One pot selective conversion of furfural to Γ-valerolactone over zirconia containing heteropoly tungstate supported on Β-zeolite catalyst

Article abstract of DOI:10.1016/j.mcat.2018.12.024

A series of metal oxide and tungstophosphoric acid (TPA) supported on β-zeolite catalysts were prepared and evaluated for the one pot selective conversion of furfural (FA) to γ-valerolactone (GVL) using transfer hydrogenation approach. The characterizations of the catalysts were derived from N₂-adsorption, FT-IR, XRD, XPS and temperature programmed desorption (TPD) techniques. The acid and base sites in the catalysts were estimated by NH₃ and CO₂ -TPD and FT-IR spectroscopy with pyridine and 2-propanol adsorption. Among the catalysts 20%ZrO₂ with 5%TPA on β-zeolite showed high activity with 85% GVL yield. The high Lewis acidic density along with basic sites are responsible for the outstanding catalytic activity of the catalyst. Based on product distribution and catalyst characteristics, a plausible mechanism was proposed. Different reaction parameters were also studied and optimum conditions were established. The catalyst was easily recovered and reused with consistent activity.

Full text of DOI:10.1016/j.mcat.2018.12.024

MolecularCatalysis466(2019)52–59
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
One pot selective conversion of furfural to γ-valerolactone over zirconia
containing heteropoly tungstate supported on β-zeolite catalyst
⁎
B. Srinivasa Raoa,b, P. Krishna Kumaria,b, Paramita Koleya,c, J. Tardioc, N. Lingaiaha,b,
a Department of Catalysis and Fine Chemicals, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500 007, India
b CSIR-Academy of Scientific and Innovative Research (CSIR-AcSIR), New Delhi, India
c Centre for Advanced Materials & Industrial Chemistry (CAMIC), School of Applied Sciences, RMIT University, GPO BOX-2476, Melbourne, 3001, Australia
A R T I C L E I N F O
A B S T R A C T
Keywords:
Furfural
γ-Valerolactone
Tungstophosphoric acid
Transfer hydrogenation
β-Zeolite
A series of metal oxide and tungstophosphoric acid (TPA) supported on β-zeolite catalysts were prepared and
evaluated for the one pot selective conversion of furfural (FA) to γ-valerolactone (GVL) using transfer hydro-
genation approach. The characterizations of the catalysts were derived from N2-adsorption, FT-IR, XRD, XPS and
temperature programmed desorption (TPD) techniques. The acid and base sites in the catalysts were estimated
by NH3 and CO2 -TPD and FT-IR spectroscopy with pyridine and 2-propanol adsorption. Among the catalysts
20%ZrO2 with 5%TPA on β-zeolite showed high activity with 85% GVL yield. The high Lewis acidic density
along with basic sites are responsible for the outstanding catalytic activity of the catalyst. Based on product
distribution and catalyst characteristics, a plausible mechanism was proposed. Different reaction parameters
were also studied and optimum conditions were established. The catalyst was easily recovered and reused with
consistent activity.
1. Introduction
and its esters. Hydrogenation can be carried by two methods (i) metal
promoted hydrogenation with hydrogen [18–21], (ii) catalytic transfer
The world depends intensely on non renewable petroleum based
carbons to produce chemicals and liquid fuels. Diminishing of petro-
leum resources and increasing demand for petrochemical products led
to find renewable resources as alternative to petroleum-derived pro-
ducts. In this way, researchers found biomass as renewable and abun-
dant alternative carbon source, as it offers multiple advantages over
petroleum [1–8]. Biomass contains cellulose and hemicellulose as major
components [9]. Furan derivatives can be obtained from biomass via
depolymerisation followed by hydrolysis. Many valuable chemicals can
be synthesized as upgraded products from these furan derivatives, such
as fuel additives and pharmaceutical intermediates [10–13]. Many
types of chemicals can be produced from furan derivatives, among them
GVL is an important chemical with wide range of applications. It is an
intermediate in fine chemical synthesis, a green solvent, building block
for polymers, flavouring agent, illuminating liquid and a lighter fluid.
GVL has low melting (−31 °C), high boiling (207 °C) points. It can be
easily recognised while leaking and spills with its smell. GVL has low
vapour pressure even at high temperatures and more importantly it is
biodegradable. Hence it is easy to store and move safely in large
quantities [14–17].
hydrogenation (CTH) using hydrogen donors like formic acid, iso-pro-
panol etc. The former process requires noble metal catalysts for hy-
drogenation which are expensive and needs high H2 pressure. In con-
trast, later CTH process proceeds over low cost metal oxide catalysts
and alcohols as cheaper and safe H-donors. CTH is considered as im-
proved non-conventional way for energy saving and scalable GVL
production.
Regarding the production of GVL through CTH, several catalytic
systems have been reported [22–27]. Bulk ZrO2 was used as a catalyst
for the synthesis of GVL from LA and its esters using iso-propanol/iso-
butanol as H-donors at 150 °C under pressurized inert gas conditions
[28]. Hydrated ZrO2 catalyst was used to convert ethyl levulinate to
GVL at 250 °C [29]. There are some drawbacks related to bulk ZrO2 as a
catalyst such as high catalyst loading, relatively high reaction tem-
perature/pressure, moderate GVL selectivity and appreciable deacti-
vation. By taking these drawbacks, few multi functional catalysts were
reported for GVL production. Zr-β-zeolite was used as more effective
catalyst compared to bulk ZrO2 [30,31]. An integrated conversion of
hemicellulose and FA to GVL was developed by the combination of Au/
ZrO2 and ZSM-5 catalyst [32]. The combination catalysts were not good
enough to get high yields as the conversion of intermediates to product
Generally GVL was prepared by hydrogenation of levulinic acid (LA)
⁎ Corresponding author at: Department of Catalysis and Fine Chemicals, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500 007, India.
E-mail address: nakkalingaiah@iict.res.in (N. Lingaiah).
https://doi.org/10.1016/j.mcat.2018.12.024
Received 27 September 2018; Received in revised form 13 December 2018; Accepted 25 December 2018
2468-8231/©2018ElsevierB.V.Allrightsreserved.

