Creation of Redox-Active PdSx Nanoparticles Inside the Defect Pores of MOF UiO-66 with Unique Semihydrogenation Catalytic Properties

Article abstract of DOI:10.1002/adfm.201908519

Semihydrogenation of alkynes to produce alkenes is very important in the industry; however, over-hydrogenation heavily complicates the postprocesses, which are highly energy consuming and not environmentally friendly. One of the most efficient pathways to solve this challenging issue is to develop highly selective catalysts that could only hydrogenate alkynes and are inactive in hydrogenation of alkenes. This work presents herein an efficient catalyst, consisting of in situ created PdS_0.53 nanoparticles as the redox-active sites inside the defect pores of metal–organic framework UiO-66, which demonstrates very high alkene selectivity (up to 99.5%) in semihydrogenation of easily over-hydrogenated terminal alkynes. In contrast to the traditional catalysts, strict control over the reaction time becomes the nonessential condition because the catalyst system is almost inactive in hydrogenation of alkenes. Therefore, this paradigm work provides a practically applicable pathway for the development of efficient catalysts with unique catalytic properties for selective semihydrogenation reactions.

Full text of DOI:10.1002/adfm.201908519

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Creation of Redox-Active PdSx Nanoparticles Inside the Defect
Pores of MOF UiO-66 with Unique Semihydrogenation
Catalytic Properties
Ming-Jie Dong, Xuan Wang, and Chuan-De Wu*
are more reactive than internal alkynes,
Semihydrogenation of alkynes to produce alkenes is very important in the
industry; however, over-hydrogenation heavily complicates the postprocesses,
which are highly energy consuming and not environmentally friendly. One
of the most efficient pathways to solve this challenging issue is to develop
highly selective catalysts that could only hydrogenate alkynes and are inactive
in hydrogenation of alkenes. This work presents herein an efficient catalyst,
consisting of in situ created PdS0.53 nanoparticles as the redox-active sites
inside the defect pores of metal–organic framework UiO-66, which demon-
strates very high alkene selectivity (up to 99.5%) in semihydrogenation of
easily over-hydrogenated terminal alkynes. In contrast to the traditional cata-
lysts, strict control over the reaction time becomes the nonessential condition
because the catalyst system is almost inactive in hydrogenation of alkenes.
Therefore, this paradigm work provides a practically applicable pathway for
the development of efficient catalysts with unique catalytic properties for
selective semihydrogenation reactions.
which could be easily over-hydrogenated.
To improve the selectivity of alkenes, sev-
eral strategies have been established in
the literature. One of the most frequently
used approaches is to develop Pd-based
catalysts in the presence of auxiliary spe-
cies, such as interacting with secondary
metals to form intermetallic alloys Pd–Ag,
Pd–Au, Pd–Cu, Pd–Ni, Pd–Zn, Pd–In,
Pd–Al, and Pd–Ga,[3] or coordinating with
organic/inorganic moieties containing
heteroatoms (N, P, and S).[4] Another
strategy is to develop Pd-free catalysts,
consisting of Au, Cu, Ni, Fe, or Co metal
species.[5] Recently, it was found that the
metal-free frustrated Lewis pairs (FLPs)
are also highly selective for alkene produc-
tion.[6] However, the high selectivity of alk-
enes, especially for the terminal alkenes,
was resulted from strict control over the
reaction time, because most of the reported semihydrogenation
catalysts are also active in alkene hydrogenation reaction.[7]
Metal–organic frameworks (MOFs) are an emerging class
of porous materials, building from the connections between
metal ions/clusters and organic linkers.[8] Attributed to their
unique characters, such as designable pore structures, high
surface areas, and tunable functionalities, MOFs demonstrate
great potential for applications in different fields.[9–11] In terms
of catalytic applications, MOFs have been directly used as
heterogeneous catalysts,[10] or as porous support matrices to
immobilize different redox-active species.[11] Unlike those of
the immobilized active species in traditional porous materials,
such as zeolites, mesoporous silicas, and activated carbons, the
microenvironments of redox-active species in MOFs are sys-
tematically designable and tunable, which thus easily realize
highly efficient and selective catalysis by synergistic work.[10j]
The Zr-MOFs, building from Zr(IV) oxo–clustered connec-
tors and multidentate carboxylate linkers, have been attracted
great interest, because they are highly stable under extreme
thermal and chemical conditions.[12] The prototype of Zr-
MOFs is the well-known UiO-66, in which each Zr6 cluster is
connecting with 12 terephthalate linkers.[12a] Recent studies
showed that the actual crystals of UiO-66 inevitably consist of
more or less missed terephthalate linkers, depending on the
synthetic methods.[13] Appropriate control over the defects in
UiO-66 could markedly improve its performances in different
application fields, including catalysis,[13e,14] gas adsorption and
1. Introduction
Selectivity is always an important and challenging issue in cata-
lytic chemistry, which could simplify the postprocesses, save
costs, and reduce wastes to meet the requirement of sustain-
able chemistry. The semihydrogenation reaction, which could
selectively convert alkynes into highly value-added alkenes, has
been one of the most crucial and essential reactions in the man-
ufacturing processes of bulky fine chemicals.[1] In this context,
the Lindlar catalyst (Pd/CaCO3 treated with Pb(OAc)2 or Pd/
BaSO4 treated with quinoline) has been stood the test of time,
routinely appeared in the textbook.[2] However, the use of the
toxic lead salt or large amounts of pollutant quinoline during
preparation of the Lindlar catalyst has been one of the serious
drawbacks in practical applications. Additionally, the selec-
tivity of alkene products is very low when terminal alkynes
were employed as the reactants, because terminal alkynes
M.-J. Dong, X. Wang, Prof. C.-D. Wu
State Key Laboratory of Silicon Materials
Department of Chemistry
Zhejiang University
Hangzhou 310027, P. R. China
E-mail: cdwu@zju.edu.cn
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.201908519.
