Selective hydrogenolysis of glycerol to 1,2-propanediol over bimetallic Cu-Ni catalysts supported on γ-Al2O3

Article abstract of DOI:10.5935/0103-5053.20150123

A series of Cu or Ni monometallic and Cu-Ni bimetallic catalysts supported on γ-Al₂O₃ were synthesized by incipient wetness impregnation method. X-ray diffraction results exhibited the formation of bimetallic Cu-Ni phase in the reduced Cu-Ni(1:1)/γ-Al₂O₃ catalyst. Among the catalyst examined for hydrogenolysis of glycerol, bimetallic catalysts exhibited higher catalytic activity than monometallic catalysts due to synergetic effect of Cu-Ni bimetal. Cu-Ni(1:1)/γ-Al₂O₃ catalyst displayed a maximum glycerol conversion of 71.6percent with 92.8percent selectivity to 1,2-propanediol at 210 °C and 4.5 MPa hydrogen pressure. The superior performance of Cu-Ni(1:1)/γ-Al₂O₃ catalyst was attributed to the formation of bimetallic Cu-Ni phase, high active metal surface area, small Cu-Ni particle size, and high acidic strength of the catalyst. Stability and reusability of Cu.Ni(1:1)/γ-Al₂O₃ catalyst was performed and detailed characterization results of fresh and used catalysts suggested that bimetallic Cu-Ni phase remained stable after reuses.

Full text of DOI:10.5935/0103-5053.20150123

http://dx.doi.org/10.5935/0103-5053.20150123
J. Braz. Chem. Soc., Vol. 26, No. 8, 1551-1564, 2015.
Printed in Brazil - ©2015 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Article
A
Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni
Catalysts Supported on γ-Al2O3
Satyanarayana M. Pudi,a Prakash Biswas,*,a Shashi Kumara and Biswajit Sarkarb
aDepartment of Chemical Engineering, Indian Institute of Technology Roorkee,
247667 Roorkee, Uttarakhand, India
bDepartment of Chemical Engineering, University at Buffalo,
The State University of New York (SUNY), 14260-4200 Buffalo-NY, USA
A series of Cu or Ni monometallic and Cu-Ni bimetallic catalysts supported on γ-Al2O3 were
synthesized by incipient wetness impregnation method. X-ray diffraction results exhibited the
formation of bimetallic Cu-Ni phase in the reduced Cu-Ni(1:1)/γ-Al2O3 catalyst.Among the catalyst
examined for hydrogenolysis of glycerol, bimetallic catalysts exhibited higher catalytic activity
than monometallic catalysts due to synergetic effect of Cu-Ni bimetal. Cu-Ni(1:1)/γ-Al2O3 catalyst
displayed a maximum glycerol conversion of 71.6% with 92.8% selectivity to 1,2-propanediol
at 210 °C and 4.5 MPa hydrogen pressure. The superior performance of Cu-Ni(1:1)/γ-Al2O3
catalyst was attributed to the formation of bimetallic Cu-Ni phase, high active metal surface area,
small Cu-Ni particle size, and high acidic strength of the catalyst. Stability and reusability of
Cu-Ni(1:1)/γ-Al2O3 catalyst was performed and detailed characterization results of fresh and used
catalysts suggested that bimetallic Cu-Ni phase remained stable after reuses.
Keywords: glycerol hydrogenolysis, Cu-Ni bimetallic catalysts, 1,2-propanediol, catalyst
stability
Introduction
glycerol to 1,2-propanediol (1,2-PDO) and 1,3-PDO is
an attractive and innovative pathway.5 1,2-PDO is a major
commodity chemical used as raw material for unsaturated
polyster resins, food additives, functional fluids (antifreeze,
de-icing and heat transfer), paints, animal feed, cosmetics
and pharmaceuticals.6-8 Other promising chemicals such as
1,3-PDO, ethylene glycol (EG), hydroxyacetone (acetol),
1-propanol (1-PO), 2-propanol (2-PO) produced by
hydrogenolysis of glycerol also have significant industrial
importance.
Various noble metal (Pt, Ru, Pd, Rh, Ir and Re) and non-
noble metal (Cu, Ni, Zn, Al, Fe, Mg, Si and Co) catalysts
have been attempted for this reaction. Noble metal catalysts
propagate the cleavage of both C−C and C−O bonds of
glycerol leading to formation of degradation products.9-16
Copper based catalysts such as Cu/Al2O3,6,9,17,18 Cu-Cr,8,19
Cu/ZnO,13 Cu-Zn-Cr-Zr,20 Cu containing bimetallic
catalysts,21 Cu/SiO2,1,22-24 Cu/MgO25 and Cu/layered double
oxides26,27 exhibited superior performance in terms of high
selectivity to 1,2-PDO, which was attributed to higher
efficiency for C−O breaking in the presence of hydrogen.20
Even though Cu-based catalysts exhibits high selectivity
toward 1,2-PDO, their activity and stability requires to be
Recently, biodiesel has received considerable attention
due to scarcity of fossil fuel reserves and global warming
problems. Worldwide production of biodiesel is estimated
to reach 1.2 billion tons by 2016, with an annual growth
rate of nearly 42%.1,2 The Indian national biofuel policy
proposed a target of 20% biofuel blending (both bio-ethanol
and biodiesel) with conventional fuels by 2017.3 Glycerol is
produced in surplus amounts (10 wt.%) as by-product in the
production of biodiesel via transesterification of vegetable
oils and fats.4 Transformation of glycerol into value-added
products is essential to improve the economic viability of
biodiesel industry and biofuel supply chain. Crude glycerol
can be utilized as a feed stock for the production of green
chemicals. In recent years, various glycerol conversion
process such as hydrogenolysis to propanediols, selective
oxidation to dihydroxyacetone, etherification to fuel
oxygenates, reforming to syn-gas and fermentation to
1,3-propanediol (1,3-PDO), etc. have been attempted.4
Among these processes, selective hydrogenolysis of
*e-mail: prakashbiswas@gmail.com; prakbfch@iitr.ernet.in

