Insights into the Mechanism of Methanol Steam Reforming Tandem Reaction over CeO2Supported Single-Site Catalysts

Article abstract of DOI:10.1021/jacs.1c03895

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool"for high hydrogen generation efficiency and carbon dioxide (CO2) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru1/CeO2 catalyst is up to 9360 mol H2 per mol Ru per hour (579 mLH2 gRu-1 s-1) with 99.5% CO2 selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO2 selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.

Full text of DOI:10.1021/jacs.1c03895

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Article
Insights into the Mechanism of Methanol Steam Reforming Tandem
Reaction over CeO2 Supported Single-Site Catalysts
Luning Chen,$ Zhiyuan Qi,$ Xinxing Peng, Jeng-Lung Chen, Chih-Wen Pao, Xibo Zhang,
Chaochao Dun, Melissa Young, David Prendergast, Jeffrey J. Urban, Jinghua Guo, Gabor A. Somorjai,*
and Ji Su*
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ABSTRACT: We demonstrated how the special synergy between a noble metal
single site and neighboring oxygen vacancies provides an “ensemble reaction pool”
for high hydrogen generation efficiency and carbon dioxide (CO2) selectivity of a
tandem reaction: methanol steam reforming. Specifically, the hydrogen generation
rate over single site Ru1/CeO2 catalyst is up to 9360 mol H2 per mol Ru per hour
(579 mLH2 gRu s−1) with 99.5% CO2 selectivity. Reaction mechanism study
−1
showed that the integration of metal single site and O vacancies facilitated the
tandem reaction, which consisted of methanol dehydrogenation, water dissociation,
and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO
adsorption and the reaction activation energy difference between methanol
dehydrogenation and WGS reaction play an important role in determining the
activity and CO2 selectivity. Our study paves the way for the further rational design
of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution
systems promises to deliver highly desirable economic and ecological benefits.
Hydrogen plays an important role in the transition to a
cleaner energy landscape.24 However, the safety of hydrogen
transportation and storage remains a bottleneck for the
upcoming hydrogen economy.25,26 Storage of hydrogen in
chemical bonds of liquid organic hydrogen carriers (LOHCs)
provides a way to overcome this limitation. Among all the
LOHCs, methanol is identified as an ideal hydrogen carrier
owing to its low cost and wide availability.27 However, direct
methanol dehydrogenation always coproduces CO, which can
poison catalysts, especially in the application of polymer
electrolyte membrane fuel cells (PEMFCs).28,29 Methanol
steam reforming (MSR), as a tandem reaction,30 consists of
two sequential reactions: methanol dehydrogenation (CH3OH
= CO + 2 H2) and water gas shift (WGS) reaction (CO + H2O
= CO2 + H2). Therefore, the total reaction of MSR (CH3OH +
H2O = CO2 + 3 H2) can not only avoid CO emissions but also
generate one more stoichiometrically equivalent hydrogen.31
In pioneering work, α-MoC-supported, single-site Pt or Ni
catalysts were discovered exhibiting extraordinary hydrogen
production activity in the aqueous-phase methanol reforming
INTRODUCTION
■
Single-site catalysts, where isolated metal atoms are anchored
on supports by bonding to N or O atoms, have opened up a
new research frontier in the catalysis field.1−6 The downsizing
of metal nanoparticles to a single atom can achieve the
maximum efficiency of utilizing noble metals and creating
more active sites.7−11 Isolated metal sites typically show
excellent activity in many catalytic reactions involving small
molecules, such as CO oxidation, water gas shift (WGS)
reaction, and methane selective oxidation.12−14 However, the
lack of ensemble sites prevents reactions that involve large
molecules and some multistep reactions.15−17 Recent research
demonstrated that “ensemble effects” between metal single
atoms and neighboring oxygen vacancies can favor oxygen
transfer and reactant adsorption, promoting catalytic reaction
efficiency with large molecules.18−20 In our previous studies,
we demonstrated the enhanced activity and selectivity of
methanol dehydrogenation and n-hexane reforming when
combining an oxygen vacancy with noble metal atoms.21−23
The mechanism study also showed that the integration of
metal single-sites and neighboring oxygen vacancies creates a
special synergy that accelerates the reaction rates by facilitating
the adsorption and activation of reactants and the trans-
formation of intermediate species.18,22 Therefore, we envi-
sioned expanding the reaction scope to tandem reactions and
studying this “ensemble effect” of single-site catalysts further.
Received: April 13, 2021
Published: July 30, 2021
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reaction.32,33 The abundant surface hydroxyls of α-MoC
provide highly active sites for water dissociation, thus
accelerating the tandem methanol-reforming reaction at the
interface between Pt1 and α-MoC. However, the underlying
tandem mechanism of MSR over single-site catalysts has
remained elusive.
CO
+ CO2 output
output
Methanol Conversion(%) =
× 100%
Methanolinput
CO2 output
+ CO2 output
CO2 Selectivity(%) =
× 100%
CO
output
Catalytic Water Gas Shift (WGS) Reaction. The catalytic water
gas shift (WGS) activities of M1/CeO2 catalysts were investigated
using the same catalyst amounts in the same continuous flow reactor
for MSR. He (28 mL/min) and CO (2 mL/min) were mixed and fed
to the reactor at 1 atm, regulated by mass flow controllers. A flow of
2.25 mL/h of water was injected into the reactor. A K-type
thermocouple was fixed in the center of catalysts, and the temperature
of the bed was controlled by a PID 697 controller. The products were
analyzed online by HP 5890 GC (HayeSep D column) equipped with
a TCD detector.
The tandem reactions catalyzed by functional nanostructures
have been effectively studied.34−37 Typically, tandem reactions
occur on the surface of multifunctional material or at the
interface of different functional materials.34,38 Our previous
mechanism studies of tandem reactions found the spatial
arrangement of the interfaces of tandem catalyst could control
the generation, diffusion, and reaction of the intermediates,
and finally favor the selectivity of desired products.39 However,
single-site catalysts, the logical end points of the downsizing,
have distinct geometric and electronic structures. Therefore,
the surface/interface reaction model that is suitable for
traditional metal nanoparticle catalysts can no longer precisely
describe the reaction behaviors of metal single-sites and needs
to be revamped.
