Porous organic polymer as an efficient organocatalyst for the synthesis of biofuel ethyl levulinate

Article abstract of DOI:10.1016/j.mcat.2020.111119

Levulinic acid (LA), a lignocellulosic biomass-derived compound has been recognized as one of the versatile building blocks for the synthesis of commodity chemicals having biofuel properties together with potential as precursor for the synthesis of several value-added pharmaceuticals and polymers. Herein, we report the synthesis of catalytically active functionalized porous organic polymer and its utilization as heterogeneous organocatalyst for the synthesis of EL from LA in very high yield. Here, sulfonic acid functionalized porous organic polymer SBZ&at;POP have been prepared via simple Friedel-Crafts alkylation of benzene with dimethoxymethane followed by sulfonation of the aromatic rings. The structure and properties of the material was examined through PXRD, N₂ sorption, HR TEM, ¹³C CP-MAS NMR, NH₃-TPD, TG-DTA and FTIR analysis. Our characterization data suggested nanoscale porosity with high surface acidity in SBZ&at;POP. The effects of reaction time, catalyst loading, molar ratio of levulinic acid to ethanol and reaction temperature were studied thoroughly to optimize the catalytic activity of SBZ&at;POP. Under optimized reaction conditions EL yield of 88 percent has been achieved with 1:15 molar ratio of LA to ethanol under refluxing conditions in 10 h. This porous organic polymer based organocatalyst displayed good recyclability for consecutive five reaction cycles suggesting the sustainable application potential of this acidic organocatalyst.

Full text of DOI:10.1016/j.mcat.2020.111119

Molecular Catalysis 494 (2020) 111119
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Porous organic polymer as an efficient organocatalyst for the synthesis of
biofuel ethyl levulinate
a,c
b
c
b
d
Mita Halder , Piyali Bhanja , Md. Mominul Islam , Sauvik Chatterjee , Aslam Khan ,
b,
c,
Asim Bhaumik *, Sk. Manirul Islam *
Department of Chemistry, University of Calcutta, Kolkata, 700009, WB, India
School of Materials Sciences, Indian Association for the Cultivation of Science, 2A & 2B, Raja S. C. Mullick Road, Jadavpur, Kolkata, 700032, India
Department of Chemistry, University of Kalyani, Kalyani, Nadia, 741235, WB, India
a
b
c
d
King Abdullah Institute for Nanotechnology, King Saud University, Riyadh, 11451, Saudi Arabia
A R T I C L E I N F O
A B S T R A C T
Keywords:
Biofuel
Porous organic polymers
Sulfonation
Ethyl levulinate
Organocatalysis
Levulinic acid (LA), a lignocellulosic biomass-derived compound has been recognized as one of the versatile
building blocks for the synthesis of commodity chemicals having biofuel properties together with potential as
precursor for the synthesis of several value-added pharmaceuticals and polymers. Herein, we report the synthesis
of catalytically active functionalized porous organic polymer and its utilization as heterogeneous organocatalyst
for the synthesis of EL from LA in very high yield. Here, sulfonic acid functionalized porous organic polymer
SBZ@POP have been prepared via simple Friedel-Crafts alkylation of benzene with dimethoxymethane followed
by sulfonation of the aromatic rings. The structure and properties of the material was examined through PXRD,
1
3
2 3
N sorption, HR TEM, C CP-MAS NMR, NH -TPD, TG-DTA and FTIR analysis. Our characterization data
suggested nanoscale porosity with high surface acidity in SBZ@POP. The effects of reaction time, catalyst
loading, molar ratio of levulinic acid to ethanol and reaction temperature were studied thoroughly to optimize
the catalytic activity of SBZ@POP. Under optimized reaction conditions EL yield of 88 % has been achieved with
1:15 molar ratio of LA to ethanol under refluxing conditions in 10 h. This porous organic polymer based orga-
nocatalyst displayed good recyclability for consecutive five reaction cycles suggesting the sustainable applica-
tion potential of this acidic organocatalyst.
Introduction
increasing concern to mitigate the problem of greenhouse gases [7]. In
this regard, biofuel offers huge promise to serve as an alternative
Human lives are gradually modernized, civilized and globalized
over the years. With this the gap between the demand and supply for
the energy is gradually increasing [1], which causes high necessity for
the exploration of energy resources as this is one of the primary re-
quirements for our existence. Few decades before the non-renewable
fossil fuels were the only source of our energy. However, since the re-
servoir of these energy sources is limited and thus it could be a massive
disaster to our existence if the issue regarding the exploration of an
alternative renewable energy sources remains neglected for long [2].
