Surface and structural properties of titania-supported Ru catalysts for hydrogenolysis of glycerol

Article abstract of DOI:10.1016/j.apcata.2010.06.013

A series of catalysts with different Ru contents supported on titania were prepared by conventional impregnation (IM) and deposition-precipitation (DP) methods. These catalysts were characterized by X-ray diffraction, temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy and CO chemisorption. The catalysts were evaluated for selective hydrogenolysis of glycerol. The glycerol conversion and the selectivity towards 1,2-propanediol depend on the method of catalyst preparation and on the Ru content. The catalyst with low Ru content exhibited maximum conversion, in turn was related to its dispersion. The catalysts prepared by DP method showed stable activity even with crude glycerol containing alkali salts as impurity. The catalyst exhibited consistent activity upon reuse. The high activity of Ru/TiO₂ catalyst is due to the presence of well-dispersed nano size Ru particles on titania. The low activity of the IM catalyst is because of large domains of Ru and because of the presence of residual Cl^- ions.

Full text of DOI:10.1016/j.apcata.2010.06.013

Applied Catalysis A: General 384 (2010) 107–114
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Surface and structural properties of titania-supported Ru catalysts for
hydrogenolysis of glycerol
M. Balarajua, V. Rekhaa, B.L.A. Prabhavathi Devib, R.B.N. Prasadb, P.S. Sai Prasada, N. Lingaiaha,∗
a Catalysis Laboratory, I&PC Division, Indian Institute of Chemical Technology, Hyderabad 500607, India
b Lipid Science &Technology Division, Indian Institute of Chemical Technology, Hyderabad 500607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of catalysts with different Ru contents supported on titania were prepared by conventional
impregnation (IM) and deposition–precipitation (DP) methods. These catalysts were characterized by
X-ray diffraction, temperature programmed reduction, transmission electron microscopy, X-ray photo-
electron spectroscopy and CO chemisorption. The catalysts were evaluated for selective hydrogenolysis
of glycerol. The glycerol conversion and the selectivity towards 1,2-propanediol depend on the method
of catalyst preparation and on the Ru content. The catalyst with low Ru content exhibited maximum con-
version, in turn was related to its dispersion. The catalysts prepared by DP method showed stable activity
even with crude glycerol containing alkali salts as impurity. The catalyst exhibited consistent activity
upon reuse. The high activity of Ru/TiO2 catalyst is due to the presence of well-dispersed nano size Ru
particles on titania. The low activity of the IM catalyst is because of large domains of Ru and because of
the presence of residual Cl− ions.
Received 18 December 2009
Received in revised form 10 June 2010
Accepted 10 June 2010
Available online 17 June 2010
Keywords:
Glycerol
Ruthenium
Titania
Hydrogenolysis
1,2-Propanediol
Deposition–precipitation
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
functionalized molecule and a variety of value added chemicals
could be derived from glycerol by different reactions [1,13,14]. The
The use of renewable feedstock is essential for the sustainable
development of society. The conversions of renewable feedstock
into chemicals and fuels are important in the present scenario, as
the availability of fossil fuels is limited. Catalysts play an important
role to convert biorenewable feedstock to commodity chemicals
and clean fuels [1–6]. In recent times, synthesis of biodiesel by
transesterification of vegetable oils and fats is identified as one
of the important conversion processes of renewable feedstock [7].
Biodiesel production in the European Union was estimated to be
about 6 Mt in 2006 and is forecasted to increase to about 12 Mt in
2010 [8]. Recently, a European Union Directive stated that by the
end of 2010, traffic fuels should contain at least 5.75% of renew-
able bio-components [1]. The global biodiesel market is estimated
to reach 37 billion gallons by 2016, growing at an average annual
rate of 42%.
broad overviews on the chemistry of glycerol and its conversion to
new products are presented in the latest reviews [12–14]. Conver-
sion of glycerol into valuable chemicals by a green catalytic process
is a challenging area of research. Among different possible valuable
chemicals, glycerol to propanediols is an important reaction.
