Cr-free Cu-catalysts for the selective hydrogenation of biomass-derived furfural to 2-methylfuran: The synergistic effect of metal and acid sites

Article abstract of DOI:10.1016/j.molcata.2014.12.001

Our work focuses on exploring Cr-free Cu-catalysts for the highly efficient conversion of biomass-derived furfural to value-added bio-fuel 2-methylfuran. Three supported Cu-catalysts (Cu/SiO₂, Cu/Al₂O₃, and Cu/ZnO) were prepared by the typical precipitation method, and Cu/SiO₂ catalyst exhibited the best catalytic performance with an 89.5% yield to 2-MF. A series of characteristic results indicated that the high yield of 2-methylfuran on Cu/SiO₂ catalyst was assigned to synergistic effect of metal and the weak acid sites. Among them, Cu/ZnO catalyst exhibited maximum furfuryl alcohol selectivity because of the large Cu particles, while Cu/Al₂O₃ catalyst had low 2-methylfuran selectivity due to the insufficient weak acid sites. For Cu/SiO₂ catalyst, the highly dispersed Cu particles and the strong metal-support interaction are propitious to its superior catalytic activity. Therefore, copper species are composed on different supports as a result of the different interaction of metal-support to affect their catalytic activity, while products selectivity is related to the acidic property of catalyst. In addition, temperature programmed desorption of furfural indicated that the adsorption-desorption properties of catalyst surface species would influence the rate of furfural hydrogenation.

Full text of DOI:10.1016/j.molcata.2014.12.001

Accepted Manuscript
Title: Cr-free Cu-catalysts for the selective hydrogenation of
biomass-derived furfural to 2-methylfuran: The synergistic
effect of metal and acid sites
Author: Fang Dong Yulei Zhu Hongyan Zheng Yifeng Zhu
Xianqing Li Yongwang Li
PII:
S1381-1169(14)00539-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.12.001
MOLCAA 9363
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
11-10-2014
20-11-2014
3-12-2014
Please cite this article as: Fang Dong, Yulei Zhu, Hongyan Zheng, Yifeng Zhu, Xianqing
Li, Yongwang Li, Cr-free Cu-catalysts for the selective hydrogenation of biomass-
derived furfural to 2-methylfuran: The synergistic effect of metal and acid sites, Journal
of Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2014.12.001
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

1
2
Cr-free Cu-catalysts for the selective hydrogenation of
biomass-derived furfural to 2-methylfuran: the synergistic
effect of metal and acid sites
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
a,b,c
a,c,*
c
a,b
c
a,c
Fang Dong , Yulei Zhu , Hongyan Zheng , Yifeng Zhu , Xianqing Li , Yongwang Li
a
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of
Sciences, Taiyuan 030001, PR China
b
c
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
Graduate University of Chinese Academy of Sciences, Beijing 100039, PR China
Synfuels China Co. Ltd., Taiyuan 030032, PR China
2
2
2
2
5
6
7
8
Corresponding author: State Key Laboratory of Coal Conversion, Institute of Coal Chemistry,
Chinese Academy of Sciences, Taiyuan 030001, PR China. Tel.: +86 351 7117097; fax: +86 351
7560668.
E-mail address: zhuyulei@sxicc.ac.cn (Y. Zhu).
1

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
Abstract
Our work focuses on exploring Cr-free Cu-catalysts for the highly efficient conversion of
biomass-derived furfural to value-added bio-fuel 2-methylfuran. Three supported Cu-catalysts
(Cu/SiO , Cu/Al , and Cu/ZnO) were prepared by the typical precipitation method, and Cu/SiO
catalyst exhibited the best catalytic performance with an 89.5 % yield to 2-MF. A series of
characteristic results indicated that the high yield of 2-methylfuran on Cu/SiO catalyst was
assigned to synergistic effect of metal and the weak acid sites. Among them, Cu/ZnO catalyst
2
2
O
3
2
2
exhibited maximum furfuryl alcohol selectivity because of the large Cu particles, while Cu/Al
2
O
3
2
catalyst had low 2-methylfuran selectivity due to the insufficient weak acid sites. For Cu/SiO
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
catalyst, the highly dispersed Cu particles and the strong metal-support interaction are propitious
to its superior catalytic activity. Therefore, copper species are composed on different supports as a
result of the different interaction of metal-support to affect their catalytic activity, while products
selectivity is related to the acidic property of catalyst. In addition, temperature programmed
desorption of furfural indicated that the adsorption-desorption properties of catalyst surface
species would influence the rate of furfural hydrogenation.
Keywords: furfural; catalytic hydrogenation; 2-methylfuran; Cu-catalysts; support effects
2

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
1. Introduction
With the fossil resources reducing, the development and use of biomass resource, as well as
biomass derives has been more and more pressing [1-4]. And Grilc et. al [5,6] have also reported
that petroleum refining-based catalysts employing mono-(Ni, Co and Mo) and bi-functional
catalysts have been proved as being rather efficient and cost effective for hydrogenation and
deoxygenation of biomass and biomass-derived compounds. Furfural (FAL) is treated as one of
the important platform molecules in biomass conversion, and its source is very wide, inexpensive,
and environmental. FAL is massively produced from carbohydrate biomass obtained from
agricultural wastes such as corncobs, wheat-straw, and bagasse, which carry through the catalytic
dehydration process [7]. FAL could be converted into all kinds of containing-oxide chemicals such
as furfuryl alcohol (FOL), 2-methylfuran (2-MF), 2-methyltetrahydrofuran, and tetrahydrofurfuryl
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
alcohol
[8-10].
Among
these
chemicals,
value-added
bio-fuel
2-MF
by
hydrogenation-deoxygenation process of FAL generated a great interest because of good fuel
performance of 2-MF [11]. Unlike hydrocarbons, 2-MF contains the oxygen atom with the better
combustion performance and the higher energy density. Especially, research octane number
(RON=103) of 2-MF is higher than that of gasoline (RON=96.8), and it would be regarding as
gasoline alternative to increase the performance on anti-explosion [12,13]. Conventional process
for the production of 2-MF relies on the petroleum resources and requires the catalytic oxidation,
an example being the oxidation of 1,3-pentadiene from the fossil energy. From the viewpoint of
green sustainable chemistry, the production of 2-MF from biomass-derived chemicals is highly
desirable. Therefore, the conversion of FAL to 2-MF could not only relieve the fossil energy crisis,
but utilize effectively a large number of surplus biomass resources. However, it is a challenging
job for catalytic researchers to develop an environmentally friendly catalyst for the highly efficient
conversion of FAL to 2-MF.
2
2
2
2
2
3
3
3
5
6
7
8
9
0
1
2
Cu-based catalysts have been reported as the most promising candidate for the conversion of
FAL to 2-MF [14]. Industrial production of 2-MF is performed on Cu-Cr catalysts for decades.
However, the heavy environmental pollution and energy crisis limited the wide use of Cu-Cr
catalysts, and the high toxicity has enforced the researchers to develop the high active Cr-free
catalysts [15-17]. Moreover, the sustainability of this platform also requires the invention of novel
and efficient catalysts for achieving the high yield of 2-MF, so the development of catalysts is very
significant. Although many studies that have been reported employed Cu/MgO [18], Cu/C [19],
and Ni-Fe [20] as catalysts in FAL hydrogenation reaction, the yield of 2-MF was still low. Yan et
3

