This is the pre-peer reviewed version of the following article: Angew. Chem.
Int. Ed. 2017, 56, 10755 –10760, which has been published in final form at
https://onlinelibrary.wiley.com/doi/10.1002/cctc.201601134. This article
DOI: 10.1002/cctc.201601134
Full Papers
may be used for non-commercial purposes in accordance with Wiley Terms
and Conditions for Use of Self-Archived Versions.

Electrochemical Effects at Surfactant–Platinum
Nanoparticle Interfaces Boost Catalytic Performance
Neyvis Almora-Barrios,[a] Gianvito Vilÿ,[b] Miquel Garcia-Ratÿs,[a] Javier Pÿrez-RamÌrez,*[b] and
NÇria LÛpez*[a]
Nanoparticles are applied in a variety of industrially relevant
transformations as heterogeneous catalysts typically with the
help of an external force (pressure, temperature, or voltage) to
steer the chemistry. The modification of platinum nanoparticles
by a phosphate–amino surfactant enables catalysis without external energy supply in the hydrogenation of nitrobenzene to
aniline. This can be attributed to the complex surfactant/metal
interface which is able to split hydrogen into protons and elec-

trons. The subsequent hydrogenation process mimics the electrochemical reduction described by Haber. The surfactant decorated Pt catalyst is two orders of magnitude more active than
the state-of-the-art Pb-poisoned Pt catalyst. Our study provides
a new approach to understand the functionality of emerging
catalytic systems and can be applied to design new materials
with optimal interfaces.

Introduction
ic activity through the formation of hot H atoms.[2] Adsorbates
can modify the catalytic response of nanoparticles. Recent experiments for the direct peroxide synthesis on Pd nanoparticles, 0.7–7 nm average diameters, have found experimental indications of heterolytic H2 dissociation if acids and halides are
present.[3]
To better control their sizes and shapes, nanoparticles are
often synthesized with the help of ligands.[4] Ligand-modified
nanoparticles can be synthesized with ionic liquids,[5] polymers
(e.g., poly(vinylpyrrolidone) or poly(vinyl alcohol)),[6] thiols,[7]
phosphines,[8] N-basis, or surfactants.[9] Thus, the variety of ligands that can be used is very large. It has been established
that these ligand-modified nanoparticles exhibit properties
that are different from those of conventional bare metals,
owing to the complex and chemically rich inorganic/organic
interface.[2a, 10] Ligands can 1) modify the ensemble size on the
catalytically active surface,[7] 2) reorient reactants or products,[11] 3) change the acidic properties in the metal/surfactant/
water interface,[12] and 4) alter the electronic structure of
metal.[9] The latter was described to be the main responsible
for the selectivity of Pt nanowires ( ⇡ 1.1 nm in diameter) decorated with ethylenediamine in the partial hydrogenation of nitroarenes to hydroxylamine.[9]
Surfactants can also act as ligands but differently from polymers, phosphines, or N-basis, they are constituted by anionic
and cationic units. This confers an extra degree of freedom
(charge separation and electric field)[11e] in the materials design
that might affect the activity and the selectivity of the samples
if used as catalysts. The recent catalytic material developed by
BASF featuring supported Pt (or Pd) nanoparticles decorated
with the hexadecyl(2-hydroxyethyl) dimethylammonium dihydrogenphosphate (HHDMA) surfactant offers a unique platform
to assess interface effects, also considering that these materials
are the first to successfully reach the market and are currently

The conversion of a reactant into a valuable product often requires a catalyst and an additional force in the form of electrons (electrocatalysis), photons (photocatalysis), temperature,
or pressure (traditional heterogeneous catalysis) to help the kinetics reaching a reasonable rate. Any of these stimuli imply
that an external energy source needs to be applied. In the
present work, we have identified that the modification of small
platinum nanoparticles by phosphate–amino surfactants enables an intrinsic self-powered electrochemical nanoarchitecture
with a pronounced catalytic promotion diminishing the
external energy consumption.
Metal nanoparticles are well-established catalytic species. If
their sizes are very small (typically below 2.5 nm),[1] their electronic structure can depart from that of the bulk material
through electron confinement effects. According to Somorjai
and co-workers, the altered electronic structure of very small
Pt nanoparticles could be responsible for the enhanced catalyt-

[a] Dr. N. Almora-Barrios, Dr. M. Garcia-Ratÿs, Prof. N. LÛpez
Institute of Chemical Research of Catalonia (ICIQ)
The Barcelona Institute of Science and Technology
¨
Av. Paısos Catalans 16
43007 Tarragona (Spain)
E-mail: nlopez@iciq.es
[b] Dr. G. Vilÿ, Prof. J. Pÿrez-RamÌrez
Institute for Chemical and Bioengineering
Department of Chemistry and Applied Biosciences
ETH Zurich
Vladimir-Prelog-Weg 1
8093 Zurich (Switzerland)
E-mail: jpr@chem.ethz.ch
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
cctc.201601134.
This manuscript is part of a Special Issue to celebrate the 50th annual
meeting of the German Catalysis Society.