Further details are available in the Supporting Information.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of M1/CeO2 Single-
Site Catalysts. Ru1/CeO2 were fabricated by an AA-assisted
reduction route (Scheme 1). The ascorbic acid was first
In this work, we studied the mechanism of tandem MSR
reaction over a series of CeO2-supported single-site catalysts
(Pt1/CeO2, Pd1/CeO2, Rh1/CeO2, Ru1/CeO2). We showed
that well-defined reaction sites consisting of a metal single
atom and neighboring oxygen vacancies possessed unique
catalytic properties. Compared to the other three single-site
catalysts, Ru1/CeO2 displayed the highest hydrogen produc-
tion rate and CO2 selectivity. Further study indicated that
superior performance could be attributed to the strong CO
adsorption and suitable elementary-step reaction activity.
Scheme 1. Schematic Presentation of Synthesis Process for
M1/CeO2 Single-Site Catalysts
a
EXPERIMENTAL METHODS
■
Synthesis of M1/CeO2 Single-Site Catalysts (M = Ru, Rh, Pt,
Pd). Porous CeO2 nanorod support was synthesized by following the
previous report.40 The single-site M1/CeO2 catalysts were synthesized
by an ascorbic acid (AA)-assisted reduction method according to our
prior work with some modifications.20 Typically, 500 mg CeO2 was
first dispersed in 175 mL of distilled water, and 1 mmol AA was added
to the solution. After being stirred at room temperature for 3 h, the
products were collected by centrifugation, washed with distilled water
several times, dried under vacuum, and denoted as CeO2-AA.
140 mg CeO2-AA particles were then redispersed in 55 mL of
distilled water, and 0.01 mmol metal precursor (H2PtCl6, PdCl2,
RhCl3, RuCl3) was added. After the mixture was stirred for 3 h at
room temperature, the products were collected by centrifugation and
washed with water several times. After being dried under vacuum, the
products were calcinated at 300 °C in the air for 5 h to remove the
excess AA and denoted as M1/CeO2.
Catalytic Methanol Steam Reforming. MSR over M1/CeO2
was performed in a continuous flow reactor. In a typical catalytic
measurement, 100 mg of catalysts was mixed with 500 mg of white
quartz (50−70 mesh particle size). Then the mixture was placed in a
U-shaped fixed-bed flow reactor with an inner diameter of 4.50 mm,
and the length of the catalyst bed is around 20 mm. Quartz wool was
placed at both ends of the reactor. Helium (30 mL/min), regulated by
a mass flow controller, was fed to the reactor at 1 atm. A methanol/
water mixture (3 mL/h) with varying ratios (pure methanol, 1:1, 1:3,
1:5) was fed into the reactor by an injection pump. A K-type
thermocouple was fixed at the center of the catalyst, and the
temperature of bed was controlled by a PID 697 controller. The
products were analyzed online by HP 5890 GC (HayeSep D column)
equipped with a TCD detector.
a
M = Pt, Rh, Pd, Ru.
employed to create Ce3+ sites on the CeO2 surface by reducing
Ce4+. Then, prereduced CeO2-AA was dispersed in the
solution. After the addition of a ruthenium precursor
(RuCl3) solution, Ru was stabilized on the CeO2 surface
with the assistance of prereduced Ce3+ sites. After calcination
in the air to remove the excess absorbed AA, the ruthenium
single-sites were anchored on the CeO2 support surface.
Powder X-ray diffraction (XRD) and high-resolution
transmission electron microscope (TEM) were employed to
identify the status of loaded Ru on CeO2. XRD patterns
(Figure S1) show no diffraction peaks attributed to metallic Ru
due to the low concentration of Ru and its single-site status.
Besides, compared to the original CeO2 support (Figure S2),
no apparent Ru nanoparticles or clusters were observed
(Figure 1a) while the signals of Ru are uniformly distributed
throughout CeO2, as shown in the element mapping (Figure
1b). Extended X-ray absorption fine structure (EXAFS) further
confirmed the atomic dispersion of ruthenium. As shown in
Figure 1d, only one notable peak attributed by Ru−O was
observed in Fourier transformed (FT) k3-weighted EXAFS
spectrum while the Ru−Ru peak was not detected (Figure S3),
indicating isolated Ru sites were atomically dispersed on CeO2
(detailed fitting parameters in Table S1).41,42 Besides, the X-
ray absorption near-edge structure (XANES) spectrum of Ru1/
CeO2 suggested (Figure 1c) that Ru atoms carry a positive
charge (Ruδ+) rather than Ru0. This was further investigated by
The conversion of methanol and selectivity of CO2 were calculated
by the following equations
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Figure 1. (a) High-resolution TEM image and (b) HAADF-STEM
image and elemental mapping images of Ru1/CeO2 single-site
catalyst. (c) Normalized XANES spectra of Ru1/CeO2, RuO2, and
bulk Ru foil at the Ru K-edge. (d) The k3-weighted Fourier transform
EXAFS spectra with hollow points as fitting results.
CO adsorption and desorption using in situ diffuse reflectance
infrared Fourier transform spectroscopy (DRIFTS) (Figure
S4). Four peaks at 2173, 2117, 2045, and 1975 cm−1 were
detected, which is similar to those observed in reported Ru
single-site catalysts.43,44 The peaks at 2045 and 1975 cm−1 are
attributed to the pair of bands of dicarbonyl species of CO
adsorbed on oxidized Ru sites, Ruδ+(CO)2, while the peaks at
2173 and 2117 cm−1 are ascribed to monocarbonyl species,
Ruδ+(CO), and tricarbonyl species, Ruδ+(CO)3, respectively.
The AA-assisted method can be extended to fabricate
various CeO2-supported noble metal single-site catalysts (i.e.,
Pt, Pd, and Rh) by simply replacing RuCl3 with other metal
precursors like H2PtCl6, PdCl2, or RhCl3. As shown in Figure
2, the noble metal elements are all uniformly distributed on
CeO2 without any nanoparticles or clusters detected (Figure
S5; corresponding energy spectra are listed in Figure S6).
EXAFS spectra in Figure 2 show peaks contributed by the
metal−oxygen bond, confirming that the status of noble metal
on CeO2 are single sites. From the XANES spectrum (Figures
S7−S9), all the metal atoms are in oxidized states rather than
metallic states.
