Highly Dispersed Copper Nanoparticles Supported on Activated Carbon as an Efficient Catalyst for Selective Reduction of Vanillin

Article abstract of DOI:10.1002/smll.201801953

Highly dispersed copper nanoparticles (Cu NPs) supported on activated carbon (AC) are effectively synthesized by one-pot carbothermal method at temperature range of 400–700 °C. The X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller analysis reveal that Cu NPs with diameters of 20–30 nm are evenly anchored in carbon matrix. The 15 wt%-Cu/AC-600 catalyst (derived at 600 °C) exhibits best bifunctional catalysis of aqueous-phase hydrodeoxygenation (HDO) and organic-phase transfer-hydrogenation reaction (THR) to selectively transform vanillin to 2-methoxy-4-methylphenol (MMP). In HDO of vanillin, the as-prepared catalyst achieves a 99.9% vanillin conversion and 93.2% MMP selectivity under 120 °C, 2.0 MPa H₂ within 5 h. Meanwhile, near-quantitative vanillin conversion and 99.1% MMP selectivity are also obtained under 180 °C within 5 h in THR of vanillin by using 2-propanol as hydrogen donor. The transforming pathways of vanillin are also proposed: vanillin is transformed into MMP via intermediate of 4-hydroxymethyl-2-methoxyphenol in HDO case and by direct hydrogenolysis of vanillin in THR course. More importantly, the activity and the selectivity do not change after 5 cycles, indicating the catalyst has excellent stability. The Cu-based catalyst is relatively cheap and preparation method is facile, green, and easy scale-up, thus achieving a low-cost transformation of biomass to bio-oils and chemicals.

Full text of DOI:10.1002/smll.201801953

FULL PAPER
Carbothermal Methods
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Highly Dispersed Copper Nanoparticles Supported on
Activated Carbon as an Efficient Catalyst for Selective
Reduction of Vanillin
Ruoyu Fan, Chun Chen,* Miaomiao Han, Wanbing Gong, Haimin Zhang,
Yunxia Zhang, Huijun Zhao,* and Guozhong Wang*
1. Introduction
Highly dispersed copper nanoparticles (Cu NPs) supported on activated
The conversion of biomass into fuels and
carbon (AC) are effectively synthesized by one-pot carbothermal method at
temperature range of 400–700 °C. The X-ray diffraction, transmission electron
microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller
analysis reveal that Cu NPs with diameters of 20–30 nm are evenly anchored
in carbon matrix. The 15 wt%-Cu/AC-600 catalyst (derived at 600 °C) exhibits
best bifunctional catalysis of aqueous-phase hydrodeoxygenation (HDO)
and organic-phase transfer-hydrogenation reaction (THR) to selectively
transform vanillin to 2-methoxy-4-methylphenol (MMP). In HDO of vanillin,
the as-prepared catalyst achieves a 99.9% vanillin conversion and 93.2%
MMP selectivity under 120 °C, 2.0 MPa H2 within 5 h. Meanwhile, near-
quantitative vanillin conversion and 99.1% MMP selectivity are also obtained
under 180 °C within 5 h in THR of vanillin by using 2-propanol as hydrogen
donor. The transforming pathways of vanillin are also proposed: vanillin is
transformed into MMP via intermediate of 4-hydroxymethyl-2-methoxyphenol
in HDO case and by direct hydrogenolysis of vanillin in THR course. More
importantly, the activity and the selectivity do not change after 5 cycles, indi-
cating the catalyst has excellent stability. The Cu-based catalyst is relatively
cheap and preparation method is facile, green, and easy scale-up, thus
achieving a low-cost transformation of biomass to bio-oils and chemicals.
chemicals is an effective way to reduce the
world dependence on fossil resources and
environment pollution simultaneously.[1,2]
As one of the three major components in
lignocellulosic biomass, lignin is the only
renewable source that can be firsthand
applied to produce aromatic compounds,
like bio-oil.[3] However, these products
cannot be directly used because of high
oxygen content.[4] Catalytic hydrodeoxy-
genation (HDO), which involves hydro-
genation of unsaturated functional groups

