Ultrafine FeCu Alloy Nanoparticles Magnetically Immobilized in Amine-Rich Silica Spheres for Dehalogenation-Proof Hydrogenation of Nitroarenes

Article abstract of DOI:10.1002/chem.201801942

A novel core–shell structured nanocatalyst (Fe₃O₄@SiO₂-NH₂-FeCu nanoparticles) with ultrafine FeCu alloy NPs magnetically immobilized in porous silica has been fabricated. The obtained catalyst revealed excellent activity and chemoselectivity for catalyzing the hydrogenation of nitroarenes to corresponding anilines using hydrazine hydrate as the hydrogen source, and the reaction could be carried out smoothly in water, which is an environmentally friendly solvent. The FeCu alloy effectively prevented the dehalogenation of halonitroarenes, and X-ray photoelectron spectroscopy (XPS) study showed that it resulted from the electron-enrichment of Fe from Cu. A kinetics study indicated that the reaction order was about 1.5 towards 4-CNB and the apparent active energy (E_a) was 48.1 kJ mol^?1, which is a relatively low value. Furthermore, the FeCu NPs are magnetically immobilized in the silica spheres (Fe₃O₄@SiO₂), therefore the catalyst can be easily recovered by use of an external magnet and also possesses a long life time.

Full text of DOI:10.1002/chem.201801942

A Journal of
Accepted Article
Title: Ultrafine FeCu Alloy Nanoparticles Magnetically Immobilized
in Amine-Rich Silica Spheres for Dehalogenation-Proof
Hydrogenation of Nitroarenes
Authors: Hong-bin Sun, Hongjie Bao, Yunong Li, Lei Liu, Yongjian Ai,
Junjie Zhou, Li Qi, Ruihang Jiang, Zenan Hu, Jingting Wang,
and Qionglin Liang
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To be cited as: Chem. Eur. J. 10.1002/chem.201801942
Link to VoR: http://dx.doi.org/10.1002/chem.201801942
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Ultrafine FeCu Alloy Nanoparticles Magnetically Immobilized in
Amine-Rich Silica Spheres for Dehalogenation-Proof
Hydrogenation of Nitroarenes
Hongjie Bao,[a]‡ Yunong Li,[a]‡ Lei Liu,[a] Yongjian Ai,[b] Junjie Zhou,[a] Li Qi,[a] Ruihang Jiang,[a] Zenan
Hu,[a] Jingting Wang,[a] Hongbin Sun*[a] and Qionglin Liang*[b]
Dedication ((optional))
Abstract: A novel core-shell structured nanocatalyst (Fe3O4@SiO2-
NH2-FeCu nanoparticles) with ultrafine FeCu alloy NPs magnetically
immobilized in porous silica has been fabricated. The obtained
catalyst revealed excellent activity and chemoselectivity for
catalyzing the hydrogenation of nitroarenes to corresponding
anilines using hydrazine hydrate as the hydrogen source, and the
reaction could be carried out smoothly in water, which is an
environmentally friendly solvent. The FeCu alloy effectively
prevented the dehalogenation of halonitroarenes, and the X-ray
photoelectron spectroscopy (XPS) study showed that it was
contributed from the electron-enrichment of Fe from Cu. A kinetics
study indicated that the reaction order was ~1.5 towards 4-CNB and
the apparent active energy (Ea) was 48.1 kJ mol-1, which was a
relatively low value. Furthermore, the FeCu NPs are magnetically
immobilized in the silica spheres (Fe3O4@SiO2), therefore the
catalyst can be easily recovered by an external magnetic and also
possess long life time.