Selective hydrogenolysis of glycerol yields to 1,2-propanediol
(1,2-PD), 1,3-propanediol (1,3-PD) and ethylene glycol (EG) as
main products [15,16]. The diols are used widely in the synthe-
sis of pharmaceuticals, polymers, agricultural adjuvants, plastics
and transportation fuel [17–19]. The commercial route to pro-
duce propylene glycol or ethylene glycols is by the hydration of
propylene oxide or ethylene oxide derived from propylene or ethy-
lene [11,15,19–23]. Heterogeneous catalytic conversion of glycerol
to propanediol is an economically and environmentally attractive
process [12].
Glycerol is the by-product in biodiesel synthesis and has been
identified as one of the top ten building blocks in the bio refin-
ery feed stocks [9–11]. Production of glycerol is increasing with
increase of biodiesel production and this leads to a glut in the mar-
ket. Utilization of crude glycerol is an alternative route to increase
the profitability of biodiesel production [12]. Glycerol is a highly
Two types of catalysts are used for glycerol hydrogenolysis
reaction. Mainly, Cu based mixed oxides and supported noble
metal catalysts are the types of catalysts used for this reac-
tion [18,19,21,23–28]. Among noble metal catalysts, supported
Ru metal catalysts are more active for selective hydrogenoly-
sis of glycerol than other catalysts [25–28]. Addition of solid
acid catalyst to a supported noble metal catalyst enhances the
conversion and selectivity in hydrogenolysis of glycerol compared
to the results for supported noble metal catalyst alone [16,28]. It is
reported that addition of solid acid to metal catalysts enhances the
∗
Corresponding author. Tel.: +91 40 27193163; fax: +91 40 27160921.
E-mail address: nakkalingaiah@iict.res.in (N. Lingaiah).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.06.013

108
M. Balaraju et al. / Applied Catalysis A: General 384 (2010) 107–114
conversion and selectivity of the reaction, as the reaction proceeds
via dehydration of glycerol to acetol over solid acid and consecutive
hydrogenation on metal catalyst [16,28–30]. The authors reported
the role of solid acid as co-catalyst and the direct relation between
acidity of the co-catalysts with glycerol conversion has been elu-
cidated [11]. Both acid and metal functionalities are required for
hydrogenolysis of glycerol. Use of a single catalyst for the selective
conversion of glycerol to 1,2-PD is more advantageous. Alhanash
et al. [23] prepared a bifunctional catalyst by loading Ru onto a
heterpoly acid salt Cs2.5H0.5(PW12O40). This catalyst showed about
96% selectivity to 1,2-propanediol with 21% glycerol conversion
at 150 ◦C for 10 h. Feng et al. [29] studied in detail about the Ru
supported catalysts for glycerol hydrogenolysis. The effect of both
support and catalyst reduction temperatures were studied and the
results suggested that the support can influence the metal parti-
cle size and thereby its activity. Among the TiO2, SiO2, NaY, and
␥-Al2O3 supports, TiO2 is a better support for obtaining high glyc-
erol conversion whereas SiO2 is choice of support for getting high
selectivity to 1,2-PD. Even so the Ru/TiO2 catalyst exhibited high
glycerol conversion the selectivity towards 1,2-PD is low. The role
of support is explained, but the detailed reasons for the low selec-
tivity are not yet explored. The role of precursor and method of
preparation of the catalysts are also important and there is a need
to understand these in detail. The precursor of Ru is also important
and the precursor with Cl− ion leads lower selectivity to 1,2-PD due
to the excessive hydrogenolysis to propanediols [31].
Temperature programmed reduction (TPR) experiments were
carried out on an Auto Chem 2910 (Micromeritics) instrument. In a
typical experiment ca.100 mg of oven-dried samples was taken in a
quartz sample tube. Prior to TPR runs, the catalyst sample was pre-
treated in argon gas at 300 ◦C for 2 h. After pretreatment, the sample
was cooled to ambient temperature and the carrier gas consisting of
5% hydrogen balance argon (50 mL/min), was allowed to pass over
the sample. The temperature of the sample was increased from
ambient to 800 ◦C at a heating rate of 10 ◦C/min and the hydrogen
consumption was monitored with a thermal conductivity detector.
