Acid-Promoter-Free Ethylene Methoxycarbonylation over Ru-Clusters/Ceria: The Catalysis of Interfacial Lewis Acid-Base Pair

Article abstract of DOI:10.1021/jacs.8b01742

The interface of metal-oxide plays pivotal roles in catalytic reactions, but its catalytic function is still not clear. In this study, we report the high activity of nanostructured Ru/ceria (Ru-clusters/ceria) in the ethylene methoxycarbonylation (EMC) re

Full text of DOI:10.1021/jacs.8b01742

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Article
Acid-Promoter-Free Ethylene Methoxycarbonylation over Ru-
Clusters/Ceria: the Catalysis of Interfacial Lewis Acid-Base Pair
Jinghua An, Yehong Wang, Jianmin Lu, Jian Zhang, Zhixin Zhang, Shutao Xu, Xiaoyan Liu, Tao
Zhang, Martin Gocyla, Marc Heggen, Rafal E. Dunin-Borkowski, Paolo Fornasiero, and Feng Wang
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b01742 • Publication Date (Web): 26 Feb 2018
Downloaded from http://pubs.acs.org on February 27, 2018
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Acid-Promoter-Free Ethylene Methoxycarbonylation over Ru-
Clusters/Ceria: the Catalysis of Interfacial Lewis Acid-Base Pair
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†
, ║, ‡
†,‡
†
†
†
†
Jinghua An,
Yehong Wang, Jianmin Lu, Jian Zhang, Zhixin Zhang, Shutao Xu, Xiaoyan
†
†
§
§
§
¶
Liu, Tao Zhang, Martin Gocyla, Marc Heggen, Rafal E. DuninꢀBorkowski, Paolo Fornasiero,
†
*
and Feng Wang
†
State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
║
University of Chinese Academy of Sciences, Beijing 100049, China
§
Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute,
Forschungszentrum Juelich GmbH, Juelich 52425, Germany
¶
Department of Chemical and Pharmaceutical Sciences, INSTM, Center of Excellence for
Nanostructured Materials (CENMAT), University of Trieste, Via L. Giorgieri 1, Trieste 34127, Italy
‡
These authors contributed equally
*
Correspondence author: F. Wang (*): wangfeng@dicp.ac.cn
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ABSTRACT:
Interface of metalꢀoxide plays pivotal roles in catalytic reactions, but its catalytic function is still not
clear. In this study, we report the high activity of nanostructured Ru/ceria (Ruꢀclusters/ceria) in the
ethylene methoxycarbonylation (EMC) reaction in the absence of acid promoter. The catalyst offers
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2% yield of MP with TOF of 8666 h , which is about 2.5 times of homogeneous Pd catalyst (~
–
1
500 h ). The interfacial Lewis acidꢀbase pair [RuꢀOꢀCeꢀVö], which consists of acidic CeꢀVö
(oxygen vacancy) site and basic interfacial oxygen of RuꢀOꢀCe linkage, acts as active site for the
dissociation of methanol and the subsequent transfer of hydrogen to the activated ethylene, which is
1
the key step in acidꢀpromoterꢀfree EMC reaction. The combination of H MAS NMR, pyridineꢀIR
and DFT calculations reveals the hydrogen species derived from methanol contains Brönsted acidity.
The EMC reaction mechanism under acidꢀpromoterꢀfree condition over Ruꢀclusters/ceria catalyst is
discussed.
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1. INTRODUCTION
Metal oxide catalysts have been widely used in the industry of petrochemical, fine chemical and
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environmental industry. Interface between nanoꢀ or subnanoꢀsized metal particles and their oxide
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supports has profound effects on the stability, activity and selectivity of heterogeneous catalysts.
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Model studies on metalꢀoxide catalysis have provided deep insights into the interfacial structure of
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a,
metalꢀoxide down to the atomic level, and have shed light onto many catalytic processes.
3
Particularly they disclose that the catalytic reactions are related to coordinately unsaturated metal
2
sites at exposed metalꢀoxide perimeters, which can accommodate O or CO adsorption and
4
activation. Very recently, Hu and coꢀworkers have found that the interfacial sites of FeO/Pt(111) are
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responsible for methanol oxidation to formaldehyde by DFT calculations. This study has
demonstrated that the interfacial oxygen significantly reduces the OꢀH cleavage barrier of methanol
I
to below 0.1 eV. In addition, Li and coꢀworkers have found that the interfacial oxygens (metal ꢀ
II
oxygenꢀmetal ) on FeO/Pt(111) and Cu
2
O/Ag(111) are important for achieving high activity in
1a
benzyl alcohol oxidation through STM and DFT calculations. Although tremendous advances have
6
been achieved on the interfacial catalysis on metal sites, little attention has been paid to the role of
interfacial acidꢀbase catalysis of metalꢀoxide systems. Actually, the interfacial acidꢀbase catalysis
should be considered particularly when oxides are used as major components, additives or supports.
Catalysis by ceria is mostly driven by its ability to store and release oxygen because of the facile
4
+
3+ 7
redox cycle of the cerium ions (Ce ↔Ce ). As such, ceria is a key catalyst in threeꢀway catalytic
7c
8
9
converters, waterꢀgas shift reaction, CO oxidation, methane combustion and complex organic
1
b, 4aꢀc, 10
reactions.
The introduction of other metals to ceria usually decreases the formation energy of
10h, 11
oxygen vacancy (Vö) and leads to unique catalytic activity.
This enables the ceriaꢀbased
catalysts to be potentially employed as multifunctional catalysts in complex reaction system.
Alkoxycarbonylation of olefins with carbon monoxide (CO) and alcohols is an atomicꢀeconomic
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2
CꢀC and CꢀO bond formation reaction. Methyl propionate (MP) is a key precursor in the synthesis
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of methyl methacrylate (MMA), a monomer for polyꢀmethyl methacrylate (PMMA) that is a highly
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demanded transparent thermoplastic. Synthesis of MP from three lowꢀcarbon building blocks, i.e.
ethylene, CO and methanol, is an ideal route as the three feedstocks can be obtained from fossil or
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renewable sources. However, the reaction requires multiple active sites and promoters to assembly
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three molecules to one by forming new bonds. So far, Pdꢀphosphine complexes catalysts with acid
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3, 15
promoters are mostly used in the ethylene methoxycarbonylation (EMC) reaction (Scheme 1).
12ꢀ13, 16
However, the catalytic systems require mineral acids as promoters, such as sulfuric acids.
Beller and coꢀworkers have reported seminal works on Pd(OAC) catalyst with sulfonic acids as
2
promoters in the EMC reaction. They found the catalytic activity could be promoted by placing
pyridine group in phosphorꢀcontained ligands, where the nitrogen of pyridine was considered to be a
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weak basic site for methanol proton transfer. Riisager and coꢀworkers have reported acidic ionic
1
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liquids function as both reaction media and acid promoters in the EMC reaction. NMR
investigations have shown that the protonated phosphine is formed through the reaction between free
ligand and in situ generated HCl, evidencing the formation of the Pd hydride species under the
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reaction conditions.
Previous studies have shown that either preꢀadded acid promoters or in situ generated HCl is
indispensable for the EMC reaction. The known reaction mechanism suggests the acid promoter is
required to preserve catalytic activity of Pdꢀcomplexes by generating and stabilizing Pd hydride
species. However, from an industrial point of view, the use of acid promoters will raise the issue of
the reaction vessel corrosion and the product separation. We conceived that if a catalyst could
generate Brönsted acid sites from a convenient hydrogen donor, it is unnecessary to use mineral
acids in the EMC reaction.
Scheme 1. Synthesis of methyl propionate (MP) from three lowꢀcarbon building blocks (ethylene,
CO and methanol) via the EMC reaction.
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We herein report the synthesis of MP via the EMC reaction over Ruꢀclusters/ceria catalyst under
acidꢀpromoterꢀfree condition. Methanol acts as hydrogen donor, reactant and solvent. The catalyst
offers 92% yield of MP, which gives 2.5 times higher of TOF value than the homogeneous Pd
systems. The unexpected good performance of the catalyst is due to its suitable spatial and electronic
structure. HRꢀTEM reveals the highly dispersed Ru clusters on ceria. The combination of in situ
XPS, XANES/EXAFS and other characterizations proves the presence of Lewis acidꢀbase pair [Ruꢀ
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OꢀCeꢀVö], verified by H MAS NMR, DFT and pyridineꢀIR, at the interface of Ru and ceria.
