Selective hydrogenolysis of biomass-derived furfuryl alcohol into 1,2- and 1,5-pentanediol over highly dispersed Cu-Al2O3 catalysts

Article abstract of DOI:10.1016/S1872-2067(15)61080-4

Cu nanoparticles supported on a variety of oxide supports, including SiO₂, TiO₂, ZrO₂, Al₂O₃, MgO and ZnO, were investigated for the hydrogenolysis of biomass-derived furfuryl alcohol to 1,2-pentanediol and 1,5-pentanediol. A Cu-Al₂O₃ catalyst with 10 wt% Cu loading prepared by a co-precipitation method exhibited the best performance in terms of producing pentanediols compared with the other materials. This catalyst generated an 85.8% conversion and a 70.3% combined selectivity for the target pentanediols at 413 K and 8 MPa H₂ over an 8-h reaction. The catalyst could also be recycled over repeated reaction trials without any significant decrease in productivity. Characterizations with X-ray diffraction, NH₃/CO₂-temperature programmed desorption, N₂ adsorption, transmission electron microscopy and N₂O chemisorption demonstrated that intimate and effective interactions between Cu particles and the acidic Al₂O₃ support in this material greatly enhanced its activity and selectivity. The promotion of the hydrogenolysis reaction was found to be especially sensitive to the Cu particle size, and the catalyst with Cu particles 1.9 to 2.4 nm in size showed the highest turnover frequency during the synthesis of pentanediols.

Full text of DOI:10.1016/S1872-2067(15)61080-4

Chinese Journal of Catalysis 37 (2016) 700–710
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Selective hydrogenolysis of biomass‐derived furfuryl alcohol into
1,2‐ and 1,5‐pentanediol over highly dispersed Cu‐Al2O3 catalysts
Hailong Liu a,b, Zhiwei Huang a,*, Haixiao Kang a, Chungu Xia a, Jing Chen a,#
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese
Academy of Sciences, Lanzhou 730000, Gansu, China
b University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Cu nanoparticles supported on a variety of oxide supports, including SiO2, TiO2, ZrO2, Al2O3, MgO and
ZnO, were investigated for the hydrogenolysis of biomass‐derived furfuryl alcohol to
1,2‐pentanediol and 1,5‐pentanediol. A Cu‐Al2O3 catalyst with 10 wt% Cu loading prepared by a
co‐precipitation method exhibited the best performance in terms of producing pentanediols com‐
pared with the other materials. This catalyst generated an 85.8% conversion and a 70.3% combined
selectivity for the target pentanediols at 413 K and 8 MPa H2 over an 8‐h reaction. The catalyst could
also be recycled over repeated reaction trials without any significant decrease in productivity.
Characterizations with X‐ray diffraction, NH3/CO2‐temperature programmed desorption, N2 ad‐
sorption, transmission electron microscopy and N2O chemisorption demonstrated that intimate and
effective interactions between Cu particles and the acidic Al2O3 support in this material greatly
enhanced its activity and selectivity. The promotion of the hydrogenolysis reaction was found to be
especially sensitive to the Cu particle size, and the catalyst with Cu particles 1.9 to 2.4 nm in size
showed the highest turnover frequency during the synthesis of pentanediols.
Received 30 January 2016
Accepted 7 March 2016
Published 5 May 2016
Keywords:
Furfuryl alcohol
1,2‐Pentanediol
1,5‐Pentanediol
Selective hydrogenolysis
Cu‐Al catalyst
© 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
alcohol (THFA) to valuable chemicals and fuels by hydrogena‐
tion and hydrogenolysis has also received increasing attention
Due to concerns regarding declining petroleum resources
and various environmental issues, the conversion of renewable
biomass to chemicals and liquid fuels has been the subject of
intense research over the past decade [1–3]. Furfural is an im‐
portant platform molecule manufactured via acid hydrolysis of
the lignocellulose found in various abundant agricultural raw
materials, such as corncobs, oats, and wheat bran, at up to 105
tons per year [4–6]. The catalytic transformation of furfural and
its derivatives furfuryl alcohol (FFA) and tetrahydrofurfuryl
in recent years [7–14]. As an example, the one‐pot hydrogenol‐
ysis of furfural or its derivatives is an attractive method for the
sustainable synthesis of useful glycols, such as 1,2‐pentanediol
(1,2‐PeD) and 1,5‐pentanediol (1,5‐PeD) [8,10,15–24].
To date, the selective hydrogenolysis of furfural and its de‐
rivatives to 1,2‐PeD and 1,5‐PeD has been accomplished pri‐
marily using noble metal catalysts, including supported Ru
[17], Rh [9,15,21,23], Pt [10,16,22] and Ir [24]. For example,
Tomishige and co‐workers [15,21,23,24] achieved 1,5‐PeD
* Corresponding author. Tel: +86‐931‐4968070; Fax: +86‐931‐4968129; E‐mail: zwhuang@licp.cas.cn
# Corresponding author. Tel: +86‐931‐4968068; Fax: +86‐931‐4968129; E‐mail: chenj@lzb.ac.cn
This work was supported by the National Natural Science Foundation of China (21133011, 21203221, 21473224) and the Natural Science Founda‐
tion of Gansu Province (1308RJZA281).
DOI: 10.1016/S1872‐2067(15)61080‐4 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 37, No. 5, May 2016

Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
701
yields up to 94% from the hydrogenolysis of THFA at 373 to
393 K and under 8 MPa H2 using acidic, low‐valent metal oxides
(ReOx, MoOx or WOx)‐modified Rh or Ir catalysts. Xu et al. [16]
attempted the direct conversion of furfural to 1,2‐PeD and
1,5‐PeD in an alcohol solvent using a Li‐modified Pt/Co2AlO4
catalyst, obtaining high conversions (approximately 100%) and
moderate yields of 1,2‐PeD (16.2%) and 1,5‐PeD (34.9%) at
413 K and 1.5 MPa H2. More recently, 1,2‐PeD (with a 73%
yield) and 1,5‐PeD (with a 78.2% yield) were separately at‐
tained over a hydrotalcite‐supported Pt catalyst [10] and a
Rh‐added Ir‐ReOx/SiO2 catalyst [20], respectively, from furfural
hydrogenolysis. In addition, Zhang et al. [17] obtained a high
yield of 1,2‐PeD (42.1%) from the hydrogenolysis of FFA over a
Ru/MnOx catalyst under mild conditions consisting of 423 K
and 1.5 MPa H2, with no formation of 1,5‐PeD. Although high
yields of 1,2‐PeD (40%) and 1,5‐PeD (30%) have been reported
from the hydrogenolysis of FFA over a copper chromite catalyst
[25], the wide application of this system has been restricted
due to the potential toxicity concerns associated with Cr and
the harsh reaction conditions required (448 K, 10–15 MPa).
