Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes

Article abstract of DOI:10.1016/j.chempr.2018.02.011

Surface and interfacial engineering of heterogeneous metal catalysts is effective and critical for optimizing selective hydrogenation for fine chemicals. By using thiol-treated ultrathin Pd nanosheets as a model catalyst, we demonstrate the development of stable, efficient, and selective Pd catalysts for semihydrogenation of internal alkynes. In the hydrogenation of 1-phenyl-1-propyne, the thiol-treated Pd nanosheets exhibited excellent catalytic selectivity (>97%) toward the semihydrogenation product (1-phenyl-1-propene). The catalyst was highly stable and showed no obvious decay in either activity or selectivity for over ten cycles. Systematic studies demonstrated that a unique Pd-sulfide/thiolate interface created by the thiol treatment was crucial to the semihydrogenation. The high catalytic selectivity and activity benefited from the combined steric and electronic effects that inhibited the deeper hydrogenation of C=C bonds. More importantly, this thiol treatment strategy is applicable to creating highly active and selective practical catalysts from commercial Pd/C catalysts for semihydrogenation of internal alkynes. The development of next-generation catalytic materials requires a methodological shift from trial-and-error to mechanism-directed design. It is highly desirable to build model catalyst systems with simplified structures to ensure maximized utilization of both state-of-the-art characterization tools and computational chemistry methods. In this work, thiol-treated palladium nanosheets are adopted as a model catalyst for the selective semihydrogenation of internal alkynes. Unexpectedly, thiol treatment created highly selective palladium catalysts with high activity toward the semihydrogenation reaction. The ultrathin nature of the as-prepared catalysts allows for the application of a variety of surface science and computational methods to resolve the complexity of metal-organic interfaces and thus elucidate the underlying mechanism. Driven by atomic-level understanding, we have realized practical, lead-free catalysts for semihydrogenation. Thiol treatment is demonstrated as a highly effective strategy for promoting the catalytic selectivity of Pd nanocatalysts in the hydrogenation of internal alkynes to alkenes.

Full text of DOI:10.1016/j.chempr.2018.02.011

Article
Thiol Treatment Creates Selective Palladium
Catalysts for Semihydrogenation of Internal
Alkynes
Xiaojing Zhao, Lingyun Zhou,
Wuyong Zhang, ..., Binghui Wu,
Gang Fu, Nanfeng Zheng
gfu@xmu.edu.cn (G.F.)
nfzheng@xmu.edu.cn (N.Z.)
HIGHLIGHTS
Thiol-treated ultrathin Pd
nanosheets are used as a model
catalyst
The catalyst exhibits both high
activity and selectivity in alkyne
semihydrogenation
Both steric and electronic effects
contribute to the enhanced
selective hydrogenation
Practical Pd catalysts for
semihydrogenation of internal
alkynes are prepared
Thiol treatment is demonstrated as a highly effective strategy for promoting the
catalytic selectivity of Pd nanocatalysts in the hydrogenation of internal alkynes to
alkenes.
Zhao et al., Chem 4, 1–12
May 10, 2018 ª 2018 Elsevier Inc.
https://doi.org/10.1016/j.chempr.2018.02.011

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
Article
Thiol Treatment Creates Selective
Palladium Catalysts for Semihydrogenation
of Internal Alkynes
Xiaojing Zhao,1,2 Lingyun Zhou,1,2 Wuyong Zhang, Chengyi Hu, Lei Dai, Liting Ren, Binghui Wu,
1
1
1
1
1
Gang Fu, * and Nanfeng Zheng1,3,*
1,
The Bigger Picture
SUMMARY
The development of next-
Surface and interfacial engineering of heterogeneous metal catalysts is effec-
tive and critical for optimizing selective hydrogenation for fine chemicals. By
using thiol-treated ultrathin Pd nanosheets as a model catalyst, we demonstrate
the development of stable, efficient, and selective Pd catalysts for semihydro-
genation of internal alkynes. In the hydrogenation of 1-phenyl-1-propyne, the
thiol-treated Pd nanosheets exhibited excellent catalytic selectivity (>97%)
toward the semihydrogenation product (1-phenyl-1-propene). The catalyst
was highly stable and showed no obvious decay in either activity or selectivity
for over ten cycles. Systematic studies demonstrated that a unique Pd-sulfide/
thiolate interface created by the thiol treatment was crucial to the semihydroge-
nation. The high catalytic selectivity and activity benefited from the combined
steric and electronic effects that inhibited the deeper hydrogenation of C=C
bonds. More importantly, this thiol treatment strategy is applicable to creating
highly active and selective practical catalysts from commercial Pd/C catalysts for
semihydrogenation of internal alkynes.
generation catalytic materials
requires a methodological shift
from trial-and-error to
mechanism-directed design. It is
highly desirable to build model
catalyst systems with simplified
structures to ensure maximized
utilization of both state-of-the-art
characterization tools and
computational chemistry
methods. In this work, thiol-
treated palladium nanosheets are
adopted as a model catalyst for
the selective semihydrogenation
of internal alkynes. Unexpectedly,
thiol treatment created highly
selective palladium catalysts with
high activity toward the
INTRODUCTION
Selective hydrogenation lies at the heart of industrial manufacture of fine chemicals,
1
–4
pharmaceuticals, nutraceuticals, and agrochemicals.
To achieve a high yield of
semihydrogenation reaction. The
ultrathin nature of the as-
target product in an economical, energy-saving, and environmentally benign way,
more and more attention has been paid to developing sustainable catalysts for
prepared catalysts allows for the
application of a variety of surface
science and computational
5
–8
selective hydrogenation.
As for heterogeneous metal catalysts, the enhanced
catalytic selectivity is mainly attributed to the electronic effects as a result of pertur-
bation of the metal coordinative environment and/or steric effects induced by
methods to resolve the
9
–13
surface modifiers.
Currently, two major approaches are used to tailor heteroge-
complexity of metal-organic
interfaces and thus elucidate the
underlying mechanism. Driven by
atomic-level understanding, we
have realized practical, lead-free
catalysts for semihydrogenation.
neous catalysts for selective hydrogenation: (1) the construction of multimetallic
nanomaterials that provide ensemble control and electronic contributions for the
adsorption of reactants and products and (2) the surface modification of metal nano-
particles for regulating the metal-organic interaction and thus improving the cata-
1
4,15
lytic selectivity.
academia and industry,
well established because of the complexity of additives (often toxic), the diverse sur-
Although the approaches have been applied for decades in
1
6,17
the structure-activity relationship has not yet been
1
8–21
faces, and the mysterious interface structure.
In the fine chemical industry, selective hydrogenation of carbon-carbon triple bonds
to carbon-carbon double bonds is a great challenge. The common industrial cata-
2
0,22–31
lysts for alkyne hydrogenation are palladium-based catalysts.
The surfaces
Chem 4, 1–12, May 10, 2018 ª 2018 Elsevier Inc.
1

