Magnetic Anchored CoPt Bimetallic Nanoparticles as Selective Hydrogenation Catalyst for Cinnamaldehyde

Article abstract of DOI:10.1007/s10562-018-2619-6

Selective hydrogenation reaction of cinnamaldehyde is crucial for its appliction in fine chemical industries. The traditional noble metal catalyst for this reaction is expensive and often involving tedious steps. In this work, the magnetic anchored CoPt/Fe₃O₄ catalyst is prepared by a simple wet-impregnation method and evaluted as catalyst for selective hydrogenation of cinnamaldehyde. Electrons transfer directly from Co to Pt NPs can enhance H₂ dissociation capability in the Co NPs interface, thereby strengthen the overall catalytic performance. Under optimum conditions, the conversion of cinnamaldehyde is 95% with 84% selectivity of cinnamyl alcohol. Furthermore, the magnetic interaction between the outer Co NPs and the Fe₃O₄ support maintains the stability of cinnamyl alcohol selectivity after repeated tests.

Full text of DOI:10.1007/s10562-018-2619-6

Catalysis Letters
https://doi.org/10.1007/s10562-018-2619-6
Magnetic Anchored CoPt Bimetallic Nanoparticles as Selective
Hydrogenation Catalyst for Cinnamaldehyde
Tao Yuan1 · Derong Liu1 · Yue Pan1 · Xiaoqin Pu1 · Yongde Xia2 · Jinbo Wang1 · Wei Xiong1
Received: 9 August 2018 / Accepted: 18 November 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Selective hydrogenation reaction of cinnamaldehyde is crucial for its appliction in fine chemical industries. The traditional
noble metal catalyst for this reaction is expensive and often involving tedious steps. In this work, the magnetic anchored CoPt/
Fe3O4 catalyst is prepared by a simple wet-impregnation method and evaluted as catalyst for selective hydrogenation of cin-
namaldehyde. Electrons transfer directly from Co to Pt NPs can enhance H2 dissociation capability in the Co NPs interface,
thereby strengthen the overall catalytic performance. Under optimum conditions, the conversion of cinnamaldehyde is 95%
with 84% selectivity of cinnamyl alcohol. Furthermore, the magnetic interaction between the outer Co NPs and the Fe3O4
support maintains the stability of cinnamyl alcohol selectivity after repeated tests.
Graphical Abstract
Keywords CoPt/Fe3O4 NPs · Electron transfer · Selective hydrogenation · Magnetic separation
1 Introduction
The limited availability of natural sources could not meet
the widespread demand of fine chemicals especially for allyl
alcohol in food, perfume and pharmaceutical industries dur-
ing the past 20 years. Moreover, it is challenging for the
traditional transformation of α, β-unsaturated aldehydes to
obtain the allyl alcohols, because selective hydrogenation
of the C=C bond is thermodynamically favoured. Noyori
and co-workers invented the highly effective and homogene-
ous Ruthenium(II)-Phosphine-diamine catalytic system that
could acquire high selectivity of C=O bond hydrogenation
under mild conditions. However, the separation and recovery
of the catalyst are still the key issues for industrialization.
Based on previous works, researchers have investigated new
solutions to tackle these problems such as phosphine and
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-018-2619-6) contains
supplementary material, which is available to authorized users.
* Wei Xiong
18875024416@163.com
1
Institute of Chemistry and Chemical Engineering,
Chongqing University of Science and Technology,
Chongqing 401331, China
2
College of Engineering, Mathematics and Physical Sciences,
University of Exeter, Exeter EX4 4QF, UK
Vol.:(0123456789)
1 3

