Vapour phase dehydration of glycerol over VPO catalyst supported on zirconium phosphate

Article abstract of DOI:10.1039/c3cy00430a

A series of VPO catalysts supported on porous zirconium phosphate with varying VPO loadings ranging from 5-30 wt% were prepared by solid-solid wetting method. The calcined catalysts are well characterized by BJH for pore size distribution, X-ray diffraction (XRD), FTIR, scanning electron microscopy (SEM), temperature programmed reduction (TPR) and UV diffuse reflectance spectroscopy. The acidic properties of the catalysts were investigated by ex-situ FTIR analysis of adsorbed pyridine and temperature programmed desorption (TPD) of NH₃. The catalytic properties were evaluated for the gas phase dehydration of glycerol to acrolein. The results of pore size distribution by the BJH method suggest that the VPO loadings considerably affect the textural properties. XRD and FTIR analysis suggest that the formation of vanadyl pyrophosphate phase on the zirconium phosphate support. SEM image of unsupported VPO catalyst clearly exhibits the formation of a rosette like structure. UV-DRS study reveals the formation of vanadyl pyrophosphate phase along with some extent of vanadium orthophosphate phase. TPR analysis suggests that the reducibility of the active VPO phase depends on the VPO loading and also the active phase strongly interacts with the support. The results of vapour phase glycerol dehydration reaction are well correlated with the acidity of the catalysts measured by the ex-situ adsorbed pyridine by FTIR and TPD of ammonia. The findings derived from several characterization techniques clearly suggest that VPO species is highly dispersed on the ZrP support.

Full text of DOI:10.1039/c3cy00430a

View Article Online
View Journal
Catalysis
Science&Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: K. V. R. Chary, P. R. N, S. R. Ginjupalli
and P. K. V, Catal. Sci. Technol., 2013, DOI: 10.1039/C3CY00430A.
This is an Accepted Manuscript, which has been through the RSC Publishing peer
review process and has been accepted for publication.
Catalysis
Science&Technology
Accepted Manuscripts are published online shortly after acceptance, which is prior
www.rsc.org/catalysis
Volume 1 | Number 1 | 2011 | Pages 0001–0100
to technical editing, formatting and proof reading. This free service from RSC
Publishing allows authors to make their results available to the community, in
citable form, before publication of the edited article. This Accepted Manuscript will
be replaced by the edited and formatted Advance Article as soon as this is available.
To cite this manuscript please use its permanent Digital Object Identifier (DOI®),
which is identical for all formats of publication.
More information about Accepted Manuscripts can be found in the
Information for Authors.
Please note that technical editing may introduce minor changes to the text and/or
graphics contained in the manuscript submitted by the author(s) which may alter
content, and that the standard Terms & Conditions and the ethical guidelines
that apply to the journal are still applicable. In no event shall the RSC be held
responsible for any errors or omissions in these Accepted Manuscript manuscripts or
any consequences arising from the use of any information contained in them.
ISSN 2044-4753
www.rsc.org/catalysis
Registered Charity Number 207890

Page 1 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
Vapour Phase Dehydration of Glycerol over VPO Catalyst
Supported on Zirconium phosphate
N. Pethan Rajan, Ginjupalli Srinivasa Rao, Vanama Pavankumar and Komandur V R Chary *
Catalysis Division, Indian Institute of Chemical Technology, Hyderabad-500 007, India.
*Corresponding author. Tel: +91-40-27193162; Fax: +91-40-27160921, E-mail: kvrchary@iict.res.in
ABSTRACT:
A series of VPO catalysts supported on porous zirconium phosphate with varying VPO
loadings ranging from 5ꢀ30 wt % were prepared by solidꢀsolid wetting method. The calcined
catalysts are well characterized by BJH for pore size distribution, Xꢀray diffraction (XRD),
FTꢀIR, scanning electron microscopy (SEM), temperature programmed reduction (TPR) and
UV diffuse reflectance spectroscopy. The acidic properties of the catalysts were investigated
by exꢀsitu FTIR analysis of adsorbed pyridine and temperature programmed desorption
(TPD) of NH3. The catalytic properties were evaluated for the gas phase dehydration of
glycerol to acrolein. The results of Pore size distribution by BJH method suggest that the
VPO loadings considerably affect the textural properties. XRD and FTIR analysis suggests
that the formation of vanadyl pyrophosphate phase on the zirconium phosphate support. SEM
image of unsupported VPO catalyst clearly exhibits the formation of rosette like structure.
UVꢀDRS study reveals the formation of vanadyl pyrophosphate phase along with some
extent of vanadium orthophosphate phase. TPR analysis suggests that the reducibility of the
active VPO phase depends on the VPO loading and also the active phase strongly interacts
with the support. The results of vapour phase glycerol dehydration reaction are well
correlated with the acidity of the catalysts measured by the exꢀsitu adsorbed pyridine by
FTIR and TPD of ammonia. The findings derived from several characterization techniques
clearly suggest that VPO species is found to be highly dispersed on ZrP support.
1. INTRODUCTION:
In the recent past glycerol received particular attention as byꢀproduct from biodiesel production. The extracted
triglycerides can undergo transesterification with methanol, yielding the methyl ester (biodiesel) and glycerol as byꢀproduct
on a stoichiometric basis. The increasing production of biodiesel has resulted in a price decline of crude glycerol. This makes
aqueous glycerol as an attractive compound for the synthesis of fine and crude chemicals. Catalytic conversion of glycerol to
acrolein by a double dehydration reaction could be an important route for using glycerol resources. However this process
would provide a cost effective and sustainable alternative to the current commercial catalytic petrochemical process based on
the oxidation of propylene over a Bi/Mo mixed oxide catalyst. Acrolein is an important and versatile chemical intermediate
and raw material for the production of acrylic acid esters, super absorber polymers, fiber treatment, detergents and
production of other valueꢀadded derivatives.1ꢀ2
Various types of solid acid catalysts such as zeolites 3, metal oxides 4ꢀ5, metal phosphates 6, heteropoly acids on
different supports 7ꢀ8, WO3ꢀZrO2 9ꢀ10, have been investigated for the glycerol dehydration reaction. Among the various metal
phosphate catalysts used for this reaction, vanadium phosphorus oxide (herein after VPO) catalyst was also studied by Wang
et al. 11 because it possesses strong acidic sites. Moreover, they found that addition of molecular oxygen with glycerol feed
greatly reduces the side product formation and maintains the glycerol conversion and acrolein yield. The same group also
investigated the effect of calcination temperature on pure VPO catalyst and found that calcination temperature affects the
Lewis acidity of the catalyst.12
Vanadium phosphorus oxides (VPO), is well known as catalyst for an industrially important selective oxidation of nꢀ
butane to maleic anhydride.13 The VPO catalyst contains several VPO phases with vanadium in 5+ oxidation state (α, β, γ,
δꢀ VOPO4), 4+ oxidation state ((VO)2P2O7) and 3+ oxidation state (VPO4) . It is generally accepted that well crystallized
vanadyl pyrophosphate is the major phase in industrial VPO catalyst for oxidation of nꢀbutane to maleic anhydride. The
activity of the VPO catalyst generally depends on the type of reagents used in the preparation, the ratio of phosphorous to
vanadium, the nature of the solvent and the conditions of the activation step. Vanadyl pyrophosphate is prepared from the
thermal treatment of another crystalline compound, the precursor VOHPO4.0.5H2O. The most recent and common
commercial formulations for the preparation of the precursor prefer organic compounds as solvents.14 The crystalline
structure and the morphology have been determined with a combination of Xꢀray diffraction and electron microscopy
1