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used to catalyze the hydrogenation of alkynes and nitroarenes.[11] By comparing this new catalyst with traditional materials in the hydrogenation of nitroarenes, we have observed
a two-order-of-magnitude increase in the activity, which can
only be attributed to the nature of the catalyst.
The surfactant–Pt-nanoparticle-mediated hydrogenation of
nitrobenzene to aniline was studied through an approach
combining experimental and theoretical methods. Special attention was paid to the description of the reaction network.
Our results suggest that the combined effect of the nanoparticle curvature, the electron confinement, as well as the high
density of electric field lines enable a catalytic process with no
external energy supply.

the structure (Figure 1 d,e). The Pb-poisoned Pt (Pt–Lindlar) catalyst, on the other hand, is characterized by spherical particles
of approximately 7–8 nm. This result is in agreement with results published in the literature.[11e,f] Since the Pt nanoparticle
size can have a significant influence on the nitroarene hydrogenation performance,[14] we opted to express the reaction
rates as turnover frequency (moles of obtained product per
moles of accessible metal and unit of time), using dispersion
data obtained by CO chemisorption and transmission electron
microscopy.
The catalysts were applied in the hydrogenation of nitrobenzene to aniline, an important reaction for the manufacture of
polymers, agrochemicals, and pharmaceuticals.[15] A continuous
microreactor was used for the materials evaluation. The results
of the catalytic tests (Figure 2) show that nitrobenzene hydrogenation on the Pt–HHDMA-decorated nanoparticles proceeds
in a broad range of temperature and pressure (including 303 K
and 1 bar), with a two orders of magnitude higher activity
than that of the reference Pt–Lindlar.[13] In Figure 2, the activity
is shown per mole of accessible surface metal. Thus, the different reactivity of the two materials cannot be attributed to the
different metal concentration and dispersion. Remarkably, an
increase of the external forces over Pt–Lindlar of 70 K and
20 bar are not sufficient to attain the same activity of Pt–
HHDMA. Hence, the difference between the two catalysts
arises from the unique reactivity intrinsic to the complex interface of Pt–HHDMA. These results are not due to transient behavior and were confirmed for several hours of steady-state
operation. Catalytic tests for the hydrogenation of chloronitrobenzene to chloronitroaniline have remarked the absence of

Results
To investigate the role of the modification of Pt with the
HHDMA surfactant, the Pt–HHDMA catalyst was compared
with the Pb-poisoned Pt catalyst.[13] The complete set of textural, compositional, and structural characterizations of the two
materials is detailed both in the Experimental Section and in
the Supporting Information (Section 1). The micrographs and
particle size distribution of the hybrid Pt-HHDMA nanoparticles
over the carbon support are shown in Figure 1 a,b. The particles of this material are spherical and have an average diameter of approximately 1.7 nm (Figure 1 c).
From the combination of different experimental and computational characterization methods (Supporting Information), it
appears that the Pt nanoparticles are decorated by the H2PO4ˇ
group, and cationic, aliphatic, quaternary amino tails protect

Figure 1. a) Scanning electron microscopy, b) high-angle annular dark-field scanning transmission electron microscopy, and c) metal size distribution of the PtHHDMA catalyst. Reproduced with permission from Ref. [11f], Copyright 2015 American Chemical Society. d) Model representation of the structure of a single
Pt nanoparticle with the full capping layer. e) Calculated structural model showing the preferential adsorption of phosphate groups on the surface of the
1.7 nm diameter Pt nanoparticle, and the external ammonia shell, Pt260([N(CH3)3CH2OH]H2PO4)57. Dark blue spheres represent metals, red oxygen, orange phosphorus, grey carbon, white hydrogen, and pale blue nitrogen. f) Molecular electrostatic potential mapped onto a 0.02 a.u. charge density isosurface for the
surfactant channel. Red (blue) values account for attractive (repulsive) interactions, respectively. The darker the color the more intense the interaction with
a positive charge.

