Dual Pd and CuFe2O4 nanoparticles encapsulated in a core/shell silica microsphere for selective hydrogenation of arylacetylenes

Article abstract of DOI:10.1039/c2cc30285c

A dual catalyst containing Pd and CuFe₂O₄ nanoparticles in a silica shell exhibits >98% conversion of arylacetylenes to related styrenes with selectivity greater than 98%, which are better than those obtained using a commercial Lindlar catalyst. The excellent synergy was likely a result of the proximal interaction between Pd and CuFe₂O ₄ nanoparticles.

Full text of DOI:10.1039/c2cc30285c

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COMMUNICATION
Dual Pd and CuFe O nanoparticles encapsulated in a core/shell silica
2
4
microsphere for selective hydrogenation of arylacetylenesw
Kyu Hyung Lee, Byeongno Lee, Kyu Reon Lee, Mi Hye Yi and Nam Hwi Hur*
Received 13th January 2012, Accepted 5th March 2012
DOI: 10.1039/c2cc30285c
A dual catalyst containing Pd and CuFe O nanoparticles in a
2
the cycloaddition of azides and alkynes, which offers significant
4
silica shell exhibits >98% conversion of arylacetylenes to
related styrenes with selectivity greater than 98%, which are
better than those obtained using a commercial Lindlar catalyst.
The excellent synergy was likely a result of the proximal
advantages over homogeneous catalysts based on soluble copper
8
complexes. This prompts us to investigate various metal
nanoparticles (NPs) supported on a porous silica as promising
candidates for heterogeneous catalysts with great selectivity.
interaction between Pd and CuFe
2
O
4
nanoparticles.
2 4
We report here that dual Pd and copper ferrite (CuFe O )
NPs encapsulated within a core/shell silica microsphere exhibit
excellent synergy in the selective hydrogenation of phenylacetylene
to styrene. This encapsulated dual catalyst demonstrates >98%
selectivity to styrene and >98% conversion of phenylacetylene
within 2.5 h, even in the absence of additives, which is better than
the performance of the Lindlar catalyst. Moreover, the catalyst
is easily separated using a magnet owing to the presence of
Selective hydrogenation of alkynes to alkenes, without further
reduction to alkanes, is of great significance in the production
1
of polymers as well as the synthesis of fine chemicals. For
example, the production of polyolefin requires the removal of
trace alkyne from the alkene feed because alkynes deactivate the
polymerization catalyst and lower the degree of polymerization.
For effective polymerization, the alkynes content should be
2 4
magnetic CuFe O NPs. The encapsulation of dual components
2
in a porous shell might provide a viable method for the synthesis
of active and robust NPs suitable for practical applications.
reduced to a low ppm level in the alkenes feed. Accordingly, a
highly selective catalyst, which can readily convert alkynes to
alkenes but does not convert alkenes to alkanes, is desired.
Earlier studies of hydrogenation catalysts have focused on
the development and utilization of supported catalysts based
The dual catalyst (SiO
2
@CuFe
2
O
4
–Pd) was prepared on the
@CoFe
2 4
microsphere. Briefly, CuFe O and Pd NPs were sequentially
basis of our previous work regarding the SiO
2
2 4
O
9
3
embedded within mesoporous shells of a core/shell silica
microsphere, after which they were dried and annealed at
elevated temperatures. The samples for control experiments,
denoted as SiO @CuFe O , SiO @Pd, SiO @CoFe O –Pd,
on palladium (Pd) metal and various supports. Among them,
a Lindlar catalyst is the most widely used owing to its high
selectivity toward hydrogenation reactions. When the Lindlar
catalyst is used, a lead complex is employed to deactivate the
Pd sites. Moreover, quinoline is usually added to prevent the
formation of alkanes and to enhance the selectivity. A drawback
of the Lindlar catalyst is that toxic additives are required for
the selective hydrogenation, which results in the production of
2
2
4
2
2
2
4
and SiO @Fe O –Pd, were prepared in the same manner as
3
2
4
the SiO
schematically in Fig. 1a, the SiO
core/shell structure in which CuFe
within porous shells. The high-resolution TEM images of typical
SiO @CuFe –Pd microspheres given in Fig. 1b confirm the
2
@CuFe
2
O
4
–Pd microsphere (see ESIw). As depicted
@CuFe –Pd catalyst has a
and Pd NPs are confined
2
2 4
O
2 4
O
4
harmful wastes. Modifications of the Pd-based catalysts by
2 4
O
alloying with less-toxic metals or by using the site-isolation
5
concept have been made, and these modified catalysts have
2
distinctive core/shell feature. The average diameter of the
spheres is 380 nm and the diameter ratio of the core/shell is
approximately 3.8. Mapping images, captured using an energy
dispersive X-ray analyzer, provide direct evidence of the presence
of Cu, Fe, and Pd atoms in the microsphere (Fig. S1, ESIw).