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
of Pd catalysts are usually passivated to prevent deep hydrogenation. With this strat-
egy, Lindlar catalyst, a Pd/CaCO
3
-based catalyst modified by a combination of both
organic (quinoline) and inorganic (lead) additives, has been developed and widely
3
2
used in industry for decades. Both the poor activity and the presence of toxic
additives make the Lindlar catalyst not ideal for many industrial processes. Inspired
by the Lindlar catalyst, increasing results have shown that surface modification of Pd
or Pt catalysts can create a metal-organic interface that enhances their catalytic per-
3
formance. The promotional effect of surface thiolates on the performance of Pd
nanocatalysts has been reported repeatedly. For instance, Medlin and co-workers
have demonstrated that the catalytic properties of Pd and Pt catalysts can be well
3
3–36
controlled by coating n-alkane thiols on their surfaces.
of thiols or other sulfur-containing species in promoting palladium catalysis has been
Although the importance
3
7–39
well understood in some Pd-complex systems,
determination of the detailed
surface and interface structure of thiolated-protected Pd nanocatalysts, and thus un-
derstanding the molecular mechanism behind the catalytic enhancements, remains
challenging.
By using ultrathin Pd nanosheets (Pd NSs) as the metal substrate, we demonstrate
here at the molecular level how thiols modify the surface of Pd nanocatalysts
to dramatically enhance the selective hydrogenation of alkynes into alkenes.
The ultrathin nature of Pd NSs makes it feasible to directly visualize the change
in the surface structure of Pd NSs upon their reaction with thiols via electron
microscopy. Our comprehensive characterizations reveal that upon adsorption,
C–S bonds in thiols can be cleaved, forming a Pd surface modified with both
thiolates and sulfides. Such a sulfide/thiolate modification creates both steric
and electronic effects to prevent the hydrogenation of alkene intermediates
during alkyne hydrogenation, endowing the modified Pd surface with high catalytic
selectivity toward alkenes. With such an understanding, we have developed
a facile strategy for preparing highly selective and stable Pd catalysts for semihy-
drogenation of internal alkynes by simply treating commercial Pd catalysts with
thiols.
RESULTS
Synthesis and Structure Characterizations of Thiolate-Protected Pd
Nanosheets
To create a model metal catalyst with metal-thiol interfaces that can be characterized
in full, we chose ultrathin two-dimensional Pd NSs as the metal substrate for thiol sur-
4
0
face modification in this work. The ultrathin feature offers a high fraction of surface
Pd atoms and thus allows the extraction of Pd-thiol interface structure information by
spectroscopic techniques that normally collect both surface and bulk signals. In this
study, uniform hexagonal Pd NSs (1.8-nm thick) with a diameter of 80 nm (Figure S1A)
were prepared by a CO-assisted method. The Pd NSs were then mixed with 3,4-di-
fluorothiol (HSPhF
2
) in N,N-dimethylformamide (DMF) to induce thiol surface modi-
ꢀ
fication. The molar ratio of HSPhF
2
/Pd was 1:1. The mixture was kept at 60 C for
1State Key Laboratory for Physical Chemistry of
Solid Surfaces, Collaborative Innovation Center
of Chemistry for Energy Materials, and
Department of Chemistry, College of Chemistry
and Chemical Engineering, Xiamen University,
Xiamen 361005, China
1
2 hr before being cooled down to room temperature and centrifuged for collection
of the product (see Supplemental Information). The as-modified Pd NSs were de-
noted as Pd@SPhF (1:1). As revealed by transmission electron microscopy (TEM)
Figure 1A), the hexagonal shape of the original Pd NSs was heavily deformed after
the thiol treatment.
2
(
2These authors contributed equally
3Lead Contact
The structure of the thiol-modified Pd NSs was characterized by various techniques.
Lattice fridges of Pd 1/3(422) were clearly observed in the high-resolution TEM
*
Correspondence: gfu@xmu.edu.cn (G.F.),
nfzheng@xmu.edu.cn (N.Z.)
(
HRTEM) image of Pd NSs (inset of Figure S1A), but it became impossible to
https://doi.org/10.1016/j.chempr.2018.02.011
2
Chem 4, 1–12, May 10, 2018

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
A
B
C
Pd
1
nm
S
overlap
5
0 nm
D
E
F
Figure 1. Structure Evolution of Pd NSs by Thiol Treatment and Their Catalytic Performance
A–C) TEM and HRTEM images of Pd@SPhF (1:1) (A) and TEM and HRTEM images (B) and EDX mapping images (C) of an individual Pd@SPhF
nanoparticle.
(
2
2
(1:1)
(
(
(
D) Catalytic performance of semihydrogenation of 1-phenyl-1-propyne with different Pd catalysts.
E) Catalytic selectivity in semihydrogenation of 1-phenyl-1-propyne with different Pd catalysts.
2
F) Catalytic stability and selectivity of the Pd@SPhF (1:1) obtained.
2
distinguish lattice fringes on Pd@SPhF (1:1) from random noise because of their
poor crystalline nature. After the reaction with thiol, the color of the Pd NSs solution
changed from blue to dark gray with the disappearance of the broad peak at
1
,100 nm in the ultraviolet-visible (UV-vis) spectrum (Figure S1B), demonstrating
that their ultrathin metallic feature was altered. Moreover, as shown in the X-ray
ꢀ
diffraction pattern of Pd@SPhF
2
(1:1), the Pd(111) peak at 40 was dramatically
broadened, and the other diffraction peaks became negligible as a result of the
formation of palladium sulfide on the surface of Pd NSs (Figures S1C and S1D).
2
Simultaneously, the poor crystallinity of Pd@SPhF (1:1) was observed in the HRTEM
analysis. High-angle annular dark field scanning transmission electron microscopy
and energy-dispersive X-ray (EDX) elemental mapping (Figures 1B and 1C) revealed
2
that both Pd and S were uniformly distributed throughout the Pd@SPhF (1:1).
All these results demonstrate that the thiol modification heavily modulated the
surface structure of Pd NSs. Because of the ultrathin nature of Pd NSs, such a struc-
ture modulation readily induced an obvious morphological change that was detect-
able by TEM. It would be impossible to directly visualize the structure changes
caused by surface ligand modification if Pd nanoparticles were used as the metal
substrate.
Chem 4, 1–12, May 10, 2018
3