Catalysis Science & Technology
Page 2 of 24
View Article Online
DOI: 10.1039/C3CY00430A
techniques. The acidity of the VPO catalysts can be attributed to the presence of surface PꢀOH groups and to coordinatively
unsaturated vanadium ions exposed on the surface coupled to V=O double bonds.15 An IR study of the acidic sites using
ammonia, pyridine and acetonitrile as probe molecules showed the existence of Lewis and Bronsted acid sites.16ꢀ21 Kamiya et
22
al. studied the acidic character of the vanadyl pyrophosphate phase and reported that this phase possesses both Bronsted
and Lewis acidic sites.
One of the extensively investigated methods to improve the catalytic performance of vanadium phosphorous oxide
catalyst is the supportation of the active phase on an oxide surface. In the case of supported catalyst, the support should have
some features including better heat transfer character, larger surface area to volume ratio of active component, better
mechanical strength, and controllable catalyst textures. The first employed supports for VPO were the classical oxides such
29
as SiO2, TiO2, Al2O3 and also new kind of materials such as SiC.23ꢀ28 Au et al.
studied the performance of SBAꢀ15
supported VPO catalyst for oxidation of nꢀbutane to maleic anhydride and they showed that the supported VPO species
dispersed well on SBAꢀ15 and mainly exists as crystalline (VO)2P2O7. There are other supports such as MCMꢀ41, AlꢀMCMꢀ
41, fumed silica, silica, alumina, titania, phosphoric acid treated zirconia are also used as the supports for VPO catalyst.30ꢀ33
It is well documented that the use of support for metal oxide catalysts favours enhancement of active phase dispersion and
also impart stability to the catalysts. The use of supported catalyst during glycerol dehydration reaction have several
advantages such as the enhancement of dispersion of the active phase on the support, the distribution of the pore size of the
support and the acidity of the catalyst.34
Porous zirconium phosphate (ZrP) has been used as a solid acid catalyst in many reactions such as dehydration,
isomerisation of olefins due to its high acidic sites.35ꢀ37 Zirconium phosphate support also exhibit high thermal stability and
high surface area due to the porous nature. Hence, these properties make ZrP as an interesting support material for other
catalytically active metal species.38 However the VPO supported on zirconium phosphate have not been investigated so far.
Hence our interest is to focus on the effect of zirconium phosphate support on VPO catalyst and the interaction between
VPO and zirconium phosphate support and to investigate the acidic nature of the catalyst.
In the present investigation we report a systematic study on the characterization of VPO catalysts supported on
zirconium phosphate by N2 adsorption desorption analysis, XRD, FTIR, SEM, UVꢀDRS analysis, exꢀsitu adsorbed pyridine
FTIR analysis, temperature programmed reduction (TPR) and temperature programmed desorption of NH3. The catalytic
properties were evaluated for the dehydration of glycerol over a series of VPO supported on zirconium phosphate catalyst.
The purpose of this work is to examine the catalytic properties of VPO supported on zirconium phosphate and also to find
the relation between the surface structural properties of the vanadium phosphorous oxide species as a function of an active
component loading and catalytic functionalities during glycerol dehydration reaction.
2. EXPERIMENTAL SECTION:
Porous zirconium phosphate support was prepared from zirconium nꢀpropoxide precursor and 85% phosphoric acid
following the procedure described elsewhere.39 About 0.01 mol of zirconium nꢀpropoxide, (70 wt% solution in 1ꢀpropanol,
Aldrich) was added drop wise to a 60 mL solution of H3PO4 (0.1 mol Lꢀ1) under stirring. After 2 h of stirring at room
temperature, the obtained mixture was transferred into a teflon lined autoclave and aged statically at 80 °C for 24 h. The final
material was filtered, dried and calcined at 400 °C for 5 hours.
The preparation of dihydrate VOPO4.2H2O has been reported elsewhere.40 Briefly, the procedure involves the
addition of a mixture of V2O5 (24 g), H3PO4 (85%, 133 mL), and H2O (577 mL) was refluxed at 115 °C for 16 h. The
reaction produced a bright yellow solid, which was collected by filtration, washed with 100 mL acetone, and dried for 10 h
under ambient conditions. VOHPO4.0.5H2O was prepared by reduction of VOPO4.2H2O in organic alcohol. A suspension of
VOPO4 .2H2O (5 g) powder in 2ꢀbutanol (50 mL) was stirred under reflux for 23 h (oil bath temperature: 101 °C). The
resulting light blue solid was collected by filtration, washed with 100 mL of acetone, and dried for 10 h under ambient
conditions.
Desired amount of VPO precursor and zirconium phosphate powders were mixed together in a mortar by physical
mixing for about 15 min, i.e. until the colour of solid mixture was perfectly uniform. Using the same procedure, various
catalysts over a wide range of VPO contents were prepared. Finally the catalysts were calcined in presence of nitrogen at 550
°C, for 4 h at the heating rate of 1 °C minꢀ1. The VPO loadings were varied from 5wt% to 30 wt%.
Xꢀray diffraction (XRD) patterns were obtained on Rigaku miniflex diffractometer using graphite filtered Cu Kα (K =
0.15406 nm) radiation. FTꢀIR spectra of the catalysts were taken on the IR (Model: GCꢀFTꢀIR Nicolet 670) spectrometer by
KBr disc method under ambient condition. The SEM analysis samples were obtained by mounting the sample on an
aluminum support using a double adhesive tape coated with gold and observed in Hitachi Sꢀ520 SEM unit. The specific
surface area of the calcined catalysts were analysed using N2 adsorption at ꢀ196 °C by the multipoint BET method taking
0.0162 nm2 as its crossꢀsectional area using Autosorb 1 (Quantachrome instruments). The Pore size distribution of the
samples were analysed by BJH method using N2 adsorption desorption isotherm obtained on Autosorb 1 instrument. The
UVꢀVis diffused reflectance spectra were recorded on a GBC UVꢀVisible Cintra 10e spectrometer with an integrating sphere
2

