Topotactic transformation of homogeneous phosphotungastomolybdic acid materials to heterogeneous solid acid catalyst for carbohydrate conversion to alkyl methylfurfural and alkyl levulinate

Article abstract of DOI:10.1039/c9ra03300a

The strong interaction of higher transition metal oxides with inorganic non-metals can be promising for generating highly acidic three-dimensional materials by design. A comprehensive controlled acidity of heteropolyacid-like catalyst and interpretation of the microstructure and mechanism of the formation of a versatile heterogeneous solid acid catalyst, HPW₄Mo₁₀O_x has been heterogenized by biomass-derived cystine as organic linkers to control the acidity of as-synthesized materials, which have greater acidity and complexity in separation from the reaction mixture. The new and unique results obtained in catalysis done in biphasic reaction. Cystine binds to the surface of HPW₄Mo₁₀O_x, and the topotactic transition occurred, change the morphology and lattice parameter. We described here a sustainable transformation of highly acidic (0.84 mmol g^-1) heteropoly acid (HPW₄Mo₁₀O_x) to cystine anchored on the active surface of the heteropoly acid and controlled the acidity (0.63 mmol g^-1) and heterogenized the materials. As synthesized materials have been showing that for the direct formation of alkyl levulinate and furanics intermediate from carbohydrates. HPW₄Mo₁₀O_x and HPW₄Mo₁₀O_x-Cys, act as acidic catalyst, and catalyse the mono- and disaccharides that are dissolved in primary and secondary alcohols to alkyl levulinate (AL) and alkyl methylfurfural at 170 °C under microwave irradiation with glucose as the substrate, AL yield reaches 62% with 84.95% selectivity. The catalyst can be easily recovered by filtration and minimum five times reused after calcination without any substantial change in the product selectivity. The analytical analysis of as-synthesis materials done by NH₃-TPD, BET, XRD, FESEM, TEM, HRTEM, FTIR, ATR, TGA, DTA to stabilized the morphology and acidity controlled mechanism.

Full text of DOI:10.1039/c9ra03300a

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Topotactic transformation of homogeneous
phosphotungastomolybdic acid materials to
heterogeneous solid acid catalyst for carbohydrate
conversion to alkyl methylfurfural and alkyl
levulinate†
Cite this: RSC Adv., 2020, 10, 705
*
*
and Kamal K. Pant
Dinesh Gupta,
Chandrakant Mukesh
The strong interaction of higher transition metal oxides with inorganic non-metals can be promising for
generating highly acidic three-dimensional materials by design. A comprehensive controlled acidity of
heteropolyacid-like catalyst and interpretation of the microstructure and mechanism of the formation of
a versatile heterogeneous solid acid catalyst, HPW4Mo10Ox has been heterogenized by biomass-derived
cystine as organic linkers to control the acidity of as-synthesized materials, which have greater acidity
and complexity in separation from the reaction mixture. The new and unique results obtained in catalysis
done in biphasic reaction. Cystine binds to the surface of HPW4Mo10Ox, and the topotactic transition
occurred, change the morphology and lattice parameter. We described here a sustainable transformation
of highly acidic (0.84 mmol gꢀ1) heteropoly acid (HPW4Mo10Ox) to cystine anchored on the active
surface of the heteropoly acid and controlled the acidity (0.63 mmol gꢀ1) and heterogenized the
materials. As synthesized materials have been showing that for the direct formation of alkyl levulinate
and furanics intermediate from carbohydrates. HPW4Mo10Ox and HPW4Mo10Ox-Cys, act as acidic
catalyst, and catalyse the mono- and disaccharides that are dissolved in primary and secondary alcohols
to alkyl levulinate (AL) and alkyl methylfurfural at 170 ꢁC under microwave irradiation with glucose as the
substrate, AL yield reaches 62% with 84.95% selectivity. The catalyst can be easily recovered by filtration
and minimum five times reused after calcination without any substantial change in the product
selectivity. The analytical analysis of as-synthesis materials done by NH3-TPD, BET, XRD, FESEM, TEM,
HRTEM, FTIR, ATR, TGA, DTA to stabilized the morphology and acidity controlled mechanism.
