Direct Hydrogenolysis of Glycerol to Biopropanols over Metal Phosphate Supported Platinum Catalysts

Article abstract of DOI:10.1007/s10562-016-1962-8

Abstract: Several metal phosphate supported platinum catalysts (Pt/AlP, Pt/TiP, Pt/ZrP and Pt/NbP) have been synthesized for the direct hydrogenolysis of glycerol to produce bio-propanols performed under mild reaction conditions. The catalysts were screened for its activity towards production of propanols from glycerol hydrogenolysis and the reaction has been optimized by studying various reaction parameters such as effect of platinum loading, reaction temperature, hydrogen flow rate, glycerol concentration and reaction time. Among the catalysts investigated, 2Pt/TiP presented a remarkable catalytic performance for vapour phase hydrogenolysis of glycerol with 100% conversion of glycerol and 97% selectivity to total propanols (1-propanol + 2-propanol) at 220 °C and atmospheric pressure. The high efficiency of 2Pt/TiP catalyst is probably be due to the strong acidity of catalyst and the uniform dispersion of small Pt particles on surface of TiP that could enable the dehydration-hydrogenation route of glycerol hydrogenolysis. Further, the structural characteristics of used catalyst have been investigated in order to understand the stability of the catalyst. Therefore, a more economical and sustainable approach of producing value added propanols from bio-derived glycerol over highly efficient catalytic system is herein presented. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1962-8

Catal Lett (2017) 147:845–855
DOI 10.1007/s10562-016-1962-8
Direct Hydrogenolysis of Glycerol to Biopropanols over Metal
Phosphate Supported Platinum Catalysts
Ponnala Bhanuchander1 · Samudrala Shanthi Priya1,2 · Vanama Pavan Kumar1 ·
Sk. Hussain1 · N. Pethan Rajan1 · Suresh K. Bhargava2 · Komandur V. R. Chary1
Received: 26 September 2016 / Accepted: 20 December 2016 / Published online: 28 February 2017
© Springer Science+Business Media New York 2017
Abstract Several metal phosphate supported platinum
catalysts (Pt/AlP, Pt/TiP, Pt/ZrP and Pt/NbP) have been
synthesized for the direct hydrogenolysis of glycerol to pro-
duce bio-propanols performed under mild reaction condi-
tions. The catalysts were screened for its activity towards
production of propanols from glycerol hydrogenolysis and
the reaction has been optimized by studying various reac-
tion parameters such as effect of platinum loading, reaction
temperature, hydrogen flow rate, glycerol concentration and
reaction time. Among the catalysts investigated, 2Pt/TiP
presented a remarkable catalytic performance for vapour
phase hydrogenolysis of glycerol with 100% conversion
of glycerol and 97% selectivity to total propanols (1-pro-
panol+2-propanol) at 220°C and atmospheric pressure.
The high efficiency of 2Pt/TiP catalyst is probably be due
to the strong acidity of catalyst and the uniform dispersion
of small Pt particles on surface of TiP that could enable the
dehydration-hydrogenation route of glycerol hydrogenoly-
sis. Further, the structural characteristics of used catalyst
have been investigated in order to understand the stability
of the catalyst. Therefore, a more economical and sustain-
able approach of producing value added propanols from
bio-derived glycerol over highly efficient catalytic system
is herein presented.
Graphical Abstract
OH
1-propanol
-H2O
+H2
-H2O
OH
+H2
-H2O
+H2
+H2
OH
HO
OH
1,2-propanediol
OH
2-propanol
OH
-H2O
-H2O
Glycerol
HO
OH
+H2
OH
1,3-propanediol
1-propanol
Keywords Biopropanols · Hydrogenolysis · Metal
phosphates · Glycerol · Platinum catalysts
1 Introduction
The use of biomass as a sustainable feedstock for the pro-
duction of chemicals and fuels has received significant
interest in recent years due to wide availability and renew-
ability. Biodiesel is among one of the promising fuel, and
it is produced by transesterification of vegetable oils with
methanol under basic conditions [1]. It is also considered
to be the attractive alternative to the fossil fuel energy
resources. Glycerol is a major byproduct of biodiesel pro-
duction and it becomes very important molecule in the
aspects of renewable biomass resources. Hence, much
attention has been paid on the conversion of biomass
derived glycerol to value added chemicals such as acrolein,
acrylic acid, glyceric acid, 1,2-propanediol, 1,3-propan-
ediol etc [2–6]. Continuous synthesis of 1,2-PDO, 1,3-PDO
and propanols from biomass derived glycerol via hydrog-
enolysis process under ambient condition is an important
process in the industrial point of view because of various
uses of these products in the synthesis of polyester resins,
* Komandur V. R. Chary
kvrchary@iict.res.in
1
Inorganic and Physical Chemistry Division, CSIR-
Indian Institute of Chemical Technology, Uppal Road,
Hyderabad 500007, India
2
Centre for Advanced Materials & Industrial
Chemistry(CAMIC), School of Applied Sciences, RMIT
University, GPO BOX 2476, Melbourne 3001, Australia
Vol.:(0123456789)
1 3