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the amine product on Pt electrodes at an external potential of
U = ˇ0.51 eV with respect to the reversible hydrogen
electrode, RHE (Scheme 1).
For nitroarene hydrogenation, water is stoichiometrically
generated in the catalytic cycle. However, on bare and alloyed
Pt catalysts, water is weakly adsorbed (ˇ0.22 eV) and easily
leaves the surface. On the hybrid Pt–HHDMA interface, the molecularly adsorbed water is further stabilized with an adsorption energy of ˇ1.20 eV, owing to electrostatic and H-bond interactions. Notice that water is then not directly bonded to the
Pt atoms but rather between hydrogenphosphate anions on
the surface. The distance between the oxygen atom of the
water molecule and the Pt surface atoms is approximately
3.37 ä (see Figure S5). We have also studied an alternative
model in which the water molecule is dissociated on the Pt–
HHDMA, but the system is not as stable as that with the
molecular adsorbed water.
The persistent presence of water molecule transforms the interface in a complex environment constituted by the metal
phase, the electric field caused by the ions, and the ionic
media (water–phosphates), leading to a network able to transport protons. As we will see in the following this has a large
effect on the way molecular hydrogen can be activated.
Hydrogen activation was investigated through DFT calculations (RPBE-D2)[18] on the Pt–HHDMA nanoparticles, 1.7 nm in
diameter, modified by phosphate groups and water, and externally shielded by the quaternary ammonia surfactant tails (Figure 1 e) stoichiometry Pt260 ([N(CH3)3CH2OH]H2PO4)57 (half this
model for the transition-state searches). Notice that the computational box volume was 40 î 40 î 40 ä3, close to the limits
of what is feasible with the present technical approach. Technical details are presented both in the Experimental Section and
in the Supporting Information, Section 2.
On the Pt–HHDMA, molecular hydrogen can be activated in
two different manners. The first one, remainder of the HP
mechanism, follows the homolytic splitting of the HˇH bond,
which leads to two final hydrogen atoms adsorbed on the
metallic surface (H2 + 2*!2 H*, Figure 3).[16] Alternatively, a heterolytic splitting of H2 can take place in the form of a dissociative Heyrovsky-like mechanism (H2 + *!H* + H + + eˇ),[19] which
leads to a hydrogen on the surface, a proton at the polarizable
interface formed by the surfactant H2PO4ˇ anionic head and
the trapped water molecules, and an electron transferred to
the metal (Figure 3). Both splitting pathways occur on the Pt–
HHDMA surface without a barrier (Figure 3). The most stable
final configuration is the formation of the proton–electron pair
(by ˇ0.26 eV) (Figure 3, Table S4). Therefore, hydrogen activation on the Pt–HHDMA containing water results in the separation of hydrogen into electrons, which are stored in the metal
phase, and protons, which are shared between the surfactant
and adsorbed water.

Figure 2. a) Conversion of nitrobenzene to aniline as a function of the hydrogen pressure and temperature over Pt–HHDMA (top) and Pt–Lindlar (PtPb/CaCO3) (bottom). b) Turnover frequency (in logarithm scale) at 323 K
temperature and 1 bar hydrogen pressure. The catalytic results are adapted
with permission from Ref. [11f]. Copyright 2015 American Chemical Society.

any drop in nitroarene conversion and aniline selectivity at
303 K and 1 bar for more than 10 h on stream;[11f] besides, elemental analyses of the catalyst before and after hydrogenation
have verified the absence of metal and HHDMA leaching.
From a mechanistic viewpoint, heterogeneously catalyzed
hydrogenations on metals are often interpreted through the
Horiuti–Polanyi mechanism, (HP),[16] comprising homolytic dissociation of molecular hydrogen on the metal, adsorption of
the organic reactant, and sequential hydrogen transfers to the
adsorbed organic moiety to yield the desired product
(Scheme 1). The formed product easily desorbs, and in the

Scheme 1. Hydrogenation of nitrobenzene following the Horiuti–Polanyi[16]
and electrochemical (Haber)[17] mechanisms displaying the external forces
required.