the manufacture of HANs compared with the other two methods
that produce pernicious substances.[1b,7] In this process,
hydrazine hydrate as a hydrogen source has great advantage in
easy handing and clean by-product nitrogen. To date, in the
heterogeneous catalyst system for the hydrogenation of HNBs,
the noble metals mainly work as the active ingredient, such as
Pd,[8] Rh,[9] Ru,[10] Pt,[11] and Au.[12] Nevertheless, there are still
some limitations for the large-scale applications including the
high price of noble metals and the appearance of
dehalogenation phenomenon caused by the hydrogenolysis of
the weak carbon−halogen bond.[13]
In this context, iron-based catalysts have aroused much
interest for their earth abundance and non-toxic nature.[14]
Meanwhile, various well-designed iron-based catalysts have
been proven to be able to improve the catalytic activity or
selectivity.[15] However, it is still challenging to enhance both the
activity and selectivity simultaneously.[16] On the one hand, the
bimetallic materials have the great potential of improving the
catalytic selectivity by the electronic modification of metal which
is suitable for the HNBs hydrogenation.[17] On the other hand,
metal NPs with ultra-small size can show different electronic and
chemical performance, and downsizing the particles is a
promising way to promote the catalytic activity thanks to the
increased number of surface vacancies and coordination
Introduction
Aromatic amines are important raw materials that have been
widely applied in synthesizing fine chemicals. Among these
substances, haloanilines (HANs) are especially important as
valuable intermediates for fabricating various products, such as
pharmaceuticals, dyes, pigments, and pesticides.[1] Accordingly,
the preparation of HANs from reduction of halonitrobenzenes
(HNBs) has come into notice in recent years. Methods for the
reduction of HNBs mainly focus on the metal/acid reduction,
sulfide reduction and catalytic transfer hydrogenation.[2]
Generally, catalytic transfer hydrogenation using ammonia
borane,[3] glycerol,[4] isopropanol[5] or hydrazine hydrate[6] as the
hydrogen source is a more environmentally benign protocol for
sites.[18] In addition,
a carrier may affect the catalytic
performance vigorously.[11] In this case, confining the active site
into the suitable core-shell structure with micro tunnels is a
towardly way to maintain the reaction activity.[19] Furthermore,
encapsulating the ultrafine nanoparticles in mesoporous shells
can also improve their stability even under harsh reaction
conditions.[20] Above all, the magnetic metal NPs which are
immobilized to the magnetic carrier can obviously prolong
lifetime of the catalyst, successfully prevent the leaching of the
nanoparticles during the reaction and the catalysts can separate
easily with an external magnet.[21]
In this work, a core-shell structured nanocatalyst was easily
fabricated with ultrafine FeCu alloy NPs magnetically
immobilized in the porous silica spheres. The catalyst was
described as Fe3O4@SiO2-NH2-FeCu NPs (Scheme 1). The
FeCu bimetallic NPs are promising active species for the
reaction. They have been successfully prepared by atomic layer
deposition[22] or co-precipitation with surfactant assisted.[23] To
the best of our knowledge, obtaining the FeCu NPs with such
ultrafine size through a simple NaBH4 reduction has not been
reported. The FeCu alloy based catalyst exhibited good activity
and chemoselectivity for the transfer hydrogenation of HNBs and
other functionalized nitroarenes using N2H4·H 2O as hydrogen
[a]
[b]
Dr. H. Bao, Dr. Y. Li, Dr. L. Liu, Dr. J. Zhou, L. Qi, R. Jiang, Dr. Z.
Hu, J. Wang, Dr. H. Sun.
Department of Chemistry, Northeastern University
Shenyang 110819, People’s Republic of China
E-mail: sunhb@mail.neu.edu.cn
Dr. Y. Ai, Dr. Q, Liang.
Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical
Biology (Ministry of Education), Department of Chemistry
Tsinghua University
Beijing 100084, People’s Republic of China
E-mail: liangql@mail.tsinghua.edu.cn
‡ This work was equally contributed.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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source. Moreover, the reaction can be carried out smoothly
using water as a green solvent. The catalyst still showed high
activity even after 10 cycles, which was attributed to the
magnetic immobilization. This work would boost the research on
the fabrication of ultrafine nanoparticles, as well as low-cost
catalysts for the highly chemoselective hydrogenation of
nitroarenes in chemical industry.
Scheme 1. The preparation of Fe3O4@SiO2-NH2-FeCu nanocatalyst (black:
Fe3O4; gray: SiO2; orange: FeCu NPs)
Figure 1. Screening of catalysts with different metal ratios
Results and Discussion
The Fe/Cu composition-dependent transfer hydrogenation of p-
nitrophenol was studied in water at 110 oC with constant catalyst
and p-nitrophenol concentrations. Figure
1
shows the
hydrogenation data of p-nitrophenol from catalysts with different
Fe/Cu compositions. Among the data, Fe5Cu is the most active
catalyst, thus, rendering the hydrogenation completed in 25 min.