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
High Catalytic Selectivity of Thiolate-Protected Pd Nanosheets in
Hydrogenation of 1-Phenyl-1-propyne
The change in the structure and composition of Pd NSs is expected to influence their
catalysis. Surprisingly, after the thiol treatment, Pd NSs readily served as a highly se-
lective catalyst for the semihydrogenation of internal alkynyl compounds. When
1
-phenyl-1-propyne was chosen as the model substance, as shown in Figures 1D
and 1E, Pd@SPhF (1:1) exhibited an excellent selectivity of 98.1% toward
-phenyl-1-propene at a conversion of 100% that was achieved within 50 min. In
2
1
comparison, when the conversion of 1-phenyl-1-propyne reached 100%, the selec-
tivity of the semihydrogenation product was only 30.5% over unmodified Pd NSs. In
contrast, the Lindlar catalyst showed better selectivity than Pd NSs. But the main
problem for the Lindlar catalyst is its low conversion rate. The conversion of
1
-phenyl-1-propyne only reaches 25% within 70 min of the reaction. More impres-
sively, no obvious decay in semihydrogenation selectivity was observed even after
full conversion when Pd@SPhF (1:1) was used. The selectivity was maintained at
97% in the ten cycles of catalysis in which very little decay in the activity was
2
ꢁ
observed (Figure 1F). In comparison, Pd NSs maintained good activity in the five
catalysis cycles, but displayed poor selectivity toward the semihydrogenation prod-
uct (Figure S2A). When the Lindlar catalyst was used, an obvious decay in activity was
2
observed although the selectivity was high (Figure S2B). Overall, Pd@SPhF (1:1) ex-
hibited much better performance in the semihydrogenation of 1-phenyl-1-propyne
than both unmodified Pd NSs and the Lindlar catalyst.
The enhanced catalytic selectivity motivated us to understand how the surface thiol
modification modulates hydrogenation catalysis. The morphological transformation
process of Pd NSs caused by surface thiol modification was first investigated by anal-
ysis of Pd NSs collected at different reaction times by TEM (Figures S3A–S3E). It was
clearly revealed that the deformation process was initiated at the edges of the Pd
NSs. Although only the edges became thicker at 0.5 hr, edge distortion was
observed at 1.5 hr. The distortion process continued until 3 hr, beyond which no
further morphological change was observed. Similarly, the optical absorption
peak of the Pd NSs gradually decreased with the reaction time and disappeared af-
ter 3 hr (Figure S3F), consistent with the TEM observations. As revealed by the time-
dependent EDX analysis (Figure S4), the sulfur content in the NSs increased with the
reaction time and eventually reached ꢁ25%. Moreover, the final morphology of Pd
NSs depended on the SPhF
by TEM and UV-vis analyses (Figure S5), whereas only edge deformation was
observed with SPhF /Pd ratios of 0.2 and 0.5, extensive distortion took place with
the SPhF /Pd ratio > 1. When the SPhF /Pd ratio increased from 0.2 to 0.5 to 1 to
2
/Pd ratio used in the modification process. As revealed
2
2
2
5
3
to 10, the S/Pd ratio in the modified NSs increased by 12%, 21%, 26%, and
0%–32% (Figure S6). The sulfur content was not linearly increased with the
SPhF
beyond 1, the content of S did not increase much. The catalytic performance of
different ratios of SPhF /Pd is given in Figure S7. With an increased amount of thiol,
the activity of the catalyst decreased and the selectivity increased. Interestingly,
Pd@SPhF (1:1) exhibited both high reactivity and high selectivity.
2 2
/Pd ratio used in the modification. When the SPhF /Pd ratio was increased
2
2
Considering the large size of SPhF
high S/Pd ratio on Pd@SPhF (1:1) suggested that S species should not be limited
to SPhF only. In order to study the nature of S, we extensively characterized the
as-obtained Pd@SPhF NSs by various means. Although the presence of SPhF on
2
, its coverage on Pd cannot be high. The rather
2
2
2
2
Pd was confirmed by Fourier transform infrared spectroscopy (Figure S8), a temper-
ature-programmed decomposition-mass spectrometry (TPD-MS) study illustrated
4
Chem 4, 1–12, May 10, 2018

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
A
B
C
D
Å
2
Figure 2. Structure Analysis of the Distorted Pd@SPhF (1:1)
High-resolution XPS spectra of (A) the S 2p region and (B) the Pd 3d region and (C) Pd K-edge
XANES and (D) FT-EXAFS spectra of the sample in comparison with untreated Pd nanosheets and
Pd foil.
that SPhF
2
on Pd underwent SÀC bond cleavage to release PhF
2
upon thermal treat-
ment (Figure S9). Considering that temperature could have a great influence on S–C
bond cleavage, the reaction was also conducted at room temperature for analysis of
ꢀ
the temperature effect. Compared with the product obtained at 60 C, only the edge
of Pd NSs was crimped at room temperature (Figure S10A). Moreover, when Na
2
S
was used to replace thiol, Pd NSs were heavily distorted as well (Figure S10B), indi-
2
À
cating that S generated by C–S cleavage should be responsible for the deforma-
tion of the Pd NSs. The low activity and high selectivity of Pd@Na S(1:1) (Figure S11)
suggested that the sulfide-treated Pd NSs were overpassivated by S
2
2
À
.
2
À
The X-ray photoelectron spectroscopic (XPS) data confirmed the co-presence of S
and thiolate on the thiol-treated Pd NSs. The overall S/Pd ratio of Pd@SPhF (1:1) was
estimated to be 27%, consistent with the EDX result. In the XPS spectra of S 2p (Fig-
2
2
À
ure 2A), two main sulfur components at 162.9 and 163.8 eV were assigned to S and
À
2À
À
2À
SR , respectively. The S /SR ratio was estimated to be 3.6. The presence of S
verified the S–C bond cleavage in the thiol modification process. Moreover,
the binding energy of Pd 3d in distorted Pd NSs displayed a slight shift toward
higher binding energy than that of unmodified NSs, indicating that Pd had been
partial oxidized (Figure 2B). The peaks at 336.7 and 342.2 eV were assigned to
2
+
2+
Pd 3d5/2 and Pd 3d3/2, respectively (Figure S12). Moreover, the XPS spectra of
Chem 4, 1–12, May 10, 2018
5