case of the ligand-modified catalysts it desorbs through the
ligand chains, which form channels of approximately 8 ä in diameter,[11e] leaving the active site available for the next catalytic
cycle. This mechanism holds for the semihydrogenation of alkynes on Pt, Pd, Pt–Lindlar, and Pd–HHDMA[11e] and for the hydrogenation of nitroarenes on Pt and Pt–Lindlar.[11f] In 1900,
Haber showed that nitroarene hydrogenations[17] in electrochemical environments occur through a different mechanism,
which involves the sequential transfer of electrons supplied
from the metal and protons available in the solution. This electron/proton transfer to the adsorbed organic moiety leads to
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Discussion
The electrochemical effects can be rationalized through
a Born–Haber cycle. For the bare Pt surface, this cycle includes
the following steps:
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MEP map thus illustrates the potential “felt” by the molecule
on its way to the active site on the surface. First, the aliphatic
barrier created by the ligand needs to be crossed but then,
once the surface is reached, there is a large difference if there
is water (and thus protons) or not (and then only atomic H).
For the clean Pt–HHDMA system, the terminal P–O moieties
and the quaternary ammonia head present red (attractive) and
blue (repulsive) areas, respectively (Figure S6). If water and hydrogen are trapped, Pt–HHDMA–water-H + , the MEP is much
more corrugated, with the electron basins (red) located at the
metal surface (Figure 1 f).
The large charge density available on the metal of the Pt–
HHDMA–water-H + catalyst enhances nitrobenzene adsorption,
ˇ0.65 eV. The electron transfer towards the adsorbate results
in the increase of the N–O distance from 1.233 to 1.312 ä and
the molecular charge (Bader) of the molecule from ˇ0.43 to
ˇ0.77 j eˇ j . Thus, adsorption is much stronger than that for
Pt–Lindlar (ˇ0.31 eV) surfaces (Table S5). From this point on,
the reduction of nitrobenzene occurs as follows: electrons are
collected from the charged nanoparticle and the protons are
added to the oxygen atoms through the water/phosphate interfacial network that acts as proton shuttle. The mechanism
consists in electron–proton transfer (ECT) steps.[23] The protons
are transferred with very low energy barriers (< 0.3 eV for the
first step, Table S7). The process mimics the electrochemical
processes in which electrons and protons are transferred sequentially. Recently, Zheng et al.[9] found that Pt nanowires
coated with ethylenediamine exhibit selectivity for the production of hydroxylamines. In our case, hydroxylamine is an intermediate species and aniline the only product (see Supporting
Information Section 3.7.2 and Figure S9). One possible explanation is that in the presence of water/phosphate interfaces the
reduction of hydroxylamine is enhanced because a protontransfer occurs to form water while the electron transfer occurs
to form the C6H5ˇNH species.
The enhanced activity observed in Figure 2 can be traced
back to the rates (Supporting Information Section 3.8). The first
H transfer (either as H in Pt–Lindlar or as H + in Pt–HHDMA) to
adsorbed nitrobenzene controls the rate for hydrogenation
[Eq. (1)]:

Figure 3. Reaction paths for the dissociation of H2 and the first hydrogenation step of nitrobenzene on Pt–Lindlar (orange) and coated HHDMA nanoparticle (wine), Pt–HHDMA with water for both the Langmuir–Hinshelwood
(dotted) and the Heyrovsky (continuous line) processes. The insets represent
the initial state structure, H + –eˇ separation, nitrobenzene adsorption, and
proton transfer to the nitro group. Same color code as in Figure 1. The intermediates in the hydrogenation process are compared to pure Pt (see Supporting Information, Section 3.7.1 and 3.7.2). A movie with the full reaction
network is uploaded as Supporting Information.

(1) Hydrogen dissociation:
1/2 H2 !H
DE = 2.3 eV[20]
(2) Hydrogen charge separation:
H!H + + eˇ
IP = 13.6 eV[20]
(3) Proton solvation:
H + + water!(H + )w Esolv = ˇ10.9 eV[21]
(4) Electron transfer to the metal:
eˇ + Pt!(eˇ)Pt
F(Pt) = 5.9 eV[20]
For which the reaction energies, DE; ionization potential, IP;
solvation energies, Esolv ; and metal work function, F, are defined. By combining steps (1)–(4), the total energy of the process is close to zero, in good agreement with previous results
in the literature.[22] For the Pt–HHDMA–water, however, the situation is different. The electron transfer to the surfactant-decorated metal is not effective because the electron affinity contribution (i.e., placing an extra electron in the nanoparticle) is
not so favorable. Furthermore, owing to the presence of an
extra term arising from the generated electric field,
Equation (4) is replaced by:

r ⇡ k 1st qnitrobenzene qH

(4’) Electron transfer to the nanoparticle:
eˇ + Pt–HHDMA!(eˇ)Pt—HHDMA EA Pt–HHDMA = ˇ0.3 eV
(4’’) Electric field contribution:
(eˇ)Pt–HHDMA + HHDMA
ECoulombÅˇ4 eV

where k1st is the kinetic coefficient for the first hydrogenation
step, and q the coverage of nitrobenzene and hydrogen, respectively. The hydrogen coverage is close to one as the adsorption barrier is below that of the reactants and not competitive and that of nitrobenzene can be expressed through
a Langmuir isotherm. The adsorption of nitrobenzene is improved in the Pt–HHDMA surface and almost doubles that of
the Pt–Lindlar system. On the other hand, the kinetic coefficient for the first hydrogen transfer, k1st, is calculated to be approximately 300 times larger for the H + transfer in Pt–HHDMA
than for hydrogen transfer on Pt–Lindlar. The combination of
both terms results in the two orders of magnitude activity enhancement observed in Figure 2 b. Notice that although water
is adsorbed at the interface, it does not block potential active