T. Yuan et al.
amine modification [1–5]. Recently, owing to the easy sepa-
ration and high catalytic properties of the supported cata-
lysts, most researchers focus on how to improve the single
noble metal catalytic performance by adding a second metal
(Sn, Fe, Co) [6–8] or metal oxides (FeOx, MoOx, CeOx,
NbOx) [9–12] and selecting some suitable 2D (RGO, CNTs,
SiC, PP-3) [13–16] or 3D (MS, MOFs, COFs) [17–19] nano-
porous materials. Metal nanoparticles (NPs) are generally
dispersed on these porous supports to maximize their avail-
ability, as porous materials can make advantageous contribu-
tions in restricting metal NPs mobility and preventing their
leakage and sintering on some unfriendly reaction condi-
tions. Moreover “Shape Selective Effect” in porous carrier
can sharply raise the selectivity to C=O bond hydrogena-
tion, which can screen the smaller steric hindrance aspect
of substrate to pass through the aperture and react with the
active components. Due to the ordered and tunable pores
and diversified structures, MOF materials have been served
as the best candidates for selective hydrogenation [20, 21].
Up to now, researchers have developed serials of novel MOF
catalysts such as NPs@MOFs [22], MOFs@NPs@MOFs
[23], and COFs@NPs@MOFs [24] to effectively boost the
C=O bond hydrogenation.
Given that the non-precious Co shows low conversion
at low temperature and low selectivity at high temperature
[31], bimetallic CoPt NPs were synthesized to cope with the
low catalytic efficiency by effectively modulating the elec-
tron state of the outer Co NPs (the electrons shift from Co to
Pt NPs). In the meantime, the magnetic Fe3O4 is employed
as excellent carrier that is not only conducive to rapid mag-
netic separation after reaction, but also the Fe cations origi-
nating from the Fe3O4 surface can act as the Lewis acid sites
to interact with the C=O bond and lower the reaction-energy
barrier [34, 35], which can contribute to the selective hydro-
genation of C=O group, as shown in Graphical Abstract.
Meanwhile, to our knowledge, there have been no stud-
ies to explore the effect of magnetic interaction between Co
NPs and Fe3O4 on the product distribution for the hydro-
genation of cinnamaldehyde transformation. In this work,
we have fabricated magnetic anchored bimetallic CoPt/
Fe3O4 catalyst. The bimetallic CoPt NPs are chosen as the
main catalytic active phase to convert cinnamaldehyde into
unsaturated alcohol. The efficient electron transfer between
Co and Pt NPs enhances Co NPs catalytic activity. The
magnetic interactions between the outer Co NPs and Fe3O4
support maintain the selectivity of unsaturated alcohol.
Consequently, we have successfully achieved high catalytic
performances of Co NPs at both low and high temperatures.
According to literature reports [25–27] the noble met-
als (Ir, Pt, Au) have been popular catalysts that are capable
of enhancing catalytic efficiency in selective hydrogenation
of α, β-unsaturated aldehyde but the catalytic processes
are tedious and the catalysts are costly. In this regard, the
nonprecious metal Co is an alternative catalyst with great
potential in catalytic hydrogenation. Zhang et al [28], have
employed ZSM-5 as carrier to support Co NPs to catalyze
the selective hydrogenation of cinnamaldehyde (CAL), and
the optimum cinnamic alcohol (COL) selectivity reaches
61.9%. Joseph et al. [29] have demonstrated that Co NPs
impregnation on the reducible metal oxides show superior-
ity in COL selectivity compared with the γ-Al2O3, SiO2 and
TiO2. The presence of TiOx (x<2) species have favourable
promotion to selective hydrogenation of C=O groups. Bi-
functional catalyst Co@CN from N-containing [Co(TPA)
(ted)0.5] has achieved 99% COL selectivity with full con-
version after 35 h [30]. The nitrogen-doped porous carbon
materials (CPNs) [31] are excellent support to impregnate
Co NPs, which demonstrates high catalytic performance
with 99% conversion and 80% COL selectivity. Apart from
the single Co catalyst, the Co–M alloy is efficient catalyst
for selective hydrogenation of cinnamaldehyde. Kalyon
et al. [32] have fabricated Co–B catalyst that could achieve
remarkable selectivity to C=O group hydrogenation because
of the special spiral structure of noncrystalline CoB. Moreo-
ver, when the CoB catalyst is modified by doping the tran-
sition metals Mo and W, the reaction rate and selectivity
to unsaturated alcohol could be significantly improved by
strengthening its structural stability [33].