Mathanol is dissociated to methoxyl and hydrogen species at CeꢀVö site. And then the hydrogen
species transferred to the activated ethylene through the interfacial oxygen of RuꢀOꢀCe. The weak
binding of interfacial oxygen makes the hydrogen act as Brönsted acid, which can avoid the addition
of mineral acids that are used in the homogeneous systems.
2. EXPERIMENTAL SECTION
Chemicals and Reagents. All chemicals are of analytical grade and used as purchased without
further purification. Most of the chemicals are purchased from J&K Chemicals and Aladdin
Chemicals, except Noble metals salt (the Non Ferrous Metal Institute of Shenyang) and NH OH
Damao Chemical Reagent Factory China). The detail list of these chemicals and the reagents are
shown in Table S1.
Catalyst Preparation. Ceria nanoparticles were prepared by a precipitation method used in our
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(
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previous studies. Nanostructured ceria with various shapes (rod, cube, and octahedron) were
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prepared by the hydrothermal method according to the literature reports. The Ru/ceria catalyst was
prepared by a wet impregnation method. 5.0 g of ceria was added into a 30 mL solution of RuCl
3
containing 0.1 g of Ru, and stirred slowly for 20 h at room temperature. The slurry was then dried at
–
2
120 °C in an oven and calcined at 200 °C. The dried solid was reduced at 350 °C in H (30 mL·min
1
)
for 4 h. Other Ru/ceria catalysts reduced at various temperatures were prepared for comparison
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and marked as Ru/ceriaꢀT (°C), such as Ru/ceriaꢀ150 °C. The same impregnation procedure was
employed for other oxidesꢀsupported Ru catalysts. The content of Ru in all mentioned catalysts was
2
wt% relative to oxide supports.
Catalytic Reactions and Product Analyses. The catalyst, methanol (4.0 mL) and a magnetic stir
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bar were loaded into a teflonꢀlined autoclave reactor, respectively. The reactor was purged with
ethylene (99.9% purity, Dalian Guangming Special Gas Products Co., Ltd.) for three times. Then,
ethylene and CO (99.9%, Kena Co., Ltd.) were charged into the reactor to a certain pressure. Then,
the reactor was sealed and placed in a preheated mantle at the desired temperature. Further care has
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to be taken as CO is a colorless, odorless, and tasteless but highly toxic gas. After reaction,
products were collected and analyzed by gas chromatographyꢀmass spectrometry (GCꢀMS) using an
Agilent 7890A/5975C instrument equipped with an HPꢀ5 MS column (30 m in length, 0.25 mm in
diameter). The yield of MP was determined by GC and calculated based on ethylene.
Characterizations of Catalysts. The microstructures of catalysts were examined by TEM using a
JEOL JEMꢀ2000EX and a FEI Tecnai G2 F30 SꢀTwin. HAADF-STEM was performed using an FEI
22
Titan 80ꢀ200 (ChemiSTEM). These facilities were located at Ernst Ruska Centre for Microscopy
and Spectroscopy with Electrons and Peter Grünberg Institute (Forschungszentrum Juelich GmbH,
Juelich, Germany). Electron microscope was operated at 200 kV, equipped with a sphericalꢀ
aberration (Cs) probe corrector (CEOS GmbH), and a highꢀangle annular dark field detector. A probe
semiꢀangle of 25 mrad and an inner collection semiꢀangle of the detector of 88 mrad were used.
Compositional maps were obtained with energyꢀdispersive Xꢀray spectroscopy (EDX) using four
largeꢀsolidꢀangle symmetrical Si drift detectors. For EDX analysis, Ru L and Ce L peaks were used.
High resolution transmission electron microscopy (HRTEM) investigations were performed using an
23
FEIꢀTitan 80ꢀ300 electron microscope equipped with a Cs corrector for the objective lens. The
microscope was operated at a voltage of 300 kV using the negativeꢀCs imaging technique (NCSI,
with Cs set at around ~ 13 ꢁm and defocus around +6 nm). In situ IR spectra were collected on a
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Bruker Tensor 27 instrument. The catalyst was pressed into a selfꢀsupporting disk (13 mm in
diameter) and placed into an IR cell. Prior to the adsorption of probe molecule (ethylene, CO,
–1
methanol or pyridine), the sample disk was reduced at 350 °C for 1 h in H
2
flow (30 mL·min ) and
then cooled down to room temperature. Subsequently, the IR cell with catalyst disk was pumped
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down to < 6×10 Pa and a spectrum was recorded as the background. Then, the probe molecule was
introduced to the IR cell for the adsorption. For the adsorption of ethylene, ethylene was introduced
to IR cell and remained at 0.4 MPa for 30 min and then desorbed by vacuum pumping for 30 min.
Each spectrum was collected after cooling down to room temperature. For the adsorption of
methanol, methanol was introduced into the cell by flowing Ar gas through a methanol bubbler. The
catalyst disk was exposed to methanol vapor at room temperature for 30 min. IR spectrum of the
chemisorbed methanol was recorded at room temperature. For the adsorption of CO, the catalyst disk
was exposed to CO at room temperature for 30 min firstly. Then, the IR cell with catalyst disk was
–
1
charged with flowing Ar gas (50 mL·min ) at room temperature for 30 min. IR spectrum of the
chemisorbed CO was recorded at room temperature. For the adsorption of pyridine to detect the
acidity, pyridine vapor was introduced into the system and then desorbed at different temperatures
ranging from room temperature to 350 °C. Each spectrum was collected after cooling down to room
temperature. For the detection of acidity of ceria or Ru/ceria after methanol preꢀadsorption, the
catalyst disk was exposed to methanol vapor firstly. And then methanol was desorbed at room
temperature. After that, pyridine vapor was introduced into the system and desorbed at different
temperatures ranging from room temperature to 350 °C. Each spectrum was collected after cooling
down to room temperature. In situ FTꢀIR was also applied in tracking the EMC reaction of ethylene,
CO and methanol over Ru/ceria. Ethylene, CO and methanol were introduced to the IR cell with a
total pressure of 0.4 MPa for 0.5 h. Then, the catalyst was treated at a desired temperature for 30 min
and then desorbed by vacuum pumping for 30 min. Each spectrum was recorded after cooling down
to room temperature. In situ X-ray photoelectron spectroscopy (XPS) analysis was performed
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using an ESCALAB250Xi (Thermo, USA), equipped with an AlꢀKα (1486.6 eV) as the exciting
source. Firstly, the catalyst was pressed into the wafers, degassed under vacuum and then put into the
2
analysis chamber for detection before reduction. Then high purity H (99.999%) was flowed into the
chamber and heated to the set temperatures ranging from room temperature to 450 °C (room
temperature, 150 °C, 250 °C, 350 °C and 450 °C) for 1 h. Spectra were started to be collected after
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δ+
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cooling to room temperature in high vacuum (1×10 Pa). The Ru / Ru ratio (molar ratio of surface
24
atoms) was calculated according to the following Eq. (1).
0.5
Ek
ni I σ
i
j
j
=
× ×
Eq. (1)
0
.5
nj I σ E
j
i
ki
δ+
0
where, i: Ru species; j: Ru species; n: the numbers of surface Ru atom; I: the intensity of XPS,
peak area; σ: photoionization crossꢀsection; AlKα: Ru 3d5/2 = 7.39; E : photoelectron kinetic energy,
= hνꢀBE (AlKα, hν = 1486.6 eV). XANES and EXAFS spectra at Ru Kꢀedge were collected at
k
25
E
k
the BL14W1 at the Shanghai Synchrotron Radiation Facility (SSRF), Shanghai, China. An energy
selection was undertaken with a double Si(311)ꢀcrystal monochromator. A Ru foil was used for the
energy calibration. Before experiments, all the samples were reduced at 350 °C in H for 4 h and
2
sealed in Kapton film to avoid exposure to air. The spectra were recorded at room temperature under
1
transmission mode. The Athena software package was used to analyze the data. H MAS NMR
spectra were collected on a Bruker Avance III 600 MHz spectrometer at room temperature using a 4ꢀ
1
mm lowꢀgamma probe. In a typical H MAS NMR experiment for methanol adsorption, 200 mg of
–1
dried sample material was placed in a quartz tube and reduced in flowing H (20 mL·min ) at
2
350 °C for 30 min. Then it was cooled down to room temperature after purging with flowing He gas
–1
(
20 mL·min ) for 30 min. Subsequently, the sample was exposed to methanol vapor, which was
–
1
introduced by flowing He gas (20 mL·min ) through a methanol bubbler into the cell. Finally, the
1
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sample was transferred to an NMR rotor for H MAS NMR spectra acquisition. H MAS NMR of
methanol and ethylene coꢀadsorption was also collected. The sample was exposed to methanol vapor
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and ethylene. Methanol vapor was introduced by flowing ethylene gas (20 mL·min ) through a
1
methanol bubbler into the cell. Finally, the sample was transferred to an NMR rotor for H MAS
NMR spectra acquisition. The general characterizations such as XRD, TPD and Raman were also
conducted and the experimental details were shown in supporting information.
