Carbon Dioxide Conversion to Methanol over Size-Selected Cu4 Clusters at Low Pressures

Article abstract of DOI:10.1021/jacs.5b03668

The activation of CO₂ and its hydrogenation to methanol are of much interest as a way to utilize captured CO₂. Here, we investigate the use of size-selected Cu₄ clusters supported on Al₂O₃ thin films for CO₂ reduction in the presence of hydrogen. The catalytic activity was measured under near-atmospheric reaction conditions with a low CO₂ partial pressure, and the oxidation state of the clusters was investigated by in situ grazing incidence X-ray absorption spectroscopy. The results indicate that size-selected Cu₄ clusters are the most active low-pressure catalyst for catalytic CO₂ conversion to CH₃OH. Density functional theory calculations reveal that Cu₄ clusters have a low activation barrier for conversion of CO₂ to CH₃OH. This study suggests that small Cu clusters may be excellent and efficient catalysts for the recycling of released CO₂.

Full text of DOI:10.1021/jacs.5b03668

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Communication
Carbon Dioxide Conversion to Methanol over
Size-selected Cu4 Clus-ters at Low Pressures
Cong Liu, Bing Yang, Eric C. Tyo, Soenke Seifert, Janae DeBartolo,
Bernd von Issendorff, Peter Zapol, Stefan Vajda, and Larry A Curtiss
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b03668 • Publication Date (Web): 26 Jun 2015
Downloaded from http://pubs.acs.org on June 28, 2015
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Carbon Dioxide Conversion to Methanol over Size-selected Cu4 Clus-
ters at Low Pressures
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Cong Liua,‡, Bing Yanga,‡, Eric Tyoa, Soenke Seifertb, Janae DeBartolob, Bernd von Issendorffc, Pe-
ter Zapola,*, Stefan Vajdaa,d-f,* and Larry A. Curtissa,*
a Materials Science Division, Argonne National Laboratory, 9700 S. Cass Ave. Lemont, IL 60439, USA;
b X-ray Science Division, Argonne National Laboratory, 9700 S. Cass Ave. Lemont, IL 60439, USA;
c Physikalisches Institut, Universität Freiburg, Stefan-Meier-Straße 21, 79104 Freiburg, Germany;
d Nanoscience and Engineering Division, Argonne National Laboratory, 9700 S. Cass Ave. Lemont, IL 60439, USA;
e Department of Chemical and Environmental Engineering, School of Engineering & Applied Science, Yale
University, 9 Hillhouse Avenue, New Haven, CT 06520, USA;
f Institute for Molecular Engineering, University of Chicago, 5801 South Ellis Avenue Chicago, Illinois 60637, USA
Supporting Information Placeholder
because of their unique electronic and catalytic properties,
ABSTRACT: The activation of CO2 and its hydrogenation to
which differ from bulk metal surfaces and larger nanoparti-
cles. Although a number of computational and experimental
studies have been focused on catalytic and electrocatalytic
CO2 reduction to fuels on various metal clusters6-8 and larger
nanoparticles9-13, there is a paucity of research on CH3OH
synthesis from CO2 and H2 on size-selected non-precious
metal clusters. Previously, we have successfully synthesized
subnanometer metal clusters with narrow size distributions
on thin film support materials (e.g., Al2O3 and Fe3O4), and
these materials have shown great potential in the catalytic
conversion of small molecules.14-16 In this contribution, we
report on Al2O3 supported Cu4 clusters as an effective cata-
lyst for the reduction of CO2 to CH3OH at a low CO2 partial
pressure (0.013 atm), with a higher activity than those of re-
cently developed low-pressure catalysts.
methanol is of much interest as a way to utilize captured
CO2. In this work we investigate the use of size-selected Cu4
clusters supported on Al2O3 thin films for CO2 reduction in
the presence of hydrogen. The catalytic activity was meas-
ured under near-atmospheric reaction conditions with a low
CO2 partial pressure, and the oxidation state of the clusters
was investigated by in situ grazing incidence X-ray absorp-
tion spectroscopy. The results indicate that size-selected Cu4
clusters are the most active low-pressure catalyst for catalytic
CO2 conversion to CH3OH. Density functional theory calcu-
lations reveal that Cu4 clusters have a low activation barrier
for conversion of CO2 to CH3OH. This study suggests that
small Cu clusters may be excellent and efficient catalysts for
recycling of released CO2.