Clearly, the selective hydrogenolysis of furfural or its deriv‐
atives to PeDs over environmentally‐friendly, Cr‐free,
non‐precious catalytic systems under mild conditions remains
challenging. Recently, we reported that highly dispersed Cu
catalysts exhibit good activity and selectivity during the hy‐
drogenolysis of C–O bonds in polyols [26–28] and cyclic car‐
bonates [29]. Since then, we have demonstrated that
non‐precious Cu‐Mg3AlO4.5 catalysts with layered double oxide
structures and weak basicity are exceptionally active and selec‐
tive during the hydrogenolysis of biomass‐derived FFA,
achieving approximately 80% combined yields of 1,2‐PeD and
1,5‐PeD under mild conditions (413 K and 6 MPa H2) [30]. Alt‐
hough basic supports are believed to be benefit for the trans‐
formation of furfural or FFA to specific PeDs, by partly sup‐
pressing the dehydration of FFA to 2‐methylfuran [16] and/or
stabilizing the hydrogenolysis intermediates of FFA [17], acidic
supports [31] or additives [8,9] have also been applied to the
hydrogenolysis of furfurals or their derivatives to diols. Herein,
we report that acidic Al2O3‐supported Cu bifunctional catalysts
with high dispersion are also active and selective during the
hydrogenolysis of FFA to 1,2‐PeD and 1,5‐PeD. The catalytic
activity and selectivity of these Cu‐Al2O3 catalysts were found
to be affected by both their structure and surface properties.
The reaction parameters, including temperature, H2 pressure,
catalyst amount and reaction time, were optimized to obtain
high yields of PeDs. Based on the data obtained, this paper also
proposes reaction pathways for formation of the main reaction
products.
ous TiO2 (15 wt%, particle size 15 nm) and ZrO2 (40 wt%, par‐
ticle size range 20 to 30 nm) solutions were obtained from the
Xuancheng Jingrui New Material Co., China. PtCl4 was pur‐
chased from the Beijing HWRK Chem. Co., Ltd., China and
HZSM‐5 zeolite (surface area 541 m2/g, Si/Al = 500) was pur‐
chased from the Nankai University Catalyst Plant, Tianjin, Chi‐
na. The copper chromite catalyst (CuCr2O4) was purchased
from the Yingkou Tianyuan Chemical Industry Research Insti‐
tute Co., Ltd., China. NH3 (99.9%), 5% N2O‐95% N2, 5% H2‐95%
Ar, 20% H2‐80% N2 and He (99.999%) were obtained from the
Lanzhou Lanmei Cryogenic Products Co., Ltd., China.
2.2. Catalyst preparation
Catalysts consisting of 10 wt% Cu supported over SiO2, TiO2
or ZrO2, were prepared by precipitation‐gel (PG) method, using
a previously reported process [27,28]. In a typical synthesis, an
aqueous solution of NaOH (4 mol/L) was added dropwise to a
Cu(NO3)2 solution (0.5 mol/L) with vigorous stirring at 303 K
until the pH was above 11, to form a Cu(OH)2 precipitate. The
desired amount of a colloidal aqueous solution of SiO2, or TiO2
or ZrO2 was subsequently added dropwise to this Cu(OH)2 pre‐
cipitate to form a gel, and these gels were aged at 303 K for 4 h,
with the exception of the Cu‐SiO2, which was aged at 373 K for
4 h. Following this, the gels were filtered and washed with dis‐
tilled H2O until the wash water showed a pH of approximately
7. Finally, the obtained solids were dried at 393 K overnight
and calcined at 773 K for 4 h in air.
The catalysts with 10 wt% Cu supported over MgO or ZnO,
as well as Cu‐Al2O3 with Cu loadings from 2 to 30 wt%, were
prepared by co‐precipitation (CP) method. Briefly, a mixed
solution of Cu(NO3)2 (0.1 mol/L) with Mg(NO3)2, Zn(NO3)2 or
Al(NO3)3 and an aqueous solution of NaOH (4 mol/L) were
concurrently added dropwise to a Na2CO3 solution (0.5 mol/L)
while maintaining the pH at approximately 10. After aging at
303 K for 24 h, the obtained solids were filtered and washed
with distilled H2O until pH of approximately 7 was obtained.
Finally, the samples were dried at 393 K overnight and calcined
at 773 K for 4 h in air.
The Al2O3‐supported 2 wt% Pt, 10 wt% Ni or 10 wt% Co
catalysts were prepared in a similar manner from PtCl4,
Ni(NO3)2 or Co(NO3)2 precursors by the CP method, respec‐
tively. The calcined samples prepared by PG or CP methods are
designated herein as ωMO‐support, while the corresponding
reduced catalysts are designated as ωM‐support, where ω rep‐
resents the nominal metal loading and M represents the active
metal employed. For comparison, 10Cu/Al2O3‐IM, 30Cu‐Al2O3‐W
and 10Cu‐Al2O3‐W (with 1 wt% W loading), 10Cu‐Al2O3‐K
(with 1 wt% K loading) and 10Cu/HZSM‐5‐IM reference cata‐
lysts were prepared by incipient wetness impregnation (IM)
method. The Al2O3 support, or calcined 30CuO‐Al2O3 or
10CuO‐Al2O3 samples (prepared by the CP method described
above), or the HZSM‐5 support were impregnated with an
aqueous solution containing the requisite amount of Cu(NO3)2,
(NH4)10W12O41·H2O or KNO3, respectively, at room tempera‐
ture, followed by drying at 393 K overnight and calcining at 773
K for 4 h in air. The pure Cu catalyst was prepared by precipi‐
2. Experimental
2.1. Materials
All reagents were analytical grade. An aqueous colloidal SiO2
solution (25.0 wt%, ammonium stabilized type, pH in the range
of 8.5 to 10.5, particle size from 10 to 20 nm) was purchased
from the Qingdao Haiyang Chemical Co., China. Colloidal aque‐

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Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
tating a Cu(NO3)2 aqueous solution (0.5 mol/L) with NaOH (4
mol/L), followed by treatment similar to that detailed above.