Page 3 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
reflectance accessory. The spectra were recorded in air at room temperature and the data was transformed according the
KubelkaꢀMunk equation f(R) = (1ꢀRα) 2/2rα.
The exꢀsitu experiments of FTꢀIR spectra of pyridine adsorbed samples were carried out to find the Brønsted and
Lewis acid sites. Pyridine was adsorbed on the activated catalysts at 120 °C until saturation. Prior to adsorption experiments
the catalysts were activated in N2 flow at 300 °C for 1h to remove moisture from the samples. After such activation the
samples were cooled to room temperature. The IR spectra were recorded using a IR (Model: GCꢀFTꢀIR Nicolet 670)
spectrometer by KBr disc method under ambient conditions.
Temperature programmed reduction studies were conducted on AutoChem 2910 (Micromeritics, USA) instrument.
In TPR experiment, 100 mg of oven dried sample was taken in a U shaped quartz sample tube. The catalyst was mounted on
a quartz wool plug. Prior to TPR studies, the catalyst sample was pretreated by passing helium gas in a flow of 50 mL/min at
200 °C for 1h. After pretreatment the sample was cooled to ambient temperature and TPR analysis was carried out in a flow
of 5% H2ꢀAr (50 mL/min) from ambient temperature to 850 °C at a heating rate of 10 °C/min. The H2 consumption & Tmax
positions are calculated using GRAMS/32 software.
TPD experiments were also conducted on AutoChem 2910 (Micromeritics, USA) instrument. In a typical experiment
for TPD studies, 100 mg of oven dried sample was taken in a U shaped quartz sample tube. The catalyst was mounted on a
quartz wool plug. Prior to TPD studies, the sample was pretreated by passage of high purity (99.995%) helium (50 mL/min)
at 200 °C for 1h. After pretreatment, the sample was saturated with highly pure anhydrous ammonia (50 mL/min) with a
mixture of 10% NH3ꢀHe at 80 °C for 1h and subsequently 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 800 °C at a heating rate of 10 °C/min.
The amount of NH3 desorbed was calculated using GRAMS/32 software.
The gas phase dehydration of glycerol was carried out under atmospheric pressure in a vertical fixed bed quartz
reactor (40 cm length, 9 mm i.d.) using 0.2g of catalyst. Prior to the reaction, the catalysts were pretreated at 300 °C for 1 h
in flowing dry N2 (16 mL.min−1). An aqueous solution containing 20wt% glycerol was fed into the reactor by a micro
syringe pump at 0.5 mL/h (WHSVꢀ2.6 hꢀ1). The reaction products were condensed in an ice–water trap and collected hourly
for analysis on a gas chromatograph GCꢀ2014 (shimadzu) equipped with a DBꢀwax 123ꢀ7033 (Agilent) capillary column
(0.32 mm i.d., 30 m long) and equipped with flame ionization detector.
3. RESULTS AND DISCUSSION:
In order to understand the textural properties of the catalyst, the N2 adsorption desorption measurements have been
carried out to measure the surface area and pore size distribution and the results are presented in the Table 1. As can be seen
the results of Table 1 that VPO loadings have shown a clear impact on the surface area of the zirconium phosphate support.
The surface area of the pure zirconium phosphate support was found to be 334 m2/g and decreases as a function of VPO
content (Table 1). This decrease of surface area with increasing VPO loading might be due to blocking the pores of the
support by crystalline vanadium phosphorous oxide. The surface area of pure VPO catalyst (unsupported) was found to be
16.5 m2/g. The N2 adsorption desorption isotherm of the pure zirconium phosphate support and VPO supported on zirconium
phosphate have shown in the Fig. Sꢀ1. The isotherm of pure zirconium phosphate support exhibits a high uptake of nitrogen
at low relative pressures (P/Po) of 0.1–0.4, indicating that the pore sizes are present in the ranges of micropore and mesopore
region.41 BJH analysis of the pore size distribution on the adsorption isotherm reveals that a narrow pore size distribution
(Fig. 1) centred around 2.0 nm. When VPO is supported on the zirconium phosphate the pore volume decreases because of
the added VPO components are occupied in the pores of the zirconium phosphate support. In order to gain more information
about the calcination effect on the pure zirconium phosphate, the BJH pore size distribution measurements ( Fig.1) was also
carried out on pure zirconium phosphate calcined at 550 °C (PꢀZrPꢀ550 °C) and the results are reported in Table 1. As can be
seen from Fig. 1 that there is a considerable change was observed in the surface area and pore volume of the pure PꢀZrPꢀ550
°C. Hence the calcination of pure ZrP at 550 °C affects the textural properties of the pure zirconium phosphate support.
However, the decrease in the pore volume and surface area for supported VPO catalyst was noticed when VPO is loaded on
the ZrP support indicates that the addition of VPO influences the pore size of the resulting catalyst.42 As VPO loading
increases on the zirconium phosphate support, the mean pore diameter of the sample is also increasing. This might be due to
filling of the micropores of zirconium phosphate support by VPO catalyst42 and these were not included in the measurement.
These findings are further confirmed by the pore size distribution profiles shown in the Fig. 1.
X ray diffraction patterns of pure zirconium phosphate support and various VPO/ZrP catalysts with VPO loadings
ranging from 5 to 30wt% are shown in Fig. 2. XRD results suggest that the synthesized zirconium phosphate is found to be
Xꢀray amorphous. As the VPO loadings are increasing on the zirconium phosphate support the diffraction peak intensity is
also increasing. At lower loadings, the supported VPO catalyst (upto 20 wt% VPO loadings) does not exhibit any peaks
corresponding to VPO species suggesting that the active phase is present in highly dispersed form. However it cannot be
ruled out for the presence of VPO crystalline species having the size with less than 4nm which is beyond the detection limit
of powder Xꢀray diffraction techniques. The higher loadings of supported VPO catalyst (25&30 wt %) shows the main
reflection peak at 2θ in the range of 23.000, 28.450, and 29.950 confirms the formation of vanadyl pyrophosphate on the
3