1552
Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni Catalysts Supported on γ-Al2O3
J. Braz. Chem. Soc.
improved. Nickel based catalysts have also been studied for
this reaction. Ni/NaX,28 Ni/γ-Al2O3,29,30 and Ni-Ce/SBA-1531
catalysts have been reported as active at 150-220 °C and
1-9 MPa hydrogen pressure. Advantages associated with
the use of Ni catalysts remain in their ability to promote
hydrogenation-dehydrogenation reaction, which is required
for obtaining important intermediate products such as
acetol. However, in comparison to noble metals, Ni-based
catalysts has disadvantage due to their low stability because
of carbon deposition that blocks the active sites and catalyst
pores.32
as reaction temperature, reaction pressure, reaction time,
glycerol concentration, and metal loading are investigated to
maximize the glycerol conversion and 1,2-PDO selectivity.
Finally, the stability/reusability of the catalysts was
investigated and the result obtained is discussed in support
of characterization results of fresh and used catalysts.
Experimental
Materials
Cu-Ru on various supports,16 Cu-X (X = Ag,Zn,Cr),21
bimetallic catalysts for hydrogenolysis of glycerol have
been reported. They suggested that bimetallic catalysts
improve the catalytic activity and product selectivity due
to their synergetic and bifunctional effects. Recently,
Cu-Ni bimetallic catalysts have been established as
effective catalysts for industrially important reactions
such as steam reforming of ethanol,33 water-gas shift
reaction,34 decomposition of methane,35 pyrolysis of
oils,36 and hydrogenation of organic functional groups.37
Gandarias et al.38,39 studied glycerol hydrogenolysis over
Cu-Ni/Al2O3 catalysts with 2-propanol and formic acid as
hydrogen donor molecules. Maximum glycerol conversion
of 70.5% with 70% selectivity to 1,2-PDO has been
reported at 4.5 MPa H2 pressure. Significant selectivity
(30%) to degradation products indicated C−C bond
cleavage over the Cu and Ni sites of the reduced catalysts.
Selective conversion of glycerol into propanediols requires
a suitable catalyst with bi-functional acid sites/metal
surface, favouring the cleavage of the glycerol C−O bonds
(dehydration/hydrogenation) by hydrogen and eliminating
C−C bond scission.9
Further development of catalysts which can provide
higher glycerol conversion and propanediol selectivity are
necessary to ensure successful development of industrial
process for hydrogenolysis of glycerol. It is important to
design highly stable, active and selective catalyst to perform
the reaction at low hydrogen pressure and temperature. It
requires catalysts both for dehydration and hydrogenation
functionality. Therefore, development of catalysts having
dual active site may be a good alternative.
In this work, we have synthesized Cu, Ni monometallic
and Cu-Ni bimetallic catalysts supported on γ-Al2O3 and
investigated their performance for selective conversion of
glycerol to 1,2-PDO. The effect of the Cu/Ni weight ratio
on the physicochemical characteristics of the catalysts
as well as the performance is evaluated. In addition, the
role of bimetallic Cu-Ni formation and its bifunctional
behavior for hydrogenolysis reaction has been demonstrated.
Furthermore, effect of various reaction parameters such
Cu(NO3)2.3H2O (> 99%, Himedia Chemicals, India),
Ni(NO3)2.6H2O (> 99%, Merck Specialities, India) were
used as metal precursors and γ-Al2O3 (> 99.5%, Merck
specialities, India) was used as catalyst support. The standard
chemicals such as glycerol (> 99%, Merck Specialities,
India), 1,2-PDO (> 99%, Merck Specialities, India), 1,3-
PDO (98%, Sigma Aldrich, Germany) and acetol (95%,
Alfa Aesar) were used as feed and product calibration,
respectively. The ultra high pure hydrogen (99.99%) and
nitrogen (99.99%) were supplied by Sigma gases, India and
used directly without any further purification.
Catalyst preparation
A series of Cu, Ni monometallic and bimetallic
catalysts supported on γ-Al2O3 with a nominal metal
loading of 20 wt.% were synthesized by conventional
wetness impregnation method. Three different weight
ratios of Cu to Ni viz. 3, 1 and 0.33 were selected for the
synthesis of bimetallic catalysts. A calculated amount
of metal precursors Cu(NO3)2.3H2O and Ni(NO3)2.6H2O
were dissolved in Millipore water. γ-Al2O3 support was
added to this metal precursor solution under stirring. The
slurry obtained was aged for 24 h at room temperature and
then dried in an oven for 12 h at 110 °C, and subsequently
calcined at 400 °C in the air for 4 h.
Catalyst characterization
N2 adsorption-desorption isotherms measurements were
performed at −196 °C using a Micromeritics Accelerated
SurfaceArea and Porosimetry (ASAP-2020) system. Prior to
the analysis, samples were degassed at 300 °C for 6 h under
vacuum. The surface area of all the samples were analysed
employing the multipoint BET method by using adsorption
data at the relative pressure (P/Po) range of 0.05-0.3. Pore
size distributions were determined by using the BJH-Halsey-
Fass correction method considering the desorption branch.
CO chemisorption experiments of the catalyst samples
were conducted at 40 °C using a MicromeriticsASAP 2020

Vol. 26, No. 8, 2015
Pudi et al.
1553
instrument. Prior to the chemisorption analysis, the catalyst
samples were degassed under vacuum for 5 h at 250 °C to
remove chemisorbed gases and moisture present, if any.
Catalyst samples of approximately 250 mg were evacuated
at 120 °C under the flow of helium for 45 min before being
reduced at 350 °C in a hydrogen flow for 90 min. After
cooling the sample under vacuum to 40 °C, the adsorption
isotherms were recorded.
X-ray diffraction (XRD) patterns were recorded with
a Bruker AXS D8 Advance diffractometer equipped with
Cu-Kα radiation source (λ = 0.154 nm). All the data were
recorded at the 2q interval of 10-80° with a steep of 0.02° s−1
and a time constant of 3s.
were collected using Quanta scanning electron microscope
(Model 200 FEG, USA) equipped with energy dispersive
X-ray spectra (EDX). Catalyst sample was dispersed
uniformly on the sample holders and coated with gold using
sputter coater (Edwards S150) and then SEM images were
taken at an acceleration voltage of 20 kV under vacuum.
The particle sizes of the fresh and spent catalysts were
recorded by transmission electron microscope (TEM)
(Tecnai G2 20 S-Twin, FEI Netherlands). The samples were
dispersed by a sonicator in ethanol before placing them on
carbon coated copper grid.
Catalytic reaction
Temperature programmed reduction (TPR) was
performed to determine the reduction behavior of
catalysts. The experiments were performed on the
Micromeritics Pulse Chemsorb 2720 equipment. Typically,
25 mg of catalyst sample was dried at 120 °C overnight
in an oven prior to TPR experiment. The dried catalyst
sample was placed in a U-shaped quartz reactor and further
pre-treated at 150 °C for 2 h under the nitrogen flow
(30 cc min−1), followed by cooling at room temperature.
After pre-treatment, the temperature was raised from room
temperature to 850 °C at a rate of 10 °C min−1 in a 10%
H2/Ar flow (20 cc min−1). A thermal conductivity detector
(TCD) was employed to determine the amount of hydrogen
consumed.
NH3-temperature programmed desorption (NH3-TPD)
was carried out on a Micromeritics Pulse Chemsorb 2720
instrument equipped with TCD. Typically, 80 mg of reduced
catalyst sample was dried at 120 °C overnight in an oven
prior to TPD experiment. The catalyst sample was further
degassed under stream of helium(20 cc min−1) at 150 °C for
2 h then cooled to room temperature. Further, sample was
saturated with NH3 by flowing 27% NH3/He gas mixture
(30 cc min−1) for 1 h. After being purged helium for 1 h
to remove the physically absorbed ammonia, the sample
was heated from 30 to 800 °C at a heating rate of 15 °C
min−1 and the NH3 desorption was monitored with a TCD.
Total Cu and Ni metal contents in fresh and used
catalysts were determined by inductive coupled plasma-
mass spectrometer (ICP-MS). Approximately 20 mg of
catalyst and 2 mL of aqua regia (0.5 mL of nitric acid
and 1.5 mL of hydrochloric acid) were placed in a 15 mL
glass vial fitted with a teflon lined cap digested in an oven
at 140 °C for 30 min. Then the samples were prepared by
dilution with Millipore water to required concentrations
(< 1 ppm). Perkin-Elmer Elan DRC-e ICP-MS was used
for the elemental detection.
Hydrogenolysis of glycerol was carried out in a 250 mL
teflon lined stainless steel autoclave reactor (Model No.
2000, Amar equipments) equipped with an electronic
temperature controller, a mechanical stirrer and a liquid
sampling port. Prior to each test, the catalyst was reduced in
a separate tubular reactor unit in a stream of pure hydrogen
(50 cc min−1) for 3 h at a temperature corresponding to
the reduction temperature obtained from the TPR study
of each catalyst. Initially, the autoclave reactor was fed
with 100 mL of aqueous glycerol (20 wt.%) along with
calculated amount of catalyst and then purged with
hydrogenfor three times. The reactor temperature was set at
210 °C and pressurized the reactor vessel with hydrogen up
to 4.5 MPa. The stirring speed was set constant at 700 rpm
and the product sample was collected after 12 h of reaction
for analysis. The stability of the catalyst was explored in
repeated experiments in order to test their reusability.
The reactant and products were analysed by gas
chromatograph (GC 6800, Newchrom Technologies)
equipped with flame ionization detector (FID) and a
Chromosorb-101 packed column (1.52 m × 3.1 mm OD ×
2 mm ID). The liquid products were centrifuged (Heraeus
Biofuge Stratos, Thermo Scientific) to separate any catalyst
particles present prior to GC analysis. For calculating
the selectivity of the products, n-butanol was used as an
internal standard. The results reported in this study are
reproduced by repeating the experiments three times and
carbon balance was 100 3.5%.
The glycerol conversion, product selectivity and yield
are defined as follows:
Moles of glycerol converted
Conversion (%) =
× 100
(1)
× 100 (2)
(3)
Total moles of glycerol in feed
Moles of carbon in speci c product
Total carbon moles in all liquid products
Conversion (%) × Selectivity (%)
Selectivity(%) =
To explore the morphology and composition of the
catalysts, scanning electron microscopy (SEM) images
Yield (%) =
100