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
al. [21] also studied the Cu-Cr catalyst for the hydrogenation of FAL and levulinic acid to FOL
+
0
and ɤ-valerolactone, respectively. R. Rao et al. [22] reported that the Cu and Cu sites of Cu-Cr
catalyst surface were responsible for the maximum activity in the catalytic process, which
produced as
a
function of reduction temperature. In addition, some common
hydrogenation-deoxygenation catalysts include precious metal, such as Ru [23], Rh [24], Pd [25],
and Re [26], which have low selectivity due to some undesirable side reactions involving C-C
bond cleavage and the high cost of catalysts. Therefore, most of catalysts are unsuitable for the
industrial application owing to some defects, such as serious environmental pollution, the low
selectivity, the high cost, and severe deactivation.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
Our previous works [27] have suggested a reaction pathway carried out scheme.1 for the
formation of FAL hydrogenation on Cu-catalysts. It is well-known that hydrogenation of FAL to
2-MF included hydrogenation of FAL to FOL, and followed by subsequent
hydrogenolysis-deoxygenation of the intermediate FOL to desired product 2-MF. Most of previous
studies reported that the Cu active sites are answering for the selective hydrogenation of C=O
bond, and relatively inactive for hydrogenolysis of the saturated C-O bond [28,29]. Lewis acid
sites would be beneficial to the breaking of the saturated C-O band [20,30]. Thus, the appropriate
combination of metal components and acidic species in reaction system is indispensable for the
effective formation of 2-MF. Notably, the nature of supports might influence the surface acidity
and basicity of catalysts which plays the vital roles in products distribution. However, little work
has been done to report about support effects on the texture and chemical characteristics of copper
catalysts, as well as their catalytic performance in FAL hydrogenation reaction. Therefore, some
Cr-free, environmental, and low cost supports, such as SiO
industry), are chosen in our work.
The purpose of this work is to investigate some environmentally friendly Cr-free Cu-catalysts
supported on SiO , Al and ZnO surface, with the help of systematical characterizations, to
explain the roles of support on copper dispersion, the interaction of metal-support, surface acidity
and FAL hydrogenation activity. For SiO support, a strong interaction of copper-silicon might
result in a higher copper dispersion, the difficult reduction of copper oxide, and the stronger acidic
property than the other two samples to improve the catalytic performance. In the case of Al and
2
, Al
2
O
3
, and ZnO (easy to be applied in
2
2
O
3
2
2
O
3
ZnO supports, a weak interaction favors the reducibility of copper oxide, but at the same time
4

1
2
3
4
promotes the agglomeration of copper particles leading to a low copper dispersion. Therefore,
Cr-free Cu/SiO
2
catalyst would be treated as a promising candidate applied to the production of
2-MF.
5
2. Experimental
6
7
2.1. Catalyst preparation
Three different catalysts (Cu/SiO
2
, Cu/Al
2
O
3
, Cu/ZnO) were prepared by the precipitation
.3H O mixed
O solution. Then
solution were simultaneously added drop wise to
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
method. In a typical preparation process, the aqueous solutions of Cu(NO
respectively with silica sol (SW-30), Alumina sol (AS-40), and Zn(NO .6H
three mixed aqueous solution and 1M NH HCO
3
)
2
2
3
)
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
4
3
200 mL deionized water under the vigorous stir, and pH value was kept in the range of 6.0-7.0.
The obtained slurry was further aged for 1.0 h, and then the suspension was washed and filtered.
Subsequently, the precipitate was dried at 120 ºC for 24 h in air. After this, the obtained precursors
were calcined under 450 ºC for 5 h with a heating rate of 1 ºC/min in air. Finally, the Cu/M
x
O
y
(M=Si, Al, Zn) precursors were obtained. The reference sample of CuO was prepared by the same
method similar to that reported previously [31].
2.2. Catalyst characterization
N
2
adsorption-desorption isotherms of calcined catalysts were obtained at -196 ºC using an
ASAP 2420 (Micromeritics, Inc). Prior to N adsorption, all samples were degassed under vacuum
2
at 90°C for 1 h and 350°C for 8 h. After degassed, BET surface area and BJH pore size
distribution were calculated according to the desorption branch of the isotherms.
ICP optical emission spectroscopy was performed on Optima2100DV, PerkinEl-mer.
X-ray diffraction (XRD) patterns were collected on a BrukerAxs D8 diffractometer with Cu
Kα radiation (λ=0.154 nm) at 30 kV and 10 mA with a scanning angle (2θ) ranging from 10º to
80º at the scanning rate of 4º/min to determine the crystalline phases.
The microstructural observations and analysis of catalyst surface were performed using a
scanning electron microscope (SEM, FEI Quanta 400F) and an energy dispersive X-ray
spectrometer (EDS). Before the EDS test, the grinded catalyst was pressed into a tablet.
The reducibility of the calcined samples was determined by H
reduction (H -TPR), which performed on Auto Chem. II2920 (Mircromeritics, USA). Before
reduction, 200 mg samples were put into a quartz tube, then it was carried out using a heating rate
2
-temperature programmed
2
3
−1
of 5 °C /min from 40 °C to 500 °C in a 10 vol% H /He mixture at a flow rate of 50 cm .min , and
2
5

1
2
the single was recorded with TCD apparatus. A 2-propanol-liquid nitrogen slurry (−89 °C) cooled
trap was used to cool the water formed during the reduced process.
3
4
5
6
7
8
9
0
N
2
O measurements were conducted in the same equipment as H
for each test. Before analysis, the CuO phase is completely reduced to metal copper with a flow
mixture of 10 vol% H /He. Then, the catalyst is purged under He. Orderly, the oxidation of surface
metal copper to Cu O is carried out by chemisorption of N O (5 vol% N O/He) at 90 ºC. After that,
the catalyst was purged with a He flow gas and cooled to room temperature. Subsequently,
-TPR was again carried out (similar to the former reduction process), in order to reduce the
surface Cu O to metal copper. Copper dispersion (DCu) was calculated by dividing the amount of
chemisorption sites into total supported copper atoms; the copper surface area (SCu) was calculated
2
-TPR using 200 mg samples
2
2
2
2
H
2
2
1
1
9
2
1
1
1
2
by assuming spherical shape of the copper metal particles and 1.47×10 copper atoms/m .
X-ray photoelectron spectroscopy (XPS) studies were performed with a Physical Electronics
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
PHI 5700 spectrometer equipped with a Mg Kα (1253.6 eV) X-ray source. Before XPS analysis,
200 mg samples were reduced in pure H
Temperature programmed desorption of NH
instrument as H -TPR. Prior to the adsorption of NH
gas at 400 ºC to clean surface impurities from moisture and other adsorbed gases. After cooling to
100 ºC, the catalyst was saturated with pure NH and then purged with He gas to remove the
physisorbed NH . Subsequently, the sample was heated to 800 ºC at a heating rate of 10 ºC/min
and the NH desorption (m/z=16) was detected by MS (Agilent).
Temperature programmed desorption of H (H -TPD) over three supported Cu-catalysts was
performed on the same instrument with H -TPR. Prior to H absorption, 200 mg samples were put
into the quartz tube reactor, and reduced in pure H (50 mL/min) gas flow at 270 ºC for 2 h.
2
at 270 °C, using a flow rate of 50 mL/min about 2 h.
(NH -TPD) was performed on the same
, 200 mg samples were pretreated with He
3
3
2
3
3
3
3
2
2
2
2
2
Subsequently, the sample was purged at 270 ºC with He (50 mL/min), then the sample was cooled
to 30 ºC with He gas flow. After this, the sample was heated to 800 ºC at 10 ºC/min with a He gas,
and the H desorption (m/z=2) was detected by a MS (Agilent).
2
Temperature programmed desorption of furfural (FAL-TPD) was performed in a self-made
reactor connected to an online mass spectrometer (OmniStar TM). Before desorption 200 mg
calcined catalysts were reduced by pure H
2
at 270 °C for 2 h, and then purged with He at the same
. Thereafter,
temperature and cooled to 40 °C overnight in order to diminish the effect of H
2
reduced catalysts were performed in FAL/He flow at 40 ◦C for 2 h, in order to absorb sufficient
furfural. After the absorption, samples were purged with He for removing the physical adsorbed
6