Cu4 clusters were synthesized using size-selected cluster
source,17 which enables single-size mass selection with atom-
ic precision without fragmentation.18 The Cu4 cluster was
chosen based on preliminary density functional (DFT) calcu-
lations indicating they are active for methanol formation. By
The industrial process of methanol (CH3OH) synthesis
from syngas (CO, CO2 and H2) is carried out at high pres-
sures (10 to 100 bar) using a Cu/ZnO/Al2O3 catalyst1. Due to
increasing emission of CO2 from fossil fuel combustion and
other anthropogenic activities, this catalytic system has also
become the focus of interest for obtaining sustainable
CH3OH by hydrogenation of captured CO2 (CO2 + 3H2→
CH3OH + H2O)2,3. Efforts have been made to modify and
improve the industrial Cu/ZnO/Al2O3 catalyst3-5. Neverthe-
less, the high pressure required for achieving a quality yield
of CH3OH using these catalysts brings a great challenge for
reducing the energy input and cost for this process. Also,
effective catalysts are in need for alternative feed streams
with lower CO2 concentrations. Thus, developing an effective
low-pressure catalyst for CO2 reduction to CH3OH is highly
attractive.
+
soft landing, 7 ng of Cu4 clusters were deposited onto a
three monolayer amorphous Al2O3 thin film prepared by
atomic layer deposition (ALD) on top of the native oxide of
silicon wafer (SiO2/Si(100)). The detailed description of the
preparation method can be found in the previous report.17
Previous studies have also shown that such a film can keep a
variety of clusters from sintering under reaction condi-
tions.15,16,19 All samples were exposed to air after synthesis and
oxidized copper clusters were identified in the subsequent
characterization. The catalytic testing and grazing-incidence
X-ray absorption near edge structure (GIXANES) measure-
ments of Al2O3 supported Cu4 clusters were performed in a
home-built reaction cell14,20,21 which allows for X-ray scatter-
ing off the sample surface at a grazing incident angle (αc =
0.18°)(Details see SI). All measurements were carried out
Recently, size-selected subnanometer transition metal
clusters have received considerable attention in catalysis,
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under in-situ conditions with 20 sccm flow of 1% CO2 and 3%
H2 gas mixture carried in helium at a total pressure of 1.25
atm.
observed TOR for methanol synthesis is fairly high in com-
parison to the numbers in the literature. 25,26 Table 1 lists the
TOR's of CO2 reduction to CH3OH for the present catalyst
(Al2O3 supported Cu4 clusters), recently developed low-
pressure catalyst (Ni5Ga3/SiO2), as well as bulk Cu materials
(Cu/ZnO/Al2O3 and polycrystalline Cu foil). It is clear that all
the materials reached the maximum activity of CH3OH in a
similar temperature range, 200-240°C. Compared to
Ni5Ga3/SiO2 and Cu/ZnO/Al2O3 at the ambient pressure, our
catalyst demonstrated much higher activity (one order of
magnitude higher) at a slightly higher total pressure (1.25
atm), but with much lower partial pressures (down by up to
two orders of magnitude) of the reaction gases (H2 and CO2),
although this activity of the supported Cu4 clusters is lower
than that of the polycrystalline Cu surface under a 6 times
higher pressure (Table 1). It clearly shows an outstanding
activity of the supported Cu4 clusters for CO2 reduction to
CH3OH at a low pressure.
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Figure 1. Oxidation state of Al2O3 supported Cu4 clusters at
different temperatures under in-situ catalytic reaction condi-
tions (3% H2, 1% CO2 and 96% He, 1.25 atm): a) Average va-
lence state of Cu4 clusters. The inserted dashed line indicates
the calculated charge from DFT for comparison. b) Linear
combination fit (LCF) results of XANES spectra using bulk
Cu foil, Cu2O and CuO powder as reference materials.