846
P. Bhanuchander et al.
detergents, flavoring agents, cosmetics, pharmaceuticals,
paints, etc [7–10]. However, bio-propanols such as 1-pro-
panol and 2-propanol are also important commodity chemi-
cals with significant applications. Hence, synthesis of these
bio-propanols from glycerol is an attractive route because
this process is renewable one and also alternative to the
available petrochemical process. Presently, 1-propanol, and
2-propanol are prepared from the hydroformylation of eth-
ylene and hydration of propylene respectively [11, 12].
Zhu et al. reported the one-step hydrogenolysis of bio-
mass-derived glycerol to propanols over different supported
Pt–H4SiW12O40 (HSiW) bi-functional catalysts in aqueous
media and they obtained yield of 94% of propanols [13].
Lin et al. studied hydrogenolysis of glycerol in a sequen-
tial two-layer bed system in a continuous-flow fixed-bed
reactor with H-β zeolite and Ni/Al2O3 catalysts. This two
bed catalytic system afforded 1-propanol selectively (69%)
with maximum glycerol conversion (∼100%) [14]. Tamura
et al. studied the promoting effect of Ru over Ir–ReOx/SiO2
catalyst for the selective hydrogenolysis of glycerol and
they found that Ru promoted Ir–ReOx/SiO2 catalyst was
efficient catalyst for the production of 1,3-propanediol and
1-propanol [15].Recently, our group also reported metal-
acid bifunctional catalysts containing platinum and differ-
ent heteropolyacids (HPA) supported on zirconia for the
hydrogenolysis of glycerol under normal atmospheric pres-
sure and we obtained excellent yield (98%) of propanols
over Pt–PTA/ZrO2 at 230°C [16].Very recently, Wang et al.
investigated hydrogenolysis of glycerol to 1-propanol by
a two layer catalytic system containing zirconium phos-
phate and supported Ru catalysts [17]. Despite of various
research efforts made earlier, it is still necessary to find an
efficient catalytic system in order to meet practical demands
of propanol production in terms of its selectivity, catalyst
stability and environmental friendly conditions.
give 1,2-propanediol and 1,3-propanediol respectively. The
propanediols thus produced undergoes further dehydration-
hydrogenation over the metal-acid catalyst to give 1-pro-
panol and 2-propanol respectively (Scheme 1). Therefore,
a highly efficient and selective catalytic system is vital to
perform direct hydyogenolysis of glycerol to propanols in
a single step.
Herein, we report here the hydrogenation of glycerol
to bio-propanols under ambient condition and continu-
ous process over a platinum catalyst supported on vari-
ous metal phosphates as supports (ZrP, TiP, NbPand AlP).
The catalysts were prepared by wet impregnation method
and characterized by XRD analysis, BET surface area,
NH3–temperature programmed desorption (NH3-TPD),
Pyridine adsorbed Fourier Transform Spectroscopy (Pyr-
FTIR), Transmission electron microscopy (TEM) and CO
pulse chemisorption. The purpose of this work is to screen
out the highly efficient catalyst for the reaction and to
understand the catalytic properties responsible for the good
catalytic activity during the hydrogenation of glycerol to
bio-propanols.
2 Experimental
2.1 Catalyst Preparation
2.1.1 Preparation of Metal Phosphates
The different metal phosphates such as Aluminum phos-
phate, Titanium phosphate, Zirconium phosphate, and
Niobium phosphates were used as support materials in the
present study and are prepared by following the previously
reported procedures [6, 7].
Preparation of Aluminium phosphate A hydrothermal
method of synthesizing amorphous aluminium phosphate
(AlP) was employed [20] in which aluminium nitrate
[Al(NO3)3·6H2O] and diammonium hydrogen phos-
phate [(NH4)2HPO4] were used as precursor materials.
