Vapor phase dehydration of glycerol to acrolein over SBA-15 supported vanadium substituted phosphomolybdic acid catalyst

Article abstract of DOI:10.1166/jnn.2015.9871

Vapor phase dehydration of glycerol to acrolein was investigated over heteropolyacid (HPA) catalysts containing vanadium substituted phosphomolybdic acid (H₄ PMo₁₁VO₄₀) supported on mesoporous SBA-15. A series of HPA catalysts with HPA loadings varying from 10-50 wt% were prepared by impregnation method on SBA-15 support. The catalysts were characterized by X-ray diffraction, Raman spectroscopy, Fourier Transform infrared spectroscopy, temperature-programmed desorption of NH₃ , pyridine adsorbed FT-IR spectroscopy, scanning electron microscopy, pore size distribution and specific surface area measurements. The nature of acidic sites was examined by pyridine adsorbed FT-IR spectroscopy. XRD results suggest that the active phase containing HPA was highly dispersed at lower loadings on the support. FT-IR and Raman spectra results confirm that the presence of primary Keggin ion structure of HPA on the support and it was not affected during the preparation of catalysts. Pore size distribution results reveal that all the samples show unimodel pore size distribution with well depicted mesoporous structure. NH₃-TPD results suggest that the acidity of catalysts increased with increase of HPA loading. The findings of acidity measurements by FT-IR spectra of pyridine adsorption reveals that the catalysts consist both the Br??nsted and Lewis acidic sites and the amount of Br??nsted acidic sites are increasing with HPA loading. SBA-15 supported vanadium substituted phosphomolybdic acid catalysts are found to be highly active during the dehydration reaction and exhibited 100% conversion of glycerol (10 wt% of glycerol) and the acrolein selectivity was appreciably changed with HPA active phase loading. The catalytic functionalities during glycerol dehydration are well correlated with surface acidity of the catalysts.

Full text of DOI:10.1166/jnn.2015.9871

Article
Journal of
Nanoscience and Nanotechnology
Vol. 15, 5391–5402, 2015
Copyright © 2015 American Scientific Publishers
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Printed in the United States of America
Vapor Phase Dehydration of Glycerol to Acrolein Over
SBA-15 Supported Vanadium Substituted
Phosphomolybdic Acid Catalyst
Balaga Viswanadham, Amirineni Srikanth, Vanama Pavan Kumar, and Komandur V. R. Chary∗
Catalysis Division, Indian Institute of Chemical Technology, Hyderabad 500007, India
Vapor phase dehydration of glycerol to acrolein was investigated over heteropolyacid (HPA) catalysts
containing vanadium substituted phosphomolybdic acid (H4PMo11VO40) supported on mesoporous
SBA-15. A series of HPA catalysts with HPA loadings varying from 10–50 wt% were prepared by
impregnation method on SBA-15 support. The catalysts were characterized by X-ray diffraction,
Raman spectroscopy, Fourier Transform infrared spectroscopy, temperature-programmed desorp-
tion of NH3, pyridine adsorbed FT-IR spectroscopy, scanning electron microscopy, pore size distribu-
tion and specific surface area measurements. The nature of acidic sites was examined by pyridine
adsorbed FT-IR spectroscopy. XRD results suggest that the active phase containing HPA was highly
dispersed at lower loadings on the support. FT-IR and Raman spectra results confirm that the pres-
ence of primary Keggin ion structure of HPA on the support and it was not affected during the
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preparation of catalysts. Pore size distribution results reveal that all the samples show unimodel
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
pore size distribution with well depicted mesoporous structure. NH3-TPD results suggest that the
Copyright: American Scientific Publishers
acidity of catalysts increased with increase of HPA loading. The findings of acidity measurements
by FT-IR spectra of pyridine adsorption reveals that the catalysts consist both the Brønsted and
Lewis acidic sites and the amount of Brønsted acidic sites are increasing with HPA loading. SBA-
15 supported vanadium substituted phosphomolybdic acid catalysts are found to be highly active
during the dehydration reaction and exhibited 100% conversion of glycerol (10 wt% of glycerol)
and the acrolein selectivity was appreciably changed with HPA active phase loading. The catalytic
functionalities during glycerol dehydration are well correlated with surface acidity of the catalysts.
Keywords: Heteropolyacid, Acidity, Mesoporosity, Glycerol Dehydration, Acrolein.
1. INTRODUCTION
acetaldehyde, acetone and leads to the formation of coke
deposits on the catalyst surface causing catalyst deacti-
vation. The presence of these by-products with acrolein
necessitates high recovery cost for separation and purifi-
cation of acrolein. Various solid acid catalysts, including
sulphates, phosphates, zeolites, heteropolyacids and solid
phosphoric acid (SPA) have been investigated for the dehy-
dration of glycerol in either gaseous or liquid phase under
severe reaction conditions.6–17 The direct use of glycerol
with water in the feed is advantageous over pure glyc-
erol for the production of acrolein because of glycerol is
usually produced as a mixture with water. It is a challeng-
ing task to achieve total conversion of glycerol with high
acrolein selectivity and longer catalyst life. Therefore, a
solid acid catalyst with better acidic and redox properties
would be beneficial for complete conversion of glycerol
The conversion of glycerol to value-added chemical inter-
mediates is a topic of enormous interest in the recent
past because glycerol is a by-product formed in huge
amounts during the production of biodiesel from renew-
able sources. Among several pathways to obtain valuable
products from glycerol, the dehydration reaction of glyc-
erol to acrolein is an interesting route using solid acid cat-
alysts to achieve a total conversion of glycerol and also to
obtain high acrolein selectivity. Acrolein is a value added
and versatile chemical intermediate employed in many
industrial applications.1–5 The dehydration of glycerol to
acrolein is generally accompanied by side reactions lead-
ing to by-products such as hydroxypropanone, propanal,
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2015, Vol. 15, No. 7
1533-4880/2015/15/5391/012
doi:10.1166/jnn.2015.9871
5391

Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
Viswanadham et al.
to obtain high selectivity of acrolein and also to minimize
the coke formation.