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
2 2
different ratios of SPhF /Pd showed that, with the increased amount of SPhF , the
2
À
À
ratio of S /SR was increased and eventually converged to about 1:5 (Figure S13).
We proposed that the cleavage of C–S began at the edge and then the generated
2
À
S
entered into the lattice of Pd NSs to form Pd
NSs were eventually fully converted into Pd S, whereas their surfaces were saturated
by thiolate groups such that the ratio of SPhF /Pd reached a constant. To better un-
x 2
S. With increasing HSPhF , Pd
x
2
derstand the local environment of Pd, we further characterized the distorted Pd
NSs by X-ray absorption fine structures (XAFS). Although Pd K-edge X-ray absorp-
2
tion near-edge structure spectrum (XANES) of Pd@SPhF (1:1) revealed the slightly
oxidized nature of Pd (Figure 2C), the extended XAFS spectrum demonstrated that
the coordination environment of Pd experienced a dramatic change upon thiol
treatment (Figure 2D). Although the Pd-Pd coordination number was decreased
from 9.7 to 4.7, a Pd-S scattering path appeared with the coordination number
2
of 1.7. The Debye-Waller factor (s ) of Pd-Pd correlation increased from 6.2 to
1
2.3 after the thiol treatment, indicating the increase of local disorder in the Pd lat-
tice (Figure S14 and Table S1). These data demonstrate that sulfur atoms entered
the first coordination shell around Pd atoms after the thiol treatment, yielding Pd
x
S
species. To further characterize the 3D distribution of Pd and S elements, we used
high-sensitivity low-energy ion scattering spectroscopy (Figure S15). Even with the
increased depth detected, enabled by Ar ion sputtering, the presence of sulfur
2
À
species was still revealed, indicating the incorporation of S into the inner lattice
of Pd.
Mechanism of the High Catalytic Selectivity by Thiolate-Protected Pd
Nanosheets
To gain insight on how the thiol treatment enhanced hydrogenation selectivity, we
performed periodic density functional theory (DFT) calculations (see Supplemental
Information for computational details). The calculation results showed that cleavage
of the C–S bond was able to take place on both Pd(111) and Pd(100) planes by
2
À
overcoming a barrier of ꢁ0.7 eV to deposit S thereon (Figures S16 and S17). As
previously reported, with increasing exposure to S-containing compounds, the as-
generated atomic S would be incorporated into the subsurface region, yielding
4
1,42
the palladium-sulfide interphase.
termediate sulfide states, such as Pd
tivity toward the hydrogenation, whereas the catalyst would be deactivated
Ni and co-workers also pointed out that the in-
4
S, Pd S, and Pd16 , still have high catalytic ac-
3
S
7
4
3
completely when Pd was fully transformed into PdS. Here, we used Pd
and Pd S(100) coated with HSPhF as models for Pd@SPhF (1:1) because they had
the lowest surface energy among the low Miller index facets (Tables S3 and S4;
Figures S18–S21). To be consistent with the experimental nomenclature, HSPhF
modified Pd S(110) and Pd S(100) surfaces are denoted as Pd S@SPhF and
Pd S@SPhF , respectively. These two models had similar composition and chemical
environment to those of Pd@SPhF (1:1) (Table S5). We used both models to explore
the observed high catalytic selectivity in the hydrogenation of internal alkynes
Figure 3A).
4
S(110)
3
2
2
2
-
4
3
4
2
3
2
2
(
To understand why the catalytic selectivity of thiol-treated Pd NSs was better than
the unmodified ones, we compared the hydrogenation of PhChCCH over
Pd S@SPhF , Pd S@SPhF and bare Pd NSs. We assumed that all sides of the slabs
3
4
2
3
2
4
4
were saturated with hydrogen under the hydrogenation conditions. Catalytic hy-
drogenations generally follow the so-called Horiuti-Polanyi mechanism with a step-
wise scheme involving the combination of co-adsorbed unsaturated hydrocarbon
molecules and hydrogen atoms. On the basis of this mechanism, previous studies
have proposed that a good catalyst for alkyne semihydrogenation should have a
6
Chem 4, 1–12, May 10, 2018

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
A
C
Pd
4
S@SPhF
S@SPhF
2
2
0
.88
0
.85
Pd3
0.8
0.6
0.4
0.2
0.0
Pd(111)
0
.72
0
.64
0
.63
0
.55
.61
0
0
.54
0
.48
0
.42
0
.41
0
.25
Pd
C
S
F
S
H
TS1
TS2
TS3
TS4
B
CʆC hydrogenation
C=C hydrogenation
IV
TS1
TS3
0
ꢂ55
0
.00
PhC CCH
.&Slab
H
TS2
0ꢂ14
3
ꢁ
H
H
H
ꢀ
I
Pd
4
S
Pd
4
S
ꢁ
I
0ꢂ68
TS3
ꢁ0ꢂ96
CH
H
3
TS1
PhC CCH
3
Ph
TS4
1ꢂ63
H
II
III
H
Pd
H
S
CH3
ꢁ
IV
2ꢂ04
4
P Pd d
4
S
ꢁ1.88 ꢁ1ꢂ84
ꢁ
II
TS4
V
TS2
PhCH
2
CH
2
CH
3
P
h
H
H
V
3ꢂ45
H
H
Pd
ꢁ
Pd
4
S
Pd
4
S
4
S
Pd S
4
Reaction Coordinate
Figure 3. Mechanism of Catalytic Selectivity of Thiolate-Treated Pd NSs
(
(
A) Constructed theoretical model of the Pd
4 2
S@SPhF surface.
B) Energies of intermediates and transition states in the mechanism of PhChCCH
3
4 2
stepwise hydrogenation on the Pd S@SPhF surface from DFT
calculations.
C) Energy barriers of transition states of PhChCCH
(
3
hydrogenation on Pd
4
2 3 2
S@SPhF , Pd S@SPhF , and Pd(111).
4
4–46
higher barrier for the hydrogenation of alkene than its desorption barrier.
ever, in our case, neither PhChCCH nor PhCH = CHCH was able to adsorb on the
hydrogen saturated surface so that hydrogenation could occur via an Eley-Rideal
How-
3
3
4
7
(
ER) type mechanism. Through the ER mechanism, unsaturated hydrocarbon mol-
ecules react with adsorbed hydrogen atoms directly. As illustrated in Figure 3B, the
first hydrogenation step (ChC to C=C) on Pd S@SPhF involved two transition
4
2
states (TS) (TS1 by the addition of the first hydrogen atom and TS2 by the addition
of the second one) and a semihydrogenated intermediate (I) of ChC hydrogenation.
The second step (C=C to C–C) also proceeded through TS3 and TS4 by the addition
of the third and fourth hydrogen atom, respectively, and one semihydrogenated in-
termediate (IV) of C=C hydrogenation. Obviously, a good semihydrogenation cata-
lyst should promote the first hydrogenation step but inhibit the second one.
Chem 4, 1–12, May 10, 2018
7

