,36 but the emergence of shale-gas
feedstocks will likely produce a shortage in the next years in
localized geographical areas, mainly in the U.S.38 Therefore, an
on-purpose technology for propylene production is an
attractive industrial target, and its production from glycerol
remains a promising route.
Glycerol conversion to propylene in a two-step system was
reported. Ir/ZrO2 catalyzed the glycerol hydrogenolysis to 1propanol, which in a second step is dehydrated to propylene by
H-ZSM-5.39 The conversion in one step catalyzed by
molybdenum oxide, Mo/C, and iron molybdate, Fe−Mo/C,
was reported in both gas40,41 and liquid phases.42,43 The
conversion in gas phase can reach 100% with 90% selectivity.

INTRODUCTION
The search of new renewable resources for key chemical
intermediates is a direct consequence of the depletion of oil
resources and the rising environmental concerns. Biomass has
emerged as an alternative renewable feedstock,1 and initiatives
to convert nonedible fractions and waste into chemical
platforms are being explored.2,3 However, biomass is a complex
raw material that includes a wide range of oxygenates as
alcohols, aldehydes, ketones, carboxylic acids, and phenols.4
Due to the high oxygen content, the preferential C−O bond
cleavage over the other bonds C−C and C−H is a must to
develop platform chemicals. In this direction, one of the most
appealing processes to reduce the oxygen content is hydrodeoxygenation (HDO),5−7 which achieves the reduction of the
oxygen content in biomass-derived molecules by its reaction
with H2 at high temperatures, producing water as a side
product. Consequently, HDO is a clean process that allows
obtaining key chemical intermediates from biomass-derived
compounds.
Potential HDO catalysts include noble (Pd, Pt, Ru, Ag, and
Rh)8−14 and non-noble metals (Cu and Ni),15,16 molybdenum
sulfides, and carbides.17−19 More recently, metal oxides have
also been proposed. For instance, molybdenum oxides showed
good selectivity in HDO of alcohols,20−22 linear ketones, and
cyclic ethers to produce olefins, and cyclic ketones and phenols
to form aromatic hydrocarbons.23,24 In these reactions, MoO3
selectively breaks the C−O bonds leading to the formation of
hydrocarbons and olefins while keeping the carbon chain.
Among the biomass derivatives, glycerol plays a major role
since it is a byproduct in the transesterification of vegetal oils
that provides biodiesel.25 Around 10 tonnes of glycerol are
© 2018 American Chemical Society

Received: June 21, 2018
Revised: October 10, 2018
Published: November 1, 2018
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56

energy of 450 eV. The Hubbard U correction was applied to
describe the 4d electrons of molybdenum atoms with Ueff = 3.5 eV.50
Solvent contributions in adsorption energies were introduced through
the VASP-MGCM57,58 code considering water as the solvent.
α-MoO3 is the most common and stable phase of MoO3, which
presents an orthorhombic unit cell with Pbnm symmetry.59 This
structure is formed by bilayers of MoO6-distorted octhaedra packed
through van der Waals contributions along the y-axis. The calculated
lattice parameters with a 11 × 3 × 11 k-point mesh were found to be a
= 3.933, b = 13.822, and c = 3.711 Å, in agreement with experimental
values.59,60 The HDO process was studied on the lowest energy facet
of α-MoO3, the (010) surface, Figure 1, which presents three oxygen

The reaction pathway was studied, and the route through
acetol, propylene glycol, acetone, and 2-propanol was
proposed.41 In the liquid phase, the reported conversion on
Mo/C was 70% with 70% selectivity. The main byproducts
were C3 compounds: 2-propenol, 1-propanol, and propylene
glycol. 2-Propanol, acetol, and 1,2-propanediol were also
detected. A small portion, 2.5%, of C2 and C1 compounds
were also obtained: methanol, ethanol, and ethylene glycol.
The reaction pathway studies suggested propylene is formed
via 2-propenol, with 1- and 2-propanol dehydration as
secondary routes.43 In addition, they found that the catalytic
sites are the reduced surface Mo centers. Thus, the presence of
surface oxygen vacancies is essential to reach high activity and
selectivity to HDO.
The rationalization of HDO processes needs first-principle
studies, but only a small number have been reported. The
mechanism of alcohol dehydration20,21 and HDO of acrolein
to propylene44 were studied on (MoO3)3 cluster models,
which cannot reproduce the bulk electronic and geometrical
structure; thus, the robustness of the computed kinetic and
thermodynamic parameters is unclear. Moreover, two studies
were performed on α-MoO3(010) using periodic slabs: the
HDO of acetaldehyde45 and acetone.46 The vacancy formation
and the HDO mechanism were reported in both studies. They
were performed with pure density functional theory (DFT),
which tends to the overdelocalization of d and f electrons of
reducible transition metal oxides (RTMOs) due to the selfinteraction error (SIE).47,48 This error results in incorrect
estimations of reaction energies and activation barriers for
redox steps in HDO processes and in the impossibility to
characterize correctly the oxygen vacancies.49,50 In addition,
HDO processes are formed by large reaction networks that
require microkinetic models to be understood. These models
are effective to obtain main reaction paths, rate-determining
step (RDS), reaction orders, and more parameters from
intricate reaction networks. However, their main drawback is
that the energy barriers of each elementary step should be
known, which is not possible from experiments. This problem
can be solved by DFT, which most of the time offers a
reasonable agreement with experiments. On the other hand,
complex reaction networks are difficult to understand only
from DFT reaction profiles, and its coupling with microkinetic
models establishes a link between the simulations and the
experimental observables giving a more powerful understanding of the system.
In this work, density functional theory has been employed to
unravel the mechanism for the conversion of glycerol to
propylene on models representing molybdenum oxide. As the
number of intermediates and connectivity of the reaction
network are very high, a microkinetic model was developed
and applied to obtain the most likely reaction path and how
the activity and selectivity of the catalyst proceeds.

■

Figure 1. Side and top views of the reduced α-MoO3(010) surface
used as catalyst. The reduced Mo center, Mocus, is marked with ∗.
Green spheres represent Mo and red stand for O.