Catalysis Science & Technology
Page 4 of 24
View Article Online
DOI: 10.1039/C3CY00430A
zirconium phosphate support.43ꢀ44 The XRD results suggested that VPO catalyst is present in the vanadyl pyrophosphate
phase on the zirconium phosphate support. Moreover the obtained vanadyl pyrophosphate sample showed a poor crystalline
in nature because the sample was calcined in the nitrogen atmosphere. The XRD results also indicates that there is no other
phase formation or compound formation taking place in the pure VPO catalyst and supported VPO catalyst.
Fig. 3 shows the FTIR spectra of pure zirconium phosphate support and different wt% of VPO loading catalyst
supported on zirconium phosphate. All the IR spectra show that the bands in the region 3400–2400 cmꢀ1 are due to surface
OH groups and the IR band at 1630 cmꢀ1 is assigned to bending adsorbed mode of water molecule by the catalyst. Pure
zirconium phosphate shows a broad band at 1020 cmꢀ1 for ZrꢀOꢀP vibration.45 While increasing the VPO loading on
zirconium phosphate support, the intensity of the peak is also increasing. At lower loadings, only one broad peak was
observed at 1062 cmꢀ1 and it does not provide any information about VPO species. This does not suggest that VPO active
phase is not detected by FTIR. It might be due to the active VPO phase present in the highly dispersed state in the pores of
the zirconium phosphate support or the detected peaks are over shaded by the most intense bands of the pure support. At
higher loadings of VPO (25wt% and 30 wt %) show characteristic clear IR peaks. At higher loadings (25wt% and 30 wt %)
of the sample there is also formation of a new peak at 968 cmꢀ1 which can be attributed to stretching frequency of V4+=O
species and further confirms the formation of vanadyl pyrophosphate phase.46 Hence FTIR spectra is a good tool for
supporting the evidence of results obtained from XRD on the formation of active vanadyl pyrophosphate phase.
The surface morphology of the samples were examined by SEM and Fig. 4 shows the representative SEM
micrographs of pure zirconium phosphate, supported VPO catalyst with different loadings and pure VPO catalyst. The pure
VPO sample has rosette like morphologies with uniform particle size distribution. The structure of the pure VPO catalyst
consists of plate like crystals, which are arranged to the characteristic rosetteꢀshape clusters. The rosette type agglomerates
are made up of agglomerates of (VO)2P2O7 platelets that preferentially expose (100) crystal planes.47ꢀ48 Pure zirconium
phosphate shows plate like morphology. From the SEM (Fig. 4) results it is observed that at lower loadings the VPO catalyst
is well dispersed on the support and at higher loadings the dispersion decreases on the support as the particles are
agglomerated.
UV VisꢀDRS investigations were carried out to obtain information of the vanadium oxidation state in VPO and
supported VPO catalyst. From the literature it is clear that V5+ exhibits the charge transfer absorption band at around 500 nm
whereas V4+ shows the charge transfer absorption band at around 220 nm.49 Fig. 5 shows the UV DRS spectra of pure
uncalcined and calcined VPO catalyst. The uncalcined VPO shows a broad charge transfer transition band at 200 to 350 nm
due to the charge transfer transition from O2ꢀ to V4+ and another transition band from 600 nm due to dꢀd transition of V4+.
After calcination in nitrogen atmosphere, the dꢀd transition band of V4+ disappears and the intensity of charge transfer band
of calcined sample remains unchanged. In general the intensity of charge transfer transition band is much higher than the dꢀd
transition of vanadium ions. These results are well in agreement with the previously reported findings of Martin et al. 50 Fig.
5 shows the UV–DRS spectra of pure zirconium phosphate and VPO catalyst supported on zirconium phosphate. The spectra
are dominated by the charge transfer (CT) transition of the type O2ꢀ to V4+ in the range of 200–400 nm with multiplicity. The
parent zirconium phosphate showed a band at 300 nm, which might be due to Zr (IV) cations interacting with the phosphate
counter anions in the framework.51 As the VPO loadings on zirconium phosphate increases, the intensity of the charge
transfer transition band of V4+ also increased. From Fig. 5 it is observed that, similar to pure VPO, the charge transfer band
of V4+ and V5+ are clearly visible at the higher loading of supported VPO catalyst. This result confirms the formation of
vanadyl pyrophosphate phase on the zirconium phosphate support along with some of the vanadium orthophosphate phase.
However, XRD results of pure VPO and supported VPO catalyst shows the presence of only vanadyl pyrophosphate phase in
the calcined sample (Fig. 2). This result reflects that various types of vanadium orthophosphate phases might be present in
the amorphous form.
The reduction behaviour of the pure VPO and supported VPO catalysts were examined by the temperature
programmed reduction (TPR) by using 5% H2/Ar. Fig. 6 shows the TPR profiles of pure VPO catalyst and different wt%
VPO loadings supported on zirconium phosphate catalyst. It is interesting to see that the VPO dispersion on zirconium
phosphate support strongly changes the reduction behaviour of vanadium present in the VPO catalyst. In the TPR profiles,
the pure VPO catalyst showing only one sharp reduction peak at 750 °C indicates that there is only one type of reducible
vanadium present in the pure VPO catalyst and it attributes to the reduction of V4+ to V3+.25 Similarly, in the case of different
wt% VPO supported on zirconium phosphate catalyst, only one peak appeared in the TPR profiles at around 700 °C due to
the reduction of V4+ to V3+. The reduction temperature and the volume of hydrogen consumption are shown in the Table 2.
As the VPO loadings are increasing the amount of hydrogen consumption by the VPO also increasing. It is very interesting
to note that the reduction temperature of the supported VPO catalyst is less than the pure VPO catalyst suggesting that there
is a significant interaction between VPO and zirconium phosphate support. It reflects that supported VPO catalysts are more
reducible than the pure VPO catalyst. The zirconium phosphate support itself was not reduced in the applied temperature
range, the observed reducibility should be attributed to the supported VPO species. At lower VPO loadings the reducibility
of the catalyst is easier than the higher loadings. The reduction temperature increased with increase in VPO loadings. This
clearly suggests that the reducibility decreasing with increasing of VPO loadings. At lower loadings the reducibility of VPO
species is much easier because of the VPO species occupied the pores of the zirconium phosphate support leading to the well
4

Page 5 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
dispersion of active phase on the support. The portion of the oxygen atoms of the VPO are shared with zirconium species
present in the zirconium phosphate leads to the enhanced stability of vanadium atoms and it increases the reducibility of the
catalyst. At higher loadings the remarkable shift in the reduction temperature of supported VPO catalyst (>20wt% loadings)
due to the VPO species are located on the surface of the support leads to the formation of bulk type VPO catalyst and it
decreases the reducibility of VPO catalyst.
The surface acidity measurements of all the samples have been carried out by ammonia TPD method. Temperature
programmed desorption (TPD) of probe molecules like ammonia and pyridine is a popular method for the determination of
acidity of solid catalysts as well as acid strength distribution because it is an easy and reproducible method. Ammonia is
used frequently as a probe molecule because of its small molecular size, stability and strong basic strength. The ammonia
TPD profiles of the pure VPO, pure zirconium phosphate support and different wt% loadings of VPO/ZrP catalysts are
presented in Fig. 7. This Figure clearly demonstrated the effect of acidic properties of different wt % of VPO loadings on
zirconium phosphate support. The pure zirconium phosphate support has shown one broad peak in the temperature range of
52
100ꢀ450 °C. According to Tanabe et al.
the strength of solid acid sites within TPD profiles can be classified by the
temperature of NH3 desorption as weak (120–300 °C), moderate (300–450 °C) and strong (above 450 °C). Thus, the
observed acidity in the TPD profile of zirconium phosphate is found to be in the weak moderate acidic region (120–450 °C).
It can be seen from the Fig. 7 that as VPO loadings are increasing the intensity of the weak moderate acidic region peak is
increasing. The pure VPO catalyst has one broad peak at the weak moderate acidic region and one sharp peak at strong
acidic region. The acidity of the VPO catalysts can be attributed to the presence of surface PꢀOH groups and to
coordinatively unsaturated vanadium ions exposed in the surface coupled to V=O double bonds. The ammonia uptake
values and the peak temperatures are summarised in Table 3. It is interesting to note that the total acidity value of pure VPO
is higher than the supported VPO catalyst. The higher acidity of pure VPO is mainly due to the presence of strong acidic
sites as shown in the Table 3. These strong acidic sites are absent in the case supported VPO catalyst. From the Table 3 we
can observe that the weak moderate acid sites are increasing with the increase of VPO loading upto 20wt% VPO/ZrP and
beyond this loading (25&30wt% VPO/ZrP) it is decreasing. It is interesting to note that the total acidity values of supported
VPO catalysts were also increasing upto 20wt% VPO/ZrP and decreasing at higher loadings (25&30wt% VPO/ZrP).
We have employed FTꢀIR analysis by using pyridine as a probe molecule which was saturated at 120 °C to find the
nature of acid sites on VPO catalysts. Usually, the IR bands appeared at 1540–1548 cm−1 and 1445–1460 cm−1 are
characteristic bands of Brønsted (B) and Lewis (L) acid sites, respectively. Furthermore, the bands correspond to
combination of both Brønsted and Lewis (B+L) acid sites are appeared at 1490ꢀ1500 cmꢀ1. It should be noted that the
intensity of the IR band is proportional to the concentration of acid sites. The FTIR spectra of pure zirconium phosphate,
supported VPO and Pure VPO obtained after pyridine adsorptions are illustrated in Fig. 8. All the catalysts have shown
bands at 1444 cm−1 corresponding to Lewis sites and the other band appeared at 1550 cm−1 is attributed to Brønsted sites. It
can also be seen from the Fig. 8 that all the catalysts contain both Lewis and Brønsted sites in different proportions
depending upon the VPO loadings on the support. The pure zirconium phosphate shows the sharp band at 1550 cmꢀ1 due to
Bronsted acidic sites. The VPO is supported on the zirconium phosphate and the Bronsted acidity decreases initially after
that it increases continuously as the VPO loadings increases until 20wt% VPO/ZrP. At higher loadings the Bronsted acidity
did not change appreciably. The Lewis acidity also increasing with VPO loadings until 20wt% VPO/ZrP after that it
decreases. The pure VPO as well as 20wt% VPO/ZrP showed the maximum intensity of Bronsted and Lewis acidic sites.
The results of vapour phase glycerol dehydration to acrolein are shown in Table 4. It is important to emphasize that
the comparison of conversion and selectivity between different catalysts is possible only at low time on stream since with
increasing time of reaction, the deactivation process becomes predominant. The catalytic results of dehydration of glycerol
over various different wt% VPO loadings on zirconium phosphate by passing nitrogen are shown in the Table 4. Pure
zirconium phosphate support exhibited complete glycerol conversion with 42% selectivity towards acrolein. The major by
products of this catalyst were acetaldehyde and acetol. When the VPO loading increases on the zirconium phosphate support,
the acrolein selectivity decreases to 30% and then it increases with the VPO loadings and reaches a maximum of 60% and
again decreases at higher loadings. Whereas the conversion of glycerol always maximum irrespective of the VPO loadings.
The pure VPO shows only 90% conversion towards glycerol and 47% selectivity towards acrolein. The major byꢀproducts
were acetol, acetaldehyde, acetic acid, allyl alchol and some minor unidentified products. From this result, it was observed
that the supported VPO catalyst showed better result compared to the pure VPO catalyst and pure zirconium phosphate
support. The Pure zirconium phosphate support gave acetol and acetaldehyde as the major byꢀproducts. At lower loadings
these byꢀproducts are formed in higher amount because the zirconium phosphate support is not covered fully by the VPO
and when the VPO loadings increases these byꢀproducts decreases as a result acrolein selectivity increases. At lower
loadings the reducibility of the catalyst also plays a key role in the conversion and selectivity towards acrolein.
11
Wang et al. studied the glycerol dehydration reaction over pure VPO catalyst by passing molecular oxygen with
nitrogen gas to maintain the glycerol conversion, acrolein yield and greatly reduces the side product formation. In the present
investigation the dehydration of glycerol was carried out over different wt% loadings of VPO on zirconium phosphate by
5