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4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
DFT calculations. All DFT calculations were performed using periodic plane wave based density
26
functional theory program VASP (Vienna Ab Initio Simulation Package). The exchange correlation
functional was described within the generalized gradient approximation by the PerdewꢀBurkeꢀ
2
7
Ernzerhof formulation (GGAꢀPBE). The electronꢀion interactions were treated by the projectorꢀ
28
augmented wave method (PAW). The kinetic energy cutoff of the planeꢀwave basis sets was fixed
2
2
2
4
7
1
to 400 eV for all calculations. The 1s valence electron of H, 2s 2p of C, 2s 2p of O, 4d 5s of Ru,
2
6
1
1
2
and 5s 5p 4f 5d 6s of Ce were explicitly considered. All selfꢀconsistent field calculations were
−
5
–1
converged to 1×10 kJ·mol . DFT+U corrections were employed to mitigate the selfꢀinteraction
29
errors for Ce with the value of UꢀJ = 5.0 eV. The DFTꢀD3 methodology by Grimme and coꢀworkers
was used to include the corrections for dispersion interactions. All atomic coordinates of the Ru
clusters, put in the cubic box with a side length of 20 Ångstroms, were fully relaxed to a force of <
–1
0
.02 eV·Å on each atom. A Brillouin zone integration was performed using the Γ point only and a
Gaussian smearing width of 0.05 eV. The lattice constant of bulk CeO
in reasonable agreement with the experimental value (a = 5.411 Å). This lattice constant was then
used to construct a periodic CeO (110) p(2×3) slab with 9 atomic layers (which are equal to 3
2
was optimized to be 5.479 Å
2
stoichiometric layers) separated by a vacuum layer of 15 Å to eliminate interactions between the slab
and its periodic images. In total, there were 27 Ce atoms and 54 O atoms in the slab. The bottom 4
atomic layers were fixed to their optimized bulk configuration during all computations, and the top 5
atomic layers and surface intermediates were fully relaxed. All atomic coordinates of the adsorbates
–1
and the atoms in the relaxed layers were optimized to a force of < 0.02 eV·Å on each atom.
Brillouin zone integration was performed using a 3×4×1 MonkhorstꢀPack grid and a Gaussian
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4
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4
4
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5
6
smearing width of 0.05 eV. The transition state of each elementary reaction step was located by a
30
31
combination of the nudged elastic band (NEB) method and the dimer method. In the NEB
method, the path between the reactant(s) and product(s) was discretized into a series of 5 structural
images. After the NEB calculation, the image which was closest to a likely transition state structure
was later employed as an initial guess structure for the dimer method.
0
1
2
3
4
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6
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8
9
0
1
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0
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1
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8
9
0
3. RESULTS AND DISCUSSION
Catalyst Screening Tests in the EMC Reaction and Optimization of the Reaction Conditions
We previously found that Ru/ceria (nanoparticle) showed excellent catalytic performance in the
32
33
carbonylation of amines to formamides. Ru catalysts are also reported in CO activation reactions.
Thus, we firstly used Ru/ceria in the EMC reaction to synthesize MP in methanol in a batch reactor.
Meanwhile, the effect of reducing temperature on the Ru/ceria performance was investigated (Table
1, entries 1–5). The results suggest that Ru/ceria reduced at 350 °C exhibited the best catalyst
activity with 53% MP yield (Table 1, entry 4) with less than 3% of pentanꢀ3ꢀone (PTO) and 1, 1ꢀ
dimethoxypropane (DMP) (Fig. S1) in the EMC reaction. Most of other common oxides including
TiO
5%) (Table 1, entries 6–12). Efforts to optimize the catalysis of these oxides could not further
increase the yield of MP. The EMC reaction did not proceed over ceria support or in the absence of
catalyst or CO (Table 1, entries 13–15). RuCl , the Ru precursor of Ru/ceria, yielded 16% MP even
2 3 3 2 2
, WO , NiO, MoO , ZrO , SiO and MgO used as support were sluggish (MP yield lower than
1
3
if extending the reaction time to 12 h (Table 1, entry 16). Ru supported on ceria with rod, cube and
octahedron shapes were prepared and applied in the EMC reaction. All of them showed comparable
activity (45ꢀ55% yield) to that of Ru/ceria (nanoparticle) (Table 1, entries 17–19). XRD did not
identify Ru, inferring Ru is highly dispersed on ceria (Fig. S2). We hereinafter employ Ru/ceria
(nanoparticle) to study the reaction details of the EMC reaction.
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[a]
Table 1. The EMC reaction over various catalysts.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
[b]
Selectivity (%)
Entry
Catalyst
Yield of MP (%)
MP
95
93
95
97
94
>99
>99
0
DMP
4
PTO
1
1
2
3
4
5
6
7
8
9
Ru/ceriaꢀRT
39
39
37
53
35
20
12
0
Ru/ceriaꢀ150 °C
Ru/ceriaꢀ250 °C
Ru/ceriaꢀ350 °C
Ru/ceriaꢀ450 °C
4
3
4
1
1
2
4
1
Ru/TiO
2
0
0
Ru/WO
3
0
0
Ru/NiO
0
0
Ru/MoO
3
0
0
0
0
1
0
Ru/ZrO
2
>99
>99
>99
0
0
0
6
11
Ru/SiO2
Ru/MgO
ceria
0
0
7
1
1
1
1
2
3
4
5
0
0
8
0
0
0
no catalyst
Ru/ceria
0
0
0
0
[
c]
d]
0
0
0
0
[
16
RuCl
3
74
94
92
95
5
21
2
16
55
51
45
1
1
1
7
8
9
Ru/ceriaꢀrod
Ru/ceriaꢀcube
4
2
6
Ru/ceriaꢀoctahedron
2
1
[
a] Reaction conditions: catalyst (0.15 g), ethylene (7.5 mmol), CO (0.9 MPa), methanol (4 mL),
1
65 °C, 6 h. MP yield is calculated based on ethylene. [b] Selectivity is determined by integrating
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1
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2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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5
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5
5
5
5
5
5
5
6
GC peak area since the major product is MP. [c] In the absence of CO. [d] RuCl
ethylene (7.5 mmol), CO (0.9 MPa), methanol (4 mL), 165 °C, 12 h.
3
(0.03 mmol),
Further optimization of the reaction conditions is conducted (Fig. S3). A increase of CO partial
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
–1
pressure slightly affects the MP yield (~60%) (Fig. S3A). The TOF reaches 8666 h at 1.0 MPa of
CO in 8 h even if assuming all isolated Ru to be active sites. Even so, the TOF is about 2.5 times of
–
1 34
Pd catalyst reported previously (~ 3500 h ). Increase of reaction temperature leads to higher MP
yield and the yield reaches 92% for 12 h at 165 °C( Fig. S3 BꢀC), the best result obtained in this
study. Removal of the Ru/ceria catalyst in 1 h over the course of the reaction nearly stopped the
conversion, and the MP yield leveled off at ~25%, indicating the reaction was heterogeneously
catalyzed (Fig. S4).