B. Srinivasa Rao et al.
MolecularCatalysis466(2019)52–59
Acidity/basicity of the catalysts was measured by using TPD ana-
lysis. NH3 and CO2 were used as probe molecule to estimate acidity and
basicity respectively. BELCAT-II equipment was utilized for TPD ana-
lysis. About 0.05 g of sample was taken in a sample tube and pre-treated
in helium flow for 1 h at 300 °C to remove any adsorbed species on the
surface of the catalyst. The catalyst sample was saturated with 10% NH3
gas for 1 h at 100 °C. The physiosorbed NH3 gas was flushed out with
flow of He gas at the same temperature. The TPD analysis was con-
ducted in the temperature range from 100 to 800 °C with heating rate of
10 °C min−1. The outlet gas was detected by using thermal conductivity
detector (TCD). 10% CO2 was used as a probe molecule in CO2-TPD
analysis. The catalyst sample was saturated with 10% CO2 gas for 1 h at
100 °C. The analysis was followed the same way as mentioned in NH3-
TPD analysis.
Powder X-ray diffraction (XRD) patterns of the catalysts were re-
corded on a Rigaku Miniflex (Rigaku Corporation, Japan) X-ray di-
fravtometer using Ni filtered Cu Kα radiation (λ = 1.5406 Å) with a
scan speed of 2° min−1 and a scan range of 10–80° at 30 kV and 15 mA.
X-ray photoelectron spectroscopy (XPS) measurements were con-
ducted on a KRATOS AXIS 165 with a DUAL anode (Mg and Al) ap-
paratus using Mg Kα anode. The nonmonochromatized Al-Kα X-ray
source (hν = 1486.6 eV) was operated at 12.5 kV and 16 mA. The XPS
instrument was calibrated using Au as standard. For energy calibration,
the carbon 1 s photoelectron line was used. The carbon 1 s binding
energy was taken as 285 eV. Charge neutralization of 2 eV was used to
balance the charge up of the sample.
Scheme 1. Schematic representation of furfural conversion to GVL through
CTH.
require different active sites. Direct conversion of FA to GVL by a single
step process using Sn-Al-β-zeolite and meso-Zr-Al-β-zeolite were effec-
tive catalysts compared to the combination of multiple catalysts
[33,34]. Development of a single bifunctional catalyst for selective
synthesis of GVL from FA is an important process as it required multiple
steps as shown in Scheme 1.
In the present study metal oxide and heteropolytungstate containing
zeolite catalysts were prepared and evaluated for direct conversion of
FA to GVL by CTH in one pot. The catalysts functionalities were derived
and correlated with their activity.
Furfuryl alcohol (FAL), iso-propopyl (2-methylfuran) ether (FE), iso-
propoxy levulinic ester (IPL), 4-hydroxy pentanoic acid ester (4-HPE).
2. Experimental section
2.3. General reaction procedure
2.1. Catalyst preparation
All the CTH reactions were performed in a 100 mL SS autoclave
reactor. The reactor was charged with 0.196 g FA in 20 mL of 2- pro-
panol with varying in amounts of catalysts (2.5–11.5 g cat./L). The
reaction was conducted at different reaction temperatures varied from
130 to 210 °C. The reaction was carried out for a period of 30 min to
11 h. After the completion of reaction for stipulated time the catalyst
was separated by filtration and the products were analyzed by gas
chromatograph (Shimadzu 2010) with FID detector and inno wax ca-
pillary column (diameter: 0.25 mm, length: 30 m). Further the products
were confirmed by GC–MS (Schimadzu GCMS-QP2010S). The products
were quantified based on the retention times and response factors of the
standard chemicals. The yields were calculated based on standard curve
of commercial samples.
The chemicals used in this study were obtained from Sigma Aldrich
and utilized as received. The support β-zeolite (Si/Al ratio 22) was
provided by SUD-Chemie India Pvt Ltd.
12-Tungstophosphoric acid (T) and metal oxides such as ZrO2 (Zr),
Al2O3 (Al), SnO2 (Sn), TiO2 (Ti), and Nb2O5 (Nb) supported on β-zeolite
catalysts were prepared by impregnation method and represented as Zr-
T-zeolite, Al-T-zeolite, Sn-T-zeolite, Ti-T-zeolite, Nb-T-zeolite respec-
tively. In a typical preparation method, calculated amount of zeolite
(7.5 g) was taken and to this, required amount (0.5 g) of TPA dissolved
in distilled water was added drop wise and then allowed to stir for
30 min. Later intended amount (2 g) of aqueous ZrO(NO3)2 solution was
suspended onto the TPA/β-zeolite (T-zeolite) solution and allowed to
stir for one more hour. The excess water was removed over rota eva-
porator and the catalyst was further dried for about 24 h in an oven.
Finally the dried catalyst was calcined at 300 °C for 2 h. Other metal
oxide catalysts also prepared in the same manner as described above.
The metal precursors Al(NO3)2, SnCl4, Ti(OHC3H6)4, NbCl4 were taken
for the oxides of Al, Sn, Ti, Nb respectively.
3. Results and discussion
3.1. Catalyst characterisation results discussion
The textural parameters of the catalysts are presented in Table 1.
The surface area and pore volume of the zeolite was decreased upon the
deposition of TPA and metal oxides. A variation in surface area was
observed for different metal oxides. The Ti and Nb oxide containing
catalysts showed high surface area compared to other metal oxide
containing catalysts. The use of organo metallic Ti(OHC3H6)4 precursor
2.2. Catalyst characterization
The BET surface area, pore volume and pore sizes were determined
by N2 adsorption-desorption method using BELSorb II Instrument,
Japan at liquid nitrogen temperature. Before measurement the samples
were degassed at 200 °C for 2 h.
The catalyst acidic sites were distinguished by taking pyridine as an
examine molecule and the adsorption studies were carried out on
DRIFT mode FT-IR spectroscopy (DIGILAB Excalibur- IR spectrometer)
at room temperature. The catalyst was degassed under vacuum at
200 °C for 3 h followed by suspending dry pyridine. FT-IR spectra of the
pyridine-adsorbed samples were recorded, after cooling the sample to
room temperature.
