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Prevalence of trans-Alkenes in Hydrogenation Processes on Metal
Surfaces: A Density Functional Theory Study
Javier Navarro-Ruiz, Damien Cornu, and Núria López*
Institute of Chemical Research of Catalonia, ICIQ, and The Barcelona Institute of Science and Technology, BIST, Av. Països
Catalans 16, 43007 Tarragona, Spain

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S
* Supporting Information

ABSTRACT: The hydrogenation of triple and double
carbon−carbon bonds in C4 molecules containing a single
unsaturation has been investigated for the lowest index
surfaces of the triad Ni, Pd, and Pt through first-principles
simulations. Both low and high hydrogen coverage have been
explored to identify the nature of the selectivity found in the
experiments. The adsorption behavior of the alkynes and
alkenes at high hydrogen concentrations differs from the
structures in the infinite dilution-limit coverage which makes a
significant contribution to selectivity. Structure sensitivity is
also a consequence of the hydrogen coverage, at high contents
(111) surfaces cannot trap the C4 molecules efficiently, and
thus, the reactivity mainly occurs on the more open (100) surfaces. The combination of fast/slow elementary steps, crucial to
eliminate trans-alkenes that are health threatening, is not possible for any of the metals studied, although some metals present
slightly better behavior. Our study paves the way towards an integrative analysis of the hydrogenation process that accounts for
high surface coverage, preferential adsorption, and kinetic contributions.

1. INTRODUCTION
Hydrogenation is one of the most traditional catalytic
processes and since the 19th century, pioneering works from
Wilde1 have made a landmark in this field. It was not until
1897 when Sabatier and Senderens2 developed an industrial
process by which trace quantities of solid nickel facilitated the
hydrogenation of alkenes at low temperatures to transform
vegetable oil into margarine.3,4 Even today, many products
such as shortenings, biscuits, pastries, and other baked
products contain them. These hydrogenated oils were well
recognized for their properties: (i) better rheology than fats
(hence easier to spread at lower temperatures);5 (ii) higher
stability than unsaturated and also saturated products (the
process of hydrogenation transforms fatty acids that are
susceptible to oxidative rancidity); (iii) a more stable
production than butter. Thus, since 1920, food industries
adopted hydrogenated fats in their production lines and their
consumption increased steadily until the 1960s.
The hydrogenation of C−C unsaturated organic compounds6,7 can take place on several metals: nickel, 8
palladium,9−16 as well as platinum17−19 at moderate temperatures and hydrogen pressures. Other transition metals,20 Ag
nanoparticles,21 and cerium22 and indium23 oxides can also
carry out the reaction at higher temperatures and in the liquid
phase poisoned Pd (Lindlar catalyst24,25) is employed. On
metals that easily activate H2,26−33 the reaction occurs through
the Horiuti−Polanyi mechanism34 where molecular hydrogen
is homolytically dissociated on the surface and the hydrogen is
© 2018 American Chemical Society

transferred sequentially to the organic molecule. However,
when starting from an alkyne, if the corresponding alkene is
still strongly bound to the surface, a second hydrogenation can
occur limiting the selectivity for the semi-hydrogenated
product. The loss of selectivity, via over hydrogenation or
oligomerization,35,36 has been analyzed in detail and factors
such particle size,37,38 impurities, or dopants,39−46 and the
addition of molecular selectivity modulators,47,48 have been
shown to regulate selectivity.
The main problem of the hydrogenation process described
above is that it preferentially leads to trans-alkenes. As early as
1956, the first evidences that trans fats could be associated with
increased risk of coronary heart disease appeared.49,50 In 1994,
the consumption of trans fats, linked to strong evidences in
obesity, diabetes, and cancer, was estimated to be the reason
behind 30 000 deaths per year in the United States. The
ultimate consequence was the establishment of stricter
government regulations to minimize the trans-fat consumption,
and thus limiting the catalytic processes that can provide less
damaging compounds.51 Therefore, it would be desirable to
maximize the obtaining of cis-alkenes, on the one hand, and to
minimize the trans-alkenes and/or overhydrogenate them, on
the other hand, according to Scheme 1.
Received: July 18, 2018
Revised: October 17, 2018
Published: October 18, 2018
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Scheme 1. Reaction Scheme Leading from Alkynes to
Alkenes and the Desired Relative Velocities To Maximize
the Production of the cis-Compound.