X-ray photoelectron spectroscopy (XPS) measurements were
conducted on a KRATOS AXIS 165 with a DUAL anode (Mg and Al)
apparatus using Mg K␣ anode. The non-monochromatized Al K␣
X-ray source (hꢁ = 1486.6 eV) was operated at 12.5 kV and 16 mA.
Before acquisition of the data each sample was out-gassed for about
3 h at 100 ◦C under vacuum of 1.0 × 10−7 T to minimize surface
contamination. The XPS instrument was calibrated using Au as
standard. For energy calibration, the carbon 1s photoelectron line
was used. The carbon 1s binding energy was taken as 285 eV. Charge
neutralization of 2 eV was used to balance the charge up of the
sample. The spectra were deconvoluted using Sun Solaris Vision-
2 curve resolver. The location and the full width at half maximum
(FWHM) value for the species were first determined using the spec-
trum of a pure sample. Symmetric Gaussian shapes were used in
all cases. Binding energies for identical samples were, in general,
reproducible within 0.1 eV.
In the present work, titania supported Ru catalysts are pre-
pared by both impregnation and deposition precipitation methods
and are studied for glycerol hydrogenolysis. The role of method of
preparation and Ru content on glycerol hydrogenolysis was stud-
ied. The influences of metal particle size, metal support interaction,
surface species and the morphology of the catalyst derived from
different characterized methods are correlated with the observed
hydrogenolysis activity.
CO chemisorption measurements were carried out using an
Auto Chem 2910 instrument. Prior to adsorption measurements,
each catalyst sample (100 mg) was reduced in a flow of hydrogen
(50 ml/min) at 300 ◦C for 2 h, and flushed subsequently in He flow
for an hour at 300 ◦C, and cooled to ambient temperature in the
samegas flow. CO uptakewas measuredbyinjectinganumber of CO
pulses through a calibrated on-line sampling valve, CO pulses were
injected until there was no more adsorption by catalyst. Ruthe-
nium metal surface area and dispersion and average particle size
were calculated assuming the stoichiometric factor for CO to Ru as
1.
2. Experimental
The morphological features of the catalysts were monitored
using a JEOL JEM 2000EXII transmission electron microscope, oper-
ating between 160 and 180 kV. The specimens were prepared by
dispersing the samples in methanol using an ultrasonic bath and
evaporating a drop of resultant suspension onto the lacey carbon
support grid.
2.1. Catalyst preparation
Titania supported Ru catalysts were prepared by conventional
impregnation (IM) and deposition–precipitation (DP) methods
using aqueous solutions of RuCl3·nH2O. In the conventional IM
method, a calculated amount of aqueous metal precursor solution
was added to TiO2 and excess water was evaporated on a water
bath followed by oven drying for 12 h at 120 ◦C. In the DP method,
the support was suspended in the aqueous solution of RuCl3·nH2O;
Ru(OH)3 was exclusively precipitated on the support by the slow
addition of 1 M Na2CO3 solution until the pH of the solution reached
a value of 10.5. The resultant solid was filtered and washed with
deionized water several times until no chloride ion was detected
in the filtrate as confirmed by AgNO3 test. The solid thus obtained
was oven dried at 120 ◦C for 12 h. Each catalyst was reduced in H2
flow at 300 ◦C for 2 h before its use for glycerol hydrogenolysis. The
numbers indicate the wt.% of Ru on support.
2.3. Activity measurements
Hydrogenolysis of glycerol was carried out in 80 ml haste alloy
PARR 4843 autoclave. In a typical experiment, the required quan-
tities of glycerol diluted with deionized water and of catalyst
were taken. Prior to the experiment the supported Ru catalyst was
reduced at 300 ◦C for 2 h with H2 (60 ml/min). The autoclave was
purged with H2 flow to drive off the air present in autoclave. After
purging, the reaction temperature and the hydrogen pressure were
raised to the required temperature and pressure. After the reac-
tion, the autoclave was cooled, the gas products were collected in a
Teflon bag, and the liquid products were separated from the catalyst
by filtration. The liquid products were analyzed by gas chro-
matography (Shimadzu 2010) using a flame ionization detector
by separating them on Inno wax capillary column. Products were
identified by using GC–MS (Shimadzu, GCMS-QP2010S) analysis.