types: (i) terminal oxygen, Ot, (ii) the oxygen bridge, Ob, and (iii)
O3c, coordinated to one, two, and three molybdenum atoms,
respectively. O3c can be considered inert. This surface model was
previously used to study oxidation of methanol to formaldehyde61,62
and the HDO of acetaldehyde45 and acetone.46 The fully oxidized
surface can only perform acid−base reactions, but the HDO process
involves redox steps. Therefore, a reduced Mo center is needed for the
reaction to occur.23 Molybdenum oxides accommodate a certain
degree of reduction, and out of the oxygens in the lattice, the terminal
ones Ot are the easiest to remove.45,50,63,64 The created vacancy
positions are the preferential adsorption sites for oxygenated
intermediates.
The α-MoO3(010) surface was represented with a slab model
containing two bilayers in a (3 × 3) supercell with a 3 × 3 × 1 k-point
sampling. The upper bilayer and the adsorbates were allowed to relax.
A vacuum of 15 Å between slabs was introduced, and a dipole
correction along the z-axis was added to avoid the spurious terms
arising from the use of asymmetric arrangement of the slabs.65 The
reaction network was studied in this slab model with one Ot vacancy
simulating the surface reduction, Figure 1; the corresponding
undercoordinated molybdenum center is labeled as Mocus. The
transition states were located with the climbing image version of the
nudge elastic band (CI-NEB)66,67 method and refined with the
improved dimer method (IDM).68,69 All relevant configurations in the
potential energy surface were confirmed through vibrational analysis,
and the reported energies are ZPVE corrected. The relevant structures
are published in the ioChem-BD database70 and can be found in ref
71.
Microkinetic Modeling. A batch reactor model was employed in
the simulations. For each species, we expressed mathematically the
variation of pressure (for gas compounds) or coverage (for
adsorbates) as the sum of the rate of all elementary steps in the
reaction network in which the species is involved. Each intermediate
is considered to occupy only one site and a simple site balance is
employed, θ∗ = 1 − Σθi. This set of equations forms an ordinary
differential equation (ODE) system. The kinetic coefficient for
adsorption/desorption steps is obtained from the Knudsen equation:

THEORETICAL METHODS

DFT. Density functional theory (DFT) performed on slabs models
with the VASP 5.3.3 package51,52 were employed to obtain the
thermodynamic and kinetic parameters for the HDO reaction
network. The generalized gradient approximation (GGA) in the
form of the Perdew−Burke−Ernzerhof (PBE) functional53 was
chosen to describe the exchange correlation energy coupled to the
van der Waals contributions from the Grimme’s semiempiric
correction vdW-D2.54 The core electrons were replaced by the
projector-augmented wave (PAW) pseudopotentials,55 whereas
valence electrons were expanded in plane waves with a kinetic cutoff

rads , A = kads , APAθ
*
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(1)
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kads , A =

Acat

2πmA kBT

Research Article

S0(T )

in experiments to obtain high activity and selectivity.42,43 The
adsorption energies for the two configurations are −0.60 and
−0.69 eV, respectively. Once the −OH groups are created, the
hydrogen atoms can be transferred from a hydroxyl group to a
neighboring surface oxygen and diffuse over the surface with
relatively low energy barriers, ca. ∼0.4−0.8 eV (Table 1).
The formation of water molecules by the recombination of
two neighboring −OH groups has low energy barriers: 0.14
and 0.22 eV from two −OtH and from −OtH + −ObH,
respectively. Thus, H2Ot molecules binding to the Mo center
are formed at the catalyst surface. The energy required for
water molecules to desorb is 1.22 eV, and therefore, they are
released under reaction conditions. The reaction energy for the
total process of vacancy formation is only 0.30 eV, being the
adsorption of hydrogen the most energy-demanding steps
(Scheme S1 and Figure S1).
Hydrodeoxygenation (HDO) Network. The glycerol
HDO process encompasses the competition between sequential and parallel dehydrations, keto−enol equilibria, and
hydrogenations reactions that are grouped in the reaction
network presented in Scheme 1. The general mechanisms for
each process are shown in Scheme 2.

(2)

In these equations PA is the pressure of A in the reaction system; θ∗
represents the fraction of free sites on the surface; Acat is the area of a
free site; mA is the mass of a single molecule A; kB is the Boltzmann’s
constant; T is the temperature of the reaction system; and S0(T) is the
sticking coefficient, which is approximated by the exponential term,
e−Ea,ads / kBT . Equivalent equations were employed for desorption. The
adsorption/desorption energies are those corrected by solvation. In
turn, the rate for each on-surface elementary step follows the
transition state theory (TST):72−74
+
rA*→ B * = kA*→ B *θA *
+
kA*→ B * =

(3)

kBT qTS −Ea+ / kBT
e
h qA *

(4)
TS

In these equations, qA and q are the vibrational contributions to
the partition function of the initial and transition states, respectively,
and Ea is the ZPVE-corrected energy difference between the transition
state and the initial state as obtained by DFT. Finally, initial
conditions correspond to those of the experiments (batch reactor of
450 mL, ca. 1.5 g of catalyst, 90 mL of 2.0 w/w % aqueous glycerol
solution, 8.0 MPa of H2, and 300 °C),42 and the number of initial
vacancies was chosen to mimic the fraction of reduced centers
described for the reduction of the catalyst at 350 °C. XPS at this
temperature shows 2.1% and 29.0% of Mo4+ and Mo5+;43 and
considering that there is only a single oxygen vacancy for every two
Mo5+,50 the number of initial vacancies was set to 15%. The ODE
system was solved numerically with Maple 13.0 software.75

Scheme 1. Reaction Network for the Complete
Hydrodeoxygenation, HDO, of Glycerol to Propylenea

■

RESULTS AND DISCUSION
HDO processes are composed by two combined cycles: (i) the
hydrogen adsorption and vacancy formation through water
formation and release and (ii) adsorption and deoxygenation
of hydrocarbonated compounds on a vacancy position. The
second one heals the vacancy and closes the catalytic cycle.
This catalytic procedure corresponds to a reverse Mars van
Krevelen mechanism. Experimentally, a prereduction of the
catalyst with H2 is carried out to form defects on the
surface.23,41,42 Moreover, it was shown that the presence H2 in
the reaction media during the process is essential to maintain
the catalytic activity.23,42
Vacancy Formation and Hydrogen Diffusion. Hydrogen molecules dissociatively adsorb forming two −OH groups
that can be either two terminal −OtH groups, with an energy
barrier for the adsorption of 1.63 eV, or one −OtH and one
−ObH group, with an energy barrier of 1.46 eV (Table 1).
These high energy barriers are due to the fact that adsorption
takes place through a homolytic H−H bond breaking without
previous activation by the surface. This explains the strong
dependence between the H2 pressure and the catalytic
performance, which results in the large H2 pressure required

a

The first step in HDO is glycerol dehydration to form the
corresponding alkenol. The mechanism proposed previously
for the dehydration of alcohols on molybdenum oxides,21
Scheme 2a, was followed. Glycerol adsorbs on a vacancy
through one of its oxygens forming a Mo−O bond. After that,
the hydroxyl proton is transferred to a terminal oxygen forming
an −OtH group. Then, in a concerted step, a β-hydrogen is
stripped away by Ob, and concomitantly, the C−O bond
breaks (Figure S2a). The imaginary frequency of the transition
state corresponds mainly to the C−H bond breaking, being the
concomitant C−O bond breaking barrierless and unavoidable.
This concerted step involves the formation of the CC
double bond of the alkenol and the MoOt bond on the
surface.

Table 1. Adsorption Energies, Eads in eV, and Energy
Barriers, Ea in eV, of H2 Adsorption and Diffusion, Using as
Reference a Clean Surface and Gas-Phase H2 Molecule
Adsorption

Diffusion

Site

Eads

Path

Ea

OtH + OtH
OtH + ObH
H2Ot
VOt

−0.60
−0.69
−0.92
0.30

OtH(a) → OtH(b)
ObH → OtH
2OtH → H2Ot
ObH+OtH → H2Ot

Double arrows indicate keto-enolic equilibria.