Table 1
Textural properties of the catalysts.
S.No
Catalyst
SBET
Pore volume
[m2 g−1
]
[cm3 g−1
]
1
2
3
4
5
6
7
zeolite
T-zeolite
563
521
392
388
398
486
431
0.28
0.23
0.19
0.17
0.16
0.13
0.12
Zr-T-zeolite
Al-T-zeolite
Sn-T-zeolite
Ti-T-zeolite
Nb-T-zeolite
2-propanol adsorbed FT-IR measurement was used to elucidate the
interaction of 2-propanol with basic sites in the catalyst. 2-propanol
adsorption study was performed in a similar fashion as that of pyridine
adsorbed FT-IR.
53

B. Srinivasa Rao et al.
MolecularCatalysis466(2019)52–59
Fig. 1. XRD patterns of the catalysts. (a) zeolite (b) Zr-T-zeolite (c) Al-T-zeolite
(d) Sn-T-zeolite (e) Ti-T-zeolite (f) Nb-T-zeolite.
Fig. 3. NH3-TPD profiles of the catalysts. (a) zeolite (b) T-zeolite (c) Zr-zeolite
(d) Zr-T-zeolite (e) Al-T-zeolite (f) Sn-T-zeolite (g) Ti-T-zeolite (h) Nb-T-zeolite.
might be the reason for high surface area.
terminal oxygen) and W-Oe-W (Oe-an edge sharing bridging oxygen
atom) of the primary Keggin ion structure [35,36]. This indicates the
retention of Keggin ion structure after it supported on zeolite.
TPD analysis was carried with NH3 as an investigate molecule to
determine the acidic strength distribution and total acidity of the cat-
alysts. Fig. 3 depicts the desorption patterns of the catalysts. In general,
three types of NH3 desorption peaks appear in TPD analysis, related to
weak, moderate and strong acidic sites. Desorption peaks related to
weak, moderate and strong acidic sites were evolved in the temperature
range of 100–250, 250–450 and 450–600 °C respectively. As shown in
Fig. 3 all the catalysts showed major desorption peak in low tempera-
ture region. The support β-zeolite and TPA/β-zeolite showed desorption
peak at 200 °C. The addition of ZrO2 content to zeolite resulted in ad-
ditional desorption peak related to moderate acidic sites, which are
mostly due to the presence of Lewis acidic sites. Zr-T-zeolite catalyst
exhibited intense desorption peaks in weak and moderate acidic region.
Al-T-zeolite and Sn-T-zeolite catalysts showed low temperature deso-
rption peak and also a low intense broad peak at high temperature
region related to moderate/strong acidic sites. Nb-T-zeolite showed
three desorption peaks related weak, moderate and strong acidic sites.
Ti-T-zeolite catalyst exhibited desorption peaks related to weak and
strong acidic sites only. The acidity values were mainly depending upon
the nature of metal oxide present in the catalyst. The total acidity of the
catalysts was presented in Table 2. The acidity of the catalysts are in the
order of Zr-T-zeolite > Al-T-zeolite > Nb-T-zeolite > Ti-T-zeolite >
Sn-T-zeolite > Zr-zeolite > T-zeolite > zeolite. The acid amount of
Zr-T-zeolite is much higher than the amount of Zr-zeolite. The basic
sites present in ZrO2 may neutralize the surface acidic sites of zeolite,
while the addition of Bronsted acidic TPA to zeolite causes increase in
acidity.
Fig. 1 illustrates the XRD patterns of the catalysts. All the catalysts
showed the same diffraction patterns corresponding to zeolite, de-
monstrating the preservation of zeolite framework upon the modifica-
tion with metal oxide and heteropoly acid. There were no diffraction
peaks related to metal oxide and heteropoly acid, indicating their high
dispersion on zeolite.
FT-IR spectra of zeolite and other supported catalysts are shown in
Fig. 2. FT-IR spectra was recorded in the fingerprint region of hetero-
poly acids i.e., 700–1200 cm−1 in order to know the retention of Keggin
ion structure of tungstophosphoric acid after supported on zeolite. Bare
zeolite was showed a band at 805 and 1040 cm−1 which are ascribed to
the symmetric and asymmetric stretching vibrations of Si–O–Al re-
spectively. Heteropoly TPA showed bands at 1082, 980, 890 and
810 cm−1. All the supported catalysts showed the extra bands that are
not observed in bare zeolite at 1082, 890 and 810 cm−1 which are
related to asymmetric stretching vibrations of P-O, W = Ot ((Ot –
Bronsted and Lewis acidic sites of the catalysts were distinguished
by FT-IR measurement using pyridine as probe molecule. The pyridine
adsorbed FT-IR spectra of catalysts are displayed in Fig. 4. All the
spectra are recorded in the region of 1200–1700 cm−1. The bands at
1445 and 1590 cm−1 were assignable to coordinated pyridine species
with Lewis acid sites. While the bands at 1550 and 1640 cm−1 were due
to the pyridinium ions bonded to Bronsted acid sites of the catalysts and
the band at 1480 cm−1 was related to both Bronsted and Lewis acidic
sites. Lewis to Bronsted acidic site ratio (L/B) of the catalysts were
calculated and presented in Table 2.
Basicity of the catalysts was measured by CO2-TPD and desorption
profiles are shown in Fig. 5. The basicity values calculated from TPD
desorption of the catalysts are presented in Table 2.The support zeolite
itself showed desorption peaks at weak and moderate temperatures.
Fig. 2. FT-IR spectra of the catalysts (a) TPA (b) Zr-T-zeolite (c) Al-T-zeolite (d)
Sn-T-zeolite (e) Ti-T-zeolite (f) Nb-T-zeolite (g) zeolite.
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B. Srinivasa Rao et al.
MolecularCatalysis466(2019)52–59
Table 2
Acidity values of the catalysts calculated from TPD of NH3.