Received 3rd May 2019
Accepted 18th November 2019
DOI: 10.1039/c9ra03300a
rsc.li/rsc-advances
hydrolysis of cellulosic biomass by mineral acid or enzymatic
pathways, which also renders the alkyl levulinate synthesis
more sustainable.3 Commercial active catalysts usually involve
1. Introduction
Replacement of mineral acids, costly heterogeneous metal
oxides and precious acidic ionic liquids by low-cost non-noble
solid acid catalysts for the selective dehydration and rehydra-
tion of carbohydrates to alkyl levulinates and furanic interme-
diates holds tremendous promise for the clean and carbon
neutral synthesis of biofuels and chemicals.1 Future unpre-
dictable crude fossil fuels prices have stimulated interest in
biomass-based fuels and chemicals synthesis as an alternative
means to catalytically convert over functionalized carbohydrates
(hexose and pentose sugars) into less oxygenated furanic fuels
and chemicals.2 Glucose and fructose can be produced by the
mineral acids (HCl, H2SO4), dual acidic metal catalysts,4,5 metal
salts6 and ionic liquids7 at a higher temperature. The thermal
instability of carbohydrates is a major hurdle in this regard, and
enzymatic hydrolysis,8 have been widely used because of their
utility at low temperature. However, separation and cost of the
enzyme is a major setback. On the other hand, specic and
controlled materials synthesis, oen improved process design,
open the new route in higher product yield and selectivity at
reduced costs of reaction. There are enormous opportunities for
the design and synthesis of acidity controlled catalytic materials
for the sustainable development of fuels and chemicals.9
Fossil-based petroleum products are currently major,
gigantic players in chemicals industry for the synthesis of
chemicals, fuels, and materials. However, pose foremost
concerns in long smoothly future utilization due to day-by-day
depletion of limited fossil resources and increasing energy
demands, create huge pressure on fossil-based chemicals and
Chemical Engineering, Indian Institute of Technology Delhi, New Delhi 110 016, India.
E-mail: kkpant@chemical.iitd.ac.in; dineshguptagkp@gmail.com
† Electronic supplementary information (ESI) available: EPMA elemental analysis
data of as-synthesis materials, TEM-EDX analysis data, SEM, TEM images at
different magnication, and NMR spectra of products. See DOI:
10.1039/c9ra03300a
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fuels market.10 The search for alternative and sustainable being proposed advantages over homogeneous highly active
energy is of crucial importance with the ever-growing pop- HPA catalyst. In this research work, we investigated the
ulation with increasing energy demands and environmental biomass-based cystine as effective linkers and binders for the
concerns, together with the limited reservoir of fossil fuels controlling the acidity and preparation of heterogeneous HPA
reserves.11 This is rise issued to the utilization of other based materials for the selective conversion of alkyl levulinate
sustainable and renewable substrate as an alternative to fossil and other furanics intermediate.
fuels and chemicals. In this regards, lignocellulosic biomass,
The effectiveness of group 6 metal chlorides, CrCl3-medi-
attract much more attention as an alternative to fossil fuels and ated microwave irradiation of cellulose and glucose, in IL as
chemicals. Direct utilization of lignocellulosic biomass has solvent explored by many previous articles and claimed to be
hurdles of its over-functionality and excess of oxygen. In this energy-efficient and cost-effective for the conversion of
regards chemist and engineered designed environmentally biomass into platform chemicals and fuels additive.24
sound reaction-design, cost-effective, and energy saving and Brønsted acidic ionic liquids were used for HMF production
atom efficiency chemical processes.12 Design of such type of from fructose.25 But, the hazardous nature of CrCl3 is a most
process, catalyst always lined center-point to minimized the signicant issue to utilization as a catalyst. Chan et al.
hazardous waste, increased the atom-efficiency and selectivity explored lower group-6 metal chlorides (WCl6) with anionic
of product in an energy-efficient manner. Given these parame- liquid in the biphasic solvent system at very low temperature
ters, research endeavors directed towards utilization of metal (room temperature to 50 ꢁC) to HMF synthesis.26 Recently
salt as catalysts,13,14 but non-separation and hazardous impact molybdenum incorporated catalyst effectively explored for
on the environment is a major hurdle to effective utilization in biomass conversion to value-added chemicals and fuels.27,28
the industry.
However, many possible inorganic materials and a metal oxide
Recently heteropoly acid (HPA) materials attract more that consist of three or more elements are still mislaid from
attention as solid acid catalysts possess and show strong previously available research articles. A few of these materials
Brønsted acidity.15 Studies at molecular level show that it have composition are mislaid because they have not been prepared
unique physicochemical properties, with their structural yet, whereas others are mislaid because of the inconsistent
mobility and multi-functionality nature, these make it an ideal into competing phases.29 Oluwafemi et al.30, used L-cysteine
catalyst for the biofuels industry.16 Due to their higher acidity, ethyl ester hydrochloride as a capping agent for the synthesis
and tunable acidic properties these are classied as a super of colloidal CdSe nanoparticles. Mntungwa31 et al. investigated
acid17 because of its strong Brønsted acidity it showed vast the effect of capping agent (L-cysteine ethyl ester hydrochlo-
application to acid catalysed reactions, HPA has attracted much ride) on the size, structure, and morphology of the as-
interest. However, a key challenge that is oen encountered is synthesized nanoparticles. Rahme32 et al. reported that
stabilization of HPA in the reaction medium and its higher synthesis of AuNPs in the presence of L-cysteine methyl ester