It has been reported that loading noble metal single-sites
(e.g., Au, Pd, Rh, and Ru) onto CeO2 can efficiently create
oxygen vacancies near the dopant cations.19,45−47 Combined
theoretical calculations and spectrum measurements have
proven that the generated oxygen vacancies are located near
the metal single sites, which created an ensemble reaction pool
with the well-defined structure.48 Synthetic methods such as
atomic layer deposition (ALD) and impregnation-coprecipita-
tion strategy would not involve the prereduction of the
support, while our AA-assisted method can create more oxygen
vacancies on the surface and thus have a higher chance to
selectively immobilize metal single sites near the oxygen
vacancy. According to XPS results (Figure S10, Table S2), the
original proportion of Ce3+ in the shallows of as-synthesized
CeO2 is around 23.8%.49 After AA reduction, the proportion of
Ce3+ increased to 41.5%, indicating a lot of O vacancies were
Figure 2. HAADF-STEM images and elemental mapping images of
(a1) Pt1/CeO2, (b1) Pd1/CeO2, and (c1) Rh1/CeO2 single-site
catalyst. (c) k3-weighted Fourier transform EXAFS spectra of (a2)
Pt1/CeO2, (b2) Pd1/CeO2, (c2) Rh1/CeO2 and their relative metal
foil and metal oxides.
created on the surface, which agreed with electron para-
magnetic resonance (EPR) spectra and Raman spectra (Figure
S11, 12).50,51 After air calcination to remove excess AA, the
Ce3+ percentages of all M1/CeO2 decreased to a certain degree
compared to CeO2-AA, but they are still much higher than the
original CeO2 supports (Table S2). This result confirms that
the introduction of metal single sites could further stabilize the
neighboring oxygen vacancies, which is consistent with the
prior report.52 Thus, more ensemble sites consisting of metal
single site and surrounding oxygen vacancies were created via
the AA-assisted method, which could be potentially applied in
multistep tandem reactions.
Methanol Reforming over Ru1/CeO2 Single-Site
Catalyst. Compared to methanol dehydrogenation, MSR
not only releases 3 H2 per methanol by utilizing the H2 from
water, achieving a high H2 gravimetric density of 18.8%, but
also avoids the generation of CO by the sequential WGS
reaction.31 Significantly, the gas products of methanol steam
reforming are H2 and CO2 without the poisoning gas CO,
which can be potentially applied in the polymer electrolyte
membrane fuel cells (PEMFCs) without any pretretments.32
We first investigated the catalytic performance of Ru1/CeO2
in both methanol dehydrogenation and MSR reactions using
different ratios of methanol and water. As shown in Figure 3a,c,
methanol dehydrogenation (black line labeled as 1:0) starts at
150 °C, and the higher reaction temperature favors the
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Figure 3. (a) Hydrogen generation rate, (b) CO2 selectivity, and (c) methanol conversion of Ru1/CeO2 single-site catalyst at different
temperatures with different ratios of methanol and water.
Figure 4. (a) Hydrogen generation rate, (b) CO2 selectivity, and (c) methanol conversion of single-site M1/CeO2 catalysts at different
temperatures with a 1:3 volume ratio of methanol and water.
methanol conversion. At 350 °C, the hydrogen production rate
is 100.4 mmolH2 gcat−1 h−1 with a methanol conversion of 6.8%.
The products of methanol dehydrogenation over Ru1/CeO2
only consist of H2 and CO, and no formaldehyde was detected.
After the introduction of water vapor into the system, CO
will further react with water through a sequential WGS
reaction (CO + H2O = CO2 + H2) over Ru1/CeO2. It will
release one more H2 and convert CO to CO2. Compared to
CO, CO2 has a weaker bonding to the Ru single site, which can
be easily removed under reaction condition to recover the
active site for the next coming methanol. Therefore,
introducing water could enhance the H2 production as well
as the conversion of methanol (Figures 3a,c). With water
cofeed (Vmethanol/Vwater = 1:1), the hydrogen generation rate
catalysts such as Cu/ZnO-based catalysts, Ru1/CeO2 also had
excellent activity and CO2 selectivity in the temperature range
of 150 to 350 °C (Table S3). Although the selectivity of CO2
could increase to 99.5% at the water/methanol ratio of 5, the
massive water vapor inhibited the methanol diffusion, leading
−1
to the lower H2 generation rate of 23.8 mmolH2 gcat h−1.
Besides, at higher water concentrations (1:3 and 1:5), the
relatively low methanol concentration will also slow down the
growth of MSR rate at higher temperatures, because the
methanol diffusion process was limited by a large amount of
water molecules in the gas phase.
In practical application, the main issue hindering the
application of single-site catalysts is their poor stability in the
catalytic process, especially at operating temperature.53 There-
fore, the stability of Ru1/CeO2 was assessed in the catalytic
reaction over time (Figure S14). The hydrogenation evolution
increased to 207.6 mmolH2 gcat h−1 at 350 °C, which is two
−1
times that of pure methanol; 24.2% of methanol was
converted, which is 4-fold that of direct methanol dehydrogen-
ation without water. The selectivity of CO2 in the product is
about 32.2% (Figure 3b) under the methanol and water ratio
of 1:1.
−1
rate was retained at 139.6 mmolH2 gcat h−1 with more than
97% CO2 selectivity within 72 h testing of methanol steam
reforming at 350 °C (Vmethanol/Vwater = 1:3), indicating its
excellent stability due to the strong interaction between Ru and
CeO2 surface.54
Further increase of the water/methanol ratio to 3:1 leads to
the methanol conversion of 25.6% and 97.8% selectivity of
CO2 at 350 °C, due to the enhanced WGS reaction facilitated
by the excess water. As the feeding rate of the water and
methanol mixture is kept the same, less methanol was injected
into the system. The lower methanol partial pressure decreases
Methanol Reforming on Different M1/CeO2 Single-
Site Catalysts. We further investigated the catalytic perform-
ance of MSR (Vmethanol/Vwater = 1:3) over different M1/CeO2
catalysts (Ru1/CeO2, Rh1/CeO2, Pt1/CeO2, Pd1/CeO2) with a
similar metal loading amount (0.14−0.15 wt %). For Pt1/
CeO2, Rh1/CeO2, and Pd1/CeO2, only a small number of
products were detected above 200 °C, of which the starting
reaction temperature is higher than that of Ru1/CeO2 catalyst
(150 °C). Similar to Ru1/CeO2, higher temperature favors the
reforming reaction rate (Figure 4a,c). Under the same reaction
−1
the generation rate of H2 to 139.6 mmolH2 gcat h−1 which is
still higher than that of the pure methanol (100.4 mmolH2
gcat−1 h−1). It also ranks the highest among the reported noble
metal catalysts in terms of CO2 selectivity and H2 generation
rate (Figure S13). When compared with transition metal
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conditions and similar metal loading amount, Ru1/CeO2
showed the highest H2 generation rate and methanol
conversion with the activity order of Ru1/CeO2 > Rh1/CeO2
> Pt1/CeO2 > Pd1/CeO2.
are in the order of Rh1/CeO2 (161.8 mmolH2 gcat−1 h−1) > Pt1/
CeO2 (152.9 mmolH2 gcat h−1) > Pd1/CeO2 (107.9 mmolH2
−1
−1
−1
gcat
h−1) > Ru1/CeO2 (100.4 mmolH2 gcat
h−1).