Besides, combustion of fossil fuels also produces huge amount of
greenhouse gases that directly causes global warming, one of the big-
gest environmental challenges of our universe. Numerous strategies
have been developed to reduce the concentration of greenhouse gases
present in the atmosphere [3–6]. Among them reduction of the
worldwide dependency on petroleum-based fuels is attracting
feedstock to fossil fuels as this is a renewable source of energy, sus-
tainable and much less polluting as far as emission is concerned [8]. Use
of biofuels is very advantageous as they are nontoxic, free from ha-
zardous components (aromatic entity, sulfur, etc.), easily biodegradable
and also low-emission fuels [9].
Levulinic acid (4-oxopentanoic, LA), has captured an enormous at-
tention over the years as a versatile platform molecule to furnish several
biofuel products, like, ethyl levulinate (EL), methyl tetrahydrofuran, γ-
valerolactone (GVL), etc. [10–16]. Besides, several other chemical in-
termediates, viz., pyrrolidinones, methylene valerolactone, 1,4-penta-
nediol, etc., can also be synthesized form this acid precursor [17–19].
Among the different target molecules having fuel properties, ethyl le-
vulinate (EL) possess unusually high lubricity, high energy density, low
toxicity, stable flash point, moderate flow properties under low tem-
perature conditions, convenient to synthesize under existing
⁎
Corresponding authors.
E-mail addresses: msab@iacs.res.in (A. Bhaumik), manir65@rediffmail.com (S.M. Islam).
https://doi.org/10.1016/j.mcat.2020.111119
Received 27 April 2020; Received in revised form 3 July 2020; Accepted 8 July 2020
2468-8231/ © 2020 Elsevier B.V. All rights reserved.

M. Halder, et al.
Molecular Catalysis 494 (2020) 111119
infrastructure and one of the most demanding additives for liquid
transportation fuels [20]. Moreover, EL is widely used as the building
block to prepare a large diversity of drug molecules and several value-
added products through the chemical transformation at the keto and
ester groups present in the molecule [21,22]. It is also demanding in
fragrance and polymer industry. EL can be synthesized through the
direct acid catalysed esterification reaction between LA and ethanol.
Conventional acid catalysed esterification reactions have encountered
several mechanical as well as technical problems [23]. This is due to the
(3 × 15 mL) with MeOH. Then the solid mass was further washed in a
Soxhlet apparatus using methanol for 2 days to remove any unreacted
linker, benzene and/or iron residue. Finally, the as-synthesized BZ@
POP material was dried under vacuum at 60 °C. The yield of the
polymer BZ@POP was 91 %.
Synthesis of sulfonic acid functionalized POP (SBZ@POP)
For the sulfonation, mixture of BZ@POP (300 mg) and dry DCM
(20 mL) in 100 mL RB flask was placed in an ice bath and stirred for
15 min to make a suspension. Then chlorosulfonic acid (6.5 mL in
10 mL dry DCM) was added dropwise to this pre-cooled reaction mix-
ture under stirring condition [45]. The stirring was continued for next
48 h at room temperature. Then the reaction mixture was slowly poured
in to ice to furnish a deep brown product, that was filtered, washed
several times with cold water to remove excess acid and finally dried
under vacuum to give sulfonic acid functionalized porous organic
polymer (SBZ@POP, 88 % yield). The schematic synthesis of SBZ@POP
is shown in Scheme 2.
use of corrosive homogeneous acid catalysts (conc. H
2 4 3 4
SO [24], H PO
[
25]) in organic solvent, elevated temperature, long reaction time and
expensive instrumental setup, etc., separation and purification of the
product, which reduces the scope of these conventional methods.
Therefore, development of sustainable and eco-friendly catalytic system
with good recyclability is highly desirable. Accordingly, Li et al. have
reported sulfonated pine needle-derived carbon catalysed synthesis of
EL [26]. Cirujano et al. have reported Zr-containing MOF catalysed
esterification to prepare EL [27]. On the other hand, the group of
Trombettoni et al. have reported the synthesis of EL using sulfonated
cation exchange resins in continuous-flow reactor [28]. Although there
are some reports for the use of functionalized porous nanomaterials as
catalyst in the conversion of LA to EL [29–31], but many of these
strategies are associated with drawbacks, like complex catalyst synth-
esis together with the involvement of expensive precursors and low
stability of the catalyst.