1554
Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni Catalysts Supported on γ-Al2O3
J. Braz. Chem. Soc.
Results and Discussion
range of 0.12-0.15 cm3 g−1, which is lower than γ-Al2O3
(0.20 cm3 g−1). Pore volume of catalysts is decreased due
to the structural collapse of precursors during calcination
of the catalyst after metal impregnation.42 Measured pore
diameter of all catalysts is in the range of 55-59 Å.
The metal dispersion values of the catalysts obtained
from CO chemisorption follow the order: Ni/γ-Al2O3 >
Cu-Ni/γ-Al2O3 > Cu/γ-Al2O3 suggests that the size of Cu
is higher than Cu-Ni and Ni size (Table 1). Therefore, the
bigger Cu particles could block the pores of the Al2O3
structure and reduce the surface accessible for adsorption.38
The metallic surface area (Sm) of the catalysts obtained from
CO chemisorption analysis is in the range of 2.5-10.8 m2 g−1
sample (Table 1).
Catalyst characterization
Nitrogen adsorption-desorption isotherms of
Cu-Ni/γ-Al2O3 catalysts with different copper to nickel
metal weight ratios are shown in Figure 1. Typical type-IV
isotherms with a pronounced hysteresis loop type H2 with
a steep incline at a relative pressure of 0.50 < P/Po < 0.90
are observed. This result represents a typical mesoporous
nature of catalysts.40,41
Al O
Cu/Al O
2
3
2
3
Cu-Ni (3:1)/Al O
2
Cu-Ni (1:1)/Al O
3
2
3
Cu-Ni (1:3)/Al O
2
Ni/Al O
3
2 3
The XRD patterns were recorded in order to identify the
crystalline phase and crystal structure of catalysts. Figure 2
shows XRD patterns of calcined Cu/γ-Al2O3, Ni/γ-Al2O3
and Cu-Ni/γ-Al2O3 catalysts, respectively.
*
*
Desorption curve
Adsorption curve
CuO
Cu Ni Al O
*
x
1-x
2
4
Al O
NiO
2
3
32
33
34
35
36
37
38
39
40
41
2θ / degree
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Ni/γ−Al O
2
3
Relative pressure / (P/P )
o
Cu-Ni (1:3)/γ−Al O
2
3
Figure 1. Nitrogen adsorption-desorption isotherms of Cu/γ-Al2O3,
Ni/γ-Al2O3 and Cu-Ni/γ-Al2O3 catalysts.
Cu-Ni (1:1)/γ−Al O
* *
2
3
Cu-Ni (3:1)/γ−Al O
2
3
*
*
For all the catalysts, textural properties such as BET
surface area (SBET), cumulative pore volume (VP) and
average pore diameter (Dp) data obtained is shown in
Table 1. The surface area of γ-Al2O3 is 107 m2 g−1, whereas
for metal doped catalysts, surface area values are in the
range of 67-78 m2 g−1. The surface areas of the catalysts
decrease nearly about 25-35% after metal impregnation.
The reduction of surface area in mesoporous supported
catalysts is more pronounced as reported earlier.23
Pore volume of all the catalysts is found to be in the
Cu/γ−Al O
*
2
3
*
10
20
30
40
50
60
70
80
2θ / degree
Figure 2. XRD patterns of calcined Cu/γ-Al2O3, Ni/γ-Al2O3 and
Cu-Ni/γ-Al2O3 catalysts with 20 wt.% metal loading at different
Cu/Ni metal ratio. Diffraction patterns in the angles between 32° and
42° (inset).
XRD pattern of Cu/γ-Al2O3 catalyst shows the
diffraction peaks at 2q = 35.5°, 38.7°, 48.6° and 61.5°,
Table 1. Textural properties of catalysts and support
Metal loadinga / wt.%
b
SBET
/
Vpb
/
COirr uptake /
(µmol g−1)
Metal dispersion,c Metallic surface area,c
Catalyst
Dpb / Å
(m2 g−1)
(cm3 g−1)
D / %
Sm / (m2 g−1 sample)
Cu
−
Ni
−
γ-Al2O3
107
77
67
78
69
71
0.20
0.15
0.13
0.15
0.12
0.12
57
59
57
56
55
55
−
−
−
Cu/γ-Al2O3
19.8
14.2
7.4
5.4
−
−
62.0
96.0
112.0
97.7
348.0
1.9
2.5
3.3
2.6
8.1
2.5
3.3
4.3
3.5
10.8
Cu-Ni(3:1)/γ-Al2O3
Cu-Ni(1:1)/γ-Al2O3
Cu-Ni(1:3)/γ-Al2O3
Ni/γ-Al2O3
8.3
11.7
16.3
16.8
aData obtained from SEM-EDX results; bdata obtained from BET adsorption-desorption isotherms; cdata obtained from CO chemisorption analysis.

