Oxidized Ni nanostructures supported by mesoporous Al2O3: Relationship between the structure and reactivity for CO oxidation studied via photoemission spectroscopy

Article abstract of DOI:10.1002/bkcs.10750

Oxidized Ni, at very small loadings, was deposited on mesoporous Al₂O₃ using atomic layer deposition. The prepared structures were used as catalysts for CO oxidation between 30 and 250 °C. Ni particles with a mean size less than 1-2 nm were shown to be reactive, even at room temperature, for CO oxidation. The room temperature reactivity for CO oxidation was decreased with increasing reaction time. However, when post-annealing at 300 °C was applied to deactivated catalysts, a higher initial CO oxidation reactivity (compared with the value of the preceding catalytic operation) was observed. Furthermore, we observed that repeated cycles of room-temperature CO oxidation and post-annealing at 300 °C gradually increased the catalytic activity for room temperature CO oxidation. X-ray photoelectron spectroscopy was used to determine the origin of this behavior and the results are discussed in detail.

Full text of DOI:10.1002/bkcs.10750

Article
DOI: 10.1002/bkcs.10750
BULLETIN OF THE
S. W. Han et al.
KOREAN CHEMICAL SOCIETY
Oxidized Ni Nanostructures Supported by Mesoporous Al O :
2
3
Relationship between the Structure and Reactivity for CO Oxidation
Studied via Photoemission Spectroscopy
†
†
†
†,‡,*
Sang Wook Han, Dae Han Kim, Il Hee Kim, and Young Dok Kim
†Department of Chemistry, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
*
E-mail: ydkim91@skku.edu,
‡
Research Center for Nanocatalysts, Korea Research Institute of Chemical Technology (KRICT),
Daejeon 305-600, Republic of Korea
Received December 24, 2015, Accepted February 11, 2016, Published online April 19, 2016
Oxidized Ni, at very small loadings, was deposited on mesoporous Al O using atomic layer deposition.
2
3
ꢀ
The prepared structures were used as catalysts for CO oxidation between 30 and 250 C. Ni particles with
a mean size less than 1–2 nm were shown to be reactive, even at room temperature, for CO oxidation.
The room temperature reactivity for CO oxidation was decreased with increasing reaction time. However,
ꢀ
when post-annealing at 300 C was applied to deactivated catalysts, a higher initial CO oxidation reactiv-
ity (compared with the value of the preceding catalytic operation) was observed. Furthermore, we
ꢀ
observed that repeated cycles of room-temperature CO oxidation and post-annealing at 300 C gradually
increased the catalytic activity for room temperature CO oxidation. X-ray photoelectron spectroscopy was
used to determine the origin of this behavior and the results are discussed in detail.
Keywords: Atomic layer deposition, CO oxidation, Nickel, Nanoparticle, Mesoporous Al O3
2
Introduction
nanoparticles, catalysts based on Mn and Cu have also
been shown to be active for CO oxidation at room
19–24
CO oxidation has been studied extensively because of the
simplicity of the reaction, which allows the reaction mech-
anism to be traced on an atomic scale. CO oxidation is also
of technological importance in exhaust gas treatments. It
is well known that Pt-group catalysts show very high reac-
tivity for CO oxidation; therefore, most of the current com-
mercial catalysts used for exhaust gas treatments rely on Pt-
temperature.
In addition, under ultra-high vacuum
(UHV) conditions, NiO-based systems have demonstrated
25
high reactivity for CO oxidation below room temperature.
1–5
Although it is challenging, finding a catalyst with both low-
temperature activity and high temperature stability is desired.
Recently, atomic layer deposition (ALD) has been uti-
26–36
lized for the synthesis of heterogeneous catalysts.
3,6–8
group elements.
ALD was shown to be efficient for incorporating catalyst
nanoparticles into the micro- and meso-pores of support-
ing materials. Nanoparticles with catalytic activity that are
confined inside deep pores of substrates can show high
resistance toward sintering and demonstrate long-term cat-
It is important that catalysts with activity at or below room
temperature be developed. In addition, catalysts should be
stable upon thermal treatment at higher temperatures. Cata-
lysts based on Pt-group transition metal nanoparticles, sup-
ported by oxides, show fairly high stability at high
27,28,31–33,35,36
alytic activity.