like C C bonds followed by the hydrogen-

olysis of C O bonds, has been deemed to
be one of the most important and effective
upgrading strategies to reduce the oxygen
content.[5–7]
As an important aromatic monomer
in lignin, vanillin can be selectively trans-
formed into 2-methoxy-4-methylphenol
(MMP), which has been widely used as fra-
grances or the intermediates of drugs and
fragrances, by the catalytic HDO over var-
ious heterogeneous catalysts.[8] Among them, noble metal-based
catalysts are predominant because of their high activity, such as
Au/carbon nanotubes,[9] Ru nanoclusters,[10] Ru/carbon nano-
tube,[11] hollow Pd/metal organic framework nanosphere,[12] Pd/
single-walled carbon nanotube-SiO2,[13] and Pd/MSMF (MSMF:
superhydrophilic mesoporous sulfonated melamine-formalde-
hyde resin),[14] Pd/SO3H-MIL-101(Cr), etc.[15] It could be easily
found that cumbersome synthetic strategies or complicated
supports were usually unavoidable for construction these high
active noble metal-based catalyst.[16–22] In addition, using noble
metal-based catalysts are prone to fall into the dilemma of low
selectivity to MMP, yielding the mixture of MMP and 4-hydroxy-
methyl-2-methoxyphenol (HMP).[13] More seriously, noble metal-
based catalysts are usually limited to practical application by
coke formation, easy deactivation, as well as their low reserves
and high cost. On these basis, there is a pressing need for devel-
oping highly active, selective and steady non-noble metal-based
catalysts with the prospects in practical application.[23,24]
R. Fan, Dr. C. Chen, Dr. M. Han, W. Gong, Prof. H. Zhang,
Prof. Y. Zhang, Prof. H. Zhao, Prof. G. Wang
Key Laboratory of Materials Physics
Centre for Environmental and Energy Nanomaterials
Anhui Key Laboratory of Nanomaterials and Nanotechnology
CAS Center for Excellence in Nanoscience
Institute of Solid State Physics
Chinese Academy of Sciences
Hefei, Anhui 230031, China
E-mail: chenchun2013@issp.ac.cn; h.zhao@griffith.edu.au;
gzhwang@issp.ac.cn
R. Fan, W. Gong
Science Island Branch of Graduate School
University of Science and Technology of China
Hefei, Anhui 230026, China
Prof. H. Zhao
Centre for Clean Environment and Energy
Gold Coast Campus
Griffith University
Queensland 4222, Australia
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.201801953.
Recently, several non-noble metal catalysts have been devel-
oped to catalyze the reaction of HDO, such as Co, Ni, and Cu
DOI: 10.1002/smll.201801953
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catalysts, which are preferable than noble metal catalysts for
the potentials of commercial application and economy. Xia
et al. reported HDO of vanillin to MMP in liquid-phase can
be achieved with a selectivity of 64.6% over a highly dispersed
Ni/nitrogen-doped carbon black catalyst.[25] Tsang et al. reported
an efficient catalyst (Co-MoS2), which exhibits high catalytic
performance in HDO of 4-methylphenol under mild reaction
conditions.[26] Chen and co-workers reported well-dispersed
Mo2C nanoparticles supported on activated carbon, exhibiting
excellent catalytic activity in HDO of vanillin but poor selectivity
for target products under mild reaction conditions.[27] Although
these catalysts have demonstrated identified activity of HDO, a
great challenge is upgrading the selectivity to the target product.
Among various types of non-noble catalysts, Cu-based heteroge-
neous catalyst has a unique advantage for chemoselective HDO
of aromatic or heterocyclic aldehydes in view of its moderate
activity and specific adsorption manner. It has reported that
the hydrogenation of aromatic or heterocyclic aldehydes over
Cu-based catalyst usually following a η1(O)-aldehyde (perpen-
dicular) configuration, in which the O atom of aldehyde group
is contacted with Cu to form η1(O)- species and at the same
time the aromatic or heterocyclic ring is repelled away from the
catalyst surface to remain largely unaffected.[28] By this adsorp-
tion manner, the reaction site can be confined to the aldehyde
group, and thus achieving chemoselective HDO of aromatic or
heterocyclic aldehydes.[29] Therefore, Cu is the desired candidate
as active metal element for selective HDO of vanillin toward
MMP. Compared with Ni- or other metallic-based catalyst, the
Cu-based catalyst possesses moderate catalytic activity and has
low tendency to catalyze aromatic or heterocyclic ring which
can prevent excessive HDO of reactant to some by-products,
thus improving its selectivity.[30] Up to now, Cu-based cata-
lysts have been widely used for the HDO reaction, such as Cu/
SiO2,[28] Cu-HZSM-5,[31] CuMgAl,[32] CuZnAl,[32] Cu/MgO,[33]
Co-Cu/SBA-15,[34] and Cu30Cr10/γ-Al2O3.[35] Lomate et al.
have studied selective hydrogenation of levulinic acid to
γ-valerolactone over Cu-SiO2 catalysts.[36] Nagaraja et al. reported
a highly efficient Cu/MgO catalyst for vapour phase hydrogena-
tion of furfural to furfuryl alcohol, in which high conversion
of furfural (98.0%) and high selectivity toward furfuryl alcohol
(98.0%) were achieved.[33] Recently, Petitjean et al prepared a
Cu-PMO (PMO: porous metal oxide) catalyst and applied it into
HDO of vanillin, which gave a 100% conversion and 90% MMP
selectivity under 180 °C and 4.0 MPa H2 pressure within
18 h.[37] Moreover, the corresponding catalyst could be extended to
catalytic reduction of other unsaturated compounds. However,
more or less, these Cu-based catalysts had some imperfections,
such as complicated or multisteps synthetic method, harsh reac-
tion conditions and easy deactivation. In addition, they could
only be used in conventional catalytic hydrogenation process
with the assistance of high pressure H2, which would induce
many drawbacks, such as high cost, low solubility, complex
reactor design, and high requirements for storage, transporta-
tion, and safety. Although catalytic conversion of vanillin were
also achieved without using molecular H2 by transfer hydro-
genation reaction (THR), the catalysts were confined to noble
metal-based materials, such as Pd50Ag50/Fe3O4/nitrogen-doped
reduced graphene oxide,[17] Ag-Pd@g-C3N4,[20] and Pd/nitrogen-
enriched highly mesoporous carbon catalysts.[38] Therefore, we
aim at developing a bifunctional non-noble metal-based catalyst,
which can not only display high activity in direct HDO of van-
illin by molecular H2, but also can efficiently convert vanillin
toward MMP with H2-free via a THR route.
Here, metallic Cu was selected as the active component.
And for constructing of highly active heterogeneous Cu-based
catalyst, an eligible support with the properties of high surface,
good thermal stability and economy is necessary, like carbon
materials. Furthermore, the use of carbon as support can also
reduce the formation of coke, which is difficult to avoid in other
supports, like Al2O3, in the course of HDO reactions. Consid-
ering that there is a strong interaction between metal ions and
carbon at high temperature (reducing property of active carbon),
a carbon supported Cu catalyst (Cu/AC) was constructed by car-
bothermal method, in which the Cu ions was reduced by carbon
and the formed Cu nanoparticles (NPs) were in situ anchored
on the carbon. In this process, the carbon was acted as the
reductant, stabilizer, dispersant, as well as the support for Cu
NPs. The Cu/AC catalyst was applied in the processes of HDO
and THR of vanillin toward MMP under a moderate reaction
condition, and their activities and selectivities were also evalu-
ated and correlated with the structures of prepared material.
2. Results and Discussion
2.1. Screen for the Cu/AC-600 Catalyst
First, we screened the structure and morphology of 15 wt%-Cu/
AC-600 catalyst and the corresponding characterization results
are shown in Figure 1. The powder X-ray diffraction (XRD) pat-
terns of the as-obtained sample displays a broad peak located at
2θ = 23.0°, which could be attributed to the characteristic peak
of amorphous carbon (Figure 1a). And another three character-
istic diffraction peaks at 2θ values of 43.3°, 50.5°, 74.2° are cor-
responded to (111), (200), (220) planes of metallic Cu (JCPDS
01-070-3039), suggesting the Cu precursors are effectively
reduced into metallic Cu by the carbothermal method. The
average size of the Cu NPs is 32.1 nm calculated by Debye–
Scherrer formula. The specific surface area of Brunauer–
Emmett–Teller (SBET) and pore volume (Vpore) of the prepared
sample were also determined by the N2 physisorption tech-
nique (Figure 1b), which displays microporous solids (pore size
of 1.4 nm) and high surface area of 822 m2 g−1, being benefit
for catalytic conversion of vanillin. In addition, the morpholo-
gies and metal dispersions of 15 wt%-Cu/AC-600 catalyst were
also characterized by transmission electron microscopy (TEM),
the formed metallic Cu NPs are well dispersed on the AC and
the average size of NPs is 31.2 3.2 nm as shown in Figure 1c,
which is consistent with XRD result. In high-resolution TEM
(HRTEM) images (Figure 1d), the characteristic spacing
of 0.208 nm agrees well with the Cu (111) crystallographic
planes, indicating the main component is metallic Cu in the
15 wt%-Cu/AC-600 catalyst.
In the characterization of catalytic properties, the obtained
15 wt%-Cu/AC-600 catalyst displays 99.9% vanillin conversion
and 93.2% MMP selectivity in vanillin HDO (Table 1, Entry 1)
under 120 °C, 2.0 MPa H2 pressure within 5 h. By contrast,
the HDO reaction does not proceed without catalyst (Table 1,
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Figure 1. The characterization of 15 wt%-Cu/AC-600 catalyst. a) X-ray diffraction patterns, b) nitrogen adsorption–desorption isotherm and DFT pore
size distributions, c) TEM image and the corresponding size distribution plot of Cu NPs (inset), and d) the HRTEM image.
Entry 2) or active metal (Table 1, Entry 3) under the identical
