MXene (Ti3C2) Vacancy-Confined Single-Atom Catalyst for Efficient Functionalization of CO2

Article abstract of DOI:10.1021/jacs.8b13579

A central topic in single-atom catalysis is building strong interactions between single atoms and the support for stabilization. Herein we report the preparation of stabilized single-atom catalysts via a simultaneous self-reduction stabilization process at room temperature using ultrathin two-dimensional Ti_3-xC₂T_yMXene nanosheets characterized by abundant Ti-deficit vacancy defects and a high reducing capability. The single atoms therein form strong metal-carbon bonds with the Ti_3-xC₂T_y support and are therefore stabilized onto the sites previously occupied by Ti. Pt-based single-atom catalyst (SAC) Pt₁/Ti_3-xC₂T_y offers a green route to utilizing greenhouse gas CO₂, via the formylation of amines, as a C₁ source in organic synthesis. DFT calculations reveal that, compared to Pt nanoparticles, the single Pt atoms on Ti_3-xC₂T_y support feature partial positive charges and atomic dispersion, which helps to significantly decrease the adsorption energy and activation energy of silane, CO₂, and aniline, thereby boosting catalytic performance. We believe that these results would open up new opportunities for the fabrication of SACs and the applications of MXenes in organic synthesis.

Full text of DOI:10.1021/jacs.8b13579

Subscriber access provided by TULANE UNIVERSITY
Article
MXene (Ti3C2) Vacancy Confined Single-Atom
Catalyst for Efficient Functionalization of CO2
Di Zhao, Zheng Chen, Wenjuan Yang, Shoujie Liu, Xun Zhang, Yi Yu, Weng-Chon Cheong, Lirong Zheng,
Fuqiang Ren, Guobing Ying, Xing Cao, Dingsheng Wang, Qing Peng, Guoxiu Wang, and Chen Chen
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b13579 • Publication Date (Web): 30 Jan 2019
Downloaded from http://pubs.acs.org on January 31, 2019
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
MXene (Ti3C2) Vacancy Confined Single-Atom Catalyst for Efficient
Functionalization of CO2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Di Zhao,†,∆ Zheng Chen,†,∆ Wenjuan Yang,†,∆ Shoujie Liu,†,‡ Xun Zhang,§ Yi Yu,§ Weng-Chon Cheong,
†
∥
†
†
1
⊥
#
Lirong Zheng, Fuqiang Ren, Guobing Ying, Xing Cao, Dingsheng Wang, Qing Peng, Guoxiu
†,*
∇
Wang, Chen Chen
†Department of Chemistry, Tsinghua University, Beijing 100084, China
‡College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, China
§School of Physical Science and Technology, Shanghai Tech University, Shanghai 201210, China
∥Beijing Synchrotron Radiation Facility, Chinese Academy of Sciences, Beijing 100049, China
⊥Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
# Department of Materials Science and Engineering, College of Mechanics and Materials, Hohai University, Nanjing
211100, China
∇Center for Clean Energy Technology, School of Mathematical and Physical Sciences, Faculty of Science, University of
Technology Sydney, NSW 2007, Australia
KEYWORDS: MXene; Vacancy; Single-Atom Catalyst; Functionalization of CO2
ABSTRACT: A central topic in single atom catalysis is to build strong interactions between single atoms and the support for
stabilization. Herein we report the preparation of stabilized single atom catalysts via a simultaneous self-reduction-
stabilization process under room temperature using ultrathin two-dimensional Ti3-xC2Ty MXene nanosheets characterized by
abundant Ti-deficit vacancy defects and high reducing capability. The single atoms therein form strong metal-carbon bonds
with the Ti3-xC2Ty support, and are therefore stabilized onto the sites previously occupied by Ti. The Pt-based single atom
catalyst (SAC) Pt1/Ti3-xC2Ty offers a green route to utilize the greenhouse gas CO2, via formylation of amines, as a C1 source in
organic synthesis. DFT calculations reveal that, compared to Pt nanoparticles, the single Pt atoms on Ti3-xC2Ty support feature
partial positive charges and atomic dispersion, which helps to significantly decrease the adsorption energy and activation
energy of silane, CO2 and aniline, thereby boosting catalytic performance. We believe that these results would open up new
opportunities for the fabrication of SACs and the applications of MXenes in organic synthesis.
INTRODUCTION
stabilizing the SACs is to build strong interactions between
the single atoms and the support. These interactions would
not only contribute to the stability of the atoms, but also
exert great influence on their electronic structures and in
turn catalytic performances.1,6 Up to date, most of the
reported SACs employ nitrogen-doped carbon, defect-rich
oxides/sulfides/nitrides and metal-organic framework
(MOF) materials as support, and are fabricated mainly via
atomic layer deposition, co-precipitation, wet impregnation
and pyrolysis of metal organic polymers or frameworks.6-10
These methods usually require a reducing atmosphere (in
H2/Ar, for instance) or high temperature. Hence, it is of
fundamental importance to explore and develop new
supporting materials and new fabrication methods for
SACs.1
Single atom catalysts (SACs) have recently drawn
extensive attention in the fields of heterogeneous catalysis
and electrochemical catalysis, by virtue of their atomic
dispersion, maximized utilization of noble metals and
unsaturated coordination.1 However, the reactions for
which SACs are applicable are still quite limited, and a large
number of catalytic reactions are yet to be explored. For
example, in organic synthesis, the utilization and
conversion of CO2 as a sustainable C1 building block has
recently evoked broad interest, since it may afford value-
added chemicals from an abundant, inexpensive, non-toxic
and renewable resource. It would be of immense
environmental and public benefit to develop SACs for such
carbon fixation reactions, since the high atomic utilization
and high recyclability of SACs would significantly elevate
the efficiency and economy of these processes.2-4
MXenes, a unique family of two-dimensional (2D) metal
carbides, nitrides or carbonitrides, have already shown
great promise in energy storage and electro-magnetic,
photo- and electro-chemical applications.11-18 Most recently,
we reported the electrochemical exfoliation of a double
transition metal MXene (Mo2TiC2Tx) with Pt foil as the
The single atoms in SACs exhibit high surface energy
owing to the atomic dispersion, and are strongly inclined to
aggregate into particles.5 Therefore, a central factor in
ACS Paragon Plus Environment

Journal of the American Chemical Society
counter electrode, in which Mo vacancies could act as the RESULTS AND DISCUSSION
Page 2 of 16
anchoring sites for single Pt atoms (Mo2TiC2Tx-PtSA).19 The
developed catalyst exhibited enhanced performance for
hydrogen evolution reaction. However, this method is
limited for other metals. In the most extensively studied
MXene, namely, Ti3-xC2Ty, each layer in its 2D structure
comprises three Ti sublayers (denoted as Ti1, Ti2, Ti3) with
carbon located at the octahedral interstitial sites, and the
neighboring two layers are connected by a more reactive Al
layer.14 When HF is used to etch the Al layer and to exfoliate
single-layered (or ultrathin multi-layered) MXenes, some
adjacent Ti atoms are also etched off even under mild
conditions, resulting in Ti single vacancies or vacancy
clusters.20 These vacancy defects are very unstable and
reactive, and the exfoliated MXene sheets are highly
reductive. When metal salt precursors are added, they can
be reduced by the MXenes even without any additional
reducing agent.20-22 Moreover, the Ti-deficit defects are
ideal sites to accommodate and stabilize the yielded single
metal atoms.8,23 In addition, after the removal of Al layers,
the surface functional groups (Tx) on Ti1 and Ti3 sublayers,
such as O2−, OH− and F−, could help to electrostatically
adsorb metal precursors, and therefore are conducive to the
subsequent reduction and anchoring of single metal
atoms.13,20 To summarize, with the unique features of high
reducing capability and suitable surface defects, Ti3-xC2Ty
MXene is expected to be an ideal candidate to support and
stabilize SACs.