General method for the synthesis of ethyl levulinate (EL)
The SBZ@POP material was used as heterogeneous acid catalyst for
the synthesis of EL from LA. The method for this esterification reaction
is discussed in electronic supplementary information (ESI).
In this context synthesis of surface functionalized porous organic
polymer (POP) with high surface area and large number of exposed
active sites have huge potential to be explored as a sustainable orga-
nocatalyst. Recently, our group have developed a number of surface-
functionalized as well as active metal centers bearing porous organic
polymer materials and also studied their catalytic applications in var-
ious organic transformations [32–35]. Porous organic materials being
devoid of any toxic metals have been successfully utilized in catalysis
Recyclability test of SBZ@POP
In order to recycle the catalyst, the conversion of LA to EL has been
performed under optimized reaction conditions (reaction conditions:
40 mg of the SBZ@POP catalyst, 10 h reaction time, refluxing tem-
perature ∼80 °C, molar ratio of LA to ethanol 1:15). After completion in
the reaction, the reaction mixture was centrifuged at 8000 rpm to se-
parate the catalyst from the reaction mixture. Thereafter, the catalyst
was thoroughly washed using ethanol, water, and finally with diethyl
ether. Then the catalyst was dried at 100 °C temperature for 2 h to re-
activate it for the next run.
[
[
36–38], adsorption [39], gas storage [40], separations [41], sensing
42] and many other frontline applications. Recently, sulfonic acid
functionalized carbazole-based monolithic hypercrosslinked polymer
material has been utilized as catalyst for synthesis of levulinate esters
[
43]. Within the scope of this work, herein we report a benzene-based
porous organic polymer (BZ@POP) through Friedel-Crafts alkylation
reaction between benzene and dimethoxymethane followed by surface
sulfonic acid functionalization to obtain sulfonated POP material SBZ@
POP. The material has been characterized thoroughly by using several
instrumental techniques and its catalytic activity have been explored
for the synthesis of ethyl ester of levulinic acid, i.e., ethyl levulinate
Result and discussion
Characterization of SBZ@POP
After synthesis, the porous polymer material SBZ@POP was thor-
oughly characterized. Elemental analysis was recorded to confirm the
elemental composition for C, H and N. Atomic percentages of C and H
were 49.23 and 4.75 %, respectively in SBZ@POP.
(
EL) (Scheme 1).
Experimental section
Nanostructure and surface area
Synthesis of benzene-based porous organic polymers (BZ@POP)
To understand whether there is any periodicity of pores in the SBZ@
POP material powder XRD pattern was recorded. Fig. 1a represents the
PXRD data of the fresh catalyst, which shows that the material is
amorphous in nature with two broad peaks present at 23° and 40° of 2θ.
This amorphous nature of the material remains nearly unchanged after
five reaction cycles (Fig. 1b). Fig. 2 represents the nitrogen gas ad-
sorption-desorption isotherm at 77 K. This isotherm can be classified as
the mixture of type I and IV isotherms [46–48] with H3 type hysteresis
loop. The total BET surface area and pore volume of the polymer have
In order to synthesize the polymer material BZ@POP, 8.0 mmol
benzene and 25 mL anhydrous 1,2-dichloroethane (DCE) were taken in
a 100 mL round bottom (RB) flask. Then after addition of formaldehyde
dimethyl acetal (dimethoxymethane, 16.0 mmol) followed by anhy-
drous FeCl
0 °C temperature under nitrogen atmosphere to complete the reaction
44]. Thereafter, the reaction mixture was cooled to room temperature
and brown coloured mass was collected through filtration and washed
3
(16.0 mmol), the reaction mixture was stirred for 48 h at
8
[
Scheme 1. Synthesis of EL from LA catalysed
by SBZ@POP.
2

M. Halder, et al.
Molecular Catalysis 494 (2020) 111119
Scheme 2. Synthesis of sulfonated porous polymer SBZ@POP.
having size of ∼ 1.2–1.4 nm are spread throughout the whole spe-
cimen. This large size nanopores are good enough for carrying out acid
catalyzed esterification reaction of small organic molecule levulinic
acid for the synthesis of ethyl levulinate. On the other hand, in the
reused SBZ@POP catalyst the individual particles are clearly seen to be
assembled together (Fig. 3b) after five reaction cycles.