The three elements are distributed over the silica surface,
been shown to have a high selectivity. However, the modified
catalysts also often require additives to increase their selectivity.
Accordingly, it is desirable to develop a new heterogeneous
catalyst that maintains high selectivity in the absence of
additives and is easily separated from the reaction mixture.
It is well known that novel metal catalysts supported on
6
oxides are stable and active for various reactions such as
7
hydrogenation and CO oxidation. We also demonstrated that
3
a supported Cu N catalyst exhibits superior activity toward
Department of Chemistry, Sogang University, Seoul 121-742, Korea.
E-mail: nhhur@sogang.ac.kr
Fig. 1 (a) Schematic procedure for the preparation of SiO
CuFe –Pd. (b) High-resolution TEM image of SiO @CuFe –Pd.
The inset is the enlarged view of the TEM image.
2
@
2
O
4
2
2 4
O
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c2cc30285c
4
414 Chem. Commun., 2012, 48, 4414–4416
This journal is c The Royal Society of Chemistry 2012

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implying that CuFe
pores. High-resolution SEM images of SiO
clearly show that several CuFe O NPs are randomly spaced
2
O
4
and Pd NPs are well encapsulated within
the SiO @Pd microsphere containing only Pd NPs. Interestingly,
2
the SiO @Pd catalyst exhibits only 3% conversion in 2.5 h
2
2
@CuFe –Pd
2
O
4
(Table 1, entry 4), even though it has high selectivity for
hydrogenation. The Pd NPs encapsulated within the silica
shell might be less reactive than the Pd NPs anchored on the
surface of the support owing in part to the structural hindrance.
2
4
on the silica surface and lots of tiny Pd dots are evenly dispersed
on the surface (Fig. S2, ESIw). The weight percentages of Cu, Fe
and Pd are 0.89%, 1.61% and 4.15% based on ICP-MS
quantitative analysis (Table S1, ESIw), respectively. The BET
2 4
Based on these findings, the CuFe O NPs only promote the
data reveal that porous shells are filled with CuFe
NPs (Table S2, ESIw). As anticipated, the surface area of
SiO @CuFe –Pd is decreased owing to the embedded
CuFe and Pd NPs into the shell. The presence of CuFe
2
O
4
and Pd
hydrogenation reaction when they are coupled with Pd NPs
within the confined structure.
2
2
O
4
It has been reported that nano-catalysts with dual compo-
nents can exhibit high activity for various reactions largely as a
2
O
4
2 4
O
1
0,11
and Pd NPs in the silica microsphere is also demonstrated by
X-ray powder diffraction (Fig. S3, ESIw). When the sample is
annealed at 573 K, crystallite sizes of Pd NPs, as calculated
using the Scherrer equation, increased significantly from 2.4 to
result of the synergistic effect of two active species.
explore the effects of CuFe on the activity of Pd in detail,
we prepared two other ferrites denoted as SiO @CoFe O –Pd
To
2 4
O
2
2
4
and SiO @Fe O –Pd in which CoFe O and Fe O NPs are
4
2
3
4
2
4
3
2
5.2 nm (Fig. S4, ESIw). The field-dependent magnetization
curves of SiO @CuFe O –Pd collected at 10 and 300 K
embedded within the shell together with Pd NPs in the same
way as the SiO @CuFe O –Pd catalyst. The three ferrites
2
2
4
2
2
4
show that SiO
Fig. S5, ESIw).