1
Synthesis and characterization of the Pt1/Ti3-xC2Ty
catalyst. As illustrated in Scheme 1, few-layered Ti3-xC2Ty
nanosheets were prepared by selective removing the Al
layer via etching from parent Ti3AlC2 in a mixed solution of
lithium fluoride and hydrochloric acid (Figure S4). During
this process, Ti–Al bonds were impaired, and some Ti atoms
(in Ti1 and Ti3 sublayers) would also be ripped off. As
shown in the high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) image in
Figure S5, single Ti vacancy or vacancy clusters were
observed in the flakes synthesized even under mild
conditions, and their concentration was strongly dependent
on the HF concentration generated during etching.23,24 X-ray
absorption spectroscopy (XAS) was further used to confirm
the defects in the exfoliated MXene. The results of Ti K-edge
X-ray absorption near-edge structure (XANES) analysis
(Figure S6a) show that the edge energy of Ti3-xC2Ty was
slightly higher than that of Ti3AlC2, suggesting that the Ti
atoms in Ti3-xC2Ty were partially oxidized due to the
terminal groups or TiOx on its surface.20 Yet the shapes of the
XANES spectral profiles of Ti3-xC2Ty and Ti3AlC2 are still
quite similar, indicating that the structure of Ti3-xC2Ty was
well preserved after the removal of Al. Extended X-ray
absorption fine-structure (EXAFS) spectra were also used
to confirm the 2D structure of the materials. Figure S6b
shows that, after removal of Al, the first-shell (Ti–C/O)
scattering was increased but the second-shell (Ti–C–Ti)
scattering was lower than that of Ti3AlC2, indicating the loss
of Ti atoms. Moreover, after the Al atoms were etched off,
they were replaced by surface terminal groups, Tx (such as -
O, -OH and -F). Therefore, here the exfoliated MXene can be
referred to as Ti3-xC2Ty. When [PtCl6]2- complex ions with
Pt4+ were injected into the MXene solution under stirring,
the [PtCl6]2- ions were uniformly adsorbed onto the surface
of Ti3-xC2Ty flakes. The Pt4+ would to be slowly reduced by
the highly unstable and reductive Ti vacancies and
stabilized thereupon, forming Pt1/Ti3-xC2Ty. Therefore, in
this strategy, adsorption and reduction of single metal
atoms takes place almost at the same time, which protects
the catalyst from suffering in the subsequent harsh
calcination reduction reaction during the multi-step
synthesis process.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Illustration of the simultaneous self-reduction-
stabilization process for preparation of Pt1/Ti3-xC2Ty.
Herein we report a novel, general and facile fabrication
The typical TEM image (Figure S7) clearly shows that the
as-synthesized Pt1/Ti3-xC2Ty samples still displayed a
nanosheet morphology. The atomic resolution HAADF-
STEM image of the Pt1/Ti3-xC2Ty (Figure 1a) presents
characteristic lattice spacings of 2.48 Å, 2.0 Å and 2.08 Å,
which are attributed to the (013), (018) and (0012) lattice
planes of Ti3-xC2Ty, respectively. Interestingly, the image
also revealed the uniformly distributed small bright dots of
Pt atoms (indicated by yellow circles) within the regular Ti3-
xC2Ty crystal lattice fringes. Figure 1b displays the magnified
image from the selected area marked by the yellow box in
Figure 1a. The inset in Figure 1b shows a scheme of columns
of atoms, which is overlaid on the experimental images for
comparison. As shown in the intensity profiles (Figure 1c)
of line 1 in Figure 1b, the single Pt atoms are much brighter
than the other atoms. Moreover, these images also showed
that all the small bright dots of Pt were located at the lattice
plane walls of the Ti columns rather than in the spacings
route to SACs via
a
simultaneous self-reduction-
stabilization process under room temperature, by
exploiting the rich Ti-deficit defects and high reducing
capability of Ti3-xC2Ty MXene. With Pt as an example, in the
prepared SAC (denoted as Pt1/Ti3-xC2Ty) with a Pt loading of
~0.2 wt%, Pt atoms occupy the Ti-deficit defect sites and
form strong Pt-C bonds with the neighboring C atoms, and
are therefore anchored on the ultrathin MXene nanosheets.