Glycerol hydrogenolysis proceeds through a dehydra-
tion-hydrogenation route as reported in the previous stud-
ies [18, 19]. Initially, the glycerol undergoes dehydration-
hydrogenation over acid and metal sites of the catalyst to
Scheme 1 Hydrogenolysis of
OH
1-propanol
-H
2O
+H2
glycerol to produce propanols
-H
-H
2O
2O
OH
+H2
2O
+H2
+H2
-H
OH
HO
OH
1,2-propanediol
OH
OH
2-propanol
-H
2O
Glycerol
HO
OH
+H2
OH
1,3-propanediol
1-propanol
1 3

Direct Hydrogenolysis of Glycerol to Biopropanols over Metal Phosphate Supported Platinum…
847
The required amounts of aluminium and phosphorous
precursors(P/Al ratio of 0.9) were dissolved in water under
constant stirring and then acidified with nitric acid. The
pH of the solution was adjusted to 8 by addition of aque-
ous ammonia. After 1 h of continuous stirring, the hydrogel
thus obtained was filtered, washed with distilled water to
remove excess solvent and dried overnight at 110°C fol-
lowed by calcinations in air for 30 min at 500°C.
and the catalysts are hereafter notated as 2Pt/AlP, 2Pt/TiP,
2Pt/ZrP and 2Pt/NbP in the following discussion. In addi-
tion, a series of platinum catalysts supported on TiP with
different platinum loadings (0.5–3 wt%) were prepared by
following the same procedure.
2.2 Catalyst Characterization
Preparation of Titanium Phosphate In a typical hydro-
thermal process [21], Titanium phosphate (TiP) was syn-
thesized by using a mixture of titanium n-butoxide (TBT)
and n-butanol to which 30 mL of 0.1 M phosphoric acid
solution was added drop wise and kept under stirring for
2 h at room temperature. The mixture obtained was aged
for 24 hat 80°C in a Teflon-lined autoclave. The product
was then filtered, washed with water, dried at 60°C for 12 h
and finally calcined at 500°C for 2 h.
X-ray diffraction (XRD) analysis of the fresh and used
catalysts were performed in the 2θ range of 2° to 65°, on
Rigaku miniflex X-ray diffractometer at a scan rate of 2°/
min with the beam voltage and a beam current of 30 kV
and 15 mA respectively.
The textural properties such as surface area, pore vol-
ume and pore diameter of the catalysts were analyzed using
N2-adsorption at −196°C by the multipoint BET method
on Autosorb 1(Quantachrome instruments, USA).
Preparation of Zirconium Phosphate Zirconium phos-
phate (ZrP) was prepared by adding 0.01 mol of Zirconium
n-propoxide (70 wt% solution in 1-propanol, Aldrich) to a
solution of 85% phosphoric acid (60 mL of 0.1 mol L−1)
under stirring at room temperature. The mixture obtained
after 2 h of stirring was transferred into a Teflon lined auto-
clave and aged at 80°C for 24 h. The final product was fil-
tered, dried and calcined at 400°C for 5 h [22].
TPD experiments were carried out on AutoChem
2910(Micromeritics, USA) instrument. In a typical experi-
ment, 100 mg of oven dried sample was pretreated by
passage of high purity (99.995%) helium (50 mL/min) at
200°C for 1 h. After pretreatment, the sample was satu-
rated with highly pure anhydrous ammonia (50 mL/min)
with a mixture of 10% NH3–He at 80°C for 1 h and sub-
sequently flushed with He flow (50 mL/min) at 80°C for
30 min to remove physisorbed ammonia. TPD analysis was
carried out from ambient temperature to 600°C at a heating
rate of 10°C/min. The amount of NH3 desorbed was calcu-
lated using GRAMS/32 software.
Preparation of Niobium Phosphate The NbP catalyst
was synthesized by the procedure reported elsewhere [23].
In a typical procedure, 2.73 g of NbCl5 was dissolved in
50 mL of H2O and 2.30 g of H3PO4 (Aldrich, 85% aque-
ous solution) was added followed by an additional 50 mL
of H2O. The reaction mixture was allowed to stir for 30 min
by maintaining the pH of the solution to 2.60 with aque-
ous ammonia. The resulting slurry was filtered and washed
by deionised water. The obtained gel then was mixed with
10 mL of H2O and 1.45 g of hexadecylamine and stirred
for 30 min. About 0.92 g H3PO4 (85%) was added to the
above solution and the pH was adjusted to 3.88 by add-
ing ammonia solution. The formed slurry was heated in
a Teflon-lined autoclave and aged statically at 110°C for
48 h. The final product was filtered, washed with deionised
water, dried 100°C overnight, and subsequently calcined at
550°C in air for 6 h.
The investigation of nature of acid sites was analyzed
by pyridine adsorption on the catalysts followed by FTIR
experiments. The FTIR spectra of the samples were taken
on the IR (Model: GC-FT-IR Nicolet 670) spectrometer by
KBr disc method under ambient condition.
CO-chemisorption measurements were carried out on
AutoChem 2910 (Micromeritics, USA) instrument. Prior
to adsorption measurements, ca. 100 mg of the sample was
reduced in a flow of hydrogen (50 mL/min) at 400°C for
3 h and flushed out subsequently in a pure helium gas flow
for an hour at 400°C. The sample was subsequently cooled
to ambient temperature in the same He stream. CO uptake
was determined by injecting pulses of 9.96% CO balanced
helium from a calibrated on-line sampling valve into the
helium stream passing over the reduced samples at 400°C.