Because the trans fats are typically large molecules with
independent functional groups, it is of interest to apply
surrogate molecules59,60 representing the unsaturated moiety
as the essential motif. In the present work, by means of density
functional theory, we have computed the reaction mechanism
for: (i) a collection of surrogates that include C4 organic
molecules with C−C triple and double bonds (ii) on three
different metals, (iii) with the two most common surface
orientations,61 and (iv) under two different hydrogenation
conditions (H-lean and rich) to understand the relative
inertness of trans-alkenes under these conditions. Our results
constitute the first complete, open (findable, accessible,
interoperable, and recyclable, FAIR)60 database for hydrogenation of alkynes and alkenes.

Experiments have shown that when hydrogenating on Pd,
trans-alkenes are the most robust semi-hydrogenation products, and thus they remain in the mixture. This can be seen as a
preference for the hydrogenation of terminal and cisalkenes.52,53 By using temperature-programmed desorption,
Doyle et al.54 have found that C5 and C2 alkanes are not
formed as hydrogenation products of the corresponding
alkenes on Pd(111) but, in contrast, they do occur on the
Pd particles under low-pressure conditions in the presence of
subsurface hydrogen. Despite this, first-principles calculations
show that the adsorption at high coverage can differ from that
of low coverage due to repulsion terms,55 consistently with
experimental infrared reflection absorption spectroscopy
data.56 On Pt(111), cis−trans isomerization of butenes has
also been addressed, Li and co-workers57,58 reported that at
low H coverage conversion from the cis to the trans isomer is
preferred, whereas on the H saturated surface the reverse
appears to be true.

2. COMPUTATIONAL DETAILS
Density functional theory calculations were performed using
the ab initio plane-wave pseudopotential approach as
implemented in the Vienna ab initio simulation package
(VASP 5.4).62,63 The Perdew−Burke−Ernzerhof64 exchange−
correlation functional within the generalized gradient approximation was chosen and van der Waals interactions were taken
into account through the D2 correction of Grimme65 in
combination with our reparameterized values66 for the metal
surfaces. The innermost electrons were replaced by a projector
augmented-wave approach67,68 while the valence monoelectronic states have been expanded in a plane-wave basis set with
a cut-off energy of 400 eV. For bulk calculations, an 11 × 11 ×
11 k-point mesh was used for all the metals. Within this setup,
the optimized face-centered cubic lattice constants were 3.515,
3.945, and 3.975 Å for Ni, Pd, and Pt respectively, in good
agreement with the experimental values (Ni: 3.516,69 Pd:

Figure 1. Adsorption structures of all the butynes studied in this work. Color code: Ni (magenta), Pd (cyan), Pt (yellow), C (gray), and H (white).
All the structures can be referred in ref 77.
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a

Table 1. Heat Map for Adsorption Energies, Eads in eV, of Butynes as a Function of Hydrogen Coverage.

a

The scale spans the energies of butynes only.

3.8907,70 Pt: 3.916 Å71). (111) and (100) metal surfaces
consist of a five-layer slab (respectively eight and nine atoms
per layer and the bottom two ones were frozen) in a p(3 × 3)
supercell (with spin polarization on the nickel surfaces). ΓCentered 5 × 5 × 1 k-point72 mesh was employed, and a
vacuum region by at least 10 Å between the periodically
repeated slabs was added. Dipole correction along the zdirection has been considered,73 and transition states were
located by the Climbing Image version of the nudged elastic
band, CI-NEB, method74,75 and were proven to show a single
imaginary frequency by the diagonalization of the numerical
Hessian with a step of 0.01 Å. All structures have been
uploaded to the ioChem-BD database76 and can be consulted
in the following link.77