reaction condition. In order to determine the active sites of Cu-
based catalyst in the HDO of vanillin to MMP, the 15 wt%-Cu/
AC-600 catalyst was further treated in air atmosphere at 200 °C.
The obtained sample (15 wt%-Cu/AC-air-200) is mainly com-
posed of copper oxide, as shown in Figure S1 (Supporting Infor-
mation), and displays no activity in HDO of vanillin (Table 1,
Entry 4), suggesting that the active sites are metallic copper
rather than copper oxide. On this base, we also further reduced
the 15 wt%-Cu/AC-air-200 catalyst in a reducing gas (H2) at
300 °C. With reduction time prolonging, copper oxides are pro-
gressively reduced to metallic copper, as shown in Figure S1
of the Supporting Information (15 wt%-Cu/AC-reduced-1h,
15 wt%-Cu/AC-reduced-3h and 15 wt%-Cu/AC-reduced-6h in
Supporting Information). Meanwhile, vanillin conversion and
MMP selectivity gradually recover and are highly correlated
with the reduction extent, as shown in Table S1 (Supporting
Information). After 6 h reduction, the sample are mainly com-
posed of metallic copper and displays 99.0% conversion and
90.7% selectivity, which are similar with the 15 wt%-Cu/AC-600
catalyst (99.9% conversion and 93.2% selectivity). Therefore,
we deduce that the active sites of the 15 wt%-Cu/AC-600 cata-
lyst are metallic Cu in HDO of vanillin. In view of the catalytic
HDO performances (reaction conditions, conversion, selectivity,
and TOF), the 15 wt%-Cu/AC-600 catalyst can be comparable
with most reported high-performance HDO catalysts, including
noble metal-based catalysts (Table S2, Supporting Information).
2.2. Aqueous-Phase HDO of Vanillin
A series of catalytic and characterization tests were conducted
to experimentally investigate the influence of key parameters
on activity of supported Cu catalysts, including carbothermal
temperature, Cu loading amount, as well as some reaction
variables.
Table 1. The catalytic performance in HDO of vanillin.
Catalysta)
Mass [g]
Conversion [%]
Selectivity [%]
MMP
HMP
1
2
3
4
15 wt%-Cu/AC-600
0.03
–
99.9
93.2
6.8
–
–
AC
–
–
–
–
–
–
2.2.1. Effect of Synthesis Parameters on Activity in HDO of Vanillin
0.03
0.03
–
15 wt%-Cu/AC-air-200
–
Firstly, we prepared a series of 15 wt%-Cu/AC samples,
which are derived from different carbothermal temperature
(400–700 °C). In these samples, the actual Cu contents are
a)Reaction conditions: vanillin (0.5 mmol), water (10 mL), P(H2) = 2.0 MPa.
Reaction temperature, 120 °C; reaction time, 5 h.
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basically same (14.4–14.8 wt% by inductively coupled plasma
(ICP) analysis, Table S3 (Supporting Information)), and are
consistent with the addition of precursors, suggesting the car-
bothermal temperature would not affect the Cu content. Con-
sequently, we conducted the catalytic performance of these
samples in aqueous-phase catalytic HDO of vanillin to MMP
under a mild condition of 120 °C, 2.0 MPa H2 within 5 h.
Figure 2 shows the correlations between carbothermal temper-
ature and catalytic performance for 15 wt%-Cu/AC catalysts.
As shown in Figure 2a, vanillin conversion raises from 29.4%
to 93.2% with the carbothermal temperature of 15 wt%-Cu/
AC catalyst increasing from 400 to 500 °C. And then near-
quantitative vanillin conversion and 93.2% MMP selectivity
are achieved when the carbothermal temperature increased
to 600 °C. Meanwhile, as shown in Figure 2b, the copper
phases are mainly composed of copper oxide at low carboth-
ermal temperature of 400 °C, in which the diffraction peaks at
35.5° and 38.7° can be attributed to (002) and (111) planes of
CuO (JCPDS 00-005-0661), and the peaks at 29.6°, 36.4°, 61.4°,
73.6°, 77.4° can be indexed to (110), (111), (220), (311), (222)
planes of Cu2O (JCPDS 01-078-2076). It could be seen clearly
that the intensity of copper oxide phases gradually decreases
with the carbothermal temperature increasing from 400 to
600 °C, and meanwhile the metallic copper becomes the main
phase. This is mainly due to the reduction of copper precursor
by AC followed as CuO→Cu2O→Cu, which is strongly associ-
ated with temperature in carbothermal process. Meanwhile, the
reacted AC is converted to carbon monoxide (CO) and some-
times carbon dioxide (CO2) to form cavity on the surface of
AC. Therefore, the values of SBET increases from 769 m2 g−1 (at
400 °C) to 840 m2 g−1 (at 700 °C) due to the formation of more
cavity on the surface of support by the stronger interaction
between AC and Cu precursor with carbothermal temperature
increase (Table S3 and Figure S2, Supporting Information).
However, the activity of 15 wt%-Cu/AC catalyst is not directly
proportional to the surface area because too high carboth-
ermal temperature would induce NPs agglomeration that could
be proved by TEM analysis. Hence, we further detected the
morphologies and metal dispersions of 15 wt%-Cu/AC cata-
lysts obtained at different temperatures (400, 500, 700 °C). As
shown in Figures 1c and 2c, it can be seen clearly that the NPs
are well dispersed on the AC substrate when the carbothermal
temperature in the range of 400–600 °C, and the sizes of NPs
are about 18.3 2.7 nm at 400 °C, 27.8 3.9 nm at 500 °C,
Figure 2. The structure–activity relationship under different carbothermal temperature. a) Catalytic activity in HDO of vanillin and b) XRD patterns of
15 wt%-Cu/AC catalysts obtained under 400, 500, 600, and 700 °C, c) TEM image of 15 wt%-Cu/AC catalysts (inset is the corresponding size distribu-
tion plot of Cu NPs) and their corresponding HRTEM at 400, 500, and 700 °C, respectively.
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Figure 3. a) The catalytic performance of Cu/AC-600 catalyst with different loading amount of Cu. (Reaction conditions: 0.5 mmol vanillin, 10 mL
water, 30 mg catalyst, 2.0 MPa H2 pressure, 120 °C reaction temperature, 5 h reaction time.) b) XRD diffraction patterns of Cu/AC-600 catalysts with
different Cu contents calcined at 600 °C in N2 for 2 h.
and 31.2 3.2 nm at 600 °C. These NPs are proved again as
copper oxide (CuO and/or Cu2O) at low carbothermal tem-
perature of 400 and 500 °C, and metallic Cu NPs are obtained
at carbothermal temperature of 600 °C, which were further
examined by HRTEM images. With the carbothermal tem-
perature increasing to 700 °C, although the NPs are displayed
in the form of metallic Cu particles, a serious agglomeration
of NPs occurs on the surface of support, which would greatly
reduce the activity in HDO of vanillin. Combining the results
of Figure 1, Table 1, and Figure 2, therefore, we deduce the
metallic Cu is the active sites in HDO of vanillin, which is con-
sistent with previous reports.[28,33,36]
In addition of carbothermal temperature, the Cu loading
amount also has a great influence on the catalytic activity
of Cu/AC-600 catalyst. Therefore, we prepared series of
Cu/AC-600 catalyst with different Cu loading amount, and
tested their catalytic activity in aqueous-phase HDO of vanillin
under a mild condition of 120 °C, 2.0 MPa H2 and 5 h. As shown
in Figure 3a, the reaction of vanillin HDO cannot occur in the
absence of metallic Cu. Then, vanillin conversion increases to
49.1% by using 5 wt%-Cu/AC-600 catalyst, suggesting metallic
Cu is the essential element for transforming vanillin. The
activity almost doubles as Cu loading amount increasing from
5 wt% to 10 wt%, indicating the metallic Cu NPs is participated
effectively in HDO reaction. And then, full vanillin conversion
is obtained when Cu loading amount is 15 wt%, which also
gives highest MMP selectivity (93.2%). The XRD patterns and
TEM images of Cu/AC-600 catalysts with different Cu loading
have been displayed in Figure 3b and Figure S3 (Supporting
Information). The XRD pattern of metallic Cu shows higher
and sharper intensity with the increase of Cu loading due to the
formation of more metallic Cu (Figure 3b), and the size of Cu
NPs is not obviously affected by Cu loading except the 20 wt%
system (Figure S3a–c, Supporting Information). These results
further indicate clearly the metallic Cu can greatly enhance
the activity and selectivity of catalytic HDO of vanillin. How-
ever, the catalytic activity of Cu/AC catalyst is reduced when the
Cu loading increasing from 15 wt% to 20 wt% probably due
to the agglomeration of metallic Cu at high loading amount
(Figure S3d, Supporting Information). In view of these results,
15 wt% loading amount of Cu in the Cu/AC catalyst can give an
optimal catalytic efficiency in aqueous-phase HDO of vanillin
to MMP.
2.2.2. Optimization of Catalytic System and Reaction
Pathway in HDO of Vanillin
The influence of the reaction temperature, time, and H2
pressure were investigated to put forward the possible reac-
tion pathway of vanillin over the 15 wt%-Cu/AC-600 catalyst,
and the corresponding results were presented in Figure 4
and Figure S4 (Supporting Information). First, the reaction
behavior of vanillin HDO varying with reaction temperature
over 15 wt%-Cu/AC-600 catalyst was depicted in Figure 4a and
Figure S4a (Supporting Information). Vanillin conversion is
enhanced evidently from 24.6% to 97.6% as reaction temper-
ature increasing from 70 to 90 °C and further elevates up to
Figure 4. Effect of reaction conditions on the HDO of vanillin over 15 wt%-Cu/AC-600 catalyst (0.5 mmol vanillin, 10 mL water, 30 mg catalyst).
a) Effect of reaction temperature at 2.0 MPa H2 pressure for 5 h. b) Effect of H2 pressure at 120 °C for 3 h. c) Product distributions as functions of
time at 120 °C and 2.0 MPa H2 pressure.
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
99.9% at 120 °C. Furthermore, the reaction temperature has a
great influence on product distribution. At the reaction temper-
ature lower than 100 °C, vanillin is mainly converted into HMP
C O bond in HMP will rupture to further generate MMP.
From these results, we can also draw a conclusion that the reac-