activity. It is reported that the initial heat of ammonia adsorp- hydrochloride as a capping agent and stored materials for 12
tion was about 200 kJ molꢀ1 for H3PW12O40, which is much months no signicant changes observed and reported high
higher than HZSM-5 and SiO2–Al2O3 catalyst.17 HPA function- stability of the colloidal solution. These above ndings indi-
alized with surface ligands can control the physical as well as cate that the interesting properties of cysteine can be
chemical properties of the resulting materials and tuned the successfully applied toward capping agent for heterogeniza-
acidity, heterogeneity, composition, and size of the material. tion of materials. The several hetrogeneuous and homoge-
Moreover, the ligand interactions between active catalytic site neous catalyst were reported for the preparation of AL, AMF
can be used to control the acidity and interparticle distance and and their derivatives from cellulose or biomass derived
lattice symmetry.18,19 Another strategy is to anchor active metal building block molecules.33–35 Magnetically recyclable carbo-
center on a support with a stronger metal-support interaction. naceous solid acid was used for syntheis of 5-ethox-
Previously, several many organmetallic20 as well as nano- ymethylfurfural (EMF) from carbohydrates.36 Zhang et al. were
materials were loaded with HPA and used as an anchored used aluminum-based mixed-acid to intensify the yield of
homogeneous catalyst for selective hydrogenation.21 Many EMF.37 ALs ned application in different sectors of the
nano-particles are modied with HPA and used as an active chemical industry, like biofuels additives, bio-solvents, an
catalyst for organic synthesis. TiO2 was modied with poly- additive for odorous, plasticizing agent and as building blocks
oxotungstates and used as photo-catalyst for dye degradation.22 for various chemical transformations.4,6,9,38 AMF not only
Zhang et al. used phosphomolybdic acid for stabilizing and decreases the boiling point but also preserving an increased
synthesis of a platinum single-atom catalyst and used as the caloric value.39 Levulinic acid (LA), methyl levulinate
hydrogenation catalyst.23 Furthermore, by selecting and (ML), ethyl levulinate (EL), propyl levulinate (PL) and butyl
manipulating the surface properties of HPA, it would be levulinate (BL) have a potentially versatile building block for
possible to control the size and shape of the resulting hetero- the synthesis of several other chemicals and excellent fuel
geneous materials. The potential for controlling the acidity by additives properties.40 As reported, EMF is an excellent fuel
cystine a biomass fraction, in combination with the hetero- additive for diesel with high energy density (8.7 kW h Lꢀ1),
genization of HPA materials, increases the “green” credentials similar to gasoline (8.8 kW h Lꢀ1), diesel (9.7 kW h Lꢀ1) and
of the catalytic reaction process, with higher selectivity, higher than ethanol (6.1 kW h Lꢀ1).41 Lew et al. reported
conversion, and yield of desired product. The catalyst recovery similar energy density of EMF 30.3 MJ Lꢀ1 (8.42 kW h Lꢀ1) and
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other fuels like gasoline 31.1 MJ Lꢀ1 (8.64 kW h Lꢀ1), diesel solution, aer addition of ꢂ5 mL, white colour disappeared,
33.6 MJ Lꢀ1 (9.34 kW h Lꢀ1) and ethanol 23.5 MJ Lꢀ1 (6.53).42 In then continuous addition, colourless solution obtained, the
the NREL technical report mentioned the energy density of EL nal
solution
composition
is
1 : 4 : 10
24.8 MJ kgꢀ1 and butyl levulinate is 27.1 MJ kgꢀ1, which is (K2HPO4 : Na2WO4$2H2O : Na2MoO4$2H2O). In colorless solu-
show vast potential of this biomass-derived oxygenates to use tion, one drop chilled H2SO4 added green precipitate formed,
as alternative fuels.43 Currently, there were several methods of aer shaking green precipitate dissolved, then continuous
the preparation of EMF and EL reported. It is undoubted that dropwise added till the green-yellowish precipitate persist. Aer
the etherication of the hydroxyl group in HMF or furfuryl that nitrogen gas was passed at the bottom for 1 h, then ltered
alcohol with ethanol is the effective route. However, the and washed with water followed by washing with methanol and
ꢁ
economical, selective and practically large-scale process of drying under vacuum in the presence of nitrogen at 120 C. As
EMF or AMF from HMF is limited due to the high production prepared materials is denoted as HPW4Mo10Ox.
and separation cost of HMF. The motivation of this work is to
(ii) Preparation of HPW4Mo10Ox-Cys: for the synthesis of
explore the composition of mislaid materials composition and HPW4Mo10Ox, with a controlled acidity and heterogenization, L-
controlling the acidity of prepared materials by using cysteine ethyl ester hydrochloride was used as a binder. In
a renewable binder. This preparation of materials in the eld a typical synthesis of HPW4Mo10Ox-Cys, step 1 and step 2 are
of catalysis-synthetic solid acid chemistry is also important same as HPW4Mo10Ox only here ammonium molybdate used as
because of the vast potential to controlled the selectivity of a precursor in place of sodium molybdate. In step 2, 1.5
desired products and easily separately by reaction mixture.
equivalent of L-cysteine ethyl ester hydrochloride dissolved in
Understanding the basic properties of heteropoly acids and 20 mL (olyal alcohol and oleic acid 1 : 1 v/v) added drop-wise
capping of ligands will help in developing new types of solid and reaction mixture stirred at room temperature to 240 ꢁC,
acid materials with improved properties which should lead to, colour change yellow then 2 mL distil water added, reddish-
for example, dehydration, etherication and hydrogenolysis brown precipitate obtained, 0.5 mL chilled H2SO4 added as
more effectively, more selectively and more efficiently. These precipitating agent, and more precipitate obtained, separated
should be capable of efficient dehydration and etherication of by aꢁcetone, lter and wash with water and methanol, dry at
carbohydrate to biofuels which could help us in our future 250 C and labelled as HPW4Mo10Ox-Cys.
design of biobased fuels and chemicals at moderate cost and
environmentally friendly manner.