Catalysis Science & Technology
Page 6 of 24
View Article Online
DOI: 10.1039/C3CY00430A
passing air along with nitrogen gas and the results are shown in the Table 4. Passing air along with nitrogen stopped the
deactivation of the catalyst as well as reduces the formation of hydroxyacetone and allyl alcohol and as a result acrolein
selectivity increases. When the VPO loading increases, the acrolein selectivity also increases until 20wt% VPO on zirconium
phosphate and decreases gradually at higher loadings. However, there is no significant decrease in the acrolein selectivity is
noticed. From the Table 4 it is observed that conversion of glycerol is always found to be 100%. It is interesting to note that
the supported VPO at lower loadings gave better acrolein selectivity in presence of air and nitrogen when compared to
passing nitrogen gas only, due to reduction of other side product formation. The results of the product distribution of
glycerol dehydration reaction at constant reaction conditions except the gas flow conditions are shown in the Table 4. The
major products of the glycerol conversion over pure zirconium phosphate support, pure VPO, different weight percentage
loadings of VPO on zirconium phosphate were acrolein, acetol, allyl alcohol, acetic acid and acetaldehyde. Products grouped
under the label of other included, acrylic acid, acetone, and some unidentified products. By passing only nitrogen as a carrier
gas, the lower loadings of VPO catalyst gave lower acrolein selectivity which might be due to the increase in the reducibility
of the catalyst and the major side products are hydroxyacetone, allyl alcohol and acetic acid. When the air was introduced in
the reaction medium, the formation of allyl alcohol and hydroxyacetone is reduced and acetic acid formation is increased.
The allyl alcohol is formed by the hydrogenation of acrolein in the reaction medium. The hydrogen is mainly produced from
the degradation of glycerol into the coke. The hydroxyacetone is produced through the dehydration at the terminal hydroxyl
group of glycerol. The oxygen presents in the air restricts the hydrogenation of acrolein and favours the dehydration at the
central hydroxyl group of the glycerol.
The effect of reaction temperature (280ꢀ340 °C) on the dehydration of glycerol was examined over 20 wt% VPO/ZrP
and the results are shown in the Fig. 9. At 280 °C the conversion of glycerol is 96% and it reaches maximum at higher
temperatures. At 300 °C this catalyst showed maximum conversion and selectivity with the increase of temperature, there is
no effect on glycerol conversion. However, at higher temperatures the acrolein selectivity decreased due to increase in the
formation of acetaldehyde, acetic acid and trace amounts of acrylic acid (8%) and few unidentified products. This result
suggests that at higher temperature (340 °C) this catalyst favours the CꢀC bond cleavage and oxidation instead of
dehydration. The major side product obtained is pure acetaldehyde formed due to CꢀC bond cleavage of glycerol and
oxidation of acetaldehyde leads to the acetic acid formation. A small amount of acrylic acid is also formed due to oxidation
of acrolein. Thus the higher reaction temperature only favours the acrolein oxidation by VPO supported catalyst due to the
increase of reducibility of vanadium in the catalyst.
The influence of the VPO loadings in the supported catalyst on the glycerol dehydration in nitrogen flow was
examined with the time on stream and the results are shown in Fig. 10. As can be seen from the Fig. 10, the decrease in
conversion with the reaction time is noticed over all the catalysts in the catalytic dehydration of glycerol. This deactivation
of the catalyst is mainly due to the formation of coke over the active sites of the catalyst.11ꢀ12 In the case of pure VPO
catalyst, deactivation was more pronounced than the supported VPO catalyst because of its strong acidic character (from
TPD of ammonia graph). The TPD profile of supported VPO catalyst shows the absence of strong acidic sites. In the case of
supported VPO catalyst, 20 & 30 wt% VPO/ZrP showed lower rate of deactivation and higher acrolein selectivity when
compared to the other tested catalysts which might be due to presence of larger pores as evidenced from the results of pore
size distribution (Table 1). When these active phases are deposited on a support, it is also possible to adjust an additional
parameter i.e the pore size of the catalyst, and thus reduce diffusion limitations. In general the pore size has a direct
influence on the selectivity of the catalysts. If pores are too narrow then it may hinder the rapid desorption and diffusion of
the reactants and of the products in the porous network of the catalyst. Thus instead of dehydration, condensation is more
likely to occur, which results in lower selectivity for acrolein and fast deactivation of the catalyst due to carbon deposition
(coke). The best results were obtained for supported VPO catalysts rather than pure VPO catalyst.
The results with the time on stream of catalytic dehydration of glycerol over pure VPO and 20 wt% VPO/ZrP by
passing air and nitrogen are shown in Fig. 11. By passing air along with nitrogen, the pure VPO catalyst exhibited maximum
conversion of 90% and maximum selectivity of 50% at the initial hour and further the conversion decreases to 30% at 20h
and the acrolein selectivity reach almost 36% at the same reaction time. Under similar reaction conditions, the 20 wt% VPO
supported on zirconium phosphate has shown almost 100% conversion and acrolein selectivity increased to 65% at 6 h of the
reaction and it shows 52% conversion and 48% selectivity of acrolein after 40h. It is interesting to that a faster deactivation
was observed after 30 h with the supported VPO catalysts whereas the pure VPO catalyst exhibited the deactivation after
10h. In the initial hours of the supported VPO catalyst, higher formation of acetaldehyde and acetic acid was observed
thereby decreases the acrolein selectivity. A comparison activity of 20wt% VPO/ZrP catalyst with the pure catalysts has
been reported in Table 5. The present catalyst 20% VPO/ZrP showed better catalytic activity with respect to the pure VPO
catalyst.
The acid strength and acid amount of the catalyst were significant for determining the catalytic activity. Inappropriate
acidity of the catalyst may cause poor results, such as lower selectivity accompanied with severe coke deposition, and short
catalyst life time. From the Fig. 12 the weak moderate acidic sites or total acidity are increasing upto 20wt% VPO/ZrP after
that it decreases significantly. The selectivity of the acrolein also follows the same order. This result suggests that the weak
moderate acidic sites are necessary for the formation of acrolein. Though pure zirconium phosphate shows more acidity than
6