The characteristic GIXANES features at the Cu K-edge22 re-
flect the evolution of the oxidation state of supported Cu4
clusters under in-situ reaction conditions, as displayed in
Figure S1(a). By comparing the absorption edge of the refer-
ence spectra (Cu foil, Cu2O and CuO bulk standards in Fig-
ure S1(b)), a gradual reduction of Cu4 clusters under reaction
conditions (CO2/H2 gas feed) can be identified upon heating
to 425oC. To show the trend in the evolution of the average
valence state of copper clusters, a quantitative linear combi-
nation fit (LCF) is performed using Cu (Cu0), Cu2O (Cu+) and
CuO (Cu2+) bulk standards. Figure 1 presents the LCF results
as well as the average valence state of Cu4 clusters with in-
creasing reaction temperature. At room temperature, Cu4
clusters can be described as primarily composed of oxidized
Cu2+ (~60%) and Cu+ (~40%), with an average valence state
of 1.60. At 75oC a partial reduction takes place, yielding an
average copper valence of 1.05. Starting at 125°C, the Cu4 clus-
ters are practically fully reduced as indicated by the ~0.1 av-
erage valence state (Figure 1). The observed non-zero value
can be ascribed to some charge transfer to a fully reduced
(i.e., Cu0) cluster from either the alumina support or adjacent
acidic hydroxyls on the surface.23,24
Figure 2. Turn-over rate (TOR) of CO2 reduction to CH3OH
over Al2O3 supported Cu4 clusters. The data plot is converted
from Fig. S2(b) (See SI), by averaging 100 data points at each
temperature.
In terms of methane formation (CO2 + 4H2→ CH4
+
2H2O), no CH4 (m/z 15) was obtained as a product below
325°C, see Figure S2. This indicates that methanation is not
favorable in this temperature range. Nevertheless, we obtain
an increasing CH4 signal at 375°C accompanied by a rise of
m/z 18 signal of water, which likely implies the preference of
methanation over methanol synthesis at higher tempera-
tures. However, above 375°C, we also observed the back-
ground desorption of hydrocarbon traces (m/z 43 and 56).
We note that the fragmentation pattern of these hydrocar-
bons may also contribute to the CH4 (m/z 15) signal in the
mass spectrometer. Thus, to draw an affirmative conclusion
on the high-temperature selectivity of CH4, further experi-
ments, e.g., with higher sample loading/purified gas feed, are
needed, which is beyond the scope of this paper.
The turn-over rate (TOR) of methanol formation from CO2
hydrogenation over supported Cu4 clusters is shown in Fig-
ure 2. Here, the TOR is defined as the yield of methanol
formed per copper atom per second. As discussed earlier,
under the reaction conditions, the catalyst becomes Cu0
when 125°C is reached. This is also the temperature at which
CH3OH starts to be produced, suggesting that the reduction
of CO2 to CH3OH is mainly catalyzed by the fully reduced
state of the Cu4 clusters. As displayed in Figure 2, the maxi-
mal TOR of ~4x10-4 molecule·s-1·atom-1 was obtained at 225°C
and the rate of methanol production drops above 325°C,
which falls into the thermodynamic-control regime.25 The
Copper may also catalyze a reverse water-gas shift reac-
tion (rWGS, CO2 + H2→ CO + H2O)26,27 at high temperatures.
A clear assignment of CO (m/z =28) with mass spectrometry
is not feasible in our experiments due to its overlap with
fragment ions of CO2 in the feedstock. However, we observe
an increasing water signal m/z 18) above 375°C when the
TOR of methanol synthesis declines (see SI). This is a strong
indication of other reaction pathways for CO2 conversion at
elevated temperatures, e.g., rWGS or methanation.
DFT calculations were carried out to help understand the
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Table 1. Comparison of turn-over rates (TOR)/turn-over frequencies (TOF) of the present work and previous studies
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Catalyst
Temperature
Total
Pressure
Partial Pres- Partial Pres- Maximum TOR/TOF of CH3OH
Refer-
ence
(molecule·s-1·atom-1)
sure of H2
sure of CO2
Cu4/Al2O3
225°C
1.25 atm
1 atm
0.038 atm
0.75 atm
0.75 atm
4.6 atm
0.013 atm
0.25 atm
0.25 atm
0.4 atm
4.0×10-4(TOR)
This work
25
Ni5Ga3/SiO2
200 - 220°C
200 - 220°C
237°C
6.7×10-5 (TOF)*
6.7×10-5 (TOF)*
1.2×10-3 (TOR)
25
26
Cu/ZnO/Al2O3
Polycrystalline Cu foil
1 atm
5 atm
*These values were converted from the graphs in ref 25
.
