Hydrogenolysis of glycerol over silica-supported copper-nanocatalyst: Effect of precipitating-agent and copper metal-loading

Article abstract of DOI:10.1016/j.mcat.2017.11.035

Preparation of various silica-supported copper-nanocatalysts (Cu/SiO₂) by deposition precipitation and impregnation methods was demonstrated. These catalysts were prepared using urea and sodium hydroxide as the precipitating-agents. All the catalysts were systematically characterized by various analytical, spectroscopic and imaging techniques including XRD, N₂ sorption analysis, N₂O chemisorption, TPD, TPR, DRUV-VIS XPS and TEM. The Cu/SiO₂ catalyst prepared using urea as the precipitating-agent exhibited uniform and narrow size distribution copper-nanoparticles to that prepared using sodium hydroxide as well as impregnation method. The performance of the catalyst with different metal loading is analyzed and a Cu-loading of 15 wt% was found to be optimum for the maximum yield. Thus, the catalytic activity of 15 wt% Cu/SiO₂ was systematically examined for the hydrogenolysis of glycerol reaction. The influence of reaction conditions and structure activity correlation were also elucidated in this work.

Full text of DOI:10.1016/j.mcat.2017.11.035

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Molecular Catalysis
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Hydrogenolysis of glycerol over silica-supported copper-nanocatalyst:
Effect of precipitating-agent and copper metal-loading
K Suthagara,b, K Shanthib, P Selvama,c,∗
a National Centre for Catalysis Research and Department of Chemistry, Indian Institute of Technology-Madras, Chennai 600 036, India
b Department of Chemistry, College of Engineering, Anna University, Chennai 600 025, India
c New Industry Creation Hatchery Center, Tohoku University, Sendai 980 8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 July 2017
Received in revised form 8 November 2017
Accepted 27 November 2017
Available online xxx
Preparation of various silica-supported copper-nanocatalysts (Cu/SiO2) by deposition precipitation and
impregnation methods was demonstrated. These catalysts were prepared using urea and sodium hydrox-
ide as the precipitating-agents. All the catalysts were systematically characterized by various analytical,
spectroscopic and imaging techniques including XRD, N2 sorption analysis, N2O chemisorption, TPD, TPR,
DRUV-VIS XPS and TEM. The Cu/SiO2 catalyst prepared using urea as the precipitating-agent exhibited
uniform and narrow size distribution copper-nanoparticles to that prepared using sodium hydroxide as
well as impregnation method. The performance of the catalyst with different metal loading is analyzed
and a Cu-loading of 15 wt% was found to be optimum for the maximum yield. Thus, the catalytic activity
of 15 wt% Cu/SiO2 was systematically examined for the hydrogenolysis of glycerol reaction. The influence
of reaction conditions and structure activity correlation were also elucidated in this work.
© 2017 Elsevier B.V. All rights reserved.
Dedicated to Dr. S. Sivaram on the occasion
of his 65th birthday.
Keywords:
Glycerol
Hydrogenolysis
1,2-propanediol
Silica-support
Copper-nanocatalyst
Cu/SiO2
1. Introduction
in the catalyst. Further, glycerol can be converted to glycerol ethers,
glycerol esters, glycerol carbonate, acrolein, epichlorohydrin and
There has been considerable interest in development of
biodiesel as an alternative fuel in recent years due to its renew-
able, non-toxic, biodegradable and environmentally benign nature.
Glycerol is the by-product in trans-esterification of vegetable oils.
Generally, 1 mol of glycerol is generated for every 3 mol of methyl
esters which corresponds to approximately 10 wt% in the total
product [1]. Effective utilization of bio-diesel as a fuel necessitates
conversion of glycerol to other valuable products to avoid wastage.
Glycerol, being a compound with multifunctional groups, can be
converted into different products by various reaction pathways
[2–4]. Hydrogenolysis of glycerol leads to 1,2- and 1,3-propanediols
depending on the dehydration pathway through intermediates
such as hydroxyacetone or 3-hydroxypropanal respectively. For-
mation of these intermediates depends on the acidity of the
catalyst. Oxidation of glycerol yields glyceric acid, tartaric acid and
oxalic acid as dictated by the particle size of active metallic species
hydrogen by the proper choice of the catalyst and process condi-
tions [1–6].
The compound, 1,2- propanediol is a product of industrial sig-
nificance which is used for the synthesis of resin, liquid detergents,
cosmetics, artificial flavors, fragrances, personal care products,
paints, anti-freezing agents, aircraft deicing fluids, chemical pro-
cess fluids and find its application in natural gas treatment [7].
1,3-propanediol is an important stating material for the synthe-
sis of polyurethanes and polyesters due to its functional character
[1–4,8]. 1,3-Propanediol is commercially obtained from acrolein by
hydration process as well as hydro formulation of ethylene oxide
whereas, 1,2- propanediol is obtained from propylene oxide [9–11].
However, these processes involve multiple steps and are not cost
effective. Therefore, hydrogenolysis of readily available bio feed-
stock, glycerol is an effective and efficient strategy to obtain both
1,3- and 1,2-propanediols. Hydrogenolysis of glycerol is a two-step
process which involves dehydration of glycerol to hydroxyacetone
(intermediate) on acidic sites and subsequent hydrogenation of the
intermediate over metallic surface gives rise to 1,2-propanediol
(Scheme 1).
∗
Corresponding author at: National Centre for Catalysis Research and Department
of Chemistry, Indian Institute of Technology-Madras, Chennai 600 036, India.
E-mail address: selvam@iitm.ac.in (P. Selvam).
https://doi.org/10.1016/j.mcat.2017.11.035
2468-8231/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: K. Suthagar, et al., Hydrogenolysis of glycerol over silica-supported copper-nanocatalyst: Effect of
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Cu/SiO2-NDP was prepared using NaOH as the precipitating-agent.