DOI: 10.1002/adfm.201908519
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Scheme 1. Schematic illustration of the in situ encapsulation processes of PdSx nanoparticles inside the defect pores of UiO-66-D.
separation,[13b,15] and decontamination.[16] To target highly effi-
cient catalysts for selective semihydrogenation of alkynes, herein
we present an effective strategy for encapsulating and further
tuning the constituents and electronic properties of PdSx nano-
species inside the defect pores of UiO-66, demonstrating high
selectivity in catalyzing semihydrogenation of alkynes with high
and steady alkene selectivity (up to 99.5%) that does not require
strict control over the reaction time and substrate conversion.
which is lower than the calculated value of 54.6% for perfect
UiO-66. Calculations based on the difference revealed that the
as-synthesized UiO-66-D consists of about five BDC ligands per
1
Zr6 cluster. Additionally, a combination of H NMR, UV–vis,
and inductively coupled plasma mass spectrometry (ICP-MS)
spectroscopy analysis results further confirmed the number of
missing organic linkers per Zr6 cluster (Figures S3–S5, Sup-
porting Information). Therefore, the formula of the defect UiO-
66-D should be [Zr6(µ3-O)4(µ3-OH)4(BDC)5(OH)(H2O)2]. The N2
sorption isotherms of UiO-66-D show the type I pattern with
a Brunauer–Emmett–Teller (BET) surface area of 1181 m2 g−1
(Figure S6a, Supporting Information). Pore size distribution
calculated by the density functional theory method revealed
that there are two major kinds of pores at ≈7 and ≈9 Å, which
are ascribed to the tetrahedral and octahedral cages in the UiO
structure, respectively (Figure S6b, Supporting Information).
The additional two kinds of lager pores with dimensions of ≈12
and ≈14 Å should be resulted from missing of the BDC ligands,
which could enlarge the pore space and sizes.
The defect coordination sites of Zr6 clusters should be occu-
pied by labile water molecules and/or hydroxyl groups, which
are easily replaced by the functional ligands consisting of
carboxylate groups, such as 3-(methylthio)propionate (MTP),
to tune the pore microenvironments and functionalities. The
postmodification process was conveniently conducted by
treating UiO-66-D with appropriate amounts of 3-(methylthio)
propionic acid (MTPA) in THF solvent at 80 °C. To quantify
the mole ratios of MTP to missing BDC (n represents the mole
ratio), the as-prepared solid samples of UiO-66-D-nMTP were
2. Results and Discussion
As shown in Scheme 1, defect UiO-66 (denoted as UiO-66-D)
was synthesized by solvothermal reaction of a mixture con-
taining equimolar amount of ZrOCl2·8H2O and 1,4-ben-
zenedicarboxylic acid (H2BDC) in acidified tetrahydrofuran
(THF) solvent.[17] Powder X-ray diffraction (PXRD) analysis
showed that the diffraction peaks of an as-synthesized sample
match well with those calculated ones from the crystal data of
UiO-66, which thus proved the identity of the as-synthesized
material (Figure S1, Supporting Information). The structure
defectivity (linker vacancy) was analyzed by thermogravimetric
analysis (TGA; Figure S2, Supporting Information).[18] The
desolvated material UiO-66-D, corresponding to the residue
at ≈400 °C in the TGA curve, referred to a chemical formula
of [ZrO(CO2)2(C6H4)] per Zr atom. The final residue, corre-
sponding to the plateau in the temperature range of 540–800 °C,
should be ZrO2. The relative weight loss between 400 and
540 °C is of 45.5 wt% (from 74.8 to 40.8 wt%) in the TGA curve,
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digested in NaOD/D2O solution. 1H NMR spectroscopy anal-
ysis results showed that the ratios between MTP and BDC in
different samples are of about 0.016, 0.054, 0.108, and 0.172,
corresponding to the n values of 0.08, 0.27, 0.54, and 0.86,
respectively (Figures S7–S10, Supporting Information). PXRD
patterns show that the diffraction peaks of UiO-66-D-nMTP are
identical to those of the parent UiO-66-D, suggesting that the
backbone structure remains unchanged during the postsynthetic
modification processes (Figure S11, Supporting Information).
Similar to the parent UiO-66-D, UiO-66-D-nMTP feature high
thermal stability with decomposition temperature at ≈480 °C as
revealed by TGA (Figure S12, Supporting Information). Com-
pared with the parent UiO-66-D, UiO-66-D-nMTP also display
the type I N2 sorption isotherms with slightly decreased BET
surface areas in the range of 800–900 m2 g−1, depending on
the contents of MTP in these materials (Figures S13–S16 and
Table S1, Supporting Information). It is worth noting that the
pore size distributions of these postmodified materials are very
similar to those of the parent UiO-66-D, which are beneficial for
the subsequent encapsulation of redox-active species.
diffraction peak ascribed to the Pd or PdSx species for all
composite materials indicates that the sizes of encapsulated
nanoparticles are very small. N2 sorption results proved that
the pore structures of these composite materials were well
reserved (Figures S27–S31, Supporting Information). The slight
decrease of the BET surface areas and the pore volumes should
be ascribed to the encapsulation of PdSx nanoparticles inside
the pore space of these composite MOF materials. Different to
the pore size distributions of UiO-66-D-nMTP, the large pores
resulted from the defects in PdSx@UiO-66-D almost disap-
peared, indicating that the encapsulated PdSx nanoparticles
should be located in the defect pores of UiO-66-D.