Page 7 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
the supported catalyst, the acrolein selectivity is low because of the presence of Lewis acidic sites. These Lewis acidic sites
can leads to single dehydration to form larger amount of hydroxyl acetone. In the case of pure VPO catalyst the maximum
conversion and selectivity is obtained in the early hour (TOS 1h) and conversion and selectivity sharply decreases with time
(Fig. 11) due to the formation of hydroxyl acetone, allyl alcohol and unidentified products. This could be due to the strong
acid sites favours side reactions among the reactant and the products such as acrolein etc. Because of these side reactions
coke is deposited on the active acidic sites leading to the decrease of the conversion of the glycerol.
To understand the role of acidic sites on the glycerol dehydration reaction, the exꢀsitu pyridine adsorbed FTꢀIR
analysis measurements were carried out and the results are shown in the Fig. 9. From the literature it is observed that the
Bronsted acidic sites are responsible for the acrolein selectivity.53 In fact, Brønsted acid sites directly protonate the
secondary hydroxyl group of glycerol, which finally leads to the formation of acrolein. The increase of acrolein selectivity
with VPO loadings is due to increase of Bronsted acidic sites until 20% VPO/ZrP after that there is no significant change in
the acrolein selectivity.
The spent sample of 20wt% VPO/ZrP after 40h reaction time was characterised by XRD, TPD of ammonia and the
exꢀsitu pyridine FTIR analysis to find the information about the changes of the active sites during the reaction. The XRD
results of 20 wt% VPO on zirconium phosphate after reaction of 40 hr shows the Xꢀray diffraction lines at 2θ = 23.000,
28.450, and 29.950 corresponding to the vanadyl pyrophosphate. This result shows that the crystallite size of VPO catalyst
increases after 40 h reaction time. It might be due to the severe reaction conditions employed which results rapid
deactivation of the catalyst. The results of TPD of ammonia of fresh and spent samples are shown in Fig 13. This result
suggests that the acidity of the catalyst decreases when compared to the fresh samples as a result the conversion and
selectivity decreases considerably. However, the peak position during TPD analysis also changed abruptly and the
temperature maximum of moderate acidic site peak also shifted to higher position. The exꢀsitu pyridine FTIR analysis of the
spent and fresh samples is shown in Fig 14. As can be seen from the Fig. 14 the Bronsted acidic sites of the spent catalyst
decreases significantly. However, a marginal decrease of Lewis acidic sites is noticed. The intensity of both acidic sites
(B+L) also decreases as a result the conversion and selectivity decreases after 40h TOS.
4. CONCLUSION:
In summary, a series of porous zirconium phosphate supported VPO catalysts were prepared by the solidꢀsolid
wetting method for acid catalysed glycerol dehydration reaction and these catalysts were characterised by various
spectroscopic and adsorption techniques. The characterization results showed that the VPO species is well dispersed on the
zirconium phosphate and present mainly in the form of vanadyl pyrophosphate phase along with small amount of vanadium
orthophosphate phase. The acidity of the catalyst plays a detrimental role in the formation of acrolein during glycerol
dehydration reaction. The supported VPO catalysts showed better conversion and selectivity towards acrolein than the pure
VPO catalyst. This is due to the fact that the appropriate acidic properties, higher surface area and higher pore diameter in
the supported VPO catalysts. Among different catalysts examined for vapour phase glycerol dehydration, 20 wt% VPO/ZrP
showed the best acitivity towards glycerol conversion (100%) and acrolein selectivity (65%) compared to other catalysts.
The spent catalyst was also characterised by TPD of ammonia and exꢀsitu pyridine FTꢀIR analysis. These results shows that
there is a significant decrease in the acidity and Bronsted acidic sites of the spent samples leading to a decrease in the
conversion and selectivity of the catalyst after 40h reaction.
ACKNOWLEDGEMENTS:
NPR, GSR and VPK thanks CSIR, New Delhi for the award of Senior Research Fellowship.
REFERENCES:
1 Y. Zheng, X. Chen and Y. Shen, Chem. Rev., 2008, 108, 5253.
2 B. Katryniok, S. Paul, V. Belliere Baca, P. Rey and F. Dumeignil, Green Chem., 2010, 12, 2079.
3
Y. Gua, N. Cuia, Q. Yua, C. Li and Q. Cuib, Appl. Catal. A: Gen., 2012, 429– 430, 9.
4 M. Massa, A. Andersson , E. Finocchio, G. Busca, F. Lenrick and L. R. Wallenberg, J. Catal., 2013, 297, 93.
5 K. Omata, S. Izumi, T. Murayama and W. Ueda, Catal. Today, 2013, 201, 7.
6 Suprun, M. Lutecki, T. Haber and H. Papp, J. Mol. Catal. A: Chem., 2009, 309, 71.
7 S. H. Chai, H. P. Wang, Y. Liang and B. Q. Xu, Green Chem., 2008, 10, 1087.
8 S. H. Chai, H. P. Wang, Y. Liang and B. Q. Xu, Appl. Catal. A: Gen., 2009, 353, 213.
9 J. L. Dubois, C. Duquenne and W. Holderich, FR2884818, 2006, to Arkema (FR).
10 J. L. Dubois, C. Duquenne and W. Holderich, FR2882052, 2006, to Arkema (FR).
11 F. Wang, J. L. Dubois and W. Ueda, J. Catal., 2009, 268, 260.
12 F. Wang, J. L. Dubois and W. Ueda, Appl. Catal. A Gen., 2010, 376, 25.
13 G. Centi, Editor, Catal. Today, 1993, 16 (l).
7