For comparison, we also prepared Fe3O4@SiO2-NH2-Fe NPs
and Fe3O4@SiO2-NH2-Cu NPs for the hydrogenation of p-
nitrophenol. As can be seen, the Fe catalyst is much more active
than the Cu one. Subsequently, 4-CNB was selected as the
substrate for the hydrogenation reaction to test the ability of
selectivity of these catalysts. As Figure
1 shows, the
dechlorination could not be avoided when using the Fe or Cu
only catalysts. More interesting, the dechlorination of 4-CNB on
FeCu alloy NPs did not occur. The FeCu alloy NPs catalyst with
the alloy effect possessed better catalytic activity and selectivity
for this hydrogenation than single metal NPs. The calculated d-
band centers of Fe and Cu are -0.92 eV and -2.67 eV,
respectively.[24] Once the FeCu alloy is formed, the d-band
center of the alloy should shift to a position between the ones of
Fe and Cu. This shift may further adjust the electronic structure
of the alloy and further optimize the alloy catalysis.
Figure 2. The Fe XPS spectra of the Fe3O4@SiO2-NH2-FeCu NPs with
different metal ratio
XPS was carried out to further discuss the reason of the good
selectivity of FeCu in 4-CNB hydrogenation (Figure 2), as the
electronic state of Fe in the catalysts was the possible influence
factor. Monometallic Fe exhibited a 2p1/2 emission peak at 724.5
eV, which is consistent with the standard value. The binding
energy of Fe for the bimetallic catalysts varied from 723.1eV
(1:1) to 724.1 eV (10:1). Bimetallic catalysts showed lower Fe
2p1/2 binding energies than monometallic Fe, indicating that Fe
atoms are electron- enriched by the second metal. A positive
dependence of p-CAN selectivity on the electron-rich nature of
Fe was observed. All of these strongly indicate that
dechlorination could be avoided as the electron density on Fe
sites changed.
Figure 3. FT-IR spectrum and XRD pattern of Fe3O4@SiO2-NH2-Fe5Cu NPs (a)
and Fe5Cu NPs (b)
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Miscellaneous characterizations were carried out toward the
Fe3O4@SiO2-NH2-Fe5Cu NPs to inquire into the existence form
and morphology. In the fourier transform infrared spectroscopy
(Figure 3a), the absorption peak at 579 cm-1 is owing to the
presence of the Fe-O bond, and the two peaks at 1084 cm-1 and
486 cm-1 are attributed to the characteristic signals of SiO2.
Absorption peaks observed at 1635 cm-1 and 1387 cm-1 confirm
the existence of amino groups.[25] The absorption peak at 3402
cm-1 is assigned to the stretching vibration of O-H of the silica
groups.
To further discuss the characteristics of Fe3O4@SiO2-NH2-
Fe5Cu NPs, powder XRD analysis was also actualized (Figure
3b). The diffraction peaks at 2θ = 31.5, 36.6, 44.7, 59.1, 64.5o
correspond to the (220), (311), (400), (511), (440) planes of the
cubic phase of Fe3O4 (JCPDS: 00-003-0862).[26] A short and
diffusion peak at 2θ= 18-23o is considered as the peak of
amorphous silica.[27] However, no intense or broad diffraction
alloy peaks were observed because of its very small size. Then
we tested FeCu NPs without a magnetic carrier, and the XRD
result verified the formation of alloy.
The magnetic properties of Fe3O4, Fe5Cu NPs, and
Fe3O4@SiO2-NH2-Fe5Cu NPs at an applied field of 10000 Oe
are shown in Figure 4. The magnetization saturation (Ms) value
of Fe3O4 and Fe5Cu NPs are 80.7 emu·g-1 and 14.8 emu·g-1,
respectively, which demonstrates that Fe5Cu NPs are
magnetically immobilized by the magnetic Fe3O4 spheres. The
Ms value of the Fe3O4@SiO2-NH2-Fe5Cu NPs is 34.5 emu·g-1,
which is put down to the coating of silica and the loading of
Fe5Cu NPs. The catalysts can be separated by an external
magnet straightforward, as shown in Figure 4, inserted one.