as oxidation and acid catalyst in which the redox and
acidic functionalities can be tuned by substitution of
the added (vanadium) transition metal substituted Keggin
units. The synthesis of vanadium containing Keggin ion
units of phosphomolybdic acid is found to be promising
heteropolyacid catalysts wherein the molybdenum metal
is partially replaced by vanadium metal. In addition, the
activities of the synthesized catalysts were evaluated in the
dehydration of glycerol to acrolein. The vanadium con-
taining phosphomolybdic acid possesses positive reduc-
tion potentials compared to pure phosphomolybdic acid
and enhances the redox properties. Thus the incorpora-
tion of V into the structure of phosphomolybdic acid
(PMA) enhances the catalytic performance (acid and redox
catalysts).34 Vanadium containing HPAs showed excellent
redox properties because substitution of vanadium stabi-
lizes the LUMOs.35 Vanadium containing HPA catalysts
are the basic components of several oxidative and acidic
reactions in homogenous and heterogeneous catalysis.36–42
In the present investigation, we report the dehydra-
tion of glycerol to acrolein over a series of HPA cata-
lyst with active phase containing H4PMo11VO40 supported
on SBA-15. The aim of this investigation is to study the
effect of HPA loading on SBA-15 during the vapor phase
dehydration glycerol under mild reaction conditions. We
also report the effect of porosity of the catalyst and cat-
alytic performance during the reaction. The purpose of
Glycerol dehydration was generally carried out in liquid
phase using heteropolyacids as catalysts.14 However, it is
difficult for product separation in liquid phase as the het-
eropolyacids tend to dissolve in polar solvents in homoge-
neous system. Comparing to liquid phase reactions using
homogenous catalysts, the heterogeneous catalyzed reac-
tions are more advantageous for the easier product separa-
tion and product recovery. Solid acids containing zeolites
and heteropolyacids of phosphotungstic acid and phospho-
molybdic acid are employed for glycerol dehydration reac-
tion. However, the activity over above solid acid catalysts
was found to be much lower and they can get deacti-
vated easily during the course of reaction time.14–17 The
heteropolyacid of vanadium containing phosphomolyb-
dic acids are beneficial over the phophomolybdic acid,
as the incorporated vanadium reduces or minimize the
deactivation or decomposition of the catalyst. However,
total conversions of glycerol and higher selectivity to
acrolein are favoured with catalysts with tuneable Brønsted
acidity coupled with larger pore size of mesoporous
support. Therefore mesoporous silica SBA-15 supported
heteropolyacid catalyst is advantageous for dehydration of
glycerol to acrolein reaction.
There is a plethora of research work published in the
recent past on nano and mesoporous materials18–25 as these
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this work is to estimate acidity of vanadium substituted
phosphomolybdic acid supported on SBA-15 as a func-
materials exhibited higher activitIyP:a6nd3.1se4l2ec.2ti2v6it.y35foOr nth:eMon, 26 Oct 2015 02:00:49
Copyright: American Scientific Publishers
synthesis of fine chemicals with stable activity. However,
tion of HPA loading and to identify structural changes of
HPA with increase of active phase loading and also to
understand relation between selectivity and acidic sites.
A comparison of catalytic performance is also made with
non-mesoporous oxides such as Y-zeolite and alumina.
The catalysts were characterized by XRD, Raman, SEM,
TPD of NH3, pyridine adsorbed FT-IR, BET surface area
and pore size distribution (PSD) to obtain the structural
information of materials of the active species and to corre-
late with catalytic functionalities during vapor phase dehy-
dration of glycerol.
the non mesoporous materials exhibit lower activity with
poor stability. This is mainly due to mesoporous mate-
rials have easy higher pore size and further easy dif-
fusion of reactants to products for long time intervals.
In above point of view, we have focused on mesoporous
materials such SBA-15. In recent years mesoporous mate-
rials like SBA-15 and MCM-41 have been successfully
employed as catalyst support in many catalytic applica-
tions apart from conventional oxides like Al2O3 and SiO2.
The advantage of these new class of mesoporous mate-
rials include high surface area and uniform pore struc-
ture. SBA-15 type of ordered mesoporous materials have
larger pore diameter, high surface area, uniform tubular
channels, high thermal stability and ordered pore structure.
These mesoporous materials are generally prepared by
using a tri-block copolymer as a template under strongly
acidic conditions relative to MCM-41. This will allow
an easier introduction of active components such as het-
eropolyacid. SBA-15 possesses well-ordered hexagonal
arrays of mesopores with pore diameters between 5 and
30 nm.26–29 Supported heteropolyacids have high surface
area, high thermal stability, especially when they are sup-
ported on mesoporous silica such as SBA-15. By varying
the amount of HPA on the surface leads to an improvement
of the catalytic performance.28–33 Bulk phosphomolybdic
acid with primary Keggin ion unit is well recognized
2. EXPERIMENTAL DETAILS
2.1. Preparation of Catalyst
V2O5, TEOS, P123, CTAB are obtained from Aldrich,
MoO3 was supplied by Fluka chemie, H3PO4 Supplied by
S.D Fine-Chem. Ltd. and protonated form of the Y-zeolite
obtained from Conteka, The Netherlands and also Al2O3
obtained from Engelhard corporation.
SBA-15 silica was prepared according to procedure
reported elsewhere28ꢀ29 by using triblock copolymers
based on poly(ethylene glycol)-poly(propylene glycol)-
poly(ethylene glycol) (P123, average molecular mass-
5800, Aldrich) as a template. About 2 g of P123 copolymer
was dissolved in a mixture of 15 g of water and 45 g
of 2 M HCl under stirring at ambient condition followed
5392
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015

Viswanadham et al.
Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
by the addition of 0.2 g of CTAB and 5.9 g of tetraethy-
lorthosilicate (TEOS). The final molar ratio of mixture
solution was 1TEOS:0.02CTMABr:3.1HCl:115H2O:0.012
polymer. The synthesis mixture was introduced into a tef-
flon bottle, sealed and kept at 100 ꢀC for 24 h. After cool-
ing the contents were filtered and washed with deionised
water and ethanol to remove the excess of template prior
one arm of the sample tube on a quartz wool bed. Prior to
TPD studies, the catalyst sample was pre-treated by pass-
ing high purity helium (50 ml/min) at 200 ꢀC for 2 h. After
pre-treatment of the sample, it was saturated by pꢀassing
(50 ml/min) high purity anhydrous ammonia at 80 C for
1 h and subsequently flushed with He flow (50 ml/min)
ꢀ
at 100 C for 2 h to remove the physisorbed ammonia.
TPD analysis was carried out from ambient temperature
ꢀ
to calcination. The solid product was dried at 25 C for
ꢀ
ꢀ
ꢀ
16 h and subsequently calcined in air at 500 C for 5 h.
to 600 C at a heating rate of 10 C/min. The ammonia
concentration in the effluent stream was monitored with
the thermal conductivity detector, and the areas under the
peaks were integrated using the software GRAMS/32 to
determine the amount of desorbed ammonia during TPD.
H4PMo11VO40 (HPA) was prepared by adding requisite
quantities of MoO3, V2O5 and H3PO4 solutions to the dis-
tilled water in a 500 ml round bottom flask and refluxed
at 100 ꢀC. The resulting solid was dried at 60 ꢀC for
16h. H4PMo11VO40 was prepared according to the proce-
dure described by Kanno et al. in literature.41 A series of
H4PMo11VO40 catalysts with H4PMo11VO40 loadings rang-
ing from 10–50 wt% supported on SBA-15 were prepared
by the impregnation method. A requisite amount of HPA
was dissolved in distilled water and SBA-15 support was
2.6. FT-IR Spectroscopy
FT-IR spectra of the catalysts were recorded on a IR
(Model: GC-FT-IR Nicolet 670) spectrometer by KBr disc
method at room temperature. The ex-situ experiments of
FT-IR spectra of pyridine adsorbed samples were carried
out to find the nature of acidity (Brønsted and Lewis acid
sites). Before the recording the IR spectra, samples pre-
ꢀ
added to it. The resultant solution was stirred at 25 C
ꢀ
for 5 h. The samples were dried atꢀ110 C for 10 h and
subsequently calcined in air at 250 C for 4 h. In similar
method Al2O3 and Y-zeolite supported HPA are prepared.