Catalysis Science & Technology
Page 8 of 24
View Article Online
DOI: 10.1039/C3CY00430A
14 G. Centi, F. Trifiro, J. R. Ebner and V. M. Franchetti, Chem. Rev., 1988, 88, 55.
15 G. Busca, G. Centi, F. Trifiro and V. Lorenzelli, J. Phys. Chem., 1986, 90, 1337.
16 F. Cavani and F. Trfiro, Appl. Catal. A Gen., 1997, 157, 195.
17 G. Busca, G. Ramis and V. Lorenzelli, J. Mol. Catal., 1989, 50, 231.
18 L. M. Cornaglia, E. A. Lombardo, J. A. Anderson and J. L. Garcia Fierro, Appl. Catal. A Gen., 1993, 100, 37.
19 L. M. Cornaglia and E. A. Lombardo, Stud. Surf. Sci. Catal., 1994, 90, 429.
20 S. Ben Abdelmalek, H. Batis and A. Ghorbel, I. Soc. Alger. Chim., 3S, 1993, 265.
21 M. Abon and J.C. Volta, Appl. Catal. A Gen., 1997, 157, 173.
22 Y. Kamiya, J. Jpn. Pet. Inst., 2003, 46, 62.
23 K. E. Birkeland, S. M. Babitz, O. K. Bethke, H. H. Kung, G. W. Coulston and S.R. Bare, J. Phys. Chem. B., 1997, 101, 6895.
24 R. A. Overbeek, A. R. C. J. Pekelharing, A. J. Van Dillen and J. W. Geus, Appl. Catal. A:Gen., 1996, 135, 231.
25 R. A. Overbeek, P. A. Warringa, M. J. D. Combag, L. M. Visser, A. J. Van Dillen and J. W. Geus, Appl. Catal. A:Gen., 1996, 135, 209.
26 J. Marc, C.C. Ledoux, P.H. Cuong, T. Vincent, K. Kostantinos, M. Patrick and L. Jan, J. Catal., 2001, 203, 495.
27 J.M.C. Buenoa, G.K. Bethkeb, M.C. Kung and H.H. Kung, Catal. Today, 1998, 43, 101.
28 Z.Q. Zhou, H.Y. Xu, W.J. Ji and Y. Chen, Catal. Lett., 2004, 96, 221.
29 X. K. Li, W. J. Ji, J. Zhao, Z. B. Zhang and C. T. Au, J. Catal., 2006, 238, 232.
30 X. K. Li, W. J. Ji, J.Zhao, Z. B. Zhang and C. T. Au, Appl. Catal. A: Gen., 2006, 306, 8.
31 W. Nie, Z. Wang, W. Ji, Y. Chen and C.T. Au, Appl. Catal. A: Gen., 2003, 244, 265.
32 C.Y. Xiao, X. Chen, Z.Y. Wang, W.J. Ji, Y. Chen and C.T. Au, Catal. Today, 2004, 93, 223.
33 R. M. Feng, X. J. Yang, W. J. Ji, Y. Chen and C. T. Au, J. Catal., 2007, 246, 166.
34 H. Atia, U. Armbruster and A. Martin, J. Catal., 2008, 258, 71.
35 A. Clearfield and D.S. Takur, J. Catal., 1980, 65, 185.
36 K. Segawa, Y. Kurusu, Y. Nakajima and M. Kinoshita, J. Catal., 1985, 94, 491.
37 A. La Ginestra, P. Partono, M.L. Berardelli, P. Galli, C. Ferragina and M.A. Massucci, J. Catal., 1987, 103, 346.
38 Ch. Srilakshmi, K. Ramesh, P. Nagaraju, N. Lingaiah and P. S. Sai Prasad, Catal. Lett., 2006, 106, 115.
39 T. Z. Ren, Z. Y. Yuan and B. L. Su, Chem. Commun., 2004, 2730.
40 N. Yamamoto, N. Hiyoshi and T. Okuhara, Chem. Mater., 2002, 14, 3882.
41 K. Narasimha Rao, A. Sridhar, A. F. Lee, S. J. Tavener, N. A. Young and K. Wilson, Green Chem., 2006, 8, 790.
42 V.N. Kalevaru, N. Madaan, A. Martin Appl. Catal. A: Gen.,2011, 391, 52.
43 G.J. Hutchings, J. Mater. Chem., 2009, 19, 1222.
44 G. Koyano, T. Okuhara and M. Misono, J. Am. Chem. Soc., 1998, 120, 767.
45 Z. Y. Yuan, A. Vantomme, A. Leonard and B. L. Su, Chem. Commun., 2003, 1558.
46 B.H. Sakakini, Y.H. Taufiq Yap and K.C. Waugh, J. Catal., 2000, 189, 253.
47 C.J. Kiely, C.J. Sajip, I.J. Ellison, M.T. Sananes, G.J. Hutchings and J. Volta, Catal. Lett., 1995, 33, 357.
48 Y.H. Taufiq Yap, M.H. Looi, K.C. Waugh, M.Z. Hussein, Z. Zainal and R. Samsuddin, Catal. Lett., 2001, 74, 99.
49 F. Cavani, S. Ligi, T. Monti, F. Pierelli, F. Trifiro, S. Albonetti and G. Mazzoni, Catal. Today, 2000, 61, 203
50 A. Martin, C. Janke and V. N. Kalevaru, Appl. Catal. A: Gen., 2010, 376, 13.
51 M. Ziyada, M. Rouimia and J. L. Portefaixb, Appl. Catal. A: Gen.,1999, 183, 93.
52 K. Tanabe, M. Misono, Y. Ono and H. Hattori, Stud. Surf. Sci. Catal. 1989, 51, 5.
53 A. Alhanash, E. F. Kozhevnikova and I. V. Kozhevnikov, Appl. Catal. A: Gen.,2010, 378, 11.
Figure captions
Fig. 1: BJH isotherm of pure ZrP and different wt% loadings of VPO
Fig. 2: XRD pattern of Pure ZrP and various VPO/ZrP
Fig. 3: FTꢀIR spectra of Pure ZrP and various VPO/ZrP
Fig. 4: SEM images of Pure ZrP and various VPO/ZrP
Fig. 5: UV DRS profiles of pure VPO and various VPO/ZrP
Fig. 6: TPR profiles of various VPO/ZrP
Fig. 7: TPD of ammonia profiles of Pure ZrP and various VPO/ZrP
Fig. 8: Exꢀsitu pyridine adsorbed FTIR of pure VPO and various VPO/ZrP
Fig. 9: Effect of temperature over 20 wt% VPO/ZrP catalyst
Fig. 10: Time on stream over VPO on zirconium phosphate by passing N2 flow
Fig. 11: Time on stream over Pure VPO and 20 wt% VPO/ZrP by passing N2 and air flow
Fig. 12: Moderate acidic strength, acrolein selectivity vs VPO loadings
Fig. 13: TPD of ammonia profiles of fresh and spent samples of 20wt% VPO/ZrP.
Fig. 14: Exꢀsitu pyridine adsorbed FTIR of fresh and spent samples of 20wt% VPO/ZrP.
8

Page 9 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
Table 1: Results of Pore size distribution of different wt% VPO on ZrP
S.No
VPO loadings
(wt %)
Pure ZrPꢀ400
BET SA
(m2/g)
334
271
214
179
161
152
148
Total pore volume
Mean pore diameter
(cc/g)
0.36
0.32
0.28
0.27
0.26
0.28
0.29
0.15
0.20
(Å)
32
32
47
60
65
74
78
39
47
1
2
3
4
5
6
7
8
9
Pure ZrPꢀ550
5
10
15
20
25
30
145
17
Pure VPO
Table 2: Results of Temperature Programmed Reduction of different wt% VPO on ZrP
S.No
VPO loadings
(wt%)
Temperature
(°C)
Amount of hydrogen
consumption (ꢀmol/g)
1
2
3
4
5
6
7
5
10
15
20
25
674
677
680
688
708
720
750
296
753
1025
1273
2019
3051
4536
30
Pure VPO
Table 3: Results of Temperature Programmed desorption of different wt% VPO on ZrP
S.No
VPO
loadings
(wt%)
Physisorbed
ammonia*
(ꢀmol/g)
Temperature
(Tmax1)
(°C)
Desorbed
ammonia
(ꢀmol/g)
Temperature
(Tmax2)
(°C)
Desorbed
ammonia
(ꢀmol/g)
Total
ammonia
desorption
(ꢀmol/g)
1123
1
2
3
4
5
6
7
Pure ZrP
2104
973
1109
583
643
393
377
358
247
244
260
268
361
358
1123
583
637
998
1291
740
685
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
5
583
637
998
1291
740
685
10
15
20
25
30
8
9
Pure VPO
Spent
ꢀꢀ
81
228
320
789
650
720
ꢀꢀ
1162
ꢀꢀ
1951
650
20wt%
* Physisorbed ammonia is not included in the total acidity value
9