Vol. 26, No. 8, 2015
Pudi et al.
1555
♦
∗
Cu-Ni (1:1)/γ−Al
O
2
3
respectively, corresponding to (111), (111), (202) and
(113) crystal planes of monoclinic CuO (JCPDS: 41-0254).
The broad peak observed at 2q = 67.5° for all catalysts is
corresponding toAl2O3 (JCPDS: 86-1410). Peak intensities
detected for Cu/γ-Al2O3 catalysts indicate that CuO is
very well crystalline in nature. In case of Cu-Ni/γ-Al2O3
bimetallic catalysts, additional peaks are detected at
2q = 43.2° and 63°, which correspond to (012) and (110)
planes of NiO (JCPDS: 44-1159).With the increase in nickel
loading, the peak intensities for NiO increase significantly
(Figure 2). For bimetallic catalysts, apart from CuO and
NiO peaks, an additional peak appears at 2q = 36.9°,
which represents mixed metal oxide phase CuxNi(1-x)Al2O4
(x = 0.25, 0.5, 0.75) (JCPDS: 78-1602, 78-1603, 78-1604)
in agreement with the previous study.43 The intensity of the
peak corresponding to mixed metal oxide phase increases
with increasing amount of Ni in bimetallic catalysts (inset
of Figure 2). The formation of mixed oxides indicates the
strong interaction of Cu, Ni with the alumina support.39,43
XRD pattern of Ni/γ-Al2O3 catalyst shows sharp peaks
at 2q = 37.3°, 43.2° and 62.8° are corresponding to NiO
(JCPDS: 44-1159), which reflect the typical rhombohedral
structure. Peak intensities of CuO and NiO in bimetallic
catalysts are of lower intense and broader than that of
monometallic catalysts, which indicate better dispersion of
metal oxide on the alumina support for bimetallic catalysts
as compared to monometallic catalysts.39
Diffraction patterns of reduced Cu/γ-Al2O3, Ni/γ-Al2O3
and Cu-Ni/γ-Al2O3 catalysts are shown in Figure 3. For
Cu/γ-Al2O3 and Cu-Ni(3:1)/γ-Al2O3 catalysts, sharp
reflection of metallic Cu is observed at 2q = 43.3°, 50.4°,
and 74.2° corresponds to (111), (200) and (220) planes of
the cubic pore structure (JCPDS: 85-1326). XRD patterns of
Cu-Ni(1:3)/γ-Al2O3 and Ni/γ-Al2O3 catalysts show peaks at
2q = 44.5°, 51.8°, and 76.4°, respectively, which represent
(111), (200) and (220) planes of cubic Ni metal (JCPDS:
04-0850). Additional peaks of nickel oxide are observed at
2q = 43.2° and 62.8° in case of Ni/γ-Al2O3 catalyst.
♦
Ni ∗ Cu
NiO
∗
♦
γ−Al O
2
3
♦
♦
42
44
46
48
50
52
54
2θ / degree
♦
♦
Ni/γ−Al O
2
3
♦
♦
Cu-Ni (1:3)/γ−Al O
♦
2
3
♦
∗
∗
Cu-Ni (1:1)/γ−Al O
∗
∗
2
3
∗
∗
Cu-Ni (3:1)/γ−Al O
2
3
∗
∗
Cu/γ−Al O
2
3
10
20
30
40
50
60
70
80
2θ / degree
Figure 3. XRD patterns of reduced Cu/γ-Al2O3, Ni/γ-Al2O3 and
Cu-Ni/γ-Al2O3 catalysts with 20 wt.% metal loading at different Cu/Ni
metal ratio. Combined peaks for Cu-Ni bimetallic phase (inset figure).
XRD pattern of Cu-Ni(1:1)/γ-Al2O3 catalyst exhibits
two combined diffraction peaks in between the 2q range
of 43.3°-44.5° and 50.4°-52° (inset of Figure 3),
corresponding to Cu-Ni combined bimetallic phase.34,44,45
For all the reduced catalysts, low intensity peaks for
γ-Al2O3 are observed at 2q = 36.8° and 67.5°, respectively.
Reflection corresponding to metallic Cu is not observed
in Cu-Ni(1:3)/γ-Al2O3 catalyst and peak corresponding to
metallic Ni is not detected in Cu-Ni(3:1)/γ-Al2O3 is may
be due to the presence of lower metal content of respective
metal or complete dispersion on the support.
The average crystallite size of CuO, NiO, CuxNi(1-x)
Al2O4 and the particle size of Cu and Ni is calculated using
the Scherrer equation from the line width of their respective
XRD peaks (Table 2).
For calcined catalysts, the average crystallite size
of CuO is estimated from X-ray line width of the peaks
corresponding to (002), (111) and (202) crystal planes,
respectively. The calculated dimension of CuO crystallite is
in the range of 37-64 nm. The average size of NiO crystallite
is in the range of 10-31 nm calculated from line width of
Table 2. Average crystallite sizes of CuO, NiO and Cu-Ni mixed oxide and Cu, Ni average particle size calculated by Scherrer equation
Average crystallite size / nm
Average particle size / nm
Reduceda
Catalyst
Calcined
CuO
37
64
56
−
NiO
−
CuxNi(1-x)Al2O4
Cu
Ni
−
Cu/γ-Al2O3
−
89
80
33
−
Cu-Ni(3:1)/γ-Al2O3
Cu-Ni(1:1)/γ-Al2O3
Cu-Ni(1:3)/γ-Al2O3
Ni/γ-Al2O3
−
28
28
32
−
−
10
30
31
22
29
39
−
−
aCatalyst reduction conditions: reduction temperature of catalysts determined by TPR analysis; H2 flow = 50 cc min−1; time = 3 h.

1556
Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni Catalysts Supported on γ-Al2O3
J. Braz. Chem. Soc.
(111), (200) and (220) crystal planes. The crystallite size
of CuxNi(1-x)Al2O4 mixed oxide phase is estimated from line
width of the peak corresponding to (311) crystal plane and
it is in the range of 28-32 nm (Table 2). For the reduced
catalysts except for Cu-Ni (1:1), the size of the Cu particle
increases due to the particle agglomeration resulted by
change of surface electronic properties of Cu particles,
which indicates less metal support interaction.22,23 In case
of Cu-Ni(1:1)/γ-Al2O3 catalyst, the size of the Cu particle
estimated from line width of the peaks corresponding to
(111), (200) and (220) crystal planes is decreased from
56 to 33 nm after the reduction. The nickel particle size
estimated from line width of the peaks corresponding to
(111), (200) and (220) crystal planes is increased from 10
to 22 nm. However, the average crystallite size of reduced
catalyst is decreased slightly from 31.3 to 27.5 nm indicates
the strong metal support interaction between Cu and Ni
atoms which prevent sintering.34
The reduction behavior of Cu-Ni catalysts is analyzed
by H2-TPR (Figure 4). The reduction profile of pure
γ-Al2O3 is characterized by a broad small intensity peak
at 670 °C, which may be due to the reduction impurity
present.46 Cu/γ-Al2O3 catalyst exhibits two reduction peaks
at 250 °C and 344 °C, respectively. The peak at the lower
temperature represents the reduction of highly dispersed
CuO on γ-Al2O3, while the peak at higher temperature
represents the reduction of bulk CuO particles.47-50 Two step
reduction of bulk CuO particles was reported earlier.47 In the
two step reduction, the first step involved for the reduction
of CuO to Cu+ at 307 °C and other peak at the 327 °C is
for the reduction of the Cu+ ion to metallic copper (Cu0).
The reduction profile obtained for Ni/γ-Al2O3 displays
a broad multiple reduction profile at 350-580 °C with a
major peak at 477 °C and two shoulder peaks at 366 °C
and 431 °C, respectively. The low intensity shoulder peak
observed at 367 °C represents the reduction of NiO to
Ni0 51,52 and weaker shoulder peak at 431 °C is associated
with the reduction of NiO having strong interaction with
the support.53 However, a broad reduction peak at 477 °C
indicates the presence of bulk NiO crystallites strongly
bonded with γ-Al2O3 support.54 The TPR patterns of
bimetallic catalysts are different from those of supported
pure monometallic CuO and NiO catalysts. They exhibit
combined broad peaks indicating that the reduction process
for the bimetallic oxide system is more complicated than
for the monometallic oxides. The reduction profiles of
Cu-Ni(3:1)/γ-Al2O3 and Cu-Ni(1:3)/γ-Al2O3 catalysts
display broad multiple reduction profile at 200-400 °C and
220-430 °C, respectively. Moreover, Cu-Ni(1:1)/γ-Al2O3
catalyst gets reduced at the temperature range of
200-340 °C. The lowest reduction temperature of 231 °C
for Cu-Ni(1:1)/γ-Al2O3 catalyst demonstrates the strong
interaction between CuO-NiO metal oxides due to the
formation of bimetallic Cu-Ni. Lin et al.34 reported the
similar kind of TPR profiles for Cu-Ni bimetallic catalysts.
The NH3-TPD patterns for all catalysts are shown
in Figure 5. The quantitative estimation of acidic site
distribution at different regions according to the desorbed
amount of ammonia is summarized in Table 3. The results
show that the acidic sites are distributed in three different
regions, i.e., at 80-250 °C, 250-500 °C and above 500 °C
for all the catalysts. It is observed from the literature that
the first region is attributed to the desorption of ammonia
from weak acidic sites, the second region refers to moderate
strength acidic sites, and the third region represents
desorption of ammonia from strong acidic sites.55,56
Ni/γ−Al
O
2
3
Cu-Ni (1:3)/γ−Al
O
2
3
477
431
Cu-Ni (1:1)/γ−Al
O
2
3
366
Ni/γ−Al O
2
3
366
Cu-Ni (3:1)/γ−Al
O
2
3
292
Cu/γ−Al
O
2
3
477
Cu-Ni (1:3)/γ−Al O
2
3
296
γ−Al
O
231
2
3
Cu-Ni (1:1)/γ−Al O
443
2
3
301
240
100
200
300
400
500
600
700
800
Cu-Ni (3:1)/γ−Al O
344
2
3
o
Temperature /
C
250
Cu/γ−Al O
2
3
670
Figure 5. NH3-TPD profiles of catalysts and support.
γ−Al O
2
3
100
200
300
400
500
600
700
800
The NH3-TPD profile of γ-Al2O3 surface displays
the peaks in all three regions and shows the highest
acidic strength of 1.203 mmol NH3 gcat.−1. The results
o
Temperature / C
Figure 4. H2-TPR profiles of catalysts and support.

