Cr-free Co-Cu/SBA-15 catalysts for hydrogenation of biomass-derived α-, β-unsaturated aldehyde to alcohol

Article abstract of DOI:10.1016/S1872-2067(15)60870-1

Cr-free bi-metallic SBA-15-supported Co-Cu catalysts were examined in the conversion of biomass-derived α-, β-unsaturated aldehyde (furfural) to value-added chemical furfuryl alcohol (FOL). Co-Cu/SBA-15 catalysts with a fixed Cu loading of 10 wt% and varying Co loadings (2.5, 5, and 10 wt%) were prepared by the impregnation method. The catalysts were characterized by X-ray diffraction, N₂ sorption, H₂ temperature-programmed reduction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, CO chemisorption, and inductively coupled plasma mass spectrometry. The influence of different reaction parameters such as temperature, pressure, catalyst dosage, and furfural concentration on the catalyst performance was evaluated. Relative to catalysts supported on amorphous silica, the current SBA-15-supported Co-Cu catalysts displayed higher performance, attaining a furfural conversion of 99% and furfuryl alcohol selectivity of 80%. The catalytic reactions were conducted in a 100-mL autoclave at 170 °C and 2 MPa H₂ pressure for 4 h.

Full text of DOI:10.1016/S1872-2067(15)60870-1

Chinese Journal of Catalysis 36 (2015) 933–942
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
Cr-free Co–Cu/SBA-15 catalysts for hydrogenation of
biomass-derived α-, β-unsaturated aldehyde to alcohol
Sanjay Srivastava a, Pravakar Mohanty b,c, Jigisha K. Parikha,*, Ajay K. Dalai d, S. S. Amritphale e,
Anup K. Khare e
a Department of Chemical Engineering, S. V. National Institute of Technology, Ichchhanath, SURAT-395 007, Gujarat, India
b Department of Chemical Engineering, Indian Institute of Technology, New Delhi-110016, India
c Sardar Patel Renewable Energy Research Institute (SPRERI), V V Nagar, Gujarat 388120, India
d Catalysis and Chemical Reaction Engineering Laboratories, Department of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon,
Saskatchewan S7N 5A9, Canada
e Advanced Material and Processes Research Institute (AMPRI), Council of Scientific & Industrial Research (CSIR), Bhopal 462064, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Cr-free bi-metallic SBA-15-supported Co–Cu catalysts were examined in the conversion of bio-
mass-derived α-, β-unsaturated aldehyde (furfural) to value-added chemical furfuryl alcohol (FOL).
Co–Cu/SBA-15 catalysts with a fixed Cu loading of 10 wt% and varying Co loadings (2.5, 5, and 10
wt%) were prepared by the impregnation method. The catalysts were characterized by X-ray dif-
fraction, N2 sorption, H2 temperature-programmed reduction, scanning electron microscopy, ener-
gy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, CO chemi-
sorption, and inductively coupled plasma mass spectrometry. The influence of different reaction
parameters such as temperature, pressure, catalyst dosage, and furfural concentration on the cata-
lyst performance was evaluated. Relative to catalysts supported on amorphous silica, the current
SBA-15-supported Co–Cu catalysts displayed higher performance, attaining a furfural conversion of
99% and furfuryl alcohol selectivity of 80%. The catalytic reactions were conducted in a 100-mL
autoclave at 170 °C and 2 MPa H2 pressure for 4 h.
Received 13 January 2015
Accepted 21 April 2015
Published 20 July 2015
Keywords:
Mesoporous catalyst
Cobalt
Copper
SBA-15
Furfural
Furfuryl alcohol
Hydrogenation
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
ered as a promising platform (as a building block) for the pro-
duction of fuel and chemicals. Furfural is mainly produced by
Over the last few decades, interest in using biomass-derived
molecules for conversion into fuels and chemicals has in-
creased considerably owing to major concerns relating to glob-
al warming from anthropogenic emissions of greenhouse gases,
climate change, and depletion of fossil fuel reserves [1]. How-
ever, biomass-derived molecules contain high oxygen contents.
Thus, efficient and environmentally friendly catalysts have
been investigated for selectively tailoring their oxygen content
to achieve the desired products [2]. Furfural has been consid-
triple dehydration of sugar (xylose) in the presence of an acid
catalyst [3–5]. Over the last two decades, the importance of
hydrogenation of furfural (FFR) in the industrial context has
grown because it can be successfully employed to synthesize a
wide range of products such as furfuryl alcohol (FOL), 2-methyl
furan (MF), tetrahydrofurfuryl alcohol (THFOL), tetrahydrofu-
ran, and furan [6]. However, the selective hydrogenation of FFR
to FOL has received the most interest because FOL has diverse
applications such as in the manufacture of thermostatic resins,
* Corresponding author. Tel: +91-261-2251689; E-mail: jk_parikh@yahoo.co.in
DOI: 10.1016/S1872-2067(15)60870-1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 7, July 2015

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Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
installation of acid-resistant bricks, and in anti-corrosion fiber
glasses, resins (liquid) used in galvanic bath tub rubbers, and
farm chemicals. FOL is also used as a non-reactive diluent for
epoxy resin, a modifier for phenolic and urea resins, an oil well,
and a carbon binder [7–12]. Furthermore, the salt of furfuryl
alcohol is used in the synthesis of lysine, vitamin C, lubricants,
and plasticizers.
lyst synthesis [28].