2.4. Catalytic testing and product analysis
The FFA hydrogenolysis reactions were carried out in a
stainless steel autoclave reactor (100 mL) at a stirring speed of
800 r/min. Prior to each reaction, the calcined catalyst sample
was reduced at 623 K in 20% H2‐80% N2 at a flow of 40
mL/min for 3 h. In a typical trial, 40 g of 10 wt% FFA dissolved
in ethanol was added into reactor together with a quantity of
the reduced catalyst. After flushing with H2, the reactor was
pressurized with H2 to 6.0 MPa, and then heated to 413 K over
the course of 0.5 h. The concentrations of the reactant and liq‐
uid products were analyzed by gas chromatography (Agilent
7890A GC) with a PONA capillary column (50 m × 0.20 mm ×
0.50 μm). Products were also identified using an Agilent
7890A/5975C gas chromatograph‐mass spectrometer (GC‐MS)
with an HP‐5MS column. The liquid products identified in this
manner consisted of 1,2‐PeD, 1,5‐PeD, 1,4‐pentanediol,
2‐methyl furan (2‐MF), 2‐methyl tetrahydrofuran (2‐MTHF),
1‐pentanol, 2‐pentanol, n‐pentane and tetrahydrofurfuryl al‐
cohol (THFA). FFA conversions and product selectivities were
calculated on the basis of the following equations.
2.3. Catalyst characterization
X‐ray powder diffraction (XRD) data were acquired using a
PANalytical X’pert Pro Diffractometer with nickel filtered Cu Kα
radiation at 40 kV and 30 mA. BET surface areas were obtained
with a Micromeritics Tristar II 3020 instrument at liquid nitro‐
gen temperature (77 K). Prior to these measurements, the
samples were pretreated with N2 at 573 K for 4 h. Transmission
electron microscopy (TEM) investigations were carried out
using a JEM2010 electron microscope at 200 kV. The TEM
samples were prepared by ultrasonically dispersing each mate‐
rial in ethanol and then dropping the dispersions onto car‐
bon‐coated Cu grids.
NH3‐temperature programmed desorption (TPD) and
CO2‐TPD were carried out with a DAX‐7000 instrument (Huasi
Technology Co., Ltd, China). Samples were pretreated at 473 K
under a He flow at 40 mL/min for 1 h and then reduced at 623
K under 5% H2‐95% Ar at 40 mL/min for 2 h. The reduced
samples were subsequently exposed to an NH3 flow (40
mL/min) at 373 K for 1 h and then heated linearly from 373 to
973 K at a rate of 10 K/min under a He flow (40 mL/min). The
desorbed NH3 was detected using a thermal conductivity de‐
tector (TCD), and the TCD signals were calibrated with specific
volumes of NH3. CO2‐TPD of the Cu catalysts was similar to the
NH3‐TPD procedure above but with the saturation adsorption
of CO2 at 313 K for 1 h.
Conversion (%) = (moles of FFA charged – moles of
FFA left)/moles of FFA charged  100%
Selectivity (%) = moles of a product generated/
(moles of FFA charged – moles of FFA left)  100%
3. Results and discussion
3.1. Structural characterization of Cu‐Al2O3 catalysts
The Cu dispersion was assessed by dissociative N2O adsorp‐
tion with H2‐temperature programmed reduction (TPR) re‐
verse titration [27,32]. After pretreatment in a He flow at 473 K
for 1 h, the samples (containing approximately 10 mg Cu) were
reduced in a 5% H2‐95% Ar flow at 40 mL/min by heating from
room temperature to 773 K at a rate of 5 K/min. This process
represented a total TPR, with reduction of both bulk and sur‐
face Cu species. At the end of the first TPR, the samples were
cooled to 323 K in the same reducing atmosphere and then
exposed to 5% N2O‐95% N2 (40 mL/min) at 323 K for 1 h.
Subsequently, the resulting surface oxidized samples were
subjected to a second TPR run from 323 to 623 K at a rate of 5
K/min (denoted as surface TPR). During the H2‐TPR runs, the
H2 consumption was tracked using a thermal conductivity de‐
tector (TCD). Assuming a spherical shape for the Cu particles,
1.46 × 1019 Cu atoms per m2 and a N2O/Cus molar ratio of 0.5
(where Cus denotes Cu atoms on the surface), the Cu dispersion
(DCu), Cu0 surface area (SCu) and average Cu particle size (dCu)
values of the Cu catalysts were calculated using Equations (1),
(2) and (3), respectively.
Fig. 1 presents the XRD patterns of calcined CuO‐Al2O3 sam‐
ples with different Cu loadings as well as both reduced and
used 10Cu‐Al2O3 catalysts. As can be seen from Fig. 1(a), mainly
broad diffraction peaks assignable to γ‐Al2O3 (JCPDS 10‐0425)
at approximately 2θ = 37.5°, 45.8° and 66.7° were observed in
all calcined CuO‐Al2O3 samples. A diffuse diffraction peak at 2θ
= 35.5° assignable to CuO (JCPDS 05‐0661) is present in the
30CuO‐Al2O3 pattern, but no CuO peaks are found in the pat‐
terns of the samples with Cu loadings below 30 wt%. This
demonstrates the high dispersion of CuO in these samples, es‐
pecially those with lower Cu loadings (2–20 wt%). After reduc‐
tion at 623 K for 3 h in H2 atmosphere, almost no diffraction
peaks associated with Cu0 and/or Cu2O are observed in the
pattern of the reduced 10Cu‐Al2O3 catalyst (Fig. 1(b)(2)),
showing the high dispersion and remarkable ability to resist
sintering of these species in the reduced catalyst. The high sta‐
bility of the catalyst is also reflected in the pattern of the used
10Cu‐Al2O3 catalyst after five cycles, as only a very broad dif‐
fraction pattern assignable to Cu0 is observed in its XRD profile
(Fig. 1(b)(3)). The crystalline size of the Cu0 species in the used
10Cu‐Al2O3 catalyst was calculated to be approximately 3 nm
by the Scherrer equation.