Platinum surface area, percentage dispersion and Pt aver-
age particle size were calculated assuming the stoichiomet-
ric factor (CO/Pt) as 1. Adsorption was deemed to be com-
plete after three successive runs showed similar peak areas.
2.1.2 Preparation of Supported Platinum Catalysts
The metal phosphate supported platinum catalysts were
prepared by wet impregnation method. An aqueous solution
of H2PtCl6·6H2O was impregnated with required amounts
of different metal phosphates individually under vigor-
ous stirring. After the excess amount of water is lost, the
impregnated sample was allowed to dry overnight at 110°C
and the resulting material was calcined at 450°C for 3 h.
The platinum loading in all the catalysts is fixed to 2 wt%
2.3 Catalyst Testing
The vapour phase hydrogenolysis of glycerol was carried
outin a vertical fixed bed quartz reactor (40 cm length,
1 3

848
P. Bhanuchander et al.
9 mm i.d.) under atmospheric pressure. Prior to the reac-
tion, the 0.5 g of catalysts were pretreated at 350°C for
2 h in flowing H2 (80 mL/min). After cooling down to the
reaction temperature (220°C), hydrogen (100 mL/min)
and an aqueous solution of 10 wt% glycerol were intro-
duced into the reactor through a heated evaporator. The
reaction products were condensed in an ice–water trap
and collected hourly for analysis on a gas chromatograph
GC-2014(Shimadzu) equipped with a DB-wax 123-7033
(Agilent) capillary column (0.32 mm i.d., 30 m long) and
equipped with flame ionization detector. The conversion
of glycerol and selectivity of products were calculated as
follows:
suggested from the XRD results. In addition, small peaks at
2θ=39.7° and 46.1° coinciding with (111) and (200) lattice
planes of platinum are observed in metal phosphate sup-
ported platinum catalysts. However, the intensity of Pt peak
is different in different metal phosphate supported platinum
catalysts. In comparison to other catalysts, 2Pt/TiP catalyst
reveals the presence of very less intense Pt peak indicating
the fine dispersion of Pt on surface of TiP.
3.1.2 Temperature Programmed Desorption of Ammonia
(NH3‑TPD)
The total acidity and the strength of acid sites in various
moles of glycerol (in) − moles of glycerol (out)
Conversion(%) =
moles of glycerol (in)
× 100
metal phosphate supported platinum catalysts was deter-
mined by the ammonia temperature programmed desorp-
tion technique. The desorption of ammonia in the tempera-
ture range 50–250°C, 250–350 and >350°C corresponds
to the presence of weak, moderate and strong acid sites
respectively [24]. The NH3-TPD profiles and the total acid-
ity (µmol/g calculated from area under the peaks) of all the
metal phosphate supported platinum catalysts are shown in
Fig. 2 and Table 1. The ammonia adsorption–desorption
technique usually enables determination of the strength
of acid sites present on the catalyst surface together with
total acidity. It is observed that 2Pt/AlP, 2Pt/ZrP and 2Pt/
NbP catalysts possess weak and moderate acid sites with
desorption in two different temperature regions.
moles of one product
Selectivity (%) =
× 100
moles of all products
3 Results and Discussion
3.1 Characterization Techniques
3.1.1 X‑ray Diffraction (XRD)
The X-ray diffraction studies of pure metal phosphates and
metal phosphate supported platinum catalysts (2Pt/AlP,
2Pt/TiP, 2Pt/ZrP and 2Pt/NbP)were carried out and the dif-
fraction patterns are presented in Fig. 1. All the synthesized
metal phosphates were found to be X-ray amorphous as
Pt
2 Pt/AlP
2 Pt/TiP
2Pt/AlP
Pure AlP
2Pt/TiP
Pure TiP
2 Pt/ZrP
2 Pt/NbP
2Pt/ZrP
Pure ZrP
2Pt/NbP
Pure NbP
100
200
300
400
500
oC)
600
700
10
20
30
40
50
60
70
Temperature (
2-Theta
Fig. 2 NH3-TPD profiles of various metal phosphate supported plati-
Fig. 1 XRD patterns of pure metal phosphates and platinum catalysts
num catalysts
1 3

Direct Hydrogenolysis of Glycerol to Biopropanols over Metal Phosphate Supported Platinum…
849
Table 1 Acidities of various metal phosphate supported platinum
catalysts
Catalyst
NH3 uptake (µmol/g)
Total
acidities
(µmol/g)
Weak
Moderate
Strong
2Pt/AlP
2Pt/TiP
2Pt/ZrP
2Pt/NbP
904
145
133
143
58
934
1198
1223
–
44
–
962
1123
1331
1366
–
It is interesting to note that, 2Pt/TiP catalyst showed
an observable desorption of ammonia in the temperature
region>350°C indicating the presence of strong acid sites
in addition to the presence of weak and moderate acid sites.