In the present study, Cr-free SBA-15-supported Co–Cu cata-
lysts were prepared with varying loadings of Co (2, 5, and 10
wt%). Co was used as a promoter to Cu metal to enhance the
activity and/or selectivity of the resulting catalysts by increas-
ing the surface area or acting as a weak acid site to polarize the
C=O bond in furfural [34]. The activity and selectivity of the
prepared catalysts were assessed toward the hydrogenation of
furfural. The catalytic performance of the SBA-15-supported
catalysts was compared with that of amorphous sili-
ca-supported catalysts reported in the literature (Table 1).
Furthermore, the effects of different operating parameters,
such as reaction temperature, hydrogen pressure, catalyst
dosage, and furfural concentration, on the catalytic perfor-
mance were studied to optimize the furfural conversion and
furfuryl alcohol selectivity.
Since the last five to six decades, bimetallic Cr–Cu catalysts
have been widely used in the hydrogenation of FFR [13–15].
However, owing to the high toxicity and environmental concern
of Cr–Cu alloys, research has focused on the development of
alternative catalysts displaying higher yields and selectivity
toward the hydrogenation of FFR [16–19]. As potential candi-
dates, Co/Cu/Zn/Zr alloy [7], Raney Ni [20,21], Raney Co
[22,23], Raney Cu [24], and various supported catalysts (Pd–Cu
[25], Ni–Fe [26], Pt–Sn [27], Ni–Cu [28], Co–Cu [28], and Cu–Ca
[29] supported on SiO2, and CoB [30], CoMoB [31], NiMoB, and
NiMo–B [32] supported on Al2O3) have been examined and
applied by various groups of researchers. However, most of the
reported catalysts are relatively expensive and provide moder-
ate product selectivity at high reaction temperatures [28].
Amorphous silica-supported catalysts have also been consid-
ered for application in the hydrogenation of FFR to FOL (Table
1). However, their application is limited by their low FFR con-
version and/or FOL selectivity.
Therefore, the goal of the present study was to develop a
modified set of mesoporous silica-supported bi-metallic cata-
lysts with high surface areas to achieve high conversions and
good selectivity for FOL. SBA-15 is a hydrothermally stable
mesoporous silica material featuring a large surface area and a
highly ordered porous structure with uniform hexagonal
channels with dimensions ranging from 5 to 30 nm [33]. It has
been widely employed as a catalyst support owing to its ad-
vantageous features such as high surface-to-volume ratio and
variable framework compositions. Its large pore size can lower
the diffusion barrier for the reactants and products [33]. Fur-
thermore, the strong interaction between Co and Cu affords
enhanced dispersion and stability of Cu in the bi-metallic cata-
2. Experimental
2.1. Materials
High purity (>99%) chemicals, tetraethyl orthosilicate
(TEOS), pluronic (P123, PEO20PPO70PEO20), Co(NO3)2·6H2O,
Cu(NO3)2·6H2O, HCl (37%), and ethanol, were procured from
Sigma-Aldrich (Mumbai, India), and demineralized water was
used in this study.
2.2. Catalyst preparation
SBA-15 was synthesized as reported by Zhao et al. [33]. In a
typical procedure, 4 g P123 was dissolved in 40 mL distilled
water at 35 ± 1 °C for 2 h, whereby P123 acted as an organic
template. Thereafter, 240 g HCl solution (2 mol/L) was added
at 40 ± 1 °C, followed by the addition of 17.0 g TEOS with stir-
ring. The mixture was stirred for 24 h at 40 ± 1 °C, then aged in
a Teflon-coated polypropylene bottle at 100 ± 2 °C for 24 h. The
final solid product was filtered, washed with deionized water,
dried in the air, and calcined at 550 ± 4 °C under static condi-
tions for 6 h, with a heating rate of 1.8 °C/min to remove the
template agent.
Table 1
Amorphous SiO2-supported catalysts used in the hydrogenation of
furfural.
Bi-metallic Co–Cu/SBA-15 catalysts were prepared by im-
pregnation techniques reported in the literature [35] using salt
solutions of Co(NO3)2·6H2O and Cu(NO3)2·6H2O. The catalysts
were dried for 12 h at 100 ± 2 °C and subsequently calcined at
450 ± 5 °C for 4 h to obtain the Cu–Co oxide catalysts. The
Co–Cu/SBA-15 catalysts (Cu 10 wt%) with 10, 5, and 2.5 wt%
of Co loadings are respectively denoted as CAT-A, CAT-B, and
CAT-C.
Conversion FOL selectivity
Catalyst
t (°C) p (bar)
Ref.