2.3 Characterization
Powder XRD patterns of the as-synthesized materials were
collected room temperature with a Phillips X Pert diffractom-
2. Experimental section
2.1 Materials
˚
eter PW 1390 Cu-Ka radiation (l ¼ 1.54056 A) source operating
at 40 kV and 30 mA. The dry powder was spread on the top of
All chemicals were of analytical purity and used without puri-
a glass substrate and was then measured in the reection
cation. Sucrose, fructose, glucose, xylose, were purchased from
Fisher Scientic Chemicals (India) and used as received. DMSO-
d6, CDCl3, 5-hydroxymethylfurfural, furfural, furfuryl alcohol,
geometry. Transmission Electron Microscopes (TEMs) and
high-resolution transmission electron microscopes (HRTEM)
were performed with a JEOL 120 kV equipped with LaB6/
levulinic acid, ethyl levulinate are purchased from Sigma-
tungsten laments and the FEI Tecnai TF20, at accelerating
Aldrich chemicals, India with high purity and used as
received. Methyl isobutyl ketone (MIBK), tetrahydrofuran (THF),
ethanol, methanol, 2-propanol, n-butanol are purchased from,
Merck chemical India, K2HPO4 from Qualigens, Na2WO4$2H2O
from a Central Drug House, and Na2MoO4$2H2O from Merck,
India, purchased.
voltage of 200 kV respectively. Samples suitable for TEM
observation were prepared by applying one tiny drop of soni-
cated materials onto the carbon coated Cu grid and allowing the
solvent to slowly evaporate at room temperature. Scanning
electron micrographs (SEMs) for as synthesis materials were
obtained with a Zeiss EVO 50 & EVO 18 and Field Emission
Scanning Electron Microscope (FESEM) with an FEI Quanta
2.2 Material preparation
200. Nitrogen adsorption isotherms were obtained with
Two types of heteropoly acidic materials prepared (i), HPW4- a Micromeritics ASAP 2010 at 77 K. Fourier transform infrared
Mo10Ox and (ii) HPW4Mo10Ox-Cys was prepared in a two-step. In spectroscopy (FTIR) spectra of as-synthesized materials were
rst step 1 equivalent dehydrated K2HPO4 dissolved in 50 mL recorded with a Fisher Scientic Nicolet iS50 spectrophotom-
hot water, labeled solution (A). In another 100 mL glass jacket, 4 eter (2 cmꢀ1 resolution and 32 scans) in dried KBr pellets and
equivalent of Na2WO4$2H2O dissolved in 50 mL hot water and a measuring range of 400–4000 cmꢀ1. For the total acidity
labeled solution (B). Solution (B), dropwise added in solution calculation of as-synthesis materials were measured by NH3-
(A) and stirred for 5 min at the hot condition, then cool the TPD analysis was performed on Micromeritics, ChemiSorb 2720
reaction mixture in an ice bath, then 2.5 mL concentrated set-up equipped with a thermal conductivity detector. Surface
H2SO4 added as precipitating agent. Aer addition of H2SO4, area of sample was determined by BET principle and pore
white precipitate form. In second step 10 equivalent of Na2- parameters of the samples were determined by BJH method
MoO4$2H2O dissolved in 60 mL distil water, stirred at room with the help of Micrometrics ASAP 2010 at 77 K. Raman
temperature for 5 min, then dropwise added in the rst step analysis was done with a Renishaw inVia Raman Microscope
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spectrometer equipped with a laser beam emitting at 514 and place of mineral acid, metal particles, both as core–shell
785 nm. 1H and 13C NMR done by Bruker Avance AV-III with 400 structures or embedded in matrices, since the HPW4Mo10Ox-
MHz spectrometers.
Cys gives an extra degree of freedom to control and tailor the
acidic properties.
The L-cysteine ethyl ester hydrochloride was capped on the
HPW4Mo10Ox surface aer the synthesis ofHPW4Mo10Ox. As
synthesis, catalyst showed 140–170 nm outer cores with 600–
700 nm total materials size. As-synthesis material was
composed of nano-sized MoOx, WOx, and incorporated with
phosphorous and hydrogen determined by various techniques
before and aer the capping the cysteine at the surface trans-
formation. Characterization of as-synthesized materials from
TEM and HRTEM are shown in Fig. 1, offered direct visualiza-
tion of the morphology of the as synthesis materials, which
looks like core–shell type of morphology adopted by materials.