0.40
0.77
0.14
0.22
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Scheme 2. Reaction Mechanism of Reactions in the Reaction Network: (a) Dehydration, (b) Keto-Enol Equilibrium, (c)
Hydrogenation, and (d) 2-Propenol Conversion to Propylenea

a

Detailed schemes of each reaction of the HDO network are shown in Schemes S2−S5.

As glycerol has two different −OH types, adsorption by the
terminal −OH triggers the formation of 1,2-enol, whereas the
secondary hydroxyl would drive the formation of 1,3-enol. The
enolates formed are in equilibrium with their keto tautomers,
acetol and hydroxypropanal (HP), respectively. These
equilibria, in aqueous phase, are thermodynamic displaced to
the keto form by −0.65 eV to acetol and −0.29 eV to HP. The
mechanism of the keto−enol interconversion is shown in
Scheme 2b. The first elementary step in the tautomeric
isomerization is the enolate adsorption on a vacancy position.
They adsorb through their enolic −OH group that interacts
with the Mocus center. Then, the −OH group dissociates
transferring a hydrogen atom to an Ot. Finally, the hydrogen of
the −OtH group is transferred either to the methylene group
(H2C) of 1,2-enol to form acetol (Figure S2b) or to the
methine group (CH−) of 1,3-enol to form HP. Thereafter,
the ketones can either desorb or remain bonded to the vacancy
to react further.
In the next step, acetol and HP are hydrogenated to form
propylene glycol (PG) and 1,3-propanediol, respectively. The
general mechanismof hydrogenations is shown in Scheme 2c.
Acetol and HP adsorb on the Mocus site through the ketone
group, and a hydrogen atom is transferred from a neighboring
−OtH group to the carbon atom of the ketone group to form a
deprotonated diol. These diols could be protonated by other
surface hydroxyls and desorb or experiment with further
dehydration (Figure SI2c). In parallel, HP could suffer a new
dehydration to form acrolein repeating the steps described
previously. This is not possible for acetol because its −OH
group does not have any β-hydrogens left to be stripped off.
Interaction of PG and 1,3-propanediol with Mocus can result
in further dehydrations. PG adsorption through its primary
hydroxyl group leads the dehydration to propen-2-ol, whereas

through the secondary hydroxyl results in the dehydration to
either 1-propenol, when the β-hydrogen of C1 is transferred to
the surface, or 2-propenol, when β-hydrogen of C3 is stripped
off. 1,3-Propanediol dehydration only can result in 2-propenol.
Acrolein is hydrogenated either at the ketonic carbon to form
2-propenol, like 1,3-propanediol, or at the methylene carbon to
form 1-propenol. Propen-2-ol and 1-propenol are enolates, and
therefore, they are in equilibrium with the corresponding keto
tautomer, propanone and propanal, respectively, which are
more stable than the corresponding enol formed by −0.60 and
−0.35 eV, respectively.
In turn, propanone and propanal adsorbed at Mocus are
hydrogenated to 2-propanol and 1-propanol, respectively.
These two compounds are dehydrated on the vacancy position
to form the final product: propylene. 2-Propenol adsorption on
undercoordinated Mo also leads to propylene. Formally, this
reaction encompasses the hydrogenation of the alkene and the
dehydration of the alcohol group, but it follows a direct
mechanism (Scheme 2d), and therefore, it cannot be included
in any of the previous reaction families. The molecule adsorbs
through the −OH group, which is dissociated by an −Ot
forming a surface hydroxyl. Then, hydrogen is transferred back
from the surface hydroxyl to the methylene group (H2C) of
the adsorbed 2-propenol at the same time that C−O bond
breaks, resulting in propylene physisorbed on the surface. A
similar mechanism to the formation of propylene from 2propenol on a Mo3O9 cluster has been proposed previously.11,43,44
Reaction and activation energies for each elemental reaction
step in glycerol HDO are shown in Figure 2. More detailed
values are in Table SI1. An analysis of the data shows that
alcohol deprotonations are always endothermic steps with
energy barriers lower than 0.75 eV. The C−O bond breaking
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medium surface reductions. Then, glycerol and PG can adsorb
directly to two undercoordinated (Mocus)2 centers through two
OH groups. Once the molecules are adsorbed, they are
dissociated easily forming two −OHt groups and two Mo−O
covalent bonds with the surface. In this step, each Mocus is oneelectron oxidized. The adsorption energy for the dissociated
molecules are −2.37 and −2.43 eV for glycerol and PG,
respectively. The dissociated glycerol double bonded to
(Mocus)2 can undergo the C−C bond breaking that results in
the formation of a ketone group in each fragment and the oneelectron reduction of the Mocus centers leading the formation
of glycoaldehyde (GA) and formaldehyde. The energy barrier
for this step is 1.66 eV. The same elementary step can occur for
PG with an activation energy of 1.65 eV, resulting in the
formation of formaldehyde (FA) again and acetaldehyde (AA).
These compounds are further hydrogenated to methanol, EG,
and ethylene.
The high energy barrier calculated for the C−C bond
cleavage and the necessity of two neighboring vacancies
explain the selectivity to three-carbon products observed
experimentally. In the reaction network, there are no more
compounds with −OH groups in adjacent carbons, and
therefore, these are the only possible one and two carbonformed products.
Microkinetic Model. The complexity of the reaction
network makes it difficult to obtain a complete understanding
and a direct mapping to the experimental activity of the HDO
process of the glycerol conversion to propylene. Therefore, a
microkinetic model76−78 was developed in order to know the
product evolution during the glycerol HDO. The microkinetic
model simulates the experimental conditions reported by
Zacharapoulou et al.: a batch reactor of 450 mL, ca. 1.5 g of
catalyst that corresponds to ∼0.2 g of MoO3 and ∼1.3 g of
activated carbon (in the experimental catalyst synthesis, 1.5 g
of MoO3 is supported on 10 g of activated carbon),41 90 mL of
2.0 w/w % aqueous glycerol solution (1.8 g of glycerol), 8.0
MPa of H2, and 300 °C.42,43 The C−C bond breaking was
excluded from the microkinetic model due to the low amount
of C2 and C1 compounds formed in their experiments
(<2.5%). Moreover, propylene was not allowed to readsorb on
the surface since they found that this compound leaves the
liquid phase after reaction.
The selectivity evolution of the products and coverage of the
different adsorbates for glycerol HDO as a function of time is
shown in Figure 3. At the beginning of the reaction, acetol and
HP are quickly formed. The adsorption energy of glycerol
through the secondary −OH is larger than through the primary
−OH, and therefore, glycerol will be preferentially dehydrated
to 1,3-enol. The fast keto−enol equilibria between 1,3-enol
and HP leads a larger selectivity of HP, which decreases
quickly until the second hour. The high energy barrier for the
first step of HP hydrogenation to 1,3-propanediol and the low
amount of available −OtH results in the dehydration of HP to
acrolein, as can be retrieved for the coverage of adsorbed
acrolein in this period. However, due to the large adsorption
energy of acrolein, and to its easy hydrogenation to 1-propanol,
acrolein reacts on the surface, and no selectivity to its production is obtained. In the first two hours, propanal selectivity is
increasing, reaching almost 50% selectivity. The fast decrease
in HP selectivity in this period, from ∼75% to ∼27%, indicates
that propanal is formed by HP dehydration to acrolein and
later hydrogenation to 1-propenol, which is in a very favorable
keto−enol equilibria with propanal. The coverage of acrolein