(%)
(%)
16
98
82
96
10
68
19
0.8
21.4
90
99
97
76
10
Pd–Cu/SiO2
Co–Cu-SiO2
Co–Ni-SiO2
Ni–Cu-SiO2
1%Pd/SiO2
10%Cu/SiO2
5%Ni/SiO2
Cu/SiO2 (I)
Cu/SiO2 (PD) 110
Cu–Ca/SiO2
Pt/SiO2
Ni/SiO2
Ru/SiO2
250
200
200
200
230
230
230
110
1
1
1
50
60
10
32
[25]
[28]
[28]
[28]
[53]
[53]
[53]
[13]
[13]
[29]
[52]
[52]
[52]
[26]
1
1
1
1
10
10
1
69
69
100
4.8
66.3
66
2.3. Catalyst characterization
X-ray diffraction (XRD) patterns were obtained on a Philips
PW-1710 X-ray diffractometer (Netherlands), equipped with
Quasar software packages, using Cu Kα radiation produced
from a PW Bragg–Brentano (BB) goniometer (θ/2θ), operating
at 45 kV and 40 mA. The samples were scanned in the ranges of
2θ = 5°–80° and 2θ = 0.5°–10° for wide-angle and small-angle
130
100
100
100
210
10
10
10
1
46
31
15
96
Ni–Fe/SiO2

Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
935
XRD analyses, respectively.
reactor was kept under N2 pressure for the leak test. A known
amount of catalyst was reduced by passing H2 at 260 ± 2 °C.
When the reactor was cooled to room temperature, furfural
and isopropyl alcohol (molar ratio of 0.13) were charged into
the reactor, which was flushed with N2. The reactor was pres-
surized with H2 (20 bar) and the reaction was carried out at
170 ± 1 °C. Each batch process experiment was subjected to
thorough mixing at 1000 r/min [36]. The reproducibility of the
experimental analysis was ensured by repeating each run three
times; the reproducibility was within acceptable limits, thereby
ensuring the absence of gas-liquid, liquid-solid, and intra-parti-
cle mass transfer limitations.
The product samples were analyzed on a Perkin Elmer Cla-
rus 500 GC system equipped with a flame ionization detector. A
Stabilwax capillary column with dimensions of 50 m × 0.25 mm
× 0.5 μm was used. In a typical procedure, the initial oven tem-
perature was maintained at 80 °C for 4 min and increased to
220 °C with a ramp of 20 °C/min, and subsequently maintained
for 4 min. The product suspension (2 μL) in isopropanol was
injected into the capillary column using a split ratio of 20:1 [7],
whereby Ar was used as a carrier gas. The formation of furfuryl
alcohol and other by-products were confirmed by gas chroma-
tography–mass spectrometry. The following equations were
used to determine the furfural conversion (XFFR), product selec-
tivity (S), and yield:
The Brunauer–Emmett–Teller (BET) surface area, pore
volume, and Barrett–Joyner–Halenda (BJH) (meso) pore size
distribution of the prepared catalysts were determined by N2
adsorption-desorption analysis conducted at −196 °C. Prior to
analysis, the catalysts were degassed under vacuum at 200 ± 2
°C on an ASAP 2010 Micromeritics instrument.
The morphology of the catalysts was determined on an xT
Nova NanoLab 200 field-emission scanning electron micro-
scope (FESEM) equipped with an EDX unit. For analysis, the
samples were sonicated in acetone (solvent) to disperse the
sample uniformly. Thereafter, small drops of the sample were
deposited on a carbon holder followed by evacuation under
high vacuum (10–5 Torr). The samples were analyzed with an
average of ten point analysis.
A Philips CM10-1990 transmission electron microscope
(TEM) was used to further assess the morphology of SBA-15
and the prepared catalysts. For analysis, the powder catalyst
material was dispersed in acetone using an ultrasonic bath for
15 min. A droplet of the suspended material was then placed on
copper grids.
SEM-energy dispersive X-ray spectroscopy (SEM-EDX) was
used to obtain rapid, qualitative, and some quantitative analy-
sis of the elemental composition of the catalysts, with a sam-
pling depth of 1–2 μm. The overall elemental molar composi-
tion of the prepared catalysts was confirmed by incluctively
coupled plasma mass spectrometry (ICP-MS). In a typical pro-
cedure, 0.1 g catalyst was dissolved in concentrated HF acid
(48%–51%) at 100–150 °C for 2 d. To ensure complete dissolu-
tion of the metals, concentrated HNO3 was added, and the sam-
ples were examined on a mass spectrometer.
XFFR = (Initial moles of furfural – final moles of furfural)/
initial moles of furfural  100%
S = Moles of desired product/moles of all products  100%
Yield = Conversion (starting material)  selectivity (desired
product)  100%
H2 temperature-programmed reduction (TPR) analysis was
carried out on a Micromeritics Pulse Chemisorption Chemisorb
2720 analyzer. In a typical procedure, 0.5 g catalyst was placed
in a quartz reactor that was introduced into a furnace. The fur-
nace temperature was increased from ambient to 800 °C, with a
heating ramp of 10 °C/min. H2 (9.9%) in Ar was used for reduc-
tion at a flow rate of 30 mL/min. H2 consumption was meas-
ured using a thermal conductivity detector.
A Micromeritics ASAP 2020 Chemisorption system was
used to measure the CO uptake on the oxide catalysts to calcu-
late the metal surface area and dispersion. Prior to the experi-
ment, the sample was subjected to vacuum and backfilled with
He at 35 °C, and then evacuated at 110 °C for 60 min. The sam-
ple was then heated to 350 °C at 10 °C /min in the presence of
H2 and maintained at 350 °C for 2 h. The sample was then
cooled to 35 °C and evacuated until the static pressure was less
than (1.3–10.5) × 10−5 bar. The chemisorption analysis was
performed by passing pulses of CO over the sample to measure
the total CO uptake at 35 °C.