Solid state 13C CP-MAS NMR analysis
Further, to confirm the presence of desired organic functional
groups in the polymer as well as the chemical environment of C atoms
corresponding to the different functionalities in SBZ@POP the solid
13
state1 C CP MAS NMR analysis has been performed. As shown in Fig. 4,
3
the C CP MAS NMR spectrum showed strong signals at 35.9 ppm and
the chemical shift further downfield at 130.0, 134.2, 139.1, 147.7 ppm
are attributed to aliphatic and aromatic carbon atoms of the polymeric
network respectively [49,50]. Thus, this solid state 13C CP MAS NMR
spectrum demonstrates the complete polyalkylation of benzene with
dimethoxymethane in the synthesis of porous organic polymer.
Fig. 1. PXRD patterns of SBZ@POP: a: as prepared, b: reused catalyst.
Acidity measurement
In order to calculate the total surface acidic sites in the porous
polymer SBZ@POP condition programmed desorption (NH
lysis has been performed at temperature ramp of 5 °C min from 25 to
00 °C. Initially the sample was subjected for outgassing in U-type glass
cell for 2 h under inert atmosphere. After cool down to room tem-
perature NH gas was purged for 30 min at flow rate of 30 mL/min.
Then helium gas was purged for 45 min to get rid of excess NH gas
3
-TPD) ana-
4
3
3
from the whole system. By increasing the temperature TCD (thermal
conductivity detector) signal was obtained. The TPD profile diagram of
the porous polymer is shown in Fig. 5 where the sharp peak appears at
74 °C due to the existence of surface acidic sites [51] and another broad
peak at 350 °C could be attributed to the decomposition of organic
groups, which agreed well with the TGA data (Fig. 6, shown below).
The total surface acidic sites of the material are estimated to be
−1
1.98 mmol g
.
Fig. 2. N
2
adsorption/desorption isotherm of SBZ@POP, where filled and
Thermal analysis
empty circles represent the adsorption and desorption points, respectively. The
pore size distribution plot estimated by using NLDFT method is shown in the
inset.
Thermogravimetric analysis has been carried out to check the
thermal stability of the porous polymer. Fig. 6a represents the TGA
analysis data, where first weight loss ∼14 % observed up to 102 °C due
to evaporation of surface adsorbed water molecule and second weight
loss starts form 195 °C for slow decomposition of organic functional
groups of the polymeric matrix. Thus TG/DTA results suggested con-
siderably good thermal stability of SBZ@POP.
been estimated as 76 m g−1 and 0.047 cc g−1, respectively. The pore
size distribution plot was obtained by employing non local density
functional theory (NLDFT) method and this is shown in the inset of
Fig. 2. As seen from this plot that this sulfonated porous polymer dis-
played a peak pore size of 1.4 nm, suggesting moderate to good porosity
in nanoscale in the porous polymer material SBZ@POP.
2
FTIR analysis
Microscopic analysis
Fig. 7 represents the FT-IR spectrum of the sulfonated porous
polymer SBZ@POP. The pair of bands nearly at 1489 and 1603 cm
−1
Fig. 3 represents the ultra-high-resolution transmission electron
microscopic images of SBZ@POP. As shown in Fig. 3a, the nanopores
could be allocated for aromatic ring stretching absorption. The vibra-
tion for aromatic C–H out-of-plane bending could be assigned by the
3

M. Halder, et al.
Molecular Catalysis 494 (2020) 111119
Fig. 3. UHR-TEM images of the porous polymer SBZ@POP: a: fresh catalyst, b: reused catalyst.
Fig. 6. TGA (a) and DTA (b) profile diagrams of porous polymer SBZ@POP.
matrix.
Fig. 4. Solid state 13C CP MAS NMR spectrum of porous polymer SBZ@POP.
Synthesis of ethyl levulinate from levulinic acid
Catalytic activity of the sulfonated porous polymer SBZ@POP was
examined in the synthesis of EL from LA under mild liquid phase re-
action conditions. The best optimum reaction condition was obtained
after performing a series of reactions with variation of reaction para-
meters (reaction time, catalyst loading, molar ratio of LA to ethanol,
reaction temperature). Fig. 8a shows the effect of reaction time on the
formation of EL using 30 mg of the catalyst under refluxing temperature
in ethanol. Conversion of levulinic acid increases with increase in re-
action time from 2 to 10 h. Upon further increase in the reaction time,
no further increase in the product formation was observed. This could
be attributed to the diminution of the concentration of LA as well as the
presence of byproduct water in this esterification reaction.