DCu (%) = 2  H2 consumption (surface TPR)/
H2 consumption (total TPR)  100%
(1)
SCu (m2/g) = (DCu  Nav)/(MCu  1.46  1019) ≈ 649  DCu (2)
Fig. 2 presents representative TEM images of the calcined
CuO‐Al2O3 samples with Cu loadings of 2, 10 and 30 wt%, and
the used 10Cu‐Al2O3 after five cycles. A sponge‐like mesopo‐
rous structure is observed in each of the samples, and it is dif‐
ficult to discriminate between CuO nanoparticles and the Al2O3
dCu (nm) = 6/(SCu  ρCu) ≈ 1.0/DCu (3)
Here Nav is Avogadro’s constant (6.02 × 1023/mol), MCu is the
relative atomic mass (63.5 g/mol) and ρCu is the Cu density
(8.92 g/mL).

Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
703
(b)
(a)
Al2O3
CuO
Al2O3
Cu0
30Cu-Al2O3
20Cu-Al2O3
(3)
(2)
10Cu-Al2O3
5Cu-Al2O3
2Cu-Al2O3
(1)
10
20
30
40
50
60
70
80
10
20
30
40
2/(o )
50
60
70
80
2/(o )
Fig. 1. XRD patterns of (a) calcined CuO‐Al2O3 samples with different Cu loadings and (b) calcined 10CuO‐Al2O3 (1), reduced 10Cu‐Al2O3 (2) and
10Cu‐Al2O3 after five cycles (3).
supports even with Cu loadings up to 30 wt%, showing the
uniform dispersion of CuO in these samples. In addition, only a
few small Cu nanoparticles with sizes < 8 nm are occasionally
observed in the image of the used 10Cu‐Al2O3 after five cycles
(Fig. 2(d)). These TEM results further support the XRD finding
that the Cu‐Al2O3 has both highly dispersed Cu species and
remarkable resistance to sintering during FFA hydrogenolysis.
It has been reported that surface acidity plays an important
role in determining the catalytic performance for THFA [9] and
5‐hydroxymethylfurfural (HMF) [31] hydrogenolysis to diols.
Thus, the acidic properties of Cu‐Al2O3 catalysts with different
Cu loadings were characterized by NH3‐TPD, with the results
presented in Fig. 3(a). As can be seen, all the Cu‐Al2O3 catalysts
exhibited NH3 desorption peaks at 373 to 523 K (weak acid
sites) and 523 to 873 K (medium and strong acid sites). The
NH3 desorption peak areas gradually decreased with increasing
Cu loading, indicating that the acidity of each Cu‐Al2O3 catalyst
declined at higher Cu loadings, in good agreement with previ‐
ous reports [33]. We also determined the surface basicity of
three representative Cu‐Al2O3 catalysts with Cu loadings of 2,
10 and 30 wt%. Each of these catalysts generated a main CO2
desorption peak centered at approximately 457 K, associated
with weakly basic sites [34]. The basic site concentrations of
these catalysts, which decreased uniformly from 95.5 to 61.4
μmol/g with increasing Cu loading from 2 to 30 wt%, are two
to three times lower than those of their acidic sites, demon‐
strating that these Cu‐Al2O3 catalysts present mainly acidity
properties. In additional experiments, WO3 and K2O were em‐
ployed to tune the surface acidity‐basicity of the Cu‐Al2O3 cata‐
lysts [34]. Fig. 3 shows that the incorporation of 1 wt% W
slightly increased the acidity of both the 10Cu‐Al2O3 and
30Cu‐Al2O3 catalysts, while doping with 1 wt% K increased the
Acid
concentration
(a)
30Cu-Al2O3-W
(mol/g)
196.7
10Cu-Al2O3-W
30Cu-Al2O3
230.5
182.8
206.6
219.9
227.1
20Cu-Al2O3
10Cu-Al2O3
5Cu-Al2O3
2Cu-Al2O3
238.5
400
500
600
700
800
900
Temperature (K)
(a)
(b)
(b)
Base
concentration
(mol/g)
10Cu-Al2O3-K
30Cu-Al2O3
10Cu-Al2O3
94.1
61.4
75.0
95.5
(c)
(d)
2Cu-Al2O3
300 400 500 600 700 800 900 1000
Temperature (K)
Fig. 3. (a) NH3‐TPD and (b) CO2‐TPD patterns of Cu‐Al2O3 catalysts with
Fig. 2. TEM images of (a) 2CuO‐Al2O3, (b) 10CuO‐Al2O3, (c) 30CuO‐Al2O3
different Cu loadings prepared by CP method.
and (d) 10Cu‐Al2O3 after five cycles.

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Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
basicity of the 10Cu‐Al2O3.
loadings from 2 to 30 wt% increased to a maximum of 61.9% in
the case of the 20Cu‐Al2O3, and then decreased to 49.5% with
further increases in the Cu loading to 30 wt% (entries 6 and 10
to 13). The selectivities for 1,2‐PeD and 1,5‐PeD over these
catalysts also increased with the Cu loading, reaching maxi‐
mum values of 48.6% and 22.7% over the 10Cu‐Al2O3, respec‐
tively. In contrast, almost no 1,2‐PeD and 1,5‐PeD were ob‐
tained over the 10Ni‐Al2O3 and 10Co‐Al2O3 catalysts; THFA was
found to be the dominant product (selectivity > 83%) with the
former catalyst being much more active (entries 15 and 16).
