Capping ligands as selectivity switchers in hydrogenation reactions

Article abstract of DOI:10.1021/nl3027636

We systematically investigated the role of surface modification of nanoparticles catalyst in alkyne hydrogenation reactions and proposed the general explanation of effect of surface ligands on the selectivity and activity of Pt and Co/Pt nanoparticles (NPs) using experimental and computational approaches. We show that the proper balance between adsorption energetics of alkenes at the surface of NPs as compared to that of capping ligands defines the selectivity of the nanocatalyst for alkene in alkyne hydrogenation reaction. We report that addition of primary alkylamines to Pt and CoPt₃ NPs can drastically increase selectivity for alkene from 0 to more than 90% with ～99.9% conversion. Increasing the primary alkylamine coverage on the NP surface leads to the decrease in the binding energy of octenes and eventual competition between octene and primary alkylamines for adsorption sites. At sufficiently high coverage of catalysts with primary alkylamine, the alkylamines win, which prevents further hydrogenation of alkenes into alkanes. Primary amines with different lengths of carbon chains have similar adsorption energies at the surface of catalysts and, consequently, the same effect on selectivity. When the adsorption energy of capping ligands at the catalytic surface is lower than adsorption energy of alkenes, the ligands do not affect the selectivity of hydrogenation of alkyne to alkene. On the other hand, capping ligands with adsorption energies at the catalytic surface higher than that of alkyne reduce its activity resulting in low conversion of alkynes.

Full text of DOI:10.1021/nl3027636

Letter
pubs.acs.org/NanoLett
Capping Ligands as Selectivity Switchers in Hydrogenation Reactions
Soon Gu Kwon,† Galyna Krylova,† Aslihan Sumer,‡ Michael M. Schwartz,‡ Emilio E. Bunel,‡
Christopher L. Marshall,‡ Soma Chattopadhyay,§ Byeongdu Lee,§ Julius Jellinek,*,‡
and Elena V. Shevchenko*,†
‡
§
†Center for Nanoscale Materials, Chemical Sciences and Engineering Division, and Advanced Photon Source, Argonne National
Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
S
* Supporting Information
ABSTRACT: We systematically investigated the role of surface modification
of nanoparticles catalyst in alkyne hydrogenation reactions and proposed the
general explanation of effect of surface ligands on the selectivity and activity
of Pt and Co/Pt nanoparticles (NPs) using experimental and computational
approaches. We show that the proper balance between adsorption energetics
of alkenes at the surface of NPs as compared to that of capping ligands
defines the selectivity of the nanocatalyst for alkene in alkyne hydrogenation
reaction. We report that addition of primary alkylamines to Pt and CoPt3
NPs can drastically increase selectivity for alkene from 0 to more than 90%
with ∼99.9% conversion. Increasing the primary alkylamine coverage on the
NP surface leads to the decrease in the binding energy of octenes and
eventual competition between octene and primary alkylamines for adsorption sites. At sufficiently high coverage of catalysts with
primary alkylamine, the alkylamines win, which prevents further hydrogenation of alkenes into alkanes. Primary amines with
different lengths of carbon chains have similar adsorption energies at the surface of catalysts and, consequently, the same effect on
selectivity. When the adsorption energy of capping ligands at the catalytic surface is lower than adsorption energy of alkenes, the
ligands do not affect the selectivity of hydrogenation of alkyne to alkene. On the other hand, capping ligands with adsorption
energies at the catalytic surface higher than that of alkyne reduce its activity resulting in low conversion of alkynes.
KEYWORDS: Nanoparticles, surface ligands, catalysis, selectivity, activity, binding energetics
partial) of capping ligand molecules. Obviously, these adsorbed
molecules can significantly impact the performance of nano-
catalysts since catalytic reactions take place at surface, and
ligands can affect the electronic characteristics of surface sites as
well as hinder the access of the substrate molecules to the
surface of NPs.42,43
atalysis is a key step in production of various chemicals
1−7
Cthat has also a significant environmental aspect.
The
quest for “green chemistries” emphasizes the importance of
catalysts with improved selectivity since they can reduce
significantly the amount of the generated chemical waste.1
High-performance catalysts also play an important role in
energy conversion and storage technologies.