Interestingly, this activity trend is different from that of MSR
in the presence of water, where H2 generation rates are in the
order of Ru1/CeO2 > Rh1/CeO2 > Pt1/CeO2 > Pd1/CeO2
(Figure 4a).
In the sequential WGS reaction (Figure 5c), Ru1/CeO2 has
the highest activity from 200 to 350 °C. Especially at a lower
temperature (200 °C), the CO conversion of Ru1/CeO2
(20.1%) is much higher than the other three catalysts, which
are 7.5%, 0.9%, and 1.3% for Pt1/CeO2, Pd1/CeO2, Rh1/CeO2,
respectively. The CO conversion of Ru1/CeO2 reached up to
100% at the high temperature (350 °C) while the WGS activity
is in the order of Ru1/CeO2 > Pt1/CeO2 > Rh1/CeO2 > Pd1/
CeO2.
The apparent activation energy (Ea) is a well-known
empirical parameter in chemical kinetics that characterizes
the dependence of the chemical rate coefficients on the
temperature and provides information to compare the intrinsic
activity of the catalysts.59 We thus calculated the apparent
activation energies for both reactions (Figure 5b,d) to
understand the reaction mechanism and chemical kinetics.
The activation energy of methanol dehydrogenation (Ea1) is in
the order of Pt1/CeO2 (79.6 6.2 kJ/mol) ≈ Rh1/CeO2 (81.4
7.2 kJ/mol) < Ru1/CeO2 (94.0 8.3 kJ/mol) < Pd1/CeO2
(102.3 17.4 kJ/mol), while the activation energy of WGS
reaction (Ea2) is in the order of Ru1/CeO2 (11.4 0.7 kJ/mol)
< Rh1/CeO2 (51.0 5.4 kJ/mol) ≈ Pt1/CeO2(51.9 8.4 kJ/
mol) ≈ Pd1/CeO2 (52.0 8.6 kJ/mol). As reported, methanol
steam reforming is a two-step reaction, where the activation
energy of methanol dissociation (first step) is much higher
than the subsequent WGS reaction (second step).30 Mean-
while, the second step, WGS reaction, has a competing step:
CO desorption. Therefore, the stronger CO adsorption and
the lower Ea2 of the WGS reaction could help the CO
intermediates efficiently convert to CO2 via the tandem
reaction and recover more active sites for methanol
dehydrogenation. Among all the studied single site catalysts,
Ru1/CeO2 has an appropriate Ea1 of methanol dehydrogen-
ation, the lowest Ea2 of WGS, and the strongest CO
adsorption, resulting in the highest H2 production rate and
CO2 selectivity. On the contrary, Pt1/CeO2 has the lowest Ea1,
but its highest Ea2, and weak bonding with CO leading to the
lowest CO2 selectivity.
More importantly, Ru1/CeO2 showed the highest CO2
selectivity of 97.8% at 350 °C, while the other three single-
site catalysts have only less than 60% CO2 selectivity (Figure
4b). The catalytic results of MSR over M1/CeO2 showed that
CO desorption and WGS are competing steps. Less CO
desorption is the key to the higher selectivity of CO2 in the
subsequent WGS reaction. It has been reported that in
comparison with Pt, Rh, and Pd, Ru has the lowest CO
adsorption energy both for bulk materials and single-atom,
indicating Ru has a much stronger bonding of CO.55,56
Therefore, CO-temperature-programmed desorption (CO-
TPD) was then applied to investigate the strength of CO
bonding on M1/CeO2 (Figure S15). The peak below 150 °C is
attributed to CO adsorption on metal sites, while the peak
between 200 to 300 °C is attributed to CO bonding on the
CeO2 support surface.57,58 Notably, different from other
metals, Ru1/CeO2 displays a CO desorption peak around
350 °C, indicating the strong bonding between CO and Ru1/
CeO2. In the reaction of methanol steam reforming, this strong
interaction will further stabilize the CO intermediates,
providing more chance for subsequential WGS reaction. On
the other side, the single site Pt, Pd, and Rh do not have this
strong bonding at 350 °C, so CO will desorb at lower
temperatures, leading to decreased CO2 selectivity.
Elementary-Step Methanol Dehydrogenation and
WGS Reaction. MSR is a tandem reaction, including
methanol dehydrogenation and the subsequent WGS reaction.
Therefore, we carried out methanol dehydrogenation and
WGS reaction over M1/CeO2 separately. As shown in Figure
5a, the methanol dehydrogenation catalyzed by different M1/
CeO2 shows various H2 generation rates. Methanol starts to
dehydrogenate over Rh1/CeO2 and Pt1/CeO2 at a lower
temperature of 150 °C, indicating superior activity toward
Ru1/CeO2 and Pd1/CeO2. The H2 generation rates at 350 °C
Proposed Reaction Mechanism. Combining our exper-
imental findings and the insights provided by the preceding
work, we proposed a reaction mechanism of tandem MSR
reaction over M1/CeO2. As shown in Scheme 2, the methanol
dehydrogenation occurs on the metal single site to release
hydrogen and form the intermediate CO, where the
neighboring O vacancies will facilitate the dissociative
adsorption of methanol.22
Depending on the binding strength, COad would either
desorb from the active sites and ends with a low CO2
selectivity (i.e., Pt1/CeO2 case) or directly react with water
to yield CO2 via the sequential WGS reaction. Dissociation of
water is generally considered a key step in WGS,60,61 and water
molecules prefer to dissociate on the reduced CeOx (O
vacancy-Ce3+) by transferring a H atom to the neighboring
surface oxygen.62,63 A recent study also revealed the synergistic
effect between Pt sites and neighboring reduced Ce sites (Pt−
O vacancy-Ce3+) at the interface of the Pt clusters and the
Figure 5. (a) H2 generation rate over M1/CeO2 catalysts at different
temperatures. (b) Arrhenius plots of methanol dehydrogenation over
M1/CeO2 catalysts. (c) CO conversion of WGS over M1/CeO2
catalysts at different temperatures. (d) Arrhenius plots of WGS over
M1/CeO2 catalysts.