With a very low amount of Pt (0.4 mmol%), the SAC can
catalyze the N-formylation of CO2 and aniline under
ambient pressure, with the conversion and selectivity both
approaching 100%, and the turnover number (TON) far
exceeding that of commercial Pt catalysts and Pt
nanoparticles (NPs) supported on Ti3-xC2Ty. The catalyst
features a maximized utilization of noble metal, and a good
recyclability during multiple test cycles. Our method here is
also applicable for other metals (Ru, Rh, Ir and Pd), and
therefore is a general and robust fabrication route to SACs.
ACS Paragon Plus Environment

Page 3 of 16
Journal of the American Chemical Society
between them, indicating that the single Pt atoms were
to 4f5/2 and 4f7/2 levels, respectively.26,27 The peak positions
1
2
3
4
5
6
7
8
stabilized in the Ti vacancies by substitution rather than
interstitial doping. Figure 1d shows the experimental
HAADF−STEM images (left two panels) and the simulated
HAADF−STEM images (on the right) using a model with a Pt
atom replacing one of surface Ti atoms. In the simulated
image, the atom column containing Pt shows higher
contrast than the nearby Ti-C atom columns as Pt has a
larger atomic number. The contrast difference is better seen
in the false colored image. The agreement between
experiment and simulation provides clear evidence that the
Pt atoms are anchored as placeholders of Ti. Moreover,
STEM images and corresponding element maps (Figure S8)
indicate that no Pt NPs can be found, and Pt single atoms are
uniformly dispersed in the Ti3-xC2Ty nanosheets.
are between those of Pt (II) and Pt (0), indicating that the Pt
atoms were reduced from Pt(VI) in its [PtCl6]2- precursor by
the highly active Ti atoms around the defects, which have
been proved to be oxidized to a higher oxidation state
(Figures S9 and S11). Figure 2c shows the Pt EXAFS Fourier
transform curves of Pt1/Ti3-xC2Tyand references. The curve
for Pt1/Ti3-xC2Ty exhibits two main peaks at about 1.5 Å and
2.2 Å, associated with the first shell of Pt-C scattering and
the higher shell of Pt-Ti, respectively. And compared with
FT curve of Pt foils, no reflection from Pt-Pt contribution is
observed, indicating the sole existence of atomically
dispersed Pt in Pt1/Ti3-xC2Ty. To further confirm this
inference, a wavelet transform (WT) analysis of the Pt L3-
edge EXAFS oscillations was performed. In Figure 2d, the
WT contour plot of Pt1/Ti3-xC2Ty in the first coordination
shell shows one intensity maximum at ∼3 Å−1, associated
with Pt−C contribution. However, for the higher
coordination shell, the WT contour plot shows an additional
maximum at ∼5 Å−1, owing to the Pt−Ti contribution.
Compared with the WT contour plot of Pt foil, there is no
intensity maximum detected near 8.5 Å-1(indexed to Pt-Pt
path), further confirming that Pt atoms are atomically
dispersed.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. (a) HAADF−STEM image of Pt1/Ti3-xC2Ty. (b)
Magnified HAADF image of the area in the yellow box in (a).
Schematic columns of atoms are overlaid on the experimental
images (inset). (c) Corresponding intensity maps obtained in
line 1 in (b). (d) Experimental raw and false colored
HAADF−STEM images (left two panels) and the simulated
HAADF−STEM images (on the right) using a model with a Pt
atom replacing one of surface Ti atoms.
To further verify that the isolated Pt atoms were
dispersed in Pt1/Ti3-xC2Ty and to unveil the atomic structure
of Pt, we performed XANES, EXAFS, X-ray diffraction (XRD)
and X-ray photoelectron spectrometry (XPS). Figure S9
presents the results of Ti K-edge XANES analysis. It shows
that, compared with Ti3-xC2Ty, the threshold value of energy
absorption of Ti K-edge for Pt1/Ti3-xC2Ty is a little higher
than that of Ti3-xC2Ty, indicating an increase in the higher
oxidation state for Ti. However, the spectral shape of
Pt1/Ti3-xC2Ty is similar to that of Ti3-xC2Ty, but different from
that of TiO2 and Ti foil. In the XRD pattern of Pt1/Ti3-xC2Ty
(Figure S10), no peaks corresponding to Pt NPs can be
observed, only the characteristic peaks of Ti3-xC2Ty
MXenes,25 indicating that the introduction of Pt atoms did
not significantly alter the structure of Ti3-xC2Ty even though
the valence state of Ti becomes slightly higher. Figure 2a
shows the XANES spectra of Pt L3-edge. The absorption edge
position of Pt1/Ti3-xC2Ty is located between those of Pt foil
and PtO2, suggesting that the single Pt atom carries positive
charge and its oxidation state is between 0 and +4. The
oxidation state of Pt was further analyzed by XPS. As shown
in Figure 2b, the Pt 4f spectrum can be deconvoluted into
two peaks centered at 75.3 eV and 72.5 eV, corresponding
Figure 2. (a) Pt L3-edge XANES spectra. (b) XPS spectra for Pt
4f of Pt1/Ti3-xC2Ty. (c) EXAFS FT k2-weighted χ(k) function
spectra of Pt1/Ti3-xC2Ty and reference. (d) WT for the k2-
weighted Pt L3-edge EXAFS signals in Pt1/Ti3-xC2Ty and Pt foil.
(e) TDOS and PDOS of Pt1/Ti3-xC2Ty. Inset: schematic model. (f)
Charge density difference of Pt1/Ti3-xC2Ty with plan view
(upper image) and side-on view (lower image). Yellow and
cyan regions represent electron accumulation and depletion,
respectively.
To obtain the detailed atomic structure and probe the
interaction of the Pt atoms with the Ti3-xC2Ty support,
quantitative EXAFS curve fitting was carried out, and the
results for Pt1/Ti3-xC2Ty are displayed in Figure 2c (black
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 16
dotted line). For comparison, the fitting results for Pt foil xC2Ty) and the Pt precursor (H2PtCl6) as catalysts, and they
1
and PtO2 are displayed in Figures S12-14. The fitting results
and the corresponding fitting parameters are listed in Table
S1. According to the fitting results, the Pt-C coordination
number for Pt1/Ti3-xC2Ty is 3.1±0.8 with bond length of
1.99±0.02 Å, implying that a single Pt atom is coordinated
with three carbon atoms on the MXene nanosheets.