At present, a clear understanding of the role of capping
ligands in catalytic reactions, wherein chemically synthesized
nanocatalysts are used, is still far from complete.44−47 Both
moderate48−50 and reduced35,40,51,52 catalytic activities have
been reported for surfactant-stabilized NPs. Surface molecules
on colloidal NPs are usually remnants of chemical compounds
introduced into reaction mixtures. Previously, it has been
shown that modification of metal surfaces (e.g., Pt, Pd, and
others) by the simple addition of strongly adsorbing chiral
molecules allowed for efficient stereoselective control over
reactions at the metal surface.53 Recently it has been also
reported that surface modification of CoPt3 NPs by long-chain
primary amines resulted in highly selective hydrogenation of
CO bonds in α,β-unsaturated aldehydes.54 This finding has
been attributed to the steric effect of the long-chain amines that
Significant progress has been made in the synthesis of high-
performance nanocatalysts using solution-based ap-
proaches.8−22 Thus the specific activity of NPs can be greatly
improved by the decrease in their size and by tuning their
composition.23−34 It has also been shown that catalytically
active NPs with certain shapes can dramatically affect the
reaction pathways and change the selectivity of reactions.35−37
For example, Pt NPs with high-index facets prepared
electrochemically showed very high catalytic activity in
electro-oxidation of formic acid and ethanol.10 Also high
surface-to-volume ratio of Pd−Pt nanodendrites was reported
to lead to their enhanced electrocatalytic activity.28 Control of
the size and shape of NPs is often achieved by the introduction
of certain surfactant molecules that play a key role in synthesis
of NPs.38−41 These molecules form complexes with the
precursors and bind onto the surface of NPs affecting their
nucleation and growth processes. As a result, the surface of the
NPs synthesized in solution is covered by a layer (full or
Received: July 25, 2012
Revised: September 12, 2012
Published: September 18, 2012
© 2012 American Chemical Society
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favors adsorption of the substrate molecules to the NPs via the
end aldehyde groups rather than adsorption of the CC bonds
located in the middle of the molecule.
reactions were performed using a stainless steel reactor under
200 psig H2 (Supporting Information Figure S2). Hydro-
genation of 4-octyne was chosen as a model catalytic reaction
(Scheme 1). The desired product in our study is 4-octene and
The goal of this combined experimental/computational
study is to examine and to understand the role of common
capping ligands, such as primary amines, trioctylphosphine
(TOP), trioctylphosphine oxide (TOPO), oleic acid, and
others on the catalytic functionality of Pt and Co/Pt NPs in
hydrogenation of alkynes. Selective hydrogenation of alkynes
into alkenes has been an important topic in the study of
catalytic hydrogenation reactions.55−63 Here we report that
addition of primary alkylamines to Pt and CoPt3 NPs can
drastically increase the selectivity for alkene from 0 to >90%
without affecting the catalytic activity. We present a computa-
tional analysis for the observed experimental effects of the
primary amine on the selectivity and activity of the NPs. We
also provide the general explanation of the effect of surface
modification of NPs on selectivity and conversion in hydro-
genation of alkynes. In particular, we show that the source of
these effects is the ligand coverage dependent difference in the
adsorption energetics of the substrate molecules and the
modifier ligands.
Scheme 1. Hydrogenation Reactions of 4-Octyne to 4-
Octene and Octane
selectivity is defined as the ratio [4-octene]/([4-octene] +
[octane]). Thoroughly washed Pt and CoPt3 NPs showed high
activity for hydrogenation reaction leading to the complete
conversion of 4-octyne into octane meaning 0% selectivity for
4-octene (Figure 1c). However, the addition of primary
alkylamine to the reaction mixture had a major effect on the
reaction products. Thus, we observed that introduction of
octylamine switched the selectivity for the desired 4-octene to a
value greater than 90% and that the apparent conversion was at
the same level as for purified NPs (∼99.9% conversion, Figure
1c). Among the isomers of 4-octene, the cis form was dominant
in the product (Supporting Information Figure S3).67
Controlled experiments using 6 nm Co NPs and 1-octylamine
showed zero activity for the alkyne hydrogenation reaction
(Supporting Information Figure S4). Thus, the observed
remarkable enhancement in the selectivity of Pt and CoPt3
nanocatalysts in the presence of octylamine was a consequence
of surface modification of these NPs with octylamine.