For which EAPt–HHDMA is the energy gained if an electron is included on the decorated nanoparticle and ECoulomb the electrostatic contribution between the electron in the metal and the
surfactant. Therefore, the energy needed to split hydrogen
into protons and electrons is compensated by the electron
transfer to the metal and the electric field existing at the interface. The electronic state of the Pt–HHDMA catalyst with
a water molecule after eˇ–H + charge separation can be described through a molecular electrostatic potential (MEP) map
(see Figure 1 f and Supporting Information Section 3.3). The
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poles (see Supporting Information Section 3.9). Compared to
the experiments on clean nanoparticles,[2b] on which the activity amplification was a three-fold increase for nanoparticles
with diameters between 4.5–1.7 nm, the combined effect
provides two orders enhancement.

Conclusions
We have found that a new catalytic formulation based on surfactant Pt nanoparticles behaves as an electrochemical system,
splitting H2 into protons and electrons. The electrons stored in
the nanoparticle are placed at high chemical potentials and
favor nitrobenzene adsorption by charge transfer. Then electron–proton transfer occurs easily. The internal force generated
at the interface of the hybrid system mimics the external potential employed in electrochemical environments without external stimuli. The performance of these hybrid nanoarchitectures breaks linear-scaling relationships[25] and sets up a new,
alternative mechanism that couples intrinsically generated
electrochemical contributions and traditional heterogeneous
catalysis, leading to a reduction in external energy
consumption.

Figure 4. Confinement and electric field effects in the electron affinity of the
different Pt structures. Left, electron affinities (circle) with respect to the
nanoparticle size. On the right, the relative alignment of the electrons in the
metal systems (column) are compared to the LUMO state of nitrobenzene
(marked as EA) to highlight if electron transfer from the metal structures to
the reactant is possible. 1) Coated HHDMA nanoparticle and 2) slab Pt structures, 3) bare nanoparticle and 4) slab configurations.

Experimental Section
Experimental details

sites for nitrobenzene adsorption because it is located in the
surroundings of the hydrogenphosphate anions.
To identify the origin of the electrochemical path in the Pt–
HHDMA–water nanostructures, we have analyzed the chemical
potential at which electrons are placed on the different Pt systems (Figure 4). The value of the electron affinity for the Pt-systems is crucial as the binding energy of nitrobenzene is dominated by the ability to inject electrons towards the LUMO
(placed at 1 eV). On the Pt(111) surface, electrons are located
at the electron affinity value, about 5.45 eV (see Supporting Information, Table S3). Reducing the size of the metal nanoparticle to 1.7 nm leads to an electron affinity (as we are storing
electrons in the nanoparticle this is the key parameter) of
2.76 eV.[24] Instead, if the Pt(111) surface is coated with the surfactant, the electron affinity for the infinitely decorated surface,
3.14 eV, decreases to 0.27 eV for the confined particle. Thus,
close enough to the potential used by Haber, 0.51 eV. Only in
the last case, electron injection towards nitrobenzene is possible. Notice that there is an apparent contradiction since hydrogen activation is rather exothermic (see Figure 3, the Heyrovsky processes in continuous line) but the electrons are placed
at high chemical potential (Figure 4). However, the total
system is stable thanks to the electrostatics between the
different units.
The origin of this important shift in the chemical potential
of the electrons can be traced back to the combined effect of:
1) electron confinement; 2) the high density of electric field
lines generated by the surfactant; and 3) the large curvature of
the small Pt nanoparticles, which is precisely the case of Pt
synthesized by HHDMA (Figure 1 a–c). This dependence is
roughly rˇ3 as for the interaction of a charge stored with diChemCatChem 2017, 9, 604 – 609

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Pt–HHDMA/C (0.8 wt.% Pt; NanoSelect Pt 100, Strem Chemicals,
ref: 78-1630), Pd–HHDMA/C (0.5 wt.% Pd; NanoSelect LF 100,
Strem Chemicals, ref: 46–1710) and Pd–Pb/CaCO3 (5 wt.% Pd and
3 wt.% Pb; Alfa Aesar, ref: 043172) were used as received. Pt–Pb/
CaCO3 (5 wt.% Pd and 1 wt.% Pb) was prepared following a published method.[26] The characterization of the catalysts is detailed in
the Supporting Information, Section 1. The catalysts were evaluated in the three-phase hydrogenation of nitrobenzene, using a fully
automated continuous-flow flooded-bed microreactor (ThalesNano
H-Cube Pro),[11e,f] at the following conditions: Wcat = 100 mg,
FG(H2) = 18 cm3 minˇ1, and FL(nitroarene + THF) = 3 cm3 minˇ1.