1
2
3
FAL at 40 °C until the baseline was stable. Finally, the FAL-TPD experiment was performed with
a heating rate of 10 °C/min in a flow of He stream from 40 °C to 800 ºC, and the desorbing
products were detected with an online MS (Agilent).
4
5
2.3. Catalytic test and analysis method
FAL hydrogenation was carried out in a fixed-bed reactor (12 mm of inner diameter, length of
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
600 mm). First of all, all the samples were completely reduced in situ at atmospheric pressure with
a 5 vol. % H
pumped to a preheater by HPLC pump, and the preheater was maintained at 140 °C to prevent
condensation of vaporized FAL. At the same time, H was introduced into the top of preheater
2
/N gas mixture at 270 °C. After reduction, the distilled FAL was continuously
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
through mass flow controller. Thereafter, FAL vaporizer mixed with pure hydrogen in the
preheater and then introduced into the fixed-bed reactor. Typical reaction conditions for FAL
conversion were as follows: 140-220°C, atmospheric pressure and weight hourly space velocity
−
1
(WHSV) = 0.5, 2.0 h . The reaction products were condensed and collected in a gas-liquid
separator, which were analyzed by the chromatography until all conditions of the reaction system
was stable. The liquid products were analyzed by an off-line gas-chromatography (GC6890,
Agilent, USA) using a FID detector and polyethandiol capillary column (AB-inowax, 30 m×0.32
mm), and the gas products were analyzed by an on-line GC 6890 (Aligent, USA) equipped with a
FID detector and polyethandiol capillary column (AB-inowax, 30 m×0.32 mm). Part of products
need to be identified by a GC-MS (6890N, Agilent, USA). The carbon balance was typically better
than 96% and the error associated with the quantification for furfural was found to be about ±3%.
The conversion, selectivity and carbon balance were calculated on basis of the following
equations:
Mole of furfural converted (mol)
2
2
2
3
4
5
Conversion(%) 
Selectivity (%) 
Carbon balance(%) 
 100
Mole of furfural fed(mol)
Mole of the product produced (mol)
Mole of furfural converted (mol)
 100
Mole of the overallcarbon fed (mol)
Mole of the overall carbon outflowed (mol)
100
2
2
2
6
7
8
TOF was calculated to investigate the intrinsic catalytic activity, which was defined as the
number of molecules of a specified product made per catalytic site and per unit time. In this paper
TOF was calculated in a low activity.
2
3
9
0
3. Results and discussion
3.1. Textural Properties of the Catalysts
7

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
The physicochemical properties of the calcined catalysts are presented in Table 1, and an
obvious distinction of BET surface area (SBET) was observed over three supported Cu-catalysts.
2
-1
Especially, Cu/SiO catalyst exhibited the largest BET surface area (161.4 m .g ). The decline of
2
2
-1
3
-1
BET surface area (from 161.4 to 14.9 m .g ) and pore volume (from 0.430 to 0.134 cm .g ) might
be attributed to the nature of support substrates [32]. Copper dispersion (DCu) is the vital parameter,
which greatly influences the physicochemical properties and the catalytic performance of catalyst
[33]. As shown in Table 1, copper dispersion from N
sequence of Cu/SiO > Cu/Al > Cu/ZnO. In addition, N
shown in Fig. 1S. Cu/SiO and Cu/Al samples exhibited isotherms with the typical hysteresis
2
O chemisorption (Table 1) followed the
2
2
O
3
2
adsorption-desorption isotherms are
2
2
O
3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
loops of mesoporous materials. Adsorption for Cu/ZnO sample shifted toward higher values,
indicating the presence of larger pores.
The XRD patterns of three Cu-catalysts obtained after calcination at 450 ºC are shown in
Fig. 1. The peaks at around 35.5ºand 38.9º (JCPDS 05-0661) are attributed to the collective
contribution of crystalline CuO, and the distinction of XRD patterns on these supported
Cu-catalysts may be linked to the existence of different copper species and the size of copper
crystalline [29]. Based on the Scherrer equation, the copper crystallite size of three supported
Cu-catalysts was respectively 8.5, 11.4 and 14.5 nm according to the full width at half maximum
of Cu (111) diffraction at 2θ of 38.7º. Evidently, Cu/SiO catalyst showed the smallest crystalline
2
size.
The SEM and face scanning energy dispersive spectrum (face scanning EDS) images of three
supported Cu-catalysts are exhibited in Fig. 2S. The purpose of energy dispersive X-ray
spectrometry (EDS) investigation is to characterize the homogeneity and determine the copper
concentration of catalyst surface. The contents of element are listed in Table 1S. Based on the
results of face scanning EDS, there were some aggregated and highly dispersed fields, suggesting
the existence of big copper particles and small copper particles. Overall, copper particle was more
uniform on Cu/SiO catalyst than the other two samples. The total copper contents, as determined
2
by EDS, are consistent with ICP-AES in Table 1.
3.2 Reduction properties and Chemical states of catalysts
3.2.1 Reduction properties of catalysts
3
3
1
2
H
2
-TPR was used to determine the reducibility of these supported Cu-catalysts, and Fig. 2
3
3
3
4
displays H -TPR profiles of the calcined samples. Generally, when copper species interacted with
2
supports by forming new surface compounds or changing the chemical states of copper, their
8