The efficacies of the dual SiO
selective hydrogenation were evaluated in a H
2
@CuFe
2
O
4
–Pd NPs are superparamagnetic
have a cubic spinel structure with a general formula of AFe
(A = Cu, Co, Fe). The two samples, SiO @CoFe –Pd and
SiO @Fe –Pd, have lower activities for the hydrogenation
of phenylacetylene than SiO @CuFe –Pd (Table S4, ESIw).
A notable feature is that the SiO @Fe –Pd catalyst shows
2 4
O
(
2
2 4
O
2
@CuFe
2
O
4
–Pd catalyst for
-filled flask. The
2
3 4
O
2
2
2 4
O
1
products were analyzed via gas chromatography and H NMR.
2
3 4
O
A notable feature is that the catalyst shows very high selectivity
reasonably high conversion (60%) and selectivity (87%), indicating
that a promotional effect can be achieved by Fe species alone.
Differences between the activities of the Pd NPs in close
contact with CoFe O , Fe O , and CuFe O NPs might be
(
over 97%), regardless of the polarity of solvents. However, the
reaction rate is strongly dependent on the nature of the solvent.
Among the tested solvents, hexane was found to be most
reliable for the hydrogenation reaction (Table S3, ESIw);
therefore it was used in subsequent reactions. Remarkably,
the dual catalyst achieved almost complete conversion (>98%)
within 2.5 h in the absence of any additives, with a high selectivity
of over 98% toward styrene (Table 1, entry 1). Conversely, the
commercial Lindlar catalyst provides only 82% conversion with
a selectivity of approximately 92% toward styrene (Table 1,
2
4
3
4
2
4
caused by an interaction between the metal (Pd) and the A-site
ion in the ferrite matrix.
In an effort to elucidate the precise role of Cu in the catalytic
reaction, we conducted the same hydrogenation reaction using
2
a SiO @CuO–Pd catalyst that contained only Cu species
along with Pd NPs in the porous shell. The catalyst is not
efficient for the hydrogenation reaction within 2.5 h (Table S4,
entry 5, ESIw), suggesting that the Cu atom might suppress
the activity of Pd NPs. This finding indicates that the high
activity of SiO @CuFe O –Pd is a result of both Cu and Fe
entry 2). Clearly, our SiO
better activity than the Lindlar catalyst.
To understand the role of CuFe O NPs in the hydro-
2 2 4
@CuFe O –Pd catalyst shows
2
4
2
2
4
genation reaction, we investigated the catalytic activity of
the SiO @CuFe O microsphere. No noticeable changes were
atoms in CuFe O . It is worth noting that Pd NPs can be
2 4
magnetized by magnetic NPs when they are in close contact,
providing direct evidence of spin transfer from magnetic to
2
2
4
observed for 46 h (Table 1, entry 3), implying that CuFe O
2
4
1
2
NPs themselves are inactive for the hydrogenation. This, in
turn, suggests that Pd NPs play a major role in catalysis of
the hydrogen reaction. The same reaction was conducted using
non-magnetic materials. This supports the supposition that
the electronic interaction between Pd and magnetic CuFe
NPs in SiO @CuFe –Pd enhances the activity of Pd.