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Scheme 2. Proposed Reaction Pathway for Methanol Steam
Reforming on M1/CeO2 Single-Site Catalysts
support, TEM images of M1/CeO2 catalyst, XPS spectra
of CeO2 and M1/CeO2, EPR and Raman spectra of
CeO2 and CeO2-AA, CO adsorption−desorption
DRIFTS of Ru1/CeO2, CO-TPD results of M1/CeO2
catalysts, stability test of Ru1/CeO2 catalyst (PDF)
AUTHOR INFORMATION
■
Corresponding Authors
Ji Su − Chemical Sciences Division and Molecular Foundry,
Lawrence Berkeley National Laboratory, Berkeley, California
94720, United States; Email: jisu@lbl.gov
Gabor A. Somorjai − Chemical Sciences Division, Lawrence
Berkeley National Laboratory, Berkeley, California 94720,
United States; Department of Chemistry, University of
California-Berkeley, Berkeley, California 94720, United
States; orcid.org/0000-0002-8478-2761;
Email: somorjai@berkeley.edu
Authors
Luning Chen − Chemical Sciences Division, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United
States; State Key Laboratory of Physical Chemistry of Solid
Surfaces, Collaborative Innovation Center of Chemistry for
Energy Materials, and Department of Chemistry, College of
Chemistry and Chemical Engineering, Xiamen University,
Xiamen 361005, China; orcid.org/0000-0001-5434-
4755
Zhiyuan Qi − Chemical Sciences Division, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United
States
Xinxing Peng − Chemical Sciences Division, Lawrence
Berkeley National Laboratory, Berkeley, California 94720,
United States; orcid.org/0000-0002-7077-8454
Jeng-Lung Chen − National Synchrotron Radiation Research
Center, Hsinchu 30076, Taiwan
support,64 and suggest only those oxygen vacancies nearby the
Pt sites are involved in the WGS. M1/CeO2 in this work
contains a similar structure, consisted of metal single sites with
neighboring O vacancies (metal-O vacancy-Ce3+). However,
we could directly create much more “ensemble sites” using the
AA-assisted synthetic approach, instead of a limited amount of
active sites only at the interface of nanocluster and support,
highlighting the great advantage of single-site catalysts. It has
also been reported that the introduction of metal heteroatoms
could efficiently create oxygen vacancy next to the dopant
cations. Therefore, in our proposed “ensemble reaction pool”,
the formed hydroxyl species adsorbed on the oxygen vacancy
will react with the neighboring COad, which avoids the
diffusion process and lead to high activity.
Chih-Wen Pao − National Synchrotron Radiation Research
CONCLUSION
Center, Hsinchu 30076, Taiwan
■
Xibo Zhang − State Key Laboratory of Physical Chemistry of
Solid Surfaces, Collaborative Innovation Center of Chemistry
for Energy Materials, and Department of Chemistry, College
of Chemistry and Chemical Engineering, Xiamen University,
Xiamen 361005, China
Chaochao Dun − Molecular Foundry, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United
States; orcid.org/0000-0002-3215-6478
Melissa Young − Department of Chemistry, University of
California-Berkeley, Berkeley, California 94720, United
States
David Prendergast − Molecular Foundry, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United
States; orcid.org/0000-0003-0598-1453
Jeffrey J. Urban − Molecular Foundry, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United
States; orcid.org/0000-0002-6520-830X
Jinghua Guo − Advanced Light Source, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United
States; orcid.org/0000-0002-8576-2172
In summary, the mechanism of methanol steam reforming
tandem reaction was investigated over a series of CeO2-
supported noble metal single site catalysts. Notably, Ru1/CeO2
displayed a much higher H2 generation rate and CO2
selectivity compared to those of the other three catalysts.
Specifically, the stronger CO-metal bonding and larger
difference of apparent activation energy between methanol
dehydrogenation and WGS reaction resulted in the higher CO2
selectivity. Importantly, different from metal nanoparticle
catalysts, the metal single sites accompanied by the
neighboring O vacancies generate an “ensemble reaction
pool” to combine methanol dehydrogenation, water dissocia-
tion, and WGS reaction efficiently in the local environment.
And this special synergy further improves the reaction
efficiency and selectivity. Ultimately, this in-depth study
highlights the benefits of well-designed single site catalysts
for multiple step catalysis and paves the way for further rational
design based on the “ensemble reaction pool” concept.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c03895.
■
sı
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c03895
Author Contributions
Experimental details, characterization data, and partial
catalytic data, including the characterization of CeO2
$L.C. and Z.Q. contributed equally to this work
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J. Am. Chem. Soc. 2021, 143, 12074−12081

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
single-atom catalyst in water gas shift reaction. J. Am. Chem. Soc. 2013,
135, 15314−15317.
Notes
The authors declare no competing financial interest.
(14) Shan, J.; Li, M.; Allard, L. F.; Lee, S.; Flytzani-Stephanopoulos,
M. Mild oxidation of methane to methanol or acetic acid on
supported isolated rhodium catalysts. Nature 2017, 551, 605−608.
(15) Jeong, H.; Kwon, O.; Kim, B. S.; Bae, J.; Shin, S.; Kim, H. E.;
Kim, J.; Lee, H. Highly durable metal ensemble catalysts with full
dispersion for automotive applications beyond single-atom catalysts.
Nat. Catal. 2020, 3, 368−375.
ACKNOWLEDGMENTS
■
This work was supported by the Hydrogen Materials Advanced
Research Consortium (HyMARC), established as part of the
Energy Materials Network by the U.S. Department of Energy,
Office of Energy Efficiency and Renewable Energy, Fuel Cell
Technologies Office, under Contract Number DE-AC02-
05CH11231, and Director, Office of Basic Energy Sciences,
Division of Chemical Sciences, Geological and Biosciences of
the U.S. Department of Energy under the same contract. This
research used resources of the Advanced Light Source, which is
a DOE Office of Science User Facility under the same contract.