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
reduction temperature would change [33,34]. Therefore, the interactions of copper components
with supports had significant influence on the chemical environment of copper, and a weak
interaction would be easy to reduce copper oxide to metal copper [35]. On the contrary, when a
strong interaction between copper species and supports occurred, CuO particles would be
difficultly reduced, and this reduced process might turn up low valence copper such as
+
uncompleted reduced Cu . The difference of H
2
-TPR cannot be solely explained in terms of
copper dispersion, also including the CuO crystallinity size and the interaction of copper-support
[32]. Among three factors mentioned in front, the interaction between metal and support may play
a key role in determining the reduction temperature in our system. Firstly, the reduction
temperature of three samples was higher than that of pure CuO (Fig. 2). In addition, the
asymmetric reduction peak of samples indicated that there were at least two different Cu species,
which might be attributed to two closely overlapping peaks of dissimilar intensities [33], reflecting
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
2
+
+
+
0
reduction in two steps (Cu → Cu at low temperature, Cu → Cu at high temperature). The
difference of the reduction temperature illustrated that SiO (228 ºC) support had the stronger
interaction with copper species than Al (217 ºC) and ZnO (202 ºC) supports. Obviously, the
variation of H -TPR peak sites states the strength of interaction, indicating that supports have
2
2
O
3
2
great influence on the reduction of copper oxide.
For three supported Cu-catalysts, the interaction is strongest when copper oxide was
2
+
0
dispersed on SiO
and resulted in the smaller copper oxide particles or the better copper oxide dispersion on SiO
support surface. The result of H -TPR is in agreement with XRD result.
3.2.2 The surface chemical states of catalysts
2
support. The reduction process (Cu → Cu ) occurred more difficult and slower,
2
2
The chemical states of copper species were determined by XPS analysis, and the spectrum of
both the calcined catalysts and the reduced catalysts is recorded in Fig. 3. The calcined samples
(Fig. 3A) displayed the main peak (Cu 2p3/2) above 933.8 ± 0.2 eV, which was attributed to the
copper oxidation state as +2 [36]. Similarly, the spectrum of the reduced samples showed a
significant shift of the main peak (Cu 2p3/2) towards the lower binding energies at 932.6 eV, which
2
+
were because of the reduction of surface Cu to the lower valence states [37] (Fig. 3B).
2
+
Meanwhile, the absence of satellite peaks at 944-945 eV (2p-3d) related to Cu were observed at
2
+
all of the reduced samples, suggesting that the Cu species (mainly from copper oxide) were
+
0
reduced completely. The reduced samples are probably inferred to have two species Cu and Cu
+
0
at 932.6 eV, which is impossible to make a distinction between Cu and Cu on the basis of
binding energy analysis alone. Following, we carried out the examination of the modified Auger
spectra (XAES). The broad and asymmetric peak shape of the Cu LMM XAES spectra (Fig. 3C)
9

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
indicated that the reduced samples could have one more chemical states of copper. The
asymmetric peaks were fitted with two symmetrical peaks: α and β, which centered at around
+
0
916.1 eV and 919.2 eV, corresponding to Cu and Cu , respectively. According to the data fitting
+
0
results, Cu/SiO
2
catalyst had the higher Cu /Cu than the other two samples (Table 1). Copper
+
oxide on the sample surface could not be reduced totally to metal copper, and these Cu species
2
+
might be generated from Cu species interacting with support after reduction [32]. In previous
works, the raise of hydrogenolysis activity for the supported metal catalysts had been attributed to
electron-deficient of the active metal and support [38,39]. The deficient of the active metal can
+
result from the donation of metal electron density to support. In our studies, the more Cu species
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
of Cu/SiO
2
catalyst might be attributed to the higher electron affinity of silicon. It is suggested that
SiO support has an important influence on the electronic structure of the active copper, which is
2
accordance with CO-FTIR analysis results (Fig. 3S).
3.3 The surface acidic properties of the catalysts
In order to explore surface acidity, NH
(Fig. 4). Generally, the strength of acid sites which is determined by the NH
temperature is classified as three types, weak acid (150–300 ºC), medium acid (300–500 ºC), and
strong acid (500–650 ºC) [40]. In our work (Fig. 4A), Cu/Al sample showed a main peak at
170 °C, which could be attributed to NH desorption from the weak acid sites. Besides, there was
a minor peak at 400°C related to the medium acid of Cu/Al surface as a result of the nature of
support. For Cu/ZnO sample, an obvious peak at 330°C might be assigned to NH desorption from
the medium acid sites produced probably by an extremely weak interaction of metal-support, and
accompanied with a faint peak at 170 °C. Evidently, Cu/SiO catalyst showed the largest peak at
around 190 ºC, indicating that it has much more the weak acid sites than the other two samples. In
addition, we also verified that pure CuO and SiO had scarcely the acidic property, but the reduced
Cu/SiO catalysts produced a huge amount of the weak acid sites (Fig. 4B). These new weak
acidic sites may be related to some low state copper species, such as Cu [39,41,42], which result
from the strong interaction of copper- silicon. Some copper species may still interact with SiO
3
-TPD was performed on three supported Cu-catalysts
3
desorption
2
O
3
3
2
O
3
3
2
2
2
+
2
support after reduction, and the deficient of these copper species may be derived from the high
electron affinity of silicon. This affinity of silicon would seize electrons from metal copper. The
transfer of electron density from metal copper to silicon would increase the electropositive (or the
oxophilic nature) of copper, and in further the improving of the oxophilic nature would contribute
to hydrogenolysis of the saturated C-O band. Therefore, acid quantity and types of Cu-catalysts,
especially the acid types, can be modulated by using some different acid/basic supports to produce
the new active sites
1
0

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
3.4 Temperature programmed adsorption-desorption experiments
Fig. 5 shows the ability of desorption hydrogen, which absorbed surface and subsurface of
these supported Cu-catalysts. The obvious desorption peak of hydrogen occurred for all of
samples at near 58 ºC, and this desorption peak might be assigned to the desorption of hydrogen
from copper surface [43,44]. A minor desorption peak was exhibited to Cu/Al
2
O
3
sample about
200 ºC, and this was probably linked to the function of Al support [45]. Besides, Cu/ZnO
2
O
3
sample about 350°C came up a broad peak, which might be related to the hydrogen desorption
from ZnO support or the interface of copper particles with support. It is known that ZnO is
capable of occluding large amounts of hydrogen both on the surface and in subsurface regions [46].
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
For Cu/SiO catalyst, the desorption peak of hydrogen came up at 58 ºC with the highest
2
desorption amount, and presented hardly the desorption peak at high temperature.
FAL-TPD experiments were done to explore the stability and strength of surface species
during desorption process over three supported Cu-catalysts in range of 40-800 ºC. Mass
characteristics of different desorption products are shown in Fig. 6, including FAL (C
96), FOL (C , m/e = 98), 2-MF (C O, m/e = 82), and H O (m/e = 18).
Fig. 6A (FAL, m/e=96) displays the desorption of reactant FAL. Desorption amount of FAL
is highest on Cu/SiO catalyst, and the desorption temperature of FAL followed the sequence of
Cu/SiO > Cu/Al > Cu/ZnO. First, Cu/SiO catalyst had the higher copper dispersion and BET
5
H
4
O
2
, m/e =
5
H
6
O
2
5
H
6
2
2
2
2
O
3
2
surface area than the other two samples, hence adsorption amount of FAL is sufficient. On the
other hand, the desorption temperature of FAL is higher than the other two samples. The two
reasons may enhance the concentration of reactant FAL on Cu/SiO
2
surface, and in further would
increase the rate of FAL hydrogenation process.
According to Fig. 6B (FOL, m/e=98), the desorption of FOL from products of FAL
hydrogenation is similar to FAL desorption on three supported Cu-catalysts. It is also found that
desorption temperature of FOL on Cu/SiO
2
catalyst is higher than the other two samples, that is to
surface. Successively, the rate of FOL
say, FOL is also hard to desorb from Cu/SiO
2
hydrogenolysis reaction may be increased with increasing the concentration of the intermediate
FOL on the catalyst surface.
Likely, Fig. 6C (2-MF, m/e=82) shows the desorption of desired product 2-MF from
hydrogenolysis of the intermediate FOL. Desorption amount of 2-MF followed the sequence of
Cu/SiO
2
> Cu/Al
2
O
3
> Cu/ZnO, and the desorption temperature of 2-MF on Cu/SiO catalyst is
2
lowest among three catalysts. Notably, the rate of hydrogenolysis reaction would increase with
decreasing the concentration of product 2-MF on catalyst surface. The largest desorption amount
11