This might lead to an obvious distinct result in the catalytic
activity. However, the total acidity of the catalysts varied
and follows the order: 2Pt/NbP>2Pt/ZrP>2Pt/TiP>2Pt/
AlP. Therefore, NH3-TPD is an important technique which
enabled to study the acidic strength of catalysts and to fur-
ther evaluate its role in the catalytic activity.
3.1.3 Pyridine Adsorbed Fourier Transform Infrared
Spectroscopy (Pyr‑FTIR)
Fig. 3 Pyr-FTIR spectra of various metal phosphate supported plati-
num catalysts
As NH3-TPD is a useful technique to determine the acidic
strength of catalysts, Pyridine adsorbed FTIR technique is
another such method used to find the nature/type of acidic
sites present in the catalyst. Figure 3 shows the Pyr-FTIR
spectra of various metal phosphate supported platinum
catalysts in the spectral range of 1400–1600 cm−1. All
the samples revealed the presence of three main bands in
the spectra. A band at 1453 cm−1 corresponding to the
adsorption of pyridine at the Lewis acid sites (L) is clearly
observed. On the other hand, a band at 1543 cm−1 due to
pyridinium ion on Brønsted acid sites [25] is confirmed
which could be attributed to the presence of P(OH) groups
in the metal phosphates. However, the intensity of band due
to Brønsted acidity varied in each catalyst and was found to
be more prominent in 2Pt/AlP catalyst compared to other
catalysts. In addition, a band at 1492 cm−1 corresponding
to the adsorbed pyridine on both Lewis and Brønsted acid
sites was also observed in all the samples.
of metal phosphates by platinum particles. A noticeable
decrease in the pore volumes and pore diameters of metal
phosphate supported platinum catalysts was also observed.
Similar findings were observed in the previous reports [26].
3.1.5 CO‑Chemisorption
In order to estimate the dispersion of platinum on various
metal phosphate supports, metal surface area and the par-
ticle diameter of platinum, CO chemisorption method was
employed and the results are tabulated in Table 3. The dis-
persion of Pt on each metal phosphate support varied and it
was found that Pt was highly dispersed (31.1%) on TiP sup-
port. The metal surface area of all the catalysts was found
to be in the range of 1.06–1.53 m2/g of catalyst whereas
the particle size varied between 3.6 and 5.2 nm. Therefore
CO chemisorption results demonstrate that 2Pt/TiP catalyst
notably displayed high Pt dispersion and small Pt particle
size compared to other catalysts. These results were found
to be in agreement with the findings of XRD studies.
3.1.4 BET Surface Area
The surface areas of the metal phosphate supported plati-
num catalysts were determined by using BET method
and are listed in Table 2. The deposition of platinum on
respective metal phosphate supports led to the significant
decrease in the surface area compared to pure metal phos-
phate supports. This is obvious due to the blockage of pores
3.1.6 Transmission Electron Microscopy (TEM)
TEM images of various metal phosphate supported
platinum catalysts presented in Fig. 4 (a–d) show the
1 3

850
P. Bhanuchander et al.
Table 2 Physicochemical properties of pure metal phosphates and
We began our studies with the preliminary screening of
different metal phosphate supported platinum catalysts for
glycerol hydrogenolysis at 220°C under atmospheric pres-
sure. The comparative results are presented in Table 4.All
the metal phosphate supported platinum catalysts exhib-
ited high activity and selectivity towards bio propanols
(1-PO+2-PO) during glycerol hydrogenolysis with appre-
ciable amount of glycerol conversions. In comparison, 2Pt/
TiP catalyst showed remarkably high activity among all
catalysts reaching a maximum selectivity of 97% to total
propanols at full conversion of glycerol. The activity of 2Pt/
ZrP and 2Pt/NbP catalysts seems to be high, although the
selectivity to propanols was slightly decreased. In contrast,
2Pt/AlP catalyst showed low activity towards the formation
of propanols from glycerol but the selectivity to 1,3-PD
was comparatively high up to 11%. Except 2Pt/TiP cata-
lyst, all other catalysts were slightly selective to propanedi-
ols (1,2-PD & 1,3-PD) besides the formation of 1-PO and
2-PO. The other products identified include acrolein, etha-
nol, ethylene glycol, methanol and acetone. However, it is
interesting to note that,1-PO was the predominant product
of glycerol hydrogenolysis on all metal phosphate sup-
ported platinum catalysts.