In this work, we prepared Ni-
ꢀ
temperatures (>500 C). However, CO oxidation activity
based catalysts supported by mesoporous Al O3 using
2
only occurs when the reaction temperature exceeds
ALD. The catalytic activity of the prepared catalysts for
CO oxidation (in the temperature range of 25–250 C)
ꢀ
3,5–9
ꢀ
100–150 C.
There are some catalysts that have been
found to show CO oxidation activity at room temperature.
The most widely known example are Au nanoparticles (with
a particle size less than ~2–3 nm), which show substantially
and the stability of their catalytic activity are presented.
Particularly, we focus on the fact that the catalysts
undergo deactivation at room temperature and that used
catalysts can be regenerated by thermal post-treatment.
Moreover, the repeated regeneration process was shown to
increase the CO oxidation activity of the Ni-based cata-
lysts at room temperature. X-ray photoelectron spectros-
copy (XPS) was employed to determine the origin of the
change in the catalytic activity after repeated regeneration
processes of the deactivated catalysts.
1
0–17
high activity for CO oxidation
; however, the CO oxida-
tion reactivity of Au nanoparticles tends to irreversibly
decrease as a function of the reaction time, even at room
temperature. This is because of the structural instability
that causes the agglomeration of nanoparticles over time
1
7,18
under reaction conditions.
This deactivation process
becomes more severe at higher temperatures. Besides Au
Bull. Korean Chem. Soc. 2016, Vol. 37, 674–679
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Wiley Online Library
674

Article
BULLETIN OF THE
ISSN (Print) 0253-2964 | (Online) 1229-5949
KOREAN CHEMICAL SOCIETY
Experimental
deposited substrates based on the N isotherm data. The
2
surface chemical state and composition of each sample
were analyzed by XPS. The UHV main chamber (base
Preparation of Ni/Al O . The Ni/Al O catalysts for the
CO oxidation experiments were fabricated by ALD.
Bis(cyclopentadienyl)nickel (Ni(Cp)2, Sigma-Aldrich,
2
3
2 3
−
10
pressure of 2.0 × 10
Torr) that was used for XPS mea-
surements was equipped with a concentric hemispherical
analyzer (PHOIBOS-Has 3500, SPECS, Berlin, Germany)
and a monochromatic X-ray source (Mg Kα, 1253.6 eV).
In order to analyze the surface chemical state of the
St. Louis, MO, USA) and O (99.99%) were used as pre-
2
cursors for depositing Ni on mesoporous Al O (mean
2
3
pore size = 11.6 nm, particle size = 1.1 mm, Sasol, Johan-
nesburg, South Africa) in the ALD process. During the
Ni deposition process, the temperature of the substrate and
Ni/Al O3 after repeated CO oxidation reactivity experi-
2
ments, the Ni/Al O was transferred from the quartz reactor
2
3
the bottle of the Ni(Cp) precursor were maintained at
that was installed inside of the glove box to the UHV main
chamber; this was done using a magnetic bar transferring-
system and did not expose the samples to air. Morphologi-
cal images of the samples were obtained by scanning elec-
tron microscopy (SEM, JSM-6700F, JEOL, Akishima,
Tokyo, Japan). Energy dispersive spectroscopy (EDS) was
also used to analyze the elemental composition of the
samples.
2
ꢀ
2
2
60 and 60 C, respectively. With a working pressure of
50 mTorr, the Ni(Cp)2 precursor was injected into the
main chamber for 200 s. After injecting Ni(Cp) , the sub-
2
strate (which was located in the center of the main cham-
ber) was exposed to the injected precursor for 30 s. The O2
precursor was injected into the main chamber with a work-
ing pressure of 1.2 Torr for 10 s; this remained in the main
chamber for 30 s after the previous Ni(Cp) pulsing and
2
exposing steps. Directly after the exposing step of each pre-
Result and Discussion
cursor, N (99.999%) gas was injected into the main cham-
2
ber for purging and subsequently pumped out by a rotary
oil pump. After the pumping step, the base pressure of the
chamber was maintained below 10 mTorr. These processes
comprise one cycle of Ni layer deposition on the substrate
in the ALD process. In this work, Ni layers were deposited
on Al O substrates with 50 ALD cycles.