ꢀ
heated at 250 C for 4 h and cooled to room temperature
then pyridine adsorption experiments were carried out by
placing a drop of pyridine on 10 mg of the HPA sample
followed by evaporation in air for 1 h at room temperature
2.2. X-Ray Diffraction Studies
X-ray powder diffraction patterns of the samples were
obtained with a model: D8 Diffractometer (Advance,
Bruker, Germany), using Cu Kꢀ radiation (1.5406 Aꢀ) at
to remove reversibly adsorbed pyridine molecules on the
42
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surface of the catalyst.
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
40 kV and 30 mA. The measurements were recorded in
Copyright: American Scientific Publishers
steps of 0.045ꢀ with a count time of 0.5 s in the range
of 2–40ꢀ.
2.7. BET Surface Area and Pore Size Distribution
The specific surface area of catalystsꢀ was estimated using
N2 adsorption isotherms at −196 C by the multipoint
BET method taking 0.162 nm2 as its cross-sectional area.
The pore size distribution was measured by N2 adsorption–
desorption isotherms using Autosorb 1 (Quantachrome
instruments). Before performing N2 gas sorption experi-
ments, the samples were evacuated at 200 ꢀC for 4 h under
vacuum in order to remove the adsorbed moisture or impu-
rities from surface of the sample. Degassing is often car-
ried out by placing a sample in a quartz cell and heating
it under vacuum or flowing helium gas. The experiments
were carried out from relative nitrogen pressures (p/p0)
range of 0.05–0.9 by using nitrogen adsorption–desorption
method. The resulting hysteresis leads to isotherm of the
sample. The surface area was calculated from 5 adsorp-
tion isotherm points at relative nitrogen pressures (p/p0)
between 0.05 and 0.3. The pore size were calculated by
BJH method.
2.3. Raman Spectroscopy
The Raman spectra of the catalyst samples were collected
with a Horbia-Jobin Yvon LabRam-HR spectrometer
equipped with a confocal microscope, 2400/900 grooves/
mm gratings, and a notch filter. The Visible Laser excita-
tion at 532 nm (visible/green) was supplied by a Yag dou-
bled diode pumped Laser (20 mW). The scattered photons
were dried and focused on to a single-stage monochroma-
tor and measured with a UV-sensitive LN2-cooled CCD
detector (Horbia-Jobin Yvon CCD-3000V).
2.4. SEM Analysis
Morphology of the catalyst samples were investigated
by scanning electron microscopy (SEM) using a S-4800
(HITHACHI Co.) microscope.
2.5. Temperature Programmed
2.8. Catalytic Activity Studies
Desorption of Ammonia
The vapor phase dehydration reaction of glycerol was car-
ried out at 225–250 C under atmospheric pressure in a
vertical fixed-bed Pyrex glass reactor of 36 cm length and
0.5 cm internal diameter with a catalyst bed set at the mid-
dle of reactor. The reactor was placed in an electrically
Temperature-programmed desorption (TPD) studies of
NH3 were conducted on Auto Chem 2910 (micromerit-
ics, USA) instrument. In a typical experiment, ca. 100 mg
of H4PMo11VO40/SBA-15 calcined sample was taken in a
U-shaped quartz cell. The catalyst sample was packed in
ꢀ
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015
5393

Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
Viswanadham et al.
heated furnace. The temperature was controlled by a ther-
mocouple which was located near to the catalyst bed and
N2 gas was used as a carrier gas. The glass reactor was
packed with 0.3 g of catalyst and above the catalyst bed
the reactor was packed with ceramic beads which serve as
a pre-heater zone to increase evaporation of liquid glyc-
erol feed before reaching the catalyst bed. The catalyst
was pretreated with N2 gas at 60 ml/min at same reac-
tion temperature for 1 h. A aqueous glycerol (10 wt%)
solution (0.5 ml/h) was fed from the top of the reac-
tor through inlet in a flow of N2 gas at 10 ml/min. The
reaction products were collected in a cold trap for every
hour and were analyzed by Gas Chromatograph (Shimadzu
GC-2014) equipped with flame ionization detector, using
(f)
(e)
(d)
(c)
(b)
(a)
DB-wax 123-7033 capillary column and methanol as an
5
10
15
20
25
30
35
40
2θ
internal standard.
Figure 2. Wide-angle X-ray diffraction patterns of various wt% of
H4PMo11VO40/SBA-15 catalysts (a) pure SBA-15, (b) 10, (c) 20, (d) 30,
(e) 40, (f) 50.
3. RESULTS AND DISCUSSION
3.1. X-Ray Diffraction and BET Surface Area
33.5ꢀ are observed with increase of H4PMo11VO40 loading
on SBA-15 support. These reflections clearly suggest the
crystallites of Keggin ion of heteropolyacid (HPA). The
diffractograms also suggest that at low loadings the XRD
peaks due to active phase of HPA are absent suggesting
that HPA is well dispersed on the support. However, it
cannot be ruled out for the presence of HPA crystallites
Low-angle powder X-ray diffraction patterns of SBA-15
and various heteropolyacid (H4PMo11VO40) catalysts sup-
ported on SBA-15 are shown in Figure 1. An examina-
tion of XRD pattern reveals that the reflections appeared
at 2ꢀ angle 0.9ꢀ, 1.7ꢀ and 1.9ꢀ corresponds to the planes
of (100), (110) and (200) and confirm the mesoporosity
with hexagonal structure of pure SBA-15. The intensity of
Delivered by Publishing Technologyhtoav:iSngtotchkehsoilzme wUinthivelersssitythLanib4ranrym. This was beyond the
above XRD reflections decreases with H4PMo11VO40 load-
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
detection limit of X-ray diffraction technique. These find-
ing from 10 to 50 wt% on the SBA-15 support. Further the
Copyright: American Scientific Publishers
ings suggest that the active phase of HPA is well dispersed
low-angle XRD results suggest that the existence of meso-
porous nature of samples irrespective of HPA loading.
The powder X-ray diffraction patterns (Wide-angle) of
SBA-15 and H4PMo11VO40 supported catalysts are shown
in Figure 2. The reflections of 2ꢀ angle at 27.5ꢀ and
on SBA-15 surface at lower loadings and forms smaller
crystallites that cannot be detected by XRD. These results
are in agreement with the findings of BET surface area
and scanning electron microscopy (SEM) studies of these
materials (Fig. 5).