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
of 2-MF on Cu/SiO catalyst might be assigned to the sufficient weak acid sites and the highest
2
+
0
Cu /Cu value, which could offer the more sufficient active sites to convert the intermediate FOL
to desired product 2-MF than the other two samples.
Fig. 6D (H O, m/e=18) expresses the desorption of water, which come mainly from the
2
hydrogenolysis of the intermediate FOL. When the intermediate FOL is converted into 2-MF, this
process would produce the equimolar amount of water. It is found that the desorption temperature
of H
2
O on Cu/SiO catalyst is the lowest among three catalysts, which is consistent with the
2
desorption of 2-MF.
Overall, Cu/SiO
2
catalyst had the sufficient adsorption amount of reactant FAL and the fast
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
desorption rate of desired product 2-MF. Adsorption of reactant FAL, conversion of the
intermediate FOL, and desorption of desired product 2-MF would have effects on the yield of
product 2-MF on Cu-catalysts surface, suggesting that the adsorption-desorption properties of
surface species would influence the rate of furfural hydrogenation
3.5 Catalytic performance in FAL hydrogenation
3.5.1. The effect of supports for the activity and the selectivity
In order to investigate support effects on catalytic performance of Cu-catalysts, we tested the
activity of all of samples (Table 2 and Fig. 4S). Obviously, hydrogenation activity of Cu/SiO
2
sample was much higher than the other two samples, and showed the highest yield of 2-MF. FAL
conversion and selectivity of 2-MF were as high as 100 % and 89.5 %, respectively. For Cu/ZnO
sample, FAL conversion and selectivity of 2-MF were both lowest among three samples. FAL
conversion on Cu/Al
catalyst is a lot lower than that of Cu/SiO
hydrogenation of FAL was performed on Ni-Fe/SiO
2
O
3
catalyst is next only to Cu/SiO
. The former literature reported that the vapor-phase
catalyst resulted in a 39.1 % selectivity to
2
, but 2-MF selectivity of Cu/Al
2
O
3
2
2
2-MF [20]. The vapor-phase hydrogenation of FAL carried out at 250 °C in a fixed bed reactor
over a multicomponent commercial catalyst (Cu: Zn: Al: Ca: Na=59:33:6:1:1) afforded an 87 %
selectivity to 2-MF [27]. The hydrogenation of FAL in supercritical CO
2
ran up to a 90 %
catalyst
selectivity of 2-MF over Cu-Cr catalyst at 240 °C [47]. Notably, we used Cr-free Cu/SiO
2
for the vapor-phase hydrogenation of FAL, selectivity of 2-MF was as high as 89.5 % and FAL
was completely converted at 220 °C, 1 atm. The compared results (Table 3) suggested that
Cu/SiO catalyst could convert FAL into 2-MF at a lower temperature, and gain the good yield of
2
desire product 2-MF. In combination with FAL-TPD (Fig. 6) experiments, the more adsorption
amount of FAL was found on Cu-catalysts surface, the higher conversion of FAL was discovered.
On the other hand, the lower desorption temperature of 2-MF were discovered on Cu-catalysts
surface, the higher selectivity of 2-MF also brought. In addition, the desorption rate of 2-MF was
1
2

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
fastest on Cu/SiO catalyst, and it was properly explained that the rate of FAL hydrogenation
2
increased with increasing the concentration of reactant (FAL), meanwhile, the reaction rate
increased with the decrease of the desorption temperature and the concentration of product on
catalyst surface. FAL-TPD experiments are in very good agreement with the obtained
experimental data displayed in Table 2.
Turnover frequency (TOF) is calculated to explore the intrinsic activity of these supported
Cu-catalysts [48]. The results (Table 2) suggested that Cu/SiO
2
catalyst achieved the highest TOF,
up to 24.3 h , which is obviously superior to the other two samples. Among these Cu-catalysts,
FAL conversion and selectivity of 2-MF are found to be in the order: Cu/SiO > Cu/Al
Cu/ZnO. The test results clearly confirmed that Cu/SiO catalyst showed the best catalytic activity
for FAL hydrogenation. Because SiO support could interact with copper species to disperse
-1
2
2
3
O >
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
2
2
0
+
uniformly copper particles with the higher loading of Cu and Cu , which might be important for
catalytic reaction such as FAL hydrogenation exemplified here, and active sites was sufficient to
convert FAL into other products. Among these Cu-catalysts, Cu/ZnO exhibited maximum furfuryl
alcohol selectivity because of the large Cu particles, while Cu/Al
selectivity due to the insufficient weak acid sites. Moreover, it is probably concluded the adequate
weak acid sites on Cu/SiO surface made the intermediate FOL convert into 2-MF by the
2
3
O catalyst had low 2-MF
2
hydrogenolysis process. These weak acid sites which had the strong oxophilic nature for the
saturated C-O band might promote C-O band hydrogenolysis, which is also in accordance with
Sitthisa’s work [20,49]. Hydrogenation of FAL to FOL might be catalyzed by the active sites of Cu
even at low temperature (140 ºC), and hydrogenolysis of the intermediate FOL is motivated by the
+
oxophilic nature of metal acid sites, which were probably attributed to Lewis acid sites (Cu ).
+
0
Moreover, XAES results also suggested that Cu/SiO
two samples, which might function as electrophilic or Lewis acid sites to polarize the saturated
-CH -OH band via the electron lone pair on oxygen [50].
3.5.2. Influence of the reaction conditions over Cu/SiO
Among three supported Cu-catalysts, Cu/SiO catalyst exhibited a promising catalytic
2
catalyst had a higher Cu /Cu than the other
2
2
catalyst
2
performance, since the following investigations of the reaction temperature and weight hourly
space velocity (WHSV) were conducted on this sample.
(1) Influence of the reaction temperature
Influence of the reaction temperature on Cu/SiO is shown in Table 4. Evidently, FOL is the
2
main product at low temperature (140 °C), and selectivity of 2-MF is sharply increased with
increasing the reaction temperature from 140 to 220 ºC. As expected, FAL conversion increased
from 98.3 % (140 °C) to 100 % (200 °C) and then remained at 100 % as the temperature elevated
1
3