X-ray photoelectron spectroscopy (XPS) was carried out to
further explore the compositions and electric environments of
the encapsulated nanoparticles in PdSx@UiO-66-D (Figure 2;
Figures S32–S34, Supporting Information). Survey XPS con-
firmed the existence of C, O, Zr, and Pd species in Pd@UiO-
66-D and the existence of C, O, Zr, Pd, and S elements in
PdSx@UiO-66-D. The high-resolution Pd 3d XPS spectra were
analyzed by assuming that each individual signal for Pd species
comprises merged 3d3/2 and 3d5/2 peaks with an intensity ratio
of 2:3 and an energy difference of about 5.3 eV.[21] As shown
in Figure 2b, there are two kinds of Pd 3d5/2 components with
binding energies of 335.85 and 336.90 eV for Pd@UiO-66-D,
which are ascribed to the metallic Pd0 and the oxidized Pd2+,
respectively. The existence of high valence state Pd2+ is con-
sistent with the literature results, because highly dispersed Pd0
nanoparticles are easily reoxidized in air.[22] Compared with that
in Pd@UiO-66-D, the 3d5/2 peak of Pd0 in PdS0.53@UiO-66-D
was positively shifted to 336.15 eV. This result indicates that the
electron density of Pd0 species in PdS0.53@UiO-66-D is lower
than that in Pd@UiO-66-D, because the bonding between Pd
and S would endow electron transfer from Pd to S atoms by
d–d feedback bond interaction.[23] The integral peak area ratio
of Pd0 to Pd2+ species is of about 3:2, which is also very close to
the value in Pd16S7. The high-resolution S 2p XPS spectra were
analyzed by assuming that each signal for an individual species
comprises merged 2p1 and 2p3 peaks with an intensity ratio of
1:2 and an energy difference of about 1.2 eV.[21] As shown in
Figure 2c, two binding energy peaks appeared at 163.30 and
164.50 eV for the S atoms in UiO-66-D-0.86MTP, which were
positively shifted to 163.96 and 165.16 eV after encapsulation of
Pd(OAc)2, respectively, indicating that the electron density of S
atoms decreased. These results demonstrate that the combina-
tion between S and Pd2+ easily rendered electron transfer from
S to Pd2+. There also appear two higher energy peaks at 166.60
and 167.80 eV for the S atoms in UiO-66-D-0.86MTP, which
were traditionally ascribed to the signals of sulfoxide or sulfone
Pd nanoparticle–encapsulated UiO-66-D (denoted as Pd@
UiO-66-D) and PdSx nanoparticle–encapsulated UiO-66-D-
nMTP (denoted as PdSx@UiO-66-D; x represents the mole ratio
of S to Pd) were prepared by a simple impregnation method
followed by H2 reduction. To reveal the compositions of the last
acquired catalysts, the solid samples of PdSx@UiO-66-D were
1
digested in NaOD/D2O solution. H NMR spectroscopy anal-
ysis results showed that there were only acetate (derived from
Pd(OAc)2) and propionate existed in the solutions, and no MTP
signal was detected (Figures S17–S21, Supporting Information).
These results indicate that MTP should be reduced to form
propionate under H2 atmosphere at 200 °C, while the S atom
in MTP was released to combine with the Pd species inside
the pores of UiO-66-D.[19] To quantify the x values in different
materials, transmission electron microscopy (TEM) and energy-
dispersive X-ray (EDX) elemental mapping were carried out to
study the compositions and structures of the encapsulated PdSx
species in PdSx@UiO-66-D (Figure 1; Figures S22–S25, Sup-
porting Information). EDX analysis results indicate that the x
values are of 0.25, 0.31, 0.37, and 0.53 for different samples.
TEM images show that the nanoparticles are uniformly distrib-
uted in PdSx@UiO-66-D and Pd@UiO-66-D with average sizes
of ≈2 nm (Figure 1a; Figures S22–S25, Supporting Informa-
tion). High-resolution TEM (HRTEM) image of Pd@UiO-66-D
revealed that the interplanar spacing of the Pd nanoparticles
is of 0.224 nm, corresponding to the (111) lattice spacing of
the face-centered cubic Pd (Figure S22, Supporting Informa-
tion).[20] In contrast, the lattice-fringe spacing of the nanoparti-
cles in PdS0.53@UiO-66-D is of 0.235 nm, which is larger than
the (111) lattice spacing of face-centered cubic Pd. This value
is very close to the (321) lattice spacing of Pd16S7 phase in the
literature.[4f] ICP-MS analysis results indicate that the Pd load-
ings in these composite materials are of 2.53, 2.16, 1.95, 1.77,
and 1.71 wt%, corresponding to x = 0, 0.25, 0.31, 0.37, and 0.53,
respectively (Table S1, Supporting Information).
1
species.[21] However, the H NMR spectrum of a digested UiO-
66-D-0.86MTP sample shows that no signal could be ascribed to
the sulfoxide or sulfone moiety. Therefore, the positive shifts of
the binding energies of S 2p should be ascribed to the combina-
tion between the strong base thioether moieties and the strong
Lewis acid ZrIV centers (denoted as C–S (ZrIV)), and the shift
values are highly depending on the contents of defects because
the Lewis acidity is roughly proportional to the contents of
defects.[13e] As expected, the binding energy peaks of S atoms
in Pd(OAc)2@UiO-66-D-0.86MTP were weakened and nega-
tively shifted to 163.96 and 165.16 eV, respectively, because the
The PXRD patterns of as-prepared Pd@UiO-66-D and
PdSx@UiO-66-D are similar to that of the parent UiO-66-D,
indicating that the framework structure remains unchanged
(Figure S26, Supporting Information). Additionally, no obvious
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Figure 1. Composition and structure analysis of PdS0.53@UiO-66-D. a,b) TEM images with different resolutions. The inset shows a histogram of the
particle size distribution for PdS0.53 nanoparticles. c) High-angle annular dark-field scanning transmission electron microscopy image. d–g) Elemental
mapping images for O, Zr, S, and Pd, respectively. h) TEM-EDX spectrum.