tion rate of C O bond cleavage is lower than the rate of C O
group hydrogenation.

by the hydrogenation of C O group of vanillin with low MMP
selectivity. When the temperature increased from 70 to 120 °C,
MMP selectivity upgrades from 9.7% to 93.2%, and then gradu-
ally approaches up to 99.5% as temperature further elevated to
We also investigated the dependence of chemical states of Cu
species and carbothermal temperature in the 15 wt%-Cu/AC
catalysts by X-ray photoelectron spectroscopy (XPS) analysis to
verify the active sites in HDO of vanillin (Figure 5). The higher
BE peak at ≈935 eV is assigned to Cu(II) in the spinel, accom-
panied by the characteristic Cu(II) shakeup satellite peaks
(938–945 eV) (Figure 5a). The lower BE peak at ≈932 eV sug-
gests the presence of Cu(I) or Cu(0) species.[29] The Cu species
are mainly composed of Cu(II) (about 60.7% content) when the
15 wt%-Cu/AC sample was obtained at 400 °C. At high tem-
perature, the reduction of AC is beneficial to the formation of
low valence copper. At carbothermal temperature of 600 °C, the
15 wt%-Cu/AC is mainly composed of Cu(0) species, a small
fraction of copper oxide appears, which is due to the oxida-
tion on the surfaces of Cu (Figure 5b). Although the sample
obtained at 700 °C is also mainly composed of Cu(0) species
(Figure 5c), its lower activity in HDO of vanillin is attributed
to serious agglomeration of NPs (Figure 2c). From the catalytic
testing result (Figure 2a), we can deduce the metallic Cu is the
active sites in Cu/AC catalyst. Interestingly, almost no changes
were observed when comparing XPS spectrum of the as-syn-
thesized and reused catalysts (Figure 5b,d), indicating excellent
stability.
Generally, the transformation of a carbonyl group into
a methyl group can proceed via three pathways: (1) direct
hydrogenolysis of C O bond, (2) hydrogenation of C O
bond and then dehydration, and (3) hydrogenation of C O
bond and then hydrogenolysis of C O.
pathway, direct hydrogenolysis of C O bond would not gen-
erate HMP. However, this product was detected in our cases,
especially displaying high selectivity at the initial period of
HDO of vanillin, as can be seen in Figure 4a,c. Therefore, the
first pathway can be excluded. The second and third pathway
both would produce the intermediate HMP by hydrogenation