Catalyst loading in the reaction mixture has significant effect in the
esterification of LA and this is illustrated in Fig. 8b. Esterification of LA
is extremely slow (9%) in the absence of catalyst, but increases gra-
dually with the increase in the amount of the catalyst. Loading of the
catalyst was varied from 10 mg to 60 mg. Upon increase in the amount
of catalyst from 20 to 40 mg, yield of the EL increases from 64 to 79 %.
An insignificant change in LA conversion was observed using 50 mg of
catalyst, while further increase in catalyst loading shows a reverse trend
in its activity, because excess concentration of the catalyst causes poor
mass transfer [54]. As esterification reaction is a reversible process,
stoichiometric ratio of LA to ethanol has a great influence in LA con-
version. However, in order to minimize the backword reaction, excess
amount of ethanol should be used to increase the rate of forward
3
Fig. 5. NH -TPD profile diagram of SBZ@POP polymer.
peak near 689 cm 1. The peak near about at 617 cm−1 is due to the
−
−1
stretching for C–S bond [52]. The bands around at 1036 and 1172 cm
are observed because of the symmetric and asymmetric stretching of
O] S]O bonds [53]. Thus, this FTIR spectroscopic results confirmed
3
the successful introduction of the –SO H group in the organic polymer
4

M. Halder, et al.
Molecular Catalysis 494 (2020) 111119
Fig. 7. FTIR spectrum of SBZ@POP material.
reaction. Fig. 8c clearly represent the effect of LA to ethanol molar ratio
of 1:5, 1:10, 1:15 1:20 and 1:25, on the esterification reaction. The yield
of EL increases gradually up to 88 %, when the molar ratio changes
from 1:5 to 1:15. Further increase in molar concentration of ethanol
decreases the LA conversion and this can be explained by the fact that,
high volume of ethanol causes dilution of the reactant as well as the
active sites of the catalyst, thereby hindering the product formation
reaction increases to some extent with the elevation in reaction tem-
perature. It is notable from Fig. 8d that with the increase in the tem-
perature from room temperature (25 °C) to 70 °C, yield of EL raises
significantly from 28 to 83 %. Best result (88 %) was obtained upon
heating the reaction mixture at refluxing temperature of ethanol
(∼80 °C). However, further increase in temperature (100 °C) product
yield decreases. This could be attributed to the evaporation of the sol-
vent at high temperature and thus the availability of liquid ethanol
decreases, which obstructs the easy diffusion of LA to the active sites of
[
55].
As esterification reaction is endothermic in nature, rate of forward
Fig. 8. Effect of reaction parameters on the production of EL from LA over SBZ@POP: a: time scan (1:10 LA to EtOH molar ratio, refluxing temp., 30 mg catalyst), b:
effect of catalyst loading (1:10 LA to EtOH molar ratio, refluxing temp., 10 h time), c: effect of LA to ethanol molar ratio (40 mg catalyst, refluxing temp., 10 h time),
and d: effect of reaction temperature (40 mg catalyst, 1:15 LA to EtOH molar ratio, 10 h time). Error bars originating from standard deviation are incorporated in each
column. The number of replicates for each assay is three.
5

M. Halder, et al.
Molecular Catalysis 494 (2020) 111119
Scheme 3. Proposed mechanistic route for the
synthesis of EL over SBZ@POP.
the catalysts. Thus, the best result in terms of ethyl levulinate yield of
catalytic activity of SBZ@POP was compared with the literature reports
(Table S1). From that table, it is quite clear that our catalyst can provide
comparatively better amount of product in terms of conversion and
selectivity and yield.
88 %, was obtained, when 40 mg of the SBZ@POP was used as catalyst
for 10 h of reaction time under refluxing temperature (∼80 °C) with a
molar ratio of LA to ethanol 1:15. The typical conversion value for the
production of EL from LA under the optimum reaction condition is 91
%
. In our present study we got ethyl levulinate as the soul product,
Conclusion
indicating 100 % selectivity of the reaction.
Our experimental observations suggested that sulfonic acid func-
tionalized porous organic polymer SBZ@POP can be prepared very
conveniently and it showed very good catalytic efficiency for the
synthesis of ethyl levulinate from levulinic acid. The porous polymer
material was characterized thoroughly by different instrumental tech-
niques to understand its framework-bonding and physical properties.
This sulfonic acid functionalized organocatalyst works efficiently under
different reaction conditions like reaction time, catalyst loading, molar
ratio of LA to EtOH and temperature, on the yield of the product EL.