Catalyst
Weak
(m.mol/g)
Moderate
(m.mol/g)
Strong
(m.mol/g)
Total acidity (m.mol/g)
L/B ratio
Total basicity
(m.mol/g)
zeolite
T-zeolite
Zr-zeolite
Zr-T-zeolite
Al-T-zeolite
Sn-T- zeolite
Ti-T-zeolite
Nb-T-zeolite
0.760
0.784
0.623
0.618
0.884
0.687
0.717
0.672
0.080
0.154
0.548
0.942
0.483
0.341
0.225
0.310
–
0.840
1.020
1.171
1.673
1.588
1.214
1.378
1.575
0.42
0.39
1.56
1.53
1.23
1.04
0.81
0.75
0.418
0.399
0.792
0.761
0.623
0.441
0.134
0.098
0.082
–
0.113
0.221
0.186
0.436
0.593
Fig. 6. 2-propanol adsorbed FT-IR specta of the catalysts. (a) Zr-T-zeolite (b) Al-
T-zeolite (c) Ti-T-zeolite (d) Nb-T-zeolite (e) Sn-T-zeolite.
Fig. 4. Pyridine adsorbed FT-IR spectra of the catalysts. (a) Zr-T-zeolite (b) Al-
T-zeolite (c) Sn-T-zeolite (d)Ti-T-zeolite (e) Nb-T-zeolite (f) zeolite.
ZrO2 containing zeolite showed the same pattern as zeolite support with
increased intensities. The presence of TPA in Zr-zeolite led to decrease
in basicity. This is due to the acidic sites of TPA may suppressed the
basic sites in Zr-zeolite. CO2 desorption profiles of Zr, Al and Sn-T-
zeolite catalysts showed a broad desorption peaks in the temperature
region related to weak and moderate basic sites. Such desorption peaks
were not observed in Ti and Nb-T-zeolite catalysts, indicating the base
site density was more in Zr, Al and Sn-T-zeolite catalysts. Among the
catalysts Zr-T-zeolite showed high basic site density.
Fig. 6 demonstrating the 2-propanol (2-PrOH) adsorbed FT-IR
spectra of the catalysts. FT-IR spectra of 2-PrOH adsorbed samples were
measured to elucidate the role of the base sites on the catalysts for CTH
reaction [37]. After degasification at 150 °C for 1 h, the sample was
exposed to saturated 2-PrOH vapour, followed by evacuation at 50 °C.
Since the base sites preferentially interact with slightly acidic CH
groups of 2-PrOH, the changes occur in the original CH stretching
modes (V(CH), Vs(CH3), and Vas(CH3)) after 2-PrOH adsorption on the
solid catalyst surface are helpful to evaluate the interaction between the
base sites and 2-PrOH. There were no large differences in Vs(CH3)
among the samples. However, the Vas(CH3) band in the spectrum for Zr-
T-zeolite and Al-T-zeolite was clearly had a shift towards lower wave-
number, compared with those of other catalysts. The Vas(CH3) bands for
Zr-T-zeolite, Al-T-zeolite, Ti-T-zeolite, Nb-T-zeolite and Sn-T-zeolite
appear at 2967, 2971, 2986, 2985 and 2984 cm−1 respectively. This
shift of the Vas(CH3) band is due to the interaction of slightly acidic
methyl hydrogen atoms in 2-propoxide with the base sites. The Vas(CH)
stretching was observed only for ZrO2 and Al2O3 based catalysts.
However, the interactions of methyl hydrogen (shift in Vas(CH3)) in 2-
PrOH and the intensities of the spectra of 2-PrOH adsorbed on Zr-T-
zeolite was more than that of other synthesized catalysts, suggesting
Fig. 5. CO2-TPD profiles of the catalysts. (a) zeolite (b) Zr-zeolite (c)Zr-T-zeo-
lite (d) Al-T-zeolite (e) Sn-T-zeolite (f) Ti-T-zeolite (g) Nb-T-zeolite.
55

B. Srinivasa Rao et al.
MolecularCatalysis466(2019)52–59
that the base sites density was more in Zr-T-zeolite sample. The results
made from 2-PrOH adsorbed FT-IR are in good agreement with CO2-
TPD results.
3.2. Activity results
3.2.1. Screening of the catalysts
Initially the reaction was carried with bare zeolite and this catalyst
showed 35% FA conversion with FAL/FE and IPL as intermediates (21%
total yield). Later the reaction carried over 20%ZrO2/β-zeolite catalyst
and it showed about 94% of furfural conversion with moderate GVL
yield of 52% within the reaction time period of 10 h. The other products
observed over this catalyst were FAL and FE. The conversion of inter-
mediate FAL/FE to levulinic ester (IPL) is low in this case as the furan
ring opening transformation requires Bronsted acidity [38]. This in-
dicates Bronsted acidity of the 20%ZrO2/β-zeolite catalyst was not
sufficient for the complete conversion of intermediate FAL/FE to le-
vulinic ester as shown in Scheme 1. However β-zeolite is a good
Bronsted acidic support; the basic sites in ZrO2 may neutralize the
acidic sites in β-zeolite which resulted the decrease in overall acidity.
This could be the reason for the decrease in conversion of intermediate
products FAL/FE to IPL with 20%ZrO2/β-zeolite. In order to know the
influence of Bronsted acidity, TPA impregnated on zeolite then used as
support for ZrO2 and this catalyst obtained high yield of GVL that
means it is able to convert intermediate FAL/FE to IPL. This indicates
the transformation of FAL/FE to IPL intermediate required more
number of Bronsted acidic sites. As the TPA containing β-zeolite
showed high activity, different contents of ZrO2 and TPA supported on
β-zeolite catalysts were prepared. Among the catalysts 20%ZrO2/
5%TPA/zeolite showed high activity. The activity results of the cata-
lysts are shown in Table 3.
