Perspective
pubs.acs.org/JPCL
Tailoring the Catalytic Properties of Metal Nanoparticles via Support
Interactions
M. Ahmadi,† H. Mistry,†,‡ and B. Roldan Cuenya*,‡
†
Department of Physics, University of Central Florida, Orlando, Florida 32816, United States
Department of Physics, Ruhr-University Bochum, 44801 Bochum, Germany
‡
ABSTRACT: The development of new catalysts for energy
technology and environmental remediation requires a
thorough knowledge of how the physical and chemical
properties of a catalyst affect its reactivity. For supported
metal nanoparticles (NPs), such properties can include the
particle size, shape, composition, and chemical state, but a
critical parameter which must not be overlooked is the role of
the NP support. Here, we highlight the key mechanisms
behind support-induced enhancement in the catalytic properties of metal NPs. These include support-induced changes in
the NP morphology, stability, electronic structure, and
chemical state, as well as changes in the support due to the
NPs. Utilizing the support-dependent phenomena described in
this Perspective may allow significant breakthroughs in the design and tailoring of the catalytic activity and selectivity of metal
nanoparticles.
T
affecting the mechanical stability of the NPs,34 modifying the
NP morphology,24,35−37 inducing strain on the NP due to
lattice mismatch,38−40 changing the electronic structure via
charge transfer processes,41−44 and enabling spillover of
reactants and reaction intermediates from the support to the
NP and vice versa.23,45−49
The support can play an important role in controlling the
stability of NPs during a reaction because support materials
which strongly bind to the NPs can prevent sintering. In this
respect, the heterogeneity of possible support sites should be
considered, as for example the presence of defect sites or
adatoms, as well as other parameters such as surface
orientation, polarity, and oxidation state. Furthermore, the
adhesion energy of the NP on the support, along with its
epitaxial relationship, can play a controlling role in the
morphology of the NP. Likewise, the reaction environment is
also important to consider when discussing NP−support
interactions,37,50,51 since it will influence the chemical state of
the NPs and the support. Unique support-enhanced reaction
mechanisms such as spillover effects can also occur in different
reaction environments.
It is pertinent to remark here that the different NP−support
interactions described above correlate with each other, and in
some cases, it is not straightforward to distinguish their
individual influences. For example, the strain induced as a result
of lattice mismatch between the NP and the support, leading to
he enormous industrial and environmental applications of
nanostructured catalysts are driving scientists to the
rational development of new materials with enhanced activity
and tunable selectivity. A number of parameters such as size,
shape, surface composition, and oxidation state are known to
affect the reactivity of nanoparticle (NP) catalysts.1−7 For
instance, size-dependent changes in the electronic structure and
surface atomic coordination of nanostructured catalysts have
been shown to influence their catalytic performance.6,8−11
Moreover, due to the different binding energy of adsorbates on
crystalline facets with different orientations, the NP shape can
also influence the reactivity and selectivity of the catalysts.5,7,12,13 The NP morphology (size and shape) may also
affect the formation and stability of surface oxides during a
reaction, which can furthermore affect reactivity, because the
presence of certain oxide species may be favorable or
detrimental for a particular reaction.14 In addition, the
adsorption of reactive species on a NP under reaction
conditions can alter its morphology.14 Therefore, in order to
gain fundamental understanding of how different parameters
control the reactivity of nanocatalysts, these effects must be
deconvoluted. Furthermore, the study of model catalytic
systems under realistic reaction environments is critical.
Within this Perspective, attention will be paid to another
crucial parameter influencing catalytic performance, namely the
NP support interaction.2,15−20 NPs with the same nominal size
and analogous shape may display different reactivity when
deposited on different supports.19,21−23 The extent of the NP/
support interaction depends on the type,15,19,24,25 structure,26−28 and composition of the support16,17,29−33 and can
influence the catalytic activity in one of the following ways:
© 2016 American Chemical Society
Received: June 1, 2016
Accepted: August 17, 2016
Published: August 17, 2016
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can serve as strong anchoring sites for metal NPs. For example,
the higher adhesion energy of Ag NPs supported on reduced
CeO2 as compared to MgO(100), as determined by adsorption
calorimetry, has been assigned to their stronger bonding to
CeO2 defect sites. This observation may explain the higher
sintering resistance obtained for late transition metals deposited
on CeO2.55,56 In addition, oxygen vacancies have been shown
to stabilize Au atoms and small clusters both on TiO2 and
MgO.57,58
Tuning the support oxidation state and degree of reduction
in the case of reducible oxide substrates can be used to alter the
bonding of the NPs and consequently, their stability. For
example, in the case of Au and Pt on TiO2(110), density
functional theory (DFT) calculations show that oxygen
vacancies are the strongest binding sites.59,60 It was found
that excess electrons at the 5-fold coordinated Ti atoms can be
transferred to highly electronegative atoms like Au and Pt and
increase adsorption at these sites, while for less electronegative
atoms (i.e., Ag, Cu, Fe, Co, Ni and Pd) the electron transfer
does not happen.60 Similarly, DFT calculations and calorimetry
measurements have shown that the adhesion energy of Au,61−63
Pt,64 Pd,65 and Ag NPs is higher on reduced CeO2(111)
supports because of their higher binding energy to the oxygen
vacancies.56,66 However, although oxygen vacancies on more
reduced supports improve NP stability for many metals-oxide
support systems, some exceptions have also been reported. As
an example, experimental measurements and DFT calculations
show the decrease in the adsorption energy of Cu on
CeO2(111) with the extent of reduction.32,67
Oxygen vacancies can also be created and stabilized by
doping the support, which will again improve the NP resistance
against sintering. For example, doping ZrO2 with yttrium can
increase the availability of oxygen vacancies by replacement of
the cation Zr4+ by a cation of lower valence. These oxygen
a modification of the NP geometrical structure, may also lead to
change in its electronic structure, as for example a shift in the dband center. Therefore, separating different support-dependent
effects in catalysis needs careful consideration.
It is clear that in order to comprehend the reactivity of
nanocatalysts, it is vital not to overlook the role of the support.
Such support-dependent phenomena will be discussed in detail
in this Perspective, with the aim of unravelling how the catalytic
activity and selectivity of NPs can be tuned via the selection of
appropriate substrates.
The support can play an important role in controlling the size,
shape, and structural stability of
metal nanoparticles in reactive
environments.
Support-Induced Structural Changes in Nanoparticles. The
support can play an important role in controlling the size,
shape, and structural stability of metal nanoparticles in reactive
environments. For example, sintering and poisoning, which are
the key causes of degradation in the catalytic activity of
nanocatalysts25,52 are heavily dependent on NP−support
interactions, and understanding their influence is critical in
the rational design of high performance catalysts.53,54
Higher bonding energy of NPs to their support should
diminish their sintering rate.25,55 Campbell reported an increase
in the adhesion energy of metals to clean oxide supports in the
order MgO(100) ≈ TiO2(110) ≤ α-Al2O3 ≤ CeO2−x(111) ≤
Fe3O4 and explained this behavior based on the stability of the
lattice oxygen, because less stable oxygen atoms will have higher
chemical potential and bind more strongly to metal atoms in
the NPs.55 Furthermore, oxygen-vacancy defects on the support
Figure 1. (a) Schematic of the size evolution of micellar Pt NPs supported on γ-Al2O3 under various thermal and chemical treatments extracted from
EXAFS and STEM data. (b) Fourier transformed magnitude of k2-weighted Pt L3-edge EXAFS spectra of similarly prepared samples measured at
450 °C in O2, H2O vapor and H2 environments. (c−f) High-angle annular dark-field (HAADF) STEM images of Pt NPs supported on γ-Al2O3
acquired (c) as-prepared, and after annealing at 450 °C in O2 (d), in H2O (e), and in H2 (f).68 Reprinted with permission from Royal Society of
Chemistry.
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Figure 2. (a) STM image of Pd NPs supported on TiO2(110) acquired at 25 °C after annealing at 1100 °C. (b) NP−support adhesion energy as a
function of the NP height obtained from STM data following the Wulff−Kaischew theorem. (c) Normalized adhesion energy of Pd NPs on
TiO2(110) as a function of the interfacial facet orientation.82,83 Reprinted with permission from American Chemical Society and Royal Society of
Chemistry.
were stabilized on the Fe2O3 surface, and it was predicted via
DFT calculations that the 3-fold hollow site on the oxygenterminated surface of Fe2O3(001) is the most probable site for
single Pt atoms.71
Aside from stabilizing NPs against sintering, the support can
influence the NP structure through strain effects. Because of
lattice mismatch between the support and metal NPs, and due
to the preference of the metal adatoms at the NP/support
interface to retain the substrate structure, strain in the NP
lattice is commonly observed, leading to bond lengths differing
from those in bulk metals.40,72 For example, TEM measurements showed a 2.9% increase in the Au lattice parameter as
compared to the bulk value for 1- to 4-nm-sized NPs supported
on MgO(100).73
Moreover, it has been shown that strain can alter the
electronic and therefore chemical properties of a metal.74−76 As
a general rule, an expansion in the metal−metal bond length
will narrow the metal d-band and shift the d-band center toward
the Fermi level. This shift to higher energy causes a stronger
binding of the reactants.76,77 The contrary trend is observed for
compressed NP lattices. For example, a combination of X-ray
absorption near-edge structure (XANES) and DFT calculations
showed that the strain on Pd NPs induced by substrate step
edges can change the lateral registry of CO on Pd NPs and
weaken the CO−metal bond, which consequently reduces the
energy barrier for certain catalytic reactions.78 In another
example, DFT calculations predicted that substrate-induced
strain will enhance the activity of Au NPs toward O2 and CO
adsorption.79 The higher binding energy of CO on Pt NPs
supported on Au was also explained based on the larger lattice
constant of Au leading to an expansion of the Pt lattice
overlayer, as measured by STM.74
Substrate-induced strain can also change the diffusion barrier
for adatoms on their support and the nucleation of metals on a
substrate. For strained Ag, DFT calculations and STM
measurements indicate that the diffusion barrier for Ag selfdiffusion on Ag(111) scales nearly linearly with the nearest
neighbor distance. In general, compressive strain will decrease
the barrier for Ag self-diffusion while tensile strain has the
reverse effect at moderate variations of the lattice parameter
(±2%).40 The presence of strain at the NP/support interface
could also modify the equilibrium shape of the NPs to
minimize the total NP energy.38,72,80,81 For example, in the case
of Pd NPs supported on MgO(100), TEM measurements
showed that the height to diameter ratio increases with
increasing NP size, reducing the strain at the interface.72 STM
vacancies enhance the activity for the dry reforming of methane
by increasing the resistance of Ni NPs against sintering and
increasing the rate of removal of deposited coke.30
On the other hand, on oxide supports, strong metal NP/
support interactions which lead to improved stabilization
against sintering have also been observed upon oxidative
sample pretreatments. For example, lower NP mobility and
higher stability against sintering of Pt NPs supported on γAl2O3 was observed in situ via extended X-ray absorption fine
structure spectroscopy (EXAFS) and corroborated ex situ via
scanning transmission electron microscopy (STEM) after
annealing in oxygen or under water-rich atmospheres. The
enhanced NP stability is concluded here by considering the
minimum change in the first nearest neighbor atomic
coordination numbers measured via EXAFS before and after
the oxidative pretreatment as well as the lack of increase in the
average NP size obtained from STEM measurements. After the
oxidative treatments, the formation of Pt−O and Pt−OH
interfacial bonds is expected, which might increase the binding
energy of the NPs to the support, leading to their enhanced
resistance stability against sintering. In comparison, Pt NPs
preannealed in H2 underwent sintering, Figure 1.68
Not only the support material and oxidation state but also
the structure of the support can influence the stability of the
NPs.69 For example, Pt NPs deposited on carbon nanotubes
(CNTs) were found to display higher resistance against
sintering compared to NPs supported on carbon black due to
the superior stability of the CNTs themselves under electrochemical oxidation conditions.69 This conclusion was made
based on the comparison of TEM and XRD data of these
samples acquired before and after reaction, showing a smaller
growth in the average NP size when the NPs were supported
on the CNTs. XPS measurements indicated that the CNTs
were less oxidized than the carbon black after the reaction,
possibly due to their closed rolled graphene structure, which is
less accessible to oxygen than the amorphous carbon black. The
presence of surface oxides was thought to lower the Pt NP−
support interaction and to enhance Pt mobility and dissolution.