We chose 3.5 nm Pt and 4.5 nm alloyed CoPt3 NPs (Figure
1a,b) as model catalysts based on good catalytic activity of Pt in
In the next experiments, we have added different capping
ligands that are commonly used in the synthesis of NPs to 4-
octyne solutions containing purified 3.5 nm Pt NPs and
monitored their effect on the catalytic performance. Addition of
trioctylamine, oleic acid, and trioctylphosphine oxide (TOPO)
affected neither the selectivity nor the activity as compared with
the “clean” Pt NPs. Addition of trioctylphosphine (TOP)
significantly lowered the activity, while 1-dodecanethiol (DDT)
almost completely deactivated Pt NPs (Figure 2). The
hydrogenation of alkynes proceeds through sequential addition
of H2 to π-bonding orbitals of unsaturated hydrocarbons
(Scheme 1). These reactions take place on the surfaces of the
NP catalysts.68,69 The effect of octylamine shown in Figures 1
and 2 suggests that among various capping ligands tested,
Figure 1. TEM images of (a) 3.5 nm Pt and (b) 4.5 nm CoPt3 NPs;
(c) composition of the reaction products formed as a result of 4-
octyne hydrogenation in the solutions containing only “clean” NPs
and NPs with 0.13 M of 1-octylamine. The concentration of Pt was 2.6
0.5 mM for both Pt and CoPt3 cases.
hydrogenation reactions.64 The Pt and CoPt3 NPs were
synthesized according to slightly modified procedures described
in refs 65 and 66, respectively. After synthesis, NPs were
thoroughly purified by repeated washing and precipitation.
According to thermogravimetric analysis (TGA), the amount of
residual alkylamine ligand on purified Pt NPs was ∼4 wt % that
corresponds to 0.1 mM in the hydrogenation reaction solution
(Supporting Information Figure S1). The hydrogenation
Figure 2. Effect of different capping ligands on activity and selectivity
of 3.5 nm Pt NPs in hydrogenation reaction of 4-octyne. The
concentration of all ligands was ∼23 mM.
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primary alkylamines allow for Reaction 1 but block Reaction 2
(Scheme 1).
solution). Further increase in the octylamine concentration
resulted in a rapid increase of selectivity that saturated at the
octylamine concentration of ∼100 mM. The total level of
conversion of 4-octyne was more than 99.9% at any
concentration of octylamine. These data indicated that the
selectivity was, indeed, defined by the degree of surface
coverage with the amines (see Supporting Information Figure
S5 for detail). Data supporting the central role of amine
coverage are also presented in Figure 3b, which shows
dependence of selectivity as a function of the amine
concentration for four different concentrations of Pt NPs. In
this experiment, the total (combined) surface area of Pt NPs
changes from case to case by a factor of ∼2. Inspection of the
graphs shows that four cases exhibit the same selectivity at
amine concentrations that also differ from one case to another
by a factor of ∼2. In other words, the amine concentrations that
furnish a given level of selectivity are proportional to the total
surface area of the NPs.
In order to get a better understanding of the role of primary
amines in alkyne hydrogenation catalyzed by Pt NPs we
analyzed the effect of surface coverage of catalyst by the
primary amines on selectivity. We gauged the degree of amine
surface coverage by the concentration of the amines in the
reaction mixture since there is a straightforward correlation
between the concentrations of added amines and adsorbed at
the surface of NPs. Thus, we have characterized the octylamine
concentration dependence of selectivity (Figure 3a). The onset
of selectivity starts at the octylamine concentration of ∼1−2
mM corresponding to a monolayer or slightly higher coverage
of the NP surface with amines if all the added octylamine
molecules would adsorb onto the NP surface (that is not
necessarily the case since there is a dynamic equilibrium
between octylamine molecules on the NP surface and in the
The data in Figure 3a,b suggest that the high coverage of
amine at the surface of NPs results in high selectivity for 4-
octene by blocking the hydrogenation of 4-octene to octane
(Reaction 2 in Scheme 1). In order to test this idea, we carried
out hydrogenation reactions of cis- and trans- forms of 4-octene
as starting reagents. We observed that the increase in amine
concentration results in the blocking of 4-octene hydrogenation
into octane (Figure 3c) leaving nearly the same amount of 4-
octene as in the case of 4-octyne hydrogenation at the same
concentrations of octylamine (Figure 3a). The relative amount
of alkene after cis- or trans-4-octene hydrogenation was slightly
(∼5%) higher than that from 4-octyne hydrogenation. This
difference can be attributed to a small fraction of 4-octyne
underwent a direct complete hydrogenation into 4-octane (cf.
refs 55 and 56). The experimental data presented in Figure 3
provide a compelling evidence for the role of primary
alkylamines as selectivity switchers/tuners. This role is to
attenuate or even block almost completely the hydrogenation
of 4-octene.
