Investigation of hollow bimetal oxide nanomaterial and their catalytic activity for selective oxidation of alcohol

Article abstract of DOI:10.1016/j.mcat.2018.01.028

The aerobic oxidation procedure utilized sustainable non-noble-metal catalysts has been a long-standing objective in laboratory and industrial research. The synthesized hollow bimetal oxide nanoparticles catalysts (HNPs) as a stable and efficient catalyst, which was applied to the selective oxidation of alcohols with molecular oxygen as oxidant, is reported. The catalytic performance of Co₃O₄/Fe₃O₄@C HNPs was tested via selective aerobic oxidation catalytic reaction of cinnamyl alcohol in the liquid phase. The results prove that the Co₃O₄/Fe₃O₄@C HNPs exhibit ～ 90% yield for alcohol oxidation, which can be conveniently separated and recycled from reaction system by an external magnetism. Forthrmore, the catalyst can be reutilized for at least 5 runs without a distinct activity reduction. A feasible reaction mechnism over the bimetal catalyst for the alcohol oxidation was proposed. The surface effect between metal oxide nanoparticle and carbon support, and relatively high and easy reducibility grant favorable catalytic activity of Co₃O₄/Fe₃O₄@C HNPs. This make the Co₃O₄/Fe₃O₄@C HNPs a very significant catalyst for aerobic catalytic oxidation reaction of alcohols in the liquid phase for industrial manufacture.

Full text of DOI:10.1016/j.mcat.2018.01.028

Molecular Catalysis 448 (2018) 63–70
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Investigation of hollow bimetal oxide nanomaterial and their catalytic
activity for selective oxidation of alcohol
Wenbin Gaoa,b, Feng Lia,b, Hongfei Huoa,b, Yuanyuan Yanga,b, Xiang Wanga,b, Yu Tanga,b
,
a,b
a,b
a,b,⁎
Pengbo Jiang , Shuwen Li , Rong Li
a
State Key Laboratory of Applied Organic Chemistry (SKLAOC), College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, PR China
Gansu Provincial Engineering Laboratory for Chemical Catalysis, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, PR China
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Metal oxide
Hollow nanoparticles
Liquid phase
Kinetic law
The aerobic oxidation procedure utilized sustainable non-noble-metal catalysts has been a long-standing ob-
jective in laboratory and industrial research. The synthesized hollow bimetal oxide nanoparticles catalysts
(
HNPs) as a stable and efficient catalyst, which was applied to the selective oxidation of alcohols with molecular
oxygen as oxidant, is reported. The catalytic performance of Co /Fe @C HNPs was tested via selective
aerobic oxidation catalytic reaction of cinnamyl alcohol in the liquid phase. The results prove that the Co
Fe @C HNPs exhibit ∼ 90% yield for alcohol oxidation, which can be conveniently separated and recycled
3
O
4
3 4
O
3 4
O /
Alcohol oxidation
3 4
O
from reaction system by an external magnetism. Forthrmore, the catalyst can be reutilized for at least 5 runs
without a distinct activity reduction. A feasible reaction mechnism over the bimetal catalyst for the alcohol
oxidation was proposed. The surface effect between metal oxide nanoparticle and carbon support, and relatively
high and easy reducibility grant favorable catalytic activity of Co
Fe @C HNPs a very significant catalyst for aerobic catalytic oxidation reaction of alcohols in the liquid phase
for industrial manufacture.
3 4 3 4 3 4
O /Fe O @C HNPs. This make the Co O /
3 4
O
1
. Introduction
In recent years, noble metal nanoparticles have shown a high ac-
tivity to effect alcohol oxidation using molecular oxygen under mod-
erate temperatures and pressures [1–3]. The heterogeneous precious
metal catalysts have been abundantly employed in aerobic oxidation
catalysis reaction of alcohols owing to their perfect catalytic property
[6], for example, many efficient catalysts based on gold [7,8], palla-
dium [9,10], and platinum [8,11], have been extensively reported and
obtained a good result. However, these catalysts possess obvious
drawbacks used in practical application, which are expensive cost,
limited availability and toxic properties [12,13]. Therefore, considering
the drawbacks of noble metal catalysts, it would be still desirable to
develop non-noble metal catalysts to affect alcohol oxidation. More-
over, a more significant shortcoming with some of these catalysts in
solid-liquid state reaction using molecular oxygen as the oxidant are
sensitive for the deactivation of alcohol oxidation due to substrates
overoxidation, and a basic condition is needed to activate and enhance
catalyst for reaction process [14–16].