The colloidal silica suspension was dispersed in 500 mL of water
with appropriate amount of Cu(NO3)2.3H2O. This suspension was
stirred for 30 min at ambient temperature and the pH of the solu-
tion was adjusted about 9–10 by drop wise addition 0.5 M NaOH
solution. The blue colored suspension thus formed was filtered
and washed with deionized water for several times. For compar-
ison, Cu/SiO2-IMP was also synthesized by impregnation method.
The obtained precipitates were dried over night at 110 ◦C followed
by calcination in air at 450 ◦C for 5 h. The prepared catalyst were
denoted as x wt% Cu/SiO2-UDP/NDP/IMP where x = 5, 10, 15 and
20. All the catalysts were pre-reduced at 400 ◦C for 4 h prior to
utilization in the hydrogenolysis of glycerol.
Scheme1. Hydrogenolysis of glycerol.
Noble metal-based catalysts such as ruthenium, rhodium, rhe-
nium, iridium and platinum are well known for their role in
hydrogenolysis reaction and the same have been extensively stud-
ied [12–22]. These noble metal based catalysts can convert glycerol
under mild conditions. However, the selectivity of noble metal
based catalyst towards propanediols is less, since the C C bond
cleavage is favored on noble metal surfaces leading to smaller
alcohols [12,14,20,21]. The transition metal-based catalyst, e.g.,
chromium, cobalt, nickel and copper, are also found to be active
for this reaction. Among these, the copper-based catalysts showed
high selectivity towards 1,2-propanediol [7,23–33]. The selectiv-
ity of the hydrogenolysis products can be enhanced by increasing
the C O bond cleavage and there by suppressing of C C bond
cleavage. Indeed, the copper-based catalysts such as Cu-ZnO and
2.3. Catalyst characterization
Powder X-Ray diffraction (XRD) patterns were recorded using
powder X-ray diffractometer (Rigaku Miniflex II) with Cu K␣
(ꢀ= 1.5405 Å) radiation source. The elemental composition of sam-
ples was analyzed by Inductively Coupled Plasma Optical Emission
Spectrometry (ICPOES, Perkin Elmer Optima 5300). Surface area
measurements were made using Brunaur − Emmet-Teller (BET)
method using porosimetry system (Micrometrics ASAP 2020).
The reducibility of the catalyst was studied by temperature pro-
grammed reduction (TPR) using Micro metrics Autochem 2010,
where 50 mg of catalyst was preheated in Ar atmosphere up to
400 ◦C and cooled to room temperature. Then 10% H2 in argon was
adsorbed on the catalyst and the temperature was increased to
500 ◦C to get H2 consumption values. Extent of metal dispersion in
the samples was calculated by N2O decomposition experiment. The
catalyst was prereduced in 10% H2 in Ar at 400 ◦C and then cooled
to 60 ◦C followed by flowing 10% N2O in Ar for 30 min. The Surface
TPR was performed by the f1owing 10% H2 in Ar up to 500 ◦C. The
metal dispersion was quantified by the amount of N2O consumed
by surface TPR analysis with the stoichiometric factor of two. Metal-
lic surface area was calculated using the formula SH = nSm Xm/ns
where, SH is the metallic surface area, nSm is the total number of
N2O consumed in surface TPR analysis, Xm is the stoichiometric
factor (two) and ns is the number of moles of Cu metal atoms per
unit surface area (1.47 × 1019 m2 g−1) [50]. Electronic spectra of the
catalysts were recorded using UV–vis spectrometer (Thermo Scien-
tific − Evolution 600). The surface morphology and particle size of
the catalyst was examined using transmission electron microscope
(TEM − JEOL JEM-2100). The oxidation state and surface compo-
sition of the catalysts was determined using X-ray photoelectron
spectroscopy (Omicron nanotechnology spectrometer with hemi-
spherical analyzer).
copper chromite (CuCr2O4) exhibit strong affinity towards C
O
bond cleavage rather than C C bond and therefore favor the forma-
tion of hydrogenolysis products rather than degradation products
[7,29–33].
The performance of copper based catalyst can be enhanced by
achieving uniform dispersion of metallic nanoparticles on high sur-
face area supports such as silica (SiO2) and are extensively studied
for this hydrogenolysis of glycerol reaction and these catalysts
are shown high selectivity towards 1,2-propanediol [32–43]. The
silica supported copper based catalysts were prepared by differ-
ent methodologies viz., impregnation, ion exchange, precipitation
deposition, sol gel, hydrothermal and encapsulation methods and
are utilized for this reaction [37,40–47]. The activity of silica sup-
ported copper nanoparticle are further enhanced by introducing
phosphorus and boron oxide are as the promotor there by stabi-
lizing the copper nanoparticle over the support [45,48]. However,
the synthesis of smaller and homogeneous copper nanoparticles
and the formation of monodispersed catalyst remain as a challenge.
Hence, in the present work an attempt has been made to synthe-
sis uniform and well dispersed copper nanoparticles supported on
SiO2 by three different methods and to analyze the performance of
the catalyst for the hydrogenolysis of glycerol.
2. Experimental
2.1. Starting materials
All the chemicals used were of analytical grade. Colloidal SiO2
(LUDOX® HS-40) was procured from Sigma Aldrich. Copper nitrate
trihydrate (99.5%), sodium hydroxide (99.0%), urea (99.5%), iso-
propyl alcohol (99.8%), glycerol (99.5%) and nitric acid (69%) were
obtained from Merck. The chemicals were used as procured without
further purification.