-
1
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
(WHSV=0.5h ). Selectivity of 2-MF increased remarkably with increasing temperature, and as
-1
high as 89.5 % at 220 °C, WHSV=0.5h . Simultaneously, selectivity of pentanone and pentanol
also increased with increasing temperature. It is apparently seen that selectivity of 2-MF at lower
temperature (<180 °C) was very low, due to the existence of the intermediate FOL, whereas the
decrease of selectivity at higher temperature was related to the formation of undesired by-products,
such as the overhydrogenolysis products 2-pentanone, 1-pentanol, and 2-pentanol, indicating that
the reaction temperature is an important condition to enhance selectivity of 2-MF, which is in
accordance with our former work [27,51].
(2) Influence of Weight hourly space velocity
-1
-1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
Influence of weight hourly space velocity (WHSV=0.5 h and 2.0 h ) for the FAL
hydrogenation reaction over Cu/SiO was studied, and the results are showed in Table 4.
2
Conversion of FAL dropped obviously with increasing WHSV at lower reaction temperature
(<180 ºC), while the conversion of FAL was a little decline with increasing WHSV at higher
temperature (>200 ºC). Concurrently, WHSV, high and low, FOL was the main product at low
temperature (<160 ºC), but selectivity of 2-MF increased rapidly with decreasing WHSV above
160 ºC. When the reaction temperature increased to 220 °C, influence of WHSV was
inconspicuous. Therefore, the raise of temperature is much more prominent for the -CH
2
-OH
hydrogenolysis of the intermediate FOL than the falling of WHSV on Cu/SiO catalyst. In addition,
2
FOL was the main product at high WHSV, because the residence time shortened correspondingly,
and FOL had no time to convert in a step further, suggesting that the long residence time favors
the acceleration of sequential hydrogenolysis of the intermediate FOL to 2-MF.
3.5.3. The stability of Cu/SiO catalyst
2
Since Cu/SiO
2
catalyst presented the best 2-MF selectivity, the long term stability of this
catalyst did not present any distinct
sample was also explored. As illustrated in Fig. 7, the Cu/SiO
2
loss in the activity within 210 h time-on-stream under high temperature (220 °C). Concurrently,
2-MF selectivity did not show obvious fluctuation during the complete test, indicating that the
Cu/SiO
provided clues concerning the good stability of Cu/SiO
the TEM images (Fig. 8) of the fresh and spent catalysts demonstrated the Cu particles were not
obviously sintered after the long term reaction (210 h). In total, the superior stability of Cu/SiO
catalyst lies in the strong interaction of the active components with support SiO , which was
responsible for the stable structure of catalyst and improved the catalytic properties.
The evolution of catalytic activity on three supported Cu-catalysts states clearly synergistic
2
catalyst was robust under the test conditions. TEM images of the fresh and spent samples
2
catalyst. As displayed in Fig. 8, similar
2
2
1
4

1
2
3
4
5
6
7
8
9
0
1
2
effect of copper dispersion and the acidic property for the selective hydrogenation of FAL to 2-MF,
which is favorable to activate the -CH=O group of reactant FAL and cleave the saturated -CH -OH
group of the intermediate FOL. Among three supported Cu-catalysts, when copper ions were
2
dispersed on SiO
2
support, the interaction was the strongest. This strong interaction would not
+
only elevate copper dispersion, but also be favorable to enhance the Cu sites of catalyst surface
and the weak acid amount. The literature [22] reported that that the maximum activity of Cu-Cr
+
0
catalyst was attributed to the co-existence of Cu and Cu sites on the catalyst surface.
Concurrently, the long term stability of Cu/SiO catalyst was exhibited about 210 h without an
2
obvious loss in the activity of catalyst and the major products selectivity, and the good stability
might be due to the strong interaction of copper-silicon. In next work, it is important in further to
1
1
1
explore the mechanism of FAL hydrogenation on Cu/SiO catalyst and develop a better
2
copper-silicon catalyst which could be applied to the industrial production.
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
4. Conclusions
Three supported Cu-catalysts were tested for the selective hydrogenation of FAL to bio-fuel
2-MF, and Cu/SiO
2
catalyst exhibited the best catalytic performance. FAL conversion and
selectivity of 2-MF were respectively as high as 100% and 89.5% under atmospheric pressure,
-
1
220 °C, WHSV=0.5h . Systematic characterizations demonstrated that Cu/SiO catalyst had some
2
major advantages, such as (1) a higher copper dispersion, (2) a more adequate weak acid sites
which emerged by the interaction of copper-silicon, and (3) a lower desorption temperature of
desired product 2-MF than Cu/Al
2
3
O and Cu/ZnO catalysts. It is suggested that the intrinsic
properties of support have significant influence on the catalytic performance of Cu-catalysts.
Meanwhile, temperature also played an important role in determining selectivity of 2-MF. In
gas-phase hydrogenation of FAL to 2-MF, the evolution of catalytic activity and products
distribution over three supported Cu-catalysts suggested synergistic effect of copper dispersion
and the acidic property, which activates the -CH=O group of reactant FAL and dissociates the
-CH
2
-OH group of the intermediate FOL. Based on our studies, SiO support would be considered
2
a promise candidate to prepare Cu-based catalysts with the high activity in the hydrogenation of
FAL to bio-fuel 2-MF.
2
3
3
9
0
1
Acknowledgments
The authors gratefully thank the financial supports of Major State Basic Research
Development Program of China (973 Program) (No. 2012CB215305).
3
2
References
1
5