Characterization of Ni/Al O . In our BET analysis of the
2
3
experimentally obtained N isotherm data, the surface areas
2
of bare and Ni-deposited Al O were determined to be
2
3
2
155.4 and 156.7 m /g, respectively; there was almost no
change in the surface area of the sample upon Ni deposition
using ALD (Table 1). Using BJH analysis, the average pore
diameters of the samples before and after Ni deposition
were also estimated to be nearly identical (11.6 and
11.4 nm for the bare Al O and the Ni/Al O , respectively).
2
3
CO Oxidation Reactivity Experiments. CO oxidation
experiments with Ni/Al O catalysts were carried out in a
2
3
continuous-flow quartz fixed-bed reactor (internal diame-
ter = 21 mm, length = 300 mm) under atmospheric pres-
sure. Ni/Al O (2.0 g) catalysts, loaded on a ceramic holder,
2
3
2 3
This is in line with the results of the surface area analysis.
This shows that the mesoporous structure of the supports
was maintained after the Ni deposition, which is probably
because of the fact that the amount of Ni deposited on the
surface of Al O by 50 ALD cycles was extremely small.
2
3
were positioned in the center of the quartz reactor. Before
each CO oxidation experiment, the Ni/Al O catalysts were
2
3
ꢀ
annealed at 300 C for 2 h. After the annealing process, the
2
3
quartz reactor was cooled down to reaction temperatures of
Using ICP-OES, the amount of Ni in the Ni/Al O was
2 3
ꢀ
250, 200, 150, and 30 C, respectively. Each catalyst
estimated to be 0.4 wt %. It is likely that the small number
of defect sites on the Al O surface resulted in the very low
reaction temperature was maintained with a temperature
controller. Dry air, which contained 1% CO, was fed into
the reactor, and the total flow of the gas was kept at 10 mL/
min throughout the reactivity experiments. The amounts of
2
3
27,37
loading of Ni.
In our previous studies, the Ni particles
of the 40-ALD-cycled Ni/SiO2 with post-annealing at
ꢀ
450 C were determined to be 1–2 nm by transmission
32
CO and CO gases were determined every 10 min via a
electron microscopy (TEM). Because metal nanoparticles
tend to become larger as the temperature of the heat-
treatment is increased, the size of the Ni particles in this
2
gas chromatograph (HP6890, Hewlett Packard, Palo Alto,
CA, USA) equipped with a capillary column (Carboxen
ꢀ
1
010 PLOT, 30 m × 0.32 nm, Supelco, Bellefonte, PA,
USA) and a flame ionization detector.
The CO oxidation experiment on Ni/Al O at 30 C for
work, which were annealed at only 300 C, should be
ꢀ
2
3
1
20 min was repeated seven times, and the sample was
ꢀ
annealed at 300 C for 2 h under dry air conditions before
each CO oxidation reactivity experiment.
Table 1. Summary of the Ni content, BET surface area, and
average pore diameter of Al
process.
2 3
O before and after the Ni ALD
Characterization of the Catalysts. The elemental compo-
sitions of the fabricated Ni/Al O catalysts were analyzed
by inductively coupled plasma-optical emission spectros-
copy (ICP-OES). Brunauer–Emmett–Teller (BET) and
Barrett–Joyner–Halenda (BJH) methods were used to
obtain the surface area and mean pore size of bare and Ni-
2
3
Ni
S
BET
2
Average pore
diameter (nm)
content (wt %)
(m /g)
Bare Al O3
Ni/Al O
2 3
0.0
0.4
155.4
156.7
11.6
11.4
2
Bull. Korean Chem. Soc. 2016, Vol. 37, 674–679
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
675

BULLETIN OF THE
Article
Oxidized Ni Supported on Mesoporous Al O3
KOREAN CHEMICAL SOCIETY
2
(a)
(b)
Figure 2. XPS spectra taken before and after the Ni ALD process:
(a) Al 2p and (b) Ni 2p of Al
Figure 1. (a) SEM image of a mechanically fractured particle of
O .