2.4. Hydrogenolysis of glycerol
2.2. Catalyst preparation
Hydrogenolysis of glycerol was performed in 100 mL stainless
steel autoclave (Parr Instruments Co.). The reaction was carried out
using 21 mL of 20 wt% of glycerol solution with typical reaction con-
ditions and stirring speed was maintained at 500 rpm. The reactant
and the prereduced catalyst were loaded into the reactor and it was
purged with H2 for several times. Once the specified reaction tem-
perature is reached, the reactor was pressurized to desired level.
Upon the complete of reaction, the products were analyzed by Gas
Chromatograph (Chemito GC 1000) using HP-FFAP capillary col-
umn (30 m X 0.32 mm X 0.25 ␮m). The product was a mixture of
1,2-propanediol (1,2-PDO), ethylene glycol (EG), hydroxyacetone
(HA), 1-propanol, 2-propanol, methanol and ethanol and the com-
Silica-supported copper nanoparticles were prepared by depo-
sition precipitation (DP) method using urea and sodium hydroxide
as the precipitating-agents. Cu/SiO2-UDP was prepared by urea as
precipitant [49]. The colloidal silica suspension was dispersed in
1000 mL of water with appropriate amount of Cu(NO3)2·3H2O and
urea. The metal precursor and urea were taken in the mole ratio of
1:3. The suspension was stirred at room temperature and the pH of
the solution was brought down to 2–3 by addition of dil.HNO3. The
temperature of the mixture was increased to 90 ◦C and stirred for
2 h and the reaction mixture was aged at this temperature for 20 h.
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Fig. 1. XRD patterns of 5 wt% Cu/SiO2 (calcined and reduced) catalyst prepared by
IMP (a, b), NDP (c, d) and UDP (e, f) methods.
Fig. 2. XRD patterns of Cu/SiO2-UDP (calcined and reduced) catalyst with different
wt% of Cu. 5 wt% (a, b), 10 wt% (c, d), 15 wt% (e, f) and 20 wt% (g, h).
ponents are quantified to determine the conversion of glycerol and
selectivity of the products.
Moles of glycerol consumed
Moles of glycerol initially charged
in Table 1. The sample prepared by various methods exhibit large
surface area (140–150 m2/g). The formation of larger particles in
Cu/SiO2-IMP and pore blockage by sodium in Cu/SiO2-NDP might
have resulted in lower surface area when compared to Cu/SiO2-
UDP. The surface area of Cu/SiO2-UDP is found to increase with
increasing Cu loading percentage, which may be ascribed to the for-
mation of filandrous copper phyllosilicate species upon hydrolysis
of urea with silica support [44,49,52]. The formation of phyl-
losilicates species is clearly evident from the XRD patterns of
as-prepared Cu/SiO2 catalyst (Fig. 3). Upon increasing the cop-
per content in the catalyst the intensity of phyllosilicate reflection
increases, and upon calcination it is converted into highly dispersed
copper nanoparticle over the support. The copper nanoparticles are
well dispersed on the support in case of Cu/SiO2-UDP when com-
pared to Cu/SiO2-NDP and Cu/SiO2-IMP. The dispersion and specific
metal surface area are found to decrease with increase in Cu loading
percentage, which may be due to agglomeration of the nanoparti-
cles over the support. Hence a copper loading of 15 wt% is found to
be optimum as evidenced by the textural properties of the samples.
Conversion % =
× 100
× 100
( )
Moles of carbon in specific product
Moles of carbon in all the products
Selectivity % =
( )
3. Results and discussion
3.1. XRD
Fig. 1 shows the XRD pattern of calcined and reduced samples
of 5 wt% Cu/SiO2 catalysts prepared by three different methods.
Prominent diffraction peaks corresponding to CuO are observed in
calcined Cu/SiO2-IMP while the XRD pattern of reduced samples of
Cu/SiO2-IMP and Cu/SiO2-NDP featured reflections corresponding
to metallic copper. Diffraction peaks corresponding to either CuO
or metallic copper are absent in case of Cu/SiO2-UDP which indi-
cates the amorphous nature of the catalyst and fine dispersion of Cu
nanoparticles on SiO2 support [51]. Diffraction patterns of calcined
and reduced Cu/SiO2-UDP with varying copper loading are shown
in Fig. 2. When percentage of loading of copper nanoparticles is
increased from 5 to 15 wt%, appearance of reflections correspond-
ing to Cu2+ or metallic copper are not observed which signifies the
uniform dispersion of the nanoparticles on the support. Presence
of Cu2O is observed for Cu/SiO2 with 20 wt% loading which may be
ascribed to the agglomeration or low dispersion of nanoparticles
leading to the formation of larger particles.
3.3. DRUV-VIS
The diffuse reflectance ultra-violet visible (DRUV-VIS) spectra
of calcined Cu/SiO2-UDP with varying percentage of Cu loading
are shown in Fig. 4. An intense band in the UV region of the
spectrum around 205–270 nm is attributed to the ligand to metal
charge transfer between surface oxygen and isolated Cu2+ ions. The
2
2Eg → T2g transition taking place in Cu nanoparticles is responsible
for the absorption band in the visible region around 650–750 nm.
The band at 650–750 nm range is due to dispersed copper nanopar-
ticles formed on the silica support which is appearing only in the
case of samples with a Cu loading of 5–15 wt% Cu/SiO2-UDP [53,54].
Further increase in the copper content to 20 wt% resulted in band
3.2. Textural properties of the catalysts
Textural characteristics of the Cu/SiO2 catalyst prepared by dif-
ferent methods and varying copper loading percentages are given
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Table 1
Textural Properties of various Cu/SiO2 catalysts.