General Characterizations of Ru/ceria
Fig. 1 presents the results of a microstructural study of the Ru/ceria catalyst using electron
microscopy. Because Ru and Ce have a similar atomic mass, HAADFꢀSTEM images cannot provide
enough contrast to visualize highly dispersed Ru on ceria. We here used STEMꢀEDX mapping to
determine the distribution of Ce and Ru on this Ru/ceria sample. EDX mappings using the Ru L line
reveal the presence of highlyꢀdispersed Ru clusters on ceria (see white arrows in Fig. 1). Guided by
EDX results, we are able to discern dropletꢀlike oblate Ru clusters with an average size of about 1
nm on the ceria surface. Furthermore, it is observed that Ru clusters are preferentially located at
defected sites like surface steps (see black arrows in Fig. 1A and Fig. 1C) or edges of the ceria
substrate (Fig. 1 BꢀD). It is also observed that during TEM and STEM investigations under electron
beam irradiation, the Ru clusters tend to be stuck at the surface defect sites (see Movie 1).
Hereinafter, Ru/ceria is marked as Ruꢀclusters/ceria to highlight the unique property of ceria for the
formation and stabilization of Ru clusters.
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0
1
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9
0
1
2
3
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5
6
7
8
9
0
1
2
3
4
5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Fig. 1. (A) HAADFꢀSTEM images, (B) EDX elemental mapping. and (C) combined HAADFꢀSTEM
image and EDX elemental mapping of Ru clusters (white arrows) on ceria. The inset in (A) show
enlarged images of the Ru clusters. (D) HRTEM image under NCSI conditions of a Ru cluster on
ceria substrate showing the lattice spacing of Ru (002).
The Raman spectra indicate the presence of rich Vö and the RuꢀOꢀCe structure on Ruꢀ
10f, 35
clusters/ceria in comparison of pristine ceria support (Fig. S5).
The formation of RuꢀOꢀCe
linkage at the interface probably maintains the positively charged Ru species. More information of
the Ru charge state is unraveled in Ru 3d spectra by in situ XPS (Fig. 2). The signal of Ru 3d5/2 is
often used for analyzing the charge state of the Ru species because another Ru 3d3/2 overlaps with
3
6
4+
C1s at around 284.0 eV. Prior to reduction, the Ru 3d5/2 at 281.51 eV is associated with Ru in
37
0
RuO
2
.
The Ru starts to appear at 150 °C and gradually increase with increase of the reduction
38
δ+
temperature, as indicated by the Ru 3d5/2 peak at 279.93 eV. After reduction and formation of Ru ,
δ+
0
δ+
the peak shifts to 280.85 eV, and is still present up to 450 °C. The Ru / (Ru + Ru ) ratios of Ruꢀ
clusters/ceria reduced at RT, 150 °C, 250 °C, 350 °C and 450 °C are calculated to be 1.00, 1.00, 0.47,
2 2
0.40 and 0.30 (Fig. S6). In addition, the result of H ꢀTPR suggests that the H consumption of
ꢀ
1
RuO
2
/ceria is ~11.7 mmol—g(RuO2) , which is lower than that of the stoichiometricallyꢀdemanded H
2
ꢀ
1
δ+
consumption (~15.1 mmol·g(RuO2) ), confirming the presence of Ru under the harsh reducing
condition (Fig. S7).
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2
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2
2
2
2
2
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3
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o
450 C
Ru 3d5/2
80.85
2
80.25
80.12
2
2
o
350 C
Ru 3d5/2
80.82
2
0
1
2
3
4
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0
1
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1
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9
0
1
2
3
4
5
6
7
8
9
0
o
250 C
Ru 3d5/2
80.70
279.93
2
o
150 C
Ru 3d5/2
2
81.13
RT
Ru 3d5/2
281.51
292
288
284
280
Binding energy (eV)
Fig. 2. In situ XPS of Ruꢀclusters/ceria stepwise reduction at different temperatures ranging from
room temperature to 450 °C.
XANES and EXAFS are applied to study the interface of Ruꢀclusters/ceria (Fig. 3). The intensity
of the white line reflects the Ru charge. The white line of Ruꢀclusters/ceria exhibits higher intensity
than that of the Ru foil, indicating Ru in Ruꢀclusters/ceria is partly positively charged (Fig. 3A),
which is in agreement with the in situ XPS results. The spectra at the Kꢀedge of Ru in kꢀspace show
that Ruꢀclusters/ceria is different to that of Ru foil (Fig. 3B). Compared with the Ru foil, the peak
intensity in the associated Fourier transforms of Ruꢀclusters/ceria is much weaker, demonstrating that
Ru in Ruꢀclusters/ceria is highly dispersed (Fig. 3C), which is in agreement with the results of
HAADFꢀSTEM and EDX elemental mapping. The dataꢀfitting results reveal that the coordination
number (CN) of Ru from RuꢀRu bond in Ruꢀclusters/ceria is 2.4, which is much smaller than the
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coordination number of Ru foil (CN = 12), indicating that Ru is present as ultraꢀsmall clusters in Ruꢀ
clusters/ceria (Fig. 3D), which well correlates with the HRTEM and STEM/EDX results. Moreover,
the fitting data also show RuꢀRulong and RuꢀCelong bond at the distance of 2.96 Å and 3.02 Å,
respectively, which are both shorter than the bond length of RuꢀRu in RuO (3.11 Å) but longer than
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
that of the Ru foil (2.68 Å), which suggests that presence of partially oxidized Ru (RuꢀRulong) and
39
interfacial linkage RuꢀOꢀCe (RuꢀCelong).
A
B
C
Ruꢀclusters/ceria
Ruꢀclusters/ceria
Ru foil
Ruꢀclusters/ceria
Ru foil
Ru foil
22050
22100
Energy (eV)
22150
22200
0
2
4
6
k
8
)
10
12
0
1
2
3
4
5
6
ꢀ1
(Å
R (Å)
D
2
2
2
Sample
Shell
CN
R (Å)
σ ×10 (Å ) ∆E (eV)
rꢀfactor (%)
0
Ru foil
RuꢀRu
12.0
2.68
0.35
ꢀ5.9
2.22
RuꢀO
2.7
2.4
1.5
1.5
2.01
2.70
2.96
3.02
0.61
0.61
0.61
0.61
ꢀ3.9
ꢀ3.9
ꢀ3.9
ꢀ3.9
RuꢀRu
Ruꢀclusters/ceria
0.68
RuꢀRulong
RuꢀCelong
Fig. 3. (A) The normalized XANES spectra at the Ru Kꢀedge. (B) The kꢀspace EXAFS spectra and
2
(
C) the corresponding Fourier transform of k ꢀweighted EXAFS spectra for a Ru foil and Ruꢀ
clusters/ceria. (D) EXAFS data fitting results of a Ru foil and Ruꢀclusters/ceria reduced at 350 °C.
CN, the coordination number for the absorberꢀback scattering pair. R, the average absorberꢀback
2
scattering distance. σ , the DebyeꢀWaller factor. ꢂE
0
, the inner potential correction. The accuracies of
2
the above parameters are estimated as CN,
±
20%; R,
±
1%; σ ,
±
20%; ꢂE
0
,
±20%.
Activation of Ethylene, CO and Methanol from the In situ IR
A series of in situ IR adsorption tests are employed to investigate the activation of ethylene, CO
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2
2
2
2
2
2
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3
3
3
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and methanol on Ruꢀclusters/ceria.
In situ IR spectra of ethylene adsorption on Ruꢀclusters/ceria presented a peak at 948 cm
–
1
−1
assigned to the ω(CꢀH) of chemically adsorbed ethylene (Fig. 4A). The two peaks at 3081 cm and
–1
40
2
989 cm are assigned to vas(CꢀH) and vs(CꢀH) of the πꢀbounded ethylene (Fig. 4B). These peaks
0
1
2
3
4
5
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9
0
1
2
3
4
5
6
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8
9
0
1
2
3
4
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9
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1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
are still maintained even after desorption at 100 °C. The πꢀbounded adsorption mode of ethylene on
Ruꢀclusters/ceria is also verified by ethyleneꢀTPD test with an ethylene desorption peak ranging
41
from 50 °C to 168 °C (Fig. S8). For comparison, no obvious peak assigned to the chemically
adsorbed ethylene is observed on pristine ceria (Fig. S9), suggesting that the πꢀbounded ethylene on
42
Ruꢀcluasters/ceria is on Ru sites. . For the adsorption of ethylene on Ru/silica, the πꢀbounded
ethylene and the diꢀσꢀbounded ethylene were found (Fig. S10), suggesting the activity of Ru clusters
for ethylene adsorption.