3. Results and discussion
3.1. Synthesis and characterization
The small-angle XRD patterns of the SBA-15 support and
CAT-A, CAT-B, and CAT-C catalysts are shown in Fig. 1. The
spectra displayed well-resolved diffraction peaks at 2θ = 0.6°,
1.5°, and 1.7°, corresponding to (100), (110), and (200) diffrac-
tion planes. These could be indexed to the hexagonal unit cell
reflections of SBA-15 [33], thereby confirming that the meso-
porous structure was preserved following loading of Cu and Co
[37–39]. However, the presence of Cu and Co on the support
led to a decrease in the intensity of the lower angle diffraction
peak (0.6°), which can be related to the scattering effects of the
metallic Cu and Co particles.
Fig. 2 depicts the wide-angle XRD patterns of the SBA-15
support and CAT-A, CAT-B, and CAT-C catalysts. All three cata-
lysts displayed sharp diffraction peaks at 2θ = 35.5° and 38.7°,
corresponding to the planes (111) and (111) of monoclinic
copper oxide (JCPDS 80-1917, 45-0937) [40,41].
2.4. Catalytic activity
This indicates the presence of large metallic crystallites in
the Co–Cu/SBA-15 catalysts. The size of the CuO crystallite was
16–40 nm, as calculated by the Scherrer formula. Furthermore,
the intensity of the diffraction peaks corresponding to the cop-
per oxide crystallites decreased with increasing amounts of
cobalt, owing to the good dispersion of the copper oxide parti-
All reactions were performed at a laboratory scale using
high pressure (SS-316) stirred autoclave of 100 mL capacity,
supplied by Amar Equipment Pvt. Ltd. (Mumbai, India),
equipped with an electrical heating jacket. Prior to reaction, the

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Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
CAT-A
CAT-B
CAT-A (spent)
CAT-C
CAT-A (freshly reduced)
SBA-15
20
30
40
50
2/(o )
60
70
80
1.0
1.5
2.0
2/(o )
2.5
3.0
3.5
Fig. 3. Wide-angle XRD patterns of freshly reduced and spent CAT-A.
Fig. 1. Small-angle XRD patterns of SBA-15, CAT-A, CAT-B, and CAT-C.
600
SBA-15
500
* CuO + CoO
*
*
CAT-A
+
CAT-A
400
CAT-B
300
200
100
CAT-C
0.0
0.2
0.4
0.6
0.8
1.0
SBA-15
60
p/p0
Fig. 4. N2 adsorption-desorption isotherms of SBA-15 and CAT-A.
0
10
20
30
2/(o )
40
50
70
The textural properties of the synthesized catalysts are
summarized in Table 2. The SBA-15 support featured a BET
surface area of 662 m2/g and a total pore volume of 0.71 mL/g.
As observed, the surface area of the bi-metallic catalysts in-
creased with increasing amounts of Co. In contrast, the pore
volume remained unchanged regardless of the Co loading con-
tent. This finding indicated that most of the metal particles
were situated on the surface of SBA-15. These results further
suggested that the loading of Co remarkably enhanced the dis-
persion of Cu and stability of Cu atoms on the support [28].
The N2 adsorption-desorption isotherms of SBA-15 and
CAT-A are presented in Fig. 4. Both samples displayed type IV
isotherms with an H1 hysteresis loop. The shape of the iso-
therm of SBA-15 was preserved even after maximum loading of
Cu and Co, indicating that the structural ordering of the parent
material was preserved following incorporation of the metals.
These results agreed with the small-angle XRD analysis.
Fig. 2. Wide-angle XRD patterns of SBA-15, CAT-A, CAT-B, and CAT-C.
cles. These observations were supported by the BET surface
area results, whereby the BET surface area of the catalysts in-
creased with increasing cobalt loadings (Table 2). A weak dif-
fraction at 2θ = 36.5°, corresponding to CoO, was also noted in
CAT-B and CAT-A, whereby the loading contents of cobalt were
high.
The presence of metallic copper (Cu0) and cobalt (Co0) on
the surfaces of CAT-A (reduced and spent) could be deduced
from the XRD patterns in Fig. 3. The characteristic diffraction
lines of Cu0, i.e., (111), (200), and (220) (fcc structure), were
visible at 2θ = 43.6°, 50.8°, and 74.4°, respectively (JCPDS
04-0836). These findings were consistent with literature re-
ports on Cu/SBA-15 [34]. In contrast, diffraction peaks corre-
sponding to cobalt were absent.
Table 2
Textural and structural characteristics of support and its supported Cu–Co catalysts.
Sample
SBA-15
CAT-A
CAT-B
CAT-C
Cu:Co a (wt%)
—
Cu:Co b (wt%)
—
10.45:10.11
9.15:5.23
8.92:2.12
Cu:Co c (wt%)
—
10.90:9.30
9.46:4.52
9.32:2.04
SBET (m2/g)
661.6
405.5
362.9
342.0
Vp (mL/g)
0.71
0.55
0.53
0.50
Dp (nm)
7.7
5.6
5.4
5.2
dp (nm)
—
42.75
54.45
72.55
10:10
10:5
10:2.5
a Loading ratio used in the synthesis.
b Evaluated by EDX analysis.
c Evaluated by ICP–MS analysis.

Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
937
The results were consistent with those obtained by EDX analy-
sis and the loading contents used in the catalyst synthesis.