the thickness of silica shell is about 20 nm (Figure 5). The Fe5Cu
NPs could not be distinguished in the HR-TEM for the ultrafine
size. But it confirmed that Fe and Cu were both existent and
dispersed well in the EDS images. The distribution area of Si is
larger than the Fe3O4 core distribution. Fe and Cu can be
observed at the sandwiched position of the silica shell, which
indicates that Fe5Cu NPs are encapsulated in the micro tunnel of
the silica spheres successfully and highly dispersed evenly. This
claim is agreed with the BET results, as the curve of the catalyst
shows a typical amorphorous silica shape (Figure S2), indicating
that the Fe5Cu alloy particles locate in the inner tunnel of the
silica shell. The HRTEM image of a selected FeCu NP floated
outside the silica sphere shows the polycrystalline nature of the
NP with a lattice fringe distance of 0.204 nm, which is smaller
than that of the Cu metal (0.208 nm), indicating that Fe alloying
effect on the change of the lattice reduction in the alloy structure
(Figure 5d). The ring-like selected area electron diffraction
(SAED) pattern shows that the Fe3O4 is in good crystallinity, and
the signal of FeCu NPs is also distinguished with a lattice fringe
distance of 0.204 nm, which indicates the FeCu alloy structure is
formed (Figure 5e). Furthermore, from the mapping of N element
(Figure S3), we can observe that the amino groups distributes
well in the micro tunnels of the silica spheres. During the catalyst
preparation, the amino groups coordinated with the metal ions to
anchor them in the micro tunnels successfully. Then the metal
ions were reduced in situ by NaBH4 in the micro tunnels.
Therefore, the ultra-small nanoparticles formed via the tunnel
confinement of the silica spheres. Notably, when the supporter
was moved away or replaced by the carbon spheres, the FeCu
did not exist as the ultrafine NPs. They agglomerated severely
or even scattered outside in a large number (Figure S4,5). Thus,
the silica sphere is the vital structure to ensure the FeCu NPs’
ultrafine and highly dispersed morphology.
Figure 4. Room-temperature hysteresis loops of (a) Fe3O4, (b) FeCu NPs, (c)
Fe3O4@SiO2-NH2-Fe5Cu NPs
The shape, size and morphology of the nanocatalyst were
further investigated by high resolution transmission electron
microscopy (HR-TEM). Fe3O4@SiO2-NH2-Fe5Cu NPs had an
inerratic spherical shape with an average size of ~400 nm and
Figure 5. HR-TEM images of (a), (c), (d) Fe3O4@SiO2-NH2-Fe5Cu NPs; (b)
Size distribution of Fe3O4@SiO2-NH2-Fe5Cu NPs; (e) Corresponding SAED
pattern; EDS mapping of (f) Fe3O4@SiO2-NH2-Fe5Cu NPs, (g) Si, (h) Fe and
(i) Cu
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Other condition exploration data is listed in Table 1. When
using water, EtOH, MeOH or isopropanol, there is no difference
in the yield. But water is the “greenest” solvent, so we choose
water as the optimized solvent in the further investigation.
However, when using isopropanol as both hydrogen source and
solvent in our catalytic system, the transfer hydrogenation
cannot be achieved. Either decreasing the reaction temperature
or reducing the dosage of hydrazine hydrate, the yield
decreases.
Table 2. The reduction of nitroarenes catalyzed by
Fe3O4@nSiO2-NH2-FeCu NPs a
Table 1. Optimization of the reaction conditions a
[a]Reaction condition: 4-nitrophenol (1 mmol), catalyst (30 wt%), solvent (2
mL); bconversion and selectivity were analyzed by GC-MS using
trimethylbenzene as external standard.
To investigate the general applicability of the catalyst, the
hydrogenation of varieties of halogenated nitrobenzenes and
nitroarenes was carried out. All of them could be converted into
corresponding amino products prosperously. As shown in Table
2, no dechlorination occurred in the reduction of
chloronitrobenzenes in our catalytic system, no matter whether
in the ortho, meta, para position or monosubstituted,
disubstituted chloro substrates (entries1-5). Besides, m-
bromonitrobenzene has also been investigated (entry 6), and the
selectivity could reach up to 99%. Except the halogenated
nitrobenzenes, other nitroarenes including reducible groups
such as acid, ester and amino could be converted into anilines
successfully without any by-product (entries 7-18). Notably, the
hydrogenation of 2,4-dinitrophenol is difficult with by-products,
but in our catalytic system, it could transform into 2-amino-4-
nitrophenol with a >98 % selectivity (entry 14).
A leaching test of the hydrazine mediated reduction of p-
nitrophenol catalyzed by Fe3O4@SiO2-NH2-FeCu NPs was
o
carried out at 110 C to study the heterogeneity of the catalyst.