J. Guo, D. Prendergast, C. Dun, J. Urban and J. Su were
supported by a User Project at The Molecular Foundry at
Lawrence Berkeley National Laboratory, which is supported by
the Office of Science of the U.S. Department of Energy under
the same contract. L. Chen and Z. Qi acknowledge the
financial support provided by catalysis research program DOE/
LBNL DE-AC02-05CH11231, FWP no. CH030201.
(16) Jeong, H.; Lee, G.; Kim, B. S.; Bae, J.; Han, J. W.; Lee, H. Fully
dispersed Rh ensemble catalyst to enhance low-temperature activity. J.
Am. Chem. Soc. 2018, 140, 9558−9565.
(17) Jeong, H.; Shin, S.; Lee, H. Heterogeneous Atomic Catalysts
Overcoming the Limitations of Single-Atom Catalysts. ACS Nano
2020, 14, 14355−14374.
(18) Wang, L.; Guan, E.; Zhang, J.; Yang, J.; Zhu, Y.; Han, Y.; Yang,
M.; Cen, C.; Fu, G.; Gates, B. C.; Xiao, F. S. Single-site catalyst
promoters accelerate metal-catalyzed nitroarene hydrogenation. Nat.
Commun. 2018, 9, 1−8.
(19) Li, T.; Liu, F.; Tang, Y.; Li, L.; Miao, S.; Su, Y.; Zhang, J.;
Huang, J.; Sun, H.; Haruta, M.; Wang, A. Maximizing the number of
interfacial sites in single-atom catalysts for the highly selective,
solvent-free oxidation of primary alcohols. Angew. Chem., Int. Ed.
2018, 57, 7795−7799.
(20) Yu, K.; Lou, L. L.; Liu, S.; Zhou, W. Asymmetric oxygen
vacancies: the intrinsic redox active sites in metal oxide catalysts. Adv.
Sci. 2020, 7, 1901970.
(21) Chen, L. N.; Hou, K. P.; Liu, Y. S.; Qi, Z. Y.; Zheng, Q.; Lu, Y.
H.; Chen, J. Y.; Chen, J. L.; Pao, C. W.; Wang, S. B.; Li, Y. B.; et al.
Efficient hydrogen production from methanol using a single-site Pt1/
CeO2 catalyst. J. Am. Chem. Soc. 2019, 141, 17995−17999.
(22) Qi, Z.; Chen, L.; Zhang, S.; Su, J.; Somorjai, G. A. Mechanism
of Methanol Decomposition over Single-Site Pt1/CeO2 Catalyst: A
DRIFTS Study. J. Am. Chem. Soc. 2021, 143, 60−64.
REFERENCES
■
(1) Kaiser, S. K.; Chen, Z.; Faust Akl, D.; Mitchell, S.; Pérez-
Ramírez, J. Single-Atom Catalysts across the Periodic Table. Chem.
Rev. 2020, 120, 11703−11809.
(2) Ji, S.; Chen, Y.; Wang, X.; Zhang, Z.; Wang, D.; Li, Y. Chemical
synthesis of single atomic site catalysts. Chem. Rev. 2020, 120, 11900−
11955.
(3) Lang, R.; Du, X.; Huang, Y.; Jiang, X.; Zhang, Q.; Guo, Y.; Liu,
K.; Qiao, B.; Wang, A.; Zhang, T. Single-Atom Catalysts Based on the
Metal-Oxide Interaction. Chem. Rev. 2020, 120, 11986−12043.
(4) Kistler, J. D.; Chotigkrai, N.; Xu, P.; Enderle, B.; Praserthdam,
P.; Chen, C. Y.; Browning, N. D.; Gates, B. C. A single-site platinum
CO oxidation catalyst in zeolite KLTL: microscopic and spectroscopic
determination of the locations of the platinum atoms. Angew. Chem.,
Int. Ed. 2014, 53, 8904−8907.
(23) Zhang, S.; Chen, L.; Qi, Z.; Zhuo, L.; Chen, J. L.; Pao, C. W.;
Su, J.; Somorjai, G. A. Insights into the Mechanism of n-Hexane
Reforming over a Single-Site Platinum Catalyst. J. Am. Chem. Soc.
2020, 142, 16533−16537.
(24) Tromp, T. K.; Shia, R. L.; Allen, M.; Eiler, J. M.; Yung, Y. L.
Potential environmental impact of a hydrogen economy on the
stratosphere. Science 2003, 300, 1740−1742.
(5) Rascón, F.; Wischert, R.; Copéret, C. Molecular nature of
support effects in single-site heterogeneous catalysts: silica vs.
alumina. Chem. Sci. 2011, 2, 1449−1456.
̆
(25) Muradov, N. Z.; Veziroglu, T. N. Green” path from fossil-based
to hydrogen economy: an overview of carbon-neutral technologies.
(6) Thomas, J. M.; Raja, R.; Lewis, D. W. Single-site heterogeneous
catalysts. Angew. Chem., Int. Ed. 2005, 44, 6456−6482.
Int. J. Hydrogen Energy 2008, 33, 6804−6839.
̆
(26) Muradov, N. Z.; Veziroglu, T. N. From hydrocarbon to
(7) 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.
hydrogen−carbon to hydrogen economy. Int. J. Hydrogen Energy
2005, 30, 225−237.
(27) Liu, W. C.; Baek, J.; Somorjai, G. A. The methanol economy:
methane and carbon dioxide conversion. Top. Catal. 2018, 61, 530−
541.
(8) Jones, J.; Xiong, H.; DeLaRiva, A. T.; Peterson, E. J.; Pham, H.;
Challa, S. R.; Qi, G.; Oh, S.; Wiebenga, M. H.; Hernández, X. I. P.;
Wang, Y. Thermally stable single-atom platinum-on-ceria catalysts via
atom trapping. Science 2016, 353, 150−154.
(28) Wang, T.; Chen, Z. X.; Yu, S.; Sheng, T.; Ma, H. B.; Chen, L.
N.; Rauf, M.; Xia, H. P.; Zhou, Z. Y.; Sun, S. G. Constructing canopy-
shaped molecular architectures to create local Pt surface sites with
high tolerance to H2S and CO for hydrogen electrooxidation. Energy
Environ. Sci. 2018, 11, 166−171.