The support structure may affect the NP electronic structure
and consequently its binding energy to particular support sites.
For example, scanning tunneling microscopy (STM) studies
show that Au adatoms are stable up to 400 °C on the narrow
hollow sites of Fe3O4(001).70 Furthermore, it was shown that
the preference of adatoms to nucleate at certain sites is related
to charge and orbital ordering within the surface and first
subsurface layer of the substrate. In another study, Pt adatoms
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Figure 3. (a) H/Pt ratio calculated from XANES spectra of Pt22 NPs normalized by the area of bulk-like NPs measured at 183 K.14 Model shapes for
low and high H coverage are shown, as well as theoretical H/Pt ratios from ref.85 (b) Pt−Pt bond length as a function of H coverage for Pt22 NPs on
γ-Al2O3 is displayed. For Pt13 NPs supported on γ-Al2O3(100), DFT optimized structures for hydrogen-covered clusters with n number of H atoms
(c) n = 0, (d) n = 6, (e) n = 18, (f) n = 38 (metastable), (g) n = 20, and (h) n = 34 are shown from ref 85. Reprinted with permission from John
Wiley and Sons.
chemical reactivity, morphology, and stability of the
NPs.37,42,43,87−91 For example, due to charge transfer from Pt
NPs to their support, OH and H species from the dissociation
of H2O were found to be more stable on Pt NPs supported on
CeO2 as compared to unsupported Pt NPs of the same size,
Figure 4a.43,89 Also, in the case of Au/CeOx/TiO2, charge
redistribution in the metal close to the Au-CeOx interface
promoted CO2 adsorption and activation for CO2 hydrogenation to methanol, Figure 4b.92 Several parameters can be
used to tune the interfacial charge transfer, including: (i) the
density of oxygen vacancies on oxide supports, (ii) the support
termination and structure, (iii) the doping of the support, and
(iv) the size and structure of the NPs.
One of the material systems for which charge transfer
phenomena have been extensively investigated is gold NPs
supported on oxide substrates, Figure 5a.41,44,93,94 Charge
transfer from F-center oxygen vacancy support defects to gold
NPs deposited on MgO has been theoretically and
experimentally confirmed, which could change both the spatial
distribution and the vibrational properties of adsorbed CO
species.95 The transfer of charge from MgO to gold NPs could
also activate O2 molecules.95,96 Au8 NPs supported on a MgO
surface without oxygen vacancies were inactive for CO
combustion, while on the surface with vacancies they became
active as a result of charge transfer from substrate F-centers to
the deposited clusters.95,97 It is worth mentioning that even in
the absence of oxygen vacancy defects, charge transfer could
happen for metals with high electron affinity by tunneling
through thin oxide films, as was demonstrated for Au on thin
MgO films (1 to 3 layers) deposited on Mo(100).97−99 In the
case of NPs supported on oxide thin films on bulk metal, charge
transfer also depends on the film thickness.37,96,98 For example,
Xiao et al. found that small Au NPs on MgO/(Mo(001) and
measurements showed a similar behavior for Pd and Pt NPs on
TiO2(110), which show lower adhesion energy to the support
for larger NPs.82 Furthermore, it was found that in order to
have the highest adhesion energy and minimum total energy,
their thermodynamically stable shape would be dictated by
their interaction with the support. In particular, nanoparticles
with (111) interfacial facets were found to display the highest
adhesion energy, which led to higher NP stability, Figure 2.83,84
It is important to consider that the influence of the support
on the NP shape may be altered in different environments. For
example, the strong interaction between Pt NPs (<3 nm) and
their γ-Al2O3 support can be lifted through the adsorption of
hydrogen. Hydrogen adsorption on small NPs lifts the surface
relaxation and can even transform the morphology from a 2D
shape, in which the NP and support have a large contact area,
to a more 3D shape with larger Pt−Pt distances, Figure 3a.14,85
However, under very high pressures of hydrogen, the tensile
strain exerted on the NP by the support can be lifted, allowing
the Pt−Pt bonds to contract, Figure 3b. A change in the NP
shape from biplanar to cuboctahedral was also predicted by
DFT85 for Pt13/γ-Al2O3. Figure 3c−h displays the most stable
geometry of Pt13 NP on Al2O3 with increasing number of
adsorbed hydrogen atoms obtained through molecular
dynamics calculations. The transition in geometry was
explained in terms of a hydrogen-mediated loss of contact
between the NP and the underlying support. On the other
hand, in the presence of oxygen, oxygen atoms will withdraw
charge from the clusters, decreasing the Pt−Pt bond length and
increasing the NP/support interaction.86
Support-Induced Electronic Changes in Nanoparticles. In
addition to structural changes, the support can affect changes
in the NP electronic structure. In particular, charge transfer
from the support to the NPs and vice versa can affect the
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MgO terraces and steps or hydroxylated MgO surface has been
claimed.94
Charge transfer can also alter the reactivity by changing the
NP morphology.35,58,93,100,101 A parameter that can be used to
tune the charge transfer and consequently the morphology of
NPs is the doping of the substrate.101,102 For example, Shao et
al. have observed a transition from 3D to 2D for gold NPs
supported on CaO by doping the support with Mo, Figure 5b−
d. This observation was explained through DFT calculations
showing the higher bonding strength of gold to the support and
the charge transfer from Mo-4d states to the Au-6s orbital.101
Another parameter that affects charge transfer is the surface
termination of the support. For example, in the case of Pt(111)
deposited on O-terminated α-Al2O3, DFT predicts that charge
would be transferred from the substrate to Pt, while the
opposite would occur for Al-terminated α-Al2O3.33 Analogously, the CO desorption temperature from Pt NPs on Oterminated ZnO(0001) is higher than on Zn-terminated
ZnO(0001) due a distinct interfacial charge transfer.35,105
Charge transfer could also depend on the support structure.
For instance, DFT calculations predicted Pt13 NPs to be
charged negatively on (100)-oriented γ-Al2O3, while on
hydroxylated (110) γ-Al2O3, the clusters became positively
charged.37
The size of the NPs is another parameter which will affect
charge transfer. In the case of Pt NPs supported on CeO2(111)
with sizes between 20 and 800 atoms, resonant photoemission
spectroscopy measurements revealed that the charge transfer
increases with increasing NP size, while the charge transfer per
platinum atom was found to reach a maximum for particles of
30−70 atoms.106,107 Also, the structure dependency of charge
transfer processes was shown for Pt NPs supported on γ-Al2O3
through XANES measurements by Behafarid et al, Figure 6.104
They showed that among several small Pt NPs (0.8−1 nm)
with different shape, those with a higher proportion of atoms in
contact with the support (Nc/Nt) would display a larger
positive shift of the Pt-L3 adsorption edge as compared to bulk
Pt, indicating more charge transfer from Pt to Al2O3.104
Furthermore, charge transfer from specific sites can dictate
the arrangement of NPs on the surface. For example, for gold
atoms on FeO/Pt(111), the Fe−O double layer exhibits a polar
moment which varies on the surface, and easily polarizable gold
atoms will be directed to the areas with the highest work
function.108
Support-Induced Chemical Changes in Nanoparticles. The
support can influence the reactivity of metal NPs by changing
Figure 4. (a) Energy profile for the dissociation of water on Pt(111),
unsupported Pt79 and Pt8 clusters, and Pt8 on CeO2(111) or Ce40O80
NP. The Pt-ceria interaction significantly enhances the ability of admetal atoms for the dissociation of the O−H bond in water
molecules.43 (b) DFT-optimized potential energy surface for CO2
hydrogenation on Au3 supported on TiO2(110) and on CeOx/
TiO2(110).92 “TS” refers to the transition state. Reprinted with
permission from American Chemical Society.
Ag(001) become charged due to electron transfer through the
thin oxide film, while in the case of thicker metal layers, the
charge transfer happens by electron donation from electronrich oxide defects such as oxygen vacancies.37 Also, the
possibility of charge transfer from electrons trapped at
divacancies (missing pairs of adjacent Mg and O ions) at the
Figure 5. (a) STM image of a Au NP on 2 ML MgO/Ag(001) in which the NP is surrounded by a bright rim, which indicates charge accumulation
at the perimeter. STM images of Au NPs on (b) bare CaO and (c) Mo-doped CaO. The insets display high resolution images of characteristic
particles. (d) Schematic of the characteristic particle shapes.101,103 Reprinted with permission from American Chemical Society and John Wiley and
Sons.
