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A first-principles study on the hydrogenation ofacetone on HxMoO3 surface
Qiyun Pan a, Liang Huang b,*, Zhong Li a, Juanjuan Han a, Nian Zhao a,Yunlong Xie a, Xiang Li a, Meifeng Liu a, Xiuzhang Wang a,Jun-Ming Liu a,c
a Institute for Advanced Materials, Hubei Key Laboratory of Pollutant Analysis &Reuse Technology,
Hubei Normal University, Huangshi 435002, Chinab The State Key Laboratory of Refractories and Metallurgy, College of Materials and Metallurgy,
Wuhan University of Science and Technology, Wuhan 430081, Chinac National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
Article history:
Received 19 December 2018
Received in revised form
4 February 2019
Accepted 6 February 2019
Available online 7 March 2019
Keywords:
First-principles study
Acetone hydrogenation
HxMoO3 surface
H content
* Corresponding author.E-mail address: [email protected]
https://doi.org/10.1016/j.ijhydene.2019.02.0320360-3199/© 2019 Hydrogen Energy Publicati
a b s t r a c t
Hydrogenation of acetone on the (010) surface of hydrogen molybdenum bronzes was
investigated by density functional theory (DFT) calculations with periodic slab models. The
formation of H-bond between the carbonyl oxygen of acetone and the terminal OH group of
the surface leads to a stable adsorption of acetone. The effect of hydrogen concentration in
the bronzes on the hydrogenation of acetone was systematically investigated, indicating
the hydrogenation reaction is a one-step concerted and exothermic process regardless of
the hydrogen contents in the bronzes surface. The 8H surface with increased H-content
shows a significantly exothermic reaction process and exhibits the smallest kinetic barrier
compared with 4H or 6H surfaces. Additionally, the selectivity for hydrogenation acetone
could increase owing the absence of CeC bond activation. The findings in this study can
help with designing of high-efficient and low-cost metal oxide catalysts for hydrogenation
of unsaturated substances.
© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction
Hydrogenation of unsaturated substances is a widely prac-
ticed process in catalytic reforming of petroleum feedstocks
and numerous other chemical production processes [1e7]. As
known, acetone is one of the typical unsaturated organic
compounds. With the development of current industrial
technology, the industrial yield of acetone has been over-
saturated, while the usage of acetone as solvent is
u.cn (L. Huang).
ons LLC. Published by Els
decreasing in recent years, so as the other fields. In order to
extend the usage of acetone, substantial experimental and
theoretical studies have been devoted onto acetone hydroge-
nation in the recent years [8e14]. Among the hydrogenated
products, isopropanol as the highly selective product of
acetone is a critical solvent in industry for fine chemical
synthesis, and enlarging the scale of isopropanol production
by various approaches has drawn a lot of attention. In addi-
tion, isopropanol is in high demand for direct isopropanol fuel
cells for hydrogen storage [15e18], and relevant technologies
evier Ltd. All rights reserved.
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 210444
possess many advantages such as high-energy production,
much lower crossover current, ease to oxidize, production of
more hydrogen, and being less toxic than other alcohols like
methanol and ethanol.
However, a highly efficient hydrogenation of acetone into
isopropanol essentially relies on specific catalysts. High effi-
ciency and cost-competitive catalysts for hydrogenation of
acetone are becoming highly concerned. Conventional cata-
lysts are mainly composed of metal materials such as nickel,
copper, platinum, rhodium and ruthenium as the active in-
gredients [19e31]. These catalysts may be categorized into
three types, namely, supported metal catalysts, alloy cata-
lysts, and metal oxide catalysts. Although the metal catalysts,
especially precious metal materials, exhibit obviously high
efficiency in acetone hydrogenation, they are more expensive
and easy to be poisoned. Moreover, these solid heterogeneous
catalysts work un-effectively, due to complicated experi-
mental procedure at high operating temperature.