Catalyst
Surface areaa
(m2/g)
Pore volume
(cm3/g)
Pore size
(nm)
Dispersionb
(%)
Cu metal areab
(m2/g of Cu)
Particle sizeb
(nm)
Cu weight
(%)c
SiO2 (LUDOX® HS-40)
5 wt% Cu/SiO2-IMP
5 wt% Cu/SiO2-NDP
5 wt% Cu/SiO2-UDP
10 wt% Cu/SiO2-UDP
15 wt% Cu/SiO2-UDP
20 wt% Cu/SiO2-UDP
198–258
147
138
153
196
–
–
–
–
–
6.8
3.9
–
0.41
0.95
0.48
0.49
0.58
0.44
10.0
25.0
12.6
9.3
8.9
6.9
16.0
30.4
46.7
44.8
38.0
25.3
100
199
302
289
245
163
4.99 (5.0)
4.90 (5.0)
4.88 (5.0)
9.14 (10.0)
14.02 (15.0)
19.81 (20)
2.2 (4.4)d
2.3 (4.6)d
2.8 (5.1)d
4.1 (7.4)d
235
240
a
BET Surface area.
Calculated from N2O decomposition method.
ICP-OES analysis (the values in parentheses are nominal weight%).
Particle size calculated from TEM.
b
c
d
Fig. 3. DRUV-VIS spectra of calcined Cu/SiO2-UDP.
broadening because of the formation of bulk copper particles on
the support. Thus 15 wt% Cu loading is proved to be optimum for
Cu/SiO2-UDP catalyst.
Fig. 4. XRD patterns of as-prepared Cu/SiO2-UDP catalyst: (a) 5 wt%, (b) 10 wt%, (c)
15 wt% and (d) 20 wt%).
3.4. TPR
support. Hence it may be inferred from the TPR profile that uniform
dispersion of Cu nanoparticles is attained with Cu loading of 5, 10
and 15 wt%, and the observation is also substantiated by XRD and
chemisorption results.
TPR given the information of the nature and distribution of Cu
nanoparticles. Fig. 5. Shows the H2-TPR profiles of 5 wt% Cu/SiO2
prepared by various methods. As far as the UDP method, a sharp
peak at low temperature appears as compared to NDP and IMP
method prepared samples. As expected, the IMP samples show a
broad reduction peak at higher temperature. Fig. 6 depicts H2-TPR
profiles of calcined Cu/SiO2-UDP with varying Cu loading. A sin-
gle TPR signal at 195.1 and 198.3 ◦C is obtained for 5 and 10 wt%
of Cu loading respectively (Table 2) which signifies the fine dis-
persion of the Cu nanoparticles on silica support. The prominent
reduction peak is shifted to 202 ◦C along with a small shoulder
peak at 212.1 ◦C for 15 wt% Cu/SiO2-UDP. When the copper content
is increased to 20 wt% the prominent low temperature peak was
shifted to 204.8 ◦C along with a well distinguished high tempera-
ture peak at 217.6 ◦C which is due to formation of large particles on
the SiO2 support. Chen et al. and Marchi et al. reported that well dis-
persed and small Cu nanoparticles are reduced at a lower reduction
temperature than that of the large or bulk copper particles [55,56].
The high temperature shoulder peak observed in the case of higher
Cu loading is an indication of the formation of large particles on the
3.5. TEM and particle size distribution
TEM images and particle size distributions of Cu/SiO2-UDP with
varying Cu loading percentages are shown Fig. 7. The Cu nanopar-
ticles were found to be small (4.4, 4.7 and 5.1 nm) and uniformly
dispersed with copper loading of 5–15 wt% and exhibit a narrow
size distribution. The formation of large Cu nanoparticles is noticed
with increase in copper percentage and large particles of diameter
7.7 nm are observed in the case of Cu/SiO2-UDP with 20 wt% loading
which may be attributed to agglomeration of Cu species occurring
at high copper loading.
3.6. NH3-TPD
NH3-TPD profiles of SiO2 and Cu/SiO2-UDP with varying Cu load-
ing are presented in Fig. 8. Three distinct peaks are observed in case
of all Cu/SiO2-UDP samples, which are arising due to weak surface
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Table 2
Summary of TPR and TPD results for Cu/SiO2-UDP catalysts.
Catalyst
Reduction peak (max (◦C)a
Hydrogen consumptionb
(m mol/g cat.)
Acidity (␮ mol/g cat)c
Weak
Moderate
Strong
Total
SiO2 (LUDOX® HS-40)
5 wt% Cu/SiO2-UDP
10 wt% Cu/SiO2-UDP
15 wt% Cu/SiO2-UDP
20 wt% Cu/SiO2-UDP
49.0
33.8
37.2
60.8
109.4
129.3
94.3
115.2
209.1
312.4
–
178.3
198.3
244.6
385.6
493.1
195
198
202, 212
205, 218
0.405
0.918
1.224
0.961
70.2
92.2
115.7
71.3
a
From TPR measurements.
Hydrogen consumption values calculated from TPR analysis.
Acidity calculated from NH3-TPD traces.
b
c
Fig. 6. TPR profiles of 15 wt% Cu/SiO2-UDP (calcined).
3.7. XPS
Fig. 5. TPR profiles of 5 wt% Cu/SiO2 (calcined) prepared by different preparation
methods.