Previous studies showed that supported Pt catalysts (with ap‐
proximately 2 wt% Pt loading) were both active and selective
during the hydrogenolysis of FA and FFA [10,16]. Under our
experimental conditions, however, the 2Pt‐Al2O3 catalyst ex‐
hibited inferior selectivity for 1,2‐PeD and 1,5‐PeD compared
with the Cu‐Al2O3 catalysts (entry 17). In addition, the conver‐
sions and combined selectivities for pentanediols over the
Cu‐Al2O3 catalysts with Cu loadings ≥ 5 wt% were noticeably
greater than those obtained using a commercial CuCr2O4 cata‐
lyst (entry 21). Clearly, the above findings show the distin‐
guished performances of the Cu‐Al2O3 catalysts prepared by CP
method with regard to generating pentanediols, especially in
the case of the catalyst with 10 wt% Cu loading. Moreover, be‐
cause the Al2O3 support itself is almost inactive in FFA hydro‐
genolysis (not shown in Table 2), while pure Cu exhibits rather
weak activity and selectivity (entry 20), the remarkable in‐
crease in both FFA conversion and selectivities obtained with
the 10Cu‐Al2O3 (entry 6) and 10Cu/Al2O3‐IM catalysts (entry
18) demonstrates that the intimate and effective interaction of
Cu and the acidic Al2O3 support is beneficial to the transfor‐
mation of FFA to the target PeDs.
Table 1 summarizes the textural properties of calcined
CuO‐Al2O3 samples prepared by CP method with different Cu
loadings, as well as the 10CuO/Al2O3‐IM reference sample syn‐
thesized using a traditional impregnation method and pure
CuO. The BET surface areas of the calcined CuO‐Al2O3 samples
declined monotonically from 297.4 to 197.1 m2/g with in‐
creasing Cu loadings from 2 to 30 wt%, likely due to the de‐
crease in the amount of the Al2O3 support, which had a surface
area as high as 285.4 m2/g. The BET surface areas of the refer‐
ence 10CuO/Al2O3‐IM and pure CuO were only 145.6 and 20.1
m2/g, much lower than those of the CuO‐Al2O3 materials. The
average pore diameters of the CuO‐Al2O3 samples in the meso‐
pore range were found to increase from 6.8 to 15.7 nm with
increasing Cu loadings from 2 to 30 wt%. The Cu dispersions
and Cu0 surface areas of the catalysts determined by N2O
chemisorption decreased gradually at higher Cu loading, and
even the 30Cu‐Al2O3 showed high dispersion and Cu0 surface
area values of 32.8% and 234.3 m2/g, respectively. As a result
of changes in dispersion, the Cu particle sizes in the catalysts
increased gradually from 1.3 to 3.0 nm with increasing Cu
loadings from 2 to 30 wt%. These small sizes are in line with
the above XRD and TEM characterizations. In contrast, the ref‐
erence 10CuO/Al2O3‐IM and the pure CuO showed much lower
dispersions of 6.0 and 2.8%, and rather large Cu particle sizes
of 16.7 and 39.3 nm, respectively.
3.2. Catalytic testing for FFA hydrogenolysis over various
catalysts
Table 2 summarizes the conversions and selectivities ob‐
tained during FFA hydrogenolysis over a wide variety of het‐
erogeneous catalysts at 413 K and 6 MPa H2. Among the
Cu‐base catalysts supported on traditional oxides (SiO2, TiO2,
ZrO2, MgO, ZnO and Al2O3), the 10Cu‐Al2O3 (having a larger
concentration of strongly acidic sites as in Fig. 3 and reference
[29]) was more active and selective for the generation of
1,2‐PeD and 1,5‐PeD. This catalyst gave 48.6% and 22.7% se‐
lectivities for 1,2‐PeD and 1,5‐PeD at 60.4% FFA conversion,
respectively (entries 1–6). In addition, 2‐MF, 1‐pentanol and
THFA were determined to be the major byproducts from
10Cu‐Al2O3, with selectivities of 10.0%, 9.9% and 3.7%, respec‐
tively. The FFA conversions of the Cu‐Al2O3 catalysts with Cu
The above characterizations (Table 1 and Fig. 3) show that
the Cu particle sizes of the Cu‐Al2O3 catalysts and their surface
acidic concentrations varied in different manners. That is, the
Cu particle sizes increased nearly linearly with increasing Cu
loadings, while the surface acidic amounts declined monoton‐
ically (Fig. 4(a)). Plotting the TOF values, defined as the moles
of 1,2‐PeD and 1,5‐PeD generated per Cu site per time, against
the Cu particle size of the Cu‐Al2O3 catalysts showed that the
TOF increased rapidly with increasing Cu size and reached a
maximum between 1.9 and 2.4 nm, then declined with further
increases in the Cu size (Fig. 4(b)). This trend indicates that
FFA hydrogenolysis over these Cu catalysts is likely a struc‐
Table 1
Textural properties of calcined CuO‐Al2O3 samples with different Cu loadings, a reference 10CuO/Al2O3‐IM sample and pure CuO.
Cu content a
(wt%)
Surface area b
(m2/g)
Average pore diameter b
(nm)
Dispersion c
(%)
Cu surface area d
(m2/g)
Particle size e
(nm)
Sample
2CuO‐Al2O3
5CuO‐Al2O3
10CuO‐Al2O3
20CuO‐Al2O3
30CuO‐Al2O3
10CuO/Al2O3‐IM
Pure CuO
1.9
4.8
9.6
19.6
27.6
10.0
100
—
297.4
254.9
229.3
210.8
197.1
145.6
20.1
6.8
8.3
84.4
69.7
57.6
45.4
32.8
6.0
548.0
452.3
374.0
294.9
234.3
39.0
1.3
1.6
1.9
2.4
3.0
16.7
39.3
—
10.4
13.3
15.7
15.6
19.2
7.4
2.8
—
18.2
—
Al2O3
285.4
a Cu content determined by ICP analysis. b BET method. c Cu dispersion obtained from dissociative N2O adsorption. d Cu0 surface area obtained from
dissociative N2O adsorption. e Mean Cu particle size calculated from dissociative N2O adsorption.

Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
705
Table 2
Conversion and selectivity during FFA hydrogenolysis over various catalysts.