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It should be mentioned that besides hindering NP activity by
covering the active sites, encapsulation can also change the
metal electronic structure. For example, Dulub et al. observed
semiconductor like behavior of Pt NPs supported on TiO2 after
encapsulation.115 In addition, in some cases even before
decoration of NPs with support atoms, reactivity has been
suppressed due to the perturbation of the electronic
structure.120
Interestingly, the reversibility of the encapsulation of Pd and
Rh monolayers supported on TiO2 has been observed after
annealing in an oxygen environment.48,109,121 Also, Ni NPs
which were encapsulated in CeO2 after annealing in H2
appeared again on the surface after annealing at the same
temperature in vacuum.117 Furthermore, Badri et al. have
studied the structure dependency of the encapsulation
reversibility for Pd supported on CeO2. Reversible encapsulation occurs more easily for Pd(111) faces and edges as
compared to the more open assemblies such as Pd(100).122
Nevertheless, in some cases SMSI can enhance the NP
reactivity. For instance, higher reactivity toward CO oxidation
has been observed on a CeO2123 or FeOx (1 < x < 2)124 layer
encapsulating Pt(111) as compared to the bare metallic Pt
surface. In addition, the SMSI effect causes a change in the
electronic structure when the catalyst changes from Pt(111) to
Pt8/CeO2(111), which results in water dissociation changing
from an endothermic to an exothermic process.125 Also, higher
selectivity to crotyl alcohol was observed for Pt NPs
encapsulated in CeO2 during the hydrogenation of crotonaldehyde.123 Another example is the improvement in the selectivity
and reactivity of Pt NPs supported on ZrO2 for liquid-phase
hydrogenation, which was explained by Pt−Zr alloy formation
at the NP interface.126
In some cases, supports can play a role in stabilizing
secondary chemical reactants. For example, in Cu/Zn/Al2O3,
which is the industrial catalyst for methanol synthesis through
CO2 hydrogenation, the presence of Znδ+ at the Cu surface due
to the SMSI effect would strengthen the binding of
intermediates and increase the catalytic activity, Figure
7.50,127,128 The coverage of Zn on the Cu surface is strongly
correlated to the catalytic activity, and the degree of Zn
coverage is furthermore dependent on the Cu NP size and the
reaction mixture.129 Also, a lower reaction barrier for CO2
hydrogenation has been measured on CeOx/Cu(111) as
compared to ZnO/Cu(111) and Cu(111), which is due to
the stabilization of CO2δ‑ on Ce3+ sites of CeOx/Cu(111).130 In
CO2 water gas shift (WGS) reaction, CO2δ+ derived from the
carboxyl intermediate is stabilized at the interface of CeOx/
Cu(111) and CeOx/Au(111), where the activation barrier is
decreased. Also, water dissociation, which is the rate limiting
factor for the WGS reaction over many catalysts, would have a
lower activation barrier on CeOx, to the point that dissociation
of water would not be rate limiting anymore.131,132
Other than SMSI and the creation of new active chemical
species, the support can also affect NP chemical stability by
diminishing surface poisoning under reaction conditions. In
particular, it was observed that the support composition can
affect coke removal from NPs.133−135 For example, a higher
coke formation rate was observed for Pt NPs supported on
Al2O3 as compared to CeO2 due to higher stability of
carbonaceous species found on Al2O3.133 In addition, the
support structure can also influence the catalyst resistance
toward poisoning. For instance, the higher content of oxygen
species on graphene as compared to other carbon structures
Figure 6. Energy shift of the Pt-L3 absorption edge of Pt NPs
supported on γ-Al2O3 with respect to bulk Pt as a function of the
relative number of atoms in contact with the support. The
measurement was done at 648 K in H2 atmosphere to prevent NP
oxidation. Nc/Nt indicates the ratio of the number of Pt atoms in
contact with the support to the total number of Pt atoms in the NP.
The model NP shapes shown were extracted from the analysis of
EXAFS and TEM data.104 Reprinted with permission from Royal
Society of Chemistry.
their chemical properties. One mechanism behind the chemical
alteration of NPs is strong metal−support interaction (SMSI).
For example, due to SMSI, metal clusters supported on TiO2
can become deactivated at elevated temperatures under a
reducing environment. Tauser et al. used the term SMSI to
explain the suppression of the reactivity based on the
decoration of the NP surface with substrate atoms.109−113
Two mechanisms have been proposed for this process: (i) NP
encapsulation and deactivation due to the decoration of the
active sites of the NP with substrate atoms, and (ii) a change in
the NP electronic structure due to charge transfer from the
substrate to the NPs.13,43,114−116
One mechanism behind the
chemical alteration of NPs is
strong metal−support interaction.
Metal clusters with high surface energy such as Pt, Pd, Ni, Rh
and Ir supported on reducible substrates such as CeO2, TiO2,
and V2O5 are suitable candidates for SMSI. Furthermore,
substrates with low work function (Φ) could easily transfer
charge to a metal cluster which has higher work function
(Φ(metal) > Φ(substrate)) and perturb their electronic
structure.111,113,117 Generally, the encapsulation mechanism
happens with the following steps: (i) reduction of the support
(MxOy) surface and formation of a cationic M-rich surface, (ii)
negative charging of the metal cluster as a result of a lowered
Fermi energy (higher work function, Φ), and (iii) migration of
MOx from the support onto the metal cluster for surface energy
minimization.111,118
Among the parameters that can affect the encapsulation rate
are the pretreatment conditions (temperature and reducing
environment), the oxidation state, the support structure, and
the NP size. To begin with, the support pretreatment can have
enormous impact on the rate of encapsulation by changing the
oxidation state of the support. For instance, a higher rate of
encapsulation has been observed for Nb-doped TiO2, TiO2
partially reduced by Ar+ bombardment, and TiO2 annealed in
H2 at 750 K.110,111,119As an example of the size effect, Jochum
et al. have shown through impedance measurements that small
Rh particles supported on TiO2 are more SMSI-sensitive than
larger ones.114
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observed for a variety of metal NPs to their support:139 Ru, Ni,
and Pt to Al2O3; from Pt to SiO2, TiO2, carbon, and Fe3O4;
from Cu to ZnO; and from Pd to SnO2 and carbon.142−146 H
spillover has a significant effect on the activity of catalysts for
the hydrogenation of aromatic hydrocarbons.147 The extent of
hydrogen spillover from Rh, Pt, and Pd NPs supported on HY
zeolite, carbon, Al2O3, and SiO2 was found to correlate with the
substrate acidic properties.148−150 For hydrogen spillover to
occur, reducible substrates are required to have electron
migration to the substrate and cation−electron formation.47
In addition, for hydrogen relocation to occur, strong M−H
bonds should break allowing hydrogen−substrate bonds to
form. In the case of irreducible substrates such as MgO,151
SiO2,152 and γ-Al2O3,153 the H atoms would be repulsed by the
substrate, preventing substrate−hydrogen bond formation.
However, it should be mentioned that the diffusion of
hydrogen to the irreducible support can happen in cases
where defects in the support are close to the NPs.47 Other than
being a reactant, the spilled-over hydrogen may induce defects
on the support and activate it for particular reactions. For
example, silica and alumina can be activated by hydrogen
spillover for ethylene and benzene hydrogenation.140
Oxygen migration is another important NP−support spillover process. The dissociation of O2 molecules and reverse
spillover of O atoms from clean Fe3O4(100) islands to Pt NPs
by annealing in oxygen was observed.145 Also, oxygen spillover
from Pt onto ceria was detected through isotope oxygen
exchange and FTIR−Raman spectroscopies.154,155 A direct
indication of oxygen spillover from Pt and Pd NPs to TiO2 was
shown through STM measurements.23,49,156 In many oxidation
reactions where reactants interact with lattice oxygen, the
presence of metal NPs on the support can accelerate oxygen
exchange with the support.45,46,157,158 For example, Figure 8b
shows that the presence of Pt NPs on CeO2(111)/Cu(111)
leads to the formation of Ce3+ at high temperatures due to
enhanced oxygen reverse spillover (O migration from the
support to the Pt NPs).45
It should be mentioned that other than H and O species,
multiatomic species have also been detected on the support due
to spillover from a metal catalyst. For example, methoxy
(CH3O) has been detected on the support during CO
hydrogenation reactions on a Ni/Al2O3 catalyst.159
In some cases, a bifunctional mechanism may occur in which
the support may provide the active site for a particular reaction
step, in addition to the metal NP. For example, for Ni NPs
supported on CeO2, lattice oxygen can contribute to the
reaction and facilitate the oxidation of ethoxy to acetate or
activate both CH4 and CO2 in dry reforming of methane.31,160
Furthermore, Pd50Rh50 NPs supported on CeO2 have shown
higher efficiency for H2 production through ethanol steam
reforming compared to the unsupported model catalysts. This
behavior was explained based on the ability of CeO2 to activate
water and spillover oxygen to the NPs.161 In another study, the
catalytic performance of Ni catalysts on doped-ceria supports
was investigated with Zr, La, or Gd as dopant, and the Zrdoped Ce showed the optimum catalytic activity due to the
higher reducibility of the support, which increased the
availability of surface lattice oxygen to participate in the partial
oxidation of methane.17 For the reforming of methane,
introducing 1% Ce to the Pt/ZrO2 catalyst leads to higher
activity and stability due to the creation of coke-resistant
oxygen vacant Ce3+ sites.16
Figure 7. (a) Cu(111), Cu(211), and CuZn(211) facets. (b) Gibbs
free energy diagram obtained from DFT calculations for CO2
hydrogenation on close-packed (black), stepped (blue), and Znsubstituted steps (red).127 (c) HRTEM images of Cu/ZnO/Al2O3
show the formation of a metastable ZnOx layer on the Cu NPs and
their transformation to rock salt and wurtzite structure after electron
beam exposure.128 Reprinted with permission from The American
Association for the Advancement of Science and John Wiley and Sons.
was shown to destabilize the poisoning CO intermediate during
methanol electro-oxidation and subsequently improve the
activity of the supported PtNi NPs.136 The oxidation state of
the support also modifies the coking rate of the catalyst either
by changing the binding energy of carbon species or by
changing the rate of oxygen donation for coke removal.137
Along these lines, higher stability against coke formation was
observed for Co deposited on reduced CeO2−x as compared to
stoichiometric CeO2.137
Synergistic Interactions between Nanoparticles and Their
Support. In many cases, a NP and its support play a combined
role in improved catalytic reactivity. One mechanism behind
this phenomenon is reactant spillover. Spillover is defined as
the migration of an adsorbate molecule or atom from one
surface to another (substrate to NP, or vice versa) upon which
it would not adsorb individually. Spillover can be one of the
steps in a chemical reaction. For instance, hydrogen and oxygen
spillover have an enormous impact on the chemical reactivity
and stability of catalysts.138−140
Hydrogen spillover is a facile spillover process. Figure 8a
shows the spillover of atomic hydrogen from a Co NP to the
Cu(111) substrate and their diffusion on the substrate at
temperatures lower than 80 K. Because the dissociation of H2 at
low temperature is not possible on Cu(111), all H atoms on the
Cu surface must have spilled over after being dissociatively
adsorbed on the Co NP.141 Hydrogen spillover has been
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Figure 8. (a) STM images showing the spillover of H atoms from Co NPs to the Cu(111) support. (b) Models of a Pt NP on CeO2(111)/Cu(111)
(left) and a thin film of CeO2(111) on Cu(111) (right). The middle panel shows the surface stoichiometry (right axis) of CeO2−x for the Pt-CeO2/
Cu(111) and CeO2/Cu(111) systems, indicating the reduction of CeO2 only in the presence of the Pt NPs.45,141 Reprinted with permission from
Nature Publishing Group and American Chemical Society.
the NPs is not covered with the atoms from the support, Figure
9.168
Another example is the partial reduction of CeO2 promoted
by Cu and Au NPs in the presence of CO or CO/H2O for the
water gas shift reaction.167 Furthermore, in the presence of H2
and CO, Pt NPs on Fe3O4(100) catalyze the reaction of the
In addition to spillover effects, another mechanism in which a
NP and its support play a combined role in enhancing reactivity
is through the creation highly reactive perimeter sites which are
positioned at the boundary between the NP and the
support.127,155,162−165 Atoms at these perimeter sites may
have an altered electronic structure which is optimal for
facilitating a particular reaction step. For example, DFT
calculations by Molina et al. revealed that the minimum energy
path for CO oxidation over Au/TiO2 catalysts involves CO and
O2 being adsorbed at the gold-support interface.163 It was
found that the active sites of Au/CeO2 and Au/TiO2 for the
water gas shift reaction are perimeter Au atoms in contact with
oxygen vacancies within the support.89,166 Moreover, for Cu
and Au NPs on CeO2, the support can also play a role in
dissociating H2O, which is the rate limiting step for the water
gas shift reaction.167
Nanoparticle-Induced Changes in the Oxide Support. Although
there are numerous studies showing how different supports can
affect the structure and chemical state of metal NPs, NPs can
also in turn have a huge impact on the support. Nanoparticles
may catalyze the reduction of their support, which can in turn
enhance their stability against sintering.3,64,65 For example, high
thermal stability against sintering and a lack of mobility were
observed by Ono et al. for gold NPs supported on SiO2 up to
1343 K. This high thermal stability was a result of oxygen
desorption and decomposition of SiO2 and consequent
desorption of volatile SiO from underneath the NPs, leading
to NPs digging channels into the underlying SiO2 support,
which hinders their mobility. It should be mentioned that this
process is different from the SMSI effect, since the surface of
Figure 9. (a) Schematic and (b) AFM image and height profile of Au
NPs supported on a SiO2(4 nm)/Si(100) substrate acquired after
annealing in UHV at 1070 °C. The Au NPs bury themselves into the
SiO2 support. Volatile SiO species escape the surface after the local
catalytic reduction of SiO2 due to the presence of the Au NPs.168
Reprinted with permission from American Chemical Society.