(29) Nilekar, A. U.; Sasaki, K.; Farberow, C. A.; Adzic, R. R.;
Mavrikakis, M. Mixed-metal Pt monolayer electrocatalysts with
improved CO tolerance. J. Am. Chem. Soc. 2011, 133, 18574−18576.
(30) Iulianelli, A.; Ribeirinha, P.; Mendes, A.; Basile, A. Methanol
steam reforming for hydrogen generation via conventional and
membrane reactors: a review. Renewable Sustainable Energy Rev. 2014,
29, 355−368.
(31) Palo, D. R.; Dagle, R. A.; Holladay, J. D. Methanol steam
reforming for hydrogen production. Chem. Rev. 2017, 107, 3992−
4021.
(9) Wang, L.; Zhang, W.; Wang, S.; Gao, Z.; Luo, Z.; Wang, X.;
Zeng, R.; Li, A.; Li, H.; Wang, M.; Zheng, X. Atomic-level insights in
optimizing reaction paths for hydroformylation reaction over Rh/
CoO single-atom catalyst. Nat. Commun. 2016, 7, 1−8.
(10) Lee, B. H.; Park, S.; Kim, M.; Sinha, A. K.; Lee, S. C.; Jung, E.;
Chang, W. J.; Lee, K. S.; Kim, J. H.; Cho, S. P.; Kim, H. Reversible
and cooperative photoactivation of single-atom Cu/TiO2 photo-
catalysts. Nat. Mater. 2019, 18, 620−626.
(11) Liu, P.; Zhao, Y.; Qin, R.; Mo, S.; Chen, G.; Gu, L.; Chevrier,
D. M.; Zhang, P.; Guo, Q.; Zang, D.; Wu, B. Photochemical route for
synthesizing atomically dispersed palladium catalysts. Science 2016,
352, 797−800.
(12) Nie, L.; Mei, D.; Xiong, H.; Peng, B.; Ren, Z.; Hernandez, X. I.
P.; DeLaRiva, A.; Wang, M.; Engelhard, M. H.; Kovarik, L.; Datye, A.
K. Activation of surface lattice oxygen in single-atom Pt/CeO2 for
low-temperature CO oxidation. Science 2017, 358, 1419−1423.
(13) Lin, J.; Wang, A.; Qiao, B.; Liu, X.; Yang, X.; Wang, X.; Liang,
J.; Li, J.; Liu, J.; Zhang, T. Remarkable performance of Ir1/FeOx
(32) Lin, L.; Zhou, W.; Gao, R.; Yao, S.; Zhang, X.; Xu, W.; Zheng,
S.; Jiang, Z.; Yu, Q.; Li, Y. W.; Shi, C. Low-temperature hydrogen
production from water and methanol using Pt/α-MoC catalysts.
Nature 2017, 544, 80−83.
12080
https://doi.org/10.1021/jacs.1c03895
J. Am. Chem. Soc. 2021, 143, 12074−12081

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
(33) Lin, L.; Yu, Q.; Peng, M.; Li, A.; Yao, S.; Tian, S.; Liu, X.; Li, A.;
Jiang, Z.; Gao, R.; Han, X.; et al. Atomically Dispersed Ni/α-MoC
Catalyst for Hydrogen Production from Methanol/Water. J. Am.
Chem. Soc. 2021, 143 (1), 309−317.
defects and surface chemistry: Implications in CO oxidation by Cu/
CeO2 catalysts. Appl. Catal., B 2018, 230, 18−28.
(52) McFarland, E. W.; Metiu, H. Catalysis by doped oxides. Chem.
Rev. 2013, 113, 4391−4427.
(53) Duan, S.; Wang, R.; Liu, J. Stability investigation of a high
number density Pt1/Fe2O3 single-atom catalyst under different gas
environments by HAADF-STEM. Nanotechnology 2018, 29, 204002.
(54) Liu, J. C.; Tang, Y.; Wang, Y. G.; Zhang, T.; Li, J. Theoretical
understanding of the stability of single-atom catalysts. Natl. Sci. Rev.
2018, 5, 638−641.
(55) Abild-Pedersen, F.; Andersson, M. P. CO adsorption energies
on metals with correction for high coordination adsorption sites−A
density functional study. Surf. Sci. 2007, 601, 1747−1753.
(56) Sarma, B. B.; Plessow, P. N.; Agostini, G.; Concepción, P.;
Pfänder, N.; Kang, L.; Wang, F. R.; Studt, F.; Prieto, G. Metal-specific
reactivity in single-atom catalysts: CO oxidation on 4d and 5d
transition metals atomically dispersed on MgO. J. Am. Chem. Soc.
2020, 142, 14890−14902.
(57) Wu, Z.; Li, M.; Overbury, S. H. On the Structure Dependence
of CO Oxidation over CeO2 nanocrystals with Well-Defined Surface
Planes. J. Catal. 2012, 285, 61−73.
(58) Zhu, H. O.; Kim, J. R.; Ihm, S. K. Characteristics of Pt/WO3/
CeO2/ZrO2 Catalysts for Catalytic Reduction of NO by CO. Appl.
Catal., B 2009, 86, 87−92.
(59) Calderón-Cárdenas, A.; Paredes-Salazar, E. A.; Varela, H.
Apparent Activation Energy in Electrochemical Multistep Reactions:
A Description via Sensitivities and Degrees of Rate Control. ACS
Catal. 2020, 10, 9336−9345.
(60) Song, W.; Hensen, E. J. Mechanistic aspects of the water−gas
shift reaction on isolated and clustered Au atoms on CeO2 (110): A
density functional theory study. ACS Catal. 2014, 4, 1885−1892.
(61) Vecchietti, J.; Bonivardi, A.; Xu, W.; Stacchiola, D.; Delgado, J.
J.; Calatayud, M.; Collins, S. E. Understanding the role of oxygen
vacancies in the water gas shift reaction on ceria-supported platinum
catalysts. ACS Catal. 2014, 4, 2088−2096.
(62) Vovchok, D.; Guild, C. J.; Dissanayake, S.; Llorca, J.; Stavitski,
E.; Liu, Z.; Palomino, R. M.; Waluyo, I.; Li, Y.; Frenkel, A. I.;
Rodriguez, J. A. In situ characterization of mesoporous Co/CeO2
catalysts for the high-temperature water-gas shift. J. Phys. Chem. C
2018, 122, 8998−9008.