Selectivity (%)
Conversion
Entry
Catalyst
1,2‐PeD
33.2
14.4
39.8
39.9
10.8
48.6
48.1
43.7
36.1
23.8
37.0
41.2
36.2
36.9
1.0
1,5‐PeD
18.0
7.9
11.5
27.4
5.9
22.7
22.2
30.9
22.3
8.5
14.0
16.2
15.7
20.4
1.3
2‐MF
1‐Pentanol
11.3
8.4
THFA
8.9
8.2
4.8
3.0
5.6
3.7
2.7
3.0
3.5
6.4
4.2
4.5
3.3
3.7
91.7
83.7
69.2
7.7
0.3
6.4
3.6
Others a
(%)
1
2
3
4
5
6
7 b
8
10Cu‐SiO2
10Cu‐TiO2
10Cu‐ZrO2
10Cu‐MgO
10Cu‐ZnO
10Cu‐Al2O3
10Cu‐Al2O3
10Cu‐Al2O3‐W
10Cu‐Al2O3‐K
2Cu‐Al2O3
29.1
14.3
45.7
54.3
8.6
60.4
85.8
52.4
42.5
20.1
42.1
61.9
49.5
52.6
7.7
13.2
16.3
5.5
20.2
47.4
16.7
11.9
71.6
4.9
10.6
12.2
4.3
1.8
10.0
9.3
7.3
9.9
13.2
10.7
6.7
3.6
4.4
9
4.0
27.4
23.1
14.8
4.9
13.8
10.9
4.9
6.6
2.0
27.4
86.7
85.8
24.5
10 c
11
12
13
14
15
16
17 c
18
19
20
21
27.6
18.3
18.4
15.8
16.3
0.8
10.6
11.6
14.5
15.2
11.8
—
5Cu‐Al2O3
20Cu‐Al2O3
30Cu‐Al2O3
30Cu‐Al2O3‐W
10Ni‐Al2O3
10Co‐Al2O3
2Pt‐ Al2O3
10Cu/Al2O3‐IM
10Cu/HZSM‐5‐IM
Pure Cu
>99
7.7
45.8
37.9
>99
7.9
—
—
7.0
4.4
0.8
1.4
15.6
9.7
—
13.6
29.6
9.9
2.1
34.1
7.3
—
21.1
1.6
9.6
0.7
3.1
0.2
CuCr2O4
24.4
10.0
12.1
Reaction conditions: 0.20 g active metal, 40 g 10 wt% FFA in ethanol, 413 K, 6 MPa H2, 8 h. PeD = Pentanediol, 2‐MF = 2‐Methyl furan, THFA = Tetra‐
a
hydrofurfuryl alcohol. These include n‐pentane, 1,4‐PeD, 2‐methyl tetrahydrofuran, 2‐pentanol and some undetermined products (for
10Cu/HZSM‐5‐IM, the main byproduct is ethyl levulinate). b 0.40 g Cu, 40 g 10 wt% FFA in ethanol, 413 K, 8 MPa H2, 8 h. c 0.05 g active metal, 40 g 2.5
wt% FFA in ethanol, 413 K, 6 MPa H2, 8 h.
ture‐sensitive reaction [35], which is in agreement with the
results of our previous study on the hydrogenolysis of FFA over
Cu‐Mg3AlO4.5 bifunctional catalysts [30]. The lower TOFs of the
catalysts with Cu sizes below 1.9 nm likely resulted from the
stronger adsorption for the reactants and products on the
smaller Cu particles, resulting in a decrease in the quantity of
vacant Cu sites, analogous to the behavior reported for Ru cat‐
alyst during glycerol hydrogenolysis [36]. The decrease in TOF
with further increases in Cu size above 2.4 nm might be caused
by steric hindrance to the approach of the C=C in the aromatic
furan ring to the surfaces of larger Cu particles [37], retarding
the activation and further transformation of the FFA molecules.
Variations in the Cu particle size would also be expected to
affect the electronic structure and the Cu‐Al interfacial sites of
the Cu‐Al2O3 catalysts, which could also change the catalytic
reactivity [38,39].
Apart from the above Cu size effect, the decreased acidity of
the catalysts with increasing Cu contents (Fig. 4(a)) might also
to some extent reduce the activities and PeD selectivities of the
catalysts with Cu loadings above 20 wt% (Cu size > 2.4 nm).
This possibility is supported by the simultaneous increases in
the surface acidic concentration (Fig. 3(a)) and catalytic per‐
formance (FFA conversion and PeDs selectivity) of the 1 wt%
W‐loaded 30Cu‐Al2O3‐W (Table 2, entry 14) as compared with
the 30Cu‐Al2O3 (Table 2, entry 13). The incorporation of W also
favors the PeDs selectivity of 10Cu‐Al2O3 (Table 2, entry 8),
albeit with a slight decrease in FFA conversion, likely due to the
partial coverage of the active Cu sites by WOx particles. None‐
3.5
3.0
2.5
2.0
1.5
1.0
250
240
230
220
210
200
190
180
170
3.0
(a)
(b)
2.5
2.0
1.5
1.0
0.5
0.0
1.0
1.5
2.0
2.5
3.0
3.5
20
Cu loading (wt%)
2
10
30
5
Cu particle size (nm)
Fig. 4. (a) Cu particle sizes and acidic group concentrations of Cu‐Al2O3 catalysts as functions of Cu loading and (b) TOF as a function of Cu particle
sizes during FFA hydrogenolysis over Cu‐Al2O3 catalysts. Reaction conditions: 40 g 10 wt% FFA in ethanol, 413 K, 6 MPa H2, approximately 20% FFA
conversion.

706
Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
theless, due to the more prevalent acid catalyzed side‐reactions
(as compared with metal catalyzed C–O bond hydrogenolysis),
such as the hydrolysis of FFA to levulinic acid [40], supports
with rather higher acidity (such as the HZSM‐5, Table 2, entry
19) were also not appropriate for FFA hydrogenolysis. Thus, it
is clear that optimal acidity favors the hydrogenolysis of FFA to
PeDs, not higher acidity. It should also be noted that, although
basic supports enhance the transformation of FA/FFA to PeDs,
as discussed above, the surface acidity of the Cu‐Al2O3 is be‐
lieved to have played a more important role in FFA hydrogena‐
tion in the present work. This is because of the much lower
concentrations of basic sites in these catalysts (Fig. 3). This
finding is also supported by the decrease in both FFA conver‐
sion and PeDs selectivity in the case of the 10Cu‐Al2O3 treated
with K2O and having increased basicity (Table 2, entry 9) as
compared with the untreated 10Cu‐Al2O3.