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
Figure 3C shows the calculated barriers for the four transition states during the
hydrogenation of PhChCCH
3
. The reaction energy profiles and the structures of
S@SPhF Pd S@SPhF , and
key transition states and intermediates on Pd
4
2
,
3
2
Pd(111) surfaces are shown in Figures S22–S26. It is clear that forming the
semihydrogenated intermediate requires a higher barrier than its further hydro-
genation. In other words, for the given catalyst, TS1 (or TS3) was higher than
TS2 (or TS4). Thus, we used the difference in energy (DETS) between TS3 and
TS1 to estimate the selectivity of semihydrogenation. DFT calculations demon-
strated that DETS values for Pd
.24 eV, respectively, higher than that on bare Pd(111) surface (0.09eV), nicely ex-
plaining why the selectivities of C=C on Pd S@SPhF and Pd S@SPhF were better
4 2 3 2
S@SPhF and Pd S@SPhF were 0.33 and
0
4
2
3
2
than on Pd NSs. Through energy decomposition analysis (see details in Table S6),
we found that such a significant difference in barrier mainly originated from
DEdef(S), the surface deformation energy. Close inspection on the transition-
state structures revealed that thiolate groups had to deviate from the original
structure to accommodate the alkene molecule (TS3), whereas the thiolate groups
nearly maintained their structures when the alkyne molecule approached the sur-
face (TS1). That is to say, it was the steric hindrance making the significant differ-
ence in DETS. Better adsorption of 1-phenyl-1-propyne on the H-free thiol-treated
Pd@SPhF
2
(1:1) nanosheets than 1-phenyl-1-propene was observed experimentally
(
Figure S27).
Because the hydrogenation occurred via the ER mechanism, the reactivity critically
depended on the adsorption energy of H. According to our calculations, the
average adsorption energies of H on Pd
and À0.03 eV, respectively, significantly weaker than that on Pd(111) (À0.52 eV).
Nevertheless, H dissociation was still feasible on the modified Pd surfaces. The
calculated barriers for the cleavage of the H–H on Pd S@SPhF and Pd S@SPhF
2
4
S@SPhF
2
and Pd
3
S@SPhF
2
were À0.05
2
4
2
3
were predicted to be 0.55 and 0.33 eV, respectively (Figure S28). The weaker
binding of H on thiol-treated Pd than on bare Pd can be attributed to the strong
2
À
electronic effects induced by the presence of surface S
determined by CO titration, the percentage of catalytic sites over the total Pd
sites in Pd@SPhF (1:1) was lower than that over Pd NSs (6% versus 20%). But
compared with that of Pd NSs, the hydrogenation activity of Pd@ SPhF (1:1) in
and thiolates. As
2
2
the selective hydrogenation of alkynes was not reduced much (Figure 1C).
We consider the weaker adsorption of H as the main reason for the observed
excellent hydrogenation activity of Pd@SPhF
‘poisoning’’ agents.
2
(1:1) despite the presence of surface
‘
More interestingly, our DFT calculations also predicted that the major hydrogena-
tion product of PhChCCH should be cis-PhCH=CHCH . The rotation barrier of
cis-SHI1 was as high as 1.41 eV so that forming trans-I was kinetically inhibited (Fig-
3
3
1
ure S29). Impressively, the H NMR data confirmed cis-PhCH=CHCH
product when the thiol-treated Pd NSs were used as the catalyst (Figure S30). More-
over, DFT calculations also indicated that hydrogenation selectivity on Pd S@SPhF
surface should be quite different between internal and terminal alkynes. For
instance, in the hydrogenation of PhChCH on the Pd S@SPhF surface, the pre-
3
as the major
4
2
4
2
dicted barrier for TS3 was only 0.65 eV (Figure S31), which was close to that of
TS3 on an unmodified Pd(111) surface (0.61 eV) (Figure S32). This indicates that
deep hydrogenation would take place when terminal alkynes are used as substrates.
Experimentally, when phenylacetylene was used, the selectivity toward styrene was
reduced to only 60.5% at 100% conversion of phenylacetylene (Figure S33), echoing
the prediction from the DFT calculations.
8
Chem 4, 1–12, May 10, 2018

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
A
modified Pd/C
R
R'
R
R'
1
atm H2
modified Pd/C
Pd/C
B
100
75
50
25
0
R= Ph
R= Ph
R= Ph
R= Ph
R= C3H7
R'= CH3
R'= C3H7 R'= COOCH3 R'= COCH3 R'= C3H7
Figure 4. Optimization of Commercial Pd Catalysts via Thiol Treatment
(
(
A) Schematic diagram of internal alkyne hydrogenation.
B) Comparison of the catalytic performances for hydrogenation of substituted internal alkynes
2
over commercial Pd/C before and after HSPhF treatment.
DISCUSSION
2
À
À
The above studies demonstrate that the surface modification of both S and RS
on Pd resulted from the reaction between thiols and Pd NSs and was essential to
the selective hydrogenation of alkynes to alkenes. We thus expected that treating
conventional Pd nanoparticulate catalysts, such as Pd/C, with thiols should be an
effective method of preparing highly selective catalysts for semihydrogenation of
internal alkynes to alkenes. Experimentally, when Pd/C was treated with HSPhF
2
ꢀ
at 60 C, the modified catalyst turned out to be an efficient and selective catalyst
for the semihydrogenation of 1-phenyl-1-propyne. In this case, there was no
obvious change in the catalyst’s morphology (Figure S34). The selectivity of the
modified catalyst was also evaluated in the hydrogenation reactions of other inter-
nal alkynes (i.e., 1-phenyl-1-pentyne, methyl phenylpropiolate, 4-phenyl-3-butyn-
2
-one, 4-octyne). Compared with the unmodified Pd/C, the modified catalyst
exhibited dramatically enhanced selectivity toward alkene products (Figure 4).
Over the modified catalyst, the selectivity at 100% conversion was 96%, 92%,
9
4%, and 95% for 1-phenyl-1-pentyne, methyl phenylpropiolate, 4-phenyl-3-
butyn-2-one, and 4-octyne, respectively (Figure S35). In comparison, the unmodi-
fied Pd/C gave poor selectivities of 32%, 10%, 36%, and 13%, respectively, under
the same conditions (Figure S36).
These results further confirm the effectiveness of simple thiol treatment for promot-
ing the catalytic selectivity of Pd nanocatalysts in the hydrogenation of internal
alkynes to alkenes. Such an organic modification strategy is expected to not only
provide a new research direction in engineering the surface of metal nanocatalysts
Chem 4, 1–12, May 10, 2018
9