The BET surface area of pure SBA-15 and
H4PMo11VO40/SBA-15 catalysts are reported in Table I.
The BET surface area of H4PMo11VO40/SBA-15 cata-
lyst decreases gradually with increase of active phase
H4PMo11VO40 loading on the support. This could be
probably due to the partial filling of the mesoporous
structure of SBA-15 silica support by the active phase
and further leads to a decrease of BET surface area of
the sample. These findings are in good agreement with
previously discussed X-ray diffraction studies.
(f)
(e)
(d)
(c)
(b)
3.2. Raman Spectroscopy
The laser Raman spectra of pure H4PMo11VO40 and vari-
ous wt% HPA supported SBA-15 are shown in Figure 3.
It can be seen from Figure 3, SBA-15 shows a sym-
(a)
metrical Si
O
Si and the Si OH stretching mode of
0
2
4
Raman bands around 500, 600, 800 cm−1 respectively.43
Raman spectroscopy is well explored to investigate the
Keggin structure of heteropolyacid catalysts. The Raman
spectrum for bulk H4PMo11VO40 show bands at 1000,
842, 676 and 300 cm−1 which are assigned to symmetric
2θ
Figure 1. Low-angle X-ray diffraction patterns of various wt% of
H4PMo11VO40/SBA-15 catalysts (a) pure SBA-15, (b) 10, (c) 20, (d) 30,
(e) 40, (f) 50.
5394
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Viswanadham et al.
Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
Table I. Results of BET surface area, pore size distribution and TPD-NH3 measurements of various wt% of H4PMo11VO40/SBA-15 catalysts.
NH3 uptake (mmol/g)
HPA
loading (wt%)
BET surface
area (m2/g)
Total pore
volume (mL/g)
Average pore
diameter (nm)
Total NH3
uptake (mmol/g)
aWeak
bModerate
cStrong
0
890
618
540
452
376
238
0.529
0.582
0.601
0.645
0.767
0.592
12.01
12.16
12.34
12.43
13.01
12.44
–
–
–
–
10
20
30
40
50
0.366
0.410
0.424
0.450
0.360
0.160
0.280
0.360
0.520
0.430
0.013
0.025
0.120
0.010
0.250
0.539
0.715
0.904
0.980
1.040
Notes: aWeak acidic sites (50 ꢀC–150 ꢀC); bModerate acidic sites (150 ꢀC–300 ꢀC); cStrong acidic sites (450 ꢀC–550 ꢀC).
(ꢀs) and asymmetric (ꢀas) vibrations of terminal oxygen
ꢀs(Mo O), ꢀas(Mo Ot), edge shared bridged oxygen
ꢀs(Mo Oc-Mo) and oxygen in the central tetrahedron
ꢀs(Mo Oa). These catalysts have shown distinct changes
in the Raman spectra with increasing the loading of active
phase from 10–50 wt% of H4PMo11VO40 on SBA-15 sup-
port. The sample with 40 wt% HPA showed clear char-
acteristic Keggin ion band at 1000 cm−1 and this band is
shifted to 997 cm−1 at higher loadings of active phase.
The stretching frequencies of ꢀas(Mo Ot) were observed
at 846 cm−1 in higher loading of HPA. The Raman spectra
of HPA/SBA-15 and bulk H4PMo11VO40 suggest that the
bands at 1000, 842, 676, 300 cm−1 characteristic of Keggin
ion of [PMo11VO40]−4. Thus Raman spectra confirm that
the Keggin structure of heteropolyacid remains intact in
1200–700 cm−1 are shown in the Figure 4. Vanadium
substituted PMA on SBA-15 materials and H4PMo11VO40
are also characterized by FT-IR spectroscopy to identify
the primary Keggin ion structure. Figure 4 shows that
all the samples exhibit four well-defined infrared bands in
the range of 1200–700 cm−1. The infrared spectra show
various vibration bands of P O, Mo O, Mo Oc-Mo
(Oc = corner sharing oxygen) and Mo Oe Mo (Oe =
798 cm−1 and 746 cm−1 respectively. It can be seen from
Figure 4 that the intensity of these four skeletal vibrations
of Keggin ion are found to increase with HPA loading on
SBA-15 support. At 40 wt% and at higher loadings, the
presence of crystalline HPA phase on the surface of SBA-
15 was observed. The characteristic bands of four skeletal
vibrations observed in all materials suggests that the pri-
mary Keggin ion structure is retained on the support and
these results well correlates with pure HPA as shown in
Figure 4. The FTIR results confirm that all the materials
possess primary Keggin ion structure.
edge sharing oxygen) observed at 1,059 cm−1, 950 cm−1
,
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all the samples even after calcination of the supported cat-
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
alysts. These findings are in good agreement with Raman
Copyright: American Scientific Publishers
spectra of H4PMo11VO40/SiO2 reported by Kanno et al.41
They have also reported that the characteristic band of
Raman spectra appeared at 1000 cm−1 and further con-
firms with FT-IR investigation.
3.4. Scanning Electron Microscopy
3.3. Fourier Transform Infrared Spectroscopy
The FT-IR spectra of pure HPA and various H4PMo11VO40
catalysts supported on SBA-15 recorded in the range
The morphology and distribution of active phase of HPA
was investigated by scanning electron microscopy and the
images are shown in Figure 5. The morphology of pure
mesoporous silica containing SBA-15 shows a uniform
Pure H4PMo11VO40
H4PMo11VO40
Mo-Oe-Mo
Mo-O
Mo-Oc-Mo
P-O
700
800
900
1000
1100
1200
200
400
600
800
1000
1200
–1
Wave number (cm
)
Wave number (cm–1
)
(e)
(d)
(c)
(e)
(d)
(c)
(b)
(b)
(a)
(a)
Mo-Oe-MoMo-OC-Mo
800 900
P-O
Mo-O
700
1000
1100
1200
200
400
600
800
1000
1200
Wave number (cm–1
)
Wave number (cm–1
)
Figure 3. Raman spectra of pure H4PMo11VO40 acid and various wt%
Figure 4. FT-IR spectra of various wt% of H4PMo11VO40/SBA-15 cat-
of H4PMo11VO40/SBA-15 catalysts (a) 10, (b) 20, (c) 30, (d) 40, (e) 50.
alysts (a) 10, (b) 20, (c) 30, (d) 40, (e) 50.
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015
5395

Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
(a) (b) (c)
Viswanadham et al.
(d)
(e)
Figure 5. SEM images of (a) pure H4PMo11VO40 acid, (b) pure SBA-15, (c) 10, (d) 40, (e) 50 wt% of H4PMo11VO40/SBA-15 catalysts.
hexagonal rod like structure. However, pure vanadium
substituted heteropolyacid of H4PMo11VO40 acid shows a
cylindrical shape like morphology. Increase of the HPA
loading from 10–40 wt% on SBA-15 support clearly
temperature-programmed desorption of ammonia profile
reveals that the 40 wt% of catalyst possesses fairly good
number of moderate acidic sites compared to other load-
ings. Among all the catalysts analyzed for acidity mea-
surements by TPD-NH , the sample containing 50 wt%
loading of HPA has shown large number of these strong
acidic sites.