S atoms are much more easily combined with the encapsulated
Pd2+ ions by strong coordination interactions. Moreover, the
binding energies of S atoms in the H2-treated sample at 200 °C
further negatively shifted to 162.37 and 163.57 eV, respectively.
These values are very close to those of sulfide species, which
should be ascribed to the signals of PdS0.53 in PdS0.53@UiO-
66-D.[21] In the high-resolution Zr 3d XPS spectrum of Pd@
UiO-66-D, the Zr 3d5/2 binding energy is of 182.77 eV, which
is 0.15 eV lower than that of PdS0.53@UiO-66-D (182.92 eV)
(Figure 2d). These results should be ascribed to the sulfur-free
nanoparticles in Pd@UiO-66-D that are easy contact with the
Zr6 clusters, which would result in electron transfer from the
encapsulated nanoparticles to ZrIV, leading to the negative shift
of the Zr 3d binding energies.
are systematically tunable. Since the catalytic properties
of redox-active Pd species are depending on the electronic
properties and electronic microenvironments, highly selec-
tive semihydrogenation of alkynes might be easily realized by
simply tuning the compositions of encapsulated PdSx nano-
species in PdSx@UiO-66-D. The hydrogenation of pheny-
lacetylene was performed under 1 atm H2 atmosphere at
25 °C in the presence of different Pd-containing catalysts.
As shown in Figure 3a, Pd@UiO-66-D exhibits low styrene
selectivity in the reaction, even at the stage of low phenyla-
cetylene conversion. The styrene selectivity reached to the
maximum of 80% when phenylacetylene was completely con-
verted, and then quickly decreased due to the easy over-hydro-
genation of styrene to phenylethane (Table 1, entries 1–3). In
contrast, the PdSx@UiO-66-D catalysts presented different
catalytic properties in the hydrogenation reaction, depending
The above results clearly demonstrate that the electronic
properties of the encapsulated Pd species in PdSx@UiO-66-D
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Figure 2. a) The XPS elemental survey spectra of Pd@UiO-66-D, UiO-66-D-0.86MTP, Pd(OAc)2@UiO-66-D-0.86MTP, and PdS0.53@UiO-66-D. b) The
high-resolution XPS spectra of PdS0.53@UiO-66-D and Pd@UiO-66-D in the Pd 3d and Zr 3p regions. c) The high-resolution XPS spectra of UiO-66-
D-0.86MTP, Pd(OAc)2@UiO-66-D-0.86MTP, and PdS0.53@UiO-66-D in the S 2p region. d) The high-resolution XPS spectra of PdS0.53@UiO-66-D and
Pd@UiO-66-D in the Zr 3d region.
Figure 3. Hydrogenation of phenylacetylene catalyzed by various Pd catalysts. a) Pd@UiO-66-D, b) PdS0.25@UiO-66-D, c) PdS0.53@UiO-66-D, and
d) 5 wt% Pd/CaCO3-Pb. Reaction conditions: phenylacetylene (0.2 mmol), catalyst (0.4 mol% based on Pd), MeOH (1.8 mL), DMSO (0.2 mL), and
H2 (1 atm) and 25 °C.
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Table 1. Semihydrogenation of phenylacetylene using various Pd catalysts.
on the contents of S species. As shown in Figure 3b, when
PdS0.25@UiO-66-D was used as a catalyst, the conversion rate
of phenylacetylene decreases and the selectivity of styrene
slightly increases, attributed to the partial Pd species that is
coordinating to the S atoms. However, over-hydrogenation of
styrene to phenylethane remains occurred, accompanying
full conversion of phenylacetylene. It is interesting that the
phenylacetylene conversion gradually increases, accompa-
nying further increase of the S contents in PdSx@UiO-66-D
(x = 0.31–0.37) (Table 1, entries 6–9; Figure S35, Supporting
Information). These results are quite different to the tradi-
tional concept that the coordination of S atoms to Pd species
could poison the active sites. Moreover, over-hydrogenation rate
of styrene to phenylethane is also markedly depressed. When
PdS0.53@UiO-66-D was used as a catalyst, the styrene selectivity
was increased to 96.5%, and the selectivity was entirely retained
even when the reaction time was intentionally prolonged
(Table 1, entries 10 and 11; Figure 3c). In other word, it is not
necessary to strictly control the reaction time for the selective
semihydrogenation reaction catalyzed by PdS0.53@UiO-66-D.
To make comparisons, we also studied the catalytic prop-
erties of the traditional catalysts, including 5 wt% Pd/C and
5 wt% Pd/CaCO3-Pb (poisoned with lead ions), for the selec-
tive hydrogenation of phenylacetylene under the identical
conditions. In sharp contrast, phenylacetylene was quickly con-
verted into styrene but further fast converted into the unde-
sired phenylethane product (Figure 3d and Table 1, entries
12–15; Figure S35c, Supporting Information). Therefore,
the catalytic properties of the PdS0.53@UiO-66-D catalyst are
Entrya)
Catalyst
t [h] Conv. [%]b)
Yield [%]b)
Alkene
Alkane
17.5
52.4
>99.9
8.8
1
Pd@UiO-66-D
Pd@UiO-66-D
2
6
96.2
>99.9
>99.9
61.7
78.7
47.6
0
2
3
Pd@UiO-66-D
12
2
4
PdS0.25@UiO-66-D
PdS0.25@UiO-66-D
PdS0.31@UiO-66-D
PdS0.31@UiO-66-D
PdS0.37@UiO-66-D
PdS0.37@UiO-66-D
PdS0.53@UiO-66-D
PdS0.53@UiO-66-D
5 wt% Pd/C
52.9
63.7
80.3
81.7
93.7
90.7
96.5
96.5
42.8
0
5
6
36.3
7.2
>99.9
87.5
6
2
7
6
18.3
6.3
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
8
2
9
6
9.3
10
11
12
13
14
15
2
3.5
6
3.5
0.5
0.75
0.5
1.5
57.2
>99.9
41.5
>99.9
5 wt% Pd/C
5 wt% Pd/CaCO3–Pb
5 wt% Pd/CaCO3–Pb
58.5
0
a)Reaction conditions: phenylacetylene (0.2 mmol), Pd catalyst (0.4 mol% based
on Pd), MeOH (1.8 mL), DMSO (0.2 mL), H2 (1 atm), and 25 °C; b)Determined
by GC-MS.