The gas phase products were analyzed using a gas chromatograph
equipped with a Porapak Q column and a thermal conductivity
detector. The products identified during glycerol hydrogenolysis
are 1,2-PD, 1,3-PD, 1-propanol (1-PO), and 2-propanol (2-PO) as
hydrogenolysis products and EG, ethanol, methanol, ethane and
methane are as degradation products.
2.2. Catalyst characterization
The BET surface areas of the catalyst samples were calculated
from N2 adsorption–desorption data acquired on an Autosorb-1
instrument (Quantachrome, USA) at liquid N2 temperature.
Powder X-ray diffraction (XRD) patterns of the catalysts were
recorded on a Rigaku Miniflex (Rigaku Corporation, Japan) X-ray
diffractometer using Ni filtered Cu K␣ radiation (ꢀ = 1.5406 Å) with
a scan speed of 2◦ min−1 and a scan range of 10–80◦ at 30 kV and
15 mA.

M. Balaraju et al. / Applied Catalysis A: General 384 (2010) 107–114
109
Table 1
Physico-chemical properties of Ru/TiO2 catalysts.
Catalyst
BET surface area (m2/g)
Dispersion (%)
Specific metal area (m2/g)
Particle size (nm)a
TiO2
52
51
49
47
44
40
–
–
–
1Ru/TiO2 (DP)
2Ru/TiO2 (DP)
5Ru/TiO2 (DP)
5Ru/TiO2 (IM)
7Ru/TiO2 (DP)
53.0
42.0
29.4
9.7
4.5
8.0
7.2
2.4
5.1
1.1
1.2
3.4
10.2
6.3
18.6
a
Particle size determined from CO chemisorption.
Conversion of the glycerol was calculated on the basis of the
following equation:
The reducibility of Ru/TiO2 catalysts was investigated by TPR;
the profiles of the catalysts are shown in Fig. 2. The TPR pattern
of the catalyst prepared by IM method is also shown in the same
figure for comparison. The catalysts exhibited one main reduction
peak between 120 and 130 ◦C related to the single stage reduction
of RuO2 to Ru. Another reduction peak at high temperature around
240–260 ◦C, which is prominent for catalysts with high Ru content,
is due to the reduction of bulk RuO2 present on the surface. The IM
catalyst showed the main reduction peaks at 194 and 234 ◦C. The
reduction of Ru at high temperature for IM catalyst might be due
to the presence of residual Cl− ions. The presence of residual Cl−
hinders easy reduction of metal oxide.
moles of glycerol consumed
Conversion (%) =
moles of glycerol intitially charged
The selectivity of the products was calculated on carbon basis.
moles of carbon in specific product
Selectivity (%) =
× 100.
moles of carbon in all delected products
3. Results and discussion
XPS analysis was carried out for reduced Ru/TiO2 catalysts and
the patterns are shown in Fig. 3. Since the binding energy of Ru 3d5/2
(∼280 eV) overlapped with that of C 1s (∼284 eV), it was difficult
to resolve the small Ru peak out from the large peak of C 1s. After
a careful deconvolution, peaks at 280, 283, 286 and 288 eV were
detected for the catalysts. The B.E. of 280 and 283 eV is related to the
chemical states of Ru0 and Run+ respectively. The Ru/TiO2 catalysts
prepared by the DP method showed an additional Ru doublet with a
B.E. of 283.4 eV attributed to Ru(IV) species [32]. The Ru(IV) species
are formed when the pre-reduced catalysts are exposed to run XPS
analyzes. The B.E. of 288 eV may be an Auger signal of a Na impurity
that may be present in the catalyst. No such Auger signal is observed
for the catalyst prepared by IM method.
The dispersion of Ru was measured by CO chemisorption; the
results are summarized in Table 1. The average particle size was cal-
culated based on CO chemisorption values by assuming spherical
particles. The CO chemisorption results suggest that the Ru particles
were highly dispersed on the support, with a particle size <5 nm.
The crystallite size of Ru particles increased with Ru loading due
to the formation of crystalline Ru particles, as noticed from XRD.