Figure 2. Reaction energy, ΔE (striped bars), and activation energy,
Ea (plain bars), for all direct elementary steps of the reaction network.
Wine color corresponding to dehydrations, orange to keto−enol
equilibrium, yellow to hydrogenations, and turquois to the 2propenol−propylene reaction. All energies are in eV. The specific
reactions are listed in Table S2.

steps in dehydrations are slightly endothermic with high energy
barriers, between 1.00 and 1.50 eV, being favored for the
removal of primary −OH groups over the secondary ones. In
these steps, the energy barrier is generated by the C−H bond
breaking, with the concomitant C−O bond cleavage
barrierless. The formation of C−H bonds in keto−enol
equilibria are highly exothermic steps with a very low energy
barrier; the tautomerism has lower energy barriers when the
enol group is in a primary carbon. Finally, the hydrogenations
of ketones are slightly endothermic steps with similar energy
barriers as C−O bond breaking, which are independent of the
position of the ketone group. The reported experimental
temperature is 300 °C,23 high enough to ensure that the
barriers can be overcome.
C−C Bond Cleavage. The fact that C−O bond breaking
prevails does not completely overrule C−C bond cleavage.
Indeed, some methanol, ethanol, and ethylene glycol (EG)
were detected as minor reaction products, about 2.5% in total,
for the reaction catalyzed on iron molybdate and molybdenum
oxide catalyst.42,43 Ethylene glycol and ethanol could be
produced from C−C bond cleavage in glycerol and propylene
glycol, respectively, which also gives methanol in both cases by
the pathway showed in Scheme 3.
In the reactions proposed in Scheme 3, glycerol and PG have
to be bonded to two neighboring Mocus through the two
hydroxyl groups of the broken C−C bond. The two reduced
Mo act as electron buffers allowing the bond breaking. The
formation of a neighboring vacancy along the z-axis has no
extra formation energy,50 and therefore, they appear at
Scheme 3. Proposed C−C Bond Cleavage Reactions and
Concomitant Formation of Methanol, Ethanol, and
Ethylene Glycola

a

GA: glycoaldehyde; FA: formaldehyde; PG: propylene glycol; AA:
acetaldehyde.
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propanediol, 1-propanol. and 2-propenol, respectively, whereas
PG was not detected. However, the coverage of adsorbed PG
increases during this period, but its fast conversion to propen2-ol prevents selectivity to this product. The propylene
selectivity is almost constant after 8 h and reaches 75% after
10 h.
A more detailed understanding of the reaction routes can be
obtained starting the reaction with some of the intermediate
products as initial reactant. The conversion and selectivity after
3 h of simulated reaction are shown in Figure 4. After 3 h,

Figure 3. (a) Product selectivity evolution as a function of time, t in
hours, under the reaction conditions (batch reactor of 450 mL, 0.2 g
of MoO3, 1.8 g of glycerol, 8.0 MPa of H2, and 300 °C). (b) Zoomed
area of the marked zone in (a). (c) Evolution of the coverage of
adsorbed species, θx, as a function of the time. (d) Zoomed area for
coverage between 0% and 1% in (c). Intermediate products with
negligible selectivity or coverage are not represented.

decreases slowly in this period, whereas the coverage of
propanal increases rapidly. This is due to the fact that the
formation of propanal is faster than the formation of acrolein,
as the latter is an endothermic process that has higher energy
barriers. Acrolein also can be hydrogenated to 2-propenol,
which has low energy barriers to its conversion to propylene,
which is slowly formed reaching 7% of selectivity in this period.
During these two hours, the selectivity of acetol remains almost
constant, around 16%, due to the high energy barriers to its
hydrogenation to PG and the low availability of −OtH groups.
The coverage of acetol increases slightly during this period
indicating that acetol slowly adsorbs to react. After this point,
propanal selectivity starts to decrease, whereas propylene
selectivity increases quickly, which points out that propylene is
formed from propanal through its hydrogenation to 1-propanol
and later dehydration to propylene. The selectivity to 1propanol rises to 3% after 3.5 h. This small selectivity to 1propanol is due to the energy barriers because its dehydration
to propylene is faster than propanal hydrogenation. The
increase in coverage of −OtH at this point supports the
hydrogenation of propanal. After 2 h, acetol also starts to
hydrogenate to PG, and its selectivity slowly decreases. PG can
be dehydrated to propen-2-ol, 1-propenol, or 2-propenol. The
lowest energy barriers found for the formation of propen-2-ol,
imply that it is rapidly isomerized to propanone. Thus, after
this time, an increase in the coverage and selectivity of
propanone is observed. After 6 h, the propylene selectivity
reaches 66%, and the main byproducts are HP and acetol,
10.4% and 8.6% of selectivity, respectively. Propanal (5.9%),
propanone (4.7%), and 1-propanol (2.2%) are also formed. If
the reaction time is extended, the coverage of −OtH increases,
constantly favoring acetol, HP, propanal, and propanone
hydrogenation to their respective products: PG, 1,3-propanediol, 1-propanol, and 2-propanol. After 10 h, low selectivity to
these products appeared: 3.4%, 2.2%, and 1.2% of 1,3-

Figure 4. Conversion and selectivity at 3 h of simulated reaction on
the microkinetic model of intermediate products as initial reactant
under the experimental reaction conditions (batch reactor of 450 mL,
0.2 g of MoO3, 1.8 g of initial intermediate, 8.0 MPa of H2, and 300
°C).