The efficient 10Cu‐Al2O3 catalyst could also be readily recy‐
cled over repeated runs without significant loss in either the
FFA conversion or the PeDs selectivities (Fig. 5). After each run,
the catalyst was easily recovered by centrifugation and re‐
charged into the autoclave together with fresh reactant for the
next run. The FFA conversions gradually decreased from 60.4%
to 47.8% over five cycles, while the selectivities for 1,2‐PeD and
1,5‐PeD underwent only moderate declines, from 48.6% and
22.7% to 41.8% and 18.2%, respectively. Additionally, almost
no leaching of Cu (< 0.5  10–6) could be detected by inductively
couple plasma‐atomic emission spectroscopy (ICP‐AES),
demonstrating the high durability of the catalyst. The slight
decrease in activity and selectivity of the catalyst are thought to
have resulted from the gradual aggregation of Cu particles
during repeated runs, as was evident from the XRD (Fig. 1(b))
and TEM (Fig. 2(d)) characterizations of the used catalyst after
five cycles.
The TOF values increased from 1.25 h–1 at 403 K to a maximum
of 2.35 h–1 at 423 K, and then declined to 2.15 h–1 with further
increase in the temperature up to 433 K. The selectivities for
1,2‐PeD and 1,5‐PeD rose sharply, from 36.5% and 18.0% at
403 K to maximums of 48.9% and 21.9% at 413 K, and then
dropped steadily to 20.0% and 6.1% at 433 K, respectively.
These findings demonstrate that 413 K is the optimal temper‐
ature for the production of PeDs with the highest selectivity
and high reactivity. The selectivities for 2‐MF and 1‐pentanol
also increased almost linearly with increasing temperature. As
2‐MF is a dehydration product of FFA through –CH2OH group
hydrogenolysis [41–43], the increase in the selectivity for this
product with temperature suggests that high temperatures
favor the direct dehydration of FFA. The greater selectivity for
1‐pentanol with increasing temperature is attributed to addi‐
tional hydrogenolysis of the PeD products [9,19]. The selectivi‐
ty for THFA, the total hydrogenation product of FFA, remained
almost constant (5.0% to 6.0%) over the temperature range of
403 to 433 K. The hydrogenolysis of THFA under more severe
conditions (433 K and 8 MPa H2) over 10Cu‐Al2O3 showed no
PeD products, suggesting that THFA is relatively stable under
hydrogenolysis conditions, which is in line with the results of
previous studies [17].
Fig. 7 plots the effect of H2 pressure on the activity and se‐
lectivity during FFA hydrogenolysis over the 10Cu‐Al2O3 cata‐
lyst. The TOF is seen to have steadily risen from 0.16 to 3.41 h–1
with increasing H2 pressure from 1 to 8 MPa. The selectivities
for 1,2‐PeD and 1,5‐PeD also increased monotonically from
19.7% and 7.0% at 1 MPa H2 to 50.2% and 22.5% at 8 MPa H2,
respectively. On the contrary, the selectivity for 2‐MF de‐
creased rapidly, from 31.6% to 7.4%, as the H2 pressure rising
to 8 MPa. These changes in the selectivities for PeDs and 2‐MF
indicate that the formations of these compounds are competi‐
tive reactions and that high pressure favors the hydrogenolysis
of the C–O bond in the furan ring while suppressing the dehy‐
dration of the –OH group in the hydroxymethyl moiety. The
slight decrease in the 1‐pentanol selectivity (from 13.0% to
7.6%) and 2‐pentanol selectivity (from 0.4% to < 0.1%, not
shown) suggests that the further hydrogenolysis of the PeD
products was also to some extent being suppressed by in‐
3.3. Effects of reaction parameters on FFA hydrogenolysis to
1,2‐PeD and 1,5‐PeD
Fig. 6 shows the activity and selectivities of the 10Cu‐Al2O3
catalyst during FFA hydrogenolysis at different reaction tem‐
peratures at approximately 20% FFA conversion and 6 MPa H2.
70
60
50
40
30
20
10
0
80
60
40
20
0
1,2-PeD
1,5-PeD
1-Pentanol
2-MF
50
45
40
35
30
25
20
15
10
5
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
1,2-PeD
1,5-PeD
THFA
0
1
2
3
4
5
400
405
410
415
420
425
430
435
Reaction temperature (K)
Number of use
Fig. 5. Reusability of the 10Cu‐Al2O3 catalyst during FFA hydrogenoly‐
sis. Reaction conditions: 0.20 g Cu, 40 g 10 wt% FFA in ethanol, 413 K,
6.0 MPa H2, 8 h.
Fig. 6. Effect of reaction temperature on FFA hydrogenolysis over the
10Cu‐Al2O3 catalyst. Reaction conditions: 0.03–0.18 g Cu, 40 g 10 wt%
FFA in ethanol, 6 MPa H2, 4 h, approximately 20% conversion.

Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
707
100
4
3
2
1
0
50
1,2-PeD
1,5-PeD
1-Pentanol
2-MF
90
80
70
60
50
40
30
20
10
0
50
40
30
20
10
0
1,2-PeD
1,5-PeD
2-MF
1-Pentanol
THFA
40
30
20
10
0
THFA
0
2
4
6
8
10 12 14 16 18 20 22 24
1
2
3
4
5
6
7
8
Reaction time (h)
H2 pressure (MPa)
Fig. 9. Effect of reaction time during FFA hydrogenolysis over the
10Cu‐Al2O3 catalyst. Reaction conditions: 0.20 g Cu, 40 g 10 wt% FFA in
ethanol, 413 K, 6 MPa H2.