various metal phosphate supported platinum catalysts
Catalyst
Surface area (m²/ Pore volume (cc/ Pore
g−1
)
g−1
)
diameter
(nm)
Pure AlP
2Pt/AlP
Pure TiP
2Pt/TiP
Pure ZrP
2Pt/ZrP
Pure NbP
2Pt/NbP
235
193
174
135
317
195
189
147
1.12
1.03
0.84
0.35
0.13
0.21
0.84
0.26
23.6
18.5
25.1
17.8
30.0
22.9
23.5
15.2
Table 3 Results of dispersion, CO uptake, metal area, and average
particle size of metal phosphate supported platinum catalysts
Catalyst
CO uptake Dispersion (%) Metal surface Particle
(µmol/g)
area (m2/g)cat
size
(nm)
2Pt/AlP
2Pt/TiP
2Pt/ZrP
29.8
31.9
24.2
29.0
31.1
23.6
21.4
1.41
1.51
1.12
1.02
3.8
3.6
4.7
5.2
The formation of acrolein clearly shows that the reac-
tion proceeds in the following way: the dehydration of
glycerol over metal phosphates gives acrolein and further
hydrogenation over metal sites gives 1-PO, whereas 2-PO
is formed by the successive dehydration of glycerol and
hydrogenation of acetol. Therefore, based on the results
obtained, 2Pt/TiP catalyst was screened out to be the most
active and selective catalyst towards the formation of 1-PO
& 2-PO during glycerol hydrogenolysis among all other
tested catalysts (Scheme 2).The high efficiency of 2Pt/TiP
catalyst could be attributed to the presence of strong acidic
sites coupled with well dispersed platinum that has facili-
tated the double dehydration-hydrogenation of glycerol to
produce propanols. The strong acidity of 2Pt/TiP catalyst,
small particle size and fine dispersion of Pt on TiP sup-
port is clearly evident from NH3-TPD analysis, XRD and
CO-chemisorption studies respectively. The catalytic activ-
ity results are in good corroboration and well correlate
with the characterization results. Therefore, further studies
were demonstrated over the most active 2Pt/TiP catalyst to
understand the optimized reaction conditions.
2Pt/NbP 22.0
morphology and distribution of platinum particles in the
catalysts. A homogeneous dispersion of the platinum
particles on the surface of metal phosphates was clearly
observed and the average size of Pt crystallites was found
to be in the range of 4–7 nm.
3.2 Catalytic Performance of the Catalysts
3.2.1 Screening of Metal Phosphate Supported Platinum
Catalysts
It is well known that hydrogenolysis of glycerol is a com-
plex reaction involving several. C–O and C–C cleavage
reactions and hence it is essential to monitor the activity
and control the selective distribution of products by the
use of highly efficient catalytic systems and ambient reac-
tion conditions. In this work, various metal phosphate sup-
ported platinum catalysts (2Pt/AlP, 2Pt/TiP, 2Pt/ZrP and
2Pt/NbP) were employed to study its activity towards glyc-
erol hydrogenolysis and examine the product distribution.
The reaction of glycerol hydrogenolysis was performed in
vapour phase using a continuous fixed-bed reactor under
atmospheric pressure. A systematic optimization of the
reaction conditions has been carried out to attain the maxi-
mum conversion of glycerol and selectivity to products.
3.2.2 Effect of Platinum Loading
The glycerol hydrogenolysis was performed over a series of
Pt/TiP catalysts with varying platinum loading (0.5–3 wt%)
in order to understand the impact of platinum loading and
find the best performed catalyst. The results of effect of
platinum loading on glycerol conversion and selectivity to
1 3

Direct Hydrogenolysis of Glycerol to Biopropanols over Metal Phosphate Supported Platinum…
851
Fig. 4 TEM images of various
metal phosphate supported
platinum catalysts
Table 4 Catalytic performance
Catalyst
Conversion (%)
Total PO
1-PO
2-PO
1,2-PD
1,3-PD
Acrolein
Others
of various metal phosphate
supported platinum catalysts
towards glycerol hydrogenolysis
2Pt/AlP
2Pt/TiP
2Pt/ZrP
2Pt/NbP
78
100
98
61
97
86
89
38
87
68
65
23
10
18
24
02
–
04
2.6
11
–
1.6
2.0
–
26
01
5.1
3.4
02
3.3
3.0
90
Reaction conditions: 0.5 g catalyst; reaction temperature: 220 oC,H2 flow rate: 100 mL/min; WHSV-
1.02 h−1; 1-PO:1-propanol, 2-PO: 2-propanol. Others include ethanol, ethylene glycol, hydroxyl acetone,
methanol and acetone
Scheme 2 Direct hydrogenoly-
2
Pt/TiP
sis of glycerol to propanols
HO
OH
OH
220 oC, 0.1 MPa H2
OH
OH
1-propanol
(major)
2-propanol
(minor)
Glycerol
1 3