The crystallite size of Ru measured from CO chemisorption is in
3.1. Catalyst characterization
The physico-chemical properties of the catalysts are reported in
Table 1. The specific surface area of support TiO2 was found to be
52 m2/g. The decrease in the BET surface area of the catalysts with
increase in Ru loading is presumably a result of pore blockage by
the crystallites of Ru.
The XRD patterns of the reduced catalysts are shown in Fig. 1.
The XRD pattern of the 5 wt.% Ru/TiO2 prepared by IM method
appears in the same figure. The catalyst samples exhibited peaks
at 2ꢂ value of 25.3, 37.8, 48.1 and 54 corresponding to the anatase
phase of titania. Small peaks related to rutile phase of titania were
observed at 2ꢂ values of 27.4, 36.1 and 54.3. No characteristic peak
related to metallic Ru was found at a loading of below 5 wt.% of Ru.
A peak at the 2ꢂ value of 44.03 related to metallic Ru was observed
for the catalysts with loading of 5 wt.% of Ru. However the catalyst
prepared by IM method showed the presence of Ru crystallites. The
absence of a crystallographic pattern of Ru metal at low Ru content
might be due to the presence of nano (<40 Å) Ru particles in a highly
dispersed state on the support.
Fig. 1. X-ray diffraction patterns of the supported Ru catalysts (ꢀ) anatase; (#) rutile
of TiO2; and (*) Ru.
Fig. 2. Temperature programmed reduction profiles of the catalysts.

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M. Balaraju et al. / Applied Catalysis A: General 384 (2010) 107–114
Table 2
Glycerol hydrogenolysis activity over Ru/TiO2 catalysts.
Selectivity (%)
Catalyst
Conversion (%)
1,2-PD
EG
Acetol
Others
5Ru/TiO2 (DP)
5Ru/TiO2 (IM)
44
31
58
59
17
24
4
2
21
15
Reaction conditions: glycerol conc.: 20 wt.%, H2 pressure: 60 bar, reaction time: 8 h,
reaction temperature: 180 ◦C, catalyst wt.: 6%.
sor contains polymeric species which favors the sintering in the
presence of Cl−. These Cl− ions remain on the support [33,34].
3.2. Glycerol hydrogenolysis activity
3.2.1. Effect of method of catalyst preparation
The catalytic activity of Ru/TiO2 catalysts prepared by both IM
and DP methods was studied for glycerol hydrogenolysis; results
are presented in Table 2. The glycerol conversions and selectivities
varied with changes in catalyst preparation method. The catalyst
prepared by the DP method showed better activity than the cata-
lyst prepared by the IM method. Hydrogenolysis activity of titania
was also tested and there was no reaction without Ru. The differ-
ence in activity with change in preparation method might be due
to the difference in the nature of the Ru species. The catalysts were
prepared using RuCl3 as precursor; during preparation, chloride
species might be present on surfaces for the catalyst prepared by IM
method. The Cl− species are not easily removed completely during
reduction for IM catalyst. The XPS analysis suggests the presence
of surface Cl− species for the catalyst prepared by the IM method.
In case of the catalyst prepared by the DP method the RuCl3 was
precipitated to Ru(OH)3 and the chloride species are removed com-
pletely. TPR pattern of the catalyst prepared by the IM method also
supports the presence of residual Cl− as it showed a high tempera-
ture reduction peak (Fig. 2). In the case of DP catalyst, the Ru(OH)3
is easily reduced during pretreatment, leading to well dispersed
Ru particles on the support. CO chemisorption and TEM results
suggest the presence of well-dispersed Ru particles compared to
IM catalyst. The presence of highly dispersed Ru particles in the
case of the DP method catalyst is responsible for the high glycerol
conversion.
Fig. 3. XPS spectra of reduced Ru/TiO2 catalysts.
good agreement with XRD results. The dispersion of Ru decreased
with increase in Ru loading. It is observed a very high dispersion for
the catalyst with 2 wt.% of Ru. The dispersion values are decreased
at high Ru loading due to the formation of large Ru ensembles.
Comparing the dispersion and particle size of the 5 wt.% Ru/TiO2
catalysts prepared by IM and DP methods reveal that the catalyst
prepared by the DP method possesses smaller Ru particles with
higher dispersion than the catalyst prepared by the IM method.