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
[1] D.M. Alonso, S. G. Wettstein, J. A. Dumesic, Chem. Soc. Rev. 41 (2012) 8075-8098.
[2] P. Gallezot, Chem. Soc. Rev. 41 (2012) 1538-1558.
[3] J.A. Melero, J. Iglesias, A. Garcia, Energy Environ. Sci. 5 (2012) 7393-7420.
[4] I. Agirrezabal-Telleria, I. Gandarias, P.L. Arias, Bioresour. Technol. 143 (2013) 258-264.
[5] M. Grilc, B. Likozar, J. Levec, Appl. Catal. B: Environ. 150– 151 (2014) 275– 287.
[6] M. Grilc, B. Likozar, J. Levec, Biomass Bioenerg. 63 (2014) 300-312.
[7] B. Danon, G. Marcotullio, W. de Jong, Green. Chem. 16 (2014) 39-54.
[8] A.P. dunlop, Ind. Eng. Chem. 40 (1948) 204-209.
[9] V. Pace, P. Hoyos, L. Castoldi, P. Dominguez de Maria, A.R. Alcantara, ChemSusChem. 5
(2012) 1369-1379.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
[10] N.S. Biradar, A.M. Hengne, S.N. Birajdar, P.S. Niphadkar, P.N. Joshi, C.V. Rode, ACS
Sustainable Chem. Eng. 2 (2014) 272-281.
[11] M. Besson, and C. Pinel, Chem. Rev. 114 (2014) 1827-1870.
[12] C. Wang, H. Xu, R. Daniel, A. Ghafourian, J.M. Herreros, S. Shuai, X. Ma, Fuel 103 (2013)
200-211.
[13] X. Ma, H. Xu, H. Ding, S. Shuai, Fuel 116 (2014) 281-291.
[14] S. Sitthisa, D.E. Resasco, Catal. Lett. 141 (2011) 784-791.
[15] L.W. Burnette, I.B. Johns, R.F. Holdren, R.M. Hixon, Ind. Eng. Chem. 40 (1948) 502-505.
[16] K. Yan, A. Chen, Fuel 115 (2014) 101-108.
[17] J.Y. Lee, D.W. Lee, K.Y. Lee, Y. Wang, Catal. Today. 146 (2009) 260-264.
[18] B.M. Nagaraja, V. Siva Kumar, V. Shasikala, A.H. Padmasri, B. Sreedhar, B. David Raju, K.S.
Rama Rao, Catal. Commun. 4 (2003) 287-293.
[19] R.S. Rao, R.T.K. Baker, M.A. Vannice, Catal. Lett. 60 (1999) 51-57
[20] S. Sitthisa, W. An, D. E. Resasco, J. Catal. 284 (2011) 90-101.
[21] Kai Yan, Aicheng Chen, Energy. 58 (2013) 357-363.
[22] R. Rao, A. Dandekar, R. T. K. Baker, M. A. Vannice, J. Catal. 171 (1997) 406-419.
[23] L.Chen, Y. Zhu, H. Zheng, C. Zhang, B. Zhang, Y. Li, Appl. Catal. A: Gen. 411-412 (2012)
95-104. � � � �
[24] A. Gutierrez, R.K. Kaila, M.L. Honkela, R. Slioor, A.O.I. Krause, Catal. Today. 147 (2009)
239-246.
[25] C. Zhao, Y. Kou, A. Lemonidou, X. Li, J.A. Lercher, Angew. Chem. Int. Ed. 48 (2009)
3987-3990.
[26] K. Murata, Y. Liu, M. Inaba, I. Takahara, Energy & Fuels 24 (2010) 2404-2409.
[27] H. Zheng, Y. Zhu, B. Teng, Z. Bai, C. Zhang, H. Xiang, Y. Li, J. Mol. Catal. A: Chem. 246
1
6

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
(2006) 18-23.
[28] Z. He, H. Lin, P. He, Y. Yuan, J. Catal. 277 (2011) 54–63.
[29] J. Gong, H. Yue, Y. Zhao, S. Zhao, L. Zhao, J. Lv, S. Wang, X. Ma, J. Am. Chem. Soc. 134
(2012) 13922-13925.
[30] K.L. Deutsch, B.H. Shanks, J. Catal. 285 (2012) 235-241.
[31] Guoqiang Ding, Yulei Zhu, Hongyan Zheng, Wei Zhang, Yongwang Li, Catal. Commun. 11
(2010) 1120–1124.
[32] A. Yin, X. Guo, W. Dai, K. Fan, J. Phys. Chem. C. 113 (2009) 11003-11013.
[33] Z. Huang, F. Cui, J. Xue, J. Zuo, J. Chen, C. Xia, Catal. Today. 183 (2012) 42-51.
[34] P. Burattin, M. Che, C. Louis, J. Phys. Chem. B. 102 (1998) 2722-2732.
[35] Z. Liu, M.D. Amiridis, Y. Chen, J. Phys. Chem. B. 109 (2005) 1251-1255.
[36] K.V.R. Chary, K.K. Seela, G.V. Sagar, B. Sreedhar, J. Phys. Chem. B. 108 (2004) 658-663.
[37] J.B. Wang, D.H. Tsai, T.J. Huang, J. Catal. 208 (2002) 370-380.
[38] U.R. Pillai, S. Deevi, Appl. Catal. B: Environ. 65 (2006) 110-117.
[39] D.G. Manly, A.P. Dunlop, J. Org. Chem. 23 (1958) 1093-1095.
[40] H. Atia, U. Armbrusterb, A. Martinb, J. Catal. 258 (2008) 71-82.
[41] P. Bera, S. Mitra, S. Sampath, M.S. Hegde, Chem. Commun. (2001) 927-928.
[42] T.H. Fleisch, G.J. Mains, Appl. Sur. Sci. 10 (1982) 51-62.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
[43] G. Anger, A. Winkler, K.D. Rendulic, Sur. Sci. 220 (1989) 1-17.
[44] T. Genger, O. Hinrichsen, M. Muhler, Catal. Lett. 59 (1999) 137–141
[45] J.T. Miller, B.L. Meyers, F.S. Modica, G.S. Lane, M. Vaarkamp, D.C. Koningsberger, J. Catal.
143 (1993) 395-408.
[46] I. Melian-Cabrera, M. Lopez Granados, J.L.G. Fierro，J. Catal. 210 (2002) 285-294.
[47] J.G. Stevens, R.A. Bourne, M.V. Twigg, M. Poliakoff, Angew. Chem. 122 (2010) 9040-9043.
[48] M. Boudart, Chem. Rev. 95 (1995) 661-666.
2
2
2
2
2
2
3
3
3
3
4
5
6
7
8
9
0
1
2
3
[49] S. Sitthisa, T. Sooknoi, Y. Ma, P. B. Balbuena, D.E. Resasco, J. Catal. 277 (2011) 1-13.
[50] L. Chen, P. Guo, M. Qiao, S. Yan, H. Li, W. Shen, H. Xu, K. Fan, J. Catal. 257 (2008)
172-180.
[51] Y. Zhu, H. Xiang, G. Wu, L. Bai, Y. Li, Chem. Commun. (2002) 254-255.
1
7

1
2
3
4
5
Scheme1 The main reaction pathway of furfural hydrogenation over the
Cu-catalysts.
FAL, furfural; FOL, furfuryl alcohol; 2-MF, 2-methylfuran; 2-MTHF,
2-methyltetrafuran; THFOL, tetrahydrofurfuryl alcohol; FU, furan; THF,
tetrahydrofuran; 2-PO, 2-pentanone; 2-PL, 2-pentanol; 1-PL, 1-pentanol.
6
7
8
OH
O
HO
THFOL
1-PL
OH
O
O
O
O
O
+
H2
-H2O
FAL
2-MF
FOL
2-MTHF
-CO
OH
O
O
O
2-PO
2-PL
FU
THF
9
0
1
1
1
1
2
1
1
1
1
1
1
1
2
3
4
5
6
7
8
9
0
Figure Captions
Fig. 1 XRD patterns of the calcined catalysts at 450 °C.
Fig. 2 H -TPR profiles of the calcined catalysts.
2
Fig. 3 (A) Cu 2p photoelectron spectra of the calcined catalysts, (B) Cu 2p photoelectron spectra
of the reduced catalysts, (C) Cu LMM XAES spectra of the reduced catalysts.
Fig. 4 NH
Fig. 5 H -TPD profiles of the reduced catalysts.
Fig. 6 FAL-TPD experiments of the reduced catalysts: (A) FAL desorption, m/e=96; (B) FOL
3
-TPD profiles: (A) the reduced catalysts; (B) Cu/Si catalysts.
2
1
8