2 3
Ni/Al O3 and (b) the EDS mapping image of the Ni K series
2
from (a).
41,42
binding energies.
It was confirmed by XPS that the
deposited Ni in the catalyst existed in the oxide and hydrox-
ide forms.
CO Oxidation Reactivity Experiments over Ni/Al O .
1
8,38,39
2
3
smaller than 1–2 nm.
Therefore, the Ni particles on
The results of the catalytic activity experiments for
Ni/Al O at various temperatures are shown in Figure 3.
the surfaces of the samples in this study were difficult to
identify by TEM (Figure S1, Supporting Information).
Figure 1 shows the cross-sectional views of Ni/Al O3
obtained with SEM; these were taken from mechanically
fractured particles. Figure 1(a) shows a regular SEM image
2
3
CO consumption in Figure 3(a) was calculated using the
following equation (Eq. (1)):
2
ÀÀ
Á
Á
COconsumptionð%Þ = ½COꢁ −½COꢁ =½COꢁin ×100
in
out
of Ni/Al O3 and Figure 1(b) shows the EDS mapping
2
ð1Þ
image of the Ni K series from the same area that is shown
in Figure 1(a). In Figure 1(b), Ni could only be detected
within the shell-region of the particle (shell thickness of
15 μm), implying that the diffusion depth of our Ni pre-
cursor in Al O3 during the ALD process was limited
In each experiment, the initially high CO consumption
decreased as the reaction time increased. Additionally, the
degree of deactivation varied significantly depending on the
reaction temperature. At room temperature, ~90% of the
initial CO consumption rapidly decreased to ~10% after
reacting for 1000 min. In the case of the experiment at
~
2
to ~15 μm.
Figure 2 shows the XPS spectra of the bare and Ni-
deposited supports. All of the peak intensities in each core
level spectrum were normalized by the respective Al 2p
peak intensities, and the binding energy scale of each spec-
trum was shifted using the position of the respective Al(III)
ꢀ
250 C, the CO consumption was nearly 100% at the
beginning; this value decreased by only ~5% after
1000 min. CO evolution was initially very low; however,
2
2
p3/2 4peaks at a binding energy of 74.4 eV (as a refer-
after an induction period of ~40 min, the CO evolution of
each experiment reached its maximum value (Figure 3(b)).
2
0
ence). In Figure 2(b), broad peaks (with the Ni 2p3/2 peak
centered at ~855 eV) appeared after the ALD process.
This can be attributed to the overlap of Ni(III) species
CO evolution is delayed with respect to CO removal. This
2
is most likely caused by the fact that the reaction intermedi-
ates, such as carbonate species, formed on the surface of
catalysts (most likely on Al O , which has a very high
(Ni O and NiOOH) and NiO at 855–856 and 854.2 eV,
2 3
respectively; their satellite peaks were located at higher
2
3
Bull. Korean Chem. Soc. 2016, Vol. 37, 674–679
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
676

BULLETIN OF THE
Article
Oxidized Ni Supported on Mesoporous Al O3
KOREAN CHEMICAL SOCIETY
2
surface area) at the beginning of each experiment. As a
result, CO oxidation took place only after some surface
sites were covered by the reaction intermediates.
the sample was not only regenerated by each annealing
process but also was actually slightly increased by repeated
annealing (Table 2).