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Figure 3. Calculated reaction pathways of CO2 reduction to CH3OH, CO and CH4 on Al2O3 supported Cu4 clusters. The catalyst
surface site is labeled as “*”. To improve legibility, “H2” was omitted from the labels after the initial state.
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reaction mechanism of the catalytic reduction of CO2. The
Al2O3 supported Cu4 cluster (Cu4/Al2O3) was constructed by
binding the Cu4 cluster onto a hydroxylated amorphous
Al2O3 surface model obtained from a molecular dynamics
(MD) simulation28. A GGA_PBE functional29 with a plane
wave basis set was used for geometry optimization and ener-
gy calculations. (see SI). The average charge on the support-
ed Cu4 cluster is found to be +0.16 |e|/atom using Bader
charge analysis30. In the cluster, the two Cu atoms that are
bound to the surface oxygens/hydroxyls have slightly positive
charges while the other two Cu atoms carry no charge (see
SI). This agrees well with the experimental measurements
that the catalyst is mainly fully reduced Cu (Figure 1). The
slightly positive charges on the bound Cu atoms are due to
the partial oxidation of Cu by the bridging O atoms and the
hydroxyl groups on the support. The calculated reaction
pathways for the CO2 reduction to CH3OH, CO and CH4 on
Cu4 are shown in Figure 3. In general, the calculated reaction
mechanism of CH3OH formation on a supported Cu4 cluster
is similar to that on bulk Cu materials as reported in previous
investigations3,8,31. The initial step of CH3OH formation is the
formation of the HCOO* species (“*” represents an adsorbed
species). The hydrogenation of the HCOO* species produces
HCOOH*, which is further hydrogenated to H2COOH*.
Cleavage of the C-OH bond of H2COOH* leads to its dissoci-
ation into H2CO* and OH*, followed by further hydrogena-
tion of H2CO* to H3CO* and OH* to H2O*. The hydrogena-
tion of H3CO* generates the final product, CH3OH. The rate-
limiting step of the CH3OH pathway on Cu4 is found to be
the hydrogenation of the HCOO* species with a predicted
barrier of 1.18 eV. This barrier for the Cu4 cluster is lower
than the predicted rate-limiting barriers for the Cu (111) sur-
face (1.60 eV) and the Cu29 cluster (1.41 eV), both of which
were calculated using a GGA_PW functional by Yang et al.8 It
is also notable that the reaction pathway of the Cu4 cluster is
energetically lower-lying than that of the Cu29 cluster, which
is lower than that of the Cu(111) surface.8 This indicates that
the Cu4 cluster could be more active for CH3OH formation
compared to bulk Cu surfaces and larger Cu nanoparticles.
The low reaction barrier for Cu4 can be explained by the
adsorption strength of the adsorbate species to the catalyst.
Under-coordinated Cu sites in Cu4 clusters lead to strong
adsorption energies of the adsorbates as found in previous
studies of subnanometer clusters,14 resulting in an energeti-
cally lower lying reaction pathway and a lower barrier. Previ-
ous work3-5 has illustrated that high CO2 and H2 pressure
increase adsorption energies and make the formation of
methanol energetically more favorable. This is why high
pressures are needed for CO2 reduction on Cu surfaces.3-5 It is
further consistent with how the strong adsorption of the
adsorbates on the under-coordinated Cu4 clusters leads to
high activity at a low CO2 and H2 pressures.
For comparison, the reaction pathways for the CO2 reduc-
tion to CO (rWGS) and CH4 were also investigated (Figure
3). In agreement with a previous DFT study,32 our calcula-
tions showed that the formation of COOH* on Cu4, which
initiates rWGS, has much higher barrier (1.08 eV) than that
of HCOO* (0.18 eV), and the rWGS pathway is energetically
higher-lying than the CH3OH pathway. This suggests that
the CH3OH formation is likely to be predominant at lower
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(4) Yang, Y.; White, M. G.; Liu, P. J. Phys. Chem. C 2011, 116, 248.
temperatures for Cu4. However, at higher temperatures
rWGS could become significant due to a bigger reaction rate
consistent with the decreasing signal of CH3OH above 325 °C
(Figure 2). CH4 formation, on the other hand, follows the
same path as CH3OH formation to form the H3CO* species.