Moreover, the coordination number for the higher shell of
Pt-Ti is 3.8 ± 0.6, with the bond length of 2.68 ± 0.02 Å. First-
principle calculations were performed to elucidate the
possible structure of Pt1/Ti3-xC2Ty. The models of O-
terminated Ti3C2 (Ti3C2O2) are chosen (inset in Figure S15)
for the simulation.28-30 A Pt atom was embedded within a
vacancy previously occupied by Ti, which is surrounded by
three carbon atoms. The atomic structure model
(Pt1/Ti3C2O2) is illustrated in inset of Figure 2e. The bond
lengths of Pt-Ti and Pt-C are 2.75 Å and 1.98 Å, respectively,
which are consistent with EXAFS results. The total density
of states (TDOS) and partial density of states (PDOS) of
Pt1/Ti3C2O2 were calculated to reveal the hybridization of
the atomic orbitals. Intact Ti3C2O2 has a metallic character
whose band gap is zero with substantial electronic states
crossing the Fermi energy (Figure S15). The PDOS of Ti
atoms contribute mostly compared with those of O and C
atoms. The PDOS of Pt atom mainly occupy the energy
below the Fermi energy. Owing to the change in the PDOS
near the Fermi energy, the electronic coupling of Pt and C or
Ti atoms is very strong, resulting in downshifting the d-
band center compared with that of Pt NPs (Figure S16).
According to the Nørskov’d-band theory, the downshift of
the Pt d-band center could pull more of the antibonding
states below the Fermi level, leading to optimal activation
energy of reactants.31-32 Figure 2f displays the charge
density difference of Pt1/Ti3-xC2Ty (Pt1/Ti3C2O2). The cyan
region denotes charge density depletion around a Pt single
atom, illustrating that the Pt is positively charged.
Moreover, Bader charge analysis demonstrates that the
charge accumulation on Pt is 0.33e, in good agreement with
XPS and EXAFS results. Therefore, we identified our
material as Pt1/Ti3-xC2Ty SACs.
barely gave any products (Figure 3b and entries 4 and 5 in
Table S2). For comparison, a sample of Pt NPs supported on
Ti3-xC2Ty (Pt-NPs/Ti3-xC2Ty) with a Pt loading of 4 wt% was
prepared and examined (Figures S17-18), which exhibited
a conversion of merely 18% under the same conditions
(Figure 3b and entry 6 in Table S2). An even lower
conversion (13%) of aniline was observed using
commercial Pt-NPs/C catalyst (Figure 3b and entry 7 in
Table S2). To further study the effect of defect
concentrations of Ti3-xC2Ty on the catalytic activity, we
prepared other Ti3-xC2Ty with different Ti vacancy
concentrations using different amounts of LiF
(corresponding samples are denoted as Pt1/Ti3-xC2Ty-0.7
and Pt1/Ti3-xC2Ty-1.5).24 As shown in Figure S19, Ti3-xC2Ty-1
and Ti3-xC2Ty-1.5 barely gave any products, and Pt1/Ti3-
xC2Ty-0.7 and Pt1/Ti3-xC2Ty-1.5 gave almost the same
conversion with Pt1/Ti3-xC2Ty, indicating that Ti vacancies
only help to stabilize the single atoms, and the impact on
catalytic activity is not significant. To summarize, Pt1/Ti3-
xC2Ty SAC displayed superior catalytic performance to Pt-
NPs. In addition, the Pt1/Ti3-xC2Ty SACs also exhibited good
reusability (Figure 3c). Figure S20 shows the HAADF-STEM
images of the recycled Pt1/Ti3-xC2Ty SAC, and atomic
dispersion of Pt atoms is well retained although the
crystallinity of support Ti3-xC2Ty becomes a little lower.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. (a) The chemical equation for N-formylation of
aniline with CO2 and Et3SiH. (b) Catalytic performance for N-
formylation of aniline using different catalysts. (c) Recycling
test of Pt1/Ti3-xC2Ty for catalytic N-formylation of aniline.
Catalytic
performance
evaluation
for
CO2
functionalization via N-formylation reaction. We next
investigated the catalytic properties of our Pt1/Ti3-xC2Ty SAC
for CO2 functionalization. CO2 is the major greenhouse gas
that is responsible for global warming, ocean acidification,
and many environmental issues.33 However, with proper
processes, CO2 can serve as an attractive, non-toxic and
abundant C1 building block in organic synthesis to afford a
wide variety of value-added chemicals.34 For our Pt1/Ti3-
xC2Ty SAC, we found that it could effectively activate CO2
with amines and silane to give formamides. For our initial
investigation, the reaction of CO2 (~1 atm) with aniline in
the presence of Pt1/Ti3-xC2Ty (~0.4 mmol% Pt with respect
to aniline) and triethylhydrosilane (Et3SiH, the reductant)
was chosen as a model reaction (Figure 3a, b), which
achieved an almost complete conversion and ~100%
selectivity. ICP-AES analysis confirmed that the content of
free Pt in the solution was below the detection limit. No
products were detected without any catalyst (entry 2 in
Table S2). And, without CO2, the reaction could not proceed
at all (entry 3), thus confirming that CO2 is indispensable for
the formylation. We also tested the prestine support (Ti3-
Next, we further explored the scope of the present
catalytic system. Table S3 shows the scope of various
amines for formylation under the same conditions. When
anilines substituted with electron-donating groups (entries
2-4, Table S3) were used, the desired products were
obtained in relatively high yields (85–96%). On the
contrary, anilines substituted with electron-withdrawing
groups showed
a
slight decrease in formylation
performance (entry 5, Table S3). Aliphatic amines and
secondary amines (entries 6–9, Table S3) could also
undergo catalytic formylation with CO2 and Et3SiH, giving
high yields (~100%) and high selectivity (~100%). Table
S4 summarizes a few works on different catalysts most
recently reported by other groups for N-formylation of
amines and CO2. It can be seen that our Pt1/Ti3-xC2Ty SAC
shows both outstanding yield and selectivity under
relatively mild reaction conditions, in particular with the
ACS Paragon Plus Environment

Page 5 of 16
Journal of the American Chemical Society
advantages of low pressure of CO2 and very low content of than those on Pt NPs ( -0.03 eV and -0.11 eV, respectively),
precious metal.