2 4
O
2
2 4
O
Inhibition of styrene (vinyl benzene) hydrogenation is
another important factor to explain the high selectivity of
a
Table 1 Hydrogenation of phenylacetylene to styrene with catalysts
SiO
genation of styrene under the same conditions using SiO
SiO @CuO–Pd, and SiO @CuFe O –Pd as the catalysts
2
@CuFe
2
O
4
–Pd. In this context, we performed the hydro-
2
@Pd,
2
2
2
4
(
Table S5, ESIw). When the SiO @Pd catalyst was used, the
2
reaction proceeded rapidly with complete conversion of styrene
Time Conversion Selectivity TOF
(h)
b
b
ꢀ1 d
(h )
to ethyl benzene occurring in 2.5 h under 1 atm of H . This
2
Entry Catalyst
(%)
(%)
facile hydrogenation was unexpected because the encapsulated
Pd catalyst showed only 3% conversion of phenylacetylene
(Table 1, entry 4) under the same conditions. The conversion
1
2
2
3
4
SiO
2
@CuFe
2
O
4
–Pd 2.5
98
82
98
—
3
98
92
76
—
98
91
64
54
0
c
Lindlar Catalyst
Lindlar Catalyst
2.5
3.5
2.5
2.5
0
c
SiO
SiO
2
2 4
@CuFe O
@Pd
of styrene by SiO
conversion rate was slower than that catalyzed by SiO
However, the SiO @CuO–Pd catalyst might not be reactive
2
@CuFe
2
O
4
–Pd was also observed, but the
2
3
2
@Pd.
a
Reaction conditions: phenylacetylene 0.91 mmol, catalyst 10 mg,
1
2
b
hexane 2 mL, H
2
balloon (about 1 atm). Confirmed by H NMR and
poisoned with a lead
toward the styrene hydrogenation. The experimental results suggest
that the CuFe O phase promotes the conversion of phenyl-
c
GC. Lindlar catalyst (ca. 5 wt% Pd on CaCO
3
d
complex, Aldrich, 10 mg). [mol product]/[mol catalyst][hour].
2
4
acetylene to styrene (the first hydrogenation step) and is less
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 4414–4416 4415

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Notes and references
1
(a) B. Bridier, N. Lo
9, 8412; (b) S. A. Nikolaev, L. N. Zanaveskin, V. V. Smirnov,
V. A. Averyanov and K. L. Zanaveskin, Russ. Chem. Rev., 2009,
78, 231; (c) D. Teschner, J. Borsodi, A. Wootsch, Z. Revay,
M. Havecker, A. Knop-Gericke, S. D. Jackson and R. Schlogl,
pez and J. Perez-Ramırez, Dalton Trans., 2010,
´ ´ ´
3
Fig. 2 Proposed reaction pathway for hydrogenation of phenylacetylene
catalyzed by Pd and CuFe . Dual activation of phenylacetylene by
Pd and CuFe
´
O
2 4
¨
¨
Science, 2008, 320, 86; (d) F. Studt, F. Abild-Pedersen, T. Bligaard,
R. Z. Sørensen, C. H. Christensen and J. K. Nørskov, Science,
2
4
O .
2
008, 320, 1320.
likely to affect the conversion of styrene to ethyl benzene
the second hydrogenation step). To support this dual func-
tion of CuFe O , we investigated the hydrogenation of about
2
(a) X.-Y. Ma, Y.-Y. Chai, D. G. Evans, D.-Q. Li and J.-T. Feng,
J. Phys. Chem. C, 2011, 115, 8693; (b) Z. Shao, C. Li, X. Chen,
M. Pang, X. Wang and C. Liang, ChemCatChem, 2010, 2, 1555;
(
2
4
´
´
(
c) S. Domı
Solano and D. Cazorla-Amoro
d) N. Semagina, A. Renken and L. Kiwi-Minsker, J. Phys. Chem. C,
007, 111, 13933.
´
nguez-Domı
´
nguez, A. Berenguer-Murcia, A. Linares-
a 1 : 1 mixture of phenylacetylene and styrene using the
SiO @CuFe –Pd catalyst (Fig. S10 and S17, ESIw).
Conversion of phenylacetylene to styrene was much faster
than that of styrene to ethyl benzene, suggesting that CuFe
´
s, J. Catal., 2008, 257, 87;
2
2 4
O
(
2
2
O
4
3 (a) Y. Wang, J. Yao, H. Li, D. Su and M. Antonietti, J. Am. Chem.
Soc., 2011, 133, 2362; (b) F.-M. McKenna, R. P. K. Wells and
J. A. Anderson, Chem. Commun., 2011, 47, 2351; (c) M. Crespo-
Quesada, A. Yarulin, M. Jin, Y. Xia and L. Kiwi-Minsker, J. Am.