Alternatively, a class of hydrogen bronzes materials in the
form of HxTMOy, where TM denotes transition metal, have
been attracting attention in recent years. They can be pre-
pared from transition metal oxides such as MoO3, WO3, and
V2O5, via hydrogen spillovermechanisms. Hydrogen spillover
phenomenon inMoO3 andWO3 was extensively studied since
the 1970s [32]. In fact, earlier investigations indicated that the
formation of hydrogen bronzes was favorable and H atoms
have high mobility in these transition metal oxides [33e37]
with low energy barrier pathways. The low barriers for pro-
ton diffusion on MoO3 (010) surface allow highly mobile pro-
tons at near ambient temperature [38]. On the other hand, a
series of previous works did demonstrate the highly selective
and effective catalytic kinetics of hydrogen bronzesmaterials
in the hydrogenation of p-conjugated organic molecules with
carbon-carbon double bond [39e42]. Recent theoretical cal-
culations also predicted that molybdenum oxide hydrogen
bronzes such as HxMoO3 were highly effective to the hydro-
genation of ethylene [42]. Compared with transition metal
catalysts, several reactions catalyzed by hydrogen bronzes
generally occur at lower temperature without unfavored by-
products [43,44]. All these earlier investigations suggest the
great potentials of hydrogen bronzes as promising hydroge-
nation catalysts of unsaturated substances. We believe,
therefore that hydrogen molybdenum bronzes may be one
kind of effective catalysts with promising applications in
acetone hydrogenation owing to the ability of hydrogen mo-
lybdenum bronzes to reversibly capture and release
hydrogen [45].
Nevertheless, so far, the hydrogenation of acetone by
hydrogen bronzes remains less touched and there is almost
no study onmicroscopic mechanism for hydrogenation of C]
O onto CeOH with these hydrogen bronzes. Therefore, the
study of hydrogenation of C]O using acetone as probe
molecule on the bronzes surface is one of the most important
topics. Given the issues discussed above, it is of essential in-
terest to address possible kinetic landscape of the acetone
hydrogenation process on the hydrogen bronzes surface,
using the first-principles calculations based on the density-
functional theory (DFT). As reported, the hydrogen concen-
trations in the lattice influence the physicochemical proper-
ties of MoO3 [45] and the reaction activity [39,40]. Therefore,
the hydrogen concentration on a specific surface of HxMoO3
and its influence on the acetone hydrogenation reaction will
be given special attention. The minimum energy pathways
caused by hydrogenation of acetone to isopropanol were
carried out. The objective of this study is to provide useful
insight into hydrogen bronzes materials as potential hydro-
genation catalysts in the hydrogenation of acetone and may
shed light on the hydrogenation mechanism of C]O.
Computational details
In our calculation, the periodic surfacemodel was constructed
by considering a (010) MoO3 surface consisting of four-atom-
layers, as done in our recent work [42] and shown in Fig. 1
for a schematic illustration. The calculated adsorption en-
ergies of acetone on the (2 � 2) MoO3 (010) slab, (3 � 3) MoO3
(010) slab and two-layer (2 � 2) MoO3 (010) slab were�4.9, �3.5
and �4.5 kcal/mol, respectively. Since MoO3 is principally
layer-packed along the [010] orientation bymeans of weak van
der Waals interactions, the effect of further increasing the
atom layers is virtually negligible. Meanwhile, high coverage
is more conducive to the adsorption of reactant. So we chose a
supercell containing one (2 � 2) MoO3 (010) slab, which is large
enough to accommodate surface reactive species. Between
adjacent slabs, a vacuum space of 15 �A was inserted to elim-
inate the artificial inter-cell interactions.
All the calculations were performed on the commercially
available code VASP (Vienna ab-initio simulation package) in
the framework of spin-polarized generalized gradient
approximation (GGA) [46,47]. The exchange-correlation po-
tential was described by the PBE functional [48], and the cut-
off energy of solving Kohh-Sham equation was chosen as
400 eV. The Monkhorst-Pack grid (3 � 3 � 1) was applied to
sample the Brillouin zone during the geometry relaxation,
while the Methfessel-Paxton technique was adopted to
include the electron smearing effect in order to minimize the
errors in Hellmann-Feynman forces and facilitate self-
consistent field convergence [49]. The geometry was consid-
ered as an equilibrium state when the energy difference in
two subsequent optimization steps was smaller than 10�3 eV
and the force was converged to be less than 0.03 eV/�A. The
structures of transition states were obtained by the climbing
image nudged elastic band (CI-NEB) method [50,51], where six
images between reactant and product were inserted to ach-
ieve a smooth energy curvewith the force tolerance of 0.05 eV/�A. The minimum energy path calculations were performed to
explore the detailed catalytic process of acetone hydrogena-
tion. This computational protocol has been proved to be well-
accurate in producing structural and energetic data for MoO3
and HxMoO3 systems [42].