The X-ray photoelectron spectra of calcined and reduced 15 wt%
Cu/SiO2-UDP catalysts are shown in Fig. 9. The spectrum of calcined
sample featured two intense peaks corresponding to Cu(2p3/2) and
Cu(2p1/2) at 935.5 eV and 955.5 eV respectively along with a charac-
teristic satellite peak at 943.6 eV, which are due to highly dispersed
divalent Cu on silica support [37,52]. The large, positive shift in the
binding energy of copper core level reveals that Cu-ions are in dif-
ferent oxidation state in the silica matrix. The peak at 935.5 eV is
deconvoluted into two peaks centered at 933.8 and 935.7 eV which
are due to isolated CuO and the charge transfer from highly dis-
persed Cu nanoparticles to the silica support respectively [37]. In
the case of reduced Cu/SiO2 −UDP, the peaks corresponding to
Cu(2p3/2) and Cu(2p1/2) are shifted to lower binding energies which
are indicative of the presence of Cu in lower oxidative state (Cu or
Cu+). Upon reduction, most of the dispersed Cu species are present
in the reduced state with the BE value of 932.6 eV in addition with
species having a BE of 935.3 eV.
acidity around 150–225 ◦C, moderate acidity around 225–300 ◦C
and strong acidity around 300–400 ◦C. The catalysts prepared by
UDP method are showing high dispersion of copper nanoparticles
and are all exposed over the support by dividing the bigger particles
into smaller nanoparticle. The surface of particles in the metal oxide
supported catalyst are constructed by exposing the planes through
corner and edges. The exposed planes are more similar with that of
ideal lattice planes and are all uniformly exposed by cutting a big-
ger crystal. Interestingly, by breaking of such metal oxygen bonds
are induce the coordinately unsaturation over the exposed metal
centers and these centers are possess high free energy, unstable
and highly reactive [51,57]. The acidity of the catalyst is found to
increase gradually with increase in Cu content. The total acidity of
the catalyst may be due to NH3 adsorbed over the reactive high
energy coordinatively unsaturated copper phyllosilicate sites and
formation of the same is enhanced with increasing Cu loading from
5 to 20 wt%, which in turn might have resulted in the increased acid-
ity of the catalyst (Table 2) [41,51,58]. The observed enhancement
in the acidity is expected to improve the performance of the catalyst
in the dehydration of glycerol into hydroxyacetone (Scheme 1).
3.8. Catalytic activity of Cu/SiO2 catalyst
The catalytic activities of 5 wt% Cu/SiO2 prepared by different
methods are shown in Fig. 10. The Cu/SiO2-UDP exhibited supe-
rior catalytic activity for glycerol conversion (63.7%) with high
selectivity (86.7%) towards 1,2-propanediol when compared to
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Fig. 7. TEM images and particle size distribution of Cu/SiO2-UDP. (a) 5 wt%, (b) 10 wt%, (c) 15 wt% and (d) 20 wt%.
Fig. 8. NH3 − TPD profiles of Cu/SiO2-UDP.
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Fig. 11. Effect of copper loading on the activity of Cu/SiO2-UDP for hydrogenolysis
of glycerol Reaction conditions: 21 mL of 20 wt% glycerol in 2-propanol: Tempera-
ture = 200 ◦C: Catalyst weight = 0.3 g: pH2 = 60 bar: Time = 6 h: RPM = 500.
Fig. 9. XP spectra of: (a) 15 wt% Cu/SiO2-UDP calcined, (b) 15 wt% Cu/SiO2-UDP
reduced, (c) 5 wt% Cu/SiO2 −NDP reduced.
Fig. 12. Effect of catalyst weight in hydrogenolysis of glycerol over 15 wt%
Cu/SiO2-UDP Reaction conditions: 21 mL of 20 wt% glycerol in 2-propanol: Tem-
perature = 200 ◦C: pH2 60 bar: Time = 6 h: RPM = 500.
ity, the reaction conditions are optimized with respect to the same
catalyst.
The effect of copper loading on Cu/SiO2-UDP in hydrogenol-
ysis of glycerol is shown in Fig. 11. Hydrogenolysis of glycerol
is a bifunctional catalytic process where the acidity and metallic
active sites are the key factor to enhance catalytic activity. Dehy-
dration of glycerol to hydroxyacetone over acidic site followed by
hydrogenation leads to propylene glycol [14,19,59]. In this present
investigation Cu/SiO2 act as the bifunctional catalyst where the
acidic sites exposed on copper phyllosilicate might influence the
dehydration and the dispersed copper metallic species act as the
hydrogenating probe for this hydrogenolysis. The total acid sites
of the Cu/SiO2-UDP catalyst are increased with increasing the Cu
loading and this might be due of the formation of the copper phyl-
losilicate phase [41,58]. Further, these catalysts show increased
number of exposed copper metal nanoparticles over the silica sup-
port. The activity of the catalyst is enhanced with increasing Cu
Fig. 10. Catalytic activity of 5 wt% Cu/SiO2 catalyst prepared by different
methods. Reaction conditions: 21 mL of 20 wt% glycerol in 2-propanol: Tem-
perature = 200 ◦C: Catalyst weight = 0.3 g: pH2 = 60 bar: Time = 6 h: RPM = 500.
(1,2-PDO = 1,2-propanediol; EG = Ethylene Glycol; Others = Ethanol, Methanol,
Hydroxyactone, 2-Propanol and 1-propanol.).
Cu/SiO2-NDP and IMP catalysts. The efficient performance of the
Cu/SiO2-UDP catalyst in glycerol hydrogenolysis reaction may be
attributed to the high metal surface area, high dispersion of Cu
nanoparticles in addition with increased specific metallic surface
area and smaller particle size than that of the catalyst prepared by
other methods (Table 1). Since Cu/SiO2-UDP exhibited high activ-
Please cite this article in press as: K. Suthagar, et al., Hydrogenolysis of glycerol over silica-supported copper-nanocatalyst: Effect of
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Fig. 13. Effect of temperature on the activity of 15 wt% Cu/SiO2-UDP in hydrogenoly-
sis of glycerol. Reaction conditions: 21 mL of 20 wt% glycerol in 2-propanol: Catalyst
weight = 0.3 g: pH2 = 60 bar: Time = 6 h: RPM = 500..