H2-TPR was used to determine the reducibility of the sup-
ported catalysts CAT-A, CAT-B, and CAT-C (Fig. 7). The
bi-metallic samples displayed complex H2-TPR profiles corre-
sponding to several reduction steps. The peaks could be as-
signed to the reduction of CoO and CuO to partially reduced
oxide species and ultimately to Cu and Co metal phases, as con-
sistent with the XRD results.
(a)
(b)
Furthermore, the TPR profiles of the catalysts changed sig-
nificantly with Co loading. This behavior may be attributed to
the stepwise reduction of CuO and its level of interaction with
Co. CAT-A, prepared at a Cu-to-Co ratio of 1, displayed a broad
peak with two shoulders at 320–360 °C. In contrast, CAT-B,
prepared at a higher Cu-to-Co ratio of 2, displayed peaks shift-
ed to slightly higher temperatures. Further increasing the
Cu-to-Co ratio to 4 generated three distinct peaks, which could
be attributed to the formation of highly dispersed CuO and CoO
at moderate temperatures and the formation of small Cu–Co
clusters at higher temperatures above 400–440 °C [42,43].
During the TPR analysis, reduction of CuO can either follow
a one-step Cu2+→Cu0 mechanism or proceed through an inter-
mediate Cu+ state. The presence of an intermediate Cu+ state
depends on the conditions employed for the reduction process
such as gas flow rate and temperature ramp. For all three cata-
lysts tested, reduction proceeded via a two-step process be-
cause of the relatively slow ramp rate and gas flow rate select-
ed for the TPR analysis. H2 consumption by both CuO and CoO
may have contributed proportionately to their available weight
proportion to the reduction process as a result of spill-over
effects [44]. Furthermore, Tien-Thao et al. [45] have suggested
that copper provides active sites for higher alcohol synthesis to
activate cobalt reduction and possibly modify cobalt by alloy-
ing. After reduction of the highly dispersed CuO, formation of
small Cu0 occurs in CAT-A (Fig. 3). Xu et al. [46] also reported
that Cu–Co alloy was responsible for higher alcohol synthesis.
Baker et al. [47] and Mohanty et al. [48] proposed that the ac-
tive center comprised metallic Co atoms on Cu clusters and the
active catalyst consisted of Cu particles supported on Co/Cr
spinel.
Fig. 5. FESEM images of SBA-15 (a) and CAT-A (b).
The FESEM images of SBA-15 and CAT-A are shown in Fig. 5.
Large fibrous structures of 20–35 μm in length and 4–5 μm in
diameter were observed for SBA-15. The fibrous structure is an
agglomerate of long fibers that constitute small rod-like
sub-particles [39]. Uniform distributions of the Cu and Co par-
ticles were observed with small agglomeration. To further
evaluate the surface composition of the catalyst sample, EDX
analysis was carried out. The results confirmed the presence of
Co and Cu in appropriate proportions. The corresponding met-
al loadings are shown in Table 2. The results were, within ac-
ceptable errors, in accordance with the loading contents used
in the synthesis process.
TEM analysis of SBA-15 (Fig. 6(a)) confirmed the presence
of hexagonal arrays of uniform channels with a typical honey-
comb morphology. Furthermore, the hexagonal symmetry of
SBA-15 was retained following loading of the metal particles
(Fig. 6(b) and (c)). Based on TEM analysis, the average particle
size was calculated as 12–45 nm (Fig. 6(d)). These results were
consistent with those from the XRD analysis.
The bulk elemental composition of the loaded catalysts was
determined by ICP-MS and the results are shown in Table 2.
(b)
(a)
CAT-A
CAT-B
CAT-C
(c)
(d)
0
100
200
300
Temperature (oC)
Fig. 7. H2-TPR profiles of CAT-A, CAT-B, and CAT-C.
400
500
600
700
Fig. 6. HRTEM images of SBA-15 (a) and CAT-A (b, c). (d) Histogram of
the size distribution of CAT-A particles.

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Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
Table 3
CO chemisorption analysis of the catalysts.
Amount of adsorbed CO
(μmol/g)
Metal dispersion
(%)
Metal surface area
(m2/g of sample)
Metal crystallite size
(nm)
Catalyst
Co (wt%)
CAT-A
CAT-B
CAT-C
10
5
1417.91
1000.74
809.98
1.39
1.14
1.01
1.75
1.32
1.10
42.75
54.45
72.55
2.5
CO chemisorption results of CAT-A, CAT-B, and CAT-C are
presented in Table 3. It could be concluded that dispersion of
Cu increased with increasing loadings of Co. The average metal
crystallite size of CAT-A, as assessed by CO chemisorption, was
42.75 nm, which was consistent with the XRD and TEM results.
The metal crystallite size increased with decreasing Co con-
tents. Furthermore, the amount of CO adsorbed on the catalysts
increased with increasing loadings of Co, thereby indicating
that the dispersion of metallic copper was higher in CAT-A
when compared with that in other catalysts. As observed, in-
creasing the amount of Co increased the dispersion of Cu that is
believed to promote catalyst activity and subsequent FOL se-
lectivity.
alcohol was obtained as the main product with small amounts
of byproducts, MF and cyclopentanol (CPL), in the presence of
the Cu-based bimetallic Co–Cu/SBA-15 catalysts. These results
agreed with the literature reported to date on copper-based
amorphous or supported catalysts [6,7,13,34].