The morphological features of 5 wt.% Ru catalysts prepared by
both IM and DP method were studied by transmission electron
microscopy. The micrographs of these catalysts are shown in Fig. 4.
The images reveal that the catalysts prepared by the DP method
possess uniformly distributed nano Ru particles on TiO2. The TEM
image of IM catalyst exhibited large ensembles of Ru particles. The
particle size of Ru estimated by TEM measurement is comparable
with the values obtained from CO chemisorption measurements.
The catalyst prepared by the DP method allowed Ru to disperse
uniformly on TiO2 thus leading to the formation of nano-sized Ru
particles. Smaller Ru metal particles are formed for Ru supported
catalysts prepared by Cl− free precursor [31]. In the case of IM
method, the aqueous solution of RuCl3 that was used as precur-
3.2.2. Effect of ruthenium loading
As the catalysts prepared by the DP method showed better activ-
ity, a series of catalysts with different Ru contents were prepared;
these catalyst activities for glycerol hydrogenolysis are shown in
Table 3. The high glycerol conversion of about 46% with 82% com-
Fig. 4. TEM images of Ru/TiO2 catalysts.

M. Balaraju et al. / Applied Catalysis A: General 384 (2010) 107–114
111
Table 3
Effect of Ru content on hydrogenolysis of glycerol.
Selectivity (%)
Catalyst
Conversion (%)
1,2-PD
EG
Acetol
Others
1Ru/TiO2 (DP)
2Ru/TiO2 (DP)
5Ru/TiO2 (DP)
7Ru/TiO2 (DP)
35
46
44
40
64
63
58
64
18
19
17
18
2
2
4
7
16
16
21
11
Reaction conditions: glycerol conc.: 20 wt.%, H2 pressure: 60 bar, reaction time: 8 h,
reaction temperature: 180 ◦C, catalyst wt.: 6%.
bined glycol selectivity was achieved at a loading of 2 wt.% of
Ru. Low Ru metal loading (2 wt.%) was sufficient to achieve opti-
mum glycerol conversion when the catalysts are prepared by the
DP method. The high activity for the catalyst with low Ru was
mainly because of well-dispersed nano Ru particles. The 2-wt.%
Ru/TiO2 catalyst exhibited the highest dispersion (Table 2). The
presence of the large particles for the catalysts with high Ru content
might be the reason for the decrease in activity. The XRD and CO
chemisorption results suggest the presence of large particles with
low dispersion for the catalyst with high Ru on titania.
Fig. 5. Effect of reaction temperature on glycerol hydrogenolysis over Ru/TiO2 cat-
alysts.
Reaction conditions: glycerol conc.: 20 wt.%, H2 pressure: 60 bar, reaction time: 8 h,
catalyst wt.: 6%.
In order to understand the role of support TiO2 for glycerol
hydrogenolysis, we carried out the reaction with Ru/TiO2 in the
presence of N2 gas instead of H2. Very low conversion (3%) of glyc-
erol was observed. However, the main product was acetol. At the
same time, the reaction was also carried with TiO2 in the presence of
H2. There is no conversion of glycerol, suggesting that TiO2 cannot
promote the hydrogenlosis of glycerol. These results suggest that
Ru is responsible for the dehydration and hydrogenation, leading
to the formation of 1,2-PD. Chiu et al. [35] reported the formation of
acetol from glycerol during catalytic reactive distillation over tran-
sition metal catalysts. The formation of acetol during the reaction
as seen in Tables 2 and 3 further suggests that the Ru based catalysts
are following dehydration followed by hydrogenation route. Sup-
ported Ru, Pd, Ni and copper-chromite catalysts dehydrate glycerol
to acetol. The intrinsic property of TiO2 is mainly in enhancing the
dispersion of Ru. The high activity of 2 wt.%Ru/TiO2 catalyst sup-
ports the above observation where the catalyst with high dispersion
showed maximum activity.
3.2.5. Effect of reaction time
Fig. 7 shows the effect of reaction time on hydrogenolysis of
glycerol. About 33.6% of conversion and 77% combined selectivity
towards 1,2-PD and EG within 4 h of reaction time was achieved.