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
for fine chemical industries but also extend our understanding of the surface coordi-
4
8
nation chemistry of metal nanomaterials.
EXPERIMENTAL PROCEDURES
Synthesis of Pd Nanosheets
2
Pd(acac) (50.0 mg), polyvinylpyrrolidone (160.0 mg), and tetra-n-butylammonium
bromide (160 mg) were mixed together with DMF (10 mL) and water (2 mL) in a glass
pressure vessel. The vessel was then charged with CO to 1 bar, heated from room
ꢀ
ꢀ
temperature to 60 C in 0.5 hr, and then kept at 60 C for another 2.5 hr before it
was cooled to room temperature. The dark blue products were precipitated by
acetone, separated via centrifugation, and further purified by an ethanol-acetone
mixture.
Synthesis of Different Ratios of Pd@SPhF
2
(1:0.2, 1:0.5, 1:1, 1:5, 1:10)
A Pd nanosheet stock solution (1 mL, 0.0137 mmol Pd) was precipitated by acetone
2
and then dispersed in 5 mL of DMF in a glass vial. HSPhF (0.3, 0.75, 1.5, 7.5, or
ꢀ
1
5 mL) was added into the mixture and then heated to 60 C for 12 hr. The products
were collected by centrifugation with acetone. The products were dispersed in
ethanol for further use.
Characterization
TEM studies were performed on a TECNAI F-30 high-resolution transmission elec-
tron microscope operating at 300 kV. The samples were prepared by dropping an
ethanol dispersion of samples onto 300-mesh carbon-coated copper grids and
immediately evaporating the solvent. All the UV-vis absorption spectra were taken
on a Cary 5000 Scan UV-vis-near-infrared spectrophotometer (Varian) with ethanol
as the solvent. Gas chromatography analyses were performed with a FuLi 9790II,
equipped with a split/splitless injector, a capillary column (KB-5, 30 m 3
0
.32 mm30.33 mm), and a flame ionization detector.
X-Ray Absorption Spectroscopy Measurements
The X-ray absorption spectra at the Pd K-edge were recorded at room temperature
in transmission mode with ion chambers at Beamline BL14W1 of the Shanghai Syn-
chrotron Radiation Facility in China. The station was operated with a Si(311) double
crystal monochromator. During the measurement, the synchrotron was operated at
energy of 3.5 GeV and a current between 150 and 210 mA. The photon energy was
calibrated with the first inflection point of Pd K-edge in Pd metal foil. The as-ob-
tained X-ray absorption spectroscopy data were processed with WinXAS version
3
.11. Reliable parameter values, such as bond distances, coordination numbers,
etc., were determined via multiple-shell R-space fitting of Pd spectra.
TPD-MS Studies of Pd@SPhF
The TPD-MS experiment was performed on a home-made TPD-time-of-flight (TOF)
analyzer. A 3 mg sample of Pd@SPhF (1:1) was pyrolyzed in a small tube heated by
2
2
heating coil. A K-type thermocouple was put inside the sample tube and insulated
from the samples for measuring the temperature. The heating coil was powered
by a precise electric source and adjusted at intervals of 10 mV. The temperature
ꢀ
of the sample tube was ramped from room temperature to 800 C smoothly at a
speed of 5 K/min controlled by computer. The desorbed species were ionized by
a UV lamp at a position very close to the sample tube with phonon energy of
1
0.6 eV and then transferred to the TOF analyzer by an ion optical system. The
TOF analyzer had a resolution of more than 5,000 and a sensitivity at ppb level.
À5
All these steps were processed in high vacuum at about 3 3 10 Pa. The mass
10
Chem 4, 1–12, May 10, 2018

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
spectrum and sample temperature were acquired and recorded every second. Each
spectrum is an accumulation of 10,000 spectra gathered at intervals of 100 s.
1
-Phenyl-1-propyne Hydrogenation
The hydrogenation of 1-phenyl-1-propyne was carried out in a well-stirred glass
ꢀ
pressure vessel (48 mL) at 30 C with stirring. A mixture of 0.05 mg of catalyst
(
Pd) and 1 mmol of substrate was dispersed in 10 mL of ethanol in the pressure
vessel. H flow was applied into the vessel for several minutes to remove oxygen.
The vessel was then pressurized by 1.0 bar H . The reaction proceeded, and
2
2
samples were withdrawn at regular intervals, filtered, and analyzed by gas chroma-
tography. The product identity was further confirmed by gas chromatography-mass
spectrometry.
SUPPLEMENTAL INFORMATION
Supplemental Information includes Supplemental Experimental Procedures, 36 fig-
ures, and 6 tables and can be found with this article online at https://doi.org/10.
1
016/j.chempr.2018.02.011.
ACKNOWLEDGMENTS
We acknowledge financial support from the Ministry of Science and Technology of
China (2017YFA0207302 and 2015CB932303), the National Nature Science Founda-
tion of China (21731005, 21420102001, 21390390, 21333008, 21373167, and
2
1573178), and the Fundamental Research Funds for the Central Universities
(
20720160046). We also thank the XAFS station (BL14W1) of the Shanghai Synchro-
tron Radiation Facility.
AUTHOR CONTRIBUTIONS
N.F.Z. conceived the idea. N.F.Z., X.J.Z., L.Y.Z., and G.F. co-wrote the paper. X.J.Z.
synthesized the nanomaterials and carried out the catalysis experiments. G.F. and
L.Y.Z. carried out the model construction and DFT calculations. W.Y.Z., C.Y.H.,
L.D., and L.T.R processed the relevant data. B.H.W. analyzed part of the data and
polished the writing of the paper. All the authors contributed to the overall scientific
interpretation and edited the manuscript.
DECLARATION OF INTERESTS
The authors declare no competing interests.
Received: September 19, 2017
Revised: November 7, 2017
Accepted: February 13, 2018
Published: March 22, 2018
REFERENCES AND NOTES
1
. Swiegers, G.F. (2008). Heterogeneous,
Homogeneous, and Enzymatic Catalysis. A
Shared Terminology and Conceptual
Platform. The Alternative of Time-
Dependence in Catalysis. In Mechanical
Catalysis: Methods of Enzymatic,
Homogeneous, and Heterogeneous
Catalysis, G.F. Swiegers, ed. (John Wiley &
Sons).
catalysts. Part 1. Effect of changes to the
catalyst during reaction. Catal. Rev. Sci. Eng.
48, 91–144.
bonds: chemo-, regio- and stereo-selectivity.
J. Mol. Catal. Chem. 173, 185–221.
5. Zafeiratos, S., Piccinin, S., and Teschner, D.
(2012). Alloys in catalysis: phase separation and
surface segregation phenomena in response
to the reactive environment. Catal. Sci.
Technol. 2, 1787–1801.
3. Vil e´ , G., Albani, D., Almora-Barrios, N., L o´ pez,
N., and P e´ rez-Ram ı´ rez, J. (2016). Advances in
the design of nanostructured catalysts for
selective hydrogenation. ChemCatChem 8,
21–33.
6
. Sankar, M., Dimitratos, N., Miedziak, P.J.,
Wells, P.P., Kiely, C.J., and Hutchings, G.J.
(2012). Designing bimetallic catalysts for a
´
2. Borodzinki, A. (2006). Selective hydrogenation
4. Moln a´ r, A., S a´ rk a´ ny, A., and Varga, M. (2001).
of ethyne in ethene-rich streams on palladium
Hydrogenation of carbon–carbon multiple
Chem 4, 1–12, May 10, 2018
11