The HPW4Mo10Ox possessed reproducibly uniform size and
shape materials; the low-magnication TEM (Fig. 1c, 4 mm)
image indicates excellent particle uniformity. The electron
contrast between the cores and shells in the high-resolution
(Fig. 1d, 100 nm) and insect of Fig. 1a and b, conrms the
formation of hollow particles. The SEM image is shown in
Fig. 1a and 1b (inset) demonstrates that the as-synthesis
materials adopted hollow-core–shell morphology and could be
prepared. Both the SEM image at a higher magnication (Fig. 1a
and b) and TEM image (Fig. 1d) reveal that the hollow-core–
shell were uniform in diameter and closed pack in arrangement
during the sample preparation. To examine the morphology of
2.4 Performance of as-synthesis catalyst in a microwave
reactor
The dehydration and etherication reactions of mono-sugars
were carried out by charging substrates, solvent, and catalyst
in a 10 mL and 100 mL Teon tube tted in the ceramic jacket,
microwave tubes. The loaded microwave tube was closed then
inserted into the programmable multiwave pro microwave
reactor and set the desired reaction temperature and time. Aer
completion of the reaction at the desired time opened and
reaction mixture rstly ltered with whatman lter paper and
separated the catalyst. For GC and HPLC analysis, solutions
were ltered through a 0.22 mm cut of syringe lter. The
quantication of the reaction product, reaction mixture
analyzed by GC and HPLC in the presence of internal standard
and purity of product conrmed by 1HNMR, using mesitylene as
an internal standard.
3. Results and discussion
3.1 Ligand exchange-induced phase transformation of
homogeneous HPW4Mo10Ox into heterogeneous
HPW4Mo10Ox-Cys
To reveal the nature of active sites that favor the selective as-synthesized materials, without capping agent and aer the
dehydration-rehydration and etheried products, multiple capping, results show in Fig. 1 and 2. Interestingly particles of
characterizations techniques were used to investigate the two different morphologies with different sizes have been
functionality and structure of the multifunctional catalyst. Aer observed. Large hexagonal hollow (3D) with average diameter
using the capping agent cystine, change the number of active 0.6–0.7 mm (edge to edge) and thickness of wall ꢂ150 nm are
acidic sites of as-synthesized materials, which enhances the seen in Fig. 1a. However, the as-synthesized HPW4Mo10Ox-Cys
selectivity of the desired product. Our approach to hetero- is small in diameter and quasi-rhombus in morphology (Fig. 2).
genized and controlling the acidity of HPA affords various The average particle diameter of these nanoparticles is 25 nm.
advantages compared to conventional heterogeneous catalysis: cystine as capping agent favors the formation of thermody-
(i) the catalyst system can show greater reactivity and selectivity namically more stable shape, stability in nature.
like a homogeneous catalyst; (ii) unlike most homogeneous
When L-cysteine ethyl ester hydrochloride used as capping
catalysts with comparable performance, the heterogenized agent with oleyl alcohol and oleic acid, ꢂ28 times size of metal
HPW4Mo10Ox-Cys can be easily recycled; (iii) signicantly particles reduce as shown in Fig. 2. Similar nanoparticle size
enhanced the selectivity of the desired product and stopped the was observed as previous report.31 Fig. 2 shows TEM images of
rehydration of furanics. Herein, we provided future direction as-synthesized HPW4Mo10Ox-Cys particles capped with
for the heterogenization of HPA and it used for the efficient cysteine. Fig. 2c–e show that cysteine capped HPW4Mo10Ox
solid acid catalyst. Cysteine has active amine functional group particles are quasi-rhombus, with an average size 25 nm. The
to be bound to the acidic sites and control the acidity and also corresponding some high-resolution TEM image (Fig. 2c and d)
heterogenization the materials. The deposition and anchoring of the cysteine capped HPW4Mo10Ox nanoparticles, reveals the
of cystine on the active sites of HPW4Mo10Ox resulted from the lock-key like an adaptation of materials. TEM images of the
ionic interaction between the amine groups of cysteine with HPW4Mo10Ox-Cys (Fig. 2) easily visible that the metal particles
a metalcenter. This interaction prevented the leaching of metal embedded by the capping agent. Electron prove-micro analysis
in the reaction mixture even under hot-liquid phase reaction (EPMA) and energy dispersive X-ray analysis (EDX) enabled
condition under microwave irradiation. The supported material quantication of the metal content in the as-synthesized
displayed no detectable leaching of metals under hot-plate materials and the extent of metal leaching during the reac-
ltration test and in this regards functioned as true heteroge- tions. X-ray photoelectron spectroscopy was utilized to deter-
neous catalysts. However, the tunable acidity of the as- mine the nature of metal oxidation state within the materials.
synthesized materials rendered these materials effective in
The FT-IR spectra of as-synthesis HPW4Mo10Ox and HPW4-
a variety of other transformation. Moreover, there is an Mo10Ox-Cys materials were to stabilize the acid strength
increasing interest in the utilization of solid acid catalyst in changes due to the free and binding state of inorganic oxygen-
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Fig. 1 Representative SEM and TEM images of monodispersed hollow core–shell particles of as-synthesized HPW4Mo10Ox materials: (a) and (b)
SEM images, scale bar 1 mm; (c) and (d) TEM images, scale bar 4 mm and 100 nm respectively.
Fig. 2 Structural and morphological characterization of the as-synthesis HPW4Mo10Ox-Cys by TEM.