2 Experimental Section
2.1 Catalyst Preparation
The CoPt NPs were prepared following the literature [36]
with minor modifications. Briefly, 2.6 mL HPtCl6 aqueous
solution (10 mM, Macklin), 300 mg PVP (K30, Macklin)
and 20 mL H2O were continuously added to a 50 mL beaker.
After the mixture was stirred at 800 rpm for 10 min until
complete dissolving of the ingredients, 20 mL freshly pre-
pared NaBH4 aqueous solution (0.5 mg/mL, Kelong) was
slowly dropwise added, and left for 20 min to form Pt nano-
particles. Then 2.6 mL Co(NO3)2 aqueous solution (10 mM,
Kelong) was introduced into the above solution and reacted
for another 20 min to obtain CoPt bimetallic nanoparticles
under stirring at 1500 rpm. All the synthesis steps were pro-
tected by N2 atmosphere. Finally, 0.5 g PVP modified Fe3O4
was added into the above solution and kept standing for 12 h.
The resulting mixture was centrifuged and washed with dis-
tilled water several times, and then dried under vacuum at
80 °C for 24 h.
2.2 Catalyst Characterization
The Powder X-Ray diffraction (PXRD) scans of the synthe-
sized CoPt/Fe3O4 catalysts were carried out from 0° to 80°,
1 3

Magnetic Anchored CoPt Bimetallic Nanoparticles as Selective Hydrogenation Catalyst for…
using an XRD-7000 X-ray diffractometer (CuKα radiation at
40 kV and 30 mA, Japan). The morphology and microstruc-
ture of the sample, the HAADF-STEM imaging and EDX
mapping of CoPt/Fe3O4 catalysts were recorded by a high
resolution electron microscopy (200 KV, FEI Talos F200x,
American) and the samples were supported by carbon coated
copper grids. The elemental valence state and content of
Fe, Co and Pt nanoparticles at the surface of Fe3O4 were
measured by X-ray photoelectron spectroscopy (XSAM800,
UK), using a double anode Mg Ka X-ray source (45 W) and
an analyzer pass energy of 20 eV. The information of con-
figuration of CoPt/Fe3O4 was characterized using Tempera-
ture-programmed desorption and Temperature-programmed
reduction (H2-TPD, H2-TPR, AutochemII 2920 (10 deg/min,
10% H2-Ar, 50 mL/min), American). The magnetic proper-
ties of sample were characterized using a vibrating sample
magnetometer (VSM, lakeshore735, Germany).
Fig. 1 PXRD patterns of the CoPt/Fe3O4 (1%) with different molar
2.3 Selective Hydrogenation Reaction
ratio of Co to Pt
The hydrogenation reaction was performed in a 0.1 L stain-
less steel autoclave equipped with a magnetic stirrer. The
detailed procedures are as follows: 0.8 mmol substrate,
5 mg catalyst doge and 5 mL i-PrOH were added into the
stainless autoclave in turn. The autoclave was kept sealed
under charging certain hydrogen after purging with nitrogen
several times. Then the autoclave was heated to the pre-set
temperature (100–180 °C) and the reaction started. After
a period of reaction time, the autoclave was cooled down
to room temperature and decompressed. The product of
the final liquid was analyzed by an Agilent GC-6890N gas
chromatography equipped with a FID detector and a Rtx-1
capillary column (30 m× 0.25 mm × 0.25 µm) with N2 as
the carrier gas. The CAL conversion and product selectivity
were calculated according to the following equations:
correspond to the (111), (220), (311), (222), (400), (422),
(511), (440) and (533) diffractions of iron oxide, respec-
tively. Compared to the standard Iron oxide (JCPDS No.26-
1136), the PXRD peaks of the catalyst are left shifted, which
could be caused by the influence of the outer magnetic Co
NPs on the iron oxide crystal phase [37]. Meanwhile, the
weak characteristic Co peaks in accord with lower Co con-
tent occurring at 2θ of 62.6° and 75.9° are assigned to (102)
and (110) of Co respectively, which initially infers the pres-
ence of Co NPs. However, no characteristic diffraction peaks
of Pt are observable from the single XRD analysis, which