glycerol has 100% conversion. The main product is propanal
(∼34%) followed by HP (∼22%), propylene (∼22%), and
acetol (∼15%). Most of the glycerol reacts to form HP that is
dehydrated and latter hydrogenated to form propanal. Some
propanal and possibly some acetol are reduced to propylene.
The use of 2-propenol as a reactant results in a complete
conversion, mainly toward propylene (∼67%). Propanal and 1propanol, which are formed through acrolein, are also
observed.
At the beginning of glycerol HDO, acetol and HP are
formed with high selectivity. Using them as reactants, the
larger conversion of HP (78% vs 39%) indicates that it reacts
faster than acetol. Propanal is the main product obtained from
HP, with 77% selectivity. The other observed compounds were
1-propanol and propylene, which came from further reactions
of propanal. On the other hand, acetol is mainly converted in
propanone.
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identify the reaction orders, simulations with different initial
pressures of hydrogen were performed. The reaction rate was
measured at two different times, 100 and 2500 s, and the
reaction order was obtained, 0.86 and 1.11, respectively
(Figure 5b). This result highlights the importance of H2 in
reaction media.
When compared to the experiments, there are some
differences between our results and the previous from
Zacharapoulou et al.42,43 The first difference is the conversion
and reaction rate of glycerol; in our model, we obtained a faster
conversion of glycerol due to nonconsideration of lateral
effects and to perform the simulations in the gas phase.
Although the final product distribution is in reasonable
agreement, we want to highlight that in the experimental
study PG and 2-propenol were detected as two of the main
reaction intermediates. They are present in our reaction
network, but they react rapidly and were not observed.
Moreover, at the beginning of the reaction, we found higher
amounts of acetol and HP, probably due to the faster
conversion of glycerol observed in our model when compared
to the experimental set up. Finally, the experiments suggests a
reaction path through 2-propenol, whereas in our model the
main path is through 1-propenol. Also, they discarded the
route through acrolein because it was not detected in the
experiments; however, we show that acrolein reacts quickly to
form 1-propenol (and 2-propenol), which would explain the
experimental results. The catalytic performance depends
strongly on several factors as the reaction conditions or
catalysts synthesis procedure. Thus, different results were
reported by this reaction catalyzed by Fe−Mo/C.41,42 Different
glycerol conversion, product distribution, and main reaction
path were found. Moreover, the approximations that demand
the state-of-the-art coupled DFT and microkinetic modeling
(lateral effects, solvent models, etc.) and difficulty to take into
account all the reaction parameters (structure sensitivity of the
catalyst, solvent interactions) are also a source for these
differences.

Both diols, PG and 1,3-propanediol, as reactants show a low
conversion (∼40%). Most PG goes back in the reaction
network toward acetol, with 56% selectivity, and the rest of PG
continues on the path to propylene, and small amounts of
intermediates are formed. The reaction profile of 1,3propanediol shows that it also goes back toward HP
(∼61%); moreover, some of the formed HP continues reacting
toward the formation of 1-propanol and propylene. Interestingly, no 2-propenol is formed from 1,3-propanediol.
Acrolein as the reactant reaches 93% conversion. Almost all
is converted to propanal (91% of selectivity). The 9% of
propylene suggests that some propanal further reacted to form
propylene. The conversion of propanal as the reactant is
∼63%, with 91% selectivity to propylene. The other observed
compound is the intermediate 1-propanol.
The two propanols show a completely different reaction
profile; 1-propanol is completely converted to propylene
(100% of conversion and selectivity), whereas 2-propanol has
only a 16% of conversion and only forms propanone.
With the insights obtained from the information in Figures 3
and 4, we can conclude that the glycerol conversion to
propylene is produced through the following path: Glycerol →
HP → Acrolein → Propanal → 1-Propanol → Propylene.
There are three factors that lead the glycerol HDO for this
reaction path: (i) The preference of glycerol adsorption is
through the secondary carbon and conversion to 1,3-enol. (ii)
The energy barriers for HP dehydration to acrolein are lower
than for its hydrogenation to 1,3-propanediol. This is
supported by the low availability of −OtH groups. (iii) The
first step in the formation of 1-propenol from acrolein is an
exothermic process, whereas the formation of 2-propenol is
endothermic, which favors the formation of the former.
Going back to the full reaction model, simulations at
different temperatures were performed, and apparent activation
energies of 1.38 and 2.03 eV were obtained at 100 and 2500 s
(Figure 5a). The apparent activation energy increases with
reaction time since in a batch reactor the consumption of
reactants decreases the reaction rate. Finally, in order to

■

CONCLUSIONS
The glycerol conversion to formaldehyde catalyzed by α-MoO3
was studied by means of density functional theory, DFT. The
conversion is produced through a hydrodeoxygenation, HDO,
process that takes place on surface vacancy defects. The
highest energy barrier in the vacancy formation cycle is the
hydrogen dissociative adsorption. This explains why high H2
pressure is needed in experiments. The adsorbed hydrogen
atoms can move over the surface with low energy barriers to
form water molecules that are released. Vacancies play a central
role in the HDO process. Oxygenated compounds adsorb on
the surface through Mo−O bonds with an undercoordinated
Mo center; after that, a selective C−O bond cleavage produces
the deoxygenated compound, while the oxygen atom remains
bonded to the Mo center healing the vacancy. The complete
HDO cycle is composed of three different sets of reactions: (i)
dehydrations, (ii) keto−enol equilibria, and (iii) hydrogenations. The combination of these three reactions on
vacancy positions results in a reaction network with 14
intermediates connected by 20 reactions where all the side
products experimentally reported are present. The high
reaction barrier for the C−C bond cleavage and the necessity
of two neighboring empty vacancies explain the selectivity to
C−O bond cleavage. The reaction mechanism unraveled in
this work can be applied to the HDO of any polyalcohol. A