Then, the breaking of the C-O bond of H3CO* leads to H3C*
and O*, after which H3C* is hydrogenated to CH4 and O* is
finally hydrogenated to H2O. The rate-limiting step of the
CH4 pathway (H3CO* → CH3* + O*) has a much higher bar-
rier (1.69 eV) than that of the CH3OH pathway, suggesting
that the CH4 formation would require a much higher reac-
tion temperature than CH3OH formation. This result sup-
ports our experimental observations that CH3OH was ob-
tained as the main product at a lower temperature range
(<375°C), and explains why Cu clusters favor the CH3OH
formation by the gas-phase hydrogenation of CO2 rather
than the CH4 formation, even though the net reaction of the
latter is thermodynamically more favorable.
(5) 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. Science 2014, 345, 546.
(6) Liu, C.; He, H.; Zapol, P.; Curtiss, L. A. Phys. Chem. Chem.Phys.
2014, 16, 26584.
(7) Kauffman, D. R.; Alfonso, D.; Matranga, C.; Qian, H.; Jin, R. J. Am.
Chem. Soc. 2012, 134, 10237.
(8) Yang, Y.; Evans, J.; Rodriguez, J. A.; White, M. G.; Liu, P.
Phys.Chem. Chem. Phys. 2010, 12, 9909.
(9) Kwak, J. H.; Kovarik, L.; Szanyi, J. ACS Catal. 2013, 3, 2449.
(10) Reske, R.; Mistry, H.; Behafarid, F.; Roldan Cuenya, B.; Strasser,
P. J. Am. Chem. Soc. 2014, 136, 6978.
(11) Centi, G.; Perathoner, S.; Win, G.; Gangeri, M. Green Chem. 2007,
9, 671.
(12) Gangeri, M.; Perathoner, S.; Caudo, S.; Centi, G.; Amadou, J.;
Bégin, D.; Pham-Huu, C.; Ledoux, M. J.; Tessonnier, J. P.; Su, D. S.
Catal. Today 2009, 143, 57.
(13) Rodriguez, J. A.; Evans, J.; Feria, L.; Vidal, A. B.; Liu, P.;
Nakamura, K.; Illas, F. J. Catal. 2013, 307, 162.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
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23
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27
28
29
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31
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41
42
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45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(14) Lei, Y.; Mehmood, F.; Lee, S.; Greeley, J.; Lee, B.; Seifert, S.;
Winans, R. E.; Elam, J. W.; Meyer, R. J.; Redfern, P. C.; Teschner, D.;
Schlogl, R.; Pellin, M. J.; Curtiss, L. A.; Vajda, S. Science 2010, 328,
224.
(15) Vajda, S.; Pellin, M. J.; Greeley, J. P.; Marshall, C. L.; Curtiss, L.
A.; Ballentine, G. A.; Elam, J. W.; Catillon-Mucherie, S.; Redfern, P.
C.; Mehmood, F.; Zapol, P. Nat. Mat. 2009, 8, 213.
(16) Lee, S.; Molina, L. M.; Lopez, M. J.; Alonso, J. A.; Hammer, B.;
Lee, B.; Seifert, S.; Winans, R. E.; Elam, J. W.; Pellin, M. J.; Vajda, S.
Angew. Chem. Inter. Ed. 2009, 48, 1467.
To conclude, to our best knowledge the Al2O3 supported
size-selected Cu4 clusters exhibit the highest reported activi-
ty to date for CO2 reduction to CH3OH at a low CO2 partial
pressure. The unique coordination environment of Cu atoms
in size-selected subnanometer clusters results in the active
sites that are superior to those of larger Cu particles. These
results for size-selected Cu clusters demonstrate their great
potential for the development of novel low-pressure catalysts
for CH3OH synthesis from catalytic conversion of CO2 using
alternative feed streams with low CO2 concentration.
(17) Yin, C.; Tyo, E.; Kuchta, K.; von Issendorff, B.; Vajda, S. J. Chem.