Please cite this article in press as: Zhao et al., Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes,
Chem (2018), https://doi.org/10.1016/j.chempr.2018.02.011
green and sustainable future. Chem. Soc. Rev.
1, 8099–8139.
22. Sa, J., Montero, J., Duncan, E., and Anderson,
J.A. (2007). Bi modified Pd/SnO catalysts for
water denitration. Appl. Catal. B Environ. 73,
8–105.
36. Marshall, S.T., O’Brien, M., Oetter, B., Corpuz,
A., Richards, R.M., Schwartz, D.K., and Medlin,
J.W. (2010). Controlled selectivity for palladium
catalysts using self-assembled monolayers.
Nat. Mater. 9, 853–858.
4
2
7
. Somorjai, G.A., and Rioux, R.M. (2005). High
technology catalysts towards 100% selectivity:
fabrication, characterization and reaction
studies. Catal. Today 100, 201–215.
9
23. Semagina, N., and Kiwi-Minsker, L. (2009).
Palladium nanohexagons and nanospheres in
selective alkyne hydrogenation. Catal. Lett.
37. Monfredini, A., Santacroce, V., Marchi o` , L.,
Maggi, R., Bigi, F., Maestri, G., and Malacria, M.
(2017). Semi-Reduction of internal alkynes with
prototypical subnanometric metal surfaces:
bridging homogeneous and heterogeneous
catalysis with trinuclear all-metal aromatics.
ACS Sustain. Chem. Eng. 5, 8205–8212.
8
. Noyori, R. (2009). Synthesizing our future. Nat.
Chem. 1, 5–6.
127, 334–338.
2
2
2
2
4. Keresszegi, C., Grunwaldt, J.D., Mallat, T., and
Baiker, A. (2003). Liquid phase oxidation of
alcohols with oxygen: in situ monitoring of the
9
. Leeuwen, P.W.N.M.v. (2004). Homogeneous
Catalysis: Understanding the Art (Kluwer
Academic Publishers).
oxidation state of Bi-promoted Pd/Al
2 3
O .
Chem. Commun. (Camb.), 2304–2305.
38. Ananikov, V.P., Orlov, N.V., Zalesskiy, S.S.,
Beletskaya, I.P., Khrustalev, V.N., Morokuma,
K., and Musaev, D.G. (2012). Catalytic adaptive
recognition of thiol (SH) and selenol (SeH)
groups toward synthesis of functionalized vinyl
monomers. J. Am. Chem. Soc. 134, 6637–6649.
1
1
1
0. Bhaduri, S., and Mukesh, D. (2014).
Homogeneous catalysis: mechanisms and
industrial applications, second edition (John
Wiley & Sons).
5. Baber, A.E., Tierney, H.L., Lawton, T.J., and
Sykes, E.C.H. (2011). An atomic-scale view of
palladium alloys and their ability to dissociate
molecular hydrogen. ChemCatChem 3,
1. Schmid, A., Dordick, J.S., Hauer, B., Kiener, A.,
Wubbolts, M., and Witholt, B. (2001). Industrial
biocatalysis today and tomorrow. Nature 409,
607–614.
39. Drost, R.M., Rosar, V., Marta, S.D., Lutz, M.,
Demitri, N., Milani, B., de Bruin, B., and
6. Armbr u¨ ster, M., Kovnir, K., Behrens, M.,
Teschner, D., Grin, Y., and Schl o¨ gl, R. (2010).
Pd-Ga intermetallic compounds as highly
selective semihydrogenation catalysts. J. Am.
Chem. Soc. 132, 14745–14747.
258–268.
Elsevier, C.J. (2015). Pd-catalyzed Z-selective
semihydrogenation of alkynes: determining
the type of active species. ChemCatChem 7,
2. Wang, D.H., Engle, K.M., Shi, B.F., and Yu, J.Q.
2010). Ligand-enabled reactivity and
(
2095–2107.
selectivity in a synthetically versatile Aryl C–H
olefination. Science 327, 315–319.
40. Huang, X., Tang, S., Mu, X., Dai, Y., Chen, G.,
Zhou, Z., Ruan, F., Yang, Z., and Zheng, N.
7. Han, P., Axnanda, S., Lyubinetsky, I., and
Goodman, D.W. (2007). Atomic-scale assembly
of a heterogeneous catalytic site. J. Am. Chem.
Soc. 129, 14355–14361.
1
1
3. Rod, T.H., and Nørskov, J.K. (2002). The surface
science of enzymes. Surf. Sci. 500, 678–698.
(
2011). Freestanding palladium nanosheets
with plasmonic and catalytic properties. Nat.
Nanotechnol. 6, 28–32.
4. Bridier, B., L o´ pez, N., and P e´ rez-Ram ı´ rez, J.
(
2010). Molecular understanding of alkyne
28. Anderson, J.A., Mellor, J., and Wells, R.P.K.
(2009). Pd catalysed hexyne hydrogenation
modified by Bi and by Pb. J. Catal. 261,
4
4
1. Radha, B., and Kulkarni, G.U. (2010). Patterned
synthesis of Pd S: chemically robust electrodes
4
and conducting etch masks. Adv. Funct. Mater.
20, 879–884.
hydrogenation for the design of selective
catalysts. Dalton Trans. 39, 8412–8419.
208–216.
1
1
1
5. Segura, Y., Lopez, N., and Perez-Ramirez, J.
(
selectivity of gold nanoparticles in alkyne plus
alkene mixtures: triple- versus double-bond
activation. J. Catal. 247, 383–386.