In order to know the reason for superior activity of 20%ZrO2/
5%TPA/zeolite catalyst, these catalysts are further characterized by
pyridine adsorbed FT-IR and TPD of CO2 analysis. Pyridine adsorbed
FT-IR spectras of different amounts of ZrO2 and TPA containing cata-
lysts are shown in Figure S1 (supplementary information). All the cat-
alysts exhibited both Bronsted and Lewis acidic sites and the Lewis
acidic sites peak intensities were increased with increase in ZrO2 con-
tent on the catalyst. The L/B ratios of 20%Zr-5%T-zeolite, 15%Zr-
10%T-zeolite and 10%Zr-15%T-zeolite catalysts are 1.53, 1.09 and 0.74
respectively. It indicates the density of Lewis acidic sites are more in
20%Zr-5%T-zeolite catalyst.
Fig. 7. Conversion of furfural to GVL over different metal oxide containing
5%TPA/β-zeolite catalysts. Reaction conditions: Furfural: 0.196 g, 2-propanol:
20 mL, Temperature: 170 °C, Catalyst Weight: 7.5 g cat./L, Time: 10 h.
The catalyst with 20%ZrO2 and 5%TPA supported on β-zeolite
showed better activity with complete furfural conversion and 90% GVL
yield. As the ZrO2, TPA containing catalyst showed reasonable activity,
a series of catalysts with different metal oxides such as Al2O3, SnO2,
TiO2, and Nb2O5 were supported on 5%TPA/β-zeolite. The activities of
these catalysts are presented in Fig. 7. The yield of GVL was depended
on the metal oxide present in TPA/β-zeolite catalyst. The FA conversion
and yield of GVL was moderate within the range of 20–50% for Nb, Ti,
Sn containg catalysts. Catalysts with Zr, Al showed high conversion
with exceptional GVL yield up to 90%. The order of the activity of the
catalysts are Zr-T-zeolite > Al-T-zeolite > Sn-T-zeolite > Ti-T-zeo-
lite > Nb-T-zeolite catalysts. According to the past reports, Lewis
acidic sites were active for the CTH reaction [39]. Coming to the re-
action of FA conversion to GVL, the function of Lewis acidic sites was
more crucial, as the Lewis acidic sites were involved in two major in-
termediate conversion steps viz., FA to FAL/FE and conversion of alkyl
levulinates to GVL [40]. However the conversion of FAL/FE to IPL
needs Bronsted acidic sites. The difference in FA conversion and GVL
yields were explained in terms of nature and type of acidity present in
the catalysts. The catalysts with lower ratio of Lewis to Bronsted acid
sites (Sn, Ti, Nb,-T-zeolite) demonstrated the lower conversion of FA
and low yield of GVL, while both Zr-T-zeolite and Al-T-zeolite catalysts
with relatively high ratio of Lewis to Bronsted acid sites showed high
FA conversion and high yield of GVL. 2-Propanol adsorbed FT-IR results
indicate the interaction of 2-propanol with basic sites in these catalysts
was more. Therefore, the high conversion and yield over Zr-T-zeolite
catalyst was might be due to the high extent of Lewis acidity and suf-
ficient amount of Bronsted acidity. The presence of base sites which
improved the 2-propanol interaction. The catalysts with poor basicity
showed less GVL yield.
The CO2-TPD profiles of Zr-T-zeolite catalysts with different
amounts of ZrO2 and TPA are shown in Figure S2 (Supplementary in-
formation). The desorption peaks were shifted to higher temperatures
with increasing ZrO2 content. This indicates that the strength of basicity
is increased with ZrO2 content. The basicity of the catalysts is in the
order of 20%Zr-5%T-zeolite > 15%Zr-10%T-zeolite > 10%Zr-15%T-
zeolite. The high proportion of Lewis acidic density and basicity is re-
sponsible for the high activity of 20%Zr-5%T-zeolite catalyst.
The catalytic transfer hydrogenation reaction was also performed
with different carbonyl group containing compounds such as 5-hydro-
xymethyl furfural (5-HMF) and levulinic acid (LA). The reaction of 5-
HMF with primary alcohols majorly produced alkyl levulinates and
with 2-propanol the major product was 2,5-dimethylfuran. The reaction
with LA in 2-propanol yielded maximum amount of 94% GVL.
The catalytic activity of the present catalyst was compared with the
earlier reported catalysts and the observations are shown in Table 4. An
integrated process was developed by Weibin Fan et. al. for FA conver-
sion to GVL using combination of Au/ZrO2 and ZSM-5 catalyst achieved
80% of GVL yield [32]. In these reports they used different catalysts
with Lewis and Bronsted acid sites with high catalyst loadings. In an-
other study Zr-Al-β-zeolite catalyst with both Bronsted and Lewis acid
sites was used for the one pot conversion of FA to GVL. This catalyst
showed 95% of GVL yield at a reaction time of 24 h [34]. Jungho Jae et.
Table 3
Screening of the catalysts for the conversion of FA to GVL.
Catalyst
FA
FAL/FE
IPL
GVL
Carbon
Conv. (%) Yield (%) Yield (%) Yield (%) Balance
zeolite
35
94
58
100
14
24
11
2
7
6
43
4
–
52
–
60
87
93
96
Zr-zeolite
T-zeolite
20%Zr-5%T-
zeolite
15%Zr-10%T-
zeolite
90
100
100
–
18
37
77
44
95
95
10%Zr-15%T-
zeolite
14
Reaction conditions: Furfural: 0.196 g, 2-propanol: 20 mL, Temperature: 170 °C,
Catalyst Weight: 7.5 g cat./L, Time: 10 h.
56

B. Srinivasa Rao et al.
MolecularCatalysis466(2019)52–59
Table 4
Synthesis of GVL over different reported catalysts.
S.No
Catalyst
Feed
Temp. (°C)
Time (h)
Feed/CAT
GVL
Ref.
Yield (%)
1
2
3
4
5
6
Au/ZrO2 + ZSM-5
Zr-Al-β zeolite
FA
FA
FA
xylose
FA
120
120
180
190
170
170
24
24
6
10
24
10
0.10
0.40
2.60
2.03
1.30
1.30
80
95
60
34
72
90
[32]
[34]
[33]
[41]
[42]
Present
study
Sn-Al-β zeolite
Zr-Al-β zeolite
Zr-Al-β zeolite
ZrO2-TPA-β zeolite
FA
al. reported moderate yield (60%) of GVL at 180 °C in 2-butanol with
Sn-Al-Zeolite catalyst [33]. Recently Juan A. Melero et.al. used Zr-Al-β-
zeolite catalyst for the direct conversion of xylose to GVL and they got a
considerable GVL yield of 34% at 190 °C with in 10 h [41] and they
achieved 72% of GVL yield at 170 °C with in 24 h using FA as feed [42].