1
2
3
4
5
6
7
8
desorption from the reaction of FAL, m/e=98; (C) 2-MF desorption from the reaction of FAL,
m/e=82; (D) H O desorption from the reaction of FAL, m/e=18.
Fig. 7 The long term stability of Cu/SiO catalyst, Reaction conditions: pure furfural, 220 °C,
atmospheric pressure, H /furfural = 17:1 (molar ratio), WHSV = 0.5 h .
2
2
-1
2
Fig. 8 TEM images of the fresh and spent Cu/SiO catalysts.
2
9
0
1
1
1

CuO


Cu/ZnO
Cu/Al O
2
3
Cu/SiO2
20
10
30
40
50
60
70
80
2
1
1
2
3
Fig. 1
CuO
Cu/ZnO
Cu/Al O
2
3
Cu/SiO2
350
100
150
200
250
300
400
Temperature (C)
1
4
1
1
1
5
6
7
Fig. 2
1
9

A
B
C

Cu/ZnO
Cu/ZnO

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
Cu/ZnO
Cu/Al O3
2
2
Cu/Al O3
Cu/Al O
2
3
Cu/SiO2
Cu/SiO2
Cu/SiO2
930
935
940
945
950
955
960
965
970
925
930
935
940
945
950
955
960
965
970
904 906 908 910 912 914 916 918 920 922 924 926 928
Kinetic Energy (eV)
BindingEnergy(eV)
Binding Energy (ev)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
Fig. 3
A
B
ReduceCu/SiO2
Cu/SiO2
SiO2
Cu/Al O3
2
Cu/ZnO
CuO
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
Temperature(C)
Temperature (C)
Fig 4
2
0

Cu/ZnO
Cu/Al O
2
3
Cu/SiO2
0
100
200
300
400
500
600
700
800
Temperature(C)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
Fig. 5
A
B
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
O
O
O
OH
FAL, m/e=96
FOL, m/e=98
Cu/SiO2
Cu/SiO2
Cu/Al O
2 3
Cu/Al O
2
3
Cu/ZnO
600
Cu/ZnO
0
100
200
300
400
500
600
700
800
0
100
200
300
400
500
700
800
Temperature (C)
Temeprature (C)
C
D
O
H2O, m/e=18
Cu/SiO2
2-MF, m/e=82
Cu/SiO2
Cu/Al O3
2
Cu/Al O3
2
Cu/ZnO
Cu/ZnO
0
100
200
300
400
500
600
700
800
0
100
200
300
400
500
600
700
800
Temperature (C)
Temperature (C)
Fig. 6
2
1

1
2
3
100
90
80
70
60
Conversion (%)
-MF selectivity (%)
5
0
2
40
30
20
10
0
0
20
40
60
80
100 120 140 160 180 200 220
Time on stream (h)
4
5
Fig. 7.
6
7
8
Fig. 8
9
1
1
0
1
Table 1 The physicochemical properties of the supported Cu-catalysts
Catalysts
S
BET
D
pore
V
pore
Cu
content (%)
22.9
d
CuO
d
Cu
D
Cu
S
Cu
+
0
X(Cu /Cu )
e
2
-1 a
a
3
-1 a
b
c
d
d
2
-1 d ( mol/mol )
(
m .g )
161.4
124.8
14.9
(nm)
8.7
(cm .g )
0.430
0.372
0.134
(nm)
(nm)
(%)
(m .g )
25.67
27.29
12.93
2
1
0
.23
.93
.91
Cu/SiO
2
8.45
5.97
16.76
15.47
8.13
Cu/Al
2
O
3
9.0
26.0
11.37 6.46
14.51 12.31
Cu/ZnO
29.4
23.5
a
1
1
2
3
Determined by N
2
-adsorption method
b
Determined by ICP.
2
2

c
d
e
1
2
Average Cu particle size calculated by Scherrer equation.
Determined by N O chemisorption.
2
3
4
5
6
Determined by XAES.
a
Table 2 Furfural conversion and selectivity of the products over the supported Cu-catalysts
b
Selectivity(%)
-1
Catalysts
Conversion（%） TOF(h )
2
-MF
FOL
RO
Others
Cu/SiO
Cu/Al
Cu/ZnO
2
100
99.2
94.5
24.3
7.1
89.5
71.6
65.3
2.4
6.0
4.9
0.4
2.1
12.8
1.4
2
O
3
10.7
32.9
5.8
a
-1
7
8
9
using pure furfural at 220
ͦ
C , atmospheric pressure , WHSV=0.5h , H
2
/FAL=17
b
2-MF=2-methylfuran, FOL=furfuryl alcohol, RO=the ring open products(i.e. 2-pentanone, 1-pentanol,
2-pentanol), Others= furan, 2-methyltetrahydrofuran, tetrahydrofurfuryl alcohol, furfural polymers
1
1
0
1
Table 3 Hydrogenation of furfural to 2-methylfuran
Catalysts
Reaction conditions
250 °C, H /FAL=25, W/F=0.1 h
250 °C, H /FAL=25, WHSV=0.3 h
240 °C, Supercritical CO
220 °C ,H /FAL=17, WHSV=0.5 h
Sel /% (Con /% )
39.1(96.3)
87(99.7)
Ref
[20]
Ni-Fe/SiO
2
2
-
1
Cu: Zn: Al: Ca: Na
Cu/Cr
2
[27]
2
,
90
[47]
-1
Cu/SiO
2
2
89.5(100)
this work
1
1
2
3
1
1
4
5
Table 4 Influence of the reaction temperature and weight hourly space velocity for furfural hydrogenation over
a
2
Cu/SiO catalyst
b
Selectivity (%)
-1
WHSV(h )
T(ºC)
140
Conversion (%)
2-MF
20.7
1.8
FOL
73.8
98.2
57.9
82.1
RO
0.1
0
Others
5.4
0
2
0
2
.5
.0
.5
.0
98.3
63.2
99.8
76.8
140
0
160
40.9
17.5
0.4
0.2
0.8
160
0.2
2
3

0
2
0
2
0
2
.5
.0
.5
.0
.5
.0
180
180
200
200
220
220
99.9
95.7
100
96.7
100
100
71.2
27.1
77.2
49.4
89.5
77.5
27.0
72.3
14.3
49.7
2.4
0.5
0.3
4.4
0.5
6.0
0.3
1.3
0.3
4.1
0.4
2.1
4.8
17.4
a
1
2
using pure furfural at atmospheric pressure, H
2
/FAL=17.
b
2-MF=2-methylfuran, FOL=furfuryl alcohol, RO=the ring open products(i.e. 2-pentanone, 1-pentanol,
3
4
5
2-pentanol), Others = furan, 2-methyltetrahydrofuran, tetrahydrofurfuryl alcohol, furfural polymers
2
4