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exhibits uniform dispersion of active phase on the surface
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:439
of the support. The morphology of pure H4PMo VO40
Copyright: A1m1 erican Scientific Publishers
was observed beyond 40 wt% and at higher HPA loading,
which is similar to the morphology of pure heteropolyacid.
The present SEM findings are well supported with X-ray
diffraction and Raman spectra of these catalysts.
3.6. Pyridine Adsorbed Fourier
Transform Infrared Spectroscopy
The nature of Brønsted and Lewis acidic sites of HPA sup-
ported on SBA-15 is also examined by pyridine adsorption
3.5. Temperature-Programmed Desorption of
Ammonia (TPDA)
Temperature-programmed desorption (TPD) profiles of
ammonia for H4PMo11VO40/SBA-15 with H4PMo11VO40
loading ranging from 10 to 50 wt% are shown in
Figure 6 and the amount of NH3 desorbed is tabulated
in Table I. TPD profiles suggest that a strong desorp-
tion peak appeared between 450 ꢀC to 550 ꢀC and a
moderate desorption peak is noticed around 150 ꢀC to
(e)
(d)
ꢀ
300 C. The peak in the high temperature region of des-
orption is attributed to strong acidic sites of the cat-
alyst and low temperature region desorption peaks are
attributed due to moderate acidic sites of the catalyst. The
strong acidic sites increased gradually from 10–30 wt%
H4PMo11VO40 supported SBA-15 and decreases consider-
ably at 40 wt% HPA. It is interesting to note that the sam-
ple containing 50 wt% H4PMo11VO40 on SBA-15 show
higher acidity (strong acid sites) than 40 wt% HPA sample.
The TPD profiles have exhibited more number of strong
acidic sites at higher loading. Whereas moderate acidic
sites increased with increase of the HPA loading up to
40 wt% catalyst and decreased at higher loadings. The
(c)
(b)
(a)
0
100
200
300
400
500
600
Temperature (ºC)
Figure 6. TPD-NH3 of various wt% of H4PMo11VO40/SBA-15 catalysts
(a) 10, (b) 20, (c) 30, (d) 40, (e) 50.
5396
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015

Viswanadham et al.
Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
ex-situ FT-IR spectroscopy. The ex-situ pyridine FT-IR
spectra of various wt% of H4PMo11VO40 on SBA-15
catalysts in the range 1600–1400 cm−1 are shown in
the Figure 7. The spectrum shows IR bands in three
regions. The vibration band appeared between 1542 and
1539 cm−1 is attributed due to Brønsted acidic sites.
The IR peak appeared at 1489–1487 cm−1 is assigned
to both Brønsted and Lewis (B + L) acidic sites. How-
ever, the vibration at 1447–1442 cm−1 band is assigned
exclusively to Lewis acidic sites. As can be seen from the
Figure 7, the Brønsted acidic sites increased with increase
of HPA loading up to 40 wt% and at higher loadings these
acidic sites considerably decreased. The Lewis acidic sites
increased gradually up to 30 wt% of HPA and decreases
at higher loadings (> 40 wt% catalyst). The intensity of
IR bands of both Brønsted and Lewis acidic sites in the
region 1489–1487 cm−1 increases with HPA loading up to
40 wt% and at higher loading the both the B + L acidic
sites are decreased. These results are in good agreement
with previously described acidity measurements by TPD-
NH3 method.
B + L
L
B
(a)
(b)
(c)
1600
1500
1400
Wave number (cm–1
)
Figure 8. Pyridine adsorbed FT-IR spectra of 40 wt% of catalysts with
(a) SBA-15, (b) Al2O3, (c) Y-zeolite.
compared to the L acidic sites of H4PMo11VO40/Al2O3 and
H4PMo11VO40/Y-zeolite. The above results clearly demon-
strate that the presences of higher amount of Brønsted
acidic sites are observed for H4PMo11VO40 supported on
SBA-15 than HPA supported on Al2O3 or Y-zeolite.
A
comparison of acidity exhibited by 40 wt%
HPA on SBA-15, Al2O3 and Y-zeolite are shown in
Figure 8. The ex-situ pyridine FT-IR spectra in the
range 1600–1400 cm−1 for 40 wt% HPA of different
supports is shown in the Figure 8. The spectra sug-
gest that the IR bands at 1538 cm−1 is assigned due
to Brønsted acidic sites. The IR peak at 1488 cm−1
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ꢀ
3.7. N Adsorption–Desorption Isotherms at − 196 C
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
2
Copyright: American Scientific Publishers
is assigned to both Brønsted and Lewis (B + L) acidic
The N2 adsorption–desorption isotherms of the pure SBA-
15 and H4PMo11VO40/SBA-15 catalysts are shown in
Figure 9 and the information derived is reported in Table I.
The N2 adsorption–desorption isotherms of all the sam-
ples show a typical type IV isotherm according to the
IUPAC classification and exhibited a H1 hysteresis loop
which is characteristic of mesoporous materials. The N2
sites and the vibration of 1444 cm−1 is assigned exclu-
sively to Lewis acidic sites. As can be shown from
Figure 8, the intensity of IR peaks of B and B+L acidic
sites of H4PMo11VO40/SBA-15 was much higher com-
pared to similar acidic sites of H4PMo11VO40/Al2O3 and
H4PMo11VO40/Y-zeolite. However, the intensity L acidic
sites peak of H4PMo11VO40/SBA-15 was found to be less
B + L
L
B
H4PMo11VO40 loading
50%
(e)
(d)
(c)
40%
30%
20%
10%
(b)
(a)
0.0%
0.0
0.2
0.4
0.6
0.8
1.0
1600
1500
1400
P/PO
Wave number (cm–1
)
Figure 9. N2 adsorption–desorption isotherms of various wt%
H4PMo11VO40/SBA-15 catalyst. (a) pure SBA-15, (b) 10, (c) 20, (d) 30,
(e) 40, (f) 50.
Figure 7. Pyridine FTIR of various wt% of H4PMo11VO40/SBA-15 cat-
alysts (a) 10, (b) 20, (c) 30, (d) 40, (e) 50.
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015
5397

Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
Viswanadham et al.
adsorption–desorption isotherm of the SBA-15 sample in
the relative pressure of P/P0 0.65–0.85 range have shown
that all catalysts have exhibited uniform pore size distribu-
tion, which is a characteristic feature of a typical capillary
condensation with uniform pores. As the loading of HPA
increases on the SBA-15 support the shift of the position of
capillary condensation is observed towards higher pressure
110
110
100
90
100
90
% conversion of glycerol
% acrolein selectivity
% acetic acid seletivity
80
80
70
70
60
60
50
50
range indicating that increase of the pore size. However,
at higher loading (> 40 wt% HPA) shift in the position of
40
40
the capillary condensation can be noticed towards lower
30
30
pressure region and confirms that at higher loading of HPA
20
20
on support, the pore size was decreased.