The present catalyst with ZrO2 and heteropolytungstate supported on
zeolite contains both Bronsted and Lewis acid sites displayed better
activity compared to other catalysts under moderate reaction condi-
tions.
3.2.2. Effect of reaction parameters
As Zr-T-zeolite catalyst showed high activity, it is used to evaluate
various reaction parameters for this reaction. In the way to study the
reaction parameters, firstly the effect of reaction temperature was
carried and the results are presented in Table 5. The reactions were
conducted in temperatures ranging from 110 to 200 °C. The furfural
conversion was 59, 82% with 26, 47% of GVL yield at 110 and 140 °C
respectively. Further increase in reaction temperature to 170 °C furfural
conversion was reached to 100% with 90% yield of GVL. Further ele-
vation of temperature to 200 °C a decrease in GVL yield was observed.
The formation of unidentified humin by-products might be the reason
for the decrease in yield of GVL. The optimum reaction temperature is
170 °C.
Fig. 8. Effect of catalyst loading for the conversion of furfural to GVL over Zr-T-
zeolite catalyst. Reaction conditions: Furfural: 0.196 g, 2-propanol: 20 mL,
Temperature: 170 °C, Catalyst Weight: 7.5 g cat./L, Time: 10 h.
Reaction conditions: Furfural: 0.196 g, 2-propanol: 20 mL,
Temperature: 140–170 °C, Catalyst Weight: 7.5 g cat./L, Time: 10 h.
The influence of catalyst weight on the reaction was investigated
and the results are shown in Fig. 8. All the reactions were carried by
varying the catalyst concentration in the range of 2.5–11.5 g cat./L.
When a low amount of catalyst (2.5 g cat./L) was used, the conversion
of furfural was only 38% with 12% of GVL and 18% IPL as major
products. A substantial increase in the conversion (100%) and yield of
GVL (79%) was noticed with the increase in catalyst amount to 5 g cat./
L. About 90% GVL yield was observed when catalyst amount was raised
to 7.5 g cat./L. A slight increase in GVL yield (92%) was observed with
the use of 9 g cat./L. Further increase in catalyst amount to 11.5 g cat./
L, GVL yield was decreased. At low catalytic amounts the number of
catalytic active species were less, led to low conversion and product
yield. At high catalyst loading the decrease in yield might be due to the
conversion of GVL into further upgraded products on available acidic
sites of the catalyst. Therefore 7.5 g cat./L was the optimum catalyst
loading for this reaction.
Fig. 9. Effect of reaction time on the conversion of furfural to GVL over Zr-T-
zeolite catalyst. Reaction conditions: Furfural: 0.196 g, 2-propanol: 20 mL,
Temperature: 170 °C, Catalyst Weight: 7.5 g cat./L, Time: 1–10 h.
In order to understand the reaction path way, the effect of time on
reaction was carried. The reaction was conducted up to 11 h and results
are presented in Fig. 9. At the initial time of 15 min, the conversion
(12%) was just started towards FAL/FE (2/7%) and IPL (3%). After
30 min of reaction the conversion was slightly increased to 18% with
6% of FE and 12% of IPL. When the reaction allowed to 45 min, 25% of
FA conversion was observed with 14% of IPL as a major product and 2%
of GVL as minor product. As the reaction progressed the GVL yield was
gradually increased. The conversion of furfural was increased with in-
creasing time and it reached the maximum at 10 h of reaction time with
90% of GVL yield. There is no considerable increase in the yield of GVL
Table 5
Conversion of furfural to GVL at different reaction temperatures over Zr-T-
zeolite catalysts.
Temperature (°C) FA
FA/FE
IPL
GVL
Carbon
Conv. (%) Yield (%) Yield (%) Yield (%) Balance
110
140
170
210
59
82
100
100
9
15
2
24
20
4
26
47
90
77
100
100
96
1
7
85
57

B. Srinivasa Rao et al.
MolecularCatalysis466(2019)52–59
Scheme 2. Possible reaction mechanism for single step conversion of furfural to GVL.
with further increase in reaction time to 11 h. Hence, 10 h was taken as
optimum reaction time for this reaction.
well established that the secondary alcohols were more effective than
the primary alcohols due to the high dehydrogenation nature of sec-
ondary alcohols [45–47]. Similar to the previous findings, the alcohols
examined here, secondary alcohols were more selective for CTH than
primary alcohols towards the production of GVL. This indicates that
CTH reaction using secondary alcohols is faster than those of primary
alcohols. Among the secondary alcohols 2-propanol showed slightly
high GVL production than 2-butanol. As shown in Fig. 10 the GVL
production rate over different alcohols is in the order of 2-pro-
panol > 2-butanol > ethanol > methanol > n-propanol > n-bu-
tanol.
Based on the product distribution during reaction time and 2-pro-
panol adsorbed FT-IR studies, a plausible reaction mechanism was
proposed as shown in Scheme 2. In the first step, iso-propanol adsorbed
on Zr surface and dissociated to generate Zr bound isopropoxide. Then
the electron rich carbonyl group of furfural might interact with Lewis
acidic sites of Zr to form six member ring. The β-hydride of the iso-
propoxide bound to zirconia attacks the carbonyl group on furfural to
yield furfuryl alcohol. The furfuryl alcohol attacked by iso-propanol to
yield FE, further the ring opening of this ether to IPL occur on the
Bronsted acidic sites of the catalyst. The ring opening of ether was
discussed clearly in earlier publications [43,44]. The isopropyl levuli-
nate to 4-HPE follows the same path as furfural to furfuryl alcohol. The
formed 4-HPE readily forms GVL through intermoleculer lactonization.