Regeneration of the Catalytic Activity for CO Oxida-
tion. In order to determine whether it is possible to recover
the initial catalytic activity of deactivated Ni/Al O by the
In order to determine the surface chemical states of the
sample before and after the repeated CO oxidation experi-
ments, XPS analysis was performed. It is worth emphasiz-
ing that our CO oxidation reactor was located in a glove
box filled with Ar; therefore, the pelletized samples that
were used for catalytic CO oxidation could be transferred
with a magnetic transfer system into the XPS analysis
chamber without being exposed to air. XPS spectra of the
2nd annealed (annealed after the 1st CO oxidation experi-
ments) and 8th annealed (annealed after the 7th CO
2
3
application of post-treatments, we repeated CO oxidation
experiments on Ni/Al O at room temperature with subse-
2
3
ꢀ
quent annealing at 300 C. The results of the repeated CO
oxidation experiments are displayed in Figure 4. In each
CO oxidation experiment, CO consumption decreased grad-
ually with reaction time. Alternatively, the CO evolution
2
initially increased and then decreased, which is analogous
to the results shown in Figure 3. The catalytic activity of
Figure 3. (a) The CO consumption and (b) the CO
2
evolution in
experiments using Ni/Al as a catalyst at reaction temperatures
2 3
O
ꢀ
of 30, 150, 200, and 250 C. Data points in the reaction time
range of 0–50 min were plotted at intervals of 10 min. The rest of
the data points were collected at 50 min intervals. Each data point
Figure 4. (a) The CO consumption and (b) the CO
from the CO oxidation reactivity experiment over Ni/Al
formed seven times. All of the data points were plotted at an inter-
2
evolution
2 3
O
per-
in (b) represents the amount of CO
0 min.
2
generated over a period of
val of 10 min. Each point in (b) represents the amount of CO
that was generated over a period of 10 min.
2
1
Table 2. The maximum value of the CO consumption, the amount of CO
2
that was generated, and the CO
3rd
2
selectivity of the CO
5th
oxidation reactivity experiment over Ni/Al
st
89.1
2
O
3
performed seven times.
1
2nd
7th
94.3
0.0124
0.63
CO consumption (%)
CO amount (mmol)
91.1
0.0089
0.64
93.6
0.0110
0.63
94.6
0.0117
0.63
2
0.0076
0.65
CO selectivity
2
Bull. Korean Chem. Soc. 2016, Vol. 37, 674–679
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
677

BULLETIN OF THE
Article
Oxidized Ni Supported on Mesoporous Al O3
KOREAN CHEMICAL SOCIETY
2
changes in the amount of C impurities bound to Ni cannot
be reflected in the C 1s spectra.
Conclusion
Ni was deposited on mesoporous Al O3 with 50 ALD
2
cycles for CO oxidation experiments. Ni/Al O showed
2
3
ꢀ
substantial CO consumption at 30 C, caused by CO oxida-
tion, at the beginning of each experiment; this consumption
gradually decreased with time. The catalytic activity of
ꢀ
Ni/Al O for CO oxidation at 30 C was regenerated after
2
3
ꢀ
an annealing process (at 300 C for 2 h) and was even
slightly increased after repeated CO oxidation and subse-
quent annealing. Using XPS, we found that the number of
active Ni sites increased upon repeated regeneration at
ꢀ
3
00 C without changing the oxidation state of Ni. This
was most likely caused by recovering the Ni sites that were
covered by C impurities by applying repeated thermal treat-
ments. If these catalysts are operated at room temperature
ꢀ
and regularly annealed at 300 C between operations, our
Ni-based catalysts have the potential to catalyze CO oxida-
tion for extended periods of time.
Acknowledgements. Y. D. Kim was supported by the
Degree and Research Center (DRC) Program (2014)
through the National Research Council of Science & Tech-
nology (NST) from the Ministry of Science, ICT and
Future Planning. The authors acknowledge the financial
support received from the National Research Council
of Science & Technology (NST) of the Republic of
Korea (B551179-11-03-00). This research was supported
by Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the
Ministry of Science, ICT and Future Planning
Figure 5. In situ XPS spectra of the Ni/Al O sample after the
2
3
CO oxidation experiment shown in Figure 4 and subsequent
annealing for 2 h compared with the same sample that has under-
gone seven consecutive CO oxidation experiments and additional
annealing for 2 h: (a) C 1 s and (b) Ni 2p.
oxidation experiments) samples are shown in Figure 5. The
intensity and the binding energy scale of each core level
spectrum were normalized and shifted by the methods used
for Figure 2.
(2015R1A2A2A01003866).
Supporting Information. Additional supporting informa-
In Figure 5(a), the C 1s peak intensities of the 2nd and
tion is available in the online version of this article.