Figure 5. (a) Reaction order of hydrogen, nH2, derived from the
microkinetic model at standard reaction conditionsand (b) Apparent
activation energy, Eapp in eV. Rates, r, and PH2 are normalized to the
value of the simulation at experimental conditions.
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(7) Wang, H.; Male, J.; Wang, Y. Recent Advances in Hydrotreating
of Pyrolysis Bio-Oil and Its Oxygen-Containing Model Compounds.
ACS Catal. 2013, 3 (5), 1047−1070.
(8) Runnebaum, R. C.; Nimmanwudipong, T.; Block, D. E.; Gates,
B. C. Catalytic Conversion of Compounds Representative of Ligninderived Bio-Oils: a Reaction Network for Guaiacol, Anisole, 4methylanisole, and Cyclohexanone Conversion Catalysed by Pt/aAl2O3. Catal. Sci. Technol. 2012, 2 (1), 113−118.
(9) Sitthisa, S.; Resasco, D. Hydrodeoxygenation of Furfural Over
Supported Metal Catalysts: A Comparative Study of Cu, Pd and Ni.
Catal. Lett. 2011, 141 (6), 784−791.
(10) Gonzalez, C.; Marin, P.; Diez, F. V.; Ordonez, S. Hydrodeoxygenation of Acetophenone over Supported Precious Metal
Catalysts at Mild Conditions: Process Optimization and Reaction
Kinetics. Energy Fuels 2015, 29, 8208−8215.
(11) Ramos, R.; Tisler, Z.; Kikhtyanin, O.; Kubicka, D. Towards
Understanding the Hydrodeoxygenation Pathways of FurfuralAcetone Aldol Condensation Products over Supported Pt Catalysts.
Catal. Sci. Technol. 2016, 6, 1829−1841.
(12) Zhou, L.; Lawal, A. Hydrodeoxygenation of Microalgae Oil to
Green Diesel over Pt, Rh and Presulfided NiMo Catalysts. Catal. Sci.
Technol. 2016, 6, 1442−1454.
(13) Nelson, R. C.; Baek, B.; Ruiz, P.; Goundie, B.; Brooks, A.;
Wheeler, M. C.; Frederick, B. G.; Grabow, L. C.; Austin, R. N.
Experimental and Theoretical Insights into the Hydrogen-Efficient
Direct Hydrodeoxygenation Mechanism of Phenol over Ru/TiO2.
ACS Catal. 2015, 5, 6509−6523.
(14) Lari, G. M.; García-Muelas, R.; Mondelli, C.; López, N.; PérezRamírez, J. Glycerol Oxidehydration to Pyruvaldehyde over Silverbased Catalysts for Improved Lactic Acid Production. Green Chem.
2016, 18 (17), 4682−4692.
(15) Witsuthammakul, A.; Sooknoi, T. Selective Hydrodeoxygenation of Bio-Oil Derived Products: Ketones to Olefins. Catal. Sci.
Technol. 2015, 5, 3639−3648.
(16) Khromova, S. A.; Smirnov, A. A.; Bulavchenko, O. A.; Saraev,
A. A.; Kaichev, V. V.; Reshetnikov, S. I.; Yakovlev, V. A. Anisole
Hydrodeoxygenation over Ni-Cu Bimetallic Catalysts: The Effect of
Ni/Cu Ratio on Selectivity. Appl. Catal., A 2014, 470, 261−270.
(17) Popov, A.; Kondratieva, R.; Mariey, L.; Goupil, J. M.; El Fallah,
J.; Gilson, J. P.; Travert, A.; Mauge, F. Bio-oil Hydrodeoxygenation
and Adsorption of Phenolic Compounds on Sulfided (Co)Mo
Catalysts. J. Catal. 2013, 297, 176−186.
(18) Wang, W.; Li, L.; Wu, K.; Zhu, G.; Tan, S.; Li, W.; Yang, Y.
Hydrothermal Synthesis of Bimodal Mesoporous MoS2 Nanosheets
and their Hydrodeoxygenation Properties. RSC Adv. 2015, 5, 61799−
61807.
(19) Chen, C.-J.; Lee, W.-S.; Bhan, A. Mo2C Catalyzed Vapor Phase
Hydrodeoxygenation of Lignin-Derived Phenolic Compound Mixtures to Aromatics under Ambient Pressure. Appl. Catal., A 2016, 510,
42−48.
(20) Li, Z.; Fang, Z.; Kelley, M. S.; Kay, B. D.; Rousseau, R.;
Dohnalek, Z.; Dixon, D. A. Ethanol Conversion on Cyclic (MO3)3 (M
= Mo, W) Clusters. J. Phys. Chem. C 2014, 118 (9), 4869−4877.
(21) Rousseau, R.; Dixon, D. A.; Kay, B. D.; Dohnalek, Z.
Dehydration, Dehydrogenation, and Condensation of Alcohols on
Supported Oxide Catalysts Based on Cyclic (WO3)3 and (MoO3)3
clusters. Chem. Soc. Rev. 2014, 43 (22), 7664−7680.
(22) Matsuda, T.; Hirata, Y.; Suga, S.; Sakagami, H.; Takahashi, N.
Effect of H2 Reduction on the Catalytic Properties of Molybdenum
Oxides for the Conversions of Heptane and 2-propanol. Appl. Catal.,
A 2000, 193 (1−2), 185−193.
(23) Prasomsri, T.; Nimmanwudipong, T.; Roman-Leshkov, Y.
Effective Hydrodeoxygenation of Biomass-derived Oxygenates into
Unsaturated Hydrocarbons by MoO3 Using Low H2 Pressures. Energy
Environ. Sci. 2013, 6 (6), 1732−1738.
(24) Prasomsri, T.; Shetty, M.; Murugappan, K.; Roman-Leshkov, Y.
Insights into The Catalytic Activity and Surface Modification of
MoO3 during the Hydrodeoxygenation of Lignin-derived Model

microkinetic analysis of the reaction network was performed,
and it was shown that glycerol conversion to propylene is
mainly produced via the formation of HP, acrolein, propanal,
and 1-propanol. A reaction order of 1 was calculated for H2,
with apparent activation energies of 1.38 and 2.03 eV at initial
and medium times, respectively. The results shown in this
study pave the way to a better understanding of the HDO
process giving insights to development of a more active and
selective catalyst.

■

ASSOCIATED CONTENT

S
* Supporting Information

The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acssuschemeng.8b02933.
ioChem-BD instructions, vacancy formation scheme and
energy profile, reactions energy data, schemes, and
optimized structures of reactions. (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: nlopez@iciq.es.
ORCID

Marcos Rellán-Piñeiro: 0000-0002-7905-9077
Núria López: 0000-0001-9150-5941
Funding

Marcos Rellán-Piñeiro and Núria López received funding from
́
Spanish Ministerio de Economia y Competitividad (MINECO): CTQ 2015−68770-R and Severo Ochoa Excellence
Accreditation 2014−2018 SEV-2013−0319 Marcos Relláń
Piñeiro received funding from Spanish Ministerio de Economia
y Competitividad (MINECO): Severo Ochoa predoctoral
grant SVP-2014−068237.
Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS
́
The authors acknowledge the Spanish Ministerio de Economia
y Competitividad (MINECO) for financial support (CTQ
2015-68770-R, Severo Ochoa Excellence Accreditation 2014−
2018 SEV-2013-0319 and Severo Ochoa predoctoral grant
SVP-2014-068237). We thank BSC-RES for providing
computational resources. In addition, we thank Dr. Rodrigo
Garc-Muelas for valuable suggestions.

■

REFERENCES

(1) Huber, G. W.; Corma, A. Synergies between Bio- and Oil
Refineries for the Production of Fuels from Biomass. Angew. Chem.,
Int. Ed. 2007, 46 (38), 7184−7201.
(2) Dapsens, P. Y.; Mondelli, C.; Pérez-Ramírez, J. Biobased
Chemicals from Conception toward Industrial Reality: Lessons
Learned and To Be Learned. ACS Catal. 2012, 2 (7), 1487−1499.
(3) Ruppert, A. M.; Weinberg, K.; Palkovits, R. Hydrogenolysis Goes
Bio: From Carbohydrates and Sugar Alcohols to Platform Chemicals.
Angew. Chem., Int. Ed. 2012, 51 (11), 2564−2601.
(4) Bridgwater, A. V. Review of Fast Pyrolysis of Biomass and
Product Upgrading. Biomass Bioenergy 2012, 38, 68−94.
(5) Furimsky, E. Catalytic Hydrodeoxygenation. Appl. Catal., A
2000, 199 (2), 147−190.
(6) Saidi, M.; Samimi, F.; Karimipourfard, D.; Nimmanwudipong,
T.; Gates, B. C.; Rahimpour, M. R. Upgrading of Lignin-derived BioOils by Catalytic Hydrodeoxygenation. Energy Environ. Sci. 2014, 7
(1), 103−129.
16176