workers.81 However, a behavior similar to that of butynes at
low H coverage is found and the binding is larger going from
Ni < Pd < Pt irrespective of the surface orientation. When
going to the open surfaces, the adsorption is stronger by 0.2 eV
for Ni, slightly lower for Pd, and around 0.3 eV for Pt. At high
H coverage, butenes are adsorbed as described for the low
hydrogen content, but they are even more weakly bound as it
has been seen for butynes. Physisorption energies are retrieved
for Pd and Pt(111), thus indicating that for these surfaces
desorption will be preferred to highly H-covered surfaces. For
the corresponding (100) orientation, the values range from 0.4
for Ni to 0.6−0.8 eV for Pd and Pt except for isobutene that
shows lowers values on Pt.
3.2. Semi-Hydrogenation Reaction of Butynes. The
hydrogenation reaction on the active metals takes place
through the Horiuti−Polanyi mechanism described previously.
384 elementary steps were calculated corresponding to the
hydrogenation of all C4 butynes and butenes on the three
metal surfaces with the two surface orientations and at both H
coverage. All the elementary steps are listed in Table S1.
Particularly, in conditions of high coverage, where there are
several H atoms around the C4 species, the H attacking the
organic moieties is always the closest and is able to carry out
the reaction (an example is given in Figure S1). Since the
description is very extensive, we have focused on three
prototypical molecules: 2-butyne as an example of alkyne and
cis- and trans-2-butene as an example of alkene.
The energy profiles are summarized in Figure 3. All the
computed energies are given with respect to the gas-phase
organic moiety plus the already adsorbed H atoms and are
presented as potential energies, thus, not considering the
entropies. Therefore, the comparison between the adsorbed
state and the first hydrogen insertion is meaningful when
considering the relative activity of the different metals, or
hydrogen coverage. In general, the hydrogenation process from
2-butyne to cis- and trans-2-butene is thermodynamically
favorable and particularly at low hydrogen regime, with values
between −1.3 and −1.5 eV, whereas in the case of a high H
content the values vary between −0.3 and −1.2 eV. In contrast,
the lowest energy barriers correspond to the H-rich metal
surfaces, ranging from 0.2 to 0.9 eV, while for the case of low
H coverage are from 0.4 to 1.2 eV. At high hydrogen coverage
conditions, however, H atoms occupy sites where C4 species
are typically present and may reduce the adsorption energy,
thus affecting hydrogenation. Trying to account for the degree
of energy lost due to the presence of the full coverage, one of
the reaction networks is evaluated at intermediate H regimes as
shown in Figure S2. As it can be seen, these regimes are
interspersed between the lowest and the highest, so
thermodynamics and kinetics can be interpolated and follow
the trends shown above. Hence, to illustrate the role of the
zero point vibrational energy (ZPVE), one of the reaction
mechanisms considering the ZPVE is reported (see Figure S3

3. RESULTS
3.1. Adsorption of Butynes and Butenes on the Low
Energy Surfaces. Here, the adsorption of all the C4
compounds (1- and 2-butyne, 1-butene, cis- and trans-2butene, and isobutene) on Ni, Pd, and Pt(111) and (100)
surfaces at low 0.11−0.13 ML and high 1.00 ML H coverage,
depending if there is a single H atom or an entire H monolayer
adsorbed per unit cell, respectively, is presented. The
adsorption structures and the corresponding energies for
butyne (and butene) isomers are summarized in Figure 1 and
Table 1 (Figure 2 and Table 2), respectively.
The conformation of butynes is similar irrespective of the
metal facet, the CC is adsorbed with the triple bond
occupying a hollow adsorption site. At low H coverage on the
(111) surfaces, butynes bind to Pt more strongly than Ni, and
this one, in turn, more than Pd. But for the (100) orientation,
the binding to Ni and Pd is comparable and stronger than for
Pt. Therefore, binding over (100) is stronger than over (111),
the energy difference being about 0.35 eV for butynes on Ni
but increasing to 0.75 eV for Pd and around 1.00 eV for Pt.
This follows the rule that more open surfaces in terms of
coordination allow stronger interactions.78,79 The situation
does not particularly change in terms of adsorption geometries
but adsorption energies are much smaller at high H coverage.
Butynes are adsorbed as described for low hydrogen content
except on Pt,38,80 in this case, in a bridge position. Instead, the
binding energies for butynes are small, around 0.5 for Ni and
0.8−0.9 eV for Pd and Pt(111). Therefore, when going from a
low to high H coverage the adsorption energies are reduced on
an average to 1/3 of the infinite dilution-limit value. For the
open surfaces, the adsorption values triple for Ni, double for
Pd but only increase slightly for Pt.
For butenes the adsorption differs from that of butynes, in
this case, CC bonds are formed between the two metal
atoms in a bridge position. In this point of view, the adsorption
energies of butenes are found to be weaker than that of
butynes on all the surfaces considered,6 the fact that follows
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Figure 2. Adsorption structures of all the butenes studied in this work. Color code: Ni (magenta), Pd (cyan), Pt (yellow), C (gray), and H (white).
All the structures and can be referred in ref 77.