Selective aerobic oxidation of alcohol to the corresponding alde-
hyde or ketone has turned out to be a very pivotal reaction process in
the current of laboratory and chemical industry. Utilization of corre-
sponding products as diverse intermediates for synthesis of key fine
chemicals is emerging as a complementary alternative the current en-
ergetically inefficient and/or environmentally unfriendly multi-step
reactions such as pharmaceuticals, agrochemicals and ploymers [1,2].
Traditionally, many toxic stoichiometric oxidative regents are per-
formed for this oxidation process, which fabricate a lot of waste and
pollutants, and are unsanctioned in viewpoint of green and environ-
mental chemistry [3]. From both green and substainable standpoints,
there are a strongly moving toward searching and developing the en-
vironmental-friendly and green oxidant in this chemosynthesis, such as
2
the air or O being the ideal oxidant from the enviromental point of
view [4]. Since these oxidants are readily securable, inexpensive, vast
pollution-free natural gas, and water is the main byproduct, that cata-
lytic process is industrially promising alternatives for available alcohol
oxidation [5].
Based on the reports of the above, and considered the past study of
the non-noble metal and non-noble oxides due to their properties such
as non-toxicity, lower cost, fine chemical stability and environmentally
⁎
Corresponding author at: State Key Laboratory of Applied Organic Chemistry (SKLAOC), College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, PR
China.
E-mail address: liyirong@lzu.edu.cn (R. Li).
https://doi.org/10.1016/j.mcat.2018.01.028
Received 28 October 2017; Received in revised form 23 January 2018; Accepted 23 January 2018
2468-8231/ © 2018 Elsevier B.V. All rights reserved.

W. Gao et al.
Molecular Catalysis 448 (2018) 63–70
friendly [17–22], for example Co
x
O
y
[23], Fe
x
O
y
[24], Mn
x
O
y
[25–28],
Mn
30], Co-Mn-Al complex oxides [31], Co-Mn oxides [32], Mo-Fe bimetal
2.3. Catalyst characterization
CeO
x
[29], VO
x
[22], and many bimetal oxides, including Co
2
3 8
O
[
The crystal phase of the materials was evaluated by X-ray dif-
fractometer (XRD) with a Rigaku D/max-2400 diffractometer using Cu-
Ka radiation (λ=1.5406 Å). Running condition of XRD and current are
40 kV and 40 mA and the X-ray source in the 2 theta range of 20−90°.
The full width at half maximum (FWHM) of the XRD line can be used
the Schere’s formula to estimate the crystallite size from the following
equation:
oxides [33] and others. Meanwhile, cobalt oxide and iron oxide are
excellent catalyst for dehydrogenation [24,34,35], CO oxidation [36],
CO
2
conversion [37], alcohol oxidation reaction [38], and others.
carbon materials due to low density, abundants surface functional
grounps, well-diffusion performances and higher specific surface area,
are a widely-applied support for plentiful catalytic nanoparticles, and
hollow nanoparticles with low density, higher surface-to-volume, their
prospective applications in catalysis and others based on nanoscale
Kirdendall effect are also proven to be fascinating catalytic support for
numerous reaction [39,40]. In addtion, the experiments have demon-
strated that the iron oxide and carbon support have special interaction,
the negatively charged surface oxygen functional groups of the carbon
support serve as strongly active sites for anchoring positively charged
D
XRD = Kλ/βcosθ
Where is the observed angular width at half maximum intensity of the
peak, K is a dimension less number (equal to 0.89), is the x-ray wave-
length (1.5418 Å for Cu Kα) and θ is the diffraction angle. And
Inductive coupled plasma optical emission spectrometer (ICP-OES)
analysis was carried out with Perkin Elmer (Optima-4300DV) to mea-
sure the metal content.
3
+
Fe
ions and lead to high dispersion of iron oxide species. These
oxygen functional groups also provide a suitable coordinate environ-
ment to increase the electron density of iron centres and form efficient
active sites for the oxidation of alcohols with molecular oxygen [41].