Chem. Soc., 2011, 133, 12787; (d) M. Choi, Z. Wu and E. Iglesia,
J. Am. Chem. Soc., 2010, 132, 9129; (e) J.-N. Park, A. J. Forman,
W. Tang, J. Cheng, Y.-S. Hu, H. Lin and E. W. McFarland, Small,
NPs act as promoters for the conversion of phenylacetylene to
styrene and also play an important role in inhibition of the
hydrogenation of styrene. This is due presumably to higher
affinity of copper to phenylacetylene than styrene. Another
important advantage of the SiO @CuFe O –Pd catalyst is
2
2
4
2
008, 4, 1694.
9
,13
that it can be easily separated by a magnet (Fig. S11, ESIw).
Virtually identical conversion and selectivity were obtained
4
5
6
(a) H. Lindlar, Helv. Chim. Acta., 1952, 34, 446; (b) H. Lindlar and
R. Dubuis, Org. Synth., 1966, 46, 89; (c) J. Rajaram, A. P. S.
Narula, H. P. S. Chawla and S. Dev, Tetrahedron, 1983, 39,
from the recycle experiment (Table S6, ESIw).
It is worth mentioning that the SiO @CuFe O –Pd catalyst
2 2 4
2
315.
(a) X. Chen, A. Zhao, Z. Shao, C. Li, C. T. Williams and C. Liang,
J. Phys. Chem. C, 2010, 114, 16525; (b) S. Domınguez-Domınguez,
A. Berenguer-Murcia, B. K. Pradhan, A. Linares-Solano and
D. Cazorla-Amoros, J. Phys. Chem. C, 2008, 112, 3827.
also shows the high selectivity for phenylacetylene derivatives.
Almost complete conversion (>98%) and high selectivity were
observed for the substrates (Table S7, ESIw). By comparison
with phenylacetylene, interestingly, the electron withdrawing
´
´
´
´
´
(a) L. Kesavan, R. Tiruvalam, M. H. Ab Rahim, M. I. Bin Saiman,
D. I. Enache, R. L. Jenkins, N. Dimitratos, J. A. Lopez-Sanchez,
S. H. Taylor, D. W. Knight, C. J. Kiely and G. J. Hutchings,
Science, 2011, 331, 195; (b) H. G. Manyar, C. Paun, R. Pilus,
D. W. Rooney, J. M. Thompson and C. Hardacre, Chem. Commun.,
3
groups (–F, –CF ) on the phenyl ring accelerate the hydro-
genation reactions while an electron donating group (–CH
slightly retards the catalytic reaction.
3
)
2
2009, 9, 1493; (d) A. Corma, P. Serna, P. Concepcion and
010, 46, 6279; (c) C. Wang, H. Daimon and S. Sun, Nano Lett.,
´
The high selectivity of SiO @CuFe O –Pd could be explained
2
2
4
in terms of four possible sequential steps, which are schematically
illustrated in Fig. 2: (i) a phenylacetylene molecule adsorbs onto a
J. J. Calvino, J. Am. Chem. Soc., 2008, 130, 8748; (e) D. K. Yi,
S. S. Lee and J. Y. Ying, Chem. Mater., 2006, 18, 2459.
(a) J. Xu, T. White, P. Li, C. He, J. Yu, W. Yuan and Y.-F. Han,
J. Am. Chem. Soc., 2010, 132, 10398; (b) H. Liu, D. Ma,
R. A. Blackley, W. Zhou and X. Bao, Chem. Commun., 2008,
7
8
2 4
CuFe O surface through a Cu atom at the triple bond; (ii) the
triple bond is converted to a double bond by the insertion of a
H atom adsorbed on the Pd surface; (iii) a second H atom
reacts with the surface bonded C atom; (iv) the styrene molecule
2
3, 2677.