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containing anion44 are shown in Fig. 3. As it is well-stabilized the support has no signicant interference on the Raman
the fact that heteropolyanion would be strongly adsorbed into scattering originated from the Keggin structure. Guo et al.51,
supports.44 In the HPW4Mo10Ox, the broad peak has been reported that P–O bonds correspond to stretching vibrations at
investigated may be due to a hydroxyl group (3600–3400 cmꢀ1
)
1009.5 cmꢀ1, W]O bonds (993.9 cmꢀ1) and W–O–W bonds
45
was assigned, which is missing in the HPW4Mo10Ox-Cys spec- correspond to 912.4 cmꢀ1. The investigation also revealed that
trum, indicate that hydroxyl group protected or bind with shis of the peak position are possible due to the strong
cysteine moiety. The characteristics peaks of HPA shown at interaction between the Keggin unit and the support. As Fig. 4,
1082 cmꢀ1 may be due to P–O interaction, metal oxygen bridged show that peak at 989 cmꢀ1 and 900 cmꢀ1 may correspond to
at 800–900 cmꢀ1 range may be due to W–O–W46 and Mo–O–Mo W]O bonds W–O–W linkage but peak at near 1010 cmꢀ1 peaks
asymmetric vibration, associated to the typical Keggin anions. is missing, which indicates that as-synthesized materials don't
At three decade ago, Nomiya et al.47, reported that immobilized contain Keggin unit. Devassy et al.52, reported that band at 998
HPA in the 1100–700 cmꢀ1 showed four stretching vibration and 974 cmꢀ1could be attributed to W]O symmetric and
frequency due to M-terminal oxygen, M–O–M octahedral edge, asymmetric stretching modes. They also claim that broad peak
corner-sharing's and heteroatom (X)-triply bridged oxygen. at 893 cmꢀ1 can be assigned due to W–O–W asymmetric
Khder et al.,48 reported that band at 1081, 982, 889, 797 and stretching mode. Popa et al.49, reported that symmetric and
595 cmꢀ1 assigned to the stretching vibrations of P–O, W–Ot, asymmetric vibrations of terminal oxygen (Mo–Ot) and corner
W–Oc–C, W–Oe–W and bending vibration of P–O, respectively. shared bridged oxygen Mo–O–Mo are lies at 983, 882, 246 and
Popa49 et al. reported that stretching vibration at 965 cmꢀ1 came 154 cmꢀ1. In the literature reported that peaks at the lower
due to Mo–Oc–Mo binding and 595 cmꢀ1 arise for the bending range might be due to Mo–O interaction. In current work, Mo
vibration P–O. In literature, well stabilized that the bands in the also interferes the lattice. Therefore two peaks at 796 cmꢀ1 and
range of 400–1000 cmꢀ1 are attributed to the stretching and 900 cmꢀ1 observed, which is shied than the characteristics
bending vibrations of metal–oxygen characteristics.49 The peak of WO3 (802 and 716 cmꢀ1),53 indicate that different
absorptions band located at 711, 600 and 523 cmꢀ1 are attrib- bonding mode of W.
uted to the Mo–O stretching vibration, reported by Song et al.50
The X-ray photoelectron spectroscopy was used to determine
They also reported that band at ꢂ1000 cmꢀ1 is related to the the chemical bonding, the valence state of W, Mo and surface
terminal oxygen atoms of Mo. We are also observed the composition of as-synthesized HPW4Mo10Ox materials. The XPS
approximately same result in HPW4Mo10Ox materials, but aer survey spectrum of materials was shown in the Fig. 5a. The
capping of cystine minimized the characteristics of HPA peaks. survey spectrum shows peaks for W, Mo, C, O, S and P. The Mo
Additionally, peak at 1610 and 1627 cmꢀ1 may be due to C]O 3d core level spectrum show 3d3/2 and Mo 3d5/2 binding energy
starching. Similarly as for HPW4Mo10Ox-Cys materials, result- for as-synthesis materials is observed at 231.65 eV and 234.76 eV
ing in the lowering the characteristic FTIR vibrations, and with spin–orbit separation of 3.11 eV and Mo d3/2/Mo5/2 ratio of
another 896 and 831 cmꢀ1 vibration spectra were observed.
0.73, as shown in Fig. 5b, which is lesser than the typical
Raman scattering spectroscopy was useful to study the characteristics peak of Mo6+and indicate the reduced form of
original Keggin structure and deformation in structure due to Mo.54 The XPS high-resolution spectra of W 4f core levels for the
support, because it is extremely sensitive to the Keggin unit, and
Fig. 3 FT-IR spectra of as-synthesized HPW4Mo10Ox, and HPW4- Fig. 4 Raman spectra of as-synthesized HPW4Mo10Ox, and HPW4-
Mo10Ox-Cys materials.
Mo10Ox-Cys materials.
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Fig. 5 XPS survey spectrum (a), 3d core-level spectrum of molybdenum (b), C 1s core level spectrum of carbon in the synthesized material (c), P
2p core level spectrum of phosphorous (d).
as-synthesized materials shown in Fig. 5c. The binding energy Mo5+ oxidation state, which is close to (231.65 and 234.65 eV)
for W 4f7/2 and W 4f5/2 levels are observed at 34.42 eV and our as-synthesis material.