852
P. Bhanuchander et al.
from 70 to 100% when the reaction was conducted from
180–260°C. A complete glycerol conversion was attained
at 220°C and remained stable until 260°C, while, the
selectivity to total propanols gradually increased with
rise in reaction temperature, and reached 97% at 220°C
beyond which it decreased. It can be seen that both 1,2-
PD and 1,3-PD existed in low selectivity at lower reaction
temperatures. Meantime, the selectivity to acrolein gradu-
ally decreased when the temperature increased from 180
to 220°C, indicating that acrolein would have underwent
a subsequent hydrogenation reaction over metal sites to
form 1-PO. The decrease in the selectivity to 1-PO & 2-PO
at higher temperatures indicates the formation of other
byproducts such as ethanol, methanol, ethylene glycol and
acetone due to excessive C–C cleavage reactions [27].The
maximum glycerol conversion and selectivity to total pro-
panols was obtained at 220 °C reaction temperature.
Fig. 5 Effect of Platinum loading on hydrogenolysis of glycerol
3.2.4 Effect of Glycerol Concentration
products are presented in Fig. 5. It was observed that all
the catalysts (0.5–3 wt% Pt/TiP) showed an appreciable
activity in glycerol conversion and selectivity to products.
On 0.5 Pt/TiP catalyst, 80% glycerol converted with 75.5%
selectivity to total propanols. There was a gradual increase
in the glycerol conversion as well in the selectivity to pro-
panols (1-PO+2-PO) when the amount of platinum loaded
on the catalyst increased from 0.5 to 2 wt%. The selectivity
to 2-PO was found to be maximum at lower loadings and
decreased with platinum loading. However, the glycerol
conversion and selectivity to propanols slightly decreased
on 3Pt/TiP catalyst which is probably due to agglomeration
of Pt on TiP, well evident from the characterization results.
Therefore, among the series of catalysts (0.5–3Pt/TiP), 2Pt/
TiPcatalyst was found to be the best catalyst giving maxi-
mum conversion and selectivity to total propanols.
The effect of glycerol concentration on glycerol hydrogen-
olysis reaction over 2Pt/TiP catalyst at 220°C was studied
by using different concentrations of glycerol (5,10,15 &
Conversion
100
80
60
40
20
0
Sel of Total PrOH
Sel of 1-PrOH
Sel of 2-PrOH
Sel of Acrolein
Sel of Others
100
80
60
40
20
0
3.2.3 Effect of Reaction Temperature
5
10
15
20
The influence of reaction temperature on glycerol hydrog-
enolysis over the 2Pt/TiP catalyst as illustrated in Table 5
show that the glycerol conversion greatly improved
Effect of Glycerol concentration (wt%)
Fig. 6 Effect of glycerol concentration on hydrogenolysis of glycerol
Table 5 Effect of reaction
Reaction
Conversion (%)
Total PO
1-PO
2-PO
1,2-PD
1,3-PD
Acrolein
Others
temperature on glycerol
hydrogenolysis over 2Pt/TiP
catalyst
Temp (oC)
180
200
220
240
260
70
82
100
100
100
74
80
97
88
84
59
67
87
80
76
15
13
10
08
08
9.0
5.4
–
–
–
3.2
2.2
–
–
–
9.3
8.7
02
4.2
01
4.5
3.7
01
7.8
15
Reaction conditions: 0.5 g catalyst; reduction temperature: 350°C, H2 flow rate: 100 mL/min; WHSV-
1.02 h−1; 1-PO: 1-propanol, 2-PO: 2-propanol. Others include ethanol, ethylene glycol, methanol and ace-
tone
1 3

Direct Hydrogenolysis of Glycerol to Biopropanols over Metal Phosphate Supported Platinum…
853
20 wt%) and the results are presented in Fig. 6. As antici-
105
100
pated, the glycerol conversion decreased with increase
in the amount of glycerol. This observation is obvious
90
because glycerol is a highly viscous liquid and the amount
95
90
85
80
of glycerol fed during the reaction increases at increased
75
glycerol concentration while the number of active sites on
the catalyst is constant [28]. Hence there was a decrease in
Conversion of glycerol
the glycerol conversion from 100 to 75% when the concen-
Selectivity of 1-PrOH + 2-PrOH
60
tration of glycerol is changed from 10 to 20 wt% although
remained constant at 5 & 10 wt%. Also, the selectivity to
45
propanols (1-PO+2-PO) was found to be decreased with
the formation of undesired byproducts at increased glyc-
30
erol concentration. It is suggested that 10 wt% glycerol was
0
5
10
15
20
found to be the optimal concentration resulting in the best
performance.