lean (100) surfaces give the cis isomer as the major
hydrogenation product (ΔEcis/trans > 0.3 eV), the H-lean
a
(111) surface gives the trans isomer (ΔEcis/trans = −0.2 eV),
a
and finally the H-rich (100) could give both isomers due to the
fact that both are very similar in energy. Using Pd, while both
orientations at low H coverage preferentially maintains the
production of the cis isomer (ΔEcis/trans > 0.1 eV), the (111)
a
surface at high H gives the trans isomer as the main

of the Supporting Information). Because the ZPVE always
corresponds to the addition of hydrogen that is activated on
the surface, these values are roughly constant, and thus have
not been applied to all cases.
Each metal shows preference for obtaining one (or the other
alkene) depending on its orientation and hydrogen content.
Defining ΔEcis/trans = Etrans − Ecis, where Ea is the energy barrier
a
a
a
of the process (see Figure 3a), for Ni the H-rich (111) and H25342

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Table 2. Heat Map for the Adsorption Energies, Eads in eV, of Butenes as a Function of Hydrogen Coverage.

a

a

The scale spans the energies of butenes only.

Figure 3. Reaction profiles of 2-butyne semi-hydrogenation to cis- and trans-2-butene on (a) Ni(111), (b) Ni(100), (c) Pd(111), (d) Pd(100), (e)
Pt(111) and (f) Pt(100) surfaces at low (gray for the first common step, orange for cis, and dark yellow for the trans-2-butene) and high (black for
the first common step, wine for cis, and red for the trans-alkene) hydrogen coverage. Relative energies are referenced with respect to the surface +
nH(ads), where n is the number of hydrogen atoms.

hydrogenated product (ΔEcis/trans = −0.3 eV). The remaining
a
situation, H-rich (100), surface could also give both alkenes,
although the energy barriers in all cases are high, even more
than for Ni. Finally, on Pt, the H-rich (100) facet is the only
situation where cis butene is predominant over the trans,
whereas the main hydrogenated product in the case of (111) is
trans-2-butene (ΔEcis/trans = 0.1 and 0.2 eV, respectively).
a
In the case of partial hydrogenation of 1-butyne to 1-butene
and, according to Figure S4, the processes occur both

thermodynamically as kinetically analogously to those achieved
for obtaining cis-2-butene from 2-butyne in all the metals,
facets, and coverage studied. In fact, all the energy barriers
computed in this work are similar or different depending on
what kind of molecule (butynes and butenes), metal (Ni, Pd,
and Pt), orientation ((100) and (111)), and coverage (H lean
and H rich) is taking part in each reaction. As a result, Ni and
Pt are more susceptible to semi-hydrogenation of triple bonds
than Pd surfaces because of the low energy barriers and
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Figure 4. Reaction profiles of cis- and trans-2-butene hydrogenation to n-butane on (a) Ni(111), (b) Ni(100), (c) Pd(111), (d) Pd(100), (e)
Pt(111) and (f) Pt(100) surfaces at low (orange for cis, dark yellow for the trans-2-butene, and gray for the second common step) and high (wine
for cis, red for the trans-alkene, and black for the second common step) hydrogen coverage. Relative energies are referenced with respect to the
surface + nH(ads), where n is the number of hydrogen atoms.

first energy barrier of 1.0 and 0.8 eV for the (111) and (100)
surfaces, respectively, which is above the adsorption energy.
Using Pd(111) at high hydrogen coverage is the one that is
more difficult, since the energy barriers of 0.9 and 0.7 eV for
the cis and trans isomers, respectively, are also higher than the
adsorption energy in line with H-rich Ni surfaces. At low H
contents, the hydrogen insertions occur and in a similar rate
for both alkenes. For the (100) surface, both coverages present
a preference for the trans-2-butene hydrogenation, especially
the H-lean one (ΔEcis/trans ≈ −0.1 eV). In the case of Pt, it
a
happens like Ni and H-lean surfaces are where the formation of
n-butane occurs favorably whilst on H-rich surfaces must
overcome energy barriers of 0.6 and 0.8 eV for the cis and
trans-alkenes, respectively, located above the Eads.
In the case of 1-butene (to n-butane, see Figure S5) and
isobutene hydrogenation (to isobutane, see Figure S6), there
are no significant differences both thermodynamically as
kinetically to those obtained by the cis and trans isomers in
all the metals, facets, and coverage studied, and only
occasionally the energy profiles are shifted to more negative
values. Thus, irrespective of the H regime, Pt(111) surfaces are
the only ones in this orientation for which cis isomer
hydrogenation clearly takes preference and Pt(100) surfaces