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Perspective
nanocatalysts requires a proper understanding of the
parameters which can affect their reactivity, such as their size,
shape, chemical state, composition, and interaction with
support. In this Perspective, we have described some of the
impressive work carried out thus far in order to unveil the effect
of the support on chemical processes catalyzed by nanoparticles.
The NP support can play a key role in stabilizing a catalyst
against sintering or in stabilizing certain NP morphologies
through strain effects. In addition, electronic interactions
between a NP and support such as charge transfer can occur,
which may alter the binding properties or even the morphology
of the NP. Chemical changes may also be induced on the NP
by the support, such as encapsulation of the particle through
strong metal−support interaction. Finally, the NP and support
may play a combined role in improving catalytic ability, for
example, by allowing for spillover of reactants or through
reactive perimeter sites. From these examples, it is clear that
structure-dependent reactivity trends in nanocatalysts cannot
be properly understood without also considering the often
critical role of the support. Furthermore, careful utilization of
support dependent phenomena could be a powerful method to
rationally engineer new nanocatalyst materials.
Outlook and Challenges. Despite tremendous work on this
topic, many challenges still remain. One such challenge is to
synthesize stable and well-defined size- and shape-selected NPs
to be able to isolate the effect of support interaction from other
parameters and also to create unique support-dependent active
sites such as interfacial and perimeter sites. Furthermore, the
interaction of the support with multimetallic alloyed nanoparticles also requires additional attention due to their extended
industrial applications. The support and its interaction with the
different metals may play an important role in alloying or
segregation within these NPs, particularly in different reactive
environmental conditions. Beyond the creation of compositionally and structurally well-defined nanostructures, these
support-enhanced active sites must be accurately resolved.
Experimentally, further advancement is needed in developing in
situ and operando techniques for investigating and quantifying
the support effect and its evolution under harsh reaction
The NP support can play a key
role in stabilizing a catalyst
against sintering or in stabilizing
certain NP morphologies through
strain effects.
lattice oxygen with CO and H2 and diffusion of Fe to the bulk
leads to the formation of a monolayer of holes in the substrate,
whereas oxygen spillover in an oxidizing environment brings Fe
atoms to the surface from the bulk to form a new Fe3O4 layer
around the Pt NPs, Figure 10.145
The transformations induced by NPs on their support also
depend on the NP synthesis method and the environment. For
example, as shown in Figure 11a, TiO2 nanostripes are
observed by annealing in UHV inverse micelle-synthesized Pt
NPs supported on TiO2(110),104 whereas annealing PVDdeposited Pt and Pd NPs on TiO2(110) leads to (1 × 2)
nanostripe growth until all the particles have been covered by
the layers of TiO2, Figure 11b.169 The formation of the
nanostripes is due to oxygen desorption from the substrate
surface and diffusion of Ti adatoms to the subsurface, whereas
in the case of annealing in oxygen, atomic oxygen spills over to
form a new layer of TiO2 close to the NPs.
In summary, the above discussion demonstrates that NPs can
catalyze significant changes on their support. Consequently,
similarly to the NPs, the support must also be considered as a
dynamical entity under reaction conditions. Due to the often
complex interdependence between the NP, support, and
catalyst reactivity, careful studies are required to identify the
true nature of a NP and its support in their working state.
Summary. During the last two decades, state of the art
experimental and theoretical techniques have been employed to
gain the fundamental understanding needed to improve the
performance nanocatalysts. In particular, significant effort has
been paid to the development of new catalytic nanomaterials
based on inexpensive metals which are highly active and
selective and able to operate under harsh environmental
conditions. Along these lines, the rational design of improved
Figure 10. STM images of Pt NPs (1−6 atoms) supported on Fe3O4(001) exposed to (a) CO, (b) H2, and (c) O2 at 550 K. (d) Schematic showing
how CO extracts O atoms from the clusters to form CO2, which desorbs from the surface, followed by the diffusion of Fe atoms into the Fe3O4 bulk.
(e) Schematic showing H2 dissociation on a Pt cluster, spill over onto the support, and reaction with O lattice atoms. (f) O2 exposure leads to the
growth of a Fe3O4(001) layer next to the Pt NPs due to the spillover of oxygen atoms on to the support, which react with Fe that diffuses out from
the bulk.145 Reprinted with permission from John Wiley and Sons.
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Figure 11. (a) STM image of a nanostripe formed attached to micellar Pt NPs on TiO2 obtained after annealing above 1000 °C in vacuum. The
schematic on the right reveals the mechanism underlying the formation of the TiO2 nanostripes via the removal of a TiO2 layer through the
desorption of oxygen and diffusion of Ti3+ species into the bulk of the TiO2(110) substrate. (b) Sequence of STM images (100 × 100 nm2) of PVDgrown Pt NPs supported on TiO2 under 1 × 10−7 mbar O2 acquired at 673 K. All the particles in the scan area have been covered by four layers of
TiO2 grown after exposure to 4092 L oxygen. The letters X and Y in (b) mark two different structures of the TiO2(110)-(1 × 2)
reconstruction.169,170 Reprinted with permission from American Chemical Society and Royal Society of Chemistry.
In terms of theory, advancements in computational methods
are needed to model more bulk-like, complex, and disordered
systems. For example, computational cost can constrain studies
to small cluster sizes and thin slab support models of only a few
atomic layers, which may not be representative of the
industrially active catalysts. In addition, when periodic
boundary conditions are used in ab initio methods to model
clusters, interactions with other supercells must also be
considered. Developing higher throughput theoretical techniques with the ability to consider the support as a bulk system,
and also allowing the investigation of larger cluster/support
systems is a necessity that, in combination with experimental
techniques, can provide insight into the most active sites of
catalyst. Progress in these areas and further understanding of
the support effect in catalytic systems will allow for the rational
development of higher performance, next generation catalysts.
conditions. In addition, development of reaction cells which can
allow for simultaneous measurements with different techniques
could give enormous insight into support-dependent reactivity.
For example, bulk averaging techniques could be complemented by local measurements to understand spatial variations
in the sample and give a complete picture of the active catalyst.
It will be critical to develop techniques that can specifically
probe the cluster−support interface underneath a particle to
resolve phenomena such as strain and charge transfer or to
resolve bonds between the NP atoms and support atoms and
distinguish these from NP−adsorbate bonds. Particularly, in
terms of support-mediated NP stability, temporal resolution is
needed in such operando techniques to follow sintering and
redispersion phenomena during a reaction. Additional outstanding experimental opportunities are expected to be
provided by the new generation of free electron lasers, which
will allow unprecedented developments in the field of catalysts
in the years to come through the possibility of monitoring
structural and chemical changes of catalysts under reaction
conditions with ultrafast temporal resolutions at the nanosecond and femtosecond time scales.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected].
Notes
The authors declare no competing financial interest.
Additional outstanding experimental opportunities are expected to be provided by the
new generation of free electron
lasers.
Biographies
Mahdi Ahmadi is a Ph.D. candidate at the University of Central
Florida (U.S.A.). He received his M.S. in atomic and molecular physics
from the University of Tehran and his B.S. in physics from Sharif
University of Technology in Iran. His research focuses on the
investigation of novel physical and chemical properties of metallic
nanostructures.
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ment in the electroreduction of CO2 over Au nanoparticles. J. Am.
Chem. Soc. 2014, 136, 16473−16476.
(12) Mistry, H.; Behafarid, F.; Zhou, E.; Ono, L. K.; Zhang, L.;
Roldan Cuenya, B. Shape-dependent catalytic oxidation of 2-butanol
over Pt nanoparticles supported on gamma-Al2O3. ACS Catal. 2014,
4, 109−115.
(13) Mostafa, S.; Behafarid, F.; Croy, J. R.; Ono, L. K.; Li, L.; Yang, J.
C.; Frenkel, A. I.; Cuenya, B. R. Shape-dependent catalytic properties
of Pt nanoparticles. J. Am. Chem. Soc. 2010, 132, 15714−15719.
(14) Mistry, H.; Behafarid, F.; Bare, S. R.; Roldan Cuenya, B.
Pressure-dependent effect of hydrogen adsorption on structural and
electronic properties of Pt/γ-Al2O3 nanoparticles. ChemCatChem
2014, 6, 348−352.
(15) Comotti, M.; Li, W.-C.; Spliethoff, B.; Schüth, F. Support effect
in high activity gold catalysts for CO oxidation. J. Am. Chem. Soc. 2006,
128, 917−924.
(16) Ö zkara-Aydınoğlu, Ş.; Ö zensoy, E.; Aksoylu, A. E. The effect of
impregnation strategy on methane dry reforming activity of Ce
promoted Pt/ZrO2. Int. J. Hydrogen Energy 2009, 34, 9711−9722.
(17) Salazar-Villalpando, M. D.; Reyes, B. Hydrogen production over
Ni/ceria-supported catalysts by partial oxidation of methane. Int. J.
Hydrogen Energy 2009, 34, 9723−9729.
(18) Datye, A. Comparison of metal-support interactions in Pt/TiO2
and Pt/CeO2. J. Catal. 1995, 155, 148−153.
(19) Croy, J. R.; Mostafa, S.; Liu, J.; Sohn, Y. H.; Heinrich, H.;
Cuenya, B. R. Support dependence of MeOH decomposition over
size-selected Pt nanoparticles. Catal. Lett. 2007, 119, 209−216.
(20) Cargnello, M.; Doan-Nguyen, V. V. T.; Gordon, T. R.; Diaz, R.
E.; Stach, E. A.; Gorte, R. J.; Fornasiero, P.; Murray, C. B. Control of
metal nanocrystal size reveals metal-support interface role for ceria
catalysts. Science 2013, 341, 771−773.
(21) Wolf, A.; Schuth, F. A systematic study of the synthesis
conditions for the preparation of highly active gold catalysts. Appl.
Catal., A 2002, 226, 1−13.
(22) Haruta, M. Size- and support-dependency in the catalysis of
gold. Catal. Today 1997, 36, 153−166.
(23) Bonanni, S.; Aït-Mansour, K.; Harbich, W.; Brune, H. Effect of
the TiO2 reduction state on the catalytic CO oxidation on deposited
size-selected Pt clusters. J. Am. Chem. Soc. 2012, 134, 3445−3450.