The nature of hydrogen donor (alcohol) also has a great influence on
CTH reaction. A series of alcohols were used as hydrogen donors and
the results are presented in Fig. 10. Since the conversion of FA to GVL
involves two reduction steps such as conversion of FA to FAL, AL to 4-
hydroxyl pentanoic acid ester. The hydrogen transfer capability of al-
cohols can largely influence the rate of the formation of GVL. It was
3.2.3. Reusability of the catalyst
The major benefit of heterogeneous catalysis is its reusability. The
reusability test was conducted by reacting furfural with 2-propanol at
170 °C for 10 h and the outcomes are presented in Fig. 11. After com-
pletion of the reaction catalyst was removed from reaction mixture and
washed with 2-PrOH, dried at 100 °C for 2 h and then reused for the
next cycle. The spent catalyst recyclability was carried up to four cycles.
These results suggest that there was no appreciable decrease in activity
of the catalyst upon reuse. A leaching test (Fig. 12) was conducted by
Fig. 10. Role of hydrogen source for the conversion of furfural to GVL over Zr-
T-zeolite catalyst. Reaction conditions: Furfural: 0.196 g, Alcohol: 20 mL,
Temperature: 170 °C, Catalyst Weight: 7.5 g cat./L, Time: 10 h.
Fig. 11. Recyclability results of Zr-T-zeolite catalyst.
58

B. Srinivasa Rao et al.
MolecularCatalysis466(2019)52–59
[2] M.E. Zakrzewska, E. Bogel-Lukasik, R. Bogel-Lukasik, Chem. Rev. 111 (2011)
397–417.
[3] J. Zhang, L. Lin, S. Liu, Energy Fuels 26 (2012) 4560–4567.
[4] P. Gallezot, Chem. Soc. Rev. 41 (2012) 1538–1558.
[5] G.W. Huber, S. Iborra, A. Corma, Chem. Rev. 106 (2006) 4044–40.
[6] R. Rinaldi, F. Schuth, Energy Environ. Sci. 2 (2009) 610–626.
[7] I. Chatterjee, F. Pong, A. Sen, Green Chem. 17 (2015) 40–71.
[8] J. Cui, J. Tan, T. Deng, X. Cui, H. Zheng, Y. Zhu, Y.w. Li, Green Chem. 17 (2015)
3084–3089.
[9] M.M. Antunes, S. Lima, P. Neves, A.L. Magalhaes, E. Fazio, A. Fernandes, F. Neri,
C.M. Silva, S.M. Rocha, M.F. Ribeiro, M. Pillinger, A. Urakawa, A.A. Valente, J.
Catal. 329 (2015) 522–537.
[10] X. Hu, R.J.M. Westerhof, L. Wu, D. Dong, C.Z. Li, Green Chem. 17 (2015) 219–224.
[11] T. Flannelly, S. Dooley, J.J. Leahy, Energy Fuels 29 (2015) 7554–7565.
[12] V. Fa bos, M.Y. Lui, Y.F. Mui, Y.Y. Wong, L.T. Mika, L. Qi, E. Csefalvay, V. Kovacs,
T. Szucs, I.T. Horvath, ACS Sustainable Chem. Eng. 3 (2015) 1899–1904.
[13] D.M. Alonso, S.G. Wettsteinb, J.A. Dumesic, Green Chem. 15 (2013) 584–595.
[14] I.T. Horvath, H. Mehdi, V. Fabos, L. Bodaab, L.T. Mika, Green Chem. 10 (2008)
238–242.
[15] H. Li, Z. Fang, S. Yang, ChemPlusChem 81 (2016) 135–142.
[16] W. Cao, W. Luo, H. Ge, Y. Su, A. Wang, T. Zhang, Green Chem. 19 (2017)
2201–2211.
[17] C.B. Chen, M.Y. Chen, B. Zada, Y.J. Ma, L. Yan, Q. Xu, W.Z. Li, Q.X. Guo, Y. Fu, RSC
Adv. 6 (2016) 112477–112485.
Fig. 12. Hot filtration test results of Zr-T-zeolite catalyst. Reaction conditions:
Furfural: 0.196 g, 2-propanol: 20 mL, Temperature: 170 °C, Catalyst Weight:
7.5 g cat./L, Time: 10 h.
[18] D.R. Jones, S. Iqbal, S. Ishikawa, C. Reece, L. Thomas, P.J. Miedziak, D.J. Morgan,
J.K. Edwards, J.K. Bartley, D.J. Willock, G.J. Hutchings, Catal. Sci. Technol. 6
(2016) 6022–6030.
[19] W. Cao, W. Luo, H. Ge, Y. Su, A. Wang, T. Zhang, Green Chem. 19 (2017)
2201–2211.
[20] X. Tang, H. Chen, L. Hu, W. Hao, Y. Sun, X. Zeng, L. Lin, S. Liu, Appl. Catal. B:
Environ. 147 (2014) 827–834.
[21] T. Yang, H. Li, J. He, Y. Liu, W. Zhao, Z. Wang, X. Ji, S. Yang, ACS Omega 2 (2017)
1047–1054.
[22] J. He, H. Li, Y. Liu, W. Zhao, T. Yang, W. Xue, S. Yang, J. Ind. Eng. Chem 23 (2016)
133–141.
[23] S. Xu, D. Yu, T. Ye, P. Tian, RSC Adv. 7 (2017) 1026–1031.
[24] A.M. Hengne, B.S. Kadu, N.S. Biradar, R.C. Chikate, C.V. Rode, RSC Adv. 6 (2016)
59753–59761.
[25] Y. Kuwahara, W. Kaburagi, Y. Osada, T. Fujitani, H. Yamashita, Catal. Today 281
(2017) 418–428.
[26] Z. Xiao, H. Zhou, J. Hao, H. Hong, Y. Song, R. He, K. Zhi, Q. Liu, Fuel 193 (2017)
322–330.
separating the catalyst from reaction mixture after 4 h of reaction and
then the filtered mixture was continued for further progress of the re-
action. After 7 h, no obvious enhancement in the FA conversion beyond
63% was accomplished as determined by GC analysis. This indicates no
leaching of the active component from the catalyst.