In situ IR spectra of CO adsorption on Ruꢀclusters/ceria showed three remarkable peaks at 2141
–
1
–1
–1
cm , 2080 cm and 2008 cm (Fig. 4C). The former two peaks are assigned to the multicarbonyl
δ+
species on the partially oxidized Ru sites [Ru (CO) ], although there is no consensus regarding the
x
4
3
–1
oxidation state of Ru (δ) and the number of carbonyl groups (
x
). The later at 2008 cm is usually
43a,
assigned to the linearly adsorbed CO on the lowꢀcoordinated Ru atoms on very small Ru particles.
43b
For comparison, no obvious peaks assigned to the CO adsorption is observed on pristine ceria
(Fig. S11).
–1
In situ IR spectra of methanol adsorption on pristine ceria indicated two peaks at 1101 cm and
–1
1027 cm (Fig. 4D), which are assigned to
v
(CꢀO) of onꢀtop and tridentate methoxy species,
1
0f, 44
respectively.
site for methanol dissociation.
which is assigned to (CꢀO) of tridentate methoxy species. Compared with that on pristine ceria, this
peak is redꢀshifted significantly, indicating the higher content of Vö on Ruꢀclusters/ceria than pristine
The presence of tridentate methoxy species suggests that Vö is actually the active
10f, 44
–1
In contrast, only 1010 cm peak is observed on Ruꢀclusters/ceria,
v
1
0f
ceria after the induction of Ru to ceria.
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9
0
1
2
3
4
5
6
7
8
9
0
–1
Fig. 4. In situ IR of ethylene adsorption on Ruꢀclusters/ceria in the regions of (A) 1000 cm –900
–
1
–1
–1
cm and (B) 3300 cm –2760 cm . The spectra are collected after ethylene desorption at room
–3
temperature or at 100 °C in vacuum (less than 6 × 10 Pa). (C) IR spectra recorded after admission
of CO and desorption at different temperatures (room temperature, 100 °C and 150 °C) on Ruꢀ
clusters/ceria. (D) In situ IR of methanol adsorption on ceria and Ruꢀclusters/ceria in the region of
−1
−1
–3
1200 cm –950 cm (less than 6 × 10 Pa).
Interfacial Lewis Acid-base Pair as Active Site for Methanol Dissociation and the Transfer of
1
Hydrogen Species Verified by H MAS NMR, in situ IR and DFT Calculations
The generated methoxyl from the dissociation of methanol has been clearly detected by in situ IR.
1
We turned to solid H MAS NMR to defect the surface hydrogen species (Fig. 5). This technique has
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been previously used for this purpose. After methanol vapor pulse to Ruꢀclusters/ceria, two signals
at 3.9 ppm and at 9.1 ppm are observed. The former is assigned to the methoxyl group, and the later
4
6
to the hydroxyl formed via the transfer of hydrogen species to oxygen. Followed by ethylene pulse,
the later signal remarkably decreases, but the signal at –0.04 ppm assigned to the ethyl group strarts
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to appear, indicating that the activated ethylene is hydrogenated to ethyl group probably with
hydroxyl group as hydrogen donor. In addition, a new signal at 4.9 ppm assigned to ethylene is also
obverved after the introduction of ethylene.
4
.9
ꢀ0.04
b
a
9
.1
3.9
20
15
10
5
0
ꢀ5
ꢀ10
Chemical shift (ppm)
1
Fig. 5. H MAS NMR of (a) methanol and (b) ethylene after preꢀadsorbed methanol on Ruꢀ
clusters/ceria.
In situ pyridineꢀIR is conducted to detect the acidity with methanol preꢀadsorption on Ruꢀ
clusters/ceria (Fig. 6A). Several peaks are assigned to the adsorption of pyridine on Brönsted acid
−1
−1
sites (1537 cm ), Lewis acid sties (1441, 1570 and 1602 cm ) and the overlapping of pyridine
–
1 47
adsorption on Lewis and Brönsted acid sites (1486 cm ). The intensities of these peaks decrease
with increase of the desorption temperature. Most of pyridine desorbs from Brönsted acid sites at
350 °C, suggesting the moderate Brönsted acidity. In comparison, no obvious pyridine adsorption
were observed on Ruꢀclusters/ceria without methanol preꢀadsorption (Fig. 6B), or on pristine ceria
with methanol adsorbed (Fig. S12). This infers that the active hydroxyl may be generated from the
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dissociation of methanol and located at the interface. Considering the function of Vö in the methanol
dissociation, it becomes reasonable that the methanol dissociation at the interfacial Lewis acidꢀbase
pair (RuꢀOꢀCeꢀVö) and the transfer of dissociated hydrogen are two primary steps in the acidꢀ
promoterꢀfree EMC reaction. Raman spectra of the recovered catalyst after three times reaction
indicate the shift of bands assigned to RuꢀOꢀCe and the weakening of Vö, suggesting the loss of
interfacial acidꢀbase pair sites. Again it verifies the key role of such pair sites in the EMC reaction.
(Fig. S13).
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A
B
350
350
2
50
00
250
200
2
1
50
00
150
100
1
RT
RT
1599 (L)
1440 (L)
B: Br nsted acid; L: Lewis acid
1
441 (L)
ö
ö
B: Br nsted acid; L: Lewis acid
1
650
1600
1550
Wavenumber
1500 ꢀ
1450
1400
1650
1600
1550
1500
1450
1400
1
)
ꢀ1
(
cm
Wavenumber (cm )
Fig. 6. (A) In situ pyridineꢀIR of Ruꢀclusters/ceria with methanol preꢀadsorption. (B) In situ
pyridineꢀIR of the Ruꢀclusters/ceria without methanol preꢀadsorption. The spectra are collected after
ethylene desorption at different temperatures (room temperature, 100 °C, 150 °C, 200 °C, 250 °C and
–3
3
50 °C) in vacuum (less than 6 × 10 Pa).
The experimental results were then combined with theoretical calculations to explain the
interfacial catalysis of Ruꢀclusters/ceria. An interfacial structure of Ru and ceria is created (Fig. 7).
Firstly, the Barder charges of the Ru atoms at interface are calculated (Fig. S14). It reveals the
presence of the positively charged Ru, which consistent with the results of XPS and XANES. The
adsorption energy of hydrogen on four kinds of oxygen are calculated (Fig. 7A). It is found that the
adsorption energy for hydrogen on [RuꢀOꢀCeꢀVö] (Site d) is only –0.20 eV, which is the lowest
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value amoung the four types of oxygen sites which either locate at the interface without Vö in
2
adjacent (Site b and Site c) or locate at CeO surface (Site a) (Site a: –0.95 eV, Site b: –0.82 eV,
Site c: –0.51 eV ) (Fig. 7B). The low adsorption energy makes the transfer of hydrogen located at
[RuꢀOꢀCeꢀVö] feasible to the Ru clusters.
0
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0
B ꢀ0.15
ꢀ0.20
Site d
ꢀ0.30
ꢀ0.45
ꢀ0.60
ꢀ0.51
Site c
ꢀ0.75
ꢀ0.90
ꢀ
0.82
Site b
ꢀ0.95
Site a
Fig. 7. (A) The adsorption types of hydrogen on different oxygen sites (Site a, Site b, Site c, Site d)
of Ru/CeO (110). (B) The adsorption energy of hydrogen on different oxygen sites in Fig. 5(A).
2
The Reaction Details of Acid-Promoter-Free EMC Reaction
Identifying the possible reaction intermediates by IR was conducted (Fig. 8A). The Ruꢀ
clusters/ceria catalyst was first saturated with ethylene, CO and methanol gas and then desorbed
–1
under vacuum at room temperature. After desorption, the peak at 922 cm is assigned to the ω(CꢀH)
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–
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of πꢀbounded ethylene (CH =CH *), while the peak at 1006 cm to the ν(CꢀO) of tridentate methoxy
2
2
species (CH
3
O*) (Fig. 8B). The target product MP appears when increasing the sample temperature
–1
–1
to higher than 80 °C. The MP product features with the peaks at 1409 cm and 1552 cm , ascribed
48
–1
to the ν
s
(OꢀCꢀO) and νas(OꢀCꢀO) of MP, respectively. The weak peak at 1154 cm is assigned to
1
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0
the νas(CꢀOꢀC) of 1,1ꢀdimethoxypropane (DMP), a byproduct. Notably, a remarkable peak at 1675
–
1
49
cm is observed, which can be attributed to the v(C=O) of the propionyl species (CH CH CO*).