Scheme 2. Semihydrogenation of terminal alkynes using PdS0.53@UiO-66-D catalyst. Reaction conditions: alkyne (0.2 mmol), PdS0.53@UiO-66-D
(0.4 mol% based on Pd), MeOH (1.8 mL), DMSO (0.2 mL), H2 (1 atm) and 25 °C. The conversions and yields were determined by GC-MS.
a) PdS0.53@UiO-66-D containing 0.8 mol% Pd. b) 1.9 mol% of side product vinylcyclohexane. c) The reaction temperature is 50 °C.
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Table 2. Semihydrogenation of alkynes using PdS0.53@UiO-66-D catalyst.
It is worth noting that PdS0.53@UiO-66-D
also presents highly selectivity in semihydro-
genation of terminal and internal alkynes.
As shown in Table 2, the internal triple bond
in 1-phenyl-1-propyne remains intact even
when the reaction time was prolonged to
12 h (entry 1). Additionally, when a mixture
of terminal alkyne and internal alkyne or a
molecule contains both terminal and internal
Entrya)
1
Substrate
Product
t [h]
Conv. [%]b)
0.5
Yield [%]b)
Alkene
Alkane
Trace
12
0.5

C C bonds was used as the substrate,
PdS0.53@UiO-66-D only selectively hydrogen-
ated those molecules containing terminal
2c)
2
6
96.8
4.2
3.2
>99.9
4.2
trace


C C bonds, while the internal C C bonds
remain intact under the catalytic conditions
(entries 2–5). The high hydrogenation selec-

tivity between terminal and internal C C

bonds should be ascribed to the internal C C
3c)
96.2
4.5
3.8
>99.9
4.5
bonds that are very difficult to access the Pd
active sites during catalysis, due to the steric
effect and nanopore confinement effect.[3g,26]
PdS0.53@UiO-66-D is very stable, which
can be simply recovered by centrifugation to
remove the supernatant, washed with meth-
anol, and subsequently reused in the succes-
sive runs with retained high catalytic activity
and selectivity (Figure S38, Supporting
Information). PXRD patterns show that the
structure of the recovered catalyst remains
intact (Figure S39, Supporting Information).
TEM images indicate no obvious aggregation
of the PdSx nanoparticles in the recovered
catalyst (Figure S40, Supporting Informa-
tion). ICP-MS analysis results showed that
there is no leached Pd species in the super-
natant, indicating that PdS0.53@UiO-66-D is
an outstanding heterogeneous porous cata-
lyst. Compared with those reported catalysts
trace
4
5
2
6
94.9
94.2
4.8
5.4
>99.9
>99.9
a)Reaction conditions: alkyne (0.2 mmol), PdS0.53@UiO-66-D (0.4 mol% based on Pd), MeOH (1.8 mL),
DMSO (0.2 mL), H2 (1 atm), and 25 °C; b)Determined by GC-MS; c)Phenylacetylene (0.1 mmol) and
1-phenyl-1-propyne (0.1 mmol) were used as the reactants.
unique, since the catalyst is almost inactive in hydrogenation
of alkenes and the selectivity is almost insensitive to the reac-
tion time, which could simplify the postprocesses in practical
applications.
for the semihydrogenation of phenylacetylene in the literature
(Table S3, Supporting Information), PdS0.53@UiO-66-D exhibits
unique catalytic properties with both high catalytic activity and
selectivity, which is very promising for its practical applications
in selective semihydrogenation reactions.
PdS0.53@UiO-66-D is also highly efficient for selective
semihydrogenation of a series of expanded terminal alkynes.
As shown in Scheme 2, a wide range of terminal alkynes
containing different functional groups, such as halogen,
amine, nitro, pyridyl, hydroxyl, and aldehyde groups, could
be smoothly transformed into the corresponding alkenes with
excellent conversions and selectivities. It is interesting that
PdS0.53@UiO-66-D is also highly active for selective semihy-
drogenation of bio-related molecules. For example, one of the
prevalent approaches to synthesize vitamin E involves the reac-
tion between 2,3,5-trimethylhydroquinone and isophytol, while
the latter mainly comes from alkenols, such as linalool and
2-methyl-3-buten-2-ol.[24] Therefore, it is of very importance to
realize facile industrial access to those alkenols.[25] As shown
in Scheme 2, alkynol 2-methyl-3-butyn-2-ol could be easily
semihydrogenated by PdS0.53@UiO-66-D with full conversion
and high selectivity of 99.5% for alkenol 2-methyl-3-buten-2-ol
(14) product.