Computational details
A combination of computational techniques, ab initio Molecular
Dynamics, and quantum-mechanical methods based on the density
functional theory (DFT) were used within the Vienna ab initio simulation package (VASP).[17a, b] Total energies and electron densities
were computed with Perdew-Burke-Ernzerhof (RPBE) functional[17c]
complemented by the dispersion D2 term as presented by Grimme[17d] with our refitted values for the metals.[17e] The projected
augmented wave (PAW) method was adopted to represent core
electrons.[27] The kinetic energy cutoff for the plane-wave basis set
expansion was set to 450 eV. A 3 î 3 î 1 k-point mesh for the slab
models, and a G-point centered mesh for cluster models were
used to sample the reciprocal space.[28]
With regard to the metal surfaces, we have adopted different strategies. The slab model represents close-packed (111) face of
metals, containing five atomic layers and a p(4 î 4) supercell with
a vacuum gap of approximately 20 ä. The three topmost layers on
one side of the slab were optimized and dipole corrections were
used in the z-direction. For Pt–Lindlar, the continuum slab model
was employed because the average diameter of the Pt–Pb nano-

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particles in the system was around 8 nm. Four platinum atoms in
the first layer of Pt(111) were substituted with lead with a 0.25 ML
coverage (Pt3Pb(111)). The Pt nanoparticle (PtNP) is a cuboctahedron containing 260 Pt atoms with a diameter of 1.7 nm (see Figure S3). For the calculation of the PtNP properties, the system was
modeled as a cubic box with dimensions of 30 î 30 î 30 ä3 and monopole corrections were used for charged systems. A summary of
the details for the calculation of electron affinity (EA) for all the
simulated systems is reported in Supporting Information, Table S2.

[8]

[9]
[10]

PtNP and Pt(111) models were capped with a number of
[N(CH3)3CH2OH]H2PO4 molecules in agreement with the experimental
concentrations.
The
Pt260
cluster
with
the
57
([N(CH3)3CH2OH]H2PO4) adsorbates was pre-equilibrated through
ab initio Molecular Dynamics at 303 K for 1 ps in a cubic simulation
cell with a volume of 40 î 40 î 40 ä3. The simulation was performed
in the NVT ensemble using VASP code. The Nosÿ–Hoover thermostat was used to control the temperature with a time step of 1 fs
and a cutoff energy of 450 eV. The configuration was equilibrated
until the total energy of the system fluctuated around a value with
an
amplitude
of
0.1 eV.
These
structures;
PtNP–
[N(CH3)3CH2OH]H2PO4, and Pt(111)–[N(CH3)3CH2OH]H2PO4, were
then taken as initial states for the study of adsorption and reaction.
For the reaction mechanism, a half of this nanoparticle (stoichiometry Pt178) and 32 units of [N(CH3)3CH2OH]H2PO4 were taken to
reduce the computational cost with a box volume of 40 î 30 î
40 ä3. The climbing image nudged elastic band (CI-NEB) algorithm[29] was used to find the transition states of the elementary
steps involved in the dissociation of H2 and the first H transfer to
the nitrobenzene. Finally, the MEP[30] has been calculated with
VASP and mapped onto a charge density isosurface using the
Visual Molecular Dynamics v.1.8.7 (VMD) software.[31] Our coordinates of all structures are already available through our repository
platform ioChem-BD.org[32] see DOI: 10.19061/iochem-bd-1-9.

[11]

[12]
[13]
[14]
[15]
[16]
[17]
[18]

Acknowledgements

[19]
[20]

Support from BSC-RES, ICIQ Foundation, MINECO (CTQ201568770-R and “Ayuda formaciÛn Post-doctoral” Fellowship
(N.A.B.)), and ETH Zurich are acknowledged.