Good recycling efficiency of this sulfonated porous polymer in the li-
quid phase esterification under mild reaction conditions suggested its
future potential as solid acid catalyst for the synthesis of various biofuel
products.
Probable mechanism for the synthesis of ethyl levulinate
The proposed mechanistic pathway for the synthesis of EL could be
described as a general Fischer esterification reaction. The schematic
diagram is presented by Scheme 3 in the presence of SBZ@POP orga-
nocatalyst. LA first get protonated in the presence of labile protons of
3
the –SO H group present in SBZ@POP to give the LA intermediate X.
Then nucleophilic oxygen of EtOH attacked to the electrophilic center
of the LA intermediate X. Thereafter, removal of water molecule furn-
ished the corresponding ester ethyl levulinate, giving back the polymer
catalyst [56].
Recyclability of the SBZ@POP polymer catalyst
CRediT authorship contribution statement
Recyclability is the key-characteristic of a heterogeneous catalyst.
To check the stability of our sulfonated porous polymer catalyst, PXRD
and TEM analysis were performed with the reused catalyst after 3rd and
Mita Halder: Investigation, Methodology, Formal analysis. Piyali
Bhanja: Investigation, Methodology, Formal analysis. Md. Mominul
Islam: Methodology, Formal analysis. Sauvik Chatterjee:
Methodology, Formal analysis. Aslam Khan: Formal analysis. Asim
Bhaumik: Supervision, Conceptualization, Methodology, Writing - re-
view & editing. Sk. Manirul Islam: Supervision, Conceptualization,
Methodology, Writing - review & editing.
4th run. The PXRD pattern (Fig. 1b) showed no significant change in the
nature of the material after 3rd run. From the TEM images (Fig. 3b)
taken in high resolution showed retention of particle morphology and
porous nanostructure of SBZ@POP after 4th cycles. The microporosity
was found to be present. The EDX data confirms the elemental ratio to
be nearly same as fresh catalyst which indicates integrity of the catalyst
has been unaltered during the catalytic reactions. EDX data of the fresh
catalyst and reused catalyst (4th cycles) are given in supporting in-
formation (Fig. S2). In Fig. 9 we have plotted the EL yields over SBZ@
POP catalyst for successive five reaction cycles. As seen from this image
that only little decrease in the EL was observed over this sulfonated
porous polymer. Thus, our catalytic data suggested that SBZ@POP is an
efficient solid acid catalyst for the synthesis of biofuels. Moreover,
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgments
SMI thankfully acknowledges the Department of Science and
Technology, DST-SERB (project reference no. EMR/2016/004956),
New Delhi, Govt. of India, the Board of Research in Nuclear Sciences
(
BRNS), Project reference No: 37(2)/14/03/2018-BRNS/37003, Govt.
of India and Council of Scientific and Industrial and Research, CSIR
project reference no 02(0284)2016/EMR-II dated 06/12/2016), New
(
Delhi, Govt. of India for providing financial support. MH and MMI
acknowledge UGC for providing MH and MMI acknowledge UGC for
provid, respectively. PB acknowledges CSIR, New Delhi for providing
CSIR-SRF. AK thanks the Researchers Supporting Project (Grant no.
RSP-2019/127), King Saud University, Riyadh, Saud Arabia for fi-
nancial support. We sincerely acknowledge the DST and UGC, New
Delhi, Govt. Of India, for providing grant under FIST, PURSE and SAP
program to the Department of Chemistry, University of Kalyani. AB
acknowledges DST-SERB, New Delhi for a core research grant (file no.
CRG/2018/000230).
Fig. 9. Recycling efficiency of SBZ@POP in the synthesis of ethyl levulinate
(reaction condition: 40 mg of the SBZ@POP catalyst, 10 h reaction time, re-
fluxing temperature (∼80 °C), molar ratio of LA to ethanol 1:15).
6

M. Halder, et al.
Molecular Catalysis 494 (2020) 111119
Appendix A. Supplementary data
[29] Z.M. Xue, Q.L. Liu, J.F. Wang, T.C. Mu, Green Chem. 20 (2018) 4391–4408.
[
30] M. Popova, P. Shestakova, H. Lazarova, M. Dimitrov, D. Kovacheva, A. Szegedi,
G. Mali, V. Dasireddy, B. Likozar, N. Wilde, R. Glaser, Appl. Catal. A: Gen. 560
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2020.111119.
(
2018) 119–131.