Herein, considering the previous reported catalysts employed in
basic condition and expensive cost limited availability, the catalytic
Scanning electron microscopy (SEM) was utilized to observe the
image of the samples daubing Carbon double-sided conductive tape
with MIRA3 TESCAN. The morphology of the synthesized catalyst was
investigated by transmission electron microscopy (TEM) and high-re-
solution transmission electron microscopy (HR-TEM) with a field
2
20
property of the Co
3
O
4
/Fe
3
O
4
@C HNPs catalysts was employed in the
emission gun transmission electron microscopy Tecnai G Tf operating
2
20
selective oxidation of alcohol with molecular oxygen in the liquid
phase, which shows > 95% alcohol conversion and ∼ 90% aldehyde
yield without any promoter (eg., NaOH). In addition, the catalyst can be
reused after at least 5 runs with a good activity and recycled with ex-
ternal magnetic. This catalyst is a useful and a meaningful candidate for
aerobic catalytic oxidation reaction of alcohols in the liquid phase
system.
at 300 kV and EDX was measured on a Tecnai G Tf microscope. The
specimens were dispersed in ethanol and on a holed carbon-coated Cu
grid. Nitrogen physisorption isotherms were carried out at −195.8 °C
on a static volumetric instrument (TriStar Ⅱ 3020 V1.04). The specific
surface area was calculated by the Brunauer–Emmett–Teller method.
A physical magnetic quality of the sample was researched by a
Quantum Design vibrating sample magnetometer (VSM) at room tem-
perature. X-ray photoelectron spectroscopy (XPS) was performed on the
PHI-5702 instruments with an Mg anode (Mg Kα hυ = 1253.6 eV) at a
2. Experimental
−8
base pressure of 5 × 10 mbar). The revision of the binding energies
BE) was implemented with the C1 s peak of extraneous C at 284.6 eV.
(
2.1. Reagents and chemicals
All reagents and chemicals were analytical grade and used as re-
2.4. Catalytic tests
ceived without any further purification. Ferric (Ⅲ) nitrate nonahydrate
Fe (NO ·9H O, 98.5%) was purchased from Chengdu Kelong
Chemical Reagents Co., Ltd. Cobalt (Ⅱ) nitrate hexhydrate (Co
NO ·6H O, 99.0%) was purchased from Shanghai Zhongqin
Chemical Reagents Co., Ltd. Sodium hydroxide (NaOH, 96.0%) was
purchased Chemical Reagents Manufacturing Co., Ltd. Sodium oleate
(C H33COONa or NaOA, 99.5%) was purchased from Tianjin Guangfu
17
Chemical Reagents Co., Ltd. Absolute ethanol and hexane was pur-
chased from Lianlong Bohua (Tianjin) Pharmaceutical Chemical Co.,
Ltd.
(
3
)
3
2
The reaction was tested in a 25 mL, a three-necked batch reactor
with a suitable match reflux condenser, oil bath, and thermocouple at
atmospheric pressure. Typically, 4 mmol of substrates, 10 mL of o-xy-
lene and 20 mg of catalyst were mixed with stirring at 393.15 K oxygen
(20 mL/min) was continuously brought in bottle and reaction time is
3 h. In addition, the reaction catalyst can be recycled and collected by
the external magnetic force, and then it was washed with deionized
water and absolute ethanol several times, and following by a heat
treatment before next time. Our reaction sample was analyzed by
GC–MS (Agilent 6,890N/5,937N).
(
3
)
2
2
The catalytic activity was calculated as follows:
conversion = 100 × ([C -C ]/[C ]), and% Yield = 100 × [C’]/[C
based on the initial [C ] and the final [C ] concentrations of organic
substrate and the reaction [C’] concentrations of aldehyde. Turnover
Frequency (TOF) = mol number of substrate converted/[moles number
of active sites × reaction time].
%
0
],
2
.2. Preparation of the catalyst
0
1
0
0
1
In brief, 1 mmol Fe(NO
3 3 2 3 2 2
) ·9H O (0.404 g), 1 mmol Co(NO ) ·6H O
(
0.291 g) and 5 mmol NaOA (1.522 g) were dissolved in the solution
with 10 mL of deionized water, 20 mL absolute ethyl alcohol, and 30 mL
of hexane. The mixture solution was heated to 70 °C with magnetic
stirring for about 30 min. Then 5 mmol of NaOH (0.200 g) was added to
the solution and the mixture solution was stirred for 4 h. After cooled
down, the mixture solution was dried at 80 °C for 12 h and a precipitate
3. Result and discussion
was obtained. The precipitate mixed with 10 g of Na
2
SO
4
was grind to
3.1. Characterizations catalyst
form the homogeneous power, which was heated to 500 °C under ni-
−
1
trogen at heating rate of 10 °C min and kept the temperature for 3 h.