As dispalyed in Figure 6, upon removing the catalyst at 15 min,
the conversion remained at the same level, indicating that the
active phase were in the heterogeneous catalyst. It also
suggests that the active sites in the catalyst are insoluble in the
reaction mixture.
[a] Reaction conditions: nitroarenes (1 mmol), hydrazine hydrate (3 mmol),
catalyst (30 wt%), water (2 mL), 110 oC. [b] Conversion and selectivity were
determined by GC-MS using trimethylbenzene as external standard.
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The reusability of both Fe3O4@SiO2-NH2-Fe5Cu NPs (1a) and
SiO2-NH2-Fe5Cu NPs (1b) were tested (Figure 7). Owning to the
strong magnetic property of the Fe3O4@SiO2-NH2-Fe5Cu NPs,
the catalysts can be recovered with an external magnet within
one minute. However, the SiO2-NH2-Fe5Cu NPs should be
separated only by centrifugation after reaction because its
magnetism is relatively weak. Both of the two catalysts exhibit
outstanding catalytic performance at first. Yet with the increasing
number of cycles, an obvious decrease in catalytic efficiency
could be observed for the catalyst SiO2-NH2-Fe5Cu NPs.
Fe3O4@SiO2-NH2-Fe5Cu NPs could be recycled at least 10
times without any changes in catalytic performance. The HR-
TEM of the recycled catalyst is shown in Figure S7, no large
FeCu NPs can be observed. As a consequence, the excellent
stability of the catalyst could be ascribed to the two facts: (1)
The Fe5Cu NPs are encapsulated in the silica spheres and
dispersed well by the amino groups, which helps to prevent
aggregation during the reaction. (2) The Fe5Cu NPs are
magnetically attracted to the magnetic core, which helps to
immobilize the active component to avoid wastage.
Figure 7. Recyclability of Fe3O4@SiO2-NH2-FeCu NPs (1a) and SiO2-NH2-
FeCu NPs (1b)
Based on the experimental data and previous literature,[29]
a
reasonable reaction mechanism has been proposed (Figure 8).
During this reaction, the nitroarenes and N2H4·H 2O diffuse
through the microporous silica channel firstly and absorbed to
the surface of the active component FeCu. Then the N2H4·H 2O
was activated by the FeCu NPs to generate active H atoms on
the surface of the FeCu NPs. The active H atoms get in touch
with the absorbed nitroarenes and the nitroarenes transform into
anilines gradually. Besides, the silica spheres can store the
active H atoms to let them release slowly.[30] The overall
procedure has been identified as: Ar-NO2 → Ar-NOOH → Ar-
N(OH)2 → Ar-N(OH) →Ar-NHOH → Ar-NH→ Ar-NH2.[31] The
interaction between Cu and Fe improves the utilization of N2H4
and then enhances the activity and selectivity, while the d-band
electron transfer from Cu to Fe depresses the activity of active H
species thus the catalyst achieves the dehalogenation-proof
hydrogenation.
Figure 6. Leaching test of Fe3O4@SiO2-NH2-FeCu NPs for the transfer
hydrogenation of p-nitrophenol
The initial rate method was applied to determine the reaction
order. The order of the reaction was 1.5 and the reaction rate
constants were 0.0450, 0.0651, 0.137 mol L-1 min-1 at 40, 50, 60
oC respectively. Besides, using the Arrhenius equation, the
apparent active energy (Ea) was computed to be 48.1 kJ mol−1.
This value is relatively low compared with even noble metal,
which can compete the reaction rapidly.[28] (more details see
supporting information)
Figure 8. Possible mechanism for the reduction of nitroarenes with
Fe3O4@SiO2-NH2-FeCu NPs
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After the reaction, the catalyst was separated by an external magnet and
the product was separated from the water after cooling down. The
catalyst was reused without further treatment.