Results and discussions
The structures and formation thermodynamics of HxMoO3
with various hydrogen contents can be found in details in
our previous publication [34]. In general, there are three
types of O atoms on the MoO3(010) surface, denoted as Ot
(terminal site), Oa (asymmetric site) and Os (symmetric
Fig. 1 e (a) Side view of MoO3 (010) surface, (b) top view of MoO3 (010) surface.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 2 10445
site) (Fig. 1.). Upon the hydrogenation of MoO3, the Ot sites
are most preferentially occupied by H atoms, followed by
the occupations at the Oa and Os sites. Since H atoms are
highly mobile in MoO3 lattice, we can rationally assume
that the Ot sites are always occupied by H atoms during the
hydrogenation process. As shown in hydrogenation of
Fig. 2 e (a) Calculated energy diagram of the hydrogenation of a
view of the acetone on the 4H molybdenum bronzes surface. Op
the 4H surface (c) initial state (AB), (d) transition state (TS) and (
HxMoO3 before adsorption, C þ D is the state of isopropanol an
ethylene, the increased hydrogen concentration could lead
to an enhanced kinetics [42]. A series of HxMoO3 systems
with varying H contents (labeled as 4H, 6H and 8H for
illustration (Figs. 2e4), were considered in our calculations
to evaluate the reactivity of HxMoO3 with various hydrogen
concentrations.
cetone on the 4H molybdenum bronzes surface. (b) The top
timized configurations of acetone absorption geometries on
e) final state (CD). (A þ B presents the state of acetone and
d HxMoO3 after hydrogenation).
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 210446
Hydrogenation of acetone on 4H molybdenum bronzessurface
The two-step hydrogenationmechanismwas proven to be the
dominant process for hydrogenation of acetone on transition
metal catalysts. However, this reactionmechanismwas found
inoperative on the HxMoO3 (010) surface. Indeed, the addition
of one hydrogen to the carbonyl carbonwas optimized to form
acetone, while the addition of one hydrogen to the carbonyl
oxygenwas optimized to produce isopropanol. In otherwords,
the intermediate free radical could not be stabilized by the
surface. The taken reaction route is for the two terminal
hydrogen atoms to migrate simultaneously from the HxMoO3
surface to form a new CeOH bonds. The calculated hydroge-
nation profile is shown in Fig. 2, and several key structural
parameters of the reactant, transition state, and product on
the 4H surface are displayed in Table 1. Initially, the acetone
molecule is attracted by the eOH groups on the surface with a
moderate adsorption strength of �4.9 kcal/mol, which is
much larger than the adsorption energy of ethylene (�2.1 kcal/
mol) [42]. The enhanced anchoring strength of acetone should
originate from the interaction between the electron enriched
O atom of C]O and the protonic H of eOH groups on molyb-
denum bronzes surface [42]. This allows a relatively strong H-
bonding given the calculated O3eH2 distance of 1.756 �A. On
the other hand, a relatively long distance betweenH1 andC1 is
observed due to the steric repulsion between themethyl group
of acetone and the eOH on the molybdenum bronzes surface.
Comparing with the gas phase acetone, the CeC bonds of
acetone are essentially unchanged upon the adsorption, sug-
gesting the fact that CeC bonds of acetone are not activated
via the H-bonding interaction. As a result, only the C]O bond
is accessible for hydrogenation, implying the superior selec-
tivity of HxMoO3 for the hydrogenation.
Subsequently, the isopropanol (hydrogenation product) is
structurally relaxed on the HxMoO3 surface to model the re-
action product (CD), as shown in Fig. 2(a). The optimized
adsorption structure of isopropanol on the surface is virtually
identical to its gas-phase configuration. The formation of
isopropanol is almost thermally neutral with a negligible
Table 1 e Optimized Structural Parameters of reactantcomplex(R), transition state(TS), and product complex(P)on the 4H, 6H, and 8H molybdenum bronzes surface a.
bond length (�A)
C1eO3 C1eH1 O3eH2 O1eH1 O2eH2
4H R 1.234 2.964 1.756 0.981 1.003
TS 1.309 2.074 1.036 1.002 1.555
P 1.442 1.106 0.979 2.334 2.080
6H site A R 1.234 2.787 1.745 0.977 0.999
TS 1.322 2.219 1.013 0.997 1.696
P 1.443 1.108 0.976 2.579 2.307
6H site B R 1.233 2.821 1.966 0.983 0.990
TS 1.352 1.906 0.988 1.017 2.028
P 1.444 1.104 0.976 2.226 2.307
8H R 1.235 2.815 1.765 0.978 1.001
TS 1.337 2.286 0.992 0.991 1.845
P 1.446 1.103 0.976 2.330 2.352
a C1, C2, H1, H2, O1, and O2 are denoted in Fig. 2(b).