150 °C because the C O bond is activated as the temperature

increases. As a result the hydrogenolysis of C O is enhanced to
generate the finally product of MMP.[22] On these basis, a plot of
ln(CVA/CVA,0) versus reaction time is depicted at different tem-
peratures (Figure S5, Supporting Information). It is found that
HDO of vanillin follows pseudo-first order kinetics. The values
of k at various temperatures were calculated from the slope
of the linear part of each plot in Figure S5a of the Supporting
Information to determine the activation energy (Ea). Figure S5b
of the Supporting Information shows the linear fitting of lnk
and 1/T. The apparent Ea could be calculated from the Arrhe-
nius equation: lnk = lnA – Ea/RT, where lnA is the intercept of
the line and R is the gas constant. Consequently, the calculated
Ea value is ≈45.7 1.9 kJ mol−1, indicating the 15 wt%-Cu/
AC-600 catalyst has high activity in the HDO of vanillin.
Besides reaction temperature, the participation amounts of H2
would also influence the catalytic activity in HDO of vanillin.
The effect of H2 pressure was investigated by varying in the
range of 0.5–4.0 MPa (Figure 4b; Figure S4b, Supporting Infor-
mation). Vanillin conversion is 39.8% at 0.5 MPa H2 pressure,
and then it reachs to 76.7% and 94.1% when the H2 pressure
increased to 1.0 and 2.0 MPa, respectively. Complete vanillin
conversion is obtained when the pressure further increased
to 4.0 MPa. Furthermore, MMP selectivity is also adjusted by
the H2 pressure especially in the range of 0.5–2.0 MPa. The
upgraded activity of 15 wt%-Cu/AC-600 catalyst could be attrib-
uted to improvement of the dissolved H2 with H2 pressure
increase. Considering catalytic efficiency, economy and energy
consumption, the H2 pressure at the favorable temperature
120 °C is 2.0 MPa for aqueous-phase HDO of vanillin.



[12,13,19]

For the first

To further prove the reaction pathway, the distribution of
products as a function of reaction time were tracked and ana-
lyzed over the 15 wt%-Cu/AC-600 catalyst in aqueous-phase
HDO of vanillin. Before studying the effect of reaction time,
the impact of heating stage on reaction results had been elimi-
nated as shown in Table S4 (Supporting Information), which
shows vanillin conversion is lower than 2.5% in the end of
heating indicating the reaction hardly takes place in the heating
stage and would not affect the catalytic results. As can be
seen in Figure 4c and Figure S4c (Supporting Information),
the reaction is accompanied by a rapid increase in vanillin
conversion with reaction time, and almost complete conver-
sion can be obtained after 3 h reaction. In initial period, the
reactant vanillin is mainly converted to HMP by hydrogena-

of C O bond. When analysis the chemical structure formula
of HMP, it can deduce that the dehydration will not take place
because the adjacent carbon of C-OH group has no H atom
in the molecular, indicating the HDO of vanillin is unlikely
to pass through the second way.[19] Therefore, we conject that
vanillin is first transformed into HMP by the hydrogenation
of branched C O group on the active sites of Cu(0) species,
and then the generated C O bond will break by the hydrog-
enolysis of C O to generate the desired product of MMP,
and the deduction lines up with the catalytic results. As such,
the metallic Cu is the active site in HDO of vanillin and
gives high selectivity to MMP. The adsorption of vanillin on
Cu(111) gives a clear evidence that high MMP selectivity can
be achieved by the as-synthesized 15 wt%-Cu/AC-600 cata-
lyst (Figure 6), and the corresponding coordinates of relaxed
geometries had been listed in the Supporting Information.
Vanillin contains three O atoms, one in the carbonyl and the
other two are located in methoxyl and phenol hydroxyl. The
adsorption energy and distance between the O atoms and
Cu(111) can reflect the adsorption properties of functional
groups on Cu(111) surface. Based on density function theory




tion of branched carbonyl group (C O). And HMP selectivity
gradually decreases, meanwhile the selectivity of target product
MMP increases obviously with reaction progressing. The result
is consistent with the reaction data in reaction temperature
(Figure 4a), further indicating HMP is the intermediate to pro-