3
2
The propionyl species (CH
hydrogenation and hydroformylation reactions. Here, assisted by in situ IR, the propionyl
CH CH CO*) species is again confirmed to be a key intermediate in the EMC reaction.
3 2
CH CO*) has been proved to be the intermediate in ethylene
5
0
(
3
2
Fig. 8. (A) In situ IR spectra for tracking the EMC reaction over Ruꢀclusters/ceria in the region of
–1
–1
1710 cm –800 cm . (B) The adsorption mode of methanol, ethylene and CO on Ruꢀclusters/ceria.
(C) The intermediate and products observed in IR. MP, methyl propionate. DMP, 1,1–
dimethoxypropane. ν , asymmetry stretching vibration. ν , symmetry stretching vibration. ω,
as
s
wagging vibration.
Baed on the aboveꢀmentioned results and the known chemistry of EMC reaction, we may
generalize how the reaction take places on Ruꢀclusters/ceria catalyst under acidꢀpromoterꢀfree
conditions. Ethylene and CO are initially activated on Ru clusters. Methanol is activated on the Ceꢀ
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Vö sites of RuꢀOꢀCeꢀVö, generating tridentate methoxy species and active hydroxyl group [Ruꢀ
O(H)ꢀCeꢀVö]. The active hydroxyls release protons to Ru clusters to attack the πꢀbounded ethylene
3 2 3 2
on Ruꢀclusters, generating adsorbed ethyl (CH CH *). The CH CH CO* intermediate is formed
through the insertion of activated CO to ethyl species. Finally, methoxyl (CH O*) reacts with
3
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CH CH CO* species via a nucleophilic attack to give MP product and the active site is restored.
3
2
4. CONCLUSION
Depite of the complexity of the threeꢀmoleculeꢀreaction, we have endeavored to classify the key
role of the interface acidꢀbase catalysis of Ruꢀclusters/ceria composite. We have employed structural,
electronic and surface techniques (XRD, TEM, HAADFꢀSTEM, EDX, Raman, XANES/EXAFS,
1
TPR, TPD, and in situ experiments including XPS, IR and H MAS NMR) to understand how the
interfacial structure of the Ruꢀclusters/ceria affects the catalytic performance and to establish their
relationship. Particularly we realize the first and successful example of the synthesis of methyl
propionate from ethylene, CO and methanol via the EMC reaction with 92% MP yield without
adding mineral acids. The catalyst also exhibits 2.5 times higher TOF value than the homogeneous
Pd catalyst. We find the interfacial oxygen of RuꢀOꢀCe linkage at the interface of Ruꢀclusters/ceria
together with adjacent CeꢀVö form a geometrically compatible Lewis acidꢀbase pair sites [RuꢀOꢀCeꢀ
Vö]. The interfacial site [RuꢀOꢀCeꢀVö] adsorbs and dissociate methanol, forming interfacial
hydroxyl [RuꢀO(H)ꢀCeꢀVö] as acidic sites to react with ethylene. This explains why the present
system does not require mineral acid additives. This work is not only fundamentally interestingbut
also practically meaningful.
SUPPORTING INFORMATION
The supporting information containing general characterizations, GC, XRD, Raman, TPR, probe
moleculeꢀTPD, in situ IR spectra and reaction optimization experiments is available free of charge
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via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
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F.W. Email: wangfeng@dicp.ac.cn
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of China (21422308), Strategic
Priority Research Program of the Chinese Academy of Sciences (XDB17020300), and Department of
Science and Technology of Liaoning province (2015020086ꢀ101). Martin Gocyla and Marc Heggen
thank the DFG for financial support within the grant HE 7192/1ꢀ1.
REFERENCES
1
.
(a) Zhao, G.; Yang, F.; Chen, Z.; Liu, Q.; Ji, Y.; Zhang, Y.; Niu, Z.; Mao, J.; Bao, X.; Hu, P.; Li, Y. Nat.
Commun. 2017, 8, 14039. (b) Kropp, T.; Paier, J.; Sauer, J. J. Am. Chem. Soc. 2014, 136, 14616ꢀ14625.
(a) Li, W.; Huang, H.; Li, H.; Zhang, W.; Liu, H. Langmuir 2008, 24, 8358ꢀ8366. (b) Zorn, K.; Giorgio,
S.; Halwax, E.; Henry, C. R.; Grönbeck, H.; Rupprechter, G. J. Phys. Chem. C 2011, 115, 1103ꢀ1111.
(a) Zhao, Y.; Cui, C.; Han, J.; Wang, H.; Zhu, X.; Ge, Q. J. Am. Chem. Soc. 2016, 138, 10191ꢀ10198. (b)
2.
3.
Strayer, M. E.; Senftle, T. P.; Winterstein, J. P.; VargasꢀBarbosa, N. M.; Sharma, R.; Rioux, R. M.; Janik, M. J.;
Mallouk, T. E. J. Am. Chem. Soc. 2015, 137, 16216ꢀ16224. (c) Pham, T. N.; Sooknoi, T.; Crossley, S. P.;
Resasco, D. E. ACS Catal. 2013, 3, 2456ꢀ2473. (d) Pappacena, A.; Rancan, M.; Armelao, L.; Llorca, J.; Ge,
W.; Ye, B.; Lucotti, A.; Trovarelli, A.; Boaro, M. J. Phys. Chem. C 2017, 121, 17746ꢀ17755. (e) Sun, Q.;
Wang, S.; Liu, H. ACS Catal. 2017, 7, 4265ꢀ4275. (f) Qu, J.; Zhou, X.; Xu, F.; Gong, X.ꢀQ.; Tsang, S. C. E. J.
Phys. Chem. C 2014, 118, 24452ꢀ24466.
4
6
2
.
(a) Liu, W.; Wang, W.; Tang, K.; Guo, J.; Ren, Y.; Wang, S.; Feng, L.; Yang, Y. Catal. Sci. Technol. 2016,
, 2427ꢀ2434. (b) Singha, R. K.; Shukla, A.; Yadav, A.; Sivakumar Konathala, L. N.; Bal, R. Appl. Catal., B
017, 202, 473ꢀ488. (c) Liu, Z.; Grinter, D. C.; Lustemberg, P. G.; NguyenꢀPhan, T. D.; Zhou, Y.; Luo, S.;
Waluyo, I.; Crumlin, E. J.; Stacchiola, D. J.; Zhou, J.; Carrasco, J.; Busnengo, H. F.; GandugliaꢀPirovano, M.
V.; Senanayake, S. D.; Rodriguez, J. A. Angew. Chem. Int. Ed. 2016, 55, 7455ꢀ7459. (d) Zhu, J.; Giordano, L.;
Lin, S.; Fang, Z.; Li, Y.; Huang, X.; Zhang, Y.; Pacchioni, G. J. Phys. Chem. C 2012, 116, 17668ꢀ17675. (e)
Widmann, D.; Behm, R. J. Chin. J. Catal. 2016, 37, 1684ꢀ1693.
5. Chen, Z.; Mao, Y.; Chen, J.; Wang, H.; Li, Y.; Hu, P. ACS Catal. 2017, 7, 4281ꢀ4290.
23
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Page 24 of 28
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
.
(a) Carrasco, J.; LopezꢀDuran, D.; Liu, Z.; Duchon, T.; Evans, J.; Senanayake, S. D.; Crumlin, E. J.;
Matolin, V.; Rodriguez, J. A.; GandugliaꢀPirovano, M. V. Angew. Chem. Int. Ed. 2015, 54, 3917ꢀ3921. (b) Li,
S.; Xu, Y.; Chen, Y.; Li, W.; Lin, L.; Li, M.; Deng, Y.; Wang, X.; Ge, B.; Yang, C.; Yao, S.; Xie, J.; Li, Y.; Liu,
X.; Ma, D. Angew. Chem. Int. Ed. 2017, 56, 10761ꢀ10765. (c) Gaudet, J. R.; de la Riva, A.; Peterson, E. J.;
Bolin, T.; Datye, A. K. ACS Catal. 2013, 3, 846ꢀ855. (d) Pham, H. N.; Sattler, J. J.; Weckhuysen, B. M.;
Datye, A. K. ACS Catal. 2016, 6, 2257ꢀ2264.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
7.