(24) Olthof, B.; Khodakov, A.; Bell, A. T.; Iglesia, E. Effects of
support composition and pretreatment conditions on the structure of
vanadia dispersed on SiO2, Al2O3, TiO2, ZrO2, and HfO2. J. Phys.
Chem. B 2000, 104, 1516−1528.
(25) Barbero, J.; Pena, M. A.; Campos-Martin, J. M.; Fierro, J. L. G.;
Arias, P. L. Support effect in supported Ni catalysts on their
performance for methane partial oxidation. Catal. Lett. 2003, 87, 211−
218.
(26) Kendelewicz, T.; Liu, P.; Doyle, C. S.; Brown, G. E.; Nelson, E.
J.; Chambers, S. A. Reaction of water with the (100) and (111)
surfaces of Fe3O4. Surf. Sci. 2000, 453, 32−46.
(27) Li, Y. Z.; Fan, Y. N.; Yang, H. P.; Xu, B. L.; Feng, L. Y.; Yang, M.
F.; Chen, Y. Strong metal-support interaction and catalytic properties
of anatase and rutile supported palladium catalyst Pd/TiO2. Chem.
Phys. Lett. 2003, 372, 160−165.
(28) Wen, C.; Zhu, Y.; Ye, Y.; Zhang, S.; Cheng, F.; Liu, Y.; Wang, P.;
Tao, F. Water−gas shift reaction on metal nanoclusters encapsulated
in mesoporous ceria studied with ambient-pressure X-ray photoelectron spectroscopy. ACS Nano 2012, 6, 9305−9313.
(29) Bozo, C.; Guilhaume, N.; Herrmann, J.-M. Role of the ceria−
zirconia support in the reactivity of platinum and palladium catalysts
for methane total oxidation under lean conditions. J. Catal. 2001, 203,
393−406.
(30) Bellido, J. D. A.; Assaf, E. M. Effect of the Y2O3−ZrO2 support
composition on nickel catalyst evaluated in dry reforming of methane.
Appl. Catal., A 2009, 352, 179−187.
(31) Wang, J. B.; Tai, Y.-L.; Dow, W.-P.; Huang, T.-J. Study of ceriasupported nickel catalyst and effect of yttria doping on carbon dioxide
reforming of methane. Appl. Catal., A 2001, 218, 69−79.
Hemma Mistry is a Ph.D. student in the Physics Department at the
University of Central Florida (U.S.A.) and Ruhr-University Bochum
(Germany). She obtained her bachelor degree in Physics from the
University of California at Berkeley. Her research is focused on
understanding the structure-dependent reactivity of model nanocatalysts using in situ and operando spectroscopy.
Beatriz Roldan Cuenya is currently a Professor of Physics at the RuhrUniversity Bochum (Germany). She received her B.S. degree in
Physics from the University of Oviedo (Spain) in 1998, her Ph.D.
degree in Physics from the University of Duisburg-Essen (Germany)
in 2001, and was a postdoctoral researcher in the Chemical
Engineering Department of the University of California Santa Barbara
(2001−2003) and full professor at the University of Central Florida
before her move to Germany in 2013. Her group’s research program
explores the novel physical and chemical properties of size and shapeselected nanostructured materials, with emphasis on in situ and
operando characterization of catalysts at work.
■
ACKNOWLEDGMENTS
The authors gratefully acknowledge financial support from the
U.S. National Science Foundation (NSF-Chemistry 1213182 an
NSF-DMR 1207065) and the German Federal Ministry of
Education and Research (Bundesministerium für Bildung und
Forschung, BMBF) under grant #03SF0523C“CO2EKAT”
and the Cluster of Excellence RESOLV at RUB (EXC 1069)
funded by the Deutsche Forschungsgemeinschaft.
■
REFERENCES
(1) Roldan Cuenya, B. Synthesis and catalytic properties of metal
nanoparticles: Size, shape, support, composition, and oxidation state
effects. Thin Solid Films 2010, 518, 3127−3150.
(2) Roldan Cuenya, B.; Behafarid, F. Nanocatalysis: size- and shapedependent chemisorption and catalytic reactivity. Surf. Sci. Rep. 2015,
70, 135−187.
(3) Merte, L. R.; Ahmadi, M.; Behafarid, F.; Ono, L. K.; Lira, E.;
Matos, J.; Li, L.; Yang, J. C.; Roldan Cuenya, B. Correlating catalytic
methanol oxidation with the structure and oxidation state of sizeselected Pt nanoparticles. ACS Catal. 2013, 3, 1460−1468.
(4) Andersen, M.; Medford, A. J.; Nørskov, J. K.; Reuter, K.
Analyzing the case for bifunctional catalysis. Angew. Chem. 2016, 128,
5296−5300.
(5) Narayanan, R.; El-Sayed, M. A. Shape-dependent catalytic activity
of platinum nanoparticles in colloidal solution. Nano Lett. 2004, 4,
1343−1348.
(6) Reske, R.; Mistry, H.; Behafarid, F.; Roldan Cuenya, B.; Strasser,
P. Particle size effects in the catalytic electroreduction of CO2 on Cu
nanoparticles. J. Am. Chem. Soc. 2014, 136, 6978−6986.
(7) Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E. Shape-controlled
synthesis of metal nanocrystals: simple chemistry meets complex
physics? Angew. Chem., Int. Ed. 2009, 48, 60−103.
(8) Shaikhutdinov, S. K.; Meyer, R.; Naschitzki, M.; Baumer, M.;
Freund, H. J. Size and support effects for CO adsorption on gold
model catalysts. Catal. Lett. 2003, 86, 211−219.
(9) Ono, L. K.; Croy, J. R.; Heinrich, H.; Roldan Cuenya, B. Oxygen
chemisorption, formation, and thermal stability of Pt oxides on Pt
nanoparticles supported on SiO2/Si(001): size effects. J. Phys. Chem. C
2011, 115, 16856−16866.
(10) Peter, M.; Flores Camacho, J. M.; Adamovski, S.; Ono, L. K.;
Dostert, K.-H.; O’Brien, C. P.; Roldan Cuenya, B.; Schauermann, S.;
Freund, H.-J. Trends in the binding strength of surface species on
nanoparticles: how does the adsorption energy scale with the particle
size? Angew. Chem., Int. Ed. 2013, 52, 5175−5179.
(11) Mistry, H.; Reske, R.; Zeng, Z.; Zhao, Z.-J.; Greeley, J.; Strasser,
P.; Roldan Cuenya, B. Exceptional size-dependent activity enhance3529
DOI: 10.1021/acs.jpclett.6b01198
J. Phys. Chem. Lett. 2016, 7, 3519−3533
The Journal of Physical Chemistry Letters
Perspective
(32) James, T. E.; Hemmingson, S. L.; Ito, T.; Campbell, C. T.
Energetics of Cu adsorption and adhesion onto reduced CeO2(111)
surfaces by calorimetry. J. Phys. Chem. C 2015, 119, 17209−17217.
(33) Cooper, V. R.; Kolpak, A. M.; Yourdshahyan, Y.; Rappe, A. M.
Supported metal electronic structure: Implications for molecular
adsorption. Phys. Rev. B: Condens. Matter Mater. Phys. 2005, 72,
081409.
(34) Min, B. K.; Wallace, W. T.; Goodman, D. W. Synthesis of a
sinter-resistant, mixed-oxide support for Au nanoclusters. J. Phys.
Chem. B 2004, 108, 14609−14615.
(35) Roberts, S.; Gorte, R. J. A comparison of Pt overlayers on αAl2O3(0001), ZnO(0001)Zn, and ZnO(0001̅)O. J. Chem. Phys. 1990,
93, 5337.
(36) Liao, F. L.; Huang, Y. Q.; Ge, J. W.; Zheng, W. R.; Tedsree, K.;
Collier, P.; Hong, X. L.; Tsang, S. C. Morphology-dependent
interactions of ZnO with Cu nanoparticles at the materials’ interface
in selective hydrogenation of CO2 to CH3OH. Angew. Chem., Int. Ed.
2011, 50, 2162−2165.
(37) Hu, C. H.; Chizallet, C.; Mager-Maury, C.; Corral-Valero, M.;
Sautet, P.; Toulhoat, H.; Raybaud, P. Modulation of catalyst particle
structure upon support hydroxylation: Ab initio insights into Pd13 and
Pt13/γ-Al2O3. J. Catal. 2010, 274, 99−110.
(38) Iddir, H.; Komanicky, V.; Ogut, S.; You, H.; Zapol, P. Shape of
platinum nanoparticles supported on SrTiO3: experiment and theory.
J. Phys. Chem. C 2007, 111, 14782−14789.
(39) Stolbov, S.; Zuluaga, S. Factors controlling the reactivity of
catalytically active monolayers on metal substrates. J. Phys. Chem. Lett.
2013, 4, 1537−1540.
(40) Brune, H.; Bromann, K.; Roder, H.; Kern, K.; Jacobsen, J.;
Stoltze, P.; Jacobsen, K.; Norskov, J. Effect of strain on surfacediffusion and nucleation. Phys. Rev. B: Condens. Matter Mater. Phys.
1995, 52, 14380−14383.
(41) Fu, Q.; Saltsburg, H.; Flytzani-Stephanopoulos, M. Active
nonmetallic Au and Pt species on ceria-based water-gas shift catalysts.
Science 2003, 301, 935−938.
(42) Ontaneda, J.; Bennett, R. A.; Grau-Crespo, R. Electronic
structure of Pd multilayers on Re(0001): the role of charge transfer. J.
Phys. Chem. C 2015, 119, 23436−23444.
(43) Bruix, A.; Rodriguez, J. A.; Ramírez, P. J.; Senanayake, S. D.;
Evans, J.; Park, J. B.; Stacchiola, D.; Liu, P.; Hrbek, J.; Illas, F. A new
type of strong metal−support interaction and the production of H2
through the transformation of water on Pt/CeO2(111) and Pt/CeOx/
TiO2(110) catalysts. J. Am. Chem. Soc. 2012, 134, 8968−8974.
(44) Sanchez, A.; Abbet, S.; Heiz, U.; Schneider, W. D.; Häkkinen,
H.; Barnett, R. N.; Landman, U. When gold is not noble: nanoscale
gold catalysts. J. Phys. Chem. A 1999, 103, 9573−9578.
(45) Vayssilov, G. N.; Lykhach, Y.; Migani, A.; Staudt, T.; Petrova, G.
P.; Tsud, N.; Skála, T.; Bruix, A.; Illas, F.; Prince, K. C.; Matolín, V. r.;
Neyman, K. M.; Libuda, J. Support nanostructure boosts oxygen
transfer to catalytically active platinum nanoparticles. Nat. Mater.
2011, 10, 310−315.
(46) Happel, M.; Mysliveček, J.; Johánek, V.; Dvořaḱ , F.; Stetsovych,
O.; Lykhach, Y.; Matolín, V.; Libuda, J. Adsorption sites, metal-support
interactions, and oxygen spillover identified by vibrational spectroscopy of adsorbed CO: A model study on Pt/ceria catalysts. J. Catal.
2012, 289, 118−126.