To figure out the unique catalytic properties of
PdS0.53@UiO-66-D in the selective semihydrogenation
reaction, we studied the selective sorption capability of
Pd@UiO-66-D and PdS0.53@UiO-66-D for phenylacetylene and
styrene molecules (Table S4, Supporting Information). After
a solvent-free sample of PdS0.53@UiO-66-D was immersed
in a mixture of phenylacetylene, dimethyl sulfoxide (DMSO),
and methanol (volume ratio of 1:10:250) at room tempera-
ture under N2 atmosphere for 6 h, gas chromatography (GC)
analysis results indicate that PdS0.53@UiO-66-D can take up a
large amount of phenylacetylene (0.032 mg mg−1) inside the
pore space. When styrene was used instead of phenylacety-
lene under the identical conditions, the adsorbed styrene is
negligible. These results indicate that PdS0.53@UiO-66-D has
the unique selective sorption capability for phenylacetylene
over styrene molecules, which could selectively accumulate
phenylacetylene molecules inside the pores to accelerate the
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catalytic reaction, and timely expel styrene molecules out of
the pores to avoid over-hydrogenation reaction. We also used
styrene instead of phenylacetylene under the same hydrogena-
tion conditions in the presence PdS0.53@UiO-66-D catalyst
(Table S5, Supporting Information). GC analysis results
revealed that the converted styrene is almost negligible (0.3%
conversion for 6 h). If there was absence of DMSO solvent in
the system, PdS0.53@UiO-66-D could take up a large amount
of styrene (0.025 mg mg−1), and the conversion of styrene was
increased to 5.9% under the otherwise identical conditions.
These results indicate that DMSO solvent also played impor-
tant roles in the hydrogenation reaction. To make a compar-
ison, we further studied the selective sorption capability of
Pd@UiO-66-D, which exhibits low selectivity between pheny-
lacetylene (0.039 mg mg−1) and styrene (0.034 mg mg−1). As
a result, Pd@UiO-66-D easily prompted hydrogenation of sty-
rene (>99.9% conversion for 6 h) under the identical condi-
tions. The different sorption capabilities of PdS0.53@UiO-66-D
and Pd@UiO-66-D for phenylacetylene and styrene molecules
indicate that the combination of S and Pd atoms could tune the
affinity between alkene molecules and Pd species, especially in
the presence of assistant sulfur-containing DMSO molecules,
and thus significantly improve the selectivity in the hydrogena-
tion reaction.
To further study the roles of the PdS0.53 species in the
semihydrogenation reaction, PdS0.53@UiO-66-D was digested
in NaOH aqueous solution. The collected solid (denoted as
PdS0.53@UiO-66-D-NaOH) was used to catalyze the semihy-
drogenation of phenylacetylene under the identical conditions
(Table S6, Supporting Information). PdS0.53@UiO-66-D-NaOH
exhibits relatively low selectivity and activity, compared with
the pristine PdS0.53@UiO-66-D, and the catalytic activity also
markedly decreased in the second catalytic cycle. These results
indicate that the defect pores of PdS0.53@UiO-66-D played
important roles to improve and stabilize the catalytic efficiency
of the encapsulated PdS0.53 nanospecies by synergistic and
confinement effect, respectively. It is interesting that the sty-
rene selectivity catalyzed by PdS0.53@UiO-66-D-NaOH remains
much higher than that catalyzed by the solid catalyst that was
synthesized by directly reducing a mixture of Pd(OAc)2 and
MTPA under H2 atmosphere at 200 °C. In addition, postsyn-
thetic modification of Pd@UiO-66-D with MTPA (denoted as
Pd@UiO-66-D-MTP) or Li2S (denoted as Pd@UiO-66-D-Li2S)
also resulted in extremely low activity and styrene selectivity,
respectively. Therefore, in situ creation of PdSx nanoparticles
inside the defect pores of UiO-66-D is a unique strategy to
realize highly selective semihydrogenation of terminal alkynes.
the most efficient catalysts for semihydrogenation of terminal
alkynes. It is reasonably believed that numerous highly efficient
catalysts for semihydrogenation reactions will be systematically
developed based on the strategy reported in this work.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
The authors are grateful for the financial support of the National Natural
Science Foundation of China (Grant Nos. 21525312 and 21872122).
Conflict of Interest
The authors declare no conflict of interest.
Keywords
defect pores, heterogeneous catalysis, metal–organic frameworks, PdSx
nanoparticles, semihydrogenation
Received: October 15, 2019
Revised: November 18, 2019
Published online:
[1] a) C. Oger, L. Balas, T. Durand, J.-M. Galano, Chem. Rev. 2013, 113,
1313; b) R. Chinchilla, C. Najera, Chem. Rev. 2014, 114, 1783.