The catalytic activities of the as-prepared supported
bi-metallic Co-Cu/SBA-15 catalysts were evaluated toward the
selective hydrogenation of furfural in liquid phase (Table 4),
and compared with those of amorphous silica-supported cata-
lysts (Table 1). As observed, the current mesoporous sili-
ca-supported bi-metallic Co–Cu catalysts featured favorable
sites to attain higher conversion when compared with the
amorphous silica-supported catalysts. Based on the physio-
chemical characterization and preliminary observations, it
could be confirmed that the high surface area and ordered po-
rous structure of SBA-15 provided a better platform to gener-
ate active sites for the reactants. Furthermore, the presence of
Co, as a promoter, in the current bi-metallic catalyst system
influenced the repartition of copper between easily reducible
and barely reducible copper phases. This phenomenon may be
the reason for the higher dispersion of the metallic sites on the
surface of SBA-15 support and the minimal changes noted in
the uniform hexagonal channels.
However, a significant decrease in the selectivity toward
furfuryl alcohol was observed for the SBA-15-supported cata-
lysts. In combination with the HRTEM analysis, it was observed
that the metal particles were generally randomly distributed in
both the pores and surface of the SBA-15 support that may act
as active sites for the transformation of furfuryl alcohol to MF
and CPL. Villaverde et al. [13] examined different Cr-free
Cu-based catalysts, such as Cu/SiO2, CuZnAl, and CuMgAl, to-
ward the liquid-phase hydrogenation of furfural. Among all
catalyst systems studied, CuMgAl was the most appropriate
catalyst for such a process. In contrast, amorphous sili-
ca-supported catalysts, which contain active sites mostly on
their surface, displayed high selectivity toward furfuryl alcohol.
In the present case, the metal particles that reside in the meso-
3.2. Catalytic studies
All synthesized catalysts were examined in the hydrogena-
tion of furfural in liquid phase using isopropanol as a solvent.
Solvent effects in hydrogenation reactions over heterogeneous
catalysts have been rationalized by correlating reaction rates
and product distributions with solvent polarity and dielectric
constant. The nature of the solvent can influence the kinetics of
competitive hydrogenation reactions of both polar and
non-polar substrates. It was observed that polar solvents en-
hance the adsorption of non-polar reactants, whereas
non-polar solvents enhance the adsorption of polar reactants
[7,27,34]. In the present work, we investigated the effect of
isopropanol in the liquid-phase hydrogenation of furfural. As
reported, this solvent is a suitable medium for the hydrogena-
tion of furfural [7,27]. The stability of isopropanol was studied
by reaction with hydrogen in the presence of CAT-A at 170 °C
and 20 bar. The result showed that isopropanol was stable as it
was fully recovered after 4 h of reaction. Additionally, the hy-
drogenation of furfural under solvent-free conditions was car-
ried out for comparison. The results revealed that in the ab-
sence of isopropanol, a furfural conversion of 40.6% and a fur-
furyl alcohol yield of 62.7% were achieved. In contrast, in the
presence of isopropanol, the conversion was 99% and the fur-
furyl alcohol selectivity was 80% (Table 4).
Table 4
Catalytic performance (conversion XFFR and selectivity S) of the cata-
lysts.
3.2.1. Efficacy of various catalysts
As mentioned previously, the hydrogenation of furfural can
result in several byproducts, such as tetrahydrofurfural,
THFOL, MF, and other C4 products. The formation of the de-
sired product, furfuryl alcohol, can be optimized by selection of
appropriate catalysts and reaction conditions. Cu-based cata-
lysts have been mostly employed for the conversion of furfural,
owing to the preferential interaction of the surface with the
carbonyl group over the furan ring [12]. In this work, furfuryl
Catalyst
Cu/SBA-15
Co/SBA-15
CAT-Aa
CAT-A
XFFR (%)
62.32
37.65
40.64
99.38
87.39
80.46
SFOL (%)
56.68
77.37
62.72
80.12
68.08
62.83
SMF (%)
9.12
8.17
Trace
8.62
7.61
SCPL (%)
—
0.86
—
10.12
9.64
8.62
CAT-B
CAT-C
6.20
Reaction conditions: 170 °C, 20 bar, furfural-to-isopropanol molar ratio
1:7, catalyst 1 g, 4 h. a In the absence of isopropanol.

Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
939
100
80
60
40
20
0
pores of SBA-15 act as active sites for the formation of inter-
mediate furfuryl alcohol, thereby allowing the formation of
byproducts such as MF, owing to restricted access.
To determine the role of individual and combined effects of
Cu and Co in the liquid-phase hydrogenation of furfural, sepa-
rate reactions were performed using either Cu or Co supported
on SBA-15. As observed, both Cu and Co supported on SBA-15
displayed low conversions of furfural of nearly 62.3% and
37.6%, respectively, with moderate selectivity of FOL. In con-
trast, by introducing cobalt as a co-metal, the activity of the
resulting bi-metallic catalysts increased (Table 4). Both the
conversion and furfuryl alcohol selectivity increased with in-
creasing Co loading; CAT-A (Cu, Co 10 wt%) displayed the
highest conversion and selectivity values. This result can be
attributed to the higher dispersion of the Cu active sites, as
influenced by the presence of Co. In combination with the N2
sorption and CO chemisorption analyses, it could be deduced
that Co enhanced the dispersion of Cu; CAT-A displayed the
highest surface area and metal dispersion. Additionally, based
on the XRD analysis of reduced CAT-A (fresh and spent), only
metallic Cu was present, which suggested that in the presence
of Co, Cu was completely reduced. Thus, metallic Cu was re-
sponsible for the excellent catalytic behavior of the
Co–Cu/SBA-15 catalysts. Furthermore, the TPR results indi-
cated that reduction of CuO either followed the Cu2+→Cu0
mechanism or proceeded through an intermediate Cu+ state.