(a) Montini, T.; Melchionna, M.; Monai, M.; Fornasiero, P. Chem. Rev. 2016, 116, 5987ꢀ6041. (b) Vile,
G.; Colussi, S.; Krumeich, F.; Trovarelli, A.; PerezꢀRamirez, J. Angew. Chem. Int. Ed. 2014, 53, 12069ꢀ12072.
c) Rodriguez, J. A.; Grinter, D. C.; Liu, Z.; Palomino, R. M.; Senanayake, S. D. Chem. Soc. Rev. 2017, 46,
(
1
6
2
8
824ꢀ1841. (d) Yashima, M. Catal. Today 2015, 253, 3ꢀ19. (e) Vivier, L.; Duprez, D. ChemSusChem 2010, 3,
54ꢀ678. (f) Mullins, D. R. Surf. Sci. Rep. 2015, 70, 42ꢀ85. (g) Paier, J.; Penschke, C.; Sauer, J. Chem. Rev.
013, 113, 3949ꢀ3985.
.
(a) Wu, K.; Sun, L. D.; Yan, C. H. Adv. Energy. Mater. 2016, 6, 1600501. (b) Senanayake, S. D.;
Stacchiola, D.; Rodriguez, J. A. Acc. Chem. Res. 2013, 46, 1702ꢀ1711. (c) Cargnello, M.; Grzelczak, M.;
RodriguezꢀGonzalez, B.; Syrgiannis, Z.; Bakhmutsky, K.; La Parola, V.; LizꢀMarzan, L. M.; Gorte, R. J.;
Prato, M.; Fornasiero, P. J. Am. Chem. Soc. 2012, 134, 11760ꢀ11766.
9
.
(a) Cargnello, M.; Montini, T.; Polizzi, S.; Wieder, N. L.; Gorte, R. J.; Graziani, M.; Fornasiero, P. Dalton
Trans. 2010, 39, 2122ꢀ2127. (b) Trovarelli, A.; Llorca, J. ACS Catal. 2017, 7, 4716ꢀ4735.
0. (a) Cargnello, M.; DoanꢀNguyen, V. V. T.; Gordon, T. R.; Diaz, R. E.; Stach, E. A.; Gorte, R. J.;
1
Fornasiero, P.; Murray, C. B. Science 2013, 341, 771ꢀ773. (b) 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, 546ꢀ550. (c) Jones, J.; Xiong, H.; DeLaRiva, A. T.; Peterson, E. J.; Pham, H.; Challa, S. R.; Qi, G.;
Oh, S.; Wiebenga, M. H.; Pereira Hernández, X. I.; Wang, Y.; Datye, A. K. Science 2016, 353, 150ꢀ154. (d)
Tamura, M.; Kitanaka, T.; Nakagawa, Y.; Tomishige, K. ACS Catal. 2016, 6, 376ꢀ380. (e) Mitsudome, T.;
Yamamoto, M.; Maeno, Z.; Mizugaki, T.; Jitsukawa, K.; Kaneda, K. J. Am. Chem. Soc. 2015, 137, 13452ꢀ
13455. (f) Tamura, M.; Satsuma, A.; Shimizu, K.ꢀi. Catal. Sci. Technol. 2013, 3, 1386ꢀ1393. (g) Yamada, Y.;
Tsung, C. K.; Huang, W.; Huo, Z.; Habas, S. E.; Soejima, T.; Aliaga, C. E.; Somorjai, G. A.; Yang, P. Nat.
Chem. 2011, 3, 372ꢀ376. (h) Barrabés, N.; Föttinger, K.; Llorca, J.; Dafinov, A.; Medina, F.; Sá, J.; Hardacre,
C.; Rupprechter, G. J. Phys. Chem. C 2010, 114, 17675ꢀ17682. (i) Aneggi, E.; Wiater, D.; De Leitenburg, C.;
Llorca, J.; Trovarelli, A. ACS Catal. 2014, 4, 172ꢀ181.
11. (a) Mao, M.; Lu, H.; Li, Y.; Yang, Y.; Zeng, M.; Li, N.; Zhao, X. ACS Catal. 2016, 6, 418ꢀ427. (b) Acerbi,
N.; Tsang, S. C.; Jones, G.; Golunski, S.; Collier, P. Angew. Chem. Int. Ed. 2013, 52, 7737ꢀ41. (c) Deng, W.;
Zhang, H.; Wu, X.; Li, R.; Zhang, Q.; Wang, Y. Green Chem. 2015, 17, 5009ꢀ5018.
12. Kalck, P.; Urrutigoïty, M. Inorg. Chim. Acta 2015, 431, 110ꢀ121.
13. GarcíaꢀSuárez, E. J.; Khokarale, S. G.; van Buu, O. N.; Fehrmann, R.; Riisager, A. Green Chem. 2014,
16, 161ꢀ166.
14. Xiang, Y.; Zhou, J.; Lin, B.; Xue, X.; Tian, X.; Luo, Z. Appl. Energy 2015, 157, 499ꢀ507.
24
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Page 25 of 28
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
1
5. (a) Amadio, E.; Cavinato, G.; Härter, P.; Toniolo, L. J. Organomet. Chem. 2013, 745, 115ꢀ119. (b) Fanjul,
T.; Eastham, G.; Haddow, M. F.; Hamilton, A.; Pringle, P. G.; Orpen, A. G.; Turner, T. P. W.; Waugh, M.
Catal. Sci. Technol. 2012, 2, 937ꢀ950. (c) Ferreira, A. C.; Crous, R.; Bennie, L.; Meij, A. M.; Blann, K.;
Bezuidenhoudt, B. C.; Young, D. A.; Green, M. J.; Roodt, A. Angew. Chem. Int. Ed. 2007, 46, 2273ꢀ2275. (d)
De la Fuente, V.; Waugh, M.; Eastham, G. R.; Iggo, J. A.; Castillon, S.; Claver, C. Chem. Eur. J. 2010, 16,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
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3
3
3
3
3
3
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4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
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9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
919ꢀ6932. (e) Dong, K.; Fang, X.; Gulak, S.; Franke, R.; Spannenberg, A.; Neumann, H.; Jackstell, R.;
Beller, M. Nat. Commun. 2017, 8, 14117.
6. (a) Gusev, O. V.; Kalsin, A. M.; Peterleitner, M. G.; Petrovskii, P. V.; Lyssenko, K. A.; Akhmedov, N. G.;
1
Bianchini, C.; Meli, A.; Oberhauser, W. Organometallics 2002, 21, 3637ꢀ3649. (b) Bianchini, C.; Meli, A.;
Oberhauser, W.; Zuideveld, M. A.; Freixa, Z.; Kamer, P. C. J.; Spek, A. L.; Gusev, O. V.; Kal'sin, A. M.
Organometallics 2003, 22, 2409ꢀ2421.
17. (a) Dong, K.; Sang, R.; Fang, X.; Franke, R.; Spannenberg, A.; Neumann, H.; Jackstell, R.; Beller, M.
Angew. Chem. Int. Ed. 2017, 56, 5267ꢀ5271. (b) Li, H.; Dong, K.; Jiao, H.; Neumann, H.; Jackstell, R.; Beller,
M. Nat. Chem. 2016, 8, 1159ꢀ1166.
18. Blanco, C.; Godard, C.; Zangrando, E.; Ruiz, A.; Claver, C. Dalton Trans. 2012, 41, 6980ꢀ6991.
19. (a) Zhang, Z.; Wang, Y.; Wang, M.; Lu, J.; Li, L.; Zhang, Z.; Li, M.; Jiang, J.; Wang, F. Chin. J. Catal.
2015, 36, 1623ꢀ1630. (b) Zhang, Z.; Wang, Y.; Wang, M.; Lu, J.; Zhang, C.; Li, L.; Jiang, J.; Wang, F. Catal.
Sci. Technol. 2016, 6, 1693ꢀ1700.
0. (a) Mai, H. X.; Sun, L. D.; Zhang, Y. W.; Si, R.; Feng, W.; Zhang, H. P.; Liu, H. C.; Yan, C. H. J. Phys.
Chem. B 2005, 109, 24380ꢀ24385. (b) Wang, Y.; Wang, F.; Song, Q.; Xin, Q.; Xu, S.; Xu, J. J. Am. Chem. Soc.
013, 135, 1506ꢀ1515.
2
2
21. It should be handled inside a wellꢀventilated hood to avoid inhalation. Besides, a CO sensor should be
installed around the bench.