8th annealed samples were almost identical. Referring to
Figure 5(b), which shows the Ni 2p XPS spectra of the
Ni/Al O3 before and after the repeated CO oxidation
2
References
experiments, the Ni 2p3/2 peak intensity of the sample was
increased by repeated annealing process. The Ni 2p3/2 peak
intensity of the as-prepared sample was slightly decreased
after being annealed twice. This may be because of a
decrease in the surface portion of Ni on the surface of the
sample; sintering of Ni mostly occurred during the 1st
1. X. Liu, J. Liu, Z. Chang, X. Sun, Y. Li, Catal. Commun.
2
011, 12, 530.
2. K. Ramesh, L. Chen, F. Chen, Y. Liu, Z. Wang, Y.-F. Han,
Catal. Today 2008, 131, 477.
3. B. K. Min, C. M. Friend, Chem. Rev. 2007, 107, 2709.
3
1
4
. G. Peng, L. R. Merte, J. Knudsen, R. T. Vang, E. Lægsgaard,
annealing process (Figure S2). Additionally, the oxidized
Ni nanoparticles that were initially contaminated by carbon
F. Besenbacher, M. Mavrikakis, J. Phys. Chem. C 2010, 114,
2
1579.
(residues of the Ni-precursor) may have gradually experi-
5
6
. C. T. Campbell, Science 2004, 306, 234.
enced carbon removal after multiple CO oxidation cycles
and subsequent annealing. This may have resulted in the
increase in the Ni 2p peak intensity in Figure 5(b). This can
be responsible for the enhanced catalytic activity with
repeated catalytic operations in Figure 4. It is worth noting
that the relative amount of Ni, with respect to the carbon
impurities in our catalysts, is very small; therefore, small
. I. Miguel-García, M. Navlani-García, J. García-Aguilar,
Á. Berenguer-Murcia, D. Lozano-Castelló, D. Cazorla-
Amorós, Chem. Eng. J. 2015, 275, 71.
7
. M. Shen, L. Lv, J. Wang, J. Zhu, Y. Huang, J. Wang, Chem.
Eng. J. 2014, 255, 40.
8. J. H. B. J. Hoebink, R. A. van Gemert, J. A. A. van den
Tillaart, G. B. Marin, Chem. Eng. Sci. 2000, 55, 1573.
Bull. Korean Chem. Soc. 2016, Vol. 37, 674–679
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
678

BULLETIN OF THE
Article
Oxidized Ni Supported on Mesoporous Al O3
KOREAN CHEMICAL SOCIETY
2
9
. G. Pattrick, E. van der Lingen, C. W. Corti, R. J. Holliday,
D. T. Thompson, Top. Catal. 2004, 30–31, 273.
28. Y. J. Pagán-Torres, J. M. R. Gallo, D. Wang, H. N. Pham,
J. A. Libera, C. L. Marshall, J. W. Elam, A. K. Datye,
J. A. Dumesic, ACS Catal. 2011, 1, 1234.
29. B. J. O’Neill, D. H. K. Jackson, A. J. Crisci, C. A. Farberow,
F. Shi, A. C. Alba-Rubio, J. Lu, P. J. Dietrich, X. Gu,
C. L. Marshall, P. C. Stair, J. W. Elam, J. T. Miller,
F. H. Ribeiro, P. M. Voyles, J. Greeley, M. Mavrikakis,
S. L. Scott, T. F. Kuech, J. A. Dumesic, Angew. Chem. Int.
Ed. 2013, 52, 13808.
1
1
0. M. Haruta, M. Daté, Appl. Catal. A 2001, 222, 427.
1. R. Liu, N. Gao, F. Zhen, Y. Zhang, L. Mei, X. Zeng, Chem.
Eng. J. 2013, 225, 245.
2. K. Y. Ho, K. L. Yeung, J. Catal. 2006, 242, 131.
3. N. Lopez, T. V. W. Janssens, B. S. Clausen, Y. Xu,
M. Mavrikakis, T. Bligaard, J. K. Nørskov, J. Catal. 2004,
1
1
2
23, 232.
1
1
4. M. Haruta, J. New Mater. Electrochem. Syst. 2004, 7, 163.
5. M. Comotti, W.-C. Li, B. Spliethoff, F. Schüth, J. Am. Chem.
Soc. 2006, 128, 917.