36.59 eV respectively, with spin–orbit separation of 2.17 eV and
Acidity analysis of as-synthesis HPW4Mo10Ox, and HPW4-
the W 4f5/2/W 4f7/2 ratio of 0.814. The energy position of the Mo10Ox-Cys material at 750 ꢁC, shows much higher total acidity
doublet is lesser than the W6+ reported in the literature55 and (0.84 mmol gꢀ1 and 0.63 mmol gꢀ1, respectively) from
best matched with W5+, and indicted that W is attached with temperature programmed desorption of ammonia (TPDA).
hydrogen.55 The XPS high-resolution spectra of P 2p core levels Which is much higher than the alumina-supported catalyst
show the binding energy 132.80 eV in Fig. 5d, indicated that (0.34 mmol gꢀ1) and silica (0.07 mmol gꢀ1).59 Alhanash et al.,60
P–O linkage in the as-synthesized materials.55 Combined with reported acidity strength on the basis of TPDA peaks at different
FTIR, XRD, and TEM analysis, it is clear that the Mo ions as the temperature range. They mentioned that absorption peaks
doping were successfully incorporated into the crystal lattice of below 300 ꢁC correspond to weak acidity, above 300 ꢁC,
WO3 and maybe W–Mo boding formed, because bonding energy moderate acidity and the peaks at more than 500 ꢁC due to the
of W and Mo had a trend to lower, suggesting the presence of stronger acidity of materials. As-synthesis materials (HPW4-
W5+ and Mo5+.56 Shpak et al., reported binding energy for W 4f7/2 Mo10Ox), show a strong peak at lower acidity range (Fig. 6) and
and W 4f5/2 levels of tungsten atoms for W5+-sates of oxide (34.8 HPW4Mo10Ox-Cys show a strong peak at higher temperature
eV), well matched with our as-synthesized catalyst.57 The narrow range. On the basis of calibrations data, total adsorption of NH3
scan of as-synthesis materials shows the O 1s core level located for every peak nd-out by instrument and acidity for each peak
at 530.42 eV, which was different than the pure WO3 (529.4 eV)56 calculated. HPW4Mo10Ox, show three peaks at 203, 394 and
trends to different nature of W–O bonding. Shpak et al., also 753 ꢁC and contributed 0.79, 0.046 and 0.0075 mmol gꢀ1
reported that binding energy of O 1s (530.6 eV) correspond to respectively. HPW4Mo10Ox-Cys show four peaks at 340, 224, 454,
O1-levels of oxygen atoms O2ꢀ in the synthesized materials57 659 ꢁC and contributed 0.15, 0.037, 0.15 and 0.29 mmol gꢀ1
5+
6+
and may be the composition written as Wx
W
1ꢀx
O
3ꢀx.
Li respectively. As graph (Fig. 6) and calculation of acidity trend
et al.58, reported that peaks at 231.7 eV and 234 eV belongs to indicate that aer using the capping agent, decreased (0.84 to
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Fig. 7 Powder-XRD patterns of as-synthesized samples.
Fig. 6 NH3-TPD profiles for the as-synthesized HPW4Mo10Ox, and
HPW4Mo10Ox-Cys catalyst.
WO3 and 20.48 (111), 23.58 (020) for the WO3$H2O. As XRD
pattern of HPW4Mo10Ox-Cys indicate that the broadening of
XRD peaks distinctly reects the nanocrystalline nature of the
materials which is more pronounced in the case of HPW4-
Mo10Ox-Cys materials. In our synthesis method, an excess of
cystine, oleic acid and oley alcohol was used to ensure stabili-
zation and restricting the size of the particles in the nano range.
The XRD pattern of as-synthesis HPW4Mo10Ox-Cys show
reections at 2q with respective d-spacing of the lattice fringes
was found to be at 22.14 (0.40 nm), 26.45 (0.34 nm), 31.89 (0.28
nm), 37.45 (0.24 nm), 53.97 (0.17 nm), 60.93 (0.15 nm), 63.29
(0.15 nm), 67.14 (0.14 nm).
To further calculate the crystallite sizes of as-synthesized
materials by Scherrer equation, which indicate that peak
width is inversely proportional to crystallite size. In hetero-
genized materials HPW4Mo10Ox-Cys, show broad reection
peaks and indicate the nano-range. As per calculation its show
10 to 30 nm size of metal nanoparticles. As an obtained result
was found to be in good agreement with the size evaluated from
TEM and prove that topotactic conversion can be achieved by
capping agent and also reducing the particle size. The genera-
tion of nano-range particles through the process of topotactic
intercalation changes the arrangement of particles that can
enhance the activity and selectivity of furanics products. We
believe that nano-range particles assembly and controlling the
acidity are these two advances promise to synthesis and modi-
cation of heteropoly anion with tunable physical properties
create new facet in catalysis.