(47) Prins, R. Hydrogen spillover. facts and fiction. Chem. Rev. 2012,
112, 2714−2738.
(48) Bennett, R. A.; Stone, P.; Bowker, M. Pd nanoparticle enhanced
re-oxidation of non-stoichiometric TiO2: STM imaging of spillover
and a new form of SMSI. Catal. Lett. 1999, 59, 99−105.
(49) Ramirez-Cuesta, A. J.; Bennett, R. A.; Stone, P.; Mitchell, P. C.
H.; Bowker, M. STM investigation and Monte-Carlo modelling of
spillover in a supported metal catalyst. J. Mol. Catal. A: Chem. 2001,
167, 171−179.
(50) Martínez-Suárez, L.; Frenzel, J.; Marx, D.; Meyer, B. Tuning the
reactivity of aCu/ZnO nanocatalyst via gas phase pressure. Phys. Rev.
Lett. 2013, 110, 086108.
(51) Addou, R.; Senftle, T. P.; O’Connor, N.; Janik, M. J.; van Duin,
A. C. T.; Batzill, M. Influence of hydroxyls on Pd atom mobility and
clustering on rutile TiO2(011)-2 × 1. ACS Nano 2014, 8, 6321−6333.
(52) Claeys, M.; Dry, M. E.; van Steen, E.; van Berge, P. J.; Booyens,
S.; Crous, R.; van Helden, P.; Labuschagne, J.; Moodley, D. J.; Saib, A.
M. Impact of process conditions on the sintering behavior of an
alumina-supported cobalt fischer−tropsch catalyst studied with an in
situ magnetometer. ACS Catal. 2015, 5, 841−852.
(53) Behafarid, F.; Roldan Cuenya, B. Coarsening phenomena of
metal nanoparticles and the influence of the support pre-treatment:
Pt/TiO2(110). Surf. Sci. 2012, 606, 908−918.
(54) Behafarid, F.; Roldan Cuenya, B. Towards the understanding of
sintering phenomena at the nanoscale: geometric and environmental
effects. Top. Catal. 2013, 56, 1542−1559.
(55) Campbell, C. T. The energetics of supported metal nanoparticles: relationships to sintering rates and catalytic activity. Acc.
Chem. Res. 2013, 46, 1712−1719.
(56) Farmer, J. A.; Campbell, C. T. Ceria maintains smaller metal
catalyst particles by strong metal-support bonding. Science 2010, 329,
933−936.
(57) Hong, S.; Rahman, T. S. Rationale for the higher reactivity of
interfacial sites in methanol decomposition on Au13/TiO2(110). J. Am.
Chem. Soc. 2013, 135, 7629−7635.
(58) Ricci, D.; Bongiorno, A.; Pacchioni, G.; Landman, U. Bonding
trends and dimensionality crossover of gold nanoclusters on metalsupported MgO thin films. Phys. Rev. Lett. 2006, 97, 036106.
(59) Wahlström, E.; Lopez, N.; Schaub, R.; Thostrup, P.; Rønnau, A.;
Africh, C.; Lægsgaard, E.; Nørskov, J. K.; Besenbacher, F. Bonding of
gold nanoclusters to oxygen vacancies on rutile TiO2(110). Phys. Rev.
Lett. 2003, 90, 026101.
(60) Cai, Y.; Bai, Z.; Chintalapati, S.; Zeng, Q.; Feng, Y. P. Transition
metal atoms pathways on rutile TiO2(110) surface: Distribution of
Ti3+ states and evidence of enhanced peripheral charge accumulation.
J. Chem. Phys. 2013, 138, 154711.
(61) Zhang, C.; Michaelides, A.; King, D. A.; Jenkins, S. J. Structure
of gold atoms on stoichiometric and defective ceria surfaces. J. Chem.
Phys. 2008, 129, 194708.
(62) Chen, Y.; Hu, P.; Lee, M.-H.; Wang, H. Au on (111) and (110)
surfaces of CeO2: A density-functional theory study. Surf. Sci. 2008,
602, 1736−1741.
(63) Hemmingson, S. L.; James, T. E.; Feeley, G. M.; Tilson, A. M.;
Campbell, C. T. Adsorption and adhesion of Au on reduced
CeO2(111) surfaces at 300 and 100 K. J. Phys. Chem. C 2016, 120,
12113−12124.
(64) Yang, Z.; Lu, Z.; Luo, G. First-principles study of thePt/
CeO2(111)interface. Phys. Rev. B: Condens. Matter Mater. Phys. 2007,
76, 075421.
(65) Yang, Z.; Lu, Z.; Luo, G.; Hermansson, K. Oxygen vacancy
formation energy at the Pd/CeO2(111) interface. Phys. Lett. A 2007,
369, 132−139.
(66) Luches, P.; Pagliuca, F.; Valeri, S.; Illas, F.; Preda, G.; Pacchioni,
G. Nature of Ag islands and nanoparticles on the CeO2(111) surface. J.
Phys. Chem. C 2012, 116, 1122−1132.
(67) Szabová, L.; Camellone, M. F.; Huang, M.; Matolín, V. r.; Fabris,
S. Thermodynamic, electronic and structural properties of Cu/CeO2
surfaces and interfaces from first-principles DFT+U calculations. J.
Chem. Phys. 2010, 133, 234705.
(68) Matos, J.; Ono, L. K.; Behafarid, F.; Croy, J. R.; Mostafa, S.;
DeLaRiva, A. T.; Datye, A. K.; Frenkel, A. I.; Roldan Cuenya, B. In situ
coarsening study of inverse micelle-prepared Pt nanoparticles
supported on γ-Al2O3: pretreatment and environmental effects. Phys.
Chem. Chem. Phys. 2012, 14, 11457.
(69) Shao, Y.; Yin, G.; Gao, Y.; Shi, P. Durability study of Pt/C and
Pt/CNTs catalysts under simulated PEM fuel cell conditions. J.
Electrochem. Soc. 2006, 153, A1093.
(70) Novotný, Z.; Argentero, G.; Wang, Z.; Schmid, M.; Diebold, U.;
Parkinson, G. S. Ordered array of single adatoms with remarkable
thermal stability: Au/Fe3O4(001). Phys. Rev. Lett. 2012, 108, 216103.
3530
DOI: 10.1021/acs.jpclett.6b01198
J. Phys. Chem. Lett. 2016, 7, 3519−3533
The Journal of Physical Chemistry Letters
Perspective
(71) Qiao, B.; Wang, A.; Yang, X.; Allard, L. F.; Jiang, Z.; Cui, Y.; Liu,
J.; Li, J.; Zhang, T. Single-atom catalysis of CO oxidation using Pt1/
FeOx. Nat. Chem. 2011, 3, 634−641.
(72) Henry, C. R. Morphology of supported nanoparticles. Prog. Surf.
Sci. 2005, 80, 92−116.
(73) Giorgio, S.; Chapon, C.; Henry, C. R.; Nihoul, G.; Penisson, J.
M. High-resolution transmission electron-microscopy study of gold
particles (greater than 1 nm), epitaxially grown on clean Mgo
microcubes. Philos. Mag. A 1991, 64, 87−96.
(74) Pedersen, M. O.; Helveg, S.; Ruban, A.; Stensgaard, I.;
Laegsgaard, E.; Norskov, J. K.; Besenbacher, F. How a gold substrate
can increase the reactivity of a Pt overlayer. Surf. Sci. 1999, 426, 395−
409.
(75) Gunter, M. M.; Ressler, T.; Bems, B.; Buscher, C.; Genger, T.;
Hinrichsen, O.; Muhler, M.; Schlogl, R. Implication of the microstructure of binary Cu/ZnO catalysts for their catalytic activity in
methanol synthesis. Catal. Lett. 2001, 71, 37−44.
(76) Yudanov, I. V.; Genest, A.; Schauermann, S.; Freund, H.-J.;
Rösch, N. Size dependence of the adsorption energy of CO on metal
nanoparticles: a DFT search for the minimum value. Nano Lett. 2012,
12, 2134−2139.
(77) Greeley, J.; Norskov, J. K.; Mavrikakis, M. Electronic structure
and catalysis on metal surfaces. Annu. Rev. Phys. Chem. 2002, 53, 319−
348.
(78) Yim, C. M.; Pang, C. L.; Hermoso, D. R.; Dover, C. M.; Muryn,
C. A.; Maccherozzi, F.; Dhesi, S. S.; Pérez, R.; Thornton, G. Influence
of support morphology on the bonding of molecules to nanoparticles.
Proc. Natl. Acad. Sci. U. S. A. 2015, 112, 7903−7908.
(79) Mavrikakis, M.; Stoltze, P.; Norskov, J. K. Making gold less
noble. Catal. Lett. 2000, 64, 101−106.
(80) Müller, P.; Kern, R. Equilibrium nano-shape changes induced by
epitaxial stress (generalised Wulf−Kaishew theorem). Surf. Sci. 2000,
457, 229−253.
(81) Silly, F.; Castell, M. R. Selecting the shape of supported metal
nanocrystals: Pd huts, hexagons, or pyramids on SrTiO3(001). Phys.
Rev. Lett. 2005, 94, 046103.
(82) Ahmadi, M.; Behafarid, F.; Roldan Cuenya, B. Size-dependent
adhesion energy of shape-selected Pd and Pt Nanoparticles. Nanoscale
2016, 8, 11635.
(83) Ahmadi, M.; Behafarid, F.; Holse, C.; Nielsen, J. H.; Roldan
Cuenya, B. Shape-selection of thermodynamically stabilized colloidal
Pd and Pt nanoparticles controlled via support effects. J. Phys. Chem. C
2015, 119, 29178−29185.
(84) Behafarid, F.; Roldan Cuenya, B. Nanoepitaxy using micellar
nanoparticles. Nano Lett. 2011, 11, 5290−5296.
(85) Mager-Maury, C.; Bonnard, G.; Chizallet, C.; Sautet, P.;
Raybaud, P. H2-induced reconstruction of supported Pt clusters:
metal-support interaction versus surface hydride. ChemCatChem 2011,
3, 200−207.
(86) Sanchez, S. I.; Menard, L. D.; Bram, A.; Kang, J. H.; Small, M.
W.; Nuzzo, R. G.; Frenkel, A. I. The emergence of nonbulk properties
in supported metal clusters: negative thermal expansion and atomic
disorder in Pt nanoclusters supported on γ-Al2O3. J. Am. Chem. Soc.
2009, 131, 7040−7054.
(87) Venezia, A. M.; Parola, V. L.; Pawelec, B.; Fierro, J. L. G.
Hydrogenation of aromatics over Au-Pd/SiO2-Al2O3 catalysts; support
acidity effect. Appl. Catal., A 2004, 264, 43−51.
(88) Lopez, N. On the origin of the catalytic activity of gold
nanoparticles for low-temperature CO oxidation. J. Catal. 2004, 223,
232−235.
(89) Rodriguez, J. A.; Wang, X.; Liu, P.; Wen, W.; Hanson, J. C.;
Hrbek, J.; Perez, M.; Evans, J. Gold nanoparticles on ceria: importance
of O vacancies in the activation of gold. Top. Catal. 2007, 44, 73−81.