22. Kovács, A.; Schierholz, R.; Tillmann, K. Journal of large-scale research facilities JLSRF 2016, 2, 43.
2
3. Thust, A.; Barthel, J.; Tillmann, K. Journal of large-scale research facilities JLSRF 2016, 2, 41.
24. Boudeville, Y.; Figueras, F.; Forissier, M.; Portefaix, J. L.; Vedrine, J. C. J. Catal. 1979, 58, 52ꢀ60.
5. Scofield, J. H. J. Electron Spectrosc. Relat. 1976, 8, 129ꢀ137.
26. Kresse, G.; Furthmüller, J. Comp. Mater. Sci. 1996, 6, 15ꢀ50.
7. Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865ꢀ3868.
28. Kresse, G.; Joubert, D. Phys. Rev. B 1999, 59, 1758ꢀ1775.
9. Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys 2010, 132, 154104.
30. Henkelman, G.; Uberuaga, B. P.; Jonsson, H. J. Chem. Phys. 2000, 113, 9901ꢀ9904.
1. (a) Henkelman, G.; Jonsson, H. J. Chem. Phys. 1999, 111, 7010ꢀ7022. (b) Heyden, A.; Bell, A. T.; Keil, F.
2
2
2
3
J. J. Chem. Phys. 2005, 123, 224101. (c) Olsen, R. A.; Kroes, G. J.; Henkelman, G.; Arnaldsson, A.; Jonsson,
H. J. Chem. Phys. 2004, 121, 9776ꢀ9792.
32. Wang, Y.; Zhang, J.; Chen, H.; Zhang, Z.; Zhang, C.; Li, M.; Wang, F. Green Chem. 2017, 19, 88ꢀ92.
33. (a) Ostrom, H.; Oberg, H.; Xin, H.; Larue, J.; Beye, M.; Dell'Angela, M.; Gladh, J.; Ng, M. L.; Sellberg,
25
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Page 26 of 28
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7
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4
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5
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5
5
5
6
J. A.; Kaya, S.; Mercurio, G.; Nordlund, D.; Hantschmann, M.; Hieke, F.; Kuhn, D.; Schlotter, W. F.;
Dakovski, G. L.; Turner, J. J.; Minitti, M. P.; Mitra, A.; Moeller, S. P.; Fohlisch, A.; Wolf, M.; Wurth, W.;
Persson, M.; Norskov, J. K.; AbildꢀPedersen, F.; Ogasawara, H.; Pettersson, L. G. M.; Nilsson, A. Science
2015, 347, 978ꢀ982. (b) Huang, B.; Kobayashi, H.; Yamamoto, T.; Matsumura, S.; Nishida, Y.; Sato, K.;
Nagaoka, K.; Kawaguchi, S.; Kubota, Y.; Kitagawa, H. J. Am. Chem. Soc. 2017, 139, 4643ꢀ4646.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
34. Abe, T.; Tanizawa, M.; Watanabe, K.; Taguchi, A. Energy Environ. Sci. 2009, 2, 315ꢀ321.
35. Lin, W.; Herzing, A. A.; Kiely, C. J.; Wachs, I. E. J. Phys. Chem. C 2008, 112, 5942ꢀ5951.
36. (a) Wang, R.; Wang, Y.; Ren, M.; Sun, G.; Gao, D.; Chin Chong, Y. R.; Li, X.; Chen, G. Int. J. Hydrog.
Energy 2017, 42, 6757ꢀ6764. (b) Wang, F.; Li, C.; Zhang, X.; Wei, M.; Evans, D. G.; Duan, X. J. Catal. 2015,
3
3
1
3
9
3
29, 177ꢀ186.
7. (a) Soin, N.; Roy, S. S.; Mitra, S. K.; Thundat, T.; McLaughlin, J. A. J. Mater. Chem. 2012, 22, 14944ꢀ
4950. (b) Singh, P.; Hegde, M. S. Chem. Mater. 2009, 21, 3337ꢀ3345.
8. Ye, X. R.; Lin, Y. H.; Wang, C. M.; Engelhard, M. H.; Wang, Y.; Wai, C. M. J. Mater. Chem. 2004, 14,
08ꢀ913.
9. (a) Farmer, J. A.; Campbell, C. T. Science 2010, 329, 933ꢀ936. (b) Esch, F.; Fabris, S.; Zhou, L.; Montini,
T.; Africh, C.; Fornasiero, P.; Comelli, G.; Rosei, R. Science 2005, 309, 752ꢀ755. (c) Cargnello, M.; Jaen, J. J.
D.; Garrido, J. C. H.; Bakhmutsky, K.; Montini, T.; Gamez, J. J. C.; Gorte, R. J.; Fornasiero, P. Science 2012,
337, 713ꢀ717.
40. (a) Jimenez Orozco, C.; Florez, E.; Moreno, A.; Liu, P.; Rodriguez, J. A. J. Phys. Chem. C 2016, 120,
13531ꢀ13540. (b) Heard, C. J.; Hu, C.; Skoglundh, M.; Creaser, D.; Grönbeck, H. ACS Catal. 2016, 6, 3277ꢀ
286. (c) Kravchuk, T.; Venugopal, V.; Vattuone, L.; Burkholder, L.; Tysoe, W. T.; Smerieri, M.; Rocca, M. J.
3
Phys. Chem. C 2009, 113, 20881ꢀ20889. (d) Rioux, R. M.; Hoefelmeyer, J. D.; Grass, M.; Song, H.; Niesz, K.;
Yang, P.; Somorjai, G. A. Langmuir 2008, 24, 198ꢀ207. (e) Parlett, P. M.; Chesters, M. A. Surf. Sci. 1996, 357,
791ꢀ795.
4
1. (a) Chen, Y.; Chen, J. Appl. Surf. Sci. 2016, 387, 16ꢀ27. (b) Kim, E.; Shin, E. W.; Bark, C. W.; Chang, I.;
Yoon, W. J.; Kim, W. J. Appl. Catal., A 2014, 471, 80ꢀ83.
2. Heard, C. J.; Siahrostami, S.; Grönbeck, H. J. Phys. Chem. C 2016, 120, 995ꢀ1003.
4
43. (a) Kantcheva, M.; Sayan, S. Catal. Lett. 1999, 60, 27ꢀ38. (b) Chin, S. Y.; Williams, C. T.; Amiridis, M.
D. J. Phys. Chem. B 2006, 110, 871ꢀ882. (c) Hadjiivanov, K.; Lavalley, J. C.; Lamotte, J.; Mauge, F.; Saintꢀ
Just, J.; Che, M. J. Catal. 1998, 176, 415ꢀ425.
4
4. (a) Wu, Z.; Li, M.; Mullins, D. R.; Overbury, S. H. ACS Catal. 2012, 2, 2224ꢀ2234. (b) D’Angelo, A. M.;
Wu, Z.; Overbury, S. H.; Chaffee, A. L. J. Phys. Chem. C 2016, 120, 27996ꢀ28008.
5. Zhang, W. P.; Xu, S. T.; Han, X. W.; Bao, X. H. Chem. Soc. Rev. 2012, 41, 192ꢀ210.
4
46. (a) Anderson, M. W.; Klinowski, J. J. Am. Chem. Soc. 1990, 112, 10ꢀ16. (b) Mastikhin, V. M.;
Mudrakovsky, I. L.; Nosov, A. V. Prog. Nucl. Magn. Reson. Spectrosc. 1991, 23, 259ꢀ299.
47. Zhang, Z.; Wang, Y.; Lu, J.; Zhang, C.; Wang, M.; Li, M.; Liu, X.; Wang, F. ACS Catal. 2016, 6, 8248ꢀ
8254.
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8. Ferencz, Z.; Erdőhelyi, A.; Baán, K.; Oszkó, A.; Óvári, L.; Kónya, Z.; Papp, C.; Steinrück, H. P.; Kiss, J.
ACS Catal. 2014, 4, 1205ꢀ1218.
49. (a) Sivasankar, N.; Frei, H. J. Phys. Chem. C 2011, 115, 7545ꢀ7553. (b) Huang, L.; Xu, Y. Catal. Lett.
2000, 69, 145ꢀ151. (c) Pien, S. I.; Chuang, S. S. C. J. Mol. Catal. 1991, 68, 313ꢀ330.
50. Wasylenko, W.; Frei, H. J. Phys. Chem. B 2005, 109, 16873ꢀ16878.
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