energy of �0.3 kcal/mol lower than the reactant. Comparing
with the ethylene case [42], where the hydrogenation of
ethylene on the 4H molybdenum bronzes surface is energet-
ically more favorable with the calculated reaction energy of
�15.3 kcal/mol. Such a low reaction energy of acetone should
be attributed to the strong repulsion between the methyl
group and the surface. Based on the obtained reactant and
product, the transition state (TS) could be identified using the
NEB algorithm by linking AB and CD. Similar to ethylene [42],
the hydrogenation of acetone would also undergo a one-step
mechanism where the two surface H atoms (H1 and H2, as
labeled in Fig. 2(b)) attack the C]O bond simultaneously. In
the TS, the C]Obond is elongated by 0.075�A compared to that
of acetone (1.234 �A), indicating the weakness of the original
double-bonding. In themeantime, the distance of both C1eH1
and O3eH2 bonds is reduced to 2.074 �A and 1.036 �A, respec-
tively, implying the formation of hydrogenation product. The
short distance of O3eH2 (1.036 �A) in the transition state is
originated from the strong H-bonding interaction, which fa-
cilitates the H migration process. As a consequence, a mod-
erate activation barrier of 17.8 kcal/mol is required to
accomplish the hydrogenation reaction. Since the isopropanol
is still adsorbed on the surface through a relatively week H-
bonding interaction between the eOH of isopropanol and the
terminal O atom on the surface with a distance of 2.080 �A, a
small desorption energy of 2.1 kcal/mol is necessary to release
the product into gas phase. Our results suggest that HxMoO3
with the 4H surface is capable of hydrogenating acetone
molecules with superior activity. It is notable the desorption
of isopropanol is facile, reducing the likelihood of subsequent
reactions, which is helpful to improve the selectivity.
Hydrogenation of acetone on 6H and 8H molybdenumbronzes surface
Similar calculations were performed on the 6H and 8H sur-
faces to address the effect of H content on the hydrogenation
reaction. For the 6H surface, two possible starting points were
considered in our calculations due to the asymmetric location
of the H atom in the second layer, as shown in Fig. 3(b and c).
Comparing with the 4H surface case, the internal H-bonding
interaction between the H atom in the second layer and the O
atom in the third layer leads to a downward movement of the
second layer Oa atoms, resulting in two reaction sites. Upon
adsorption of acetone on the surface, the acetone is somewhat
locked by the four eOH groups on the surface. The reaction
space at site A is more open (:OeMoeO ¼ 94.1�), while the
adsorption region at site B is somewhat embedded with a
reduced :OeMoeO ¼ 85.4�. Therefore, the site A should be
more accessible for acetone molecule during the hydrogena-
tion. Indeed, the optimized adsorption structures indicate that
both the O3eH2 and C1eH1 distances at site A are much
shorter than the value at site B (Table 1). As a consequence,
the acetone adsorption at site A is energetically more favor-
able than that at site B by 1.9 kcal/mol in the energy difference.
As described in the 4H case, the acetone hydrogenation on
the 6H surface also follows the one step reaction mechanism.
Table 1 summarizes the structural parameters of the opti-
mized geometries along the reaction. At the transition state of
site A, a small surface relaxation is observed with negligible
Fig. 3 e (a) Calculated energy diagram of the hydrogenation of acetone on the 6H molybdenum bronzes surface. The two
possible reaction pathways are denoted as black for site A and red for site B. Optimized configurations of possible acetone
absorption geometries on the 6H molybdenum bronzes surface with (b) 6H site A (1) initial state(AB), (2) transition state(TS)
and (3) finial state(CD). (c) 6H site B. (4) initial state(AB), (5) transition state(TS) and (6) finial state(CD). (For interpretation of
the references to colour in this figure legend, the reader is referred to the Web version of this article.)