may be because the Pt clusters are fully covered by the outer
Co NPs. Therefore, the high resolution transmission electron
microscopy (HRTEM) was conducted to further validate the
composition, morphology and microstructure of the CoPt/
Fe3O4 catalyst (as shown in Fig. 2). The mean particle size
of the CoPt/Fe3O4 is 173.7 35.4 nm. Its morphology shows
cubic or spherical polyhedron, and the active ingredients
(CoPt NPs) locate on the margin of Fe3O4 polyhedron as
shown in the red cycles in Fig. 2b. In addition, Fig. 2c shows
that the formation CoPt morphology is similar to core–shell
structure which is developed from a Pt cluster core. The
thickness of outer Co NPs is estimated as 5.0–12.6 nm. In
Fig. 2d, two different lattice spacing of approximately 0.148
and 0.286 nm are observed, which are originated from the
Co (102) and Fe3O4 (220) respectively. Finally, from the
EDS elemental mapping in Fig. 2f–h, the presence of Fe,
Co element are clearly observed and the blurring Pt map-
ping image in Fig. 2h further confirms the XRD results that
the majority of Pt clusters is covered by the outer Co NPs.
CAL before reaction − CAL after reaction
Conversion =
× 100%
CAL before reaction
Desired product
Selectivity =
× 100% (all unit ∶ mole)
CAL consumed
3 Results and Discussion
3.1 Catalyst Characterization
To better understand the catalysts, they are fully character-
ized by XRD, TEM, XPS, H2-TP and VSM. The PXRD pat-
terns of 1%CoPt/Fe3O4 (1% define as the whole Co and Pt
loading, Table S1) catalysts (n (Co/Pt)= 1/2, 1/1 and 2/1)
are shown in Fig. 1. The main peaks at 2θ around 18.3°,
30.1°, 35.5°, 37.1°, 43.1°, 53.4°, 57.0°, 62.6° and 75.1°,
1 3

T. Yuan et al.
Fig. 2 HRTEM images of CoPt/Fe3O4 (1%) catalyst (a, b, c, d), e HAADF-STEM image, and elemental mapping for f Fe, g Co and h Pt
In an effort to understanding the content and valence
of Co and Pt at the surface of Fe3O4, X-ray photoelectron
spectrum of the CoPt/Fe3O4 (1%) catalyst was employed.
From Fig. 3a (the elemental analysis result based on the
XPS spectrum), due to the outer Co NPs, the XPS can’t
accurately detect the real core Pt content, which gives the
Fig. 3 a XPS spectra of Pt@Co/
Fe3O4 (1%), b Fe 2p spectrum,
c Co 2p spectrum, d Pt 4f
spectrum
1 3

Magnetic Anchored CoPt Bimetallic Nanoparticles as Selective Hydrogenation Catalyst for…
atomic ratio of Co/Pt=1.72/0.02, far exceeding the original
Co/Pt=2/1. However, the elemental contents of Co and Pt
from XPS analysis result are similar to their content derived
from elemental mapping in EDS. In addition, the peak posi-
tions of Fe 2p3/2 and Fe 2p1/2 are, at 710.6 eV and 724.1 eV
respectively, in agreement with the binding energy of stand-
ard of Fe3O4 [38]. For Co species, the doubling peaks at
binding energy of 802.5 and 782.2 eV are attributed to the
chemical environment of Co 2p1/2 and Co 2p3/2 from CoOx,
due to the oxidation of the Co shell after exposure to air
atmosphere. The other pair of doubling peaks for Co 2p1/2
and Co 2p3/2 from Co(OH)2 appeared at binding energy of
796.2 and 780.4 eV, which are validated by published reports
[33, 36]. In addition, a satellite peak can be found at around
785.5 eV. Considering the typical peak position of Co 2p3/2
for Co(OH)2 is at 780.9 eV, it is clearly that this peak in the
catalyst is left shifted, which implies the Co layer is losing
electron. In addition, the Pt 4f7/2 binding energy for Pt0 is
at 70.6 eV that is evidently reduced by 0.4 eV compared
with the typical Pt0 peak position at 71.0 eV, indicating the
electrons shift from the Co to Pt NPs [39]. The Co NPs with
electron deficiency could be benefit the high catalytic activ-
ity in the reaction of cinnamaldehyde transformation.
reduction of CoOx shifting to lower temperature since the
metallic Pt atoms are able to dissolve hydrogen molecules
into hydrogen atom [40, 42].