DOI: 10.1021/acssuschemeng.8b02933
ACS Sustainable Chem. Eng. 2018, 6, 16169−16178

ACS Sustainable Chemistry & Engineering

Research Article

to Propene over Molybdena-Based Catalysts. ChemSusChem 2018, 11,
264−275.
(44) Moberg, D. R.; Thibodeau, T. J.; Amar, F. G.; Frederick, B. G.
Mechanism of Hydrodeoxygenation of Acrolein on a Cluster Model
of MoO3. J. Phys. Chem. C 2010, 114 (32), 13782−13795.
(45) Mei, D.; Karim, A. M.; Wang, Y. Density Functional Theory
Study of Acetaldehyde Hydrodeoxygenation on MoO3. J. Phys. Chem.
C 2011, 115 (16), 8155−8164.
(46) Shetty, M.; Buesser, B.; Roman-Leshkov, Y.; Green, W. H.
Computational Investigation on Hydrodeoxygenation (HDO) of
Acetone to Propylene on α-MoO3(010) Surface. J. Phys. Chem. C
2017, 121 (33), 17848−17855.
(47) Lutfalla, S.; Shapovalov, V.; Bell, A. T. Calibration of the DFT/
GGA+U Method for Determination of Reduction Energies for
Transition and Rare Earth Metal Oxides of Ti, V, Mo, and Ce. J.
Chem. Theory Comput. 2011, 7 (7), 2218−2223.
(48) Getsoian, A. B.; Bell, A. T. The Influence of Functionals on
Density Functional Theory Calculations of the Properties of
Reducible Transition Metal Oxide Catalysts. J. Phys. Chem. C 2013,
117 (48), 25562−25578.
(49) Capdevila-Cortada, M.; Łodziana, Z.; López, N. Performance of
DFT+U Approaches in the Study of Catalytic Materials. ACS Catal.
2016, 6 (12), 8370−8379.
(50) Rellán-Piñeiro, M.; López, N. One Oxygen Vacancy, Two
Charge States: Characterization of Reduced α-MoO3(010) through
Theoretical Methods. J. Phys. Chem. Lett. 2018, 9, 2568−2573.
(51) Kresse, G.; Furthmueller, J. Efficient Iterative Schemes for ab
initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys.
Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169−11186.
(52) Kresse, G.; Furthmuller, J. Efficiency of ab-initio Total Energy
Calculations for Metals and Semiconductors Using a Plane-Wave
Basis Set. Comput. Mater. Sci. 1996, 6, 15−50.
(53) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient
Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868.
(54) Grimme, S. Semiempirical GGA-type Density Functional
Constructed with a Long-range Dispersion Correction. J. Comput.
Chem. 2006, 27, 1787−1799.
(55) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the
Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter
Mater. Phys. 1999, 59, 1758−1775.
(56) Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.;
Sutton, A. P. Electron-energy-loss Spectra and the Structural Stability
of Nickel Oxide: An LSDA+U Study. Phys. Rev. B: Condens. Matter
Mater. Phys. 1998, 57 (3), 1505−1509.
(57) Garcia-Ratés, M.; López, N. Multigrid-Based Methodology for
Implicit Solvation Models in Periodic DFT. J. Chem. Theory Comput.
2016, 12 (3), 1331−1341.
(58) Garcia-Ratés, M.; García-Muelas, R.; López, N. Solvation
Effects on Methanol Decomposition on Pd(111), Pt(111), and
Ru(0001). J. Phys. Chem. C 2017, 121 (25), 13803−13809.
(59) Scanlon, D. O.; Watson, G. W.; Payne, D. J.; Atkinson, G. R.;
Egdell, R. G.; Law, D. S. L. Theoretical and Experimental Study of the
Electronic Structures of MoO3 and MoO2. J. Phys. Chem. C 2010, 114
(10), 4636−4645.
(60) Magnéli, A.; Andersson, G.; Blomberg, B.; Kihlborg, L.
Identification of Molybdenum and Tungsten Oxides by X-Ray
Powder Patterns. Anal. Chem. 1952, 24 (12), 1998−2000.
(61) Rellán-Piñeiro, M.; López, N. The Active Molybdenum Oxide
Phase in the Methanol Oxidation to Formaldehyde (Formox
Process): A DFT Study. ChemSusChem 2015, 8 (13), 2231−2239.
(62) Choksi, T.; Greeley, J. Partial Oxidation of Methanol on MoO3
(010): A DFT and Microkinetic Study. ACS Catal. 2016, 6 (11),
7260−7277.
(63) Coquet, R.; Willock, D. J. The (010) Surface of a-MoO3, a DFT
+ U Study. Phys. Chem. Chem. Phys. 2005, 7 (22), 3819−3828.
(64) Lei, Y. H.; Chen, Z. X. DFT+U Study of Properties of MoO3
and Hydrogen Adsorption on MoO3(010). J. Phys. Chem. C 2012, 116
(49), 25757−25764.