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 2 10447
increase of angle :OeMoeO. Here, the O3eH2 distance is
slightly shorter than the value obtained on the 4H surface, in
line with the facile accessibility of site A. The calculated
activation energy of 16.8 kcal/mol (Fig. 3(a)) is also lower than
the value on the 4H surface. Thermodynamically, the hydro-
genation of acetone at site A become more exothermic than
the 4H case with the calculated reaction energy of �7.3 kcal/
mol (Fig. 3(a)). Alternatively, the hydrogenation reaction could
also proceed at site B, where the four eOH groups are pushed
slightly toward each other. In principle, the acetone molecule
should be a little bit far from the surface at the transition state
due to the poor accessibility of site B. However, the optimized
structure at the transition state shows that the acetone is very
close to the surface and both the O3eH2 and C1eH1 distances
are even shorter than the values at site A. The unexpected
approaching of acetone is attributed to the considerable sur-
face relaxation during the hydrogenation, as reflected by the
significantly increased angle :OeMoeO from 85.4� of the
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 210448
initial state to 96.1� at the transition state. It is worth noting
that the internal H-bonding between the second and third
layers is weakened since the Oa-H distance is elongated by
0.228 �A during the surface relaxation. Consequently, although
the acetone is closer to the surface at site B than that at site A,
the calculated activation barrier at site B is much higher
(20.4 kcal/mol) due to the intensive surface relaxation, which
consumes additional energies to open the reaction site. Again,
a relatively lower desorption energy (0.8 kcal/mol at site A,
1.3 kcal/mol at site B) is required to release the final product to
the gas phase at either site A or site B.
The catalytic reactivity of acetone hydrogenation on the 8H
surface is also explored and the energy profile is shown in
Fig. 4(a). Similarly to the 6H surface, the H atoms at the
asymmetric O site (Oa) in the second layer on the 8H surface
move downwards to interact with the O atom in the third
layer, leading to an open interaction space surrounded by the
four terminal OH groups (Fig. 4(b)). Considering the higher H
content, the 8H surface is expected to present favorable re-
action kinetic properties. Kinetically, the 8H surface shows a
lower activation barrier (7.9 kcal/mol) than those of the 4H and
6H (site A) surfaces. Thermodynamically, the hydrogenation
process on the 8H surface is extremely exothermic with the
calculated reaction energy of �25.2 kcal/mol. Therefore, the
highly protonic nature of the terminal H is a dominant factor
Fig. 4 e (a) Calculated energy diagram of the hydrogenation of
structure of acetone on the 8H surface (a) initial state(AB), (b) tr
in the acetone hydrogenation. Besides, higher concentration
of hydrogen bronzes materials is also necessary to exhibit
faster reaction kinetics for acetone hydrogenation [34].
Discussion
In order to analyze the distribution of electrons in each orbital
during hydrogenation, the calculated electronic density of
states (DOS) profiles for the pristine 4H bronzes surface, the 4H
surface with acetone, and the surface with isopropanol were
displayed in Fig. 5. Upon acetone adsorption, there is almost
no obvious change in the electronic structure of the 4H
bronzes surface except for 1s orbital of H, reflecting the for-
mation of H-bond between acetone and the hydrogen bronzes
surface. The two p orbitals around �7.5 and 2.5 eV are attrib-
uted to the C]O bonds of acetone, accompanied with the
minor change of orbitals of oxygen (Fig. 5(2)). After the for-
mation of isopropanol (Fig. 5(3)), the electronic structure of Mo
around the Fermi level experiences significant changes as
expected, where the Mo atoms linked to the terminal OeH
group are oxidized, and the C]O orbitals of acetone disap-
pears as one CeH bond and one OeH bond are formed.
The DOS of 6H and 8H were also calculated, as shown in
Fig. 6. Generally, the conductor-like electronic structure of
bronzes surface is preserved along the reaction pathway. The
acetone on the 8H molybdenum bronzes surface. The
ansition state(TS) and (c) finial state(CD).
Fig. 5 e Calculated electronic DOS of (1) the 4H bronzes surface, (2) the 4H bronzes surface with acetone, (3) the 4H bronzes
surface with isopropanol after reaction.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 2 10449
adsorption of acetonewould not result in any obvious changes
in the electronic structures of bronze with the selected sur-
faces, reflecting their weak physical adsorption properties.
While the formation of isopropanol could lead to significant
changes around the Fermi level, due to oxidization of the
terminal OeH group.
Fig. 7 shows the relationship between the calculated ther-
mochemical energies and activation barriers of acetone hy-
drogenation on the HxMoO3 surfaces with selected hydrogen
contents. This phenomenon fits well with the BEP (Brønsted-
Evans-Polanyi) Relations, which is able to predict energy bar-
riers of the reaction under different chemical environment of
the reactive center [52]. From the calculate results we can see
that, as the content of hydrogen in these compounds in-
creases, the catalytic activity of HxMoO3 for acetone hydro-
genation increases significantly, which fits to our previous
study for ethylene hydrogenation elucidated the potential
positive effects of increasing H content on the bronzes surface
to suppress the energy barrier for hydrogenation [34]. The
calculated activation energies range from 17.8 to 7.9 kcal/mol,
depending on the content of H in the hydrogen bronzes.