Glycerol conversion increased with increase in a reaction time from
4 to 16 h. High glycerol conversion of about 56% was achieved at
a reaction time of 16 h. The selectivity to 1,2-PD increased with
time and at the same time selectivity to EG is decreased. At short
reaction times, Ru promotes the cleavage of C–C bond along with
hydrogenation, leading to formation of EG. This is expected at ini-
tial stages, as the Ru is more active and promotes the secondary
reaction by the cleavage of 1,2-PD.
3.2.6. Influence of glycerol concentration
Influences of glycerol concentration or water content on glycerol
hydrogenolysis were studied; the results are presented in Fig. 8. A
decrease in glycerol conversion was noticed with increase in glyc-
erol concentration. It is known that glycerol conversion is higher
at low glycerol concentration [12,17]. The low conversion at high
glycerol concentration is as expected, since the available number
of Ru sites is constant. No formation of any other by-products at
high glycerol concentration.
3.2.3. Effect of reaction temperature
As the 2-wt.% Ru/TiO2 catalyst showed better activity, this
catalyst was studied as system catalyst to evaluate the reaction
parameters for glycerol hydrogenolysis. The influence of reac-
tion temperature on the hydrogenolysis of glycerol was studied;
the results are shown in Fig. 5. The glycerol conversion gradu-
ally increased from 34 to 67% as the temperature of the reaction
increased from 160 to 220 ◦C. The optimum reaction temperature
lies between 180 and 200 ◦C, as at these temperatures it showed
high selectivity to desired 1,2-PD with reasonable conversion. High
glycerol conversion was obtained above 200 ◦C; however the selec-
tivity to 1,2-PD and EG was relatively low. It is known that, at high
temperature, propanediol will undergo further hydrogenolysis to
yield lower alcohols [12,20].
3.2.4. Influence of hydrogen pressure
The influence of H2 pressure on hydrogenolysis was studied by
carrying out the reaction under various values of H2 pressure from
20 to 80 bar. Fig. 6 shows the effect of hydrogen pressure on con-
version and selectivity during glycerol hydrogenolysis. The glycerol
conversion gradually increased with increase in reaction pressure.
There was not much variation in selectivity with change in H2 pres-
sure. The high conversion of glycerol with increase in H2 pressure is
due to the availability of more amounts of hydrogen for the hydro-
genation of acetol that formed during the reaction.
Fig. 6. Effect of hydrogen pressure on glycerol hydrogenolysis over Ru/TiO2 cata-
lysts.
Reaction conditions: glycerol conc.: 20 wt.%, reaction time: 8 h, reaction temperature:
180 ◦C, catalyst wt.: 6%.

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M. Balaraju et al. / Applied Catalysis A: General 384 (2010) 107–114
Table 4
Hydrogenolysis of crude glycerol over 2-wt.% Ru/TiO2 (DP) catalyst.
Selectivity (%)
Catalyst
Conversion (%)
1,2-PD
EG
Acetol
Others
2Ru/TiO2 (DP)
2Ru/TiO2 (DP)a
2Ru/TiO2 (DP)b
46
44
42
63
63
59
19
19
22
2
2
2
16
16
17
Reaction conditions: glycerol conc.: 20 wt.%, H2 pressure: 60 bar, reaction time: 8 h,
reaction temperature: 180 ◦C, catalyst wt.: 6%.
a
Crude glycerol.
Glycerol with 5% sodium sulphate.
b
Table 5
Activity of titania supported Ru catalysts during Recycling experiments.
Selectivity (%)
No. of cycles
Conversion (%)
1,2-PD
EG
Acetol
Othersa
Fresh
46
48
49
51
63
64
64
63
19
18
18
18
2
3
3
4
16
15
15
15
Cycle-I
Cycle-II
Cycle-III
Fig. 7. Variation of glycerol activity with reaction time over Ru/TiO2 catalysts.
Reaction conditions: glycerol conc.: 20 wt.%, H2 pressure: 60 bar, reaction tempera-
ture: 180 ◦C, catalyst wt.: 6%.