Compounds into Aromatic Hydrocarbons under Low Hydrogen
Pressures. Energy Environ. Sci. 2014, 7 (8), 2660−2669.
(25) Lari, G. M.; Pastore, G.; Haus, M.; Ding, Y.;
Papadokonstantakis, S.; Mondelli, C.; Pérez-Ramírez, J. Environmental and Economical Perspectives of a Glycerol Biorefinery. Energy
Environ. Sci. 2018, 11 (5), 1012−1029.
(26) Yang, F.; Hanna, M. A.; Sun, R. Value-Added Uses for Crude
Glycerol - a Byproduct of Biodiesel Production. Biotechnol. Biofuels
2012, 5, 13−13.
(27) Quispe, C. A. G.; Coronado, C. J. R.; Carvalho, J. A., Jr.
Glycerol: Production, Consumption, Prices, Characterization and
New Trends in Combustion. Renewable Sustainable Energy Rev. 2013,
27, 475−493.
(28) Lari, G. M.; Chen, Z.; Mondelli, C.; Pérez-Ramírez, J.
Bifunctional Hierarchical Zeolite-Supported Silver Catalysts for the
Conversion of Glycerol to Allyl Alcohol. ChemCatChem 2017, 9 (12),
2195−2202.
(29) Lari, G. M.; Pastore, G.; Mondelli, C.; Pérez-Ramírez, J.
Towards Sustainable Manufacture of Epichlorohydrin from Glycerol
Using Hydrotalcite-Derived Basic Oxides. Green Chem. 2018, 20 (1),
148−159.
(30) Lari, G. M.; de Moura, A. B.; Weimann, L.; Mitchell, S.;
Mondelli, C.; Pérez-Ramírez, J. Design of a Technical Mg−Al mixed
Oxide Catalyst for the Continuous Manufacture of Glycerol
Carbonate. J. Mater. Chem. A 2017, 5 (31), 16200−16211.
(31) Lari, G. M.; Mondelli, C.; Pérez-Ramírez, J. Gas-Phase
Oxidation of Glycerol to Dihydroxyacetone over Tailored Iron
Zeolites. ACS Catal. 2015, 5 (3), 1453−1461.
(32) Morales, M.; Dapsens, P. Y.; Giovinazzo, I.; Witte, J.; Mondelli,
C.; Papadokonstantakis, S.; Hungerbü
hler, K.; Pérez-Ramírez, J.
Environmental and Economic Assessment of Lactic Acid Production
from Glycerol Using Cascade Bio-and Chemocatalysis. Energy
Environ. Sci. 2015, 8 (2), 558−567.
(33) Lari, G. M.; Mondelli, C.; Papadokonstantakis, S.; Morales, M.;
Hungerbü K.; Pérez-Ramírez, J. Environmental and Economic
hler,
Assessment of Glycerol Oxidation to Dihydroxyacetone over
Technical Iron Zeolite Catalysts. Reaction Chemistry & Engineering
2016, 1 (1), 106−118.
(34) Werpy, T.; Petersen, G. Top Value Added Chemicals from
Biomass; National Renewable Energy Laboratory, U.S. Department of
Energy, 2004.
(35) Thurmond, W. Biodiesel 2020: Global Market Survey, Feedstock
Trends and Forecasts; Emerging Markets Online, 2008. https://
docplayer.net/43198174-Biodiesel-2020-global-market-surveyfeedstock-trends-and-forecasts.html (accessed November 2018).
(36) Calamur, N.; Carrera, M. Propylene. In Kirk-Othmer
Encyclopedia of Chemical Technology; John Wiley & Sons, Inc., 2000.
(37) Carr, C. North American Propylene Supply Study; IHS Chemical,
2013.
(38) Peplow, M. How Fracking is Upending the Chemical Industry.
Nature 2017, 550 (7674), 26.
(39) Yu, L.; Yuan, J.; Zhang, Q.; Liu, Y.-M.; He, H.-Y.; Fan, K.-N.;
Cao, Y. Propylene from Renewable Resources: Catalytic Conversion
of Glycerol into Propylene. ChemSusChem 2014, 7 (3), 743−747.
(40) Sousa Fadigas, J. C.; Gambetta, R.; Araujo Mota, C. J.;
Conceicao Goncalves, V. L. D. Preparation of Heterogeneous
Catalysts Used in Selective Hydrogenation of Glycerin to Propylene
and Hydrogenation Process. U.S. Patent US20110184216A1, 2011.
(41) Mota, C. J. A; Gonç
alves, V. L. C; Mellizo, J. E.; Rocco, A. M.;
Fadigas, J. C.; Gambetta, R. Green Propene through the Selective
Hydrogenolysis of Glycerol over Supported Iron-Molybdenum
Catalyst: The Original History. J. Mol. Catal. A: Chem. 2016, 422,
158.
(42) Zacharopoulou, V.; Vasiliadou, E. S.; Lemonidou, A. A. OneStep Propylene Formation From Bio-Glycerol over Molybdena-based
Catalysts. Green Chem. 2015, 17 (2), 903−912.
(43) Zacharopoulou, V.; Vasiliadou, E. S.; Lemonidou, A. A.
Exploring the Reaction Pathways of Bioglycerol Hydrodeoxygenation
16177

DOI: 10.1021/acssuschemeng.8b02933
ACS Sustainable Chem. Eng. 2018, 6, 16169−16178

ACS Sustainable Chemistry & Engineering

Research Article

(65) Makov, G.; Payne, M. C. Periodic Boundary Conditions in ab
initio Calculations. Phys. Rev. B: Condens. Matter Mater. Phys. 1995, 51
(7), 4014−4022.
(66) Henkelman, G.; Uberuaga, B. P.; Jonsson, H. A climbing image
nudged elastic band method for finding saddle points and minimum
energy paths. J. Chem. Phys. 2000, 113, 9901−9904.
(67) Henkelman, G.; Jónsson, H. Improved Tangent Estimate in the
Nudged Elastic Band Method for Finding Finimum Energy Paths and
Saddle Points. J. Chem. Phys. 2000, 113, 9978−9985.
(68) Henkelman, G.; Jónsson, H. A Dimer Method for Finding
Saddle Points on High Dimensional Potential Surfaces Using only
First Derivatives. J. Chem. Phys. 1999, 111 (15), 7010−7022.
(69) Heyden, A.; Bell, A. T.; Keil, F. J. Efficient Methods for Finding
Transition States in Chemical Reactions: Comparison of Improved
Dimer Method and Partitioned Rational Function Optimization
Method. J. Chem. Phys. 2005, 123 (22), 224101.
(70) Á lvarez-Moreno, M.; de Graaf, C.; López, N.; Maseras, F.;
Poblet, J. M.; Bo, C. Managing the Computational Chemistry Big
Data Problem: The ioChem-BD Platform. J. Chem. Inf. Model. 2015,
55 (1), 95−103.
(71) Rellán-Piñeiro, M.; López, N. Data Set for: A coupled Density
Functional Theory-Microkinetic modeling on the hydrodeoxiygenation of glycerol to propylene on MoO3. DOI: 10.19061/iochem-bd1-81.
(72) Chorkendorff, I.; Niemantsverdriet, J. W. Concepts of Modern
Catalysis and Kinetics; John Wiley & Sons, 2003.
(73) Eyring, H. Statistical Mechanical Treatment of the Activated
Complex in Chemical Reactions. J. Chem. Phys. 1935, 3, 107−15.
(74) Evans, M. G.; Polanyi, M. Application of the Transition-State
Method to the Calculation of Reaction velocities, Especially in
Solution. Trans. Faraday Soc. 1935, 31, 875−94.
(75) Maple 13; Maplesoft, a division of Waterloo Maple, Inc.,
Waterloo, Ontario, 2009.
(76) Teschner, D.; Novell-Leruth, G.; Farra, R.; Knop-Gericke, A.;
Schlö R.; Szentmiklósi, L.; Hevia, M. G.; Soerijanto, H.;
gl,
Schomä
cker, R.; Pérez-Ramírez, J.; López, N. In Situ Surface
Coverage Analysis of RuO2-Catalysed HCl Oxidation Reveals the
Entropic Origin of Compensation in Heterogeneous Catalysis. Nat.
Chem. 2012, 4, 739.
(77) Li, Q.; García-Muelas, R.; López, N. Microkinetics of Alcohol
Reforming for H2 Production from a FAIR Density Functional
Theory Database. Nat. Commun. 2018, 9 (1), 526.
(78) Frei, M. S.; Capdevila-Cortada, M.; García-Muelas, R.;
Mondelli, C.; López, N.; Stewart, J. A.; Curulla Ferré, D.; PérezRamírez, J. Mechanism and Microkinetics of Methanol Synthesis via
CO2 Hydrogenation on Indium Oxide. J. Catal. 2018, 361, 313−321.

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DOI: 10.1021/acssuschemeng.8b02933
ACS Sustainable Chem. Eng. 2018, 6, 16169−16178