[21]
[22]
[23]

Keywords: density functional calculations · hydrogenation ·
interfaces · platinum · surfactants

[24]
[25]

[1] a) L. Li, F. Abild-Pedersen, J. Greeley, J. K. Nørskov, J. Phys. Chem. Lett.
2015, 6, 3797 – 3801; b) L. Li, A. H. Larsen, N. A. Romero, V. A. Morozov,
C. Glinsvad, F. Abild-Pedersen, J. Greeley, K. W. Jacobsen, J. K. Norskov, J.
Phys. Chem. Lett. 2013, 4, 222 – 226.
[2] a) C. A. Witham, W. Huang, C.-K. Tsung, J. N. Kuhn, G. A. Somorjai, F. D.
Toste, Nat. Chem. 2010, 2, 36 – 41; b) H. Lee, I. I. Nedrygailov, C. Lee,
G. A. Somorjai, J. Y. Park, Angew. Chem. Int. Ed. 2015, 54, 2340 – 2344;
Angew. Chem. 2015, 127, 2370 – 2374; c) J. Y. Park, H. Lee, J. R. Renzas, Y.
Zhang, G. A. Somorjai, Nano Lett. 2008, 8, 2388 – 2392.
[3] N. M. Wilson, D. W. Flaherty, J. Am. Chem. Soc. 2016, 138, 574 – 586.
[4] N. Almora-Barrios, G. Novell-Leruth, P. Whiting, L. M. Liz-Marzµn, N.
LÛpez, Nano Lett. 2014, 14, 871 – 875.
[5] a) S. W. Boettcher, S. A. Berg, M. Schierhorn, N. C. Strandwitz, M. C. Lonergan, G. D. Stucky, Nano Lett. 2008, 8, 3404 – 3408; b) V. Cimpeanu, M.
ˇ
Kocevar, V. I. Parvulescu, W. Leitner, Angew. Chem. Int. Ed. 2009, 48,
1085 – 1088; Angew. Chem. 2009, 121, 1105 – 1108.
[6] F. Cµrdenas-Lizana, C. Berguerand, I. Yuranov, L. Kiwi-Minsker, J. Catal.
2013, 301, 103 – 111.
[7] a) S. T. Marshall, M. O’Brien, B. Oetter, A. Corpuz, R. M. Richards, D. K.
Schwartz, J. W. Medlin, Nat. Mater. 2010, 9, 853 – 858; b) D. Albani, G.

ChemCatChem 2017, 9, 604 – 609

www.chemcatchem.org

[26]

[27]
[28]
[29]
[30]

[31]
[32]