0.63 mmol gꢀ1) the total acidity and most signicantly, change
the trend of acidity pattern. Without the capping agent as-
synthesized poly-metallic acidic catalyst show strong peaks
and acidity strength (0.79 mmol gꢀ1) at a lower temperature
(203 ꢁC) range, while aer the capping, strong strength
(0.29 mmol gꢀ1) show at 659 ꢁC. The change of material acidity
nature provides to design the more selective synthesis of
a desired product.
A wide range of etherication, dehydration and rehydration
reactions can be efficiently catalyzed by these materials, which
can be designed to the synthesis of control acidity as well as
high degrees of reaction selectivity of the desired product. The
elemental analysis of as synthesis materials was performed with
the help of electron probe micro-analyser (EPMA) with LaB6 gun
as shown in Tables S1 and S2.† Tables S1 and S2† show the 10-
point analysis of as-synthesis materials with ranges minimum-
to maximum 0.49% to 1.79 mol% of phosphorous, 4.04 to
22.33 mol% of oxygen, 0 to 1.49 mol% of nitrogen, 8.84 to
35.6 mol% of molybdenum, 6.66 to 28.02 mol% of tungsten in
HPW4Mo10Ox-Cys catalyst. As-synthesis HPW4Mo10Ox catalyst
show minimum-to maximum 1.13% to 1.47 mol% of phos-
phorous, 10.76 to 25.68 mol% of oxygen, 22.7 to 29.7 mol% of
molybdenum, 28.02 to 37.20 mol% of tungsten. The estimated
value of the metal higher and in regular pattern in HPW4Mo10Ox
compare to HPW4Mo10Ox-Cys.
Fig. 7 shows the powder-X-ray diffraction patterns of as-
synthesized materials with the capping agent and without the
capping agent. As far as the as-synthesized materials with
capping agent (HPW4Mo10Ox-Cys), show broad characteristics
peaks of metal oxide indicate that nano-range particles are
formed. Without capping agent materials (HPW4Mo10Ox) show
that various intensive and sharp peaks at corresponding 2q
value and respective d-spacing of the lattice fringes was found to
be, 10.91 (0.81 nm), 15.0 (0.59 nm), 18.88 (0.47 nm), 21.85 (0.41
nm), 24.35 (0.36 nm), 26.79 (0.33 nm), 30.93 (0.29 nm), 32.79
(0.27 nm), 36.35 (0.25 nm), 39.58 (0.22 nm), 42.77 (0.21 nm),
44.20 (0.20 nm), 47.02 (0.193 nm), 48.45 (0.19 nm), 51.05 (1.79
nm), 52.33 (0.175 nm), 54.88 (0.17 nm), 56.10 (0.16 nm), 58.49
(0.16 nm), 63.11 (0.15 nm), and 65.39 (0.14 nm). In literature
peak at 23.12 (002), 23.58 (020) and 24.38 (200) correspond to
Fig. 8 depicts the thermogravimetric curves of the HPW4-
Mo10Ox and HPW4Mo10Ox-Cys materials. The HPW4Mo10Ox
show 24.39 weight%, mass loss whereas HPW4Mo10Ox-Cys only
5.2% weight loss from room temperature to 600 ꢁC, result
indicate that HPW4Mo10Ox-Cys, show higher thermal stability
in compared to without capping agent. At initial weight loss
were attributed to the loss of physically-adsorbed and chemi-
cally bonded water.
3.2 Catalytic dehydration and rehydration of mono-sugars
The basis for dehydration, etherication and rehydration of
carbohydrate
to
5-hydroxymethylfurfural
(HMF),
5-
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Fig. 8 TG curves of as-synthesized materials of HPW4Mo10Ox and HPW4Mo10Ox-Cys.
alkoxymethylfurfural (AMF) and alkyl levulinates (ALs) are out- 22.45% selectivity to HMF, 42.68% selectivity to EMF, 12.82%
lined in Scheme 1. We explored economically feasible mono- selectivity to EL as well as a formylated and other products
sugar (glucose) for the one-pot dehydration and etherication 6.10% at a glucose conversion of 84% and isolated mol% yield
of respective AMF and AL. Dehydration and etherication of (56%). Notably, the etherication and rehydration product
glucose into HMF and the etherication of HMF to AL are acid- selectivity followed a fairly linear trend for HPW4Mo10Ox, with
catalyzed reactions, it rationally proceeds into two separable reaction time (Table 1, entries 2 and 3). As Table 1, entry 3, show
reactions into the one-pot reaction.
that dehydration and re-hydration of glucose to HMF and ring
opening are a time-dependent reaction, ꢂ95% ring-opening
product formed at 30 min. In our quest for a compatible cata-
lyst, HPW4Mo10Ox-Cys use for controlled rehydration of HMF
and possessing the ability to selective dehydration of glucose to
HMF and etheried product EMF. As shown in Table 1, entry 5,
50.12% HMF selectivity achieved, which is 5.6 times more than
selectivity obtains from HPW4Mo10Ox. As shown in Table 1,
3.3 Dehydration and etherication of glucose
We initially prepared HPW4Mo10Ox and HPW4Mo10Ox-Cys
macro and nanocatalysts respectively by a simple one-pot
synthesis process and then applied it to glucose dehydration