Fig. 14. Effect of H2 pressure on the activity of 15 wt% Cu/SiO2-UDP in hydrogenol-
ysis of glycerol. Reaction conditions: 21 mL of 20 wt% glycerol in 2-propanol:
Temperature = 210 ◦C: Catalyst weight = 0.3 g: Time = 6 h: RPM = 500.
loading from 5 to 15 wt% which may be due to increased acidity,
high dispersion and improved textural properties with respect to
copper loading. The conversion of glycerol increased from 63.7% to
86.3% with increasing copper loading from 5 to 15 wt%, while fur-
ther increment in the copper percentage to 20 wt% has resulted
in a drop in conversion to 81.9%. This deterioration in the per-
formance of the catalyst may be ascribed the formation of larger
particles which decreases the dispersion of copper nanoparticles
at higher loading (20 wt%). Hence, the 15 wt% Cu/SiO2-UDP cata-
lyst was chosen for further optimization of reaction conditions. The
hydrogenolysis of glycerol over 15 wt% Cu/SiO2-UDP became more
efficient when the weight of the catalyst is increased form 150 mg
to 300 mg and further addition of the catalyst has not resulted in
any remarkable improvement (Fig. 12) and from this observation
300 mg of the catalyst was found to be optimum for maximizing the
yield. The effect of reaction temperature on the hydrogenolysis of
glycerol over 15 wt% Cu/SiO2-UDP is shown in Fig. 13. The conver-
sion of glycerol increases while increasing the reaction temperature
from 190 ◦C to 220 ◦C and approached a maximum conversion of
99.6% at 220 ◦C. However the C C bond cleavage is favored at higher
temperature (220 ◦C) has resulted in a drop in the selectivity of
1,2-propanediol and favored the formation of lower alcohols.
The effect of H2 pressure in the catalytic activity of 15 wt%
Cu/SiO2-UDP is shown in Fig. 14, where both conversion and
selectivity towards 1,2-propanediol were found to increase with
increasing the H2 pressure up to 60 bar and the activity of the
catalyst was remain unaffected with further increase in H2 pres-
sure to 70 bar. The observed improvement in the selectivity of
1,2-propanediol with an increase in H2 pressure may be ascribed to
the conversion of intermediate, hydroxyacetone (the formation of
this intermediate is favored at lower pressure) to 1,2-propanediol.
The hydrogenolysis of glycerol over 15 wt% Cu/SiO2-UDP increases
linearly with reaction time and reaches a maximum conversion of
98.4% as shown in Fig. 15 and the selectivity of propanediol is main-
tained constant at 87% during 2 − 8 h of reaction time. Hence a
reactiontimeof 8 h wouldyieldoptimumresultsfor hydrogenolysis
of glycerol over Cu/SiO2-UDP. The effect of glycerol concentration
on activity of 15 wt% Cu/SiO2-UDP is shown in Fig. 16. The selec-
tivity of 1,2-propanediol gradually increases from 85 to 90% with
increasing the concentration of glycerol while the conversion drops
down when the concentration of glycerol in 2-propanol is increased
from 10 to 50 wt%.
Fig. 15. Effect of reaction time on the activity of 15 wt% Cu/SiO2-UDP in hydrogenol-
ysis of glycerol. Reaction conditions: 21 mL of 20 wt% glycerol in 2-propanol:
Temperature = 210 ◦C: Catalyst weight = 0.3 g: pH2 = 60 bar: RPM = 500..
The influence of the solvents on the catalytic activity of 15 wt%
Cu/SiO2-UDP is shown in Fig. 17. The activity of the catalyst
for the conversion of glycerol (98%) and its selectivity towards
1,2-propanediol (87%) are similar in case of 2-propanol and 1,4-
dioxane, whereas the catalytic activity is found to reduce in the
case of water. Upon using 2-propanol as the solvent the agglomera-
tion of copper nanoparticles growth under the reaction conditions
were controlled for boron incorporated Cu/SiO2 catalyst and this
catalyst exhibited high activity for hydrogenolysis of glycerol in 2-
propanol when compared aqueous medium [45]. Wang et al. and
Zhu et al., reported that the nature of solvent plays a crucial role
in conversion and selectivity of products and use of water as sol-
vent which influence in increasing the particle size of catalyst under
the reaction conditions when compared to other solvents [45,60].
The decrease in activity in water may be due to the aggregation of
Please cite this article in press as: K. Suthagar, et al., Hydrogenolysis of glycerol over silica-supported copper-nanocatalyst: Effect of
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Fig. 18. Recyclability of the 15 wt% Cu/SiO2-UDP catalyst for the hydrogenolysis
of glycerol Reaction conditions: 21 mL of 20 wt% glycerol in 2-propanol: Tempera-
ture = 200 ◦C: Catalyst weight = 0.3 g: pH2 = 60 bar: Time = 8 h: RPM = 500.
Fig. 16. Effect of glycerol concentration on the activity of 15 wt% Cu/SiO2-UDP.
Reaction conditions: Temperature = 210 ◦C: Catalyst weight = 0.3 g: pH2 = 60 bar:
Time = 8 h: RPM = 500.
Fig. 19. XRD pattern of 15 wt% Cu/SiO2-UDP recycled catalyst.
3rd cycle) which will eventually result in reduced number of active
sites leading to substandard activity of the catalyst.
Fig. 17. Influence of solvent in hydrogenolysis of glycerol over 15 wt% Cu/SiO2-
UDP. Reaction conditions: 21 mL of 20 wt% glycerol: Temperature = 210 ◦C: Catalyst
weight = 0.3 g: pH2 = 60 bar: Time = 8 h: RPM = 500.
4. Conclusion
copper particles which decreases the number of active sites on the
silica support.