Phys. 2014, 140, 174201.
(18) Lu, J.; Cheng, L.; Lau, K. C.; Tyo, E.; Luo, X.; Wen, J.; Miller, D.;
Assary, R. S.; Wang, H.-H.; Redfern, P.; Wu, H.; Park, J.-B.; Sun, Y.-
K.; Vajda, S.; Amine, K.; Curtiss, L. A. Nat. Commun. 2014, 5, 4895.
(19) Vajda, S.; Lee, S.; Sell, K.; Barke, I.; Kleibert, A.; von Oeynhausen,
V.; Meiwes-Broer, K. H.; Rodriguez, A. F.; Elam, J. W.; Pellin, M. M.;
Lee, B.; Seifert, S.; Winans, R. E. J. Chem. Phys. 2009, 131, 121104.
(20) Wyrzgol, S. A.; Schafer, S.; Lee, S.; Lee, B.; Di Vece, M.; Li, X. B.;
Seifert, S.; Winans, R. E.; Stutzmann, M.; Lercher, J. A.; Vajda, S.
Phys. Chem. Chem.Phys. 2010, 12, 5585.
(21) Sungsik, L.; Byeongdu, L.; Seifert, S.; Vajda, S.; Winans, R. E.
Nuclear Instruments & Methods in Physics Research, Section A
(Accelerators, Spectrometers, Detectors and Associated Equipment)
2011, 649, 200.
ASSOCIATED CONTENT
Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Corresponding authors: zapol@anl.gov (PZ), vajda@anl.gov
(SV) and curtiss@anl.gov (LAC).
(22) Stotzel, J.; Lutzenkirchen-Hecht, D.; Frahm, R.; Kimmerle, B.;
Baiker, A.; Nachtegaal, M.; Beier, M. J.; Grunwaldt, J. D. 14th
International Conference on X-Ray Absorption Fine Structure
(Xafs14), Proceedings 2009, 190.
Author Contributions
‡These authors contributed equally.
Notes
(23) Mason, M. G. Phys. Rev. B 1983, 27, 748.
(24) Hellman, A.; Gronbeck, H. J. Phys. Chem. C 2009, 113, 3674.
(25) Studt, F.; Sharafutdinov, I.; Abild-Pedersen, F.; Elkjær, C. F.;
Hummelshøj, J. S.; Dahl, S.; Chorkendorff, I.; Nørskov, J. K. Nat.
Chem. 2014, 6, 320.
(26) Yoshihara, J.; Parker, S. C.; Schafer, A.; Campbell, C. Catal. Lett.
1995, 31, 313.
(27) Matsubu, J. C.; Yang, V. N.; Christopher, P. J. Am. Chem. Soc.
2015, 137, 3076.
(28) Adiga, S. P.; Zapol, P.; Curtiss, L. A. The J. Phys. Chem. C 2007,
111, 7422.
(29) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77,
3865.
(30) Tang, W. J. Phys. Cond. Matt. 2009, 21, 084204.
(31) Grabow, L. C.; Mavrikakis, M. ACS Catal. 2011, 1, 365.
(32) Zhang, R.; Wang, B.; Liu, H.; Ling, L. J. Phys. Chem. C 2011, 115,
19811.
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was supported by the U.S. Department of Energy,
Office of Science, BES-Division of Materials Science and En-
gineering and BES-Scientific User Facilities under Contract
DE-AC02-06CH11357. We acknowledge the computing re-
sources operated by the Laboratory Computing Resource
Center (ANL), and the ANL Center for Nanoscale Materials.
We also thank Dr. Alex Martinson (ANL) for ALD coating.
REFERENCES
(1) Waugh, K. C. Catal.Today 1992, 15, 51.
(2) Olah, G. A. Angew. Chem. Inter. Ed. 2005, 44, 2636.
(3) Behrens, M.; Studt, F.; Kasatkin, I.; Kühl, S.; Hävecker, M.; Abild-
Pedersen, F.; Zander, S.; Girgsdies, F.; Kurr, P.; Kniep, B.-L.; Tovar,
M.; Fischer, R. W.; Nørskov, J. K.; Schlögl, R. Science 2012, 336, 893.
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