3.2 Optimization of Reaction Conditions
Various reaction conditions including temperature, H2
pressure, duration and solvent types were investigated for
optimization. The influence of temperature on the selective
hydrogenation of cinnamaldehyde is presented in Fig. 5a.
The conversion of cinnamaldehyde has sharply increased
from 14 to 95% with increasing temperature until 160 °C.
Afterwards, the conversion starts to decrease. Surpris-
ingly, the COL selectivity does not change significantly
and largely holds at 81–88%. The selectivity of HCAL and
HCOL shows in an opposite way, the selectivity of HCAL
declines from 8 to 2% while that for HCOL increases from
5 to 17%. Moreover, the effect of hydrogen pressure on the
catalytic activity is depicted in Fig. 5b. The conversion goes
up from 68 to 95% with the hydrogen pressure changing
from 2 to 3 MPa, which reveals that the hydrogen pressure
increase is beneficial to the conversion. Unfortunately, the
COL selectivity reduces from 87 to 81% slightly. The HCAL
and HCOL selectivity is in line with the trend of the tem-
perature influence. As shown in Fig. 5c, the reaction dura-
tion mainly influences the CAL conversion. With duration
extending to 180 min, the conversion increases from 65 to
95%. However, the COL selectivity slightly changes (only
4% fluctuation). In addition, Fig. 5d implies that the polar
solvents such as alcohols are beneficial to the C=O group
selective hydrogenation, as the carbonyl group tends to form
hydrogen bonds in alcohols, thus enhancing the polarization
of the carbonyl group and in favor of the carbonyl group
selective hydrogenation. Among those alcohols, i-PrOH has
the highest conversion up to 95% with 84% COL selectivity
To investigate the configuration of CoPt/Fe3O4 catalyst,
the H2-TPD and H2-TPR characteraction were conducted.
The analysis result displays that there exist two peaks of H2
desorption in the H2-TPD profile (Fig. 4a). The first peak of
obvious H2 desorption centre appears at 440 °C, which is
consistent with the CoOx [40]. Another broad and weak peak
locates between 600 and 800 °C which indicates that Fe3O4
support was reduced [41]. From the H2-TPR profile(Fig. 4b),
the first-stage reduction temperature locates at 388 °C which
is lower than Co2O3 or Co3O4 reduction temperature [42].
It demonstrates that there exists interaction between Pt and
CoOx causing by the hydrogen spillover, which results in the
Fig. 4 The H2-TP profiles of CoPt/Fe3O4 catalyst, a H2-TPD and b H2-TPR
1 3

T. Yuan et al.
Fig. 5 The optimization of reaction conditions of CoPt/Fe3O4 (1%)
(n (Co/Pt=2/1)) catalyst including temperature (a), H2 pressure (b),
duration (c) and solution type (d). a Reaction condition: 5 mg cata-
lyst dose, 5 mL i-PrOH, 0.8 mmol substrate, 180 min, P(H2)=3 MPa,
b reaction condition: 5 mg catalyst dose, 5 mL i-PrOH, 0.8 mmol
substrate, 160 °C, 180 min, c reaction condition: 5 mg catalyst dose,
5 mL i-PrOH, 0.8 mmol substrate, 160 °C, P(H2)=3 MPa, d reaction
condition: 5 mg catalyst dose, 0.8 mmol substrate, 160 °C, 180 min,
P(H2)=3 MPa
than other alcohols, which indicates that the alcohol’s spatial
structure could influence the yield including both conversion
and selectivity. Apart from the optimization of reaction con-
ditions, the stability and recycling possibility of the prepared
catalysts in selective hydrogenation of cinnamaldehyde are
investigated in detail (ESI, Fig. S1). There is no observable
change of COL selectivity and it maintains unchanged at
around 84%, even after five successive tests.
adding the Pt atom, significant increase in the conversion
of cinnamaldehyde is observed for the PtCo/Fe3O4 catalyst
(8%) and the CoPt/Fe3O4 catalyst (27%).