[2] a) H. Lindlar, Helv. Chim. Acta 1952, 35, 446; b) H. Lindlar,
R. Dubuis, Org. Synth. 1966, 46, 89.
[3] a) A. J. McCue, J. A. Anderson, J. Catal. 2015, 329, 538; b) Q. Jin,
Y. He, M. Miao, C. Guan, Y. Du, J. Feng, D. Li, Appl. Catal., A 2015,
500, 3; c) H. Zhou, X. Yang, L. Li, X. Liu, Y. Huang, X. Pan, A. Wang,
J. Li, T. Zhang, ACS Catal. 2016, 6, 1054; d) S. Song, K. Li, J. Pan,
F. Wang, J. Li, J. Feng, S. Yao, X. Ge, X. Wang, H. Zhang, Adv.
Mater. 2017, 29, 1605332; e) X. Li, Z. Wang, Z. Zhang, G. Yang,
M. Jin, Q. Chen, Y. Yin, Mater. Horiz. 2017, 4, 584; f) Q. Feng,
S. Zhao, Y. Wang, J. Dong, W. Chen, D. He, D. Wang, J. Yang,
Y. Zhu, H. Zhu, J. Am. Chem. Soc. 2017, 139, 7294; g) Y. Lu, X. Feng,
B. S. Takale, Y. Yamamoto, W. Zhang, M. Bao, ACS Catal. 2017, 7,
8296; h) M. Armbrüster, K. Kovnir, M. Behrens, D. Teschner, Y. Grin,
R. Schlögl, J. Am. Chem. Soc. 2010, 132, 14745.
[4] a) S. Yun, S. Lee, S. Yook, H. A. Patel, C. T. Yavuz, M. Choi, ACS
Catal. 2016, 6, 2435; b) T. Mitsudome, Y. Takahashi, S. Ichikawa,
T. Mizugaki, K. Jitsukawa, K. Kaneda, Angew. Chem., Int. Ed. 2013,
52, 1481; c) M. Crespo-Quesada, R. R. Dykeman, G. Laurenczy,
P. J. Dyson, J. Catal. 2011, 279, 66; d) W. Long, N. A. Brunelli,
S. A. Didas, E. W. Ping, C. W. Jones, ACS Catal. 2013, 3, 1700;
e) A. J. McCue, A. Guerrero-Ruiz, C. Ramirez-Barria, J. Catal. 2017,
355, 40; f) Y. Liu, A. J. McCue, J. Feng, S. Guan, D. Li, J. A. Anderson,
J. Catal. 2018, 364, 204; g) X. Zhao, L. Zhou, W. Zhang,
C. Hu, L. Dai, L. Ren, B. Wu, G. Fu, N. Zheng, Chem 2018, 4,
1080.
3. Conclusion
In summary, we demonstrated an effective strategy for in situ
creation of PdSx nanospecies inside the defect pores of UiO-
66-D, which realized highly chemoselective semihydrogena-
tion of various terminal alkynes to produce highly value-added
alkenes. In sharp contrast to the traditional catalysts, the semi-
hydrogenation selectivity is not dependent on the reaction
time, which surpasses most of the literature work, including
the commercial Pd/C and Lindlar catalysts, making it one of
[5] a) G. Li, R. Jin, J. Am. Chem. Soc. 2014, 136, 11347; b) A. Fedorov,
H.-J. Liu, H.-K. Lo, C. Copéret, J. Am. Chem. Soc. 2016, 138,
16502; c) T. N. Gieshoff, A. Welther, M. T. Kessler, M. H. Prechtl,
©
Adv. Funct. Mater. 2019, 1908519
1908519 (8 of 9)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
A. J. von Wangelin, Chem. Commun. 2014, 50, 2261; d) K. Tokmic,
A. R. Fout, J. Am. Chem. Soc. 2016, 138, 13700; e) H. Konnerth,
M. H. G. Prechtl, Chem. Commun. 2016, 52, 9129; f) B. S. Takale,
X. Feng, Y. Lu, M. Bao, T. Jin, T. Minato, Y. Yamamoto, J. Am. Chem.
Soc. 2016, 138, 10356.
51, 6443; f) D. Feng, Z. Y. Gu, J. R. Li, H.-L. Jiang, Z. Wei, H.-C. Zhou,
Angew. Chem., Int. Ed. 2012, 51, 10307; g) H. Furukawa, F. Gándara,
Y.-B. Zhang, J. Jiang, W. L. Queen, M. R. Hudson, O. M. Yaghi, J. Am.
Chem. Soc. 2014, 136, 4369; h) V. Bon, I. Senkovska, I. A. Baburin,
S. Kaskel, Cryst. Growth Des. 2013, 13, 1231.
[6] K. Chernichenko, Á. Madarász, I. Pápai, M. Nieger, M. Leskelä,
T. Repo, Nat. Chem. 2013, 5, 718.
[7] a) X. Li, Y. Pan, H. Yi, J. Hu, D. Yang, F. Lv, W. Li, J. Zhou, X. Wu,
A. Lei, L. Zhang, ACS Catal. 2019, 9, 4632; b) Y. Kuwahara,
H. Kango, H. Yamashita, ACS Catal. 2019, 9, 1993.
[8] H.-C. Zhou, S. Kitagawa, Chem. Soc. Rev. 2014, 43, 5415.
[9] a) H. Furukawa, K. E. Cordova, M. O’Keeffe, O. M. Yaghi, Science
2013, 341, 1230444; b) G. Maurin, C. Serre, A. Cooper, G. Férey,
Chem. Soc. Rev. 2017, 46, 3104; c) B. Li, H.-M. Wen, Y. Cui, W. Zhou,
G. Qian, B. Chen, Adv. Mater. 2016, 28, 8819; d) W. P. Lustig,
S. Mukherjee, N. D. Rudd, A. V. Desai, J. Li, S. K. Ghosh, Chem. Soc.
Rev. 2017, 46, 3242; e) Q.-G. Zhai, X. Bu, X. Zhao, D.-S. Li, P. Feng,
Acc. Chem. Res. 2017, 50, 407.
[13] a) M. J. Cliffe, W. Wan, X. Zou, P. A. Chater, A. K. Kleppe, M. G. Tucker,
H. Wilhelm, N. P. Funnell, F.-X. Coudert, A. L. Goodwin, Nat.
Commun. 2014, 5, 4176; b) H. Wu, Y. S. Chua, V. Krungleviciute,
M. Tyagi, P. Chen, T. Yildirim, W. Zhou, J. Am. Chem. Soc. 2013, 135,
10525; c) G. C. Shearer, S. Chavan, J. Ethiraj, J. G. Vitillo, S. Svelle,
U. Olsbye, C. Lamberti, S. Bordiga, K. P. Lillerud, Chem. Mater.
2014, 26, 4068; d) O. V. Gutov, M. G. l. Hevia, E. C. Escudero-Adán,
A. Shafir, Inorg. Chem. 2015, 54, 8396; e) F. Vermoortele, B. Bueken,
G. l. Le Bars, B. Van de Voorde, M. Vandichel, K. Houthoofd,
A. Vimont, M. Daturi, J. Am. Chem. Soc. 2013, 135, 11465.
[14] a) Y. Liu, R. C. Klet, J. T. Hupp, O. Farha, Chem. Commun. 2016,
52, 7806; b) F. Cirujano, A. Corma, F. L. i. Xamena, Chem. Eng. Sci.
2015, 124, 52.