Hence, it could be deduced that Co played an important role in
the reduction of Cu. CAT-C and CAT-B (low Co contents of 2.5
and 5 wt%, respectively) displayed two broad peaks that sug-
gested the presence of Cu+ and Cu0. The concentration of Cu0
increased with increasing loading amounts of Co, as indicated
by the increased intensity of the secondary peaks. In contrast,
reduction seemed to follow a Cu2+→Cu0 mechanism in the
presence of CAT-A (higher Co content of 10 wt%), as consistent
with the XRD analysis. It has been reported that in Co–Cu bi-
metallic catalyst systems, under O2 conditions, both metals
oxidize and Cu segregates from the surface as Cu+. In contrast,
under H2 conditions, Co is reduced and Cu is fully reduced on
the surface to Cu0 [49]. In addition, Nagaraja et al. [50] pro-
posed that the presence of more Cu0 and Cu+, as opposed to
CuO, promoted high selectivity of furfuryl alcohol. Var-
gas-Hernandez et al. [34] reported a furfural conversion of 54%
and FOL selectivity above 95% in the presence of 15 wt% Cu
supported on SBA-15 at 170 °C. The high FOL selectivity was
due to the presence of the more stable Cu0 (Table 1). In this
work, Co enhanced the dispersion of Cu particles and hence
improved the overall conversion at a relatively low copper
content of 10 wt%.
XFFR
SFOL
SMF
SCPL
150
160
170
180
190
Temperature (oC)
Fig. 8. Effect of temperature on the conversion of furfural to furfuryl
alcohol using CAT-A. Reaction conditions: 20 bar, catalyst 1 g, 4 h, fur-
fural-to-isopropanol molar ratio 1:7.
further increases in temperature. Furthermore, the selectivity
of MF increased at the expense of furfuryl alcohol. The substan-
tial decrease in the selectivity of furfuryl alcohol may be at-
tributed to further hydrogenolysis of FOL to MF at high tem-
peratures that promotes C–O hydrogenolysis toward the
cleavage of the carbonyl group. It is noteworthy that hydro-
genation of furfural to FOL is dominant at low temperatures,
whereas C–O hydrogenolysis is dominant at high temperatures
owing to the higher activation of the latter process. Further-
more, the polymerization of FOL, owing to its adsorption onto
the catalyst surface, is favored at high temperatures. These
results agreed with literature reports [25,37,51]. Thus, a reac-
tion temperature of 170 °C was employed in the subsequent
experiments.
3.2.2.2. Effect of pressure
To optimize the H2 pressure parameters, XFFR and SFOL were
investigated in the presence of CAT-A at 170 °C and varying
pressures of 10–40 bar. As observed, both the conversion and
selectivity increased with increasing pressures up to 20 bar,
after which no significant changes were noted (Fig. 9).
100
80
60
XFFR
SFOL
SMF
SCPL
40
20
0
3.2.2. Optimization study
3.2.2.1. Effect of temperature
To examine the influence of temperature on the conversion
of FFR (XFFR) and selectivity of FOL (SFOL), reactions were per-
formed in the presence of CAT-A at varying temperatures
within a range of 150–190 °C at a H2 pressure (PH2) of 20 bar.
As observed from Fig. 8, both XFFR and SFOL increased with
increasing temperatures up to 170 °C, then decreased with
10
15
20
25
30
35
40
Pressure (bar)
Fig. 9. Effect of H2 pressure on the conversion of furfural to furfuryl
alcohol using CAT-A. Reaction conditions: 170 °C, catalyst 1 g, 4 h, fur-
fural-to-isopropanol molar ratio 1:7.

940
Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
100
80
60
40
20
0
Table 5
Catalytic cyclic performance of CAT-A toward hydrogenation of furfural.
Catalyst
XFFR (%)
99.38
95.46
SFOL (%)
80.12
79.48
SMF (%)
8.62
8.46
SCPL (%)
10.12
9.65
CAT-A (fresh)
CAT-A (1st cycle)
CAT-A (2nd cycle)
Reaction conditions: 170 °C, 20 bar, furfural-to-isopropanol molar ratio
1:7, catalyst 1 g, 4 h.
94.26
79.24
8.82
9.78
XFFR
SFOL
SMF
SCPL
3.2.2.4. Effect of furfural-to-solvent molar ratio
The furfural-to-solvent ratio was varied from 1:3 to 1:9 to
examine its effect on the catalytic process in the presence of
CAT-A (Fig. 11). As observed, both XFFR and SFOL decreased with
increasing furfural concentrations owing to the availability of
fewer active sites to convert furfural to furfuryl alcohol. This
finding revealed that higher yields could be obtained at low
furfural concentrations (i.e., high molar ratios). Moreover, high
furfural concentrations are often detrimental to the stability of
active sites on the catalyst surface, thereby reducing the rate of
hydrogenation. As reported, high furfural concentrations in
liquid-phase hydrogenation of furfural do not favor overall
conversion or selectivity of the desired products [13]. Accord-
ingly, a molar ratio of 1:7 was employed in the subsequent
studies.