Obviously, the CoPt/Fe3O4 catalyst exhibited much higher
catalytic performances and its conversion achieves 3.8 times
and the COL selectivity 6.6 times of those of the single Co/
Fe3O4 catalyst, respectively. This indicates that the presence
of Pt acting as the core is capable of enhancing the catalytic
activity. Furthermore, the CoPt/Fe3O4 catalytic conversion
is slightly superior to the Pt/Fe3O4 catalyst. Among the stud-
ied different catalyst supports, the magnetic Fe3O4 support
exhibits the highest selectivity of 84% with respect to the
γ-Al2O3 (68%) and TiO2 (71%) supports. The main reason
lies in that the Fe cation efficiently interacts with the C=O
group and activates it at the surface of Fe3O4. Meanwhile,
the catalytic performance of the diverse magnetic catalysts
M-Pt/Fe3O4 (M is Fe, Co, Ni, and n(M/Pt)=1/1) is further
investigated and the results are also listed in Table 1 (Entry
3.3 Activities of Various Catalysts
Based on the above results, the optimized reaction conditions
(temperature, pressure, etc.) were adopted for further study.
Different catalysts in the reaction of selective hydrogena-
tion of cinnamaldehyde have been systematically studied and
the catalytic performances are listed in Table 1 (Entry 1–6).
The conversion of the single magnetic anchored Co/Fe3O4
catalyst only reaches 7% with 13% of COL selectivity. After
1 3

Magnetic Anchored CoPt Bimetallic Nanoparticles as Selective Hydrogenation Catalyst for…
Table 1 Comparison of different catalysts in selective hydrogenation
Co content, the reaction conversion has sharply ascended
from 29 to 95%, but the selectivity of COL keeps almost
constant. Further study is required to deep insight into the
relevant phenomenon occurring in the selectivity which is
not yet fully understood. Other Co based catalysts in recent
published references is displayed in ESI Table S2. As non-
precious Co metal is chosen as the active ingredients, the Co
loading and catalyst dosage is far higher than noble metal
catalysts. Moreover, the Co based catalysts have low cata-
lytic activity at low temperature and needs long reaction
time. Meanwhile, it is hard to achieve high selectivity of
unsaturated alcohol at high temperatures. However, adding
trace amount of Pt to form CoPt NPs is capable of enhancing
the catalytic activity. Even if the reaction is carried out at
160 °C, the CoPt/Fe3O4 catalyst still shows excellent selec-
tivity of COL (84%).
of cinnamaldehyde under various conditions
Entry Catalysts
Conv. (%) SCOL (%) SHCAL (%) SHCOL (%)
A
1
2
3
1% Co/Fe3O4
7
24
8
13
88
75
15
7
25
0
4
0
A
1% Pt/Fe3O4
1% PtCo/
A
Fe3O4
4
1% CoPt/
27
41
18
16
90
51
29
84
68
71
89
39
84
84
10
23
20
11
26
9
7
10
10
0
A
Fe3O4
5
1% CoPt/γ-
A
Al2O3
6
1% CoPt/
A
TiO2
7
1% FePt/
B
Fe3O4
8
1% NiPt/
36
7
B
Fe3O4
Table 2 presents the selective hydrogenation of various
α, β-unsaturated aldehydes with CoPt/Fe3O4 (1%) catalyst.