B. S. Lee, M. Yi, S. Y. Chu, J. Y. Lee, H. R. Kwon, K. R. Lee,
D. Kang, W. S. Kim, H. B. Lim, J. Lee, H.-J. Youn, D. Y. Chi and
N. H. Hur, Chem. Commun., 2010, 46, 3935.
2 4
detaches from the CuFe O surface. It has been well-documented
that Cu species catalyze 1,3-dipolar cycloaddition reactions in
9 K. R. Lee, S. Kim, D. H. Kang, J. I. Lee, Y. J. Lee, W. S. Kim,
D.-H. Cho, H. B. Lim, J. Kim and N. H. Hur, Chem. Mater., 2008,
1
4
which the Cu ions activate the triple bond in alkyne. This
indicates that the Cu ion favors interaction with the triple
bond although the Cu effect in the selective hydrogenation of
phenylacetylene has not been fully understood yet.
2
0, 6738.
1
1
0 (a) H.-L. Jiang and Q. Xu, J. Mater. Chem., 2011, 21, 13705;
(b) S. Sitthisa, T. Pham, T. Prasomsri, T. Sooknoi,
R. G. Mallinson and D. E. Resasco, J. Catal., 2011, 280, 17;
(
c) B. Bridier and J. Pe
32, 4321.
˘
1 (a) J. Muslehiddinoglu, J. Li, S. Tummala and R. Deshpande,
rez-Ramırez, J. Am. Chem. Soc., 2010,
´ ´
In summary, we have synthesized a SiO @CuFe O –Pd
2
2
4
1
2 4
catalyst in which dual Pd and CuFe O NPs were encapsulated
¨
within a core/shell silica microsphere. The dual catalyst shows
excellent activity and selectivity for the hydrogenation of
phenylacetylenes to related styrenes. Our experimental results
Org. Process Res. Dev., 2010, 14, 890; (b) N. N. Kariuki, X. Wang,
J. R. Mawdsley, M. S. Ferrandon, S. G. Niyogi, J. T. Vaughey and
D. J. Myers, Chem. Mater., 2010, 22, 4144; (c) M. P. R. Spee,
J. Boersma, M. D. Meijer, M. Q. Slagt, G. van Koten and
J. W. Geus, J. Org. Chem., 2001, 66, 1647.
2 4
demonstrate that magnetic CuFe O NPs in close contact with
Pd NPs not only promote the catalytic reaction, but also act as
magnets for easy separation of the catalyst, which opens up
the possibility for development of highly selective and recyclable
heterogeneous catalysts for practical applications.
12 (a) Y. N. Kim, E. K. Lee, Y. B. Lee, H. Shim, N. H. Hur and
W. S. Kim, J. Am. Chem. Soc., 2004, 126, 8672; (b) Z. Celinski,
B. Heinrich, J. F. Cochran, W. B. Muir, A. S. Arrott and
J. Kirschner, Phys. Rev. Lett., 1990, 65, 1156.
13 V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara and
J.-M. Bassett, Chem. Rev., 2011, 111, 3036.
We thank the Converging Research Centre Program
1
4 (a) M. Meldal and C. W. Tornøe, Chem. Rev., 2008, 108, 2952;
b) V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B.
Sharpless, Angew. Chem., Int. Ed., 2002, 41, 2596; (c) R. Huisgen,
G. Szeimies and L. Moebius, Chem. Ber., 1965, 98, 4014.
(
2010K001050) and the NRL program (2010-0018937) funded
(
by the Ministry of Education, Science, and Technology through
the National Research Foundation of Korea.
¨
4
416 Chem. Commun., 2012, 48, 4414–4416
This journal is c The Royal Society of Chemistry 2012

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Showcasing research from Professor Nam Hwi Hur’s
laboratory, Sogang University, Korea.
As featured in:
Dual Pd and CuFe O nanoparticles encapsulated in a core/shell
2
4
silica microsphere for selective hydrogenation of arylacetylenes
A dual Pd and CuFe O catalyst supported on a core/shell silica
2
4
microsphere exhibits >98% conversion from arylacetylenes to
related styrenes with selectivity greater than 98%, which are better
than those obtained using a commercial Lindlar catalyst.
See Nam Hwi Hur et al.,
Chem. Commun., 2012, 48, 4414.
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