(90) Häkkinen, H.; Abbet, S.; Sanchez, A.; Heiz, U.; Landman, U.
Structural, Electronic, and Impurity-Doping Effects in Nanoscale
Chemistry: Supported Gold Nanoclusters. Angew. Chem., Int. Ed. 2003,
42, 1297−1300.
(91) Carrasco, J.; López-Durán, D.; Liu, Z.; Duchoň, T.; Evans, J.;
Senanayake, S. D.; Crumlin, E. J.; Matolín, V.; Rodríguez, J. A.;
Ganduglia-Pirovano, M. V. In situ and theoretical studies for the
dissociation of water on an active Ni/CeO2 catalyst: importance of
strong metal-support interactions for the cleavage of O-H bonds.
Angew. Chem., Int. Ed. 2015, 54, 3917−3921.
(92) Yang, X.; Kattel, S.; Senanayake, S. D.; Boscoboinik, J. A.; Nie,
X.; Graciani, J.; Rodriguez, J. A.; Liu, P.; Stacchiola, D. J.; Chen, J. G.
Low pressure CO2 hydrogenation to methanol over gold nanoparticles
activated on a CeOx/TiO2 interface. J. Am. Chem. Soc. 2015, 137,
10104−10107.
(93) Harding, C.; Habibpour, V.; Kunz, S.; Farnbacher, A. N.-S.;
Heiz, U.; Yoon, B.; Landman, U. Control and manipulation of gold
nanocatalysis: effects of metal oxide support thickness and
composition. J. Am. Chem. Soc. 2009, 131, 538−548.
(94) Pacchioni, G.; Freund, H. Electron transfer at oxide surfaces. the
MgO paradigm: from defects to ultrathin films. Chem. Rev. 2013, 113,
4035−4072.
(95) Yoon, B.; Hakkinen, H.; Landman, U.; Worz, A. S.; Antonietti, J.
M.; Abbet, S.; Judai, K.; Heiz, U. Charging effects on bonding and
catalyzed oxidation of CO on Au8 clusters on MgO. Science 2005, 307,
403−407.
(96) Roldán, A.; Ricart, J. M.; Illas, F.; Pacchioni, G. O2 activation by
Au5 clusters stabilized on clean and electron-rich MgO stepped
surfaces. J. Phys. Chem. C 2010, 114, 16973−16978.
(97) Landman, U.; Yoon, B.; Zhang, C.; Heiz, U.; Arenz, M. Factors
in gold nanocatalysis: oxidation of CO in the non-scalable size regime.
Top. Catal. 2007, 44, 145−158.
(98) Pacchioni, G.; Giordano, L.; Baistrocchi, M. Charging of metal
atoms on ultrathin MgO/Mo(100) films. Phys. Rev. Lett. 2005, 94,
226104.
(99) Repp, J.; Meyer, G.; Olsson, F. E.; Persson, M. Controlling the
charge state of individual gold adatoms. Science 2004, 305, 493−495.
(100) Mammen, N.; Narasimhan, S.; Gironcoli, S. d. Tuning the
morphology of gold clusters by substrate doping. J. Am. Chem. Soc.
2011, 133, 2801−2803.
(101) Shao, X.; Prada, S.; Giordano, L.; Pacchioni, G.; Nilius, N.;
Freund, H.-J. Tailoring the shape of metal ad-particles by doping the
oxide support. Angew. Chem., Int. Ed. 2011, 50, 11525−11527.
(102) Stavale, F.; Shao, X.; Nilius, N.; Freund, H.-J.; Prada, S.;
Giordano, L.; Pacchioni, G. Donor characteristics of transition-metaldoped oxides: Cr-doped MgO versus Mo-doped CaO. J. Am. Chem.
Soc. 2012, 134, 11380−11383.
(103) Lin, X.; Yang, B.; Benia, H. M.; Myrach, P.; Yulikov, M.;
Aumer, A.; Brown, M.; Sterrer, M.; Bondarchuk, O.; Kieseritzky, E.;
et al. Charge-mediated adsorption behavior of CO on MgO-supported
Au clusters. J. Am. Chem. Soc. 2010, 132, 7745−7749.
(104) Behafarid, F.; Ono, L. K.; Mostafa, S.; Croy, J. R.; Shafai, G.;
Hong, S.; Rahman, T. S.; Bare, S. R.; Cuenya, B. R. Electronic
properties and charge transfer phenomena in Pt nanoparticles on
gamma-Al2O3: size, shape, support, and adsorbate effects. Phys. Chem.
Chem. Phys. 2012, 14, 11766−11779.
(105) Petrie, W. T.; Vohs, J. M. Interaction of platinum films with the
(0001̅) and (0001) surfaces of ZnO. J. Chem. Phys. 1994, 101, 8098.
(106) Lykhach, Y.; Kozlov, S. M.; Skála, T.; Tovt, A.; Stetsovych, V.;
Tsud, N.; Dvořaḱ , F.; Johánek, V.; Neitzel, A.; Mysliveček, J.; Fabris,
S.; Matolín, V.; Neyman, K. M.; Libuda, J. Counting electrons on
supported nanoparticles. Nat. Mater. 2015, 15, 284−288.
(107) James, T. E.; Campbell, C. T. Catalysis: Quantifying charge
transfer. Nature Energy 2016, 1, 16002.
(108) Nilius, N.; Rienks, E. D. L.; Rust, H. P.; Freund, H. J. Selforganization of gold atoms on a polar FeO(111) surface. Phys. Rev.
Lett. 2005, 95, 066101.
(109) Linsmeier, C.; Taglauer, E. Strong metal-support interactions
on rhodium model catalysts. Appl. Catal., A 2011, 391, 175−186.
(110) Berkó, A.; Ulrych, I.; Prince, K. C. Encapsulation of Rh
nanoparticles supported on TiO2(110)-(1 × 1) surface: XPS and STM
studies. J. Phys. Chem. B 1998, 102, 3379−3386.
(111) Fu, Q.; Wagner, T.; Olliges, S.; Carstanjen, H. D. Metal-oxide
interfacial reactions: Encapsulation of Pd on TiO2(110). J. Phys. Chem.
B 2005, 109, 944−951.
3531
DOI: 10.1021/acs.jpclett.6b01198
J. Phys. Chem. Lett. 2016, 7, 3519−3533
The Journal of Physical Chemistry Letters
Perspective
(131) Mudiyanselage, K.; Senanayake, S. D.; Feria, L.; Kundu, S.;
Baber, A. E.; Graciani, J.; Vidal, A. B.; Agnoli, S.; Evans, J.; Chang, R.;
Axnanda, S.; Liu, Z.; Sanz, J. F.; Liu, P.; Rodriguez, J. A.; Stacchiola, D.
J. Importance of the metal-oxide interface in catalysis: in situ studies of
the water-gas shift reaction by ambient-pressure X-ray photoelectron
spectroscopy. Angew. Chem., Int. Ed. 2013, 52, 5101−5105.
(132) Graciani, J.; Mudiyanselage, K.; Xu, F.; Baber, A. E.; Evans, J.;
Senanayake, S. D.; Stacchiola, D. J.; Liu, P.; Hrbek, J.; Sanz, J. F.;
Rodriguez, J. A. Highly active copper-ceria and copper-ceria-titania
catalysts for methanol synthesis from CO2. Science 2014, 345, 546−
550.
(133) Ciambelli, P.; Palma, V.; Ruggiero, A. Low temperature
catalytic steam reforming of ethanol. 1. The effect of the support on
the activity and stability of Pt catalysts. Appl. Catal., B 2010, 96, 18−
27.
(134) Choong, C. K. S.; Zhong, Z.; Huang, L.; Wang, Z.; Ang, T. P.;
Borgna, A.; Lin, J.; Hong, L.; Chen, L. Effect of calcium addition on
catalytic ethanol steam reforming of Ni/Al2O3: I. Catalytic stability,
electronic properties and coking mechanism. Appl. Catal., A 2011, 407,
145−154.
(135) Carrero, A.; Calles, J. A.; Vizcaíno, A. J. Effect of Mg and Ca
addition on coke deposition over Cu−Ni/SiO2 catalysts for ethanol
steam reforming. Chem. Eng. J. 2010, 163, 395−402.
(136) Hu, Y.; Wu, P.; Yin, Y.; Zhang, H.; Cai, C. Effects of structure,
composition, and carbon support properties on the electrocatalytic
activity of Pt-Ni-graphene nanocatalysts for the methanol oxidation.
Appl. Catal., B 2012, 111−112, 208−217.
(137) da Silva, A. M.; de Souza, K. R.; Mattos, L. V.; Jacobs, G.;
Davis, B. H.; Noronha, F. B. The effect of support reducibility on the
stability of Co/CeO2 for the oxidative steam reforming of ethanol.
Catal. Today 2011, 164, 234−239.
(138) Rozanov, V. V.; Krylov, O. V. Hydrogen spillover in
heterogeneous catalysis. Usp. Khim. 1997, 66, 117−130.
(139) Conner, W. C.; Falconer, J. L. Spillover in heterogeneous
catalysis. Chem. Rev. 1995, 95, 759−788.
(140) Teichner, S. J. Recent studies in hydrogen and oxygen spillover
and their impact on catalysis. Appl. Catal. 1990, 62, 1−10.
(141) Lewis, E. A.; Marcinkowski, M. D.; Murphy, C. J.; Liriano, M.
L.; Sykes, E. C. H. Hydrogen dissociation, spillover, and desorption
from Cu-supported Co nanoparticles. J. Phys. Chem. Lett. 2014, 5,
3380−3385.
(142) Tsang, S. C.; Bulpitt, C. D. A.; Mitchell, P. C. H.; RamirezCuesta, A. J. Some new insights into the sensing mechanism of
palladium promoted tin (IV) oxide sensor. J. Phys. Chem. B 2001, 105,
5737−5742.
(143) Contescu, C. I.; Brown, C. M.; Liu, Y.; Bhat, V. V.; Gallego, N.
C. Detection of hydrogen spillover in palladium-modified activated
carbon fibers during hydrogen adsorption. J. Phys. Chem. C 2009, 113,
5886−5890.
(144) Zielinski, M.; Wojcieszak, R.; Monteverdi, S.; Mercy, M.;
Bettahar, M. Hydrogen storage in nickel catalysts supported on
activated carbon. Int. J. Hydrogen Energy 2007, 32, 1024−1032.
(145) Bliem, R.; van der Hoeven, J.; Zavodny, A.; Gamba, O.;
Pavelec, J.; de Jongh, P. E.; Schmid, M.; Diebold, U.; Parkinson, G. S.
An atomic-scale view of CO and H2 oxidation on a Pt/Fe3O4 model
catalyst. Angew. Chem., Int. Ed. 2015, 54, 13999−14002.
(146) Huizinga, T.; Prins, R. Behavior of titanium3+ centers in the
low- and high-temperature reduction of platinum/titanium dioxide,
studied by ESR. J. Phys. Chem. 1981, 85, 2156−2158.
(147) Lin, S. Hydrogenation of aromatic hydrocarbons over
supported Pt catalysts.I. benzene hydrogenation. J. Catal. 1993, 143,
539−553.
(148) Benseradj, F.; Sadi, F.; Chater, M. Hydrogen spillover studies
on diluted Rh/Al2O3 catalyst. Appl. Catal., A 2002, 228, 135−144.