In order to uncover the mechanism by which the amine
ligands affect the selectivity in catalytic hydrogenation of
alkynes, we performed density functional theory (DFT) studies
of the energetics relevant to the processes at hand. In particular,
we evaluated the adsorption energies of 4-octyne, cis-/trans-4-
octene, and octylamine on the same site of a clean and
octylamine-covered (111) surface of Pt as represented by a 35-
atom Pt cluster (see Methodological Details and Supporting
Information Figure S6 for details). The DFT computations
showed that 4-octyne has the highest affinity to the clean
surface of Pt while alkylamine has the lowest (Figure 4,
Supporting Information Table S1). Figure 4 clearly shows that
as the number of the coadsorbed octylamines increases, the
adsorption energies of all four species decrease. Increasing the
octylamine coverage on Pt surface reduces the adsorption
energy of amines, alkenes, and alkynes due to the steric
interactions between hydrocarbon chains. At all coverages, the
adsorption energy of 4-octyne is higher than those of either
form of 4-octene or octylamine. Notably, higher coverage of
amine on the Pt surface affects the adsorption energy of CC
double bonds the most (Figure 4a). At sufficiently high
coverage of Pt surface with amines, the change in the order of
adsorption energies tilts the competition between 4-alkenes and
octylamines for binding sites on the catalyst surface in favor of
amines (Figure 4a). At high concentrations of amine in the
solution, the coverage of amine on the surface of the Pt NPs
Figure 3. (a) Selectivity and conversion of 4-octyne hydrogenation at
different concentrations of octylamine. The concentration of Pt was
∼3 mM. (b) Amine concentration-dependent selectivity for different
[Pt]surf as indicated on the curves. (c) Composition of 4-octene in the
product from trans-/cis-4-octene. Relative amount of alkene is defined
as [alkene] normalized to the initial concentration of alkene or alkyne.
In the inset, conversion for 4-octene hydrogenation is defined as 1-[4-
octene]final/[4-octene]initial
.
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Figure 5. Kinetic data demonstrating the conversion (upper section)
and the selectivity (lower section) of 4-octyne hydrogenation using 3.5
nm Pt NPs as a function of octylamine concentration (shown on the
right). The concentration of Pt was 2.6 0.5 mM in all experiments.
The data points shown in blue and red represent high and low
selectivity regimes, respectively.
selectivities show a gradual decline with time. The rate of this
decline decreases as the octylamine concentration increases
(Figure 5) and this correlates with the decrease in the 4-octene
adsorption energy as the octylamine coverage of the Pt
nanocatalyst increases (Figure 4). Thus the theoretical
calculations are in a very good agreement with the experimental
results shown in Figures 3−5 and explain high selectivity and
full conversion of alkynes at the surface of nanocatalysts densely
covered with molecules of primary alkylamines.
DFT calculations also indicate that the adsorption energetics
of alkenes (CnH2n, n = 3, 4) as compared to that of amines
defines hydrogenation selectivity. It was found that at high
coverage of Pt surface with octylamine adsorption energies of 4-
octene and 3-hexene are lower than that of octylamine while 1-
octene has higher adsorption energy (Figure 6). As a result we
can expect high yield of alkene in hydrogeneation reactions of
4-octyne and 3-hexyne and conversion of 1-octyne into octane.
Indeed, experimentally, we observed selectivities greater than
80% from hydrogenation reactions of 3-hexyne, 4-octyne, and
5-decyne; however, selectivity of ∼4% was observed in case of
1-octyne hydrogenation (Figure 7).
In order to provide further insights into selective exclusion of
alkene from the surface of Pt NPs by the primary amines, we
examined the effect of the hydrocarbon chain length of amine
on the selectivity in 4-octyne hydrogenation reaction. The DFT
calculations demonstrated that primary alkylamines with
different chain lengths have approximately the same adsorption
energy on Pt (Figure 8a) and, therefore, should have similar
effect on selectivity. Our experiments corroborate this
prediction. Experimentally, as in the case of octylamine, we
observed the same high selectivity (in the range between ∼83
and 91%) for all studied primary alkylamines (Figure 8b).