After cooled down, the black product was washed with deionized water
and absolute ethanol, and it was dried at 60 °C for 12 h. Finally the
metal nanoparticles (MNPs) loaded on the carbon (MNPs/C) nano-
composites was prepared, which was heated in air 400 °C for 2 h at
To characterize and prove the morphology of Co
HNPs@C, the TEM, HRTEM-mapping and EDX were carried out. Fig. 1a
presents a typical TEM image of Co /Fe HNPs@C, which clearly
exhibits a hollow structure metal oxide nanoparticles of the catalyst,
and the sample of Co /Fe HNPs@C was successfully obtained.
3 4 3 4
O /Fe O
3
O
4
3 4
O
3
O
4
3 4
O
−1
heating rate of 5 °C min , the metal oxide nanoparticles (MONPs)
loaded on the carbon (MOHNPs@C) nanocomposites was obtained.
Fig. 1b showed a part of a HNSs with HRTEM and the corresponding
morphology sketch. It was observed that the shell of a thin layer of
64

W. Gao et al.
Molecular Catalysis 448 (2018) 63–70
3 4 3 4
Fig. 1. TEM images (a, b), and EDX (c) and mapping results (d, e, f, g and h) of Co O /Fe O @C.
Scheme 1. Schematic caption the synthesis procedure of the
material.
Co
3
O
4
/Fe
3
O
4
HNPs. The EDX spectrum of the Co
3
O
4
/Fe
3
O
4
HNPs
oxide material. The peaks of black line at 2-Theta value of 44.29°,
51.61° and 75.91° in Fig. 2(a) was indicated to cubic Co (JCPDS 00-015-
0806). The red line at 2-Theta value of 44.68°, 65.08° and 82.37° and
the blue line at 2-Theta value of 37.68°, 42.81°, 43.67° 44.68°, and
49.28° in Fig. 2(a) were displayed to cubic Fe (JCPDS 01-087-0721) and
(
Fig. 4c) exhibited the presence of strong signals of C, Cu, Co, Fe and O
elements (the scanned region from Fig. 1c) The mapping results of
Fig. 1d zone are presented in Fig. 1e–h, in which the distributions of Co,
Fe and O elements are the very same. The zone of the distribution of C
element was larger than that of Co, Fe, and O, which was consisted with
the result that carbon coated on the surface of Co O /Fe O HNSs.
3 4 3 4
Meanwhile, these indicated that Co and Fe elements were evenly dis-
persed among O element in the inner HNSs layer and carbon was coated
on the Co
phology of the material, the SEM were presented in Fig. S1. The a-c are
CoFe/C and d-f are Co /Fe @C. Heated under N atmosphere, it is
Fe
31.29°, 36.82°, 44.84°, 59.40° and 65.32° in Fig. 2(b) was indicated to
cubic Co (JCPDS 00-043-1003). The read line at 2-Theta value of
3
C (JCPDS 00-065-0393). The peaks of black line at 2-Theta value of
3 4
O
30.04°, 35.73°, 57.61°, and 62.59° and the blue line at 2-Theta value of
24.20°, 33.31°, 35.65°, 40.94°, 49.51°, 54.10°, and 62.59° in Fig. 2(b)
3 4 3 4
O /Fe O HNSs. In addition, to further insight the mor-
were manifested to cubic Fe
3 4
O (JCPDS 00-082-1533) and rhombohe-
3
O
4
3
O
4
2
dral Fe (JCPDS 00-033-0664). No other peaks were observed in
2 3
O
clean that metal NPs/C precuror were obtained and metal nanoparticles
were dispered evenly with the carbon nanosheet (see a-c of Fig. S1).
Afterwards, the nanocomposites were heated in air, during the proce-
dure, the carbon of the metal NPs/Carbon sheets partly was oxidized
and metal NPs transferred to metal oxide HNSs (see d-f of Fig. S1 and
TEM) (Scheme 1).