(149) Miller, J. Hydrogen temperature-programmed desorption (H2
TPD) of supported platinum catalysts. J. Catal. 1993, 143, 395−408.
(150) Modica, F. S.; Miller, J. T.; Meyers, B. L.; Koningsberger, D. C.
Role of spill-over hydrogen in the hydrogenolysis of neopentane.
Catal. Today 1994, 21, 37−48.
(112) Aizawa, M.; Lee, S.; Anderson, S. L. Sintering, oxidation, and
chemical properties of size-selected nickel clusters on TiO2(110). J.
Chem. Phys. 2002, 117, 5001−5011.
(113) Bernal, S.; Calvino, J. J.; Cauqui, M. A.; Gatica, J. M.; Cartes, C.
L.; Omil, J. A. P.; Pintado, J. M. Some contributions of electron
microscopy to the characterisation of the strong metal-support
interaction effect. Catal. Today 2003, 77, 385−406.
(114) Jochum, W.; Eder, D.; Kaltenhauser, G.; Kramer, R. Impedance
measurements in catalysis: charge transfer in titania supported noble
metal catalysts. Top. Catal. 2007, 46, 49−55.
(115) Dulub, O.; Hebenstreit, W.; Diebold, U. Imaging cluster
surfaces with atomic resolution: The strong metal-support interaction
state of Pt supported on TiO2(110). Phys. Rev. Lett. 2000, 84, 3646−
3649.
(116) Fu, Q.; Wagner, T. Interaction of nanostructured metal
overlayers with oxide surfaces. Surf. Sci. Rep. 2007, 62, 431−498.
(117) Caballero, A.; Holgado, J. P.; Gonzalez-delaCruz, V. M.; Habas,
S. E.; Herranz, T.; Salmeron, M. In situ spectroscopic detection of
SMSI effect in a Ni/CeO2 system: hydrogen-induced burial and dig
out of metallic nickel. Chem. Commun. 2010, 46, 1097−1099.
(118) Pesty, F.; Steinrück, H.-P.; Madey, T. E. Thermal stability of Pt
films on TiO2(110): evidence for encapsulation. Surf. Sci. 1995, 339,
83−95.
(119) Bowker, M.; Sharpe, R. Pd deposition on TiO2(110) and
nanoparticle encapsulation. Catal. Struct. React. 2015, 1, 140−145.
(120) Belzunegui, J. P.; Sanz, J.; Rojo, J. M. Contribution of physical
blocking and electronic effect to establishment of strong metal support
interaction in Rh/TiO2 catalysts. J. Am. Chem. Soc. 1992, 114, 6749−
6754.
(121) Bernal, S.; Botana, F. J.; Calvino, J. J.; Lopez, C.; PerezOmil, J.
A.; RodriguezIzquierdo, J. M. High-resolution electron microscopy
investigation of metal-support interactions in Rh/TiO2. J. Chem. Soc.,
Faraday Trans. 1996, 92, 2799−2809.
(122) Badri, A.; Binet, C.; Lavalley, J.-C. Metal-support interaction in
Pd/CeO2 catalysts. Part 2.-Ceria textural effects. J. Chem. Soc., Faraday
Trans. 1996, 92, 1603.
(123) Abid, M.; Paul-Boncour, V.; Touroude, R. Pt/CeO2 catalysts in
crotonaldehyde hydrogenation: Selectivity, metal particle size and
SMSI states. Appl. Catal., A 2006, 297, 48−59.
(124) Sun, Y. N.; Qin, Z. H.; Lewandowski, M.; Carrasco, E.; Sterrer,
M.; Shaikhutdinov, S.; Freund, H. J. Monolayer iron oxide film on
platinum promotes low temperature CO oxidation. J. Catal. 2009, 266,
359−368.
(125) Hardacre, C.; Ormerod, R. M.; Lambert, R. M. Platinumpromoted catalysis by ceria a study of carbon monoxide oxidation over
Pt(111)/CeO2. J. Phys. Chem. 1994, 98, 10901−10905.
(126) Yarulin, A.; Berguerand, C.; Alonso, A. O.; Yuranov, I.; KiwiMinsker, L. Increasing Pt selectivity to vinylaniline by alloying with Zn
via reactive metal−support interaction. Catal. Today 2015, 256, 241−
249.
(127) Behrens, M.; Studt, F.; Kasatkin, I.; Kuhl, S.; Havecker, M.;
Abild-Pedersen, F.; Zander, S.; Girgsdies, F.; Kurr, P.; Kniep, B. L.;
Tovar, M.; Fischer, R. W.; Norskov, J. K.; Schlogl, R. The active site of
methanol synthesis over Cu/ZnO/Al2O3 industrial catalysts. Science
2012, 336, 893−897.
(128) Lunkenbein, T.; Schumann, J.; Behrens, M.; Schlögl, R.;
Willinger, M. G. Formation of a ZnO overlayer in industrial Cu/ZnO/
Al2O3 catalysts induced by strong metal-support interactions. Angew.
Chem. 2015, 127, 4627−4631.
(129) Kuld, S.; Thorhauge, M.; Falsig, H.; Elkjær, C. F.; Helveg, S.;
Chorkendorff, I.; Sehested, J. Quantifying the promotion of Cu
catalysts by ZnO for methanol synthesis. Science 2016, 352, 969−974.
(130) Senanayake, S. D.; Ramírez, P. J.; Waluyo, I.; Kundu, S.;
Mudiyanselage, K.; Liu, Z.; Liu, Z.; Axnanda, S.; Stacchiola, D. J.;
Evans, J.; Rodriguez, J. A. Hydrogenation of CO2 to methanol on
CeOx/Cu(111) and ZnO/Cu(111) catalysts: role of the metal−oxide
interface and importance of Ce3+ sites. J. Phys. Chem. C 2016, 120,
1778−1784.
3532
DOI: 10.1021/acs.jpclett.6b01198
J. Phys. Chem. Lett. 2016, 7, 3519−3533
The Journal of Physical Chemistry Letters
Perspective
(151) Colbourn, E. A.; Mackrodt, W. C. Theoretical aspects of H2
and CO chemisorption on MgO surfaces. Surf. Sci. 1982, 117, 571−
580.
(152) Karna, S. P.; Pugh, R. D.; Shedd, W. M.; Singaraju, B. B. K.
Interaction of H+/H0 with O atoms in thin SiO2 films: a firstprinciples quantum mechanical study. J. Non-Cryst. Solids 1999, 254,
66−73.
(153) Ahmed, F.; Alam, M. K.; Suzuki, A.; Koyama, M.; Tsuboi, H.;
Hatakeyama, N.; Endou, A.; Takaba, H.; Del Carpio, C. A.; Kubo, M.;
Miyamoto, A. Dynamics of hydrogen spillover on Pt/γ-Al2O3 catalyst
surface: a quantum chemical molecular dynamics study. J. Phys. Chem.
C 2009, 113, 15676−15683.
(154) Holmgren, A.; Duprez, D.; Andersson, B. A model of oxygen
transport in Pt/Ceria catalysts from isotope exchange. J. Catal. 1999,
182, 441−448.
(155) Bamwenda, G. R.; Tsubota, S.; Nakamura, T.; Haruta, M. The
influence of the preparation methods on the catalytic activity of
platinum and gold supported on TiO2 for CO oxidation. Catal. Lett.
1997, 44, 83−87.
(156) Bowker, M.; Fourré, E. Direct interactions between metal
nanoparticles and support: STM studies of Pd on TiO2(110). Appl.
Surf. Sci. 2008, 254, 4225−4229.
(157) Salazar-Villalpando, M. D.; Berry, D. A.; Cugini, A. Role of
lattice oxygen in the partial oxidation of methane over Rh/zirconiadoped ceria. Isotopic studies. Int. J. Hydrogen Energy 2010, 35, 1998−
2003.
(158) Martin, D.; Duprez, D. Mobility of Surface Species on Oxides.
1. Isotopic Exchange of 18O2 with 16O of SiO2, Al2O3, ZrO2, MgO,
CeO2, and CeO2-Al2O3. Activation by Noble Metals. Correlation with
Oxide Basicity. J. Phys. Chem. 1996, 100, 9429−9438.
(159) Glugla, P. G.; Bailey, K. M.; Falconer, J. L. Isotopic
identification of surface site transfer on nickel/alumina catalysts. J.
Phys. Chem. 1988, 92, 4474−4478.
(160) Xu, W.; Liu, Z.; Johnston-Peck, A. C.; Senanayake, S. D.; Zhou,
G.; Stacchiola, D.; Stach, E. A.; Rodriguez, J. A. Steam reforming of
ethanol on Ni/CeO2: reaction pathway and interaction between Ni
and the CeO2 support. ACS Catal. 2013, 3, 975−984.
(161) Divins, N. J.; Angurell, I.; Escudero, C.; Perez-Dieste, V.;
Llorca, J. Influence of the support on surface rearrangements of
bimetallic nanoparticles in real catalysts. Science 2014, 346, 620−623.
(162) Remediakis, I. N.; Lopez, N.; Norskov, J. K. CO oxidation on
rutile-supported Au nanoparticles. Angew. Chem. 2005, 117, 1858−
1860.
(163) Molina, L. M.; Rasmussen, M. D.; Hammer, B. Adsorption of
O2 and oxidation of CO at Au nanoparticles supported by TiO2(110).
J. Chem. Phys. 2004, 120, 7673.
(164) Green, I. X.; Tang, W. J.; Neurock, M.; Yates, J. T.
Spectroscopic observation of dual catalytic sites during oxidation of
CO on a Au/TiO2 catalyst. Science 2011, 333, 736−739.
(165) Chen, M.; Goodman, D. W. Catalytically active gold: from
nanoparticles to ultrathin films. Acc. Chem. Res. 2006, 39, 739−746.
(166) Williams, W. D.; Shekhar, M.; Lee, W.-S.; Kispersky, V.;
Delgass, W. N.; Ribeiro, F. H.; Kim, S. M.; Stach, E. A.; Miller, J. T.;
Allard, L. F. Metallic corner atoms in gold clusters supported on rutile
are the dominant active site during water−gas shift catalysis. J. Am.
Chem. Soc. 2010, 132, 14018−14020.
(167) Rodriguez, J. A.; Liu, P.; Hrbek, J.; Evans, J.; Pérez, M. Water
gas shift reaction on Cu and Au nanoparticles supported on
CeO2(111) and ZnO(000): intrinsic activity and importance of
support interactions. Angew. Chem., Int. Ed. 2007, 46, 1329−1332.
(168) Ono, L. K.; Behafarid, F.; Cuenya, B. R. Nano-gold diggers: Au
assisted SiO2 decomposition and desorption in supported nanocatalysts. ACS Nano 2013, 7, 10327−10334.
(169) Stone, P.; Smith, R. D.; Bowker, M. The structure and
reactivity of anchored nanoparticles on a reducible support. Faraday
Discuss. 2004, 125, 379−390.
(170) Behafarid, F.; Roldan Cuenya, B. Nano pinstripes: TiO2
nanostripe formation by nanoparticle-mediated pinning of step
edges. J. Phys. Chem. Lett. 2012, 3, 608−612.
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