principally at open (100) surfaces, since the alkynes are more
strongly adsorbed making the H-insertions surmountable.
3.3. Hydrogenation Reaction of Butenes. Once 2butyne is partially hydrogenated to cis- or trans-2-butene, these
could further react to give the fully saturated product, nbutane. The energy profiles are summarized in Figure 4. In
general, this second hydrogenation process is also thermodynamically favorable for all conditions, with reaction energies
ranging from 0.6 for Pt(100) to 0.8 eV for Pd(100) at low
hydrogen coverage and from 0.1 for the Pt(100) to 0.7 eV for
the Pt(111) in the case of high H contents, values that are
about half of those obtained for the first hydrogenation
process. The most energy-demanding step is always the first H
insertion, especially in the case of (111) surface orientations.
In addition, it seems that the process is more difficult at high
hydrogen regimes and that the adsorption of alkene is the key
factor.
On Ni, the reaction takes place preferentially at low H
coverage although the different orientations drive the
preference for alkene hydrogenation, trans isomer is faster on
the (111) surface, while cis-2-butene is faster on the open
(100) surface (ΔEcis/trans ≈ |0.1| eV). At high coverage, H
a
insertions are slower because both surfaces must overcome a
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are, in conjunction with Pd(100), suitable for the trans
butenes.
3.4. cis−trans Isomerization. The partial hydrogenation
of 2-butyne produces both isomers of 2-butene and, in
posteriori second hydrogenation, it produces n-butane as a
fully hydrogenated product. Hence, from the latter H insertion,
it is possible to induce a cis−trans isomerization depending on
the kinetics of each reaction. To do this, by comparing from
Figure 4 the energy barrier for going from sec-butyl (the
intermediate formed) to n-butane and to cis- or trans-alkene it
is possible to point out which are the suitable catalysts.
At high H coverage, (111) surfaces give no isomerization
because the second transition state (final H insertion, TS4*) is
lower in energy than the first one (first H insertion of the
alkene, TS3*). In contrast, (100) surfaces could produce the
isomerization due to an inversion in the energy barriers (TS3*
< TS4*). According to this, Pt(100) and to a lesser extent
Ni(100) are the best to enhance isomerization. In Pt, the
reaction goes from trans to cis alkene while on Ni the opposite
direction is preferred. On Pd(100), on the other hand, both
isomerization and hydrogenation processes are competitive as
the two reaction energies are very similar. Additionally, there is
no energy difference between cis and trans isomers and hence
both could be obtained. Regarding low H contents, both Pt
orientations are the only ones that can lead to isomerization.
On the Pt(100) surface the same path follows as in H-rich;
however, on Pt(111) both energy barriers are exactly the same
from the sec-butyl intermediate and also very close to H
insertion, and subsequently they compete. Therefore, Pt(100)
is the best candidate for converting trans-alkenes to cis and
hence to maximize the preferred isomer.

Figure 5. Desorption and hydrogenation energies of 1-butene (dark
yellow), cis-2-butene (orange), trans-2-butene (wine), and isobutene
(cyan) on (a) Ni, (b) Pd, and (c) Pt surfaces. Legend: triangles
represent (111) surfaces, squares represent (100) surfaces, empty
symbols represent low H coverage, and filled symbols represent high
H coverage.

4. DISCUSSION
Brønsted−Evans−Polanyi (BEP) relationships15,48 have been
developed between different variables studied and are
represented in Figure S7 of the Supporting Information.
Although it is true that there is an approximately linear trend
between the variables, unfortunately it is not enough precise
due to the dispersion of points and this explains why some
steps require more energy than others as they follow the
thermodynamic request. To understand the resilience of transalkenes in these processes, a set of plots are represented in
Figure 5. They contain the competing steps: on the x-axis the
desorption of the alkenes from the surfaces under different
conditions is presented while the y axis presents the lowest
barrier for the hydrogenation of the corresponding alkene.
Both terms are affected by zero-point vibrational contributions
and entropic ones, but for simplicity they are considered to
cancel here. This is equivalent to the approaches of
thermodynamic selectivity30,82 and the competition between
over hydrogenation and desorption.83−85
The 1:1 rule means that desorption and hydrogenation are
equally likely. Therefore, points below the 1:1 line will be
further hydrogenated while those above the line indicate that
desorption is preferred. The results are crucial to understand
the key role of the surface hydrogen content on the selectivity
of the process. At low hydrogen contents, hydrogenation is not
surface sensitive and none of the metals and orientations
inspected could allow a selective hydrogenation process.
However, at high hydrogen content the behavior of the
different metals diverges, and the analysis needs to be
performed in a more detailed manner. For Ni, the points are
clustered in a very small energy and reactivity region