(63) Aranifard, S.; Ammal, S. C.; Heyden, A. On the importance of
metal−oxide interface sites for the water−gas shift reaction over Pt/
CeO2 catalysts. J. Catal. 2014, 309, 314−324.
(64) Li, Y.; Kottwitz, M.; Vincent, J. L.; Enright, M. J.; Liu, Z.;
Zhang, L.; Huang, J.; Senanayake, S. D.; Yang, W. C. D.; Crozier, P.
A.; Nuzzo, R. G. Dynamic structure of active sites in ceria-supported
Pt catalysts for the water gas shift reaction. Nat. Commun. 2021, 12,
1−9.
(34) Yamada, Y.; Tsung, C. K.; Huang, W.; Huo, Z.; Habas, S. E.;
Soejima, T.; Aliaga, C. E.; Somorjai, G. A.; Yang, P. Nanocrystal
bilayer for tandem catalysis. Nat. Chem. 2011, 3, 372−376.
(35) Rayder, T. M.; Adillon, E. H.; Byers, J. A.; Tsung, C. K. A
Bioinspired Multicomponent Catalytic System for Converting Carbon
Dioxide into Methanol Autocatalytically. Chem. 2020, 6, 1742−1754.
(36) Ma, H.; Ma, G.; Qi, Y.; Wang, Y.; Chen, Q.; Rout, K. R.;
Fuglerud, T.; Chen, D. Nitrogen-Doped Carbon-Assisted One-pot
Tandem Reaction for Vinyl Chloride Production via Ethylene
Oxychlorination. Angew. Chem., Int. Ed. 2020, 59, 22080−22085.
(37) Cho, H. J.; Kim, D.; Li, J.; Su, D.; Xu, B. Zeolite-encapsulated
Pt nanoparticles for tandem catalysis. J. Am. Chem. Soc. 2018, 140,
13514−13520.
(38) Chen, L.; Zhang, X.; Zhou, J.; Xie, Z.; Kuang, Q.; Zheng, L. A
nano-reactor based on PtNi@ metal−organic framework composites
loaded with polyoxometalates for hydrogenation−esterification
tandem reactions. Nanoscale 2019, 11, 3292−3299.
(39) Su, J.; Xie, C.; Chen, C.; Yu, Y.; Kennedy, G.; Somorjai, G. A.;
Yang, P. Insights into the mechanism of tandem alkene hydro-
formylation over a nanostructured catalyst with multiple interfaces. J.
Am. Chem. Soc. 2016, 138, 11568−11574.
(40) Mai, H. X.; Sun, L. D.; Zhang, Y. W.; Si, R.; Feng, W.; Zhang,
H. P.; Liu, H. C.; Yan, C. H. Shape-selective synthesis and oxygen
storage behavior of ceria nanopolyhedra, nanorods, and nanocubes. J.
Phys. Chem. B 2005, 109, 24380−24385.
(41) Ravel, B.; Newville, M. A.T.H.E.N.A. ATHENA, ARTEMIS,
HEPHAESTUS: data analysis for X-ray absorption spectroscopy using
IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537−541.
(42) Sarma, B. B.; Kim, J.; Amsler, J.; Agostini, G.; Weidenthaler, C.;
Pfänder, N.; Arenal, R.; Concepción, P.; Plessow, P.; Studt, F.; Prieto,
G. One-pot cooperation of single-atom Rh and Ru solid catalysts for a
selective tandem olefin isomerization-hydrosilylation process. Angew.
Chem., Int. Ed. 2020, 59, 5806−5815.
(43) Thang, H. V.; Tosoni, S.; Fang, L.; Bruijnincx, P.; Pacchioni, G.
Nature of Sintering-Resistant, Single-Atom Ru Species Dispersed on
Zirconia-Based Catalysts: A DFT and FTIR Study of CO Adsorption.
ChemCatChem 2018, 10, 2634−2645.
(44) Qiu, J. Z.; Hu, J.; Lan, J.; Wang, L. F.; Fu, G.; Xiao, R.; Ge, B.;
Jiang, J. Pure Siliceous Zeolite-Supported Ru Single-Atom Active Sites
for Ammonia Synthesis. Chem. Mater. 2019, 31, 9413−9421.
(45) 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.
(46) Shapovalov, V.; Metiu, H. Catalysis by doped oxides: CO
oxidation by AuxCe1−xO2. J. Catal. 2007, 245, 205−214.
(47) Tang, W.; Hu, Z.; Wang, M.; Stucky, G. D.; Metiu, H.;
McFarland, E. W. Methane complete and partial oxidation catalyzed
by Pt-doped CeO2. J. Catal. 2010, 273, 125−137.
(48) Liu, C.; Chen, Z.; Yan, H.; Xi, S.; Yam, K. M.; Gao, J.; Du, Y.;
Li, J.; Zhao, X.; Xie, K.; Xu, H. Expedient synthesis of E-hydrazone
esters and 1H-indazole scaffolds through heterogeneous single-atom
platinum catalysis. Sci. Adv. 2019, 5, 1537.
(49) Chen, J.; Wanyan, Y.; Zeng, J.; Fang, H.; Li, Z.; Dong, Y.; Qin,
R.; Wu, C.; Liu, D.; Wang, M.; Kuang, Q.; Xie, Z.; Zheng, L. Surface
engineering protocol to obtain an atomically dispersed Pt/CeO2
catalyst with high activity and stability for CO oxidation. ACS
Sustainable Chem. Eng. 2018, 6, 14054−14062.
(50) Khan, M. E.; Khan, M. M.; Cho, M. H. Ce3+-ion, surface
oxygen vacancy, and visible light-induced photocatalytic dye
degradation and photocapacitive performance of CeO2-graphene
nanostructures. Sci. Rep. 2017, 7, 1−17.
(51) Lykaki, M.; Pachatouridou, E.; Carabineiro, S. A.; Iliopoulou,
E.; Andriopoulou, C.; Kallithrakas-Kontos, N.; Boghosian, S.;
Konsolakis, M. Ceria nanoparticles shape effects on the structural
12081
https://doi.org/10.1021/jacs.1c03895
J. Am. Chem. Soc. 2021, 143, 12074−12081