The DFT calculations also provide the rationale explanation
for the observed low performance of trioctylamine as a
selectivity promoter and for TOP being an activity attenuator
(Figure 2). The calculated adsorption energy of trioctylamine
on the Pt surface is 0.84 eV, which is lower than those of the
primary amines, while the adsorption energy of TOP is 2.55 eV,
which is higher than that of even 4-octyne. The lower
adsorption energy of trioctylamine makes it a less favorable
candidate for substitution of 4-octene. The high adsorption
energy of TOP makes it a poison for catalyst. These findings
Figure 4. (a) Plots of the adsorption energies of 4-octyne, cis-4-
octene, trans-4-octene, and 1-octylamine on clean and 1-octylamine
decorated (111) Pt surface (35 atom cluster) as a function of
octylamine coverage. Adsorption energies were obtained from DFT
computation. Dash red circle highlights the difference in the Eads of 4-
octene and octylamine. (b) Depiction of the structures used in DTF
calculations.
increases so that the adsorption energy of amines becomes
higher than those of alkene and, as a result, impedes the
adsorption of alkene molecules, blocking the conversion of 4-
octene into octane (Scheme 1). On the other hand, the
adsorption energy of 4-octyne is still substantially higher than
those of primary amine even at the high coverage of amine and,
hence, the hydrogenation of 4-octyne to 4-octene is not
impeded at any amine concentration. The coverage-dependent
trends and changes in the adsorption energies of substrates and
capping ligands provide the rational for understanding the role
of primary amines as selectivity switchers in catalytic hydro-
genation on Pt nanoparticles.
The presented picture is also consistent with the results of
our kinetic measurements shown in Figure 5. The activity
(conversion of 4-octyne) is ∼99.9% over all time scales
considered. The selectivity, however, exhibits different patterns
of time-dependence at different amine concentrations. At the
lowest concentration of octylamine (0.1 mM), the selectivity of
∼45% at t = 15 min drops to 0% at t = 30 min meaning that all
4-octyne is converted into octane. At the highest amine
concentration (210 mM), the selectivity is above 90% and
negligibly changes with time. This is consistent with the
displacement of all 4-octenes from the catalyst surface by
octylamines as soon as 4-octenes are generated from 4-octynes.
At intermediate octylamine concentrations, the initial high
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Figure 6. Summary of the DFT calculations on the effect of position of CC bond on the adsorption energy.
hydrogen as reactants, and alkylamines, oleic acid, trioctylphos-
phine, and trioctylphosphine oxide as capping ligands, we show
that the balance between the adsorption energetics of substrates
and capping ligands determines the selectivity and activity of
catalyst. A judicious selection of capping ligands with
appropriate adsorption energies on catalyst can lead to a
remarkable enhancement in its selectivity. We demonstrate that
sufficient concentrations of primary alkylamine ligands result in
higher than 90% selectivity toward selective hydrogenation at
an overall activity of 99.9%. Capping ligands with too low
adsorption energies, as compared to those of the subtrates, have
little or no effect on selectivity. Capping ligands with too high
adsorption energies significantly reduce activity. We expect the
general findings and methodology of this study to become an
efficient tool in rational use of capping ligands as modifiers of
catalytic functionality at the nanoscale.
Methodological Details. Synthesis of NPs. The synthesis
of Pt NPs was carried out by a method described in ref 65 with
minor modification. A reaction mixture was prepared by adding
0.2 g of Pt(acac)2, 0.89 g of oleic acid, and 0.81 g of oleylamine
into 10 mL of 1-octadecene. It was degassed at 100 °C for 20
min and heated at 120 °C for 30 min under nitrogen
atmosphere to form a clear yellow solution. It was further
heated to 200 °C at the rate of 4 °C/min and then kept at that
temperature for 30 min. After the reaction was stopped, Pt NPs
were separated and washed with excess acetone two times.
CoPt3 NPs were synthesized following the methods from ref
66.
Figure 7. Selectivity in hydrogenation reactions of different alkyne
molecules. All reactions were carried out with the fixed concentration
of 1-octylamine at 39 mM using 3.5 nm Pt NPs. The concentration of
P was 2.6 0.5 mM.
and considerations point to the importance of adsorption
energy as a guiding parameter for a judicious selection of
capping ligands with desired activity and selectivity effects.
In summary, this combined experimental/computational
study addresses the general subject of capping ligands as
modifiers of catalytic functionality of nanoparticles and presents
a methodology for understanding the role of surface
modification in defining/affecting the catalysts’ activity and/or
selectivity. In particular, we emphasize the role of capping
ligands as a means for substantial enhancement of selectivity.