1
implying that CO2 and aniline would preferentially be
adsorbed on Pt1 rather than on Pt NPs (Figures S25-26).
Moreover, the reactions of CO2 insertion into the Pt-H bond
and aniline reaction are endothermic with transition
barrier energies TS1 and TS2 on Pt1 which are 1.03 eV and
1.04 eV, respectively. The last step is Si-OH reductive
elimination with the transition barrier energy TS3 being
1.24 eV. The transition barrier energies of TS1, TS2, TS3 on
Pt NPs are 1.05 eV, 2.57 eV and 1.28 eV, respectively, all
higher than that on Pt1, especially TS2. The larger steric
hindrance and Pt-Pt coordination environment of Pt NPs
result in the difficulty of aniline reduction and enhances the
TS2 barrier energy, which hampers the entire catalytic
process. From the viewpoint of adsorption energies and
transition state barrier energies, the reaction pathway
along single Pt atom is more feasible with respect to that on
Pt NPs. Meanwhile, the inactivity of H2PtCl6 could be easily
understood, because it could not be further oxidized, which
is required for the Si-H activation. To summarize, the lower
barrier energy of CO2 insertion into a Pt-H bond (TS1), the
aniline reaction (TS2), the reductive elimination (TS3) by
the dispersed single atoms and the partially positively-
charged Pt appear to contribute strongly to the superior
catalytic performance.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. (a) DFT calculations proposed reaction pathway for
functionalization of CO2 to amide with amines on isolated Pt of
Pt1/Ti3-xC2Ty. (b) The calculated energy profiles for Pt1/Ti3-
xC2Ty (red line) and Pt NPs (black line).
DFT calculations were conducted to unveil the reaction
mechanism and to shed light on the fact that the Pt-SAC has
superior catalytic performance to Pt-NPs. The atomic
structure of Pt NPs is shown in Figure S21. The
configuration of Pt1/Ti3-xC2Ty has Pt single atoms
surrounded by titanium atoms and three carbon atoms with
bond lengths of 2.75 Å and 1.98 Å, respectively. As shown in
Figure 4a and Tables S5-6, the Pt1/Ti3-xC2Ty-catalyzed CO2
hydrosilylation reaction follows the Chalk-Harrod
mechanism,35 which consists of Si-H oxidative addition to a
Pt atom (I-II) and subsequent CO2 insertion into the Pt-H
bond to yield HCOO (III-TS1-IV, Transition state (TS1)).
Then the produced HCOO reacts with amines to generate
formamides (V-TS2-VI), followed by Si-OH reductive
elimination and silanol escape (TS3). Figure 4b shows the
calculated energy profile of reaction pathways with detailed
reactants, products and intermediate species (red line of Pt-
SAC; black line of Pt-NPs with its reaction cycle shown in
Figure S22). In the first step of silane activation (Step ⅰ),
the various configurations were tested and the lowest-
energy configurations were obtained with the formation of
Pt-H bonds on Pt1/Ti3-xC2Ty (adsorption energy: -2.52 eV)
and Pt NPs (-2.35 eV) (Figures S23-24). In the second (Step
ⅱ) and third steps (Step ⅲ) of CO2 insertion and amines
reaction, the adsorption energies of CO2 and aniline on Pt1
is -0.03 eV and -1.63 eV, respectively, which are smaller
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 16
Figure 5. HAADF-STEM images and corresponding element
maps showing distributions of Ti (red) and metal (green): (a)
Ru; (b) Ir; (c) Rh; (d) Pd, respectively.
containing of 492 μL H2PtCI6·6H2O (0.1 g/mL) were mixed
1
2
3
4
5
6
7
8
in a 500 mL wide-mouth flask and stirred to form a
homogenous solution, followed by heating and refluxing at
80 °C for 3h under air. The Pt NPs were precipitated by
acetone and collected by centrifugation. The resulting Pt
NPs were dispersed in 50 ml distilled water and sonicated
for half an hour. Then 12 ml Ti3-xC2Ty MXene suspension
were dispersed in 250 mL of distilled water under magnetic
stirring to form a transparent solution. Then the Pt NPs
solution was added into the Ti3-xC2Ty MXene solution under
agitated stirring. After stirring for 8 h, the Pt-NPs/Ti3-xC2Ty
were precipitated by acetone for half an hour and collected
by centrifugation with acetone. The product was vacuum
dried at 60 °C for one night.
To investigate the generality of this preparation method
for SACs, we extended this method to fabricate Ti3-xC2Ty
with single atom sites of other metals (M1/Ti3-xC2Ty,
including Ru, Ir, Rh and Pd). By HAADF-STEM (Figure 5),
element mappings and XRD (Figures S27-30), we can see
that no metal NPs could be found, and the metal atoms were
uniformly dispersed in the Ti3-xC2Ty nanosheets. The mass
loading of noble metals in Ru1/Ti3-xC2Ty, Ir1/Ti3-xC2Ty,
Rh1/Ti3-xC2Ty and Pd1/Ti3-xC2Ty are 0.08 wt%, 0.19 wt%,
0.05 wt% and 0.04 wt%, respectively. The results of their
corresponding aberration-corrected HAADF-STEM images
also demonstrated that many individual bright dots were
located at the Ti positions in Ru1/Ti3-xC2Ty, Ir1/Ti3-xC2Ty,
Rh1/Ti3-xC2Ty and Pd1/Ti3-xC2Ty, respectively, confirming
that this method is a general fabrication route for other
noble metal SACs. Furthermore, we also extended our
approach to synthesizing non-noble metal SACs. As shown
in Figure S31, the STEM images, corresponding element
mappings and HAADF-STEM images preliminary
demonstrated that the method can also be used for
synthesis of a series of metal SACs (M1/Ti3-xC2Ty).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Characterizations. TEM images were performed on a
Hitachi H-800 TEM operated at 100 kV. XRD data were
measured on a Rigaku RU-200b with Cu Kα radiation (λ =
1.5406 Å). HAADF-STEM images were performed on using
a Titan Themis 60-300 STEM operated at 300 kV, equipped
with a spherical probe aberration corrector. The metal
concentration measurement was conducted by ICP-OES.