duce MMP. Therefore, the branched C O group of vanillin is
initially adsorbed and activated on the surface of metallic Cu
and vanillin is converted to HMP quickly. The new formed
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Figure 5. XPS spectrums of Cu/AC (15 wt%) catalysts. a) Cu/AC-400, b) Cu/AC-600, c) Cu/AC-700, and d) Cu/AC-600-reused.
(DFT) calculations, the carbonyl group (Figure 6a) gives the
lowest adsorption energy (−39.6 2.2 kJ mol−1) and shortest
distance between Cu(111) and O atom when compared with
methoxyl (Figure 6b) and phenol hydroxyl groups (Figure 6c).
Therefore, the 15 wt%-Cu/AC-600 catalyst can selectively
adsorb carbonyl group on active sites resulting in activation
and hydrogenation of carbonyl group. Consequently, vanillin
is highly converted to MMP.
Entry 1), indicating water cannot use as a hydrogen donor at
this condition.[38] When, we added a bit of 2-propanol into the
water (Vwater:V2-propanol = 9:1), 3.5% vanillin can transform into
MMP (Table 2, Entry 2), and the efficiency increases to 26.1%
when the proportion of water and 2-propanol was 1:1 (Table 2,
Entry 3). And near-quantitative vanillin conversion and 99.1%
MMP selectivity can be obtained when the solvent water was
replaced by 2-propanol (Table 2, Entry 4). These results dem-
onstrates that the protic solvent of 2-propanol can replace
molecular H2 to provide active H, which can be used as sol-
vent and hydrogen donor, simultaneously. In addition, similar
to the HDO reaction, the THR reaction also do not proceed
without catalyst (Table S5, Entry 1, Supporting Information)
or active metal (Table S5, Entry 2, Supporting Information).
Notably, even the use of 15 wt%Cu/AC-air-200, which is mainly
composed of copper oxide, also displays no activity in THR of
vanillin (Table S5, Entry 3, Supporting Information) under the
identical reaction condition (Table S5, Supporting Information).
2.3. Organic-Phase THR of Vanillin over Cu/AC
2.3.1. Hydrogen Donor in THR of Vanillin
We had demonstrated that the 15 wt%-Cu/AC-600 catalyst has
high activity in aqueous-phase HDO of vanillin at 70–150 °C.
However, even though the temperature increased to 180 °C,
almost no activity is observed without using H2 (Table 2,
Figure 6. DFT Optimized geometries of oxygen functional groups in vanillin for adsorption configuration on Cu(111). a) C=O group, b) methoxyl group,
and c) phenol hydroxyl group. Red, brown, and white spheres represent oxygen, carbon, and hydrogen atoms, respectively.
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Table 2. The results of the solvent effect in THR of vanillin.
in the process of vanillin THR to MMP over the 15 wt%-Cu/
AC-600 catalyst.
Entrya)
Solvent
H2O
Conversion [%]
MMP selectivity [%]
1
2
3
4
–
–
2.3.2. Optimization of Catalytic System and Reaction
Pathway on THR of Vanillin
3.5
99.9
99.7
99.1
Vwater:V2-propanol = 9:1
Vwater:V2-propanol = 1:1
2-propanol
26.1
99.8
The influence of reaction temperature on the catalytic THR of
vanillin over the 15 wt%-Cu/AC-600 catalyst was investigated
and the result is shown in Figure 7a. The vanillin THR is
hardly taken place when the reaction temperature lower than
170 °C. When the temperature reached 180 °C, the activity of
THR is suddenly woken up and almost all of vanillin is trans-
formed into MMP under this reaction condition. One of the
most important steps is to generate active hydrogen from protic
solvent by dehydrogenation. For example, the dehydrogenation
of 2-propanol will generate acetone and hydrogen.[41] At low
reaction temperature, it is hard to take place dehydrogenation
of protic solvent to release hydrogen, which will further restrict
vanillin THR. To prove this, we evaluated the catalytic activity
of 15 wt%-Cu/AC-600 catalyst in dehydrogenation of 2-pro-
panol under reaction temperatures of 150–180 °C (Figure S6,
Supporting Information). Only trace amount of acetone was
detected at 150 °C indicating dehydrogenation is hardly taken
place at low reaction temperature, and the dehydrogenation is
greatly enhanced as the temperature elevating to 180 °C. The
result is consistent with Figure 7a. Therefore, it is important
to provide sufficient energy to drive active hydrogen releasing
from protic solvent and it will be the rate controlling step to
THR.
To further investigate the reaction pathway, the distribution
of products as a function of reaction times was tracked over
the 15 wt%-Cu/AC-600 catalyst in THR of vanillin, as shown in
Figure 7b. Interestingly, the converted reactant is almost com-
pletely transformed into MMP in the THR of vanillin under
180 °C in the overall reaction, which is quite different from
HDO of vanillin. MMP selectivity can reach 90.1% at the ini-
tial reaction stage, and then up to 99.1% as the reaction time
prolonging to 5 h. Therefore, the pathway in THR of vanillin
is probably distinguished with the reaction route in HDO of
vanillin. For the possible reaction route, active H is first gener-
ated from dehydrogenation of 2-propanol on the active metallic
Cu, and then it contacts with vanillin on the surface of catalyst
a)Reaction conditions: vanillin, 0.5 mmol; solvent, 10 mL; 15 wt%-Cu/AC-600
catalyst, 30 mg (Cu loading amount was 15 wt%); reaction temperature, 180 °C;
reaction time, 5 h.
Table 3. The results of the THR of vanillin with different alcohols.
Entrya)
Solvent
H2O
Conversion [%]
MMP selectivity [%]
1
2
3
4
5
6
–
–
Methanol
Ethanol
17.3
73.2
88.6
84.1
99.8
74.4
98.5
95.1
93.3
99.1
n-propanol
n-butanol
2-propanol
a)Reaction conditions: vanillin, 0.5 mmol; solvent, 10 mL; 15 wt%-Cu/AC-600
catalyst, 30 mg (Cu loading amount was 15 wt%); reaction temperature, 180 °C;
reaction time, 5 h.
A series of alcohols were also selected as hydrogen donors
to study the effect of solvents in the catalytic THR of vanillin to
MMP. The THR tests were examined within 5 h under 180 °C
reaction temperature, and products are mainly composed of
MMP (Table 3). When using primary alcohols as the solvent and
hydrogen donors, vanillin conversion and MMP selectivity are
proportional to the chain length from the C1 to C4: n-butanol ≈
n-propanol > ethanol > methanol. When using 2-propanol
instead of primary alcohols, vanillin conversion and MMP
selectivity are almost close to 100% indicating the vanillin can
be completely converted into MMP under this circumstance.
Moreover, the condensation reaction between vanillin and
alcohol is also more likely to take place by using primary alco-
hols than that of 2-propanol.[39,40] Therefore, 2-propanol is one
of the optimal candidates as the solvent and hydrogen donors
Figure 7. Effect of reaction temperature and time on the vanillin THR over 15 wt%-Cu/AC-600 catalyst (reaction conditions: 0.5 mmol vanillin, 30 mg
catalyst, 10 mL 2-propanol). a) Effect of reaction temperature (reaction time 5 h). b) Product distributions as functions of time (reaction temperature
180 °C).
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Figure 8. a) Recycling performance for the conversion of vanillin and selectivity to MMP after 5 cycles over the 15 wt%-Cu/AC-600 catalyst. b) A