Overall, the reaction pathway to hydrogenate acetone on the
8H surface is the most feasible in kinetics, with a barrier of
only 7.9 kcal/mol. It fits to our previous study for ethylene
hydrogenation elucidated the potential positive effects of
increasing H content on the bronze surface to suppress the
Fig. 6 e Calculated electronic DOS. (1)the bronze surface of 6H, (2) the 6H bronze surface upon acetone adsorption, (3) the 6H
bronze surface upon hydrogenation to form isopropanol; (4)the bronze surface of 8H, (5) the 8H bronze surface upon acetone
adsorption, (6) the 8H bronze surface upon hydrogenation to form isopropanol.
Fig. 7 e The relationship between calculated
thermochemical energies (DEr) and the activation energies
(Ea) of acetone hydrogenation on the HxMoO3 with various
hydrogen concentrations.
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 210450
energy barrier for hydrogenation. It is worth mentioning that,
compared to the reported activation energies of acetone hy-
drogenation on the Pt(111) surface (14.3 kcal/mol) and on the
Ni tetramer cluster (17.4 kcal/mol), hydrogenation of acetone
catalyzed by HxMoO3 appears to be kineticallymore favorable.
Compared with ethylene hydrogenation on hydrogen
bronzes HxMoO3 surface, it can be observed that the acetone
hydrogenation is quite different from the case of ethylene
hydrogenation (Table 2). Different from ethylene that requires
the C]C bond activation, the polar C]O bond in acetone
would definitely facilitate the proton transfer from the ter-
minal OH group to the carbonyl oxygen via an H-bond attack,
so that hydrogenation of acetone exhibits lower activation
energy. It is noteworthy that the hydrogenation activity and
activation energy between hydrogenation of acetone and
ethylene on hydrogen bronzes HxMoO3 surface are different,
indicating HxMoO3 may be a promising and effective catalyst
for selective hydrogenation of unsaturated substances con-
taining C]O and C]C bond simultaneously. It may be a
meaningful research for HxMoO3 as the hydrogenation cata-
lyst for methyl vinyl ketone [53].
Table 2 e The comparison about hydrogenation of acetone and ethylene on molybdenum bronzes surface.
Contrast Unsaturated bond Reaction mechanism Lowest activation energy(kcal/mol) H concentration effect
Acetone C¼O One step 7.9 Fits to BEP
Ethylene C¼C One step 9.3 þ 0.9 Fits to BEP
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 4 ( 2 0 1 9 ) 1 0 4 4 3e1 0 4 5 2 10451
Conclusion
The surface catalytic activity of hydrogen bronzes MoO3 with
different hydrogen contents towards acetone hydrogenation
was investigated by means of plane wave density functional
theory. The adsorption of acetone on the HxMoO3 surfaces is
favorable due to the formation of H-bond between acetone
and the surfaces. There is virtually no CeC bond activation
during the adsorption of acetone, allowing for excellent
selectivity for hydrogenation. Our calculations suggest that
the hydrogenation of acetone is a one-step concerted and
exothermic reaction. Increase of H concentration (i.e., 8H
surface) expectedly decreases the kinetic barrier. The hydro-
genation of acetone on 8H surface is extremely exothermic
(�25.2 kcal/mol) with the smallest activation barrier (7.9 kcal/
mol), even appearing to be kinetically more favorable than Pt
(111) surface and Ni tetramer cluster. Additionally, the dif-
ference of hydrogenation activity of acetone and ethylene on
HxMoO3 surface indicate the potential application of
hydrogen bronzes as selective hydrogenation catalysts. Our
results suggest HxMoO3 could be an effective catalyst for
acetone hydrogenation and provide a novel insight for
designing low-cost hydrogen bronzes MoO3 catalysts.
Acknowledgements
This work was financially supported by National Natural Sci-
ence Foundation of China (Grant No. 51702241), Hubei Key
Laboratory of Pollutant Analysis & Reuse Technology (Grant
No. PA20170203), the Research Project of Hubei Provincial
Department of Education (Grant No. B2018147).
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.ijhydene.2019.02.032.
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