[31] S. Gadamsetti, N. Mathangi, S. Hussain, V.K. Velisoju, K.V.R. Chary, Mol. Catal. 451
2018) 192–199.
(
[
[
[
32] S.S. Islam, S. Riyajuddin, R.A. Molla, N. Yasmin, K. Ghosh, S.M. Islam, New J.
Chem. 44 (2020) 1979–1987.
33] S.S. Islam, N. Salam, R.A. Molla, S. Riyajuddine, N. Yasmin, D. Das, K. Ghosh,
S.M. Islam, Mol. Catal. 477 (2019) 110541–110551.
34] S. Ghosh, S. Riyajuddin, S. Sarkar, K. Ghosh, S.M. Islam, ChemNanoMat 6 (2020)
160–172.
References
[1] G.J. Kramer, M. Haigh, Nature 462 (2009) 568–569.
[
2] D. Tilman, R. Socolow, J.A. Foley, J. Hill, E. Larson, L. Lynd, S. Pacala, J. Reilly,
T. Searchinger, C. Somerville, R. Williams, Science 325 (2009) 270–271.
3] A.E. Farrell, R.J. Plevin, B.T. Turner, A.D. Jones, M. O’Hare, D.M. Kammen, Science
[
[
[35] T.K. Dey, P. Bhanja, P. Basu, A. Ghosh, S.M. Islam, ChemistrySelect 4 (2019)
14315–14328.
[36] J. Schmidt, D.S. Kundu, S. Blechert, A. Thomas, Chem. Commun. 50 (2014)
3
11 (2006) 506–508.
4] T.Z. Lei, Z.W. Wang, X. Chang, L. Lin, X.Y. Yan, Y.C. Sun, X.G. Shi, X.F. He, J.L. Zhu,
Energy 95 (2016) 29–40.
3
347–3349.
[
[
[
[
[
5] P. Bhanja, A. Modak, A. Bhaumik, Chem. Eur. J. 24 (2018) 7278–7297.
6] L.P. Da Silva, Mol. Catal. 474 (2019) UNSP 110425.
7] H.J. Berchmans, S. Hirata, Bioresour. Technol. 99 (2008) 1716–1721.
8] A. Demirbas, Energy Convers. Manage. 50 (2009) 14–34.
9] S. Murillo, J.L. Miguez, J. Porteiro, E. Granada, J.C. Moran, Fuel 86 (2007)
[37] E. Verde-Sesto, M. Pintado-Sierra, A. Corma, E.M. Maya, J.G. De la Campa,
M. Iglesias, F. Sanchez, Chem. Eur. J. 20 (2014) 5111–5120.
[38] K. Huang, J. –Y. Zhang, F. Liu, S. Dai, ACS Catal. 8 (2018) 9079–9102.
[39] A. Modak, M. Nandi, J. Mondal, A. Bhaumik, Chem. Commun. 48 (2012) 248–250.
[
40] R.L. Martin, C.M. Simon, B. Smit, M. Haranczyk, J. Am. Chem. Soc. 136 (2014)
1
765–1771.
5006–5022.
[
41] H.A. Patel, S.H. Je, J. Park, Y. Jung, A. Coskun, C.T. Yavuz, Chem. Eur. J. 20 (2014)
[10] S.M. Kang, J.X. Fu, G. Zhang, Renew. Sustain. Energy Rev. 94 (2018) 340–362.
[11] L. Filiciotto, A.M. Balu, J.C. Van der Waal, R. Luque, Catal. Today 302 (2018) 2–15.
[12] G. Metzker, A.C.B. Burtoloso, Chem. Commun. 51 (2015) 14199–14202.
[13] J. Zhou, R. Zhu, J. Deng, Y. Fu, Green Chem. 20 (2018) 3974–3980.
[14] T. Mizugaki, K. Togo, Z. Maeno, T. Mitsudome, K. Jitsukawa, K. Kaneda, ACS
Sustainable Chem. Eng. 4 (2016) 682–685.
772–780.
[42] J.L. Novotney, W.R. Dichtel, ACS Macro Lett. 2 (2013) 423–426.
[43] M.M. Islam, S. Bhunia, R.A. Molla, A. Bhaumik, S.M. Islam, ChemistrySelect 1
(2016) 6079–6085.
[
44] R.T. Woodward, L.A. Stevens, R. Dawson, M. Vijayaraghavan, T. Hasell,
I.P. Silverwood, A.V. Ewing, T. Ratvijitvech, J.D. Exley, S.Y. Chong, F. Blanc,
D.J. Adams, S.G. Kazarian, C.E. Snape, T.C. Drage, A.I. Cooper, J. Am. Chem. Soc.