Using Pt and CoPt3 NPs as catalysts, hydrocarbons and
Catalytic Studies. The hydrogenation reaction was carried
out in a stainless steel reactor at room temperature for 3 h
under H2 atmosphere (200 psig). In a standard condition, the
Figure 8. (a) Summary of the DFT calculations on the adsorption energy of primary alkylamines. (b) The effect of the carbon chain length in
primary amines on the selectivity in 4-octyne hydrogenation reaction using 3.5 nm Pt NPs. C6, C8, C12, and C18 are abbreviations for 1-hexyl-, 1-
octyl-, 1-dodecyl-, and 1-octadecylamine, respectively. The concentrations of amines were 39 mM. The concentration of Pt was 2.6 0.5 mM.
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Notes
reaction solution was prepared by dispersing Pt nanoparticles in
1.0 mL dodecane containing 3.75 wt % (255 mM) of 4-octyne.
The amount of Pt in the solution was controlled in the range of
0.4−0.6 mg, which was confirmed by inductively coupled
plasma (ICP) analysis. [Pt]surf is defined as the concentration of
Pt atoms at the surface of Pt NPs in the solution. The value of
[Pt]surf is calculated based on the net amount of Pt atoms in the
solution and the size of Pt NPs from TEM. During the reaction,
the solution was stirred at ∼7000 rpm. After the reaction, the
solutions were purged with nitrogen to remove any residual
hydrogen. Otherwise stated, the concentration of amine in the
reaction solution was controlled by adding 1-octylamine. On
the basis of the composition data from the reaction product,
conversion and selectivity of the catalytic reaction of 4-octyne
are defined as follow: (Conversion) = 1 − [4-octyne]/[4-
octyne]initial; (Selectivity) = [4-octene]/([4-octene] + [oc-
tane]).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Use of the Center for Nanoscale Materials was supported by
the U.S. Department of Energy, Office of Science, Office of
Basic Energy Sciences, under Contract No. DE-AC02-
06CH11357 (S.G.K., G.K., E.V.S.). This work was also
supported by the Office of Basic Energy Sciences, Division of
Chemical Sciences, Geosciences and Biosciences, U.S. Depart-
ment of Energy under Contract No. DE-AC02-06CH11357
(M.M.S., E.E.B., S.C., B.L., J.J.), and by the Institute for Atom-
efficient Chemical Transformations (IACT), an Energy
Frontier Research Center funded by the U.S. Department of
Energy, Office of Science, Office of Basic Energy Sciences (A.S.,
C.L.M., J.J.).
Characterization. Samples for transmission electron micros-
copy (TEM) were prepared by dropping and drying of 1−2 μL
of toluene solution of NPs on a carbon-coated copper grid
(Ted Pella). TEM measurements were performed using a JEOL
2100F microscope operated at 200 kV. Thermogravimetric
analysis was carried out using a Mettler Toledo TGA/
SDTA851e instrument. The sample was heated from 25 to
600 °C at the heating rate of 3 °C/min. The composition of the
solution after hydrogenation reaction was analyzed by gas
chromatography−mass spectrometry (GC-MS) instrument
composed of an Agilent 6890 GC system and a 5973 Network
Selective Detector.
Computational Framework. The computations were
performed within density functional theory with the PBE
exchange-correlation functional, double-ζ basis sets, and
Goedecker−Teter−Hutter type pseudopotentials as imple-
mented in the CP2K package.70 The size of the computation
cell was 30 × 30 × 30 Å. The adsorption energies were
computed using Supporting Information equations S3 and S4.
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ASSOCIATED CONTENT
■
S
* Supporting Information
TGA data on washed Pt NPs (Figure S1); a photo of a stainless
steel hydrogenation reactor (Figure S2); chromatogram of the
product from 4-octyne hydrogenation reaction (Figure S3);
composition data of the product from 4-octyne hydrogenation
reactions using Co NPs and 1-octylamine in the place of
catalyst (Figure S4); DFT calculation data for the adsorption
energies of 4-octyne, cis-4-octene, trans-4-octene, and 1-
octylamine on clean Pt surface and 4- and 5-amine decorated
Pt surfaces (Table S1); DFT calculation data for the adsorption
energies of different types of ligands on clean Pt surface (Table
S2); competitive adsorption model theory for competitive
binding of 4-octene and 1-octylamine onto the surface of Pt
NPs (Figure S5); EXAFS measurements data on CoPt3 NPs
before and after catalytic reactions (Tables S3 and S4);
computational methodology and Pt35 cluster model (Figure
S6). This material is available free of charge via the Internet at
http://pubs.acs.org.
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AUTHOR INFORMATION
■
Corresponding Author
*Tel: +1-630-252-3463. Fax: +1-630-252-7633. E-mail: (J.J.)
jellinek@anl.gov; (E.V.S.) eshevchenko@anl.gov.
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