30. H. O. Seo, J. K. Sim, K.-D. Kim, Y. D. Kim, D. C. Lim,
S. H. Kim, Appl. Catal. A 2013, 451, 43.
31. S. W. Han, D. H. Kim, M.-G. Jeong, K. J. Park, Y. D. Kim,
Chem. Eng. J. 2016, 283, 992.
32. M.-G. Jeong, E. J. Park, B. Jeong, D. H. Kim, Y. D. Kim,
Chem. Eng. J. 2014, 237, 62.
33. C. Detavernier, J. Dendooven, S. Pulinthanathu Sree,
K. F. Ludwig, J. A. Martens, Chem. Soc. Rev. 2011,
40, 5242.
34. J. Lee, D. H. K. Jackson, T. Li, R. E. Winans, J. A. Dumesic,
T. F. Kuech, G. W. Huber, Energy Environ. Sci. 2014,
7, 1657.
35. D. H. Kim, J. K. Sim, J. Lee, H. O. Seo, M.-G. Jeong,
Y. D. Kim, S. H. Kim, Fuel 2013, 112, 111.
36. S. P. Sree, J. Dendooven, K. Masschaele, H. M. Hamed,
S. Deng, S. Bals, C. Detavernier, J. A. Martens, Nanoscale
2013, 5, 5001.
37. J. Greeley, Electrochim. Acta 2010, 55, 5545.
38. J. Sehested, J. A. Gelten, S. Helveg, Appl. Catal. A 2006,
309, 237.
1
1
1
1
2
2
6. A. A. Herzing, C. J. Kiely, A. F. Carley, P. Landon,
G. J. Hutchings, Science 2008, 321, 1331.
7. M. Valden, X. Lai, D. W. Goodman, Science 1998,
2
81, 1647.
8. F. Yang, M. S. Chen, D. W. Goodman, J. Phys. Chem. C
009, 113, 254.
9. J. W. Saalfrank, W. F. Maier, Angew. Chem. Int. Ed. 2004,
3, 2028.
0. H. Yen, Y. Seo, S. Kaliaguine, F. Kleitz, Angew. Chem. Int.
Ed. 2012, 51, 12032.
1. G. J. Hutchings, A. A. Mirzaei, R. W. Joyner,
M. R. H. Siddiqui, S. H. Taylor, Appl. Catal. A 1998,
2
4
1
66, 143.
2. M. Krämer, T. Schmidt, K. Stöwe, W. Maier, Appl. Catal. A
006, 302, 257.
2
2
2
2
3. G. Wu, N. Guan, L. Li, Catal. Sci. Technol. 2011, 1, 601.
4. G. Fortunato, H. R. Oswald, A. Reller, J. Mater. Chem. 2001,
1
1, 905.
39. C. H. Bartholomew, W. L. Sorensen, J. Catal. 1983, 81, 131.
40. W. Stickle, P. Sobol, K. Bomben, Handbook of X-Ray Photo-
electron Spectroscopy, Physical Electronics Inc., Eden Prairie,
MN, 1995.
2
5. J. Knudsen, L. R. Merte, G. Peng, R. T. Vang, A. Resta,
E. Lægsgaard, J. N. Andersen, M. Mavrikakis,
F. Besenbacher, ACS Nano 2010, 4, 4380.
2
6. T. D. Gould, A. Izar, A. W. Weimer, J. L. Falconer,
J. W. Medlin, ACS Catal. 2014, 4, 2714.
41. M. C. Biesinger, B. P. Payne, L. W. Lau, A. Gerson,
R. S. C. Smart, Surf. Interface Anal. 2009, 41, 324.
42. A. P. Grosvenor, M. C. Biesinger, R. S. C. Smart,
N. S. McIntyre, Surf. Sci. 2006, 600, 1771.
2
7. B. J. O’Neill, D. H. K. Jackson, J. Lee, C. Canlas, P. C. Stair,
C. L. Marshall, J. W. Elam, T. F. Kuech, J. A. Dumesic,
G. W. Huber, ACS Catal. 2015, 5, 1804.
Bull. Korean Chem. Soc. 2016, Vol. 37, 674–679
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
679