XPS was performed on an ULVAC PHI Quantera microscope.
The high-resolution XPS spectra of Pt 4f regions were
carried out at the Catalysis and Surface Science End station
of the BL11U beamline at the National Synchrotron
Radiation Laboratory (NSRL) in Hefei, China.
CONCLUSION
Structure modelling and HAADF STEM image
simulation. We prepared a model for image simulation by
random doping of 4 Pt atoms in Ti positions. HAADF-STEM
image simulations were performed using a plane wave
reciprocal space interpolated scattering matrix (PRISM)
method.37 The accelerating voltage is 300 kV and the
interpolation factor we used is 5. The maximum alpha
convergence angle is 25 mrad, probe alpha and collection
angle were set at 25mrad and 75-200 mrad, respectively. In
order to get closer to the experimental data, Poisson white
noise was added to the simulated images (Supplementary
Fig. S3). Structure models shown in this work were drawn
using VESTA software.38
In conclusion, ultrathin Ti3-xC2Ty MXene nanosheets
featuring with highly reductive capability could firmly
accommodate and stabilize single metal atoms on the Ti-
deficit defect sites by forming metal-carbon bonds at room
temperature. The catalysis tests showed that our Pt1/Ti3-
xC2Ty catalyst, in the presence of a diverse range of amines
and silanes, could readily fixate the greenhouse gas CO2 and
yield value-added amides with very high conversion and
selectivity as well as a TON far exceeding that for Pt NPs.
This work introduced a new and ideal family of 2D materials
as the support, and expanded the applications of MXene
materials. Moreover, this is the first report of SACs being
used for formylation of amines from CO2, and the SAC here
outperforms the already reported heterogeneous catalysts.
These results promise very exciting prospects in both
fundamental studies and industrial applications.
XAFS measurements and analysis. XANES spectra of Pt
L3-edge and Ni K-edge were all collected at the 1W1B
station in the Beijing Synchrotron Radiation Facility using a
fixed-exit Si (111) double crystal monochromator operated
at 2.5 GeV with a maximum current of 250 mA. The Ti K-
edge XANES data were recorded in transmission mode. Ti
foil and TiO2 were used as references. The Pt L3-edge XANES
data were recorded in a fluorescence mode. Pt foil and PtO2
were used as references.
EXPERIMENTAL SECTION
Synthesis of Pt1/Ti3-xC2Ty. In a typical synthesis of Pt1/Ti3-
xC2Ty, 8 ml Ti3-xC2Ty MXene suspension were dispersed in 20
mL of distilled water under magnetic stirring to form a
transparent solution A. Solution B was prepared by adding
10 μL H2PtCI6·6H2O (0.1 g ml-1) solutions to 50 ml distilled
water. Then solution A and solution B were sonicated for 1
h and 10 minutes, respectively. The solution B was slowly
added into solution A dropwise under agitated stirring.
After reaction for 8 h, the Pt1/Ti3-xC2Ty were precipitated by
acetone for half an hour and collected by centrifugation
with acetone. The product was vacuum dried at 60 °C for
one night.
Catalysis testing. Typically, the formylation of amines was
carried out in a 10 mL standard Schlenk tube outfitted with
a temperature controller and stirrer. Catalyst (0.4 mmol%;
≈100mg) was added into the reactor with DMF (2 mL), and
then sonicated for half an hour. Then amine (0.25 mmol)
and Et3SiH (1.75 mmol) were added into the above mixture,
and then the mixture was sealed with CO2 balloon
o
(99.999%). Finally, the mixture was heated to 140 C and
vigorously stirred (750 rpm) for 10 hours. When the
reaction was over, the selectivity and conversion are
determined by GC-MS and GC analysis with dodecane as
internal standard. The active sites of the Pt-based catalysts
were measured by ICP-AES experiments.
Synthesis of Pt-NPs/Ti3-xC2Ty. First, Pt nanoparticles (Pt
NPs) were prepared according to the previous reference.36
PVP (133 mg, Mw=30,000) and methanol solution (180 mL)
ACS Paragon Plus Environment

Page 7 of 16
Journal of the American Chemical Society
(7) Shan, J. J.; Li, M. W.; Allard, L. F.; Lee, S.; Flytzani-
The details of the XAFS analysis and theoretical
calculations are shown in the Supporting Information.
Stephanopoulos, M., Mild oxidation of methane to methanol or
acetic acid on supported isolated rhodium catalysts. Nature 2017,
551, 605-608.
1
2
3
4
5
6
7
8
ASSOCIATED CONTENT
*Supporting Information
The Supporting Information is available free of charge on
the ACS Publications website.
Detailed experimental procedures, characterization
methods, extended figures, and tables.
(8) Liu, P. X.; Zhao, Y.; Qin, R. X.; Mo, S. G.; Chen, G. X.; Gu, L.;
Chevrier, D. M.; Zhang, P.; Guo, Q.; Zang, D. D.; Wu, B. H.; Fu, G.;
Zheng, N. F., Photochemical route for synthesizing atomically
dispersed palladium catalysts. Science 2016, 352, 797-801.
(9) Liu, G. L.; Robertson, A. W.; Li, M. M.; Kuo, W. C. H.; Darby, M. T.;
Muhieddine, M. H.; Lin, Y. C.; Suenaga, K.; Stamatakis, M.; Warner, J.
H.; Tsang, S. C. E., MoS2 monolayer catalyst doped with isolated Co
atoms for the hydrodeoxygenation reaction. Nat. Chem. 2017, 9,
810-816.
(10) Yang, S.; Kim, J.; Tak, Y. J.; Soon, A.; Lee, H., Single-atom catalyst
of platinum supported on titanium nitride for selective
electrochemical reactions. Angew. Chem. Int. Ed. 2016, 55, 2058-
2062.