presenting very minor differences on (111) and (100) surfaces,
so the structure sensitivity found is very small. In stark
contrast, Pd and Pt have structure sensitivity and show
dispersion on the patterns for desorption and reactivity
depending on the surface openness. The structures corresponding to the Pd(100) surface cluster very close to 1:1 rule,
but this is slightly less true for Pd(111). As alkenes are very
weakly bound to H-rich Pd(111) (around −0.3 eV), the
reaction would mainly go through the open (100) surface. On
the contrary, the situation for Pt is clearer. The butenes on the
close Pt(111) surface are well aligned (not clustered) but
located above the 1:1 rule, and therefore, susceptible to desorb,
while on the Pt(100) surface three of the alkenes are close in
energy and 1:1 rule, and one (isobutene) is separated from
these tendencies, resulting to be less reactive.
In summary, the easiest descriptor for semi-hydrogenation,
the thermodynamic selectivity, might be employed in the low
hydrogen coverage regime but selectivity towards different
reactants (cis, trans or terminal) only appears at high hydrogen
coverage and only for some surface orientations (structure
sensitivity) of some metals. For Ni no significant structure
sensitivity exists. Low coverage leads to structure insensitivity
for Pd, but at high coverage sensitivity appears (100) surfaces
being more active than (111). For these, the terminal alkenes
would react first, and the second to be adsorbed would be the
cis conformations. This explains while trans are the most
resilient and the only ones left once hydrogenation process
occurs. On Pt(100) orientation, the ratio of trans would be
smaller than on the Pd(100) facet.
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5. CONCLUSIONS
We have employed density functional theory on slab models to
ascertain the causes of the resilience of trans-alkenes in
hydrogenation processes. To this end, two kinds of models at
low and high hydrogen coverage have been investigated on the
most common hydrogenation metals: Ni, Pd, and Pt in the two
most common orientations (111) and (100). We have found
that the adsorption energies of alkynes and alkenes are the
strong functions of the hydrogen coverage, and indeed organic
species adsorption decreases by roughly 2/3 when dense H
layers are present. No structure sensitivity is found in the lean
H regime for any of the metals explored and the reason is that
neither the electronic density nor the adsorption site is
compromised. As it can be seen, the stronger the bond the
larger the hydrogenation step in agreement with the
Brønsted−Evans−Polanyi rules. Indeed, BEP rules appear for
the dehydrogenation steps in agreement with previous
observations. However, when hydrogen is present, structure
sensitivity appears for Pd and Pt and as the organic molecules
are weakly adsorbed for the (111) surface the reactions will
preferentially occur on the (100) areas of the catalyst.
Moreover, on Pd(100) at high coverage terminal and cisalkenes would react prior to trans conformations, and only on
Pt, where the cis−trans proportion would be slightly better.
Our work represents the first full set of thermodynamic and
kinetic parameters for C4 alkynes and alkene hydrogenations.
Such systematic studies pave the way to the understanding of
complexity in catalysis as they incorporate surface sensitivity
and coverage terms and can indicate potential developments to
increase the selectivity towards desired products avoiding those
that are potentially harmful.

■

computer resources at Caesaraugusta and LaPalma, and the
technical support provided by BIFI and IAC respectively
(RES-ActivityID QCM-2017-3-0015 and QCM-2018-1-0017).
D.C. thanks the COFUND Marie Curie program (Grant No.
2014-51588) and MINECO for support through Severo
Ochoa Excellence Accreditation (SEV-2013-0319).

■

ASSOCIATED CONTENT

S
* Supporting Information

The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpcc.8b06880.
Examples of H atoms involved in an H-rich hydrogenation and of a reaction profile as a function of the H
coverage and by including ZPVE corrections (Figures
S1, S2 and S3, respectively); complete reaction profiles
of 1-butyne semi-hydrogenation (Figure S4), 1-butene
and isobutene hydrogenations (Figures S5 and S6,
respectively), and BEP relations (Figure S7); finally, the
list of reaction energies, energy barriers, and imaginary
frequencies (Table S1) (PDF).

■

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AUTHOR INFORMATION

Corresponding Author

*E-mail: nlopez@iciq.es. Tel: +34 977920237.
ORCID

Javier Navarro-Ruiz: 0000-0002-3604-9338
Núria López: 0000-0001-9150-5941
Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS
This project has received funding from the European Union’s
Horizon 2020 research and innovation program under grant
agreement No. 686163. The authors acknowledge the
MINECO (Grant No. CTQ2015-68770-R) for financial
support. The authors also thankfully acknowledge the
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