The pore size distributions measured by BJH method
10
10
50
10
20
30
40
HPA loading (wt %)
of various H4PMo11VO40/SBA-15 catalysts are shown in
Figure 10. All the samples have shown uniformed pore
Figure 11. The conversion of aqueous glycerol/acrolein selectivity and
size distribution with majority of pores present in meso-
porous range. As the loading of HPA increases on support
from 10 to 50 wt%, the average pore diameter increases
gradually from10 to 40 wt% HPA and decreased at higher
loading (i.e., 50 wt% HPA). The decrease of pore size at
higher loading is probably due to formation of crystalline
phase of HPA supported on SBA-15. These results sug-
gest that with increasing HPA loading the textural prop-
erties like pore volume and pore diameter increase up to
40 wt% and then decreased at higher loading. The decrease
of these properties at higher loading is also probably due
to blockage of pores by the crystalline phase formation
of heteropolyacid on the SBA-15 support. The pore size
wt% of H4PMo11VO40/SBA-15 catalyst at 225 ꢀC.
distribution results are good agreement with X-ray diffrac-
tion patterns of the different wt% of HPA on support.
A comparison study on pore size distribution (PSD)
showed by 40 wt% HPA on SBA-15, Al2O3 and Y-zeolite
are reported in Table IV. The PSD results for 40 wt%
HPA of different supports was shown that the average pore
diameter decreased with respect to support are following in
the order HPA/SBA-15 > HPA/Al2O3 > HPA/zeolite. This
was due to lower average pore diameter of Al2O3 and
zeolite compare to SBA-15. When HPA impregnated on
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non-mesoporous support, the pores of support blocked by
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
active component and it was located outside pores of sup-
Copyright: American Scientific Publishers
port compare to SBA-15 support. Thus SBA-15 has more
pore diameter than alumina and zeolite then HPA was
highly dispersed and strongly interacts within the pores
of SBA-15 support. The above results clearly reveal that
higher average pore diameter observed for H4PMo11VO40
supported on mesoporous SBA-15 than HPA supported on
Al2O3 or Y-zeolite.
(f)
(e)
(d)
(c)
3.8. Dehydration of Glycerol
The catalytic properties of various wt% vanadium con-
taining phosphomolybdic acid catalysts supported SBA-
15 was investigated for the vapor phase dehydration of
Table II. Product distribution results of various H4PMo11VO40/SBA-15
(b)
(a)
catalyst with 10 wt% aqueous glycerol solution at 225 ꢀCX .
Selectivity (%)
HPA loading
(wt%)
aCgly (%)
bAc
cAce
dAceta
yOther
10
20
30
40
50
100
100
100
100
100
34
41
58
74
51
48
42
34
17
40
2
2
2
4
4
16
15
6
5
5
0
10
20
30
40
50
Notes: xData on the conversion and selectivity of the mean values in the initial reac-
Pore diameter (nm)
tion period 4 h; Reaction conditions : catalyst weight = 0ꢀ3 g, feed= 0ꢀ5 mL h−1
,
10 mL min−1 gas flow rate (N2), 10 wt% aqueous glycerol solution, reaction
temperature = 225 ꢀC; yHydroxyacetone, acetone, other products; aConversion of
glycerol; bAcrolein selectivity; cAcetic acid selectivity dAcetaldehyde selectivity.
Figure 10. BJH Pore size distribution
H4PMo11VO40/SBA-15 catalysts (a) pure SBA-15, (b) 10, (c) 20, (d) 30,
(e) 40, (f) 50.
of various
wt%
5398
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015

Viswanadham et al.
Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
ꢀ
glycerol at 225 C under atmospheric pressure are shown
in Figure 11 and the product distribution is reported in
Table II. As can be seen from Figure 11, the results clearly
demonstrate that acrolein selectivity during the glycerol
dehydration depends on the HPA loading on mesoporous
SBA-15 support. It was found that acrolein selectivity
increased up to 40 wt% of HPA and then decreased
at higher loading of H4PMo11VO40 on SBA-15. TPD of
ammonia results shows that moderate acidic sites are
increased with increase in HPA loading and decreased at
higher loading. The above results clearly suggested that
acrolein selectivity depends on acidity of catalyst deter-
mined by TPD-NH3. An evidence from FT-IR studies of
pyridine adsorbed samples suggest that Brønsted acidic
sites increases with HPA loading as shown in Figure 7.
This result confirms that increase of acrolein selectivity
is due to increase of Brønsted acidic sites in the catalyst.
A considerable decrease of selectivity towards acrolein is
noticed at 50 wt% HPA catalyst as this sample possesses
more number of Lewis acidic sites (Fig. 7) and also less
amount of moderate acidic sites (Table I). The 40 wt%
HPA/SBA-15 exhibited 74% acrolein selectivity and it pos-
sesses large number of moderate acidic sites as determined
by TPD of ammonia.
Atia et al.7 reported that addition of alkaline metals like
Li, K and Cs proved to be another tool to tune the proper-
ties of HPA on the support and to improve its performance
in glycerol dehydration, in particular acrolein selectivity.
But the added alkaline metal considerably decreases the
activity. Garbay et al.10 have shown that ZrNbO catalysts
improve the acrolein selectivity and prevent faster deac-
tivation of the catalysts. Sancho et al.11 discussed, the
ZrNbO catalysts undergo deactivation easily in the dehy-
dration of glycerol reaction. However, in the present work
the glycerol dehydration was carried out with the vana-
dium incorporated or substituted phosphomolybdic acid
catalyst, which exhibits excellent catalytic performance in
the dehydration of glycerol to acrolein. Among all the cat-
alysts examined the 40 wt% HPA has exhibited complete
conversion of glycerol with 74% acrolein selectivity.
The superior catalytic functionalities of HPA/SBA-15
catalysts are compared with HPA supported on Al2O3 and
Y-zeolite (Table III). The acrolein selectivity was found
to be more in the case of SBA-15 support compare to
other supports of Al2O3 and Y-zeolite. The enhanced selec-
tivity of acrolein over HPA/SBA-15 was probably due
to availability of large number of Brønsted acidic sites
(Fig. 8). The acetic acid selectivity was higher in the case
of Y-zeolite compared to other supports, HPA/Y-zeolite has
more number of L acidic sites as shown in Figure 8. It is
interesting to note that irrespective of support used in the
The acetic acid selectivity was decreased with increase
of the HPA loading up to 40 wt% of HPA on support and
further increased at higher loading of catalyst (Table II).