9
AUTHOR INFORMATION
Corresponding Author
*cchen@mail.tsinghua.edu.cn
Author Contributions
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(11) Xia, Y.; Mathis, T. S.; Zhao, M. Q.; Anasori, B.; Dang, A.; Zhou, Z.
H.; Cho, H.; Gogotsi, Y.; Yang, S., Thickness-independent
capacitance of vertically aligned liquid-crystalline MXenes. Nature
2018, 557, 409-412.
∆ D. Z., Z. C. and W. J. Y. contributed equally.
Notes
(12) Ghidiu, M.; Lukatskaya, M. R.; Zhao, M. Q.; Gogotsi, Y.; Barsoum,
M. W., Conductive two-dimensional titanium carbide 'clay' with
high volumetric capacitance. Nature 2014, 516, 78-81.
(13) Lukatskaya, M. R.; Mashtalir, O.; Ren, C. E.; Dall’Agnese, Y.;
Rozier, P.; Taberna, P. L.; Naguib, M.; Simon, P.; Barsoum, M. W.;
Gogotsi, Y., Cation intercalation and high volumetric capacitance of
two-dimensional titanium carbide. Science 2013, 341, 1502-1505.
(14) Shahzad, F.; Alhabeb, M.; Hatter, C. B.; Anasori, B.; Hong, S. M.;
Koo, C. M.; Gogotsi, Y., Electromagnetic interference shielding with
2D transition metal carbides (MXenes). Science 2016, 353, 1137-
1140.
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by Beijing Natural Science
Foundation (JQ18007), National Key R&D Program of China
(2017YFA0700101, 2016YFA0202801), National Natural
Science Foundation of China (21872076, 21573119,
21590792, 51651201, 21866032, and 21805184), China
(15) Di, J.; Yan, C.; Handoko, A. D.; Seh, Z. W.; Li, H.; Liu, Z., Ultrathin
two-dimensional materials for photo- and electrocatalytic
hydrogen evolution. Mater. Today 2018, 21, 749-770.
(16) Handoko, A. D.; Fredrickson, K. D.; Anasori, B.; Convey, K. W.;
Johnson, L. R.; Gogotsi, Y.; Vojvodic, A.; Seh, Z. W., Tuning the basal
plane functionalization of two-dimensional metal carbides
(MXenes) to control hydrogen evolution activity. ACS Appl. Mater.
Interfaces 2017, 1, 173-180.
(17) Li, P. K.; Zhu, J. G.; Handoko, A. D.; Zhang, R. F.; Wang, H. T.;
Legut, D.; Wen, X. D.; Fu, Z. H.; Seh, Z. W.; Zhang, Q. F., High-
throughput theoretical optimization of the hydrogen evolution
reaction on MXenes by transition metal modification. J. Mater.
Chem. A 2018, 6, 4271-4278.
(18) Handoko, A. D.; Khoo, K. H.; Tan, T. L.; Jin, H. M.; Seh, Z. W.,
Establishing new scaling relations on two-dimensional MXenes for
CO2 electroreduction. J. Mater. Chem. A 2018, 6, 21885-21890.
(19) Zhang, J. Q.; Zhao, Y. F.; Guo, X.; Chen, C.; Dong, C. L.; Liu, R. S.;
Han, C. P.; Li, Y. D.; Gogotsi, Y.; Wang, G. X., Single platinum atoms
immobilized on an MXene as an efficient catalyst for the hydrogen
evolution reaction. Nat. Catal. 2018, 1, 985-992.
(20) Li, Z.; Cui, Y. R.; Wu, Z. W.; Milligan, C.; Zhou, L.; Mitchell, G.; Xu,
B.; Shi, E.; Miller, J. T.; Ribeiro, F. H.; Wu, Y., Reactive metal–support
interactions at moderate temperature in two-dimensional
niobium-carbide-supported platinum catalysts. Nat. Catal. 2018, 1,
349-355.
Postdoctoral
2018M631444, and 2018M631486) and the National
Postdoctoral Program for Innovative Talents
(BX201700131). We thank the 1W1B station for XAFS
measurements in the Beijing Synchrotron Radiation Facility
(BSRF). We thank Tsinghua National Laboratory for
Information Science and Technology for providing grid
resources that have contributed to calculation results. Also,
we thank Dr. C. Zhang for the help in preparing this
manuscript.
Science
Foundation
(2018M631445,
REFERENCES
(1) Wang, A. Q.; Li, J.; Zhang, T., Heterogeneous single-atom
catalysis. Nat. Rev. Chem. 2018, 2, 65-81.
(2) Liu, X. F.; Li, X. Y.; Qiao, C.; Fu, H. C.; He, L. N., Betaine catalysis
for hierarchical reduction of CO2 with amines and hydrosilane to
form formamides, aminals, and methylamines. Angew. Chem. Int.
Ed. 2017, 56, 7425-7429.
(3) Zhang, L.; Han, Z. B.; Zhao, X.; Wang, Z.; Ding, K. l., Highly
efficient ruthenium-catalyzed N-formylation of amines with H2 and
CO2. Angew. Chem. Int. Ed. 2015, 54, 6186-6189.
(4) Handoko, A. D.; Wei, F.; Jenndy; Yeo, B. S.; Seh, Z. W.,
Understanding heterogeneous electrocatalytic carbon dioxide
reduction through operando techniques. Nat. Catal. 2018, 1, 922-
934.
(5) Wei, S. J.; Li, A.; Liu, J. C.; Li, Z.; Chen, W. X.; Gong, Y.; Zhang, Q.
H.; Cheong, W. C.; Wang, Y.; Zheng, L. R.; Xiao, H.; Chen, C.; Wang, D.
S.; Peng, Q.; Gu, L.; Han, X. D.; Li, J.; Li, Y. D., Direct observation of
noble metal nanoparticles transforming to thermally stable single
atoms. Nat. Nanotechnol. 2018, 13, 856-861.
(6) Chen, Z. P.; Vorobyeva, E.; Mitchell, S.; Fako, E.; Ortuno, M. A.;
Lopez, N.; Collins, S. M.; Midgley, P. A.; Richard, S.; Vile, G.; Perez-
Ramirez, J., A heterogeneous single-atom palladium catalyst
surpassing homogeneous systems for Suzuki coupling. Nat.