SiO2 supported copper-nanocatalysts have been successfully
synthesized by deposition precipitation method using urea and
sodium hydroxide as the precipitants. Urea, when used as the
precipitant has resulted in uniform and fine dispersion of Cu
nanoparticles on the support. As the percentage of Cu loading is
increased, acidity of the catalyst is found to improve, leading to
improved activity and the catalyst with 15 wt% Cu exhibited supe-
rior performance. Though the acidity is increased when copper
loading is increased beyond 15 wt%, agglomeration of nanocatalyst
occurs at higher loading and the same is found to be detrimen-
tal for the catalytic performance. 15 wt% Cu/SiO2-UDP catalyst
exhibited 98% conversion of glycerol with 87% selectivity towards
The catalytic performance of 15 wt% Cu/SiO2-UDP was analyzed
for the hydrogenolysis of glycerol under the optimized reaction
conditions. The fresh catalyst exhibited conversion of 98.4% with
a selectivity of 87.2% towards 1, 2- propanediol. The performances
of the fresh and recycled catalyst are shown in Fig. 18. The catalytic
activity of recycled catalyst deteriorated gradually when compared
to fresh catalyst. The XRD pattern and TEM images of the recycled
catalyst are shown in Figs. 19 and 20, respectively. The agglomer-
ation of the Cu nanoparticles during the reaction is evident from
XRD pattern and the TEM images of the recycled catalyst (after the
Please cite this article in press as: K. Suthagar, et al., Hydrogenolysis of glycerol over silica-supported copper-nanocatalyst: Effect of
precipitating-agent and copper metal-loading, Mol. Catal. (2017), https://doi.org/10.1016/j.mcat.2017.11.035

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[14] T. Miyazawa, S. Koso, K. Kunimori, K. Tomishige, Appl. Catal. A 318 (2007)
244–251.
[15] L. Ma, D. He, Z. Li, Chem. Commun. 9 (2008) 2489–2495.
[16] M. Tamura, Y. Amada, S. Liu, Z. Yuan, Y. Nakagawa, K. Tomishige, J. Mol. Catal.
A. 388–389 (2014) 177–187.
[17] S. Koso, H. Watanabe, K. Okumura, Y. Nakagawa, K. Tomishige, Appl. Catal. B
111–112 (2012) 27–37.
[18] G.D. Yadav, P.A. Chandan, D.P. Tekale, Ind. Eng. Chem. Res. 51 (2012)
1549–1562.
[19] M. Balaraju, V. Rekha, P.S.S. Prasad, B.L.A.P. Devi, R.B.N. Prasad, N. Lingaiah,
Appl. Catal. A 354 (2009) 82–87.
[20] L. Ma, D. He, Top. Catal. 52 (2009) 834–844.
[21] S. Zhu, Y. Qiu, Y. Zhu, S. Hao, H. Zheng, Y. Li, Catal. Today 212 (2013) 120–126.
[22] L. Ma, D. He, Catal. Today 149 (2010) 148–156.
[23] X. Guo, Y. Li, R. Shi, Q. Liu, E. Zhan, W. Shen, Appl. Catal. A 371 (2009) 108–113.
[24] X. Guo, Y. Li, W. Song, W. Shen, Catal. Lett. 141 (2011) 1458–1463.
[25] J. Zhao, W. Yu, C. Chen, H. Miao, H. Ma, J. Xu, Catal. Lett. 134 (2010) 184–189.
[26] A. Perosa, P. Tundo, Ind. Eng. Chem. Res. 44 (2005) 8535–8537.
[27] C. Liang, Z. Ma, L. Ding, J. Qiu, Catal. Lett. 130 (2009) 169–176.
[28] W. Yu, J. Zhao, H. Ma, H. Miao, Q. Song, J. Xu, Appl. Catal. A 383 (2010) 73–78.
[29] N.D. Kim, S. Oh, J.B. Joo, K.S. Jung, J. Yi, Top. Catal. 53 (2010) 517–522.
[30] R.B. Mane, A.M. Hengne, A.A. Ghalwadkar, S. Vijayanand, P.H. Mohite, H.S.
Potdar, C.V. Rode, Catal. Lett. 135 (2010) 141–147.
[31] L. Huang, Y.-L. Zhu, H.-Y. Zheng, Y.-W. Li, Z.-Y. Zeng, J. Chem. Technol.
Biotechnol. 83 (2008) 1670–1675.
[32] A. Bienholz, F. Schwab, P. Claus, Green Chem. 12 (2010) 290–295.
[33] M. Balaraju, V. Rekha, P.S. Sai Prasad, R.B.N. Prasad, N. Lingaiah, Catal. Lett.
126 (2008) 119–124.
Fig. 20. TEM image and particle size distribution of 15 wt% Cu/SiO2-UDP recycled
catalyst after 3rd cycle on hydrogenolysis of glycerol.
[34] E.S. Vasiliadou, E. Heracleous, I.A. Vasalos, A.A. Lemonidou, Appl. Catal. B 92
(2009) 90–99.
[35] S. Bolado, R.E. Trevin˜o, M.T. García-Cubero, G. González-Benito, Chem.
Commun. 12 (2010) 122–126.
[36] M. Balaraju, V. Rekha, B.L.A.P. Devi, R.B.N. Prasad, P.S.S. Prasad, N. Lingaiah,
Appl. Catal. A 384 (2010) 107–114.
1,2-propanediol under the optimized reaction conditions with
good recyclability.
[37] Z. Huang, F. Cui, H. Kang, J. Chen, X. Zhang, C. Xia, Chem. Mater. 20 (2008)
5090–5099.
Acknowledgement
[38] L.C. Meher, R. Gopinath, S.N. Naik, A.K. Dalai, Ind. Eng. Chem. Res. 48 (2009)
1840–1846.
[39] Z. Yuan, L. Wang, J. Wang, S. Xia, P. Chen, Z. Hou, X. Zheng, Appl. Catal. B 101
(2011) 431–440.