Vol. 26, No. 8, 2015
Pudi et al.
1557
reported in Table 3 depict that, the acidic strength
of catalysts is decreased significantly after metal
impregnation. The concentration of acidic sites is decreased
in the order: Cu-Ni(1:3)/γ-Al2O3 > Cu-Ni(3:1)/γ-Al2O3 >
Cu-Ni(1:1)/γ-Al2O3 > Cu/γ-Al2O3 > Ni/γ-Al2O3. The total
acidity of the bimetallic catalysts was higher due to the
synergetic interaction of copper, nickel and γ-Al2O3 support.
Table 3. NH3-TPD results for all catalysts
Acidity / (mmol NH3 gcat.−1)
Catalyst
Weak
0.409
0.347
0.315
0.446
0.192
0.625
Medium
0.153
0.356
0.251
0.382
0.205
0.455
Strong Total acidity
Cu/γ-Al2O3
−
0.562
0.703
0.609
0.893
0.407
1.203
Cu-Ni(3:1)/γ-Al2O3
Cu-Ni(1:1)/γ-Al2O3
Cu-Ni(1:3)/γ-Al2O3
Ni/γ-Al2O3
−
0.043
0.065
0.010
0.123
γ-Al2O3
The crystal morphology of all the reduced catalysts is
similar to quasi-spherical, agglomerated nanoparticles of
ca. 50 nm (Figure 6a-e). Particle agglomeration is caused
by sintering of particles during heat treatments.57 EDX
elemental mapping is used to determine the distribution of
Cu, Ni metal on the surface of γ-Al2O3 and the elemental
compositions obtained are summarized in Table 1.
Theoretical metal loading and the metal loading obtained
by EDX show an error within 5-10%. Similar kind of results
were also reported earlier.58
Figure 6. SEM images of (a) Cu/γ-Al2O3, (b) Cu-Ni(3:1)/γ-Al2O3,
(c) Cu-Ni(1:1)/γ-Al2O, (d) Cu-Ni(1:3)/γ-Al2O and (e) Ni/γ-Al2O3 catalysts.
metallic surface area (4.3 m2 g−1), small average Cu-Ni
particle size (27 nm), and higher metal dispersion (3.3%).
Turnover frequency (TOF) values calculated for all Cu-Ni
catalysts after 12 h of reaction are shown in Table 4. TOF
values are in the range of 4.7 to 53.4 h−1. The highest TOF
of 53.4 h−1 is obtained for Cu-Ni(1:1)/γ-Al2O3 catalyst
indicates that glycerol conversion rates are correlated with
TOF values. High TOF values for bimetallic catalysts due
to the synergetic effect between metals in these catalysts
that enhanced the overall hydrogenolysis activity. Similar
TOF values were reported in literature for Ru/C,15
Catalytic performance
Catalytic activity and product selectivity are examined
over Cu, Ni monometallic and bimetallic catalysts at
210 °C and 4.5 MPa hydrogen pressure. The effect of the
Cu/Ni weight ratio on catalytic activity, product selectivity
and 1,2-PDO yield are determined. The catalytic results
obtained are shown in Table 4.
60
Cu/layered double oxides,27 Ru/CsPW,59 and Ru-Cu/TiO2
Bimetallic catalysts exhibit glycerol conversion in
the range of 45.4-59.3%, which are higher than that of
monometallic catalysts (Table 4). This higher glycerol
conversion for Cu-Ni bimetallic catalysts is due to the
presence of bi-functionality12,17,59 and high acidic strength
(0.61-0.90 mmol NH3 gcat.−1).21,27 Cu-Ni(1:1)/γ-Al2O3
catalyst exhibits the highest glycerol conversion of 59.3%,
whereas, Cu-Ni(3:1)/γ-Al2O3 and Cu-Ni(1:3)/γ-Al2O3
catalysts display a slightly lower glycerol conversion of
46.8% and 45.4%, respectively. Higher glycerol conversion
over Cu-Ni(1:1)/γ-Al2O3 catalyst can be attributed to
synergetic effect of Cu-Ni bimetal along with high
catalysts. Recently, it has been reported that the activity of
20 wt.% Cu/SiO2 catalyst increases with increasing metal
surface area and TOF was higher for the catalysts with
small particle size.23 The linear dependency of the turn
over number (TON) with copper metal surface area has
been reported and it has been shown that the higher TON
found with CuO(60)-ZnO(40) catalyst having the highest
metallic surface.24
Cu/γ-Al2O3 and Ni/γ-Al2O3 catalysts exhibit lower
glycerol conversion of 21% and 14.5%, respectively. Lower
conversion of Cu/γ-Al2O3 catalyst can be explained by the
presence of weak acidic strength (0.562 mmol NH3 gcat.−1)