Vilÿ, S. Mitchell, P. T. Witte, N. Almora-Barrios, R. Verel, N. LÛpez, J. PÿrezRamÌrez, Catal. Sci. Technol. 2016, 6, 1621 – 1631.
I. Cano, M. A. Huertos, A. M. Chapman, G. Buntkowsky, T. Gutmann, P. B.
Groszewicz, P. W. N. M. van Leeuwen, J. Am. Chem. Soc. 2015, 137,
7718 – 7727.
G. Chen, C. Xu, X. Huang, J. Ye, L. Gu, G. Li, Z. Tang, B. Wu, H. Yang, Z.
Zhao, Z. Zhou, G. Fu, N. Zheng, Nat. Mater. 2016, 15, 564 – 569.
a) C. Wang, R. Ciganda, L. Salmon, D. Gregurec, J. Irigoyen, S. Moya, J.
Ruiz, D. Astruc, Angew. Chem. Int. Ed. 2016, 55, 3091 – 3095; Angew.
Chem. 2016, 128, 3143 – 3147; b) P. T. Witte, M. De Groen, R. M. De Rooij,
P. Bakermans, H. G. Donkervoort, P. H. Berben, J. W. Geus in Studies in
Surf. Sci. and Catalysis, Vol. 175, (Eds.: E. M. Gaigneaux, M. Devillers, S.
Hermans, P. A. Jacobs, J. A. Martens, P. Ruiz), Elsevier, Amsterdam, 2010,
pp. 135 – 143.
a) P. T. Witte, S. Boland, F. Kirby, R. vanMaanen, B. F. Bleeker, D. A. M.
deWinter, J. A. Post, J. W. Geus, P. H. Berben, ChemCatChem 2013, 5,
582 – 587; b) P. T. Witte, P. H. Berben, S. Boland, E. H. Boymans, D. Vogt,
J. W. Geus, J. G. Donkervoort, Top. Catal. 2012, 55, 505 – 511; c) S. W. T.
Price, K. Geraki, K. Ignatyev, P. T. Witte, A. M. Beale, J. F. W. Mosselmans,
Angew. Chem. Int. Ed. 2015, 54, 9886 – 9889; Angew. Chem. 2015, 127,
10024 – 10027; d) G. Vilÿ, D. Albani, N. Almora-Barrios, N. LÛpez, J. PÿrezRamÌrez, ChemCatChem 2016, 8, 21 – 33; e) G. Vilÿ, N. Almora-Barrios, S.
Mitchell, N. LÛpez, J. Pÿrez-RamÌrez, Chem. Eur. J. 2014, 20, 5926 – 5937;
f) G. Vilÿ, N. Almora-Barrios, N. LÛpez, J. Pÿrez-RamÌrez, ACS Catal. 2015,
5, 3767 – 3778.
D. Albani, Q. Li, G. Vilÿ, S. Mitchell, N. Almora-Barrios, P. T. Witte, N.
LÛpez, J. Pÿrez-RamÌrez, Green Chem. 2017, DOI:10.1039/C6GC02586B.
H. Lindlar, Helv. Chim. Acta 1952, 35, 446 – 450.
F. Zhao, Y. Ikushima, M. Arai, J. Catal. 2004, 224, 479 – 483.
a) A. Corma, P. Serna, Science 2006, 313, 332 – 334; b) H.-U. Blaser, H.
Steiner, M. Studer, ChemCatChem 2009, 1, 210 – 221.
I. Horiuti, M. Polanyi, Trans. Faraday Soc. 1934, 30, 1164 – 1172.
F. Haber, Angew. Chem. 1900, 13, 433 – 439.
a) G. Kresse, J. Furthm¸ller, Phys. Rev. B 1996, 54, 11169 – 11186; b) G.
Kresse, J. Furthm¸ller, Comput. Mater. Sci. 1996, 6, 15 – 50; c) B. Hammer,
L. B. Hansen, J. K. Nørskov, Phys. Rev. B 1999, 59, 7413 – 7421; d) S.
Grimme, J. Comput. Chem. 2006, 27, 1787 – 1799; e) N. Almora-Barrios,
G. Carchini, P. Blonski, N. Lopez, J. Chem. Theory Comput. 2014, 10,
5002 – 5009.
´
J. Heyrovsky, Recl. Trav. Chim. Pays-Bas 1927, 46, 582 – 585.
a) J. A. Kerr in CRC Handbook of Chemistry and Physics, 84th ed. (Ed: D. R.
Lide), CRC, Boca Raton, 2003, pp. 9 – 55; b) T. M. Miller, Ibidem, pp. 10 –
178; c) J. S. Miller, Ibidem, pp. 12 – 130.
Y. Marcus, J. Chem. Soc. Faraday Trans. 1991, 87, 2995 – 2999.
J. K. Nørskov, T. Bligaard, A. Logadottir, J. R. Kitchin, J. G. Chen, S. Pandelov, U. Stimming, J. Electrochem. Soc. 2005, 152, J23 – J26.
a) M. H. V. Huynh, T. J. Meyer, Chem. Rev. 2007, 107, 5004 – 5064;
b) M. T. M. Koper, Chem. Sci. 2013, 4, 2710 – 2723.
Y. Zhang, O. Pluchery, L. Caillard, A.-F. Lamic-Humblot, S. Casale, Y. J.
Chabal, M. Salmeron, Nano Lett. 2015, 15, 51 – 55.
J. K. Norskov, T. Bligaard, J. Rossmeisl, C. H. Christensen, Nat. Chem.
2009, 1, 37 – 46.
U. B. Siegrist, P. Baumeister, H. U. Blaser, M. Studer in Catalysis of Organic
Reactions, Vol. 75 (Ed.: F. E. Herkes), Marcel Dekker, New York, 1998,
pp. 207 – 219.
G. Kresse, D. Joubert, Phys. Rev. B 1999, 59, 1758 – 1775.
H. J. Monkhorst, J. D. Pack, Phys. Rev. B 1976, 13, 5188 – 5192.
G. Henkelman, B. P. Uberuaga, H. JÛnsson, J. Chem. Phys. 2000, 113,
9901 – 9904.
M. Orozco, F. J. Luque in Molecular Electrostatic Potentials: Concepts and
Applications, Vol. 3 (Eds: J. S. Murray, K. Sen), Elsevier, Amsterdam, 1996,
pp. 181 – 218.
W. Humphrey, A. Dalke, K. Schulten, J. Mol. Graphics 1996, 14, 33 – 38.
M. çlvarez-Moreno, C. de Graaf, N. LÛpez, F. Maseras, J. M. Poblet, C. Bo,
J. Chem. Inf. Model. 2015, 55, 95 – 103.

Manuscript received: September 11, 2016
Accepted Article published: October 4, 2016
Final Article published: November 29, 2016

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