This is probably due to the decrease of ratio of L/B acidic
sites up to 40 wt% HPA loading. HoweCveorpthyerigrahtti:oAs omfeLr/iBcan Scientific Publishers
ciably due to the redox nature of HPA
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reaction, the glycerol conversion has not changed appre-
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
36–39ꢁ41ꢁ46–54
with
acidic sites are increasing at higher HPA loading. As can
be seen from Table II the conversion of glycerol did not
appreciably change with HPA loading. The use of low wt%
of glycerol in the fed minimises coke formation and also
do not effect redox properties. However, the glycerol con-
version decreases with high concentration of glycerol fed
into the reactor (Table V). The presence of Lewis acidic
sites favours the formation of hydroxy acetone, which is
further converted to acetaldehyde and acetic acid by the
solid acid catalysts. Thus catalytic activity results are well
correlates with the nature of acidic sites and acidity of the
catalyst.
10 wt% of glycerol. However, the supports considerably
affect the selectivity of acrolein and other products. The
catalytic selectivities obtained over H4PMo11VO40 on vari-
ous supports is shown in Table III are well correlated with
acidity of catalysts measured by pyridine adsorbed FTIR
spectra (Fig. 8).
The textural properties or porosity of different supported
HPA are reported in Table IV. The pore size of the support
also influences the acrolein selectivity as it is decreased
from 74% (HPA/SBA-15) to 46% (HPA/Y-zeolite) during
the reaction. This could be due to decrease of pore size
from 13.10 to 2.61 nm. The activity is same in all the
Table III. Product distribution results of 40 wt% H4PMo11VO40 on
different supported catalysts with 10 wt% aqueous glycerol solution at
225 ꢀCX .
Table IV. Product distribution results of 40 wt% H4PMo11VO40/SBA-
15 catalyst with 10 wt% aqueous glycerol solution at
225 ꢀC–250 ꢀCX .
Selectivity (%)
Selectivity (%)
HPA on
support
Pore diameter
(nm)
Reaction
temperature (ꢀC)
aCgly (%) bAc cAce dAceta yOther
aCgly (%)
bAc
cAce
dAceta
yOther
SBA-15
Al2O3
Y-zeolite
13ꢀ01
6ꢀ68
2ꢀ61
100
100
100
74
53
46
17
28
36
4
5
3
5
13
15
225
250
100
100
74
48
17
23
4
14
5
15
Notes: xData on the conversion and selectivity of the mean values in the ini-
tial reaction period 4 h; Reaction conditions: catalyst weight= 0ꢀ3 g, feed =
0ꢀ5 mL h−1, 10 mL min−1 gas flow rate (N2), 10 wt% aqueous glycerol solu-
tion, reaction temperature = 225ꢀ–250 ꢀC; y Hydroxyacetone, acetone, other prod-
ucts; aConversion of glycerol; bAcrolein selectivity; cAcetic acid selectivity;
dAcetaldehyde selectivity.
Notes: xData on the conversion and selectivity of the mean values in the initial reac-
tion period 4 h; Reaction conditions : catalyst weight = 0ꢀ3 g, feed = 0ꢀ5 mL h−1
,
10 mL min−1 gas flow rate (N2), 10 wt% aqueous glycerol solution, reaction
temperature= 225 ꢀC; y Hydroxyacetone, acetone, other products; aConversion of
glycerol; bAcrolein selectivity; cAcetic acid selectivity; dAcetaldehyde selectivity.
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015
5399

Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
Viswanadham et al.
175
175
catalysts but the acrolein selectivity is observed high in
% conversion of glycerol on HPA/SBA-15
the case of SBA-15 supported HPA compared to zeolite
supported HPA catalysts. This is probably due to decrease
in pore diameter of HPA/Y-zeolite.
Several authors studied the vapor phase dehydration
% acrolein selectivity on HPA/SBA-15
% conversion of glycerol on HPA/Al2O3
% acrolein selectivity on HPA/Al2O3
% conversion of glycerol on HPA/zeolite
% acrolein selectivity on HPA/zeolite
150
150
125
100
75
125
of glycerol to acrolein using different supported HPA
100
catalysts.4ꢀ44ꢀ45 The influence of selected support materi-
75
als on acrolein formation was studied under similar reac-
tion conditions. The selectivity of acrolein on various HPA
catalysts our present study follows the order SBA-15 >
50
50
Al2O3 > Y-zeolite.
25
25
The effect of reaction temperature on the dehydration
of glycerol was examined over 40 wt% HPA on SBA-
0
1
2
3
4
5
6
7
8
9
10 11
Time on stream (h)
15 and product distribution given in Table IV. From the
Table IV it is observed that the selectivity of acrolein and
acetic acid varies with reaction temperature. But the con-
version of glycerol remains same with increase of reaction
Figure 12. Catalytic properties over 40 wt% HPA on SBA-15, Al2O3
and Y-zeolite supports at 225 ꢀC.
ꢀ
ꢀ
temperature from 225 C–250 C. This might be due to
the oxidative property of vanadium containing heteropoly-
acids during the reaction.36–39ꢀ41ꢀ46–54 As the temperature
materials as a catalyst supports are advantageous for glyc-
erol dehydration reaction for obtaining high stable con-
version and high selectivity of acrolein. The decrease of
conversion and acrolein selectivity in HPA supported on
Y-zeolite and alumina is might be due to significant deac-
tivation of the catalysts or loss of Keggin ion structure
of HPA.
ꢀ
ꢀ
increases from 225 C to 250 C, the acrolein selectivity
decreases from 74 to 48% whereas acetic acid selectivity
increases from 17 to 23% during reaction. The significant
change in product selectivity is due to oxidation ability
of vanadium containing phosphomolybdic anion at higher
reaction temperature favours C C bond cleavage.
Several authors reported that the activity of catalyst
decreases because of coke formation on the surface of
Tao et al.6 reported that the gas-phase dehydration reac-
13ꢀ15
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catalysts.
However, the H4PMo11VO40 show redox
ꢀ
36–39ꢀ46–54
tion of glycerol was carried outIPa:t 6331.5142C.2u2n6d.e3r5aOtmno:-Mon, 26 Oct 2015 02:00:49
properties to reduce the coke formation with time
spheric pressure. Kim et al.13 reported the vapour phase
Copyright: American Scientific Publishers
on stream up to 10 h. Hence the vanadium substituted
PMA supported on SBA-15 has novel importance to the
catalytic studies than alumina and zeolite under mild reac-
tion conditions.
dehydration of glycerol ꢀto acrolein over H-zeolites car-
ꢀ
ried out at 290 C–340 C temperature. However, in the
present work the vapor-phase dehydration of glycerol to
acrolein was carried out at mild reaction temperature
A comparison is made with other supported cata-
lysts such as zirconia supported 12-tungstophosphoric acid
(TPA) with the present results during glycerol dehydra-
tion. Chai et al.55 reported that TPA/ZrO2 catalysts have
shown 67% conversion and 47% selectivity to acrolein.