1558
Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni Catalysts Supported on γ-Al2O3
J. Braz. Chem. Soc.
Table 4. Catalytic behavior of Cu-Ni catalysts in glycerol hydrogenolysis
Selectivity / %
1,2-PDO
yield / %
Catalyst
Conversion / %
TOFb / h−1
1,2-PDO
91.1
Acetol
1-Propanol
Othersa
0.8
Cu/γ-Al2O3
21.0
46.8
59.3
45.4
14.5
3.3
1.4
0.6
1.0
3.0
4.8
8.0
7.8
8.1
2.8
19.1
41.2
51.3
39.2
12.7
32.5
50.6
53.4
49.1
4.7
Cu-Ni(3:1)/γ-Al2O3
Cu-Ni(1:1)/γ-Al2O3
Cu-Ni(1:3)/γ-Al2O3
Ni/γ-Al2O3
88.2
2.3
86.6
4.9
86.4
4.4
87.9
6.1
aOthers: ethylene glycol, 2-propanol, traces of ethanol and methanol; bTOF calculated by the number of moles of glycerol converted per moles of exposed
copper atom per unit time (h−1). Reaction conditions: glycerol concentration: 20 wt.%; reaction temperature: 210 °C; H2 pressure: 4.5 MPa; reaction time:
12 h; catalyst wt.: 2 g; rpm: 700.
(Table 3) and larger Cu particle size (89 nm) (Table 2).
For Ni/γ-Al2O3 catalysts, the catalytic activity is found
low although the metal dispersion (8.1%) and the metallic
surface area (10.8 m2 g−1) are higher. For Ni/γ-Al2O3 catalyst,
the selectivity to other products (EG and methanol) is higher
(6.1%), which indicates the formation of degradation
products (EG and methanol) due to the breaking of C−C
bond by following a different reaction path. This result
explains that, Cu is more active and selective to 1,2-PDO as
compared to Ni. In contrast to our results, 35 wt.% Ni/Al2O3
catalyst showed comparable activity to Cu-Ni bimetallic
catalysts at 220 °C, 4.5 MPa N2 pressure in the presence
of formic acid as a hydrogen donor.39 It is claimed that Ni
played an active role in utilizing the hydrogen coming from
formic acid. In the present study, the selectivity results
suggest that, Ni promotes C−C bond cleavage, which
tend to act as a source of carbon that blocks the active
sites and catalyst pores. Ni/γ-Al2O3 catalyst is found to be
least active, which may be related to lack of active sites
on Ni/γ-Al2O3.
For all catalysts, main reaction products are 1,2-PDO,
acetol and 1-propanol (Table 4). Minor amounts of other
products such as ethylene glycol, 2-propanol, ethanol and
methanol are also detected.All catalysts show high selectivity
of 86-91% towards 1,2-PDO and combined selectivity to all
remaining products including propanols, acetol, ethylene
glycol, ethanol and methanol is in the range of 9-13%.
Transformation of glycerol to 1,2-PDO can proceed in
two possible reaction routes. First one is a two-step process:
dehydration of glycerol to acetol and hydrogenation of
acetol to 1,2-PDO.6,8,17-24,60-62 The second route is a three-
step process: glycerol dehydrogenates to glyceraldehydes
then dehydration to 2-hydroxyacrolein followed by
hydrogenation to 1,2-PDO.10,11,15,27 Product distribution
obtained in this study suggests that the reaction proceeds
through the first reaction route. A very high selectivity
for 1,2-PDO (> 86%) and very low selectivity (< 3.5 %)
for acetol are found after 12 h of reaction in the presence
of Cu-Ni bimetallic catalysts. These selectivity values
indicate a very fast hydrogenation of acetol to 1,2-PDO.
Low selectivity of acetol suggests that acetol is formed by
dehydration of glycerol in the presence of acidic sites of
catalysts quickly hydrogenated to 1,2-PDO in presence of
active metal sites.38 Selectivity for 1-propanol and other
degradation products obtained by the cleavage of C−C bond
is less than 5%. This result indicates that Cu-Ni/γ-Al2O3
catalysts propagate selective hydrogenation of C−O bonds
and limits C−C bond scission.
High glycerol conversion (59.3%) is obtained in the
presence of Cu-Ni(1:1)/γ-Al2O3 catalyst at 210 °C and
4.5 MPa hydrogen pressure. Under this reaction condition,
1,2-PDO selectivity and yield are 86.6% and 51.3%,
respectively. This suggests that, bimetallic Cu-Ni promotes
C−O hydrogenolysis of glycerol and limits the selectivity
of cracked products. Recently, 31% conversion of glycerol
has been reported over Cu (28 wt.%)-Ni (7.7 wt.%)/Al2O3
catalysts at comparatively higher reaction temperature
(220 °C) at this reaction condition, 84.7% selectivity and
26.2% yield for 1,2-PDO has been reported.39 Glycerol
conversion obtained in the present study is comparable
with literature at relatively lower copper-nickel metal
loading, lower catalyst concentration, and at relatively
lower reaction temperature of 210 °C. However, 1,2-PDO
selectivity (86.6%) and yield (51.3%) obtained are
significantly higher than previously reported values.
Reaction parameter studies
To optimize glycerol conversion and 1,2-PDO
selectivity, the effect of reaction temperature, hydrogen
pressure, reaction time, glycerol concentration, catalyst
amount, and metal loading on hydrogenolysis of glycerol
is examined in the presence of Cu-Ni(1:1)/γ-Al2O3 catalyst.
In the following sections, we discussed the influence of
those reaction parameters on the role of Cu-Ni(1:1)/γ-Al2O3
catalyst in glycerol conversion and 1,2-PDO selectivity.

Vol. 26, No. 8, 2015
Pudi et al.
1559
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Effect of reaction temperature
Glycerol conversion increases from 17.5% (190 °C) to
73.2% (230 °C) (Figure 7) at 4.5 MPa H2 pressure in the
presence of Cu-Ni(1:1)/γ-Al2O3 catalyst.
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Glycerol conversion
1.2-PDO
1-Propanol
Others
Yield 1.2-PDO
Glycerol conversion
1.2-PDO
1-Propanol
Others
1
2
3
4
5
6
Yield 1.2-PDO
H pressure / MPa
2
Figure 8. Effect of hydrogen pressure on conversion, selectivity and
yield over Cu-Ni(1:1)/γ-Al2O3 catalyst. Others: ethylene glycol, acetol,
2-propanol, traces of ethanol and methanol. Reaction conditions: glycerol
concentration: 20 wt.%; reaction temperature: 210°C; reaction time: 12 h;
catalyst wt.: 2 g; rpm: 700.
190
200
210
220
230
o
Temperature /
C
selectivity for 1-propanol found to be ca. 10% and the
selectivity of other degradation products decreased from
25.3 to 3.6%. Overall 1,2-PDO yield increases from 25.9%
at 1.5 MPa to 57.7% at 6 MPa hydrogen pressure.
Figure 7. Effect of reaction temperature on conversion, selectivity and
yield over Cu-Ni(1:1)/γ-Al2O3 catalyst. Others: ethylene glycol, acetol,
2-propanol, traces of ethanol and methanol. Reaction conditions: glycerol
concentration: 20 wt.%; H2 pressure: 4.5 MPa; reaction time: 12 h; catalyst
wt.: 2 g; rpm: 700.
Effect of reaction time
The selectivity of 1,2-PDO decreases from 96.1% at
190 °C to 40% at 230 °C and selectivity for 1-propanol and
other products increases with increasing temperature. The
overall yield of 1,2-PDO increased from ca. 15% at 190 °C
to a maximum of 51.3% at 210 °C, and then decreased on
further increase in temperature (Figure 7). TOF values are
observed in the range of 15.4-64.2 h−1, as the temperature
increases from 190 to 230°C. These results suggest that at
higher temperature (> 210 °C), 1,2-PDO undergoes further
hydrogenolysis that lead to C−C bond cleavage and produce
1-propanol and low molecular alcohols such as ethylene
glycol, ethanol, and methanol.6,8,25
Glycerol conversion increases with increasing reaction
time and reaches ca. 94% after 36 h of reaction (Figure 9).
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Glycerol conversion
1.2-PDO
1-Propanol
Others
Yield 1.2-PDO
Effect of hydrogen pressure
Glycerol conversion and 1,2-PDO selectivity are
increased from 34% to 62% and 69.2% to 93%, respectively,
when increase in hydrogen pressure from 1.5 MPa to 6 MPa
(Figure 8).
The increase in glycerol conversion with increasing
pressure is due to the availability of more hydrogen species
at the catalyst surface at elevated hydrogen pressures.8,17
TOF values are found to be in the range of 32.7-53.4 h−1
with increasing pressure from 1.5 to 6 MPa. At higher
hydrogen pressure, the concentration of active hydrogen
species increases on the metal surface, which enhances
the rate of hydrogenation of acetol to 1,2-PDO.19,29 The
5
10
15
20
25
30
35
Reaction time / h
Figure 9. Effect of reaction time on conversion, selectivity and yield over
Cu-Ni(1:1)/γ-Al2O3 catalyst. Others: ethylene glycol, 2-propanol, traces
of ethanol and methanol. Reaction conditions: glycerol concentration:
20 wt.%; reaction temperature: 210 °C; H2 pressure: 4.5 MPa; catalyst
wt.: 2 g; rpm: 700.
Initially, 93.6% selectivity of 1,2-PDO is achieved
after 3 h of reaction, and it decreases to 43.6% after 36 h.
Simultaneously, the selectivity of 1-propanol increases
from 1.7 to 47.9% and of other products increases from 4.7
to 10%, respectively. The decrease in 1,2-PDO selectivity