Fig. 2, which indicated that the metal/C nanocomposites and metal
oxide HNSs@C of corresponding phase were synthesized. The the
average particles of Fe
were 19.4 nm, 29.3 nm and 20.4 nm in Table 1
The specific surface area and pore size distribution of the porous
carbon material structure were certified via N adsorption-desorption
analysis. As shown in Fig. 3, the results manifest that the adsorption-
3 4 2 3 3 4 3 4 3 4
O Fe O @C, Co O @C and Fe O /Co O @C,
2
Fig. 2 presents the XRD patterns of the synthesized metal and metal
65

W. Gao et al.
Molecular Catalysis 448 (2018) 63–70
Fig. 2. XRD patterns of (a) MNPs/C; (b) MOHNPs@C.
peak of Co3+ located at 779.9 eV and Co2+ located at 781.5 eV can be
clearly seen from Fig. 4a, which are corresponded with the single Co
38,42]. The two peaks position O 1 s (Fig. 4b) were found to be located
at 529–530 eV, which is well-defined in the Co [42], the other two
Table 1
The summary of parameters of the catalyst.
3 4
O
[
Sample
Surface
Pore
Average
pore
width (nm)
Particle
size (nm) kJ/
mol
E
a
ΔH
a
c
3 4
O
area
volume
kJ/
mol
2
3
b
peaks values located at ∼531 eV, and ∼532 eV, can be appointed to
carbonyl and carboxylic groups on the carbon surface [38]. And also,
Fig. 4c present Fe 2p pattern. The levels of Fe 2p3/2 and Fe 2p1/2 are
(
m /g)
(cm /g)
Fe Fe
Co/C
3
C/C
141
239
332
33
0.24
0.27
0.34
0.16
7.99
6.61
5.89
18.66
36.2
22.0
15.1
2+
3+
7
10.3 eV and 724 eV for Fe , and 711.7 eV and 724.8 eV for Fe
,
FeCo/C
Fe
which are corresponded with that observed from single Fe [43,44].
3 4
O
O
3 4
/
19.4
30.0 12.6
Fe
2
-
The O 1 s XPS spectrum on the basis of binding energy of O 1 s has been
reported in the literature [24,43].
O
3
@C
@C
/
Co
Co
3
O
4
13
28
0.06
0.15
23.25
26.83
27.2
10.4
27.3 8.9
20.4 4.6
3
O
4
3
Fe -
3.2. Catalysts performance
O
4
@C
a
Pore volume is the total pore volume.
Average pore width is the desorption average pore width.
Particle size calculated by the Schere’s formula of XRD.
Table 2 presents the catalytic activity of the different Cobalt and
b
c
iron-base catalysts. The obvious difference in the catalytic performance
of metal-based catalysts and metal oxide-based catalysts can be ascribed
to the higher catalytic reaction activity of metal oxide catalysts com-
pared to metal-base catalysts. Also, we study the molar ratio of the
range from 3:1, 1:1 and 1:3 of Fe:Co, it was found that Co O /Fe O @C
3 4 3 4
with molar ratio of the 1:1 of Fe:Co can obtain ∼90% yield of cinnamyl
desorption isotherm of the prepared material was a typical type IV
isotherm (according to the IUPAC classification) with a hysteresis loop
at relatively high P/P , indicating the presence of mesoporous mor-
0
phology of the carbon support. It is clearly that the metal-based ma-
terials have higher surface area than metal oxide-based material, which
can be attribute to change of pore structure. The result was presented in
Table 1.
To gain further insight into the catalyst stucture, XPS character-
ization was performed to investigate the chemical elements valence
aldehyde, which is attributed that the more amount of Fe can probably
form Fe O , and the less amount of Fe make the active conment reduce.
2 3
The result proves that the oxidation procedure is structure sensitive for
cobalt oxide and iron oxide, which were demonstrated by dynamic
c
experiment calculated with different global kinetic constant (k ), ad-
sorption equilibrium constant (Kads) as shown in Table S1, activation
energy (Eact), and adsorption heat (ΔQ) as shown in Table 1, due to
their specific stable surface oxygen vacancies [23,24], favorable
states of Co, Fe and O on the surface of Co
3 4 3 4
O /Fe O @C. The results
were shown in Fig. 4. The Co 2p is spilt into Co 2p1/2 and Co 2p3/2, the
2
Fig. 3. N adsorption-desorption isotherms of (a) MNPs/C, (b) MOHNPs@C.
66

W. Gao et al.
Molecular Catalysis 448 (2018) 63–70
3 4 3 4
Fig. 4. (a) Co 2p, (b) O 1 s XPS pattern of Co O (c) Fe 2p and (d) O1 s XPS pattern of Fe O .
reducibility [24,45], specific surface properties [18,46], and multi-
component oxide crystal properties [17,47]. Moreover, and Co
possess the higher catalytic activity compared to the Fe /Fe @C,
is inactive in aerobic oxidation of
reaction temperature for conversion of cinnamyl alcohol, product se-
lectivity and yield, and turnover frequency (TOF). Fig. 5a and c show
the catalytic performance of the Co O /Fe O @C along with the in-
3 4 3 4
3 4
O
3
O
4
2
O
3
which was attributed to that Fe
alcohol [24].