representative TEM image of the as-synthesized and reused 15 wt%-Cu/AC-600 catalyst after five runs, respectively.
to directly take place hydrogenolysis reaction to form the target
product MMP. These results reveal that the15 wt%-Cu/AC-
600catalyst not only has high catalytic performance in HDO of
vanillin, but also demonstrated excellent activity in THR with
2-propanol as the hydrogen donor for transforming vanillin
into MMP. So far, the studies of carbonyl compounds THR,
like vanillin or furfural, are mostly focused on the noble metal
catalysts. Our study also proved that the Cu-based catalyst has
an outstanding catalytic performance in carbonyl compounds
THR.[38]
of the intermediate HMP, which is formed by hydrogenation
of carbonyl group in vanillin. Near-quantitative vanillin con-
version and 93.2% MMP selectivity are achieved within 5 h
under reaction temperature 120 °C and 2.0 MPa H2 pressure,
which is one of the optimal conditions in identical reaction
based on catalytic and energy efficiency. When we applied the
15 wt%-Cu/AC-600 to THR of vanillin, it also presents superior
catalytic performance, in which 99.8% vanillin conversion and
99.1% MMP selectivity are obtained within 5 h under 180 °C by
using 2-propanol as the solvent and hydrogen donor. And the
cycle test suggests the prepared catalyst has good stability. In
general, the facilely prepared Cu/AC by one-pot carbothermal
method provides an alternative to noble-metal (Pt, Pd, Ru,
and Rh) catalysts in the conversion of vanillin toward MMP in
practical application.
2.3.3. Catalyst Reusability
The reusability of 15 wt%-Cu/AC-600catalyst had also been
investigated in THR of vanillin (Figure 8). The catalyst is quite
stable and the conversion and selectivity do not change for
reusing 5 cycles (Figure 8a). The TEM images of the as-synthe- 4. Experimental Section
sized and reused catalytic reaction show that the morphology of
Chemicals and Materials: All reagents with AR purity (analytical
the15 wt%-Cu/AC-600 catalyst do not change after 5 cycle reac-
tion, and no catalyst loss or agglomeration occurs (Figure 8b).
Furthermore, the excellent stability of 15 wt%-Cu/AC-600 cata-
lyst could also be testified by XRD analysis of as-synthesized
and used catalyst, in which there are almost no changes in the
XRD diffraction peaks (Figure S7, Supporting Information).
Besides, according to ICP analysis, the Cu contents in the as-
synthesized and reused 15 wt%-Cu/AC-600 are 14.5 wt% and
14.3 wt%, respectively, suggesting that no leaching of Cu in
reaction process.
reagent grade) were used as received without further purification. Cupric
nitrate (Cu(NO3)2·3H2O), methanol, anhydrous ethanol, 2-propanol,
and 2-butanol were purchased from the Sinopharm Chemical Reagent.
The n-propanol, n-butanol, ethyl acetate, vanillin, and activated carbon
(AC) were purchased from Aladdin reagent (Shanghai) Co. Ltd.
Deionized water with a resistance larger than 18.2 MΩ used throughout
the experiments.
Preparation of Catalysts: The supported Cu catalyst was synthesized
by carbothermal reduction method, in which Cu precursor was calcined
to copper oxide and then reduced to metallic Cu by AC under a certain
temperature. Typically, 0.57 g Cu(NO3)2·3H2O was dissolved in 1 mL
deionized water. Then 1 g AC was added into the above solution. After
the solution completely impregnated into the AC, the sample was dried
under vacuum at 60 °C for 24 h. The dried sample was then treated
in N2 at 600 °C for 2 h at a heating rate of 5 °C min−1 to obtain the
15 wt%-Cu/AC-600 catalyst. Correspondingly, the catalysts derived
at other carbothermal temperature (400, 500, and 700 °C) were also
prepared and compared with 15 wt%-Cu/AC-600.
3. Conclusion
In summary, we show that Cu/AC catalyst, which was pre-
pared by one-pot carbothermal method, not only has efficient
catalytic performance in aqueous-phase HDO of vanillin, but
also exhibits high activity in organic-phase THR of vanillin. The
15 wt%-Cu/AC-600 catalyst obtained at 600 °C displays uni-
form dispersed metallic Cu NPs which acts as active sites in
the two reaction processes. In aqueous-phase HDO of vanillin,
the desired product MMP is generated through hydrogenolysis
Characterization of the Catalysts: The crystalline structures of the
samples were identified by XRD analysis (Philips X’ pert PRO) using
Ni-filtered monochromatic Cu Kα radiation at 40 kV and 40 mA. The
morphology and structure of the products were characterized using TEM
(JEOL-2010, 200 kV) with an energy dispersive X-ray spectrometer (EDS
Oxford, Link ISIS). The specific surface areas and the pore distributions
of the samples were calculated by nitrogen adsorption (Micrometrics
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ASAP 2020M) at −196 °C using the BET equation. Quantitative
determination of the metal ion content (Cu) was performed by ICP or
inductively coupled plasma mass spectrometry (ICP-MS). XPS analysis
was performed on an ESCALAB 250 X-ray photoelectron spectrometer
(Thermo, USA) equipped with Al Kα1,2 monochromatized radiation at
1486.6 eV X-ray source.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
HDO of Vanillin: The reactions were carried out in a 25 mL stainless
steel autoclave equipped with a magnetic stirrer. Certain amount of
Cu/AC catalyst (30 mg) was introduced into the reactor together with
0.5 mmol of vanillin (reagent) in 10 mL water (solvent). When the reactor
had been pressurized with H2 to a relevant pressure (0.5–4.0 MPa), the
reactor was heated to a setting temperature (70–170 °C) and maintained
at this temperature for a setting reaction time with 600 rpm stirring.
After reaction, the reactor was cooled down quickly. The product mixture
and used catalyst were separated by centrifugation.
Acknowledgements
This work was financially supported by the National Natural Science
Foundation of China (Grant Nos. 51432009, 51502297, and 51372248),
and Instrument Developing Project of the Chinese Academy of Sciences
(Grant No. yz201421).
THR of Vanillin: N2 gas was used to replace H2 gas and the solvent of
water was replaced by some protic solvents. The other procedure of THR
of vanillin was similar with HDO of vanillin.
Conflict of Interest
The authors declare no conflict of interest.
Product Analysis: In HDO reaction, the liquid products were
extracted by ethylacetate (3 mL/time × 3 time) and the organic phase
was collected. In THR reaction, the liquid products were collected by
centrifugation. The samples were identified by gas chromatography-mass
spectrometry (GC-MS, Thermo Fisher Scientific-TXQ Quntum XLS), and
were quantitatively analyzed by GC (Shimadzu, GC-2010 Plus), equipped
with FID and a KB-WAX capillary column (30 m × 0.25 mm × 0.25 µm,
Kromat Corporation, USA) using n-octanol as an internal standard.
Vanillin conversion, MMP selectivity and mass balance (based on
carbon) were calculated according to Equations (1–3)
Keywords
carbothermal, copper, hydrodeoxygenation, transfer-hydrogenation,
vanillin
Received: May 22, 2018
Revised: June 25, 2018
Published online:
CVA,0 − CVA