136 (2014) 9028–9035.
[
[
[
15] G.Q. Li, H.H. Yang, M. Cheng, W. Hu, L.H. Tian, W.X. Mao, R.F. Nie, Mol. Catal. 455
(2018) 95–102.
16] M.P. Pachamuthu, V.V. Srinivasan, R. Karvembu, R. Luque, Microporous
Mesoporous Mater. 287 (2019) 159–166.
17] Y. Wei, C. Wang, X. Jiang, D. Xue, J. Li, J. Xiao, Chem. Commun. 49 (2013)
[45] W. Lu, D. Yuan, J. Sculley, D. Zhao, R. Krishna, H.-C. Zhou, J. Am. Chem. Soc. 133
2011) 18126–18129.
[46] D. Chandra, A. Bhaumik, J. Mater. Chem. 19 (2009) 1901–1907.
(
5
408–5410.
[
47] S. Dutta, A. Patra, S. De, A. Bhaumik, B. Saha, ACS Appl. Mater. Interfaces 4 (2012)
[18] L.E. Manzer, Appl. Catal. A: Gen. 272 (2004) 249–256.
[19] M. Li, G. Li, N. Li, A. Wang, W. Dong, X. Wang, Y. Cong, Chem. Commun. 50 (2014)
1560–1564.
1
414–1416.
20] Z.W. Wang, T.Z. Lei, L. Liu, J.L. Zhu, X.F. He, Z.F. Li, BioResources 7 (2012)
972–5982.
[48] C. Xu, Z. Bacsik, N. Hedin, J. Mater. Chem. A 3 (2015) 16229–16234.
49] A. Modak, J. Mondal, A. Bhaumik, Appl. Catal. A: Gen. 459 (2013) 41–51.
[
[
5
[50] M. Okamura, A. Takagaki, M. Toda, J.N. Kondo, K. Domen, T. Tatsumi, M. Hara,
S. Hayashi, Chem. Mater. 18 (2006) 3039–3045.
[51] S. Mondal, J. Mondal, A. Bhaumik, ChemCatChem 7 (2015) 3570–3578.
[52] W.Y. Lou, Q. Guo, W.J. Chen, M.H. Zong, H. Wu, T.J. Smith, ChemSusChem 5
(2012) 1533–1541.
[21] Z. Yang, Y.B. Huang, Q. Guo, Y. Fu, Chem. Commun. 49 (2013) 5328–5330.
[22] F. Su, L. Ma, D.Y. Song, X.H. Zhang, Y.H. Guo, Green Chem. 15 (2013) 885–890.
[23] M.G. Kulkarni, R. Gopinath, L.C. Meher, A.K. Dalai, Green Chem. 8 (2006)
1
056–1062.
[
[
24] J.M. Marchetti, A.F. Errazu, Biomass Bioenergy 32 (2008) 892–895.
25] D.A.G. Aranda, R.T.P. Santos, N.C.O. Tapanes, A.L.D. Ramos, O.A.C. Antunes, Catal.
Lett. 122 (2008) 20–25.
[53] S. Suganuma, K. Nakajima, M. Kitano, S. Hayashi, M. Hara, ChemSusChem 5 (2012)
1
841–1846.
[54] M.L. Tao, H.Y. Guan, X.H. Wang, Y.C. Liu, R.F. Louh, Fuel Process Technol. 138
2015) 355–360.
(
[26] N. Li, X.‑L. Zhang, X.‑C. Zheng, G.‑H. Wang, X.‑Y. Wang, G.‑P. Zheng, Catal. Surv.
Asia 23 (2019) 171–180.
[55] Q. Shu, J.X. Gao, Z.S. Nawaz, Y.H. Liao, D.Z. Wang, J.F. Wang, Appl. Energy 87
[
[
27] F.G. Cirujano, A. Corma, F.X.L. Xamena, Chem. Eng. Sci. 124 (2015) 52–60.
28] V. Trombettoni, L. Bianchi, A. Zupanic, A. Porciello, M. Cuomo, O. Piermatti,
A. Marrocchi, L. Vaccaro, Catalysts 7 (2017) 235–248.
(2010) 2589–2596.
[
56] D. Song, S. An, B. Lu, Y. Guo, J. Leng, Appl. Catal. B: Environ. 179 (2015) 445–457.
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