Fig. 7. Effects of H2 pressure on FFA hydrogenolysis over the
10Cu‐Al2O3 catalyst. Reaction conditions: 0.06–0.25 g Cu, 40 g 10 wt%
FFA in ethanol, 413 K, 4 h, approximately 20% conversion.
1,5‐PeD were the major products, and their selectivities in‐
creased to maximums of 48.6% and 22.7% after 8 h, respec‐
tively. The 1,2‐PeD selectivity subsequently underwent a grad‐
ual decrease to 43.8% with increasing time, while the 1,5‐PeD
selectivity essentially plateaued. From these results, it is evi‐
dent that 1,2‐PeD is more prone to excessive hydrogenolysis
compared to 1,5‐PeD, in agreement with previous reports [9].
The continual decrease in 2‐MF selectivities can be attributed
to further hydrogenation to 2‐MTHF (for which the selectivity
increased from 0.2% to 3.3%, not shown) and further C–O hy‐
drogenolysis to 1‐pentanol and 2‐pentanol [16].
creasing H2 pressure.
Fig. 8 summarizes the effects of the active Cu amount on the
conversion and PeDs selectivity during FFA hydrogenolysis.
The FFA conversion increased almost linearly, from 45.3% to
82.6%, as the active Cu amount was raised from 0.10 to 0.40 g.
In contrast, the combined selectivity for 1,2‐PeD and 1,5‐PeD
over the 10Cu‐Al2O3 catalyst was nearly constant at approxi‐
mately 70%, while the value for the material with 0.20 g active
Cu was a bit higher (71.3%). These data reveal that a high cata‐
lyst amount favors the generation of PeDs from FFA hydrogen‐
olysis, which is consistent with previously reported results
[10]. Based on the above findings, 1,2‐PeD (48.1% selectivity)
and 1,5‐PeD (22.2% selectivity) with a combined yield up to
approximately 60% at 85.8% FFA conversion were attained
when using the 10Cu‐Al2O3 with a higher catalyst amount at
413 K, 8 MPa H2 and 8‐h reaction time (Table 2, entry 7).
The effect of reaction time was investigated when using
10Cu‐Al2O3 to elucidate the reaction pathways of FFA hydro‐
genolysis (Fig. 9). The conversion of FFA increased drastically,
to 60.4%, in the first 8 h, and then rose gradually to 87.6% as
the reaction time was extended to 24 h. Both 1,2‐PeD and
Based on the above analytical results and the existing liter‐
ature [17,44,45], we propose the reaction pathways for FFA
hydrogenolysis over a Cu‐Al2O3 bifunctional catalyst shown in
Scheme 1. Initially, the FFA is adsorbed on the Lewis acid sites
of the Al2O3 support via the –OH group [45], analogous to the
adsorption of FFA on the basic sites of hydrotalcite [10,30].
Subsequently, the C2=C3 or C4=C5 bond in the furan ring of FFA
is partially hydrogenated to form semi‐hydrogenated species
[17,44], most likely via hydrogenation of the C2 or C5 atoms.
This induces the ring opening reaction by decreasing the barri‐
er to C–O cleavage [17,37,44]. Finally, the ring‐opened species
are rapidly hydrogenated to the target products 1,2‐PeD or
1,5‐PeD. Because of the steric hindrance of the –CH2OH group,
it is more likely that the active H species on the Cu particles will
partially hydrogenate the C4=C5 bond to form the key interme‐
diate that generates 1,2‐PeD, as opposed to partially hydrogen‐
ating the C2=C3 to eventually produce 1,5‐PeD. Therefore, a
much higher selectivity for 1,2‐PeD is predicted over the Cu
catalysts, which is consistent with previous studies regarding
the hydrogenolysis of FFA over Ru/MnOx [17,44] and
Cu‐Mg3AlO4.5 catalysts [30]. It should be noted that the Lewis
acid sites of the Al2O3 support could also assist in the dehydra‐
tion of the –OH group of FFA to give 2‐MF, which is a major
competitive reaction during the production of PeDs from FFA.
In addition, these Lewis acid sites could also induce secondary
reactions of the PeDs products to 1‐pentanol or 2‐pentanol by
dehydration. Due to the weak affinity of Cu for C=C bonds
[8,37], the complete hydrogenation of FFA to THFA and of 2‐MF
100
80
60
40
20
0
90
80
70
60
50
40
30
20
10
0
1,2-PeD
1,5-PeD
0.1
0.2
0.3
0.4
Active Cu amount (g)
Fig. 8. Effect of the active Cu amount in the 10Cu‐Al2O3 catalyst during
FFA hydrogenolysis. Reaction conditions: 40 g 10 wt% FFA in ethanol,
413 K, 6.0 MPa H2, 8 h.

708
Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
Scheme 1. The proposed reaction paths for FFA hydrogenolysis over a Cu‐Al2O3 bifunctional catalyst.
2011, 133, 12675–12689.
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cidate the reaction pathways and mechanism associated with
PeD generation from FFA over Cu‐based bifunctional catalysts.
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Cu‐Al2O3 bifunctional catalysts with Cu loadings from 2 to
30 wt% were prepared by co‐precipitation and tested in the
hydrogenolysis of biomass‐derived FFA to 1,2‐PeD and
1,5‐PeD. At 413 K and 8 MPa H2, the best catalyst, having 10
wt% Cu content, generated 85.8% conversion and 70.3% com‐
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Hailong Liu et al. / Chinese Journal of Catalysis 37 (2016) 700–710
709
Graphical Abstract
Chin. J. Catal., 2016, 37: 700–710 doi: 10.1016/S1872‐2067(15)61080‐4
Selective hydrogenolysis of biomass‐derived furfuryl alcohol
into 1,2‐ and 1,5‐pentanediol over highly dispersed Cu‐Al2O3
catalysts
Hailong Liu, Zhiwei Huang*, Haixiao Kang, Chungu Xia, Jing Chen*
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences
The size and cooperative effects of highly dispersed Cu nanoparti‐
cles and an acidic Al2O3 support are significant factors affecting the
selective hydrogenolysis of furfuryl alcohol to 1,2‐ and
1,5‐pentanediols over Cu‐Al2O3 catalysts.
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