Coc
CVA,0
AVA
AOC

Conversion % =
× 100% = 1−
× fVA
×
× 100%
(
)



CVA,0

[1] H. H. Khoo, P. N. Sharratt, P. Das, R. K. Balasubramanian,
P. K. Naraharisetti, S. Shaik, Bioresour. Technol. 2011, 102, 5800.
[2] L. Petrus, M. A. Noordermeer, Green Chem. 2006, 8, 861.
[3] T. H. Parsell, B. C. Owen, I. Klein, T. M. Jarrell, C. L. Marcum,
L. J. Haupert, L. M. Amundson, H. I. Kenttamaa, F. Ribeiro,
J. T. Miller, M. M. Abu-Omar, Chem. Sci. 2013, 4, 806.
[4] G. W. Huber, S. Iborra, A. Corma, Chem. Rev. 2006, 106, 4044.
[5] H. Zacher, M. V. Olarte, D. M. Santosa, D. C. Elliott, S. B. Jones,
Green Chem. 2014, 16, 491.
(1)
A
AOC
Ai

MMP 
Coc × fMMP
×
CMMP




MMP selectivity % =
× 100% =
× 100%
× 100% (2)
(
)
Ci
∑
Coc × fi ×




∑
AOC
Ci + CVA
CVA,0
∑
Massbalance =
(3)
[6] J. Yang, C. L. Williams, A. Ramasubramaniam, P. J. Dauenhauer,
Green Chem. 2014, 16, 675.
[7] J. N. Chheda, G. W. Huber, J. A. Dumesic, Angew. Chem., Int. Ed.
2007, 46, 7164.
[8] M. Fache, B. Boutevin, S. Caillol, ACS Sustainable Chem. Eng. 2016,
4, 35.
[9] X. Yang, Y. Liang, X. Zhao, Y. Song, L. Hu, X. Wang, RSC Adv. 2014,
4, 31932.
[10] L Zhu, Y Jiang, J Zheng, N Zhang, C Yu, Y Li, CW Pao, JL Chen,
C Jin, JF Lee, CJ Zhong, B Chen, Small 2015, 11, 4385.
[11] X. Yang, Y. Liang, Y. Cheng, W. Song, X. Wang, Z. Wang,
Catal. Commun. 2014, 47, 28.
[12] M Wan, X Zhang, M Li, B Chen, J Yin, H Jin, L Lin, C Chen,
N Zhang, Small 2017, 13, 1701395.
[13] S. Crossley, J. Faria, M. Shen, D. E. Resasco, Science 2010, 327, 68.
[14] Z. Lv, Q. Sun, X. Meng, F. S. Xiao, J. Mater. Chem. A 2013, 1, 8630.
[15] F. M. Zhang, Y. Jin, Y. H. Fu, Y. J. Zhong, W. D. Zhu, A. A. Ibrahim,
M. S. El-Shall, J. Mater. Chem. A 2015, 3, 17008.
[16] Y. Z. Chen, G. Cai, Y. Wang, Q. Xu, S. H. Yu, H. L. Jiang,
Green Chem. 2016, 18, 1212.
[17] A. K. Singh, S. Jang, J. Y. Kim, S. Sharma, K. C. Basavaraju,
D. P. Kim, ACS Catal. 2015, 5, 6964.
where, CVA,0 is the initial concentration of vanillin, CVA is the
concentration of vanillin in mixed product after reaction, and Coc is the
concentration of n-octanol. AVA and AOC represent the peak areas of
vanillin and n-octanol detected by GC-FID, and the fVA is the correction
factor between vanillin and n-octanol. CMMP is the concentration of MMP
in product and Ci is the concentration of product i (including MMP,
HMP and trace amount other products), AMMP and Ai are attributed to
the peak areas of MMP and product i in GC-FID chromatogram, and fi is
the correction factor between product i and n-octanol. The mass balance
(based on carbon) was checked in every experimental run and detected
to be higher than 98%.
Computational Methods: All the calculations were performed within
the framework of DFT, using the Vienna Ab initio Simulation Package
with Perdew–Burke–Ernzerhof generalized gradient approximation
function. The projector augmented wave method were used to describe
the inert core electrons. The structures were relaxed until the total
energy changes within 1 × 10−4 eV per atom and the Hellmann–Feynman
force on each atomic site was less than 0.05 eV Å−1, with a 300 eV
cutoff energy. Cu(1 1 1) slab model was constructed with three metal
layers and 20 Å vacuum space. The Gamma(Γ)-point Monkhorst–Pack
sampling was used for the Brillouin zone. In all the calculations, the top
two layers of the surfaces were allowed to relax together with adsorbates,
while the bottom one layer was keep fixed to present the bulk properties.
The adsorption energy, Eads, is given by the following equation:
[18] A. Aijaz, Q. L. Zhu, N. Tsumori, T. Akitaa, Q. Xu, Chem. Commun.
2015, 51, 2577.
[19] X. Xu, Y. Li, Y. Gong, P. Zhang, H. Li, Y. Wang, J. Am. Chem. Soc.
2012, 134, 16987.
Eads = Eslab/ads – Emolecule
.
©
Small 2018, 1801953
1801953 (10 of 11)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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www.small-journal.com
[20] S. Verma, R. B. N. Baig, M. N. Nadagoudab, R. S. Varma, Green
Chem. 2016, 18, 1327.
[21] A. A. Ibrahim, A. Lin, F. M. Zhang, K. M. AbouZeid, M. S. El-Shall,
ChemCatChem. 2017, 9, 469.
[22] F. M. Zhang, S. Zheng, Q. Xiao, Y. J. Zhong, W. D. Zhu,
M. S. El-Shall, Green Chem. 2016, 18, 2900.
[23] K. Yan, J. Y. Liao, X. Wu, X. M. Xie, RSC Adv. 2013, 3, 3853.
[24] B. J. ONeill, D. H. K. Jackson, A. J. Crisci, C. A. Farberow, F. Y. Shi,
P. M. Voyles, Angew. Chem. 2013, 125, 14053.
[31] X. Kong, L. Chen, Catal. Commun. 2014, 57, 45.
[32] M. M. Villaverde, N. M. Bertero, T. F. Garetto, A. J. Marchi,
Catal. Today 2013, 213, 87.
[33] B. M. Nagaraja, V. S. Kumar, V. Shasikala, A. H. Padmasri,
B. Sreedhar, B. D. Raju, Catal. Commun. 2003, 4, 287.
[34] S. Srivastava, N. Solanki, P. Mohanty, K. A. Shah, J. K. Parikh,
A. K. Dalai, Catal. Lett. 2015, 145, 816.
[35] J. C. Ma, S. Liu, X. J. Kong, X. P. Fan, X. L. Yan, L. Chen,
Res. Chem. Intermed. 2012, 38, 1341.
[25] R. F. Nie, H. Yang, H. F. Zhang, X. L. Yu, X. H. Lu, D. Zhou,
Q. H. Xia, Green Chem. 2017, 19, 3126.
[36] S. Lomate, A. Sultana, T. Fujitani, Catal. Sci. Technol. 2017, 7,
3073.
[26] G. L. Liu, A. W. Robertson, M. M. J. Li, W. C. H. Kuo, M. T. Darby,
M. H. Muhieddine, Y. C. Lin, K. Suenaga, M. Stamatakis,
J. H. Warner, S. C. E. Tsang, Nat. Chem. 2017, 9, 810.
[27] L. He, Y. Qin, H. Lou, P. Chen, RSC Adv. 2015, 5, 43141.
[28] S. Sitthisa, T. Sooknoi, Y. Ma, P. B. Balbuena, D. E. Resasco,
J. Catal. 2011, 277, 1.
[37] L. Petitjean, R. Gagne, E. S. Beach, D. Xiao, P. T. Anastas, Green
Chem. 2016, 18, 150.
[38] R. F. Nie, X. L. Peng, H. F. Zhang, X. L. Yu, X. H. Lu, D. Zhou,
Catal. Sci. Technol. 2017, 7, 627.
[39] M. J. Taylor, L. J. Durndell, M. A. Isaacs, C. M. A. Parlett, K. Wilson,
A. F. Lee, Appl. Catal., B 2016, 180, 580.
[29] P. Liu, E. J. M. Hensen, J. Am. Chem. Soc. 2013, 135, 14032.
[30] S. Nishimura, Handbook of Heterogeneous Catalytic Hydrogenation
for Organic Synthesis, John Wiley & Sons, Inc, USA 2001.
[40] B. Chen, F. Li, Z. Huang, G. Yuan, Appl. Catal., A 2015, 500,
23.
[41] J. Lee, T. Ryu, S. Park, P. H. Lee, J. Org. Chem. 2012, 77, 4821.
©
1801953 (11 of 11)
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