1560
Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni Catalysts Supported on γ-Al2O3
J. Braz. Chem. Soc.
is due to over hydrogenolysis of 1,2-PDO which produces
1-propanol and other products.19,23 The yield of 1,2-PDO
initially increases from 19.4% to 51.3% after 12 h of
reaction. Thereafter, it remains constant (ca. 52%) up to
30 h and finally it decreases to 41% after 36 h. The decrease
in 1,2-PDO yield after 30 h reaction time can be attributed
to the formation of by-products due to excessive C−C bond
scission. The calculated TOF values are found to be in the
range of 26.1-76.4 h−1 as the increasing time from 3 to 36 h.
2 g (Figure 11). Further increase in catalyst amount (> 2 g),
a gradual increase in glycerol conversion is observed. The
maximum glycerol conversion of 71.5% is obtained in the
presence of 4 g of catalyst in the reaction mixture. The
conversion increases with increasing catalyst amount is
attribute to the increase in accessibility of active catalyst
surface.8,25 The selectivity to 1,2-PDO increased from 67%
to 94% when the amount of catalyst increases from 0.5 to
4 g. Overall 1,2-PDO yield increases from 8.6 to 66.4%.
1-Propanol selectivity decreases from 28.4 to 2.5% with
increasing catalyst amount and the change in selectivity to
other products is insignificant. As the increase in catalyst
amount from 0.5 to 4 g, the TOF data is found to be in the
range of 24.1-53.4 h−1. This results suggest that, high active
surface area favours the selective conversion of glycerol to
1,2-PDO following the dehydration-hydrogenation route
eliminating the side reaction which produce the degradation
products.
Effect of glycerol concentration
The conversion of glycerol decreases with increasing
glycerol concentration (Figure 10). Possible reason for the
decrease in glycerol conversion is due to the availability of
a limited number of active sites to convert glycerol to 1,2-
PDO. The decrease in glycerol conversion with increasing
glycerol concentration is consistent with the published
literature.20,25,27 TOF was calculated at different glycerol
concentration and it varies in the range of 25.1-76.8 h−1.
Overall selectivity of 1,2-PDO decreases from 95.2% to
65.5% with increasing glycerol concentration from 10 to 80
wt.%. However, the extent of decrease in selectivity is higher
at lower glycerol concentration and 1,2-PDO selectivity
becomes almost constant (ca. 70%) above 30 wt.%. The
decreasing trend of 1,2-PDO selectivity with increasing
glycerol concentration can be attributed to formation of
1-propanol.Yield of 1,2-PDO decreased from 58.2% to 15%
as glycerol concentration increases from 10 wt.% to 80 wt.%.
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Glycerol conversion
1.2-PDO
1-Propanol
Others
Yield 1.2-PDO
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Catalyst amount / g
Figure 11. Effect of catalyst amount on conversion, selectivity and
yield over Cu-Ni(1:1)/γ-Al2O3 catalyst. Others: ethylene glycol, acetol,
2-propanol, traces of ethanol and methanol. Reaction conditions: glycerol
concentration: 20 wt.%; reaction temperature: 210 °C; H2 pressure:
4.5 MPa; reaction time: 12 h; rpm: 700.
Glycerol conversion
1.2-PDO
1-Propanol
Others
Yield 1.2-PDO
Effect of total metal loading in catalyst
As the metal loading increases from 5 to 20 wt.%,
glycerol conversion increases from 32 to 59.3%, 1,2-PDO
selectivity decreases slightly from 89.4 to 86.6%, and
overall yield of 1,2-PDO increases from 28.6 to 51.3%
(Figure 12). The increase in glycerol conversion with
increasing metal loading (up to 20 wt.%) can be attributed
to the increase in active metallic sites.6,63 Further increase in
metal loading up to 30 wt.%, results a marginal decrease in
glycerol conversion (57.3%), which is due to the presence
of larger catalyst particles. It is reported earlier that at
higher metal loading (4 mmol Cu g−1 support), the total
active meta sites decreases due to the formation of larger
10
20
30
40
50
60
70
80
Glycerol concentration / wt.%
Figure 10. Effect of glycerol concentration on conversion, selectivity and
yield over Cu-Ni(1:1)/γ-Al2O3 catalyst. Others: ethylene glycol, acetol,
2-propanol, traces of ethanol and methanol. Reaction conditions: reaction
temperature: 210 °C; H2 pressure: 4.5 MPa; reaction time: 12 h; catalyst
wt.: 2 g; rpm: 700.
Effect of catalyst amount
A sharp increase in glycerol conversion (12.9-59.3%)
is observed when amount of catalyst increases from 0.5 to