Nanotechnol. 2018, 13, 702-707
(21) Xie, X. H.; Chen, S. G.; Ding, W.; Nie, Y.; Wei, Z. D., An
extraordinarily stable catalyst: Pt NPs supported on two-
dimensional Ti3C2X2 (X = OH, F) nanosheets for oxygen reduction
reaction. Chem. Commun. 2013, 49, 10112-10114.
(22) Zhang, Z. W.; Li, H. N.; Zou, G. D.; Fernandez, C.; Liu, B. D.;
Zhang, Q. R.; Hu, J.; Peng, Q. M., Self-reduction synthesis of new
MXene/Ag composites with unexpected electrocatalytic activity.
ACS Sustain. Chem. Eng. 2016, 4, 6763-6771.
(23) Anasori, B.; Lukatskaya, M. R.; Gogotsi, Y., 2D metal carbides
and nitrides (MXenes) for energy storage. Nat. Rev. mater. 2017, 2,
16098.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 16
(24) Sang, X.; Xie, Y.; Lin, M. W.; Alhabeb, M.; Van Aken, K. L.;
(34) Das Neves Gomes, C.; Jacquet, O.; Villiers, C.; Thuery, P.;
Gogotsi, Y.; Kent, P. R. C.; Xiao, K.; Unocic, R. R., Atomic defects in
monolayer titanium carbide (Ti3C2Tx) MXene. ACS Nano 2016, 10,
9193-9200.
(25) Zhao, D.; Clites, M.; Ying, G. B.; Kota, S.; Wang, J.; Natu, V.; Wang,
X.; Pomerantseva, E.; Cao, M. H.; Barsoum, M. W., Alkali-induced
crumpling of Ti3C2Tx (MXene) to form 3D porous networks for
sodium ion storage. Chem. Commun. 2018, 54, 4533-4536.
(26) Xia, B. Y.; Wang, B.; Wu, H. B.; Liu, Z.; Wang, X.; Lou, X. W.,
Ephritikhine, M.; Cantat, T., A diagonal approach to chemical
recycling of carbon dioxide: Organocatalytic transformation for the
reductive functionalization of CO2. Angew. Chem. Int. Ed. 2012, 51,
187-90.
(35) Chalk, A. J.; Harrod, J. F., Homogeneous catalysis. II. The
mechanism of the hydrosilation of olefins catalyzed by group VIII
metal complexes. J. Am. Chem. Soc. 1965, 87, 16-21.
(36) Shen, J.; Yin, X.; Karpuzovb, D.; Semagina, N., PVP-stabilized
mono- and bimetallic Ru nanoparticles for selective ring opening.
Catal. Sci. Technol., 2013, 3, 208-221.
(37) Ophus, C., A fast image simulation algorithm for scanning
transmission electron microscopy. Adv. Struct. Chem. Imaging
2017, 3, 13, 92-101.
(38) Momma, K.; Izumi, F., VESTA 3 for three-dimensional
visualization of crystal, volumetric and morphology data. J. Appl.
Cryst. 2011, 44, 1272-1276.
1
2
3
4
5
6
7
8
Sandwich-structured
TiO2-Pt-graphene
ternary
hybrid
electrocatalysts with high efficiency and stability. J. Mater. Chem.
2012, 22, 16499-16505.
(27) Chen, Y. J.; Ji, S. F.; Sun, W.; Chen, W.; Dong, J. C.; Wen, J. F.;
Zhang, J.; Li, Z.; Zheng, L. R.; Chen, C.; Peng, Q.; Wang, D. S.; Li, Y. D.,
Discovering partially charged single-atom Pt for enhanced anti-
markovnikov alkene hydrosilylation. J. Am. Chem. Soc. 2018, 140,
7407-7410.
(28) Luo, Y. R.; Chen, G. F.; Ding, L., Chen, X. Z.; Ding, L. X.; Wang, H.
H.; Efficient electrocatalytic N2 fixation with MXene under ambient
conditions. Joule, 2018, 3, 1-11.
(29) Ran, J. R.; Gao, G. P.; Li, F. T.; Ma, T. Y.; Du, A. J.; Qiao, S. Z., Ti3C2
MXene co-catalyst on metal sulfide photo-absorbers for enhanced
visible-light photocatalytic hydrogen production. Nat. Commun.
2017, 8, 13907.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(30) Naguib, M.; Mochalin, V. N.; Barsoum, M. W.; Gogotsi, Y., 25th
anniversary article: MXenes: a new family of two-dimensional
materials. Adv. Mater. 2014, 26, 992-1005.
(31) Meng, C.; Ling, T.; Ma, T.Y.; Wang, H.; Hu, Z. P.; Zhou, Y.; Mao, J.;
Du, X. W.; Jaroniec. M.; Qiao, S. Z., Atomically and electronically
coupled Pt and CoO hybrid nanocatalysts for enhanced
electrocatalytic performance. Adv. Mater. 2017, 29, 201604607.
(32) Medford, A. J.; Vojvodic, A.; Hummelshøj, J. S.; Voss, J.; Abild-
Pedersen, F.; Studt, Felix.; Bligaard, T.; Nilsson, A.; Nørskov, J. K.,
From the Sabatier principle to a predictive theory of transition-
metal heterogeneous catalysis. J. Catal. 2015, 328, 36-42.
(33) Kobayashi, K.; Kikuchi, T.; Kitagawa, S.; Tanaka, K., Selective
generation of formamides through photocatalytic CO2 reduction
catalyzed by ruthenium carbonyl compounds. Angew. Chem. Int. Ed.
2014, 53, 11813-11817.
ACS Paragon Plus Environment

Page 9 of 16
Journal of the American Chemical Society
Table of Contents
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
9
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1
ACS Paragon Plus Environment

Page 11 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2
ACS Paragon Plus Environment

Page 13 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 14 of 16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4
ACS Paragon Plus Environment

Page 15 of 16
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5
445x883mm (72 x 72 DPI)
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 16 of 16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table of Contents
ACS Paragon Plus Environment