The reused catalyst was characterized by XPS to know any changes
in the environment of active metal state. The XPS spectra of the active
metal ions Zr 3d and W 4f are presented in Figure S3 (supplementary
information). The binding energy of Zr core line 3d5/2 was found at
182.4 eV for Zr in both fresh and used catalyst, similar to the reported
values in the literatures [48]. The W 4f spectra reveal the characteristic
doublet at binding energies at 35.53 eV and 37.65 eV for W4f7/2 and
W4f5/2, respectively for both fresh and used catalysts. The 4f doublet
lines are separated by a binding energy of 2.1 eV, which is well matched
with reported literature [49]. The W 4f7/2 peak corresponds to tungsten
in the +6 oxidation state (W+6). These observations indicating that the
catalyst is stable and there are no structural changes observed even
after the reuse of catalyst.
[27] F. Li, L.J. France, Z. Cai, Y. Li, S. Liu, H. Lou, J. Long, X. Li, Appl. Catal. B: Environ.
4 (2017) 67–77.
[28] M. Chia, J.A. Dumesic, Chem. Commun. 47 (2011) 12233.
[29] X. Tang, H. Chen, L. Hu, W. Hao, Y. Sun, X. Zeng, L. Lin, S. Liu, Appl. Catal. B:
Environ. 147 (2014) 827–834.
[30] H.Y. Luo, D.F. Consoli, W.R. Gunther, Y. Roman-Leshkov, J. Catal. 320 (2014)
198–207.
[31] L. Bui, H. Luo, W.R. Gunther, Y. Romn-Leshkov, Angew. Chem. 125 (2013)
8180–8183.
[32] S. Zhu, Y. Xue, J. Guo, Y. Cen, J. Wang, W. Fan, ACS Catal. 6 (2016) 2035–2042.
[33] H.P. Winoto, B.S. Ahn, J. Jae, J. Ind. and Eng. Chem. 40 (2016) 62–71.
[34] S. Song, L. Di, G. Wu, W. Dai, N. Guan, L. Li, Appl. Catal. B: Environ. 205 (2017)
393–403.
[35] P.K. Kumari, B.S. Rao, D.D. Lakshmi, N.R.S. Paramesh, C. Sumana, N. Lingaiah,
Catal. Today (2018), https://doi.org/10.1016/j.cattod.2018.06.047.
[36] Ch. Ramesh Kumar, K.T. Venkateshwara Rao, P.S. Sai Prasad, N. Lingaiah, J. Mol.
Catal. A: Chem. 337 (2011) 17–24.
[37] T. Komanoya, K. Nakajima, M. Kitano, M. Hara, J. Phys. Chem. C 119 (2015)
26540–26546.
4. Conclusions
Different metal oxides and tungstophosphoric acid were supported
on β-zeolite by impregnation method. These catalysts are active for one
pot conversion of furfural to GVL using 2-propanol as hydrogen source.
The yield of GVL is guided by metal oxide present in catalyst. The
presence of Bronsted acidic TPA is essential for the conversion of in-
termediate FAL/FE to alkyl levulinates step. The presence of Lewis
acidic sites and base sites in the catalysts was essential for efficient
catalytic transfer hydrogenation to realize more GVL yield. The con-
version and yield are also depended on the reaction time, temperature,
catalyst amount and also on the nature of hydrogen donor alcohols. The
catalysts are easy to separate and reusable with consistent activity.
[38] B. Tang, W. Dai, X. Sun, G. Wu, N. Guan, M. Hunger, L. Li, Green Chem. 17 (2015)
1744–1755.
[39] V.L. Sushkevich, I.I. Ivanova, S. Tolborg, E. Taarning, J. Catal. 316 (2014) 121–129.
[40] M.M. Antunes, S. Lima, P. Neves, A.L. Magalhaes, E. Fazio, F. Neri, M.T. Pereira,
A.F. Silva, C.M. Silva, S.M. Rocha, M. Pillinger, A. Urakawa, A.A. Valente, Appl.
Catal. B: Environ. 182 (2016) 485–503.
[41] J.A. Meleroa, G. Moralesa, J. Iglesiasa, M. Paniaguaa, C. Lopez-Aguado, K. Wilson,
A. Osatiashtiani, Green Chem. 19 (2017) 5114–5121.
[42] J.A. Melero, G. Morales, J. Iglesias, M. Paniagua, C. Lopez-Aguado, Ind. Eng. Chem.
Res. 57 (1028) (2018) 11592–11599.
[43] B.S. Rao, P.K. Kumari, D.D. Lakshmi, N. Lingaiah, J. Mol. Catal. A Chem. 427
(2017) 80–86.
Acknowledgements
[44] B.S. Rao, P.K. Kumari, D.D. Lakshmi, N. Lingaiah, Catal. Today 309 (2018)
269–275.
[45] Y. Kuwahara, W. Kaburagi, Y. Osada, T. Fujitani, H. Yamashita, Catal.Today 281
The authors B. S. Rao and Paramita thanks to University Grants
Commission (UGC), New Delhi, India and RMIT, Australia for the fi-
nancial support in the form of Junior Research Fellowship.
(2017) 418–428.
[46] X. Tang, L. Hu, Y. Sun, G. Zhao, W. Hao, L. Lin, RSC Adv. 3 (2013) 10277–10284.
[47] X. Tang, H. Chen, L. Hu, W. Hao, Y. Sun, X. Zeng, L. Lin, S. Liu, Appl. Catal. B:
Environ. 147 (2014) 827–834.
[48] Y. Tang, E. Zong, H. Wan, Z. Xu, S. Zheng, D. Zhu, Microporous Mesoporous Mater.
References
155 (2012) 192–200.
[49] K.N. Rao, A. Sridhar, A.F. Lee, S.J. Tavener, N.A. Young, K. Wilson, Green Chem. 8
(2006) 790–797.
[1] E. Kilic, S. Yılmaz, Ind. Eng. Chem. Res. 54 (2015) 5220–5225.
59