2
O
3
crease of reaction time, the conversion and yield are gradually raised
and the selectivity is gradually reduce from 97% to 91%. And the TOF
−
1
Fig. 5 presents the catalytic results along with reaction time and
based conversion were moderate (ie., 45% and 18 h ). These results
Table 2
The catalytic activity of the different catalysts a,b
.
Entry
Catalyst
Conversion of 1 [%]
Selectivity of 2 [%]
Yield of 2 [%]
1
2
3
4
5
6
7
No catalyst
No catalyst(N )
2
Trace
No
12
10
21
70
80
85
96
Trace
No
10.8
9.2
21
45.5
76
78
∼90
82
Fe
3
C/C
90
92
99
65
96
92
93
91
Co/C
CoFe/C
Fe
3
O
4
2
/Fe O
3
@C
Co
Co
Co
Co
Co
3
3
3
3
3
O
4
O
4
O
4
O
4
O
4
@C
c
8
/Fe
/Fe
/Fe
/Fe
3
O
O
O
O
4
@C
@C
@C
9
1
1
3
3
3
4
4
4
0d
1
90
Trace
@C(N
2
)
Trace
a
b
c
The reaction was carried out using 20 mg of the catalyst, cinnamyl alcohol (4 mmol) and o-xylene (10 mL) in O
Determined by GC–MS measurement.
Fe-Co mixed oxides with molar ratio of the range from 1:3.
2
with 20 mL/min at 120 °C for 10 h.
d
Fe-Co mixed oxides with molar ratio of the range from 3:1.
67

W. Gao et al.
Molecular Catalysis 448 (2018) 63–70
Fig. 5. Performance evaluation conversion, selectivity and yield, and TOFa of Co
TOF based on the conversion of 1 h.
3 4 3 4
O /Fe O @C with (a) (c) reaction time and (b) (d) reaction temperature.
a
indicated that the decrease of selectivity and the TOF is due to by-
products (ie., acid). The sample was further tested at various reaction
temperature, the catalytic results are shown in Fig. 4b and Fig. 5d. As
the reaction temperature increased, the selectivity of cinnamyl alde-
hyde decreased from 98% to 37% and TOF based converion increased
3.3. Kinetic study
The reaction kinetics of the oxidation of cinnamyl alcohol to cin-
namyl aldehyde on the Co O /Fe O @C catalyst with a series of cin-
3 4 3 4
namyl alcohol concentrations were researched employing the initial
reaction rate method. The result was presented the Supplementary
Materials. The overall kinetics equation of the reaction can be defined
as:
−1
from 19 to 27.6 h , but the based TOF based yield decreased from 19
−1
to 10 h
and conversion decreased from 96 to 85% at 120 to150 °C.
This phenomenon might not only be attributed to byproducts, but also
be influenced for the surface activity or the catalysts particle aggregated
by the higher temperature. And also, it is proved by the dynamic ex-
periments (Fig. S5 and Table S2) with different surface adsorption rate
constant.
1
2
k
[alcohol] + O → [aldehyde] + H O
2
2
(1)
Substituting [O ] as a constant, from earlier arguments, and con-
2
To further obtain the substrate scope of the different selective al-
cohols oxidation reaction over the catalyst, various substrates including
aliphatic and aromatic alcohols were carried out. The result was got in
Table 3. It is clear that a range aliphatic alcohols (Entry 1–4) presented
suit for the formation of the corresponding aldehydes or ketone,
achieving moderate to good yields within 10 h. And the aliphatic al-
cohols (Entry 1–4) displayed higher activity than aromatic alcohols
sidering reaction mechanism, the reaction process kinetics equations
can be completed. The kinetic rate equation of absorption equilibrium
was deduced with an equilibrium constant Kads defined as:
[
alcohol]ads
K
ads
=
[alcohol] [cat]
0
(2)
and that the reaction mechanism for absorbed process of alcohol
(
Entry 5–9), this can be attributed the bimetallic oxide system, the
dehydrogenation refer to two sequential procedures according to [50]:
coexistence of Fe and Cu in metal oxide leads to a modification of
electronic and catalytic activity [48,49]. Moreover, the side reactions of
the saturated and unsaturated alcohols are main the corresponding
acid, and a spots of the unsaturated alcohols are the corresponding
epoxide. Meanwhile, the para substituent of the electron-donating
group (Entry 6) and the electron-withdraw group (Entry 7–9) have an
obvious influence on the oxidation of alcohols and high electron density
could improve the oxidative reaction of alcohol.