The authors thank the Ministry of New and Renewable Energy
(MNRE) for the NREF fellowship for one of the authors, K. Sutha-
gar. Thanks are also due to the New Millennium Indian Technology
Leadership Initiative (NMITLI) programme (No. 5/258/52/2006-
NMITLI) of Council of Scientific and Industrial Research (CSIR), New
Delhi for financial support. The authors also thank the Depart-
ment of Science and Technology, New Delhi for funding NCCR,
IIT-Madras. Authors acknowledge Prof. B. Viswanathan for fruitful
discussions.
[40] Z. Huang, F. Cui, H. Kang, J. Chen, C. Xia, Appl. Catal. A 366 (2009) 288–298.
[41] K.-T. Li, C.-H. Wang, H.-C. Wang, J. Taiwan Inst. Chem. Eng. 52 (2015) 79–84.
[42] A. Bienholz, H. Hofmann, P. Claus, Appl. Catal. A 391 (2011) 153–157.
[43] Z. Huang, F. Cui, J. Xue, J. Zuo, J. Chen, C. Xia, Catal. Today 183 (2012) 42–51.
[44] S. Zhu, X. Gao, Y. Zhu, W. Fan, J. Wanga, Y. Li, Catal. Sci. Technol. 5 (2015)
1169–1180.
[45] S. Zhu, X. Gao, Y. Zhu, Y. Zhu, H. Zheng, Y. Li, J. Catal. 303 (2013) 70–79.
[46] Z. Huang, H. Liu, F. Cui, J. Zuo, J. Chen, C. Xia, Catal. Today 234 (2014) 223–232.
[47] E.S. Vasiliadou, A.A. Lemonidou, Appl. Catal. A 396 (2011) 177.
[48] C. Sepúlvedaa, L. Delgadoa, R. Garcíaa, M. Melendrezb, J.L.G. Fierroc, I.T.
Ghampsond, N. Escalona, Catal. Today 279 (2017) 217–223.
[49] C.J.G. Van Der Grift, P.A. Elberse, A. Mulder, J.W. Geus, Appl. Catal. 59 (1990)
275–289.
[50] K.V.R. Chary, G.V. Sagar, D. Naresh, K.K. Seela, B. Sridhar, J. Phys. Chem. B 109
(2005) 9437–9444.
[51] F. Zaccheria, N. Scotti, M. Marelli, R. Psaro, N. Ravasio, Dalton Trans. 42 (2013)
1319–1328.
[52] Z. Huang, F. Cui, J. Xue, J. Zuo, J. Chen, C. Xia, J. Phys. Chem. C 114 (2010)
16104–16113.
[53] H. Praliaud, S. Mikhailenko, Z. Chajar, M. Primet, Appl. Catal. B 16 (1998)
359–374.
[54] J. Liu, W. Song, C. Xu, J. Liu, Z. Zhao, Y. Wei, A. Duan, G. Jiang, RSC Adv. 5 (2015)
104923–104931.
[55] L.-F. Chen, P.-J. Guo, M.-H. Qiao, S.-R. Yan, H.-X. Li, W. Shen, H.-L. Xu, K.-N. Fan,
J. Catal. 257 (2008) 172–180.
[56] A.J. Marchi, J.L.G. Fierro, J. Santamaría, A. Monzón, Appl. Catal. A 142 (1996)
375–386.
[57] G. Busca, Phys. Chem. Chem. Phys. 1 (1999) 723–736.
[58] F. Dong, Y. Zhu, H. Zhaoa, Z. Tang, Catal. Sci. Technol. 7 (2017) 1880–1891.
[59] D. S1un, Y. Yamada, S. Sato, W. Ueda, Appl. Catal. B 193 (2016) 75–92.
[60] C. Wang, H. Jiang, C. Chen, R. Chen, W. Xing, Chem. Eng. J. 264 (2015) 344–350.
References
[1] C.H.C. Zhou, J.N. Beltramini, Y.X. Fan, G.Q. Lu, Chem. Soc. Rev. 37 (2008)
527–549.
[2] A. Corma, S. Iborra, A. Velty, Chem. Rev. 107 (2007) 2411–2502.
[3] Y. Wang, J. Zhou, X. Guo, RSC Adv. 5 (2015) 74611–74628.
[4] M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, C. Della Pina, Angew. Chem. Int.
Ed. 46 (2007) 4434–4440.
[5] S. Mahendran, P. Selvam, Adv. Porous Mater. 2 (2014) 1–6.
[6] K. Suthagar, B., Viswanathan, P. Selvam, Indian Patent 277097, (2010).
[7] M.A. Dasari, P.P. Kiatsimkul, W.R. Sutterlin, G.J. Suppes, Appl. Catal. A 281
(2005) 225–231.
[8] J. Chaminand, L. Djakovitch, P. Gallezot, P. Marion, C. Pinel, C. Rosier, Green
Chem. 6 (2004) 359–361.
[9] T. Haas, D. Arntz, US Patent 5364987, 1994.
[10] A. Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Green Chem. 10 (2008)
13–30.
[11] G.A. Kraus, Clean 36 (2008) 648–651.
[12] I. Furikado, T. Miyazawa, S. Koso, A. Shimao, K. Kunimori, K. Tomishige, Green
Chem. 9 (2007) 582–588.
[13] Y. Shinmi, S. Koso, T. Kubota, Y. Nakagawa, K. Tomishige, Appl. Catal. B 94
(2010) 318–326.
Please cite this article in press as: K. Suthagar, et al., Hydrogenolysis of glycerol over silica-supported copper-nanocatalyst: Effect of
precipitating-agent and copper metal-loading, Mol. Catal. (2017), https://doi.org/10.1016/j.mcat.2017.11.035