Time (h)
Fig. 8 Effect of reaction time on hydrogenolysis of glycerol
3.2.5 Effect of Hydrogen Flow Rate
3.2.6 Effect of Reaction Time
It is important to understand the influence of hydrogen
flow rate on glycerol conversion and selectivity to products
as hydrogen is one of the reactants in the glycerol hydrog-
enolysis reaction. The reaction was performed over 2Pt/
TiP catalyst at 220°C under atmospheric pressure by vary-
ing the rates of hydrogen flow from 60 mL/min to 140 mL/
min. As shown in Fig. 7, the glycerol conversion greatly
improved from 55 to 100% with increase in the hydrogen
flow rate from 60 to 100 mL/min and remained constant
with further increase to 140 mL/min hydrogen flow rate.
However, there was not much variation in the selectivity
of 1-PO & 2-PO although a slight decline was observed at
higher flow rates of hydrogen with increase in the degra-
dation products. A similar trend of hydrogen flow rate on
glycerol conversion and selectivity was reported in previ-
ous studies [29].
The stability of the 2Pt/TiP catalyst has been studied by
examining the course of glycerol hydrogenolysis reaction
over a period of 20 h at 220°C and the results are presented
in Fig. 8. The catalytic performance of 2Pt/TiP was found
to be excellent and remained stable for maximum hours.
A complete conversion of glycerol was attained in 4 h
and was found to be steady until 13 h after which slightly
decreased and reached 86% at the end of 20 h. The similar
trend was observed in case of selectivity where it increased
from 83 to 97% within a reaction time of 5 h and retained
till 14 h. A slow decrease in the selectivity of total pro-
panols (88.9%) was however observed towards the end of
20 h. This behavior of decrease in glycerol conversion and
selectivity of propanols is attributed to the catalyst deac-
tivation by coke formation [30]. The time on stream stud-
ies suggest the catalyst is quite stable for a long period of
time resulting in good catalytic activity during glycerol
hydrogenolysis.
Conversion
Sel of Total PrOH
100
80
60
40
20
0
100
80
60
40
20
0
Sel of 1-PrOH
Sel of 2-PrOH
Sel of Acrolein
Sel of Others
3.2.7 Studies on Spent Catalyst
To further confirm the stability of 2Pt/TiP catalyst, the
reaction was repeated with spent catalyst (after 1st reac-
tion cycle) under the same reaction conditions. The spent
catalyst was characterized to understand the changes that
the catalyst has undergone during glycerol hydrogenolysis
reaction and the results are shown in Fig. 9 and Table 6.
The conversion of glycerol and the selectivity to total pro-
panols (1-PO+2-PO) did not vary significantly over the
spent catalyst. There were not much changes observed in
the XRD, SEM and TPD patterns of the spent2Pt/TiP cat-
alyst compared to those of the fresh catalyst as shown in
60
80
100
120
140
Hydrogen flow rate (mL/min)
Fig. 7 Effect of hydrogen flowrate on hydrogenolysis of glycerol
1 3

854
P. Bhanuchander et al.
Fig. 9 XRD and NH3-TPD
patterns of fresh and used 2Pt/
TiP catalyst
(a)
2Pt/TiP (Used)
2Pt/TiP(Fresh)
100
200
300
400
500
Temparature(oC)
(b)
Table 6 Studies of spent
Catalyst
Conversion (%)
Selectivity of
1-PO+2-PO
Acidity
CHNS analysis (%)
catalyst 2Pt/TiP
NH3-TPD
(µmol/g)
C
H
N
S
2Pt/TiP (fresh)
2Pt/TiP (used)
100
98
97
95
1123
1115
--
1.4
0.3
0.3
0.5
0.1
--
--
Fig. 9, which indicates that the structure of 2Pt/TiP catalyst
was rather stable during the catalytic reaction.
complete conversion of glycerol among a series of metal
phosphate supported platinum catalysts. The excellent cata-
lytic activity of 2Pt/TiP catalyst is attributed to the strong
acidity of the catalyst and well dispersed platinum on the
surface of titanium phosphate. The catalyst was found to be
quite stable for 20 h reaction time and reusable with a slight
decline in the catalytic activity.
4 Conclusions
In summary, a sustainable and economic viable one step
process of glycerol hydrogenolysis to propanols was
described over metal phosphate supported platinum cata-
lysts in vapour phase. It was found that 2Pt/TiP catalyst
showed superior performance in glycerol hydrogenolysis
with 97% selectivity to total propanols (1-PO+2-PO) at
Acknowledgements The authors PB and SKH thank Univer-
sity Grants Commission (UGC), New Delhi for the award of Junior
Research Fellowship. SSP thanks IICT-RMIT collaboration for the
award of fellowship. This work is supported by Indus-Magic program
of CSIR network projects under the 12th 5 year plan.
1 3

Direct Hydrogenolysis of Glycerol to Biopropanols over Metal Phosphate Supported Platinum…
855
15. Tamura M, Amada Y, Liu S, Yuan Z, Nakagawa Y, Tomishige K
(2014) J Mol Catal A 388–389, 177–187
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