Vol. 26, No. 8, 2015
Pudi et al.
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100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
0
The yield of 1,2-PDO is decreased from 51.3 to 41.4%.
The reason for decreased glycerol conversion is related to
the loss of the catalyst during filtration and reuse process.
Similar observation has also been reported in the literature
for Cu-based catalysts during recycling studies.23,27,64-66 To
verify the reason of slight deactivation of the catalyst in
the reuse experiments, the fresh reduced and recycle-3
catalysts were characterized by various techniques. The
results obtained are discussed in the following section.
Glycerol conversion
1.2-PDO
1-Propanol
Others
Yield 1.2-PDO
0
Characterization of used catalysts
5
10
15
20
25
30
Total metal loading / wt.%
Used catalyst (after cycle-3) was characterized by XRD,
SEM-elemental mapping, ICP-MS and TEM methods
and the results are compared with the fresh catalyst. XRD
patterns of reduced, used catalysts for cycle-1 and cycle-3
are presented in Figure 13.
Figure 12. Effect of total metal loading on conversion, selectivity and
yield over Cu-Ni(1:1)/γ-Al2O3 catalyst. Others: ethylene glycol, acetol,
2-propanol, traces of ethanol and methanol. Reaction conditions: glycerol
concentration: 20 wt.%; reaction temperature: 210 °C; H2 pressure:
4.5 MPa; reaction time: 12 h; catalyst wt.: 2 g; rpm: 700.
Cu crystallites in Cu/Al2O3 catalyst, which decreases the
dispersion and facilitates the blockage of pores on the
support as well.6 1,2-PDO selectivity (86%) and yield
(50%) are almost constant above 20 wt.% metal loading.
1-Propanol selectivity increases from 5 to 10.5% and of
other products remains unchanged throughout.
♦
∗
♦
Spent: Cycle-3
Cu
∗
♦
Ni
Spent: Cycle-1
♦
∗
Al O
2
3
Cu-Ni (1:1)/γ−Al
O
2
3
♦
∗
42
44
46
48
50
52
2θ / degree
♦
∗
Spent: Cycle-3
Reusability of catalyst
♦
∗
Spent: Cycle-1
Deactivation behavior and reusability of 20 wt.%
Cu-Ni(1:1)/γ-Al2O3 catalyst are examined at 210 °C and
4.5 MPa H2 pressure with 20 wt.% glycerol as feed for 12 h.
Prior to each cycle of experiment, the catalyst was separated
by filtration and washed with deionised water followed
by ethanol, and then dried overnight at 110 °C. This dried
catalyst was reduced under hydrogen environment at 350 °C
before further testing. Results obtained for four successive
reactions are summarized in Table 5.
Glycerol conversion was moderately decreased in each
cycle and it is varied from 59.3 to 44.4% in the successive
cycles (Table 5). 1,2-PDO selectivity is increased from 85.6
to 93.1%, and selectivity of 1-propanol and other products
are decreased from 7.8 to 3% and 5.5 to 4%, respectively.
∗♦
Cu-Ni (1:1)/γ−Al
O
2
3
10
20
30
40
50
60
70
80
2θ / degree
Figure 13. XRD patterns of Cu-Ni(1:1)/γ-Al2O3 catalyst after reaction.
Combined peaks for Cu-Ni bimetallic phase (inset figure).
XRD profile of reduced catalyst shows two combined
diffraction peaks of bimetallic Cu-Ni phases at the 2q
value range of 43.3-44.5° and 50.4-52°. Whereas, the XRD
profiles of the spent catalyst in cycle-1 and cycle-3 exhibit
mixed peaks of bimetallic Cu-Ni phase with high intensity
at the same 2q values (inset Figure 13). This result suggests
Table 5. Catalytic behavior over Cu-Ni (1:1)/γ-Al2O3 catalyst during recycling experiments
Selectivity / %
Cu/Ni ratio
No. of cycles
Conversion / %
1,2-PDO yield / %
Theoretical (Actual)a
1,2-PDO
86.6
1-Propanol
Othersb
5.5
Fresh reduced
Cycle-1
1.0 (1.15)
1.0 (1.21)
−
59.3
52.2
47.7
44.4
7.8
2.8
3.6
2.9
51.3
48.1
44.0
41.4
92.1
5.1
Cycle-2
92.3
4.1
Cycle-3
1.0 (1.08)
93.1
4.0
aMetal contents determined by ICP-MS analysis; bothers: ethylene glycol, acetol, 2-propanol, traces of ethanol and methanol; reaction conditions: reaction
temperature: 210°C; H2 pressure: 4.5 MPa; reaction time: 12 h; rpm: 700; catalyst/glycerol = 10 wt.%.

1562
Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni Catalysts Supported on γ-Al2O3
J. Braz. Chem. Soc.
that the bimetallic Cu-Ni phase remain stable and strong
metal-support interactions exist after prolonged contact
time under hydrogen environment at 210 °C and 4.5 MPa
H2 pressure.
catalyst even after four consecutive experiments. Thus
the structural stability of the Cu-Ni(1:1)/γ-Al2O3 catalyst
under the reaction condition remain intact. Therefore,
Cu-Ni(1:1)/γ-Al2O3 catalyst is reusable and is promising
for commercial applications.
In order to check any possible metal loss by leaching
during the reaction, the elemental composition of Cu and
Ni metals in the fresh and used catalysts are determined by
ICP-MS analysis. The theoretical and actual Cu/Ni ratios
are presented in Table 5. The reported actual Cu and Ni
metal compositions are slightly higher than the theoretical
value. The Cu/Ni ratios of the spent catalysts during cycle-1
(1.21) and cycle-3 (1.08) are closer to the fresh catalyst
(1.15), which confirms that the metallic properties are
stable during the course of successive reactions. TEM
images and selected area electron diffraction (SAED)
patterns (Figure 14a-d) suggest that the morphology of used
catalyst (cycle-3) remains similar to that of fresh catalyst.
The SAED pattern of fresh reduced catalyst confirms the
poly crystalline nature of the particles presenting diffraction
planes (111), (220) associated with Cu metal (JCPDS
No. 85-1326) and planes (200), (311) for metallic Ni
(JCPDS No. 04-0850). The used catalyst (cycle-3) shows
the diffraction planes of (111), (220) for metallic copper
and (311), (331) for metallic Ni, respectively. The particle
size distribution (10-60 nm) of used catalyst is similar to
that of fresh reduced catalyst, which is in good agreement
with XRD results (Table 2). These results suggest that
particle size and dispersion of used catalysts remain the
same to that of the fresh reduced Cu-Ni(1:1)/γ-Al2O3
Conclusions
Cu/γ-Al2O3, Ni/γ-Al2O3 monometallic, and
Cu-Ni/γ-Al2O3 bimetallic catalysts were prepared by
incipient wetness impregnation method and evaluated for
liquid phase hydrogenolysis of glycerol. Cu-Ni bimetallic
catalysts showed higher activity (45.4-59.3%) and
1,2-PDO selectivity (86-91%) than monometallic catalysts.
Cu-Ni(1:1)/γ-Al2O3 catalyst exhibited maximum glycerol
conversion of 59.3% at 210 °C and 4.5 MPa hydrogen
pressure in the presence of 2 g catalyst and after 12 h. Higher
catalytic activity was ascribed to the formation of bimetallic
Cu-Ni phase, high metallic surface area (4.3 m2 g−1), small
Cu-Ni particle size (27 nm), and higher metal dispersion
(3.3%). The bimetallic Cu-Ni phase favoured selective
conversion of glycerol to 1,2-PDO (ca. 90% selectivity) via
dehydration-hydrogenation pathway. Detailed parametric
study with 20 wt.% Cu-Ni(1:1)/γ-Al2O3 catalyst suggested
that maximum glycerol conversion of 71.6% with 93%
selectivity to 1,2-PDO can be achieved at 210 °C, H2
pressure of 4.5 MPa, glycerol concentration (20 wt.%),
12 h, and in presence of 4 g of catalyst. Reusability and
structural stability of 20 wt.% Cu-Ni(1:1)/γ-Al2O3 catalysts
were verified. ICP-MS analysis data and TEM images of
fresh and used catalysts showed the catalyst morphology
remain stable after successive reuses.
Acknowledgements
The authors thank DEAN, SRIC, Indian Institute of
Technology Roorkee, Uttarakhand, India for supporting
this work from SRIC-Fund under F.I.G. (Scheme-A). The
authors are also grateful to the Department of Science
and Technology (DST), Government of India for financial
support under the FTYS scheme (SR/FTP/ETA-0032/2011,
DATED 21.2.2012). S. N. M. P. thank MHRD for the award
of fellowship.
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Submitted: November 28, 2014
Published online: May 15, 2015