Conclusions
In summary, we have constructed a novel ultrafine FeCu alloy
nanoparticles with a simple and versatile method. The FeCu
alloy is magnetically immobilized in porous silica to form a core-
shell structured nanocatalyst Fe3O4@SiO2-NH2-FeCu NPs. This
heterogeneous catalyst can remarkably achieve both the high
activity and excellent chemoselectivity for the reduction of
various functionalized nitroarenes to corresponding anilines in
water. The catalytic activity can be improved by the ultrafine size
of the FeCu NPs, and the excellent selectivity is attributed to the
electron-enriched Fe sites modified by Cu. The catalyst has a
long lifetime that can be recycled at least 10 times, whereas the
catalyst SiO2-NH2-FeCu NPs without a magnetism core hs a
weak reusability. Therefore, such a low-cost, high activity,
strongly stable and environmental friendly catalysts provides a
promising platform and has latent capacity for application in
other catalytic reduction reactions.
Chemical kinetics study: 1 mmol 4-CNB, 30 wt% catalyst, 20 mmol
hydrazine hydrate and 2 mL H2O were added in a 5 mL round-bottom
flask. The reaction was carried out with a magnetic stirring vigorously at
40, 50, 60 ℃ respectively. The conversion was determined every 5 mins
by HPLC.
Acknowledgements ((optional))
This work was financially supported by the Ministry of Science
and Technology (Nos.2017YFC0906902 and 2017ZX09301032),
National Natural Science Foundation of China (No. 21621003)
and Macau Science and Technology Development Fund
(129/2017/A3 and 089/2013/A3), Fundamental Research Funds
for the Central Universities (N160504002).
Keywords: Ultrafine FeCu alloy • Core-shell structure•
Magnetical immobilization• Dehalogenation-Proof
hydrogenation• Electronic modification
Experimental Section
Preparation of Fe3O4@nSiO2-NH2 (Step 1, 2, Scheme 1): The silica
coated magnetite was fabricated by a modified Stöber method.[32] First,
Fe3O4 (0.2 g) was treated with 60 mL HCl solution (0.1 M) under
ultrasonic conditions for 10 min. The activated magnetite were dispersed
in a mixture of ethanol (160 mL), water (40 mL) and 25% NH3·H2O. With
vigorous stirring, tetraethyl orthosilicate (TEOS, 1 mL) was added
dropwise to the solution and then stirred vigorously at room temperature
for 6 h. Next, the solid was separated from the suspension, and treated
with a solution of APTES (0.5 mL) in isopropanol (200 mL) at 80 ℃ for 3
h to modify the silica with amine groups. Finally, the product was
separated and washed with ethanol for several times.
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typically procedure for synthesis of support attached FeCu alloy NPs is
as follows: the prepared Fe3O4@nSiO2-NH2 was dispersed in 100 mL
methanol, then 0.2 mmol Fe(NO3)3·9H2O and 0.2 mmol Cu(NO3)2·3H2O
(the total molar is 0.4 mmol) were dissolved in the methanol. Ar was
passed to purge out all dissolved oxygen and the mixture was
magnetically stirred for 1 h. Then 10 mL of a methanol solution of NaBH4
(0.4 g) was added dropwise to the reaction mixture under the protection
of argon. The whole setup was maintained at ambient temperature and
stirred for 6 h. After washing with ethanol and water, the whole synthesis
of the catalyst was completed. A similar scheme was applied to
synthesize various catalysts by adjusting the molar ratio of Fe/Cu
precursors.
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Preparation of SiO2-NH2-FeCu NPs: Silica nanospheres with a particle
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solution with ammonia to TEOS mole ratio of 4. After 6 h reaction, the
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Catalytic transfer hydrogenation and product analysis: 1 mmol of
nitro compound, 30 wt% of catalyst and 3 mmol of hydrazine hydrate
were added into a sealed tube. 2 mL of water was added as solvent. The
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1. A dehalogenation-proof
hydrogenation catalyst is fabricated
with FeCu alloy.
Hongjie Bao,[a]‡ Yunong Li,[a]‡ Lei Liu,[a]
Yongjian Ai,[b] Junjie Zhou,[a] Li Qi,[a]
Ruihang Jiang,[a] Zenan Hu,[a] Jingting
Wang,[a] Hongbin Sun*[a] and Qionglin
Liang*[b]
2. The ultrafine FeCu NPs is confined
in micro tunnel of silica shell.
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3. The electronic modification from
Cu to Fe enhances the activity and
selectivity.
Ultrafine FeCu Alloy Nanoparticles
Magnetically Immobilized in Amine-
Rich Silica Spheres for
Dehalogenation-Proof Hydrogenation
of Nitroarenes
4. The FeCu NPs are magnetically
immobilized to prolong the life time of
the catalyst.
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