k
1
[
alcohol]ads → [alkoxy]ads
(3)
(4)
k
2
[alkoxy]ads → [aldehyde]
ads
the first dehydrogenation reaction rate constant of the alcohol is
1
defined as k , and the second dehydrogenation reaction rate constant of
2
the alcohol yielding to aldehyde is defined k . Nevertheless, in practice
reaction process, these two procedures cannot be obtained and the
degree of surface adsorption of substrate was considered [51].
68

W. Gao et al.
Molecular Catalysis 448 (2018) 63–70
Fig. 6. Variation of the (a) Eact and (b) ΔQ for cinnamyl alcohol oxidation with alcohol on different catalysts.
Fig. 7. The proposed mechanism for selective oxidation alcohol over
the Co /Fe @C.
3
O
4
3 4
O
λ[alcohol]0
adsorption heat equation:
θ =
1
+λ[alcohol]0
(5)
ΔQ
R
1
T
lnKads= -
⎛
⎝
⎞+C
θ = ° of catalyst surface occupied by the substrate. λ = adsorption
equilibrium constant.
(10)
⎠
Where ΔQ is the adsorption heat of the reaction, C is the constant, R is
the molar gas constant and T is the reaction temperature.
The overall reaction kinetic equation can be transformed to [50–52]
Kadskc[cat][alcohol]0
Activation energy linearly and adsorption heat linearly are sig-
nificantly different over the catalysts. It is indicated that the reaction
underwent different reaction pathway over the catalysts (Fig. 6).
r0 =
1
+kads[alcohol]0
(6)
(7)
where k
c
is a global kinetic constant
Which after linearization is converted into:
3.4. Proposed reaction mechanism
1
r0
1
1
=
+
Kadskc[cat][alcohol]0
kc[cat]
3 4 3 4
Based on the above results and discussion and the Co O /Fe O @C
can presents an effective performance for selective oxidation of alcohol,
an integrated reaction mechanism of selective oxidation of alcohol over
Thus, via plotting the inverse of the initial reaction rate versus the
inverse of the various initial concentration of alcohol, from the inter-
cept and slope of the straight at the origin of the fitted equation, the
c
values of k and kads can be obtained. The parallelism of experiment
data to Eq. (7) in this work at different temperature is depicted in Fig.
S4. Table S1 are summarized for the calculated kinetic and adsorption
constants.
Activation energies Eact were calculated from the measured rate
constants at different temperatures according to the Arrhenius equa-
tion:
the Co
mechanism of aldehyde formation form the alcohol oxidation. The
blank catalytic tests were conducted in N and O (Table 2 Entry 1 and
). Under the condition, both the reaction condition do not exhibit
3 4 3 4
O /Fe O @C is proposed and shown in Fig. 7. To clarify the
2
2
2
catalytic activities, which imply the existence of a dehydrogenation
mechanism in which aldehyde formation occurs in the absence of
oxygen. The optimum catalyst carried out under N was inactive, which
2
indicated that the molecular is adsorbed and activated on the oxygen
vacancy. Meanwhile, the oxygen adsorbed the oxygen vacancy will
capture the transferred electrons and be activated, and the corre-
sponding metal (Fe3+ and Co ) were reduced. The catalytic active
center and the overall redox cycle of Fe O and Co O were completed.
The activated oxygen attacks the alcohol to form CeO bond, and along
with rapture of the CeH bond. The broken H atom transfers to the
oxygen site to form OeH bond (CeOH group). Nevertheless, the two-
-Eact/RT
k
c
=Ae
(8)
3+
Eact
1
lnkc=lnA-
⎛
⎞
3
4
3 4
R ⎝ T ⎠
(9)
where Eact activation energy, R is the molar gas constant, T is the re-
action temperature and A is the pre-exponential factor. Adsorption heat
ΔQ of cinnamyl alcohol over the catalyst were obtained via the
2
OH is not stable and will be rearrangement to C]O and H O. The
69

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