The above catalysts have shown rapid decrease in the glyc-
erol conversion during the time on stream studies at TOS
9–10 h (35%). However, H4PMo11VO40/SBA-15 catalysts
employed in the present study exhibited total conversion of
glycerol with 65% acrolein selectivity at TOS 9–10 h. The
above findings suggest that H4PMo11VO40 supported on
SBA-15 exhibits better catalytic properties than TPA/ZrO2.
The stable activity shown by H4PMo11VO40/SBA-15 dur-
ing time on stream is probably due to the mesopores with
higher pore size of SBA-15 support.
ꢀ
(225 C) under atmospheric pressure. Thus mild reaction
temperature conditions are beneficial than the high reaction
temperature in this vapor phase dehydration of glycerol
reaction.
The effect of time on stream on catalytic properties dur-
ing glycerol dehydration by using 40 wt% H4PMo11VO40
on different supports are shown in Figure 12. As can
be seen from Figure 12, HPA/SBA-15 exhibited com-
plete conversion of glycerol with 74% acrolein selectivity
(10 wt% aqueous glycerol solution) with stable activity
for a period of 10 h of the continuous operation. How-
ever, HPA/Al2O3 shows stable activity up to 7 h and
decreases gradually with time. Similarly, acrolein selectiv-
ity also decreases with time. In the case of HPA/zeolite
the stable activity is noticed only up to 4 h and it was
decreased later. The stable activity of SBA-15 supported
catalysts compared to other supported catalysts can be
explained based on the mesoporous nature of the SBA-
15 support and also on the acidic and redox behaviour.
However, the acrolein selectivity obtained in the case of
HPA/SBA-15 stable during course of reaction compare
to HPA/Al2O3 and HPA/Y-zeolite. Thus the mesoporous
The vapor phase dehydration of glycerol reaction was
carried out at 225 C with 40 wt% HPA/SBA-15 by vary-
ꢀ
ing feed concentration of glycerol and the catalytic results
are reported in Table V. The catalyst exhibited high activ-
ity on 10 wt% glycerol concentration amounting to 100%
glycerol conversion at 74% acrolein selectivity. However,
the conversion and acrolein selectivity decreased sharply
with increase in concentration of glycerol feed. This is
5400
J. Nanosci. Nanotechnol. 15, 5391–5402, 2015

Viswanadham et al.
Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium
Table V. Product distribution results of 40 wt% of H4PMo11VO40/SBA-
the phosphomolybdic acid shows tuneable redox and acid
properties and improves catalyst stability to retard deacti-
vation with high selectivity to acrolein. The catalyst shows
better catalytic performance with 10 wt% glycerol solu-
tion than the other concentrations of glycerol. Mesoporous
SBA-15 supported HPA with large average pore diame-
ter was more efficient than the corresponding macroporous
supported HPA and also the best acrolein selectivity was
obtained with HPA supported on mesoporous SBA-15.
15 catalyst with 10–40 wt% aqueous glycerol solution at 225 ꢀCX .
Selectivity (%)
Glycerol
concentration (Wt%)
aCgly (%)
bAc
cAce
dAceta
y other
10
20
30
40
100
96
89
74
66
53
38
17
24
27
32
4
2
4
8
5
8
16
22
78
Notes: xData on the conversion and selectivity of the mean values in the initial reac-
tion period 4 h; Reaction conditions : catalyst weight = 0ꢀ3 g, feed = 0ꢀ5 mL h−1
,
10 mL min−1 gas flow rate (N2), 10 wt% aqueous glycerol solution, reaction
temperature = 225ꢀC; yHydroxyacetone, acetone, other products; aConversion of
glycerol; bAcrolein selectivity; cAcetic acid selectivity; dAcetaldehyde selectivity.
Acknowledgments: The authors Balaga Viswanadham,
Vanama Pavan Kumar Thank CSIR, New Delhi for the
award of Senior Research Fellowship and Amirineni
Srikanth thanks Director, IICT for Project Assistant
fellowship.
due to significant coke was deposited on the catalyst
surface during the course of reaction and decreases avail-
able active sites with increase of glycerol concentration.
Thus catalytic activity and acrolein selectivity decreases
with increase in concentration of glycerol solution due to
the fact that the number of available active sites of cata-
lysts decreased due to deactivation of the catalysts caused
by coke formation.
References and Notes
1. C. H. Zhou, J. N. Beltramini, Y. X. Fana, and G. Q. Lu, Chem. Soc.
Review. 37, 527 (2008).
2. C. J. Jia, Y. Liu, W. Schmidt, A. H. Lu, and F. Schuth, J. Catal. 269,
71 (2010).
3. B. Katryniok, S. Paul, M. Capron, and F. Dumeignil, Chem. Sus.
Chem. 2, 719 (2009).
4. K. Benjamin, P. Sebastien, B. B. Virginie, R. Patrick, and D. Franck,
Green. Chem. 12, 2079 (2010).
5. M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, and C. D. Pina,
Ang. Chem. Inter. Edt. 46, 4434 (2007).
4. CONCLUSIONS
This work presents a comprehensive characterization, cat-
alytic properties and investigation of the acidity and textu-
ral properties of H4PMo11VO40 supported on mesoporous
6. L. Z. Tao, S. H. Chai, Y. Zuo, W. T. Zheng, Y. Liang, and B. Q. Xu,
Catal. Today. 158, 310 (2010).
Delivered by Publishing Technology to: Stockholm University Library
IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
silica SBA-15. The vanadium substituted HPA supported
on SBA-15 are found to be highly active for the vapor
phase dehydration of glycerol to acrolein at moderate reac-
tion temperature under normal atmospheric pressure. The
XRD and SEM findings suggest that high dispersion of
HPA on support was observed at lower loadings. The FT-
IR and Raman spectral findings confirm the existence of
primary Keggin ion structure of HPA and it was intact
in all the prepared materials of HPA on SBA-15. TPD
of ammonia results suggests that 40 wt% HPA has more
number of moderate acidic sites and well correlates with
pyridine adsorbed FT-IR results. The pore size distribution
(PSD) results show that the pore size increased at lower
wt% of HPA and decreased at higher loading and also
mesoporous SBA-15 support exhibits large pore size than
the Al2O3 and Y-zeolite. The pore size of the heteropoly-
acids supported on SBA-15 also influences the activity and
selectivity.
The catalytic properties during the vapor phase glycerol
dehydration reaction results are well correlated with acidic
and textural properties of the catalysts. The vanadium con-
taining HPA supported on SBA-15 has shown excellent
catalytic performances during the dehydration reaction at
225 ꢀC under atmospheric pressure than the other non
mesoporous supported systems. The HPA catalysts sup-
ported on mesoporous SBA-15 exhibited higher and sta-
ble activity compared to HPA supported on alumina and
Y-zeolite. It was found that incorporation of vanadium to
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IP: 63.142.226.35 On: Mon, 26 Oct 2015 02:00:49
Copyright: American Scientific Publishers
Received: 23 April 2014. Accepted: 24 May 2014.
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