2007). Origin of the superior hydrogenation
2
3
3
3
3
9. Liu, M., Zhang, J., Liu, J., and Yu, W.W. (2011).
Synthesis of PVP-stabilized Pt/Ru colloidal
nanoparticles by ethanol reduction and their
catalytic properties for selective hydrogenation
of ortho-chloronitrobenzene. J. Catal. 278, 1–7.
2. Love, J.C., Wolfe, D.B., Haasch, R., Chabinyc,
M.L., Paul, K.E., Whitesides, G.M., and Nuzzo,
R.G. (2003). Formation and structure of self-
assembled monolayers of alkanethiolates on
palladium. J. Am. Chem. Soc. 125, 2597–2609.
6. Garcia-Mota, M., Bridier, B., Perez-Ramirez, J.,
and Lopez, N. (2010). Interplay between carbon
monoxide, hydrides, and carbides in selective
alkyne hydrogenation on palladium. J. Catal.
0. Mei, D., Neurock, M., and Smith, C.M. (2009).
Hydrogenation of acetylene-ethylene mixtures
over Pd and Pd-Ag alloys: first-principles-
based kinetic Monte Carlo simulations.
J. Catal. 268, 181–195.
43. Zhang, Q., Xu, W., Li, X., Jiang, D., Xiang, Y.,
Wang, J., Cen, J., Romano, S., and Ni, J. (2015).
Catalytic hydrogenation of sulfur-containing
nitrobenzene over Pd/C catalysts: in situ
2
73, 92–102.
7. Garcia-Mota, M., Gomez-Diaz, J., Novell-
Leruth, G., Vargas-Fuentes, C., Bellarosa, L.,
Bridier, B., Perez-Ramirez, J., and Lopez, N.
(
’
x y
sulfidation of Pd/C for the preparation of Pd S
catalysts. Appl. Catal. Gen. 497, 17–21.
1. Tew, M.W., Emerich, H., and van Bokhoven,
J.A. (2011). Formation and characterization of
PdZn alloy: a very selective catalyst for alkyne
semihydrogenation. J. Phys. Chem. C 115,
2011). A density functional theory study of the
mythic’ Lindlar hydrogenation catalyst. Theor.
44. Zhao, X., Zhao, Y., Fu, G., and Zheng, N. (2015).
Origin of the facet dependence in the
hydrogenation catalysis of olefins: experiment
and theory. Chem. Commun. (Camb.) 51,
12016–12019.
Chem. Acc. 128, 663–673.
8457–8465.
1
1
2
2
8. Chen, G., Xu, C., Huang, X., Ye, J., Gu, L., Li, G.,
Tang, Z., Wu, B., Yang, H., Zhao, Z., et al. (2016).
Interfacial electronic effects control the
reaction selectivity of platinum catalysts. Nat.
Mater. 15, 564–569.
2. L o´ pez, N., and Vargas-Fuentes, C. (2012).
Promoters in the hydrogenation of alkynes in
mixtures: insights from density functional
theory. Chem. Commun. (Camb.) 48, 1379–
45. Li, J., Fleurat-Lessard, P., Zaera, F., and
Delbecq, F. (2014). Mechanistic investigation of
the cis/trans isomerization of 2-butene on
Pt(111): DFT study of the influence of the
hydrogen coverage. J. Catal. 311, 190–198.
1391.
9. Ye, R., Hurlburt, T.J., Sabyrov, K., Alayoglu, S.,
and Somorjai, G.A. (2016). Molecular catalysis
science: perspective on unifying the fields of
catalysis. Proc. Natl. Acad. Sci. USA 113, 5159–
3. Schoenbaum, C.A., Schwartz, D.K., and Medlin,
J.W. (2014). Controlling the surface
46. Studt, F., Abild-Pedersen, F., Bligaard, T.,
Sørensen, R.Z., Christensen, C.H., and Nørskov,
J.K. (2008). Identification of non-precious metal
alloy catalysts for selective hydrogenation of
acetylene. Science 320, 1320–1322.
environment of heterogeneous catalysts using
self-assembled monolayers. Acc. Chem. Res.
5
166.
47, 1438–1445.
0. Pachulski, A., Schoedel, R., and Claus, P. (2011).
Performance and regeneration studies of
34. Kahsar, K.R., Schwartz, D.K., and Medlin, J.W.
(2014). Control of metal catalyst selectivity
through specific noncovalent molecular
Pd-Ag/Al
hydrogenation of acetylene. Appl. Catal. Gen.
00, 14–24.
2
O
3
catalysts for the selective
47. Delbecq, F., Loffreda, D., and Sautet, P. (2010).
Heterogeneous catalytic hydrogenation: is
double bond/surface coordination necessary?
J. Phys. Chem. Lett. 1, 323–326.
4
interactions. J. Am. Chem. Soc. 136, 520–526.
1. Astruc, D., Lu, F., and Aranzaes, J.R. (2005).
Nanoparticles as recyclable catalysts: the
frontier between homogeneous and
heterogeneous catalysis. Angew. Chem. Int.
Ed. 44, 7852–7872.
35. Pang, S.H., Schoenbaum, C.A., Schwartz, D.K.,
and Medlin, J.W. (2013). Directing reaction
pathways by catalyst active-site selection using
self-assembled monolayers. Nat. Commun. 4,
2448.
48. Liu, P., Qin, R., Fu, G., and Zheng, N. (2017).
Surface coordination chemistry of metal
nanomaterials. J. Am. Chem. Soc. 139, 2122–
2131.
12
Chem 4, 1–12, May 10, 2018