[10] a) C. Wang, D. Liu, W. Lin, J. Am. Chem. Soc. 2013, 135, 13222;
b) T. Islamoglu, S. Goswami, Z. Li, A. J. Howarth, O. K. Farha,
J. T. Hupp, Acc. Chem. Res. 2017, 50, 805; c) L. Jiao, Y. Wang, H. Jiang,
Q. Xu, Adv. Mater. 2018, 30, 1703663; d) J. Liu, L. Chen, H. Cui, J. Zhang,
L. Zhang, C.-Y. Su, Chem. Soc. Rev. 2014, 43, 6011; e) X. Lian, Y. Fang,
E. Joseph, Q. Wang, J. Li, S. Banerjee, C. Lollar, X. Wang, H.-C. Zhou,
Chem. Soc. Rev. 2017, 46, 3386; f) W.-Y. Gao, M. Chrzanowski,
S. Ma, Chem. Soc. Rev. 2014, 43, 5841; g) A. H. Chughtai, N. Ahmad,
H. A. Younus, A. Laypkov, F. Verpoort, Chem. Soc. Rev. 2015, 44, 6804;
h) M. Yoon, R. Srirambalaji, K. Kim, Chem. Rev. 2012, 112, 1196;
i) A. Dhakshinamoorthy, H. Garcia, Chem. Soc. Rev. 2014, 43, 5750;
j) C.-D. Wu, M. Zhao, Adv. Mater. 2017, 29, 1605446.
[11] a) H. R. Moon, D. W. Lim, M. P. Suh, Chem. Soc. Rev. 2013, 42,
1807; b) A. Aijaz, A. Karkamkar, Y. J. Choi, N. Tsumori, E. Rönnebro,
T. Autrey, H. Shioyama, Q. Xu, J. Am. Chem. Soc. 2012, 134, 13926;
c) P. Hu, J. V. Morabito, C.-K. Tsung, ACS Catal. 2014, 4, 4409;
d) K. Na, K. M. Choi, O. M. Yaghi, G. A. Somorjai, Nano Lett. 2014,
14, 5979; e) Y.-Z. Chen, Y.-X. Zhou, H. Wang, J. Lu, T. Uchida, Q. Xu,
S.-H. Yu, H.-L. Jiang, ACS Catal. 2015, 5, 2062.
[15] M. W. Anjum, F. Vermoortele, A. L. Khan, B. Bueken, D. E. De Vos,
I. F. Vankelecom, ACS Appl. Mater. Interfaces 2015, 7, 25193.
[16] a) A. M. Plonka, Q. Wang, W. O. Gordon, A. Balboa, D. Troya,
W. Guo, C. H. Sharp, S. D. Senanayake, J. R. Morris, C. L. Hill,
J. Am. Chem. Soc. 2017, 139, 599; b) E. López-Maya, C. Montoro,
L. M. Rodríguez-Albelo, S. D. Aznar Cervantes, A. A. Lozano-Pérez,
J. L. Cenís, E. Barea, J. A. Navarro, Angew. Chem., Int. Ed. 2015, 54,
6790.
[17] P. Ji, T. Drake, A. Murakami, P. Oliveres, J. H. Skone, W. Lin, J. Am.
Chem. Soc. 2018, 140, 10553.
[18] L. Valenzano, B. Civalleri, S. Chavan, S. Bordiga, M. H. Nilsen,
S. Jakobsen, K. P. Lillerud, C. Lamberti, Chem. Mater. 2011, 23,
1700.
[19] F.-M. McKenna, J. A. Anderson, J. Catal. 2011, 281, 231.
[20] B. Lim, M. Jiang, J. Tao, P. H. Camargo, Y. Zhu, Y. Xia, Adv. Funct.
Mater. 2009, 19, 189.
[21] J. F. Moulder, W. F. Stickle, P. E. Sobol, K. D. Bomben, Handbook
of X-Ray Photoelectron Spectroscopy, Physical Electronics Division,
Perkin-Elmer Corporation, Eden Prairie, MN 1992.
[12] a) J. H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti,
S. Bordiga, K. P. Lillerud, J. Am. Chem. Soc. 2008, 130, 13850;
b) J. E. Mondloch, W. Bury, D. Fairen-Jimenez, S. Kwon, E. J. DeMarco,
M. H. Weston, A. A. Sarjeant, S. T. Nguyen, P. C. Stair, R. Q. Snurr,
O. K. Farha, J. T. Hupp, J. Am. Chem. Soc. 2013, 135, 10294;
c) D. Feng, W. C. Chung, Z. Wei, Z. Y. Gu, H.-L. Jiang, Y. P. Chen,
D. J. Darensbourg, H.-C. Zhou, J. Am. Chem. Soc. 2013, 135, 17105;
d) C. Wang, J.-L. Wang, W. Lin, J. Am. Chem. Soc. 2012, 134, 19895;
e) W. Morris, B. Volosskiy, S. Demir, F. Gandara, P. L. McGrier,
H. Furukawa, D. Cascio, J. F. Stoddart, O. M. Yaghi, Inorg. Chem. 2012,
[22] A. F. Lee, S. F. Hackett, J. S. Hargreaves, K. Wilson, Green Chem.
2006, 8, 549.
[23] S. A. Best, P. Brant, R. D. Feltham, T. B. Rauchfuss, D. M. Roundhill,
R. A. Walton, Inorg. Chem. 1977, 16, 1976.
[24] P. Grafen, H. Kiefer, H. Jaedicke, (BASF SE), U.S. 5468883, 1995.
[25] M. Crespo-Quesada, A. Yarulin, M. Jin, Y. Xia, L. KiwiMinsker, J. Am.
Chem. Soc. 2011, 133, 12787.
[26] a) J. Zhang, J. S. Moore, J. Am. Chem. Soc. 1992, 114, 9701;
b) C. A. Hamilton, S. D. Jackson, G. J. Kelly, R. Spence, D. de Bruin,
Appl. Catal., A 2002, 237, 201.
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