From Table 2, it is clear that α, β-unsaturated aldehydes
with different substituents greatly affect the conversion and
selectivity of the reaction turning them into unsaturated
alcohol. The cinnamaldehyde conversion is up to 95% with
84% COL selectivity. But for furfural, the conversion is only
24%, which may be closely related to the strength of con-
jugated aromaticity. Furfural is more stable than cinnamal-
dehyde in the conjugated aromatic structure, so reaction of
the conjugated C=O bond is more challenging for selective
hydrogenation. Besides, the types of branched chain and the
position of branched chain of α, β-unsaturated aldehyde are
other important factors which influence the final products of
the selective hydrogenation.
9
1% CoPt/
B
Fe3O4
10
1% CoPt/
12
3
C
Fe3O4
n(Co/Pt=1/2)
11
12
1% CoPt/
51
95
84
84
9
2
7
C
Fe3O4
n(Co/Pt=1/1)
1% CoPt/
14
C
Fe3O4
n(Co/Pt=2/1)
AReaction conditions: 5 mg catalyst dose, 5 mL i-PrOH, 0.8 mmol
substrate, 120 °C, 120 min, A3,4,5,6(n(Co/Pt)=1/1)
BReaction condition: 5 mg catalyst dose, 5 mL i-PrOH, 0.8 mmol
substrate, 160 °C, 180 min, (n(M/Pt)=1/1)
CReaction condition: 5 mg catalyst dose, 5 mL i-PrOH, 0.8 mmol
substrate, 160 °C, 180 min
Finally, the vibrating sample magnetometer (VSM) of
CoPt/Fe3O4 (1%) before and after reaction was measured.
For clarity, the magnetization hysteresis loop of CoPt/Fe3O4
(1%) is presented in Fig. 6. The saturation magnetization of
the CoPt/Fe3O4 catalyst is 93.6 emu/g. After five successive
tests, its saturation magnetization slightly declines but still
shows 79.7 emu/g. This suggests that the catalyst remains
favourable magnetic separation performance when it is dis-
persed into the ethanol solution again.
7–9). The CoPt/Fe3O4 catalyst shows excellent catalytic
activity and the conversion is up to 95% with 84% COL
selectivity. However, it is noticeable that totally different
catalytic results are observed for FePt/Fe3O4 catalyst and
NiPt/Fe3O4 catalyst. The FePt/Fe3O4 catalyst has high COL
selectivity of 89% with low conversion of 16%. Conversely,
the conversion of NiPt/Fe3O4 reaches 97% with COL selec-
tivity of only 39%. These catalytic results are closely link
with the electron arrangement in d orbits of the M metals.
The Fe NPs has the higher holes in 3d energy bands which
can be acted as electron acceptor, it can therefore efficiently
interact with C=O groups in CAL to boost its hydrogenation.
However, the Fe NPs is against H2 dissociation and
results in low conversion. Rather, the Ni NPs is in favour
of H2 dissociation but lacks of the capability of activating
C=O groups, thereby leading to the hydrogenation of C=C
groups. Additionally, different molar ratio of Co/Pt greatly
influences the catalytic efficiency of the CoPt/Fe3O4 cata-
lysts as shown in Table 1 (Entry 10–12). With increasing
4 Conclusions
The magnetic Fe3O4 is employed as support for effective
anchoring bimetallic CoPt NPs by a simple wet-impreg-
nation method. The prepared CoPt/Fe3O4 (1%) catalyst
exhibits excellent catalytic performance in hydrogenation
of CAL with conversion up to 95% and COL selectivity of
84%. Moreover, the prepared CoPt/Fe3O4 catalyst remains
excellent magnetic separation performance even after five
successive tests. Under optimized experimental condi-
tions, the conversion is greatly affected by the different
1 3

T. Yuan et al.
Table 2 Selective
hydrogenation of different α,
β-unsaturated aldehydes with
CoPt/Fe3O4 (1%) catalyst
Reaction conditions: 5 mg catalyst dose, 5 mL i-PrOH, 0.8 mmol substrate,160 °C,180 min, P(H2)
= 3 MPa
Compliance with Ethical Standards
Conflict of interest The authors declare that they have no conflict of
interest.
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Acknowledgements The authors are grateful for the financial support
from the Basic and Frontier Research Project of Chongqing in China
(No. cstc2016jcyjA0139). Moreover, I very much appreciate my tutors
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