Reaction conditions: glycerol conc.: 20 wt.%, H2 pressure: 60 bar, reaction time: 8 h,
reaction temperature: 180 ◦C, catalyst wt.: 6%.
results in a maximum conversion of about 43% with 63% selectiv-
ity toward 1,2-propanediol and 19% selectivity towards ethylene
glycol. These results are similar to the results obtained using ana-
lytical grade glycerol. It is noteworthy to mention that the present
catalyst is resistant towards the salts and other impurities present
in glycerol.
3.2.8. Reusability of the catalyst
It is important to study the reusability of glycerol hydrogenol-
ysis catalyst. The hydrogenolysis was carried out under relatively
harsh conditions and the glycerol contains impurities. There is a
possibility of structural changes during the reaction and poisoning
of active metal sites. Recyclability of the catalyst was studied; the
results are listed in Table 5. The catalyst was separated after the
reaction by centrifugation and washed with distilled water, fol-
lowed by methanol. This semi-dried catalyst is used for recyclic
experiments, as the recovery of the catalyst was quantitative. The
recycling results suggest the consistent activity upon reuse. In fact,
the conversion of glycerol increased marginally during the recy-
cling above that of the fresh catalyst. The selectivity towards 1,2-PD
and EG remains same during recycling. A marginal increment of
glycerol conversion with reuse might be due to complete reduc-
tion of Ru during reaction, as hydrogen is present in the reaction.
This might be allowing Ru to maintain its high dispersion on TiO2
during the experiments [30].
The used catalyst was characterized by XRD, XPS and TEM and
results were compared with values of the virgin catalyst (Fig. 9). The
XRD patterns of the fresh and three times-used catalysts are pre-
sented in Fig. 9a. Both fresh and used catalysts showed similar XRD
patterns. This suggests that the catalysts structural features were
intact during reaction. The XPS analysis also implies that the surface
species retained their identity upon reuse (Fig. 9b). TEM images of
fresh and used catalysts (Fig. 9c) suggest that similar morphology
was maintained during hydrogenolysis of glycerol. There was no
indication of any agglomeration during the glycerol hydrogenoly-
sis. The results suggest the structural stability of the catalyst under
glycerol hydrogenolysis conditions.
Fig. 8. Influence of glycerol concentrations during its hydrogenolysis over Ru/TiO2
catalysts.
Reaction conditions: H2 pressure: 60 bar, reaction time: 8 h, reaction temperature:
180 ◦C, catalyst wt.: 6%.
3.2.7. Effect of salt on hydrogenolysis of glycerol
Glycerol, which is to be obtained from the biodiesel industry,
contains trace amounts of alkali salts like sodium sulphate and
other impurities. Each transesterification reaction is carried out
over base catalysts like sodium hydroxide and the products will
be neutralized in down stream process with acid. The nuetraliza-
tion leads to the formation of salts. The hydrogenolysis of crude
glycerol and the glycerol with added sodium salts was carried over
the present catalyst to test its tolerance towards impurities; the
results are shown in Table 4. Synthetically 5% sodium sulphate
was added to pure glycerol to study the effect of salt on glycerol
hydrogenolysis. The crude glycerol was obtained as a by-product
from transesterification of sunflower oil with methanol using NaOH
as catalyst. The reaction was carried out at room temperature with
6:1 molar ratio of methanol to oil and 1% of sodium hydroxide cata-
lyst by weight of sunflower oil. The crude glycerol contained excess
methanol and other impurities and is highly basic (pH = 14). The
crude glycerol was purified by sequential removal of NaOH with
the addition of sulphuric acid. Excess methanol and water were
removed by the evaporation.
4. Conclusions
Selective hydrogenolysis of glycerol to propylene glycol was
studied over titania supported Ru catalysts prepared by both IM
and DP methods. Catalyst preparation method can influence the
The demethanolized crude glycerol was used for hydrogenoly-
sis of glycerol to propanediols. The hydrogenolysis of crude glycerol

M. Balaraju et al. / Applied Catalysis A: General 384 (2010) 107–114
113
Fig. 9. Characterization of used catalyst (a) X-ray diffraction, TiO2: (ꢀ) anatase and (#) rutile; (b) XPS; and (c) TEM images.
conversion and selectivity during glycerol hydrogenolysis. Cata-
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