Catalysis Science & Technology
Page 10 of 24
View Article Online
DOI: 10.1039/C3CY00430A
Table 4: Product distribution results of glycerol dehydration over various catalysts obtained in TOS: 1ꢀ2 hr (N2 flow) and 4ꢀ
5h (Air+N2 flow).
S.No
VPO loadings
(wt%)
Selectivity (mol %)
Acet
Conversion
(mol %)
Acrolein
Hydroxy
acetone
16 (16)
23 (ꢀ)
10 (ꢀ)
8 (ꢀ)
Acetic
acid
Others
aldehyde
9 (9)
5 (10)
10 (9)
1
2
3
4
5
6
7
8
Pure ZrP
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
90 (90)
42 (42)
30 (52)
46 (58)
52 (62)
60 (66)
55 (63)
48 (62)
47 (50)
3 (3)
30 (30)
28 (17)
16 (16)
18 (12)
17 (9)
20 (11)
28 (9)
30 (27)
5
10
15
20
25
14 (21)
18 (17)
9(18)
3 (14)
3 (12)
2 (17)
13 (18)
13 (8)
4 (ꢀ)
16 (11)
18 (14)
8 (12)
12 (ꢀ)
14 (ꢀ)
2 (ꢀ)
30
Pure VPO
8 (4)
Reaction conditions: 0.2 g catalyst was used and diluted with 1.0 g of quartz . The aqueous glycerol (20% wt/wt) was
fed at the speed of 0.5 g h-1 by syringe pump under 16 mL.min-1 N2 atmosphere i.e the reactant fed composition gly:
H2O: N2 was 1.37: 50.0: 42.83 in molar ratio and reaction temperature was 300 °C. In paranthesis, the same reaction
condition except the reactant fed composition gly: H2O: N2: Air was 1.37: 50.0: 32.12: 10.7 in molar ratio.
Table 5: Comparison results of VPO/ZrP with pure VPO catalyst over dehydration of glycerol.
S.No
Catalyst
Calcination
temperature
(°C)
Composition of fed gases
(molar ratio)
Glycerol
conversion
(mol %)
100
Acrolein
selectivity
(mol %)
41
References
1.
2.
3.
4.
VPO
VPO
VPO
550
N2:O2:H2O:glycerol
57.2:12.7:28.7:1.4
N2:O2:H2O:glycerol
66.6:1.7:30.3:1.5
N2:O2:H2O:glycerol
66.6:1.7:30.3:1.5
11
12
12
ꢀꢀ
500
600
550
47
61
39
33
65
20%
gly:H2O: N2: Air
100
VPO/ZrP
1.37: 50.0: 32.12: 10.7
10

Page 11 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
0.6
0.5
0.4
0.3
0.2
0.1
0.0
ZrP-400
ZrP-550
5wt% VPO/ZrP
20wt% VPO/ZrP
30wt% VPO/ZrP
10
20
30
40
50
60
70
80
Pore Diameter [Å]
Fig. 1
11

Catalysis Science & Technology
Page 12 of 24
View Article Online
DOI: 10.1039/C3CY00430A
Fig. 2
12

Page 13 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
Fig. 3
13

Catalysis Science & Technology
Page 14 of 24
View Article Online
DOI: 10.1039/C3CY00430A
Pure ZrP
5 wt% VPO/ZrP
15 wt% VPO/ZrP
20 wt% VPO/ZrP
30 wt% VPO/ZrP
Pure VPO
Fig. 4
14

Page 15 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
V4+ CT band
V5+ CT band
Calcined VPO
d-d transition of V4+
uncalcined VPO
700 800
200
300
400
500
600
Wave number (nm)
V4+ CT band
V5+ CT band
VPO wt%
30%
25%
20%
15%
10%
5%
Pure ZrP
200
300
400
500
600
700
800
Wave number (nm)
Fig. 5
15

Catalysis Science & Technology
Page 16 of 24
View Article Online
DOI: 10.1039/C3CY00430A
VPO (wt%)
100 %
30 %
25 %
20 %
15 %
10 %
5 %
200
100
300
400
500
600
700
800
Temperature (0C)
Fig. 6
16

Page 17 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
VPO wt%
30%
25%
20%
15%
10%
5%
VPO
ZrP
100
200
300
400
500
600
700
Temperature (oC)
Fig. 7
17

Catalysis Science & Technology
Page 18 of 24
View Article Online
DOI: 10.1039/C3CY00430A
Fig. 8
18

Page 19 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
100
90
80
70
60
50
40
% conversion
% selectivity
280
300
320
340
Temperature (0C)
Fig. 9
19

Catalysis Science & Technology
Page 20 of 24
View Article Online
DOI: 10.1039/C3CY00430A
70
60
50
40
30
20
10
5 wt% VPO/ZrP
20 wt% VPO/ZrP
30 wt% VPO/ZrP
Pure VPO
1
2
3
4
5
Time on stream (hour)
A
100
80
60
5 wt% VPO/ZrP
20 wt% VPO/ZrP
30 wt% VPO/ZrP
Pure VPO
40
20
1
2
3
4
5
Time on stream (hour)
B
Fig. 10 (A&B)
20

Page 21 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
100
90
80
70
60
50
40
30
20
10
X gly VPO/ZrP
X gly VPO
S acr VPO/ZrP
S acr VPO
0
5
10
15
20
25
30
35
40
Time on stream (h)
Fig. 11
21

Catalysis Science & Technology
Page 22 of 24
View Article Online
DOI: 10.1039/C3CY00430A
Fig. 12
Fresh
Used
100
200
300
400
500
600
700
Temperature (0C)
Fig. 13
22

Page 23 of 24
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C3CY00430A
Fig. 14
23

Catalysis Science & Technology
Page 24 of 24
View Article Online
DOI: 10.1039/C3CY00430A
Vapour Phase Dehydration of Glycerol over VPO Catalyst
Supported on Zirconium phosphate
N. Pethan Rajan, Ginjupalli Srinivasa Rao, Vanama Pavankumar and Komandur V R Chary *
Catalysis Division, Indian Institute of Chemical Technology, Hyderabad-500 007, India.
*Corresponding author. Tel: +91-40-27193162; Fax: +91-40-27160921, E-mail: kvrchary@iict.res.in
VPO/ZrP
O
O
HO
OH
OH
Bronsted acidic
sites
Acrolein
3-Hydroxy
propanaldehyde
VPO/ZrP
OH
O
Lewis acidic
sites
Glycerol
OH
Hydroxy acetone