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Catalyst loading (g)
Fig. 10. Effect of catalyst dose on the conversion of furfural to furfuryl
alcohol using CAT-A. Reaction conditions: 20 bar, 170 °C, 4 h, furfu-
ral-to-isopropanol molar ratio 1:7.
These observations were in agreement with the justifica-
tions as reported by Sharma et al. [7]. By increasing the pres-
sure to 20 bar, the rate of reaction and conversion of furfural to
furfuryl alcohol increased owing to the enhanced hydrogen
solubility in the reaction mixture. At pressures above 20 bar,
steady state conditions were attained. Therefore, a hydrogen
pressure of 20 bar was chosen for the subsequent experiments.
3.2.3. Stability of catalyst in the hydrogenation of furfural
CAT-A catalyst that exhibited the best catalytic efficiency
was recycled twice to evaluate its stability. Owing to possible
carbon deposits from the organic reactants or products on the
surface of the catalyst during the catalytic reactions, a reaction
temperature of 500 °C was used for calcination to remove po-
tentially adsorbed or deposited carbon species. XRD was em-
ployed to monitor structural changes in the spent and the
freshly reduced catalysts. The XRD patterns are shown in Fig. 3.
As expected, similarly to the freshly reduced CAT-A, most sta-
ble Cu0 species were detected in the spent CAT-A catalyst, as
indicated by the diffraction peaks at 2θ = 43.6°, 50.8°, and
74.4°, which were respectively indexed as (111), (200), and
(220) (fcc structure) [14]. The catalytic cyclic performance of
CAT-A is presented in Table 5. A slight decrease in the conver-
sion of FFR (nearly 5%) was observed. However, no changes in
the selectivity of the desired product (FOL) were observed.
Hence, the catalyst was stable for liquid-phase hydrogenation
of furfural.
3.2.2.3. Effect of catalyst dosage
The influence of catalyst dosage was investigated by in-
creasing the catalyst weight from 0.5 to 2.0 g (Fig. 10). As ob-
served, XFFR and SFOL increased with increasing catalyst dosages
owing to the availability of more active sites. The highest con-
version and selectivity were observed using 1 g of catalyst.
Further increases in the catalyst dosage resulted in minimal
changes. However, using higher catalyst dosages of 1.5 and
2.0 g resulted in faster reactions when compared with the reac-
tion rate obtained in the presence of 1.0 g catalyst. Accordingly,
a catalyst dosage of 1.0 g was considered in the subsequent
studies.
100
80
60
4. Conclusions
XFFR
SFOL
SMF
A series of bi-metallic Co–Cu catalysts supported on SBA-15,
with a fixed Cu loading and varying Co loadings, were synthe-
sized by the impregnation method. These catalysts were ex-
amined in the hydrogenation of furfural and compared with
amorphous silica-supported catalyst counterparts. The results
showed that the SBA-15-supported catalysts achieved higher
conversions with considerable improvements in the selectivity
of furfuryl alcohol when compared with literature-reported
catalysts supported on amorphous silica. Furthermore, it was
concluded that the selective structure of the mesoporous silica
40
SCPL
20
0
1:3
1:5
1:7
1:9
Furfural-to-isopropanol molar ratio
Fig. 11. Effect of furfural-to-isopropanol molar ratio on the conversion
of furfural to furfuryl alcohol using CAT-A. Reaction conditions: 20 bar,
170 °C, 4 h, catalyst 1 g.

Sanjay Srivastava et al. / Chinese Journal of Catalysis 36 (2015) 933–942
941
Graphical Abstract
Chin. J. Catal., 2015, 36: 933–942 doi: 10.1016/S1872-2067(15)60870-1
Cr-free Co–Cu/SBA-15 catalysts for hydrogenation of
biomass-derived α-, β-unsaturated aldehyde to alcohol
Sanjay Srivastava, Pravakar Mohanty, Jigisha K. Parikh *,
Ajay K. Dalai, S. S. Amritphale, Anup K. Khare
S. V. National Institute of Technology, India;
Indian Institute of Technology, India;
Sardar Patel Renewable Energy Research Institute (SPRERI), India;
University of Saskatchewan, Saskatoon, Saskatchewan, Canada;
Council of Scientific & Industrial Research (CSIR), India
Hydrogenation, 170 °C, 20 bar
100
80
60
40
20
0
FFR
FOL
MF
This work presents the hydrogenation of furfural in liquid phase,
as a direct step for bio-oil upgradation, using bi-metallic Co–Cu
catalysts supported on SBA-15 (Cu 10 wt%; Co 2.5, 5, 10 wt%).
CPL
150
160
170
180
190
Temperature ( oC)
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network favored C–O hydrogenolysis and furan ring arrange-
ment, generating 2-methyl furan and cyclopentanol. The pres-
ence of Co played an important role as a promoter in the hy-
drogenation activity by improving the dispersion of the Cu ac-
tive sites. Co–Cu/SBA-15 (Cu 10 wt%, Co 10 wt%) attained a
conversion of 99% and furfuryl alcohol selectivity of 80% at
170 °C, 20 bar H2 pressure, using a catalyst dosage of 1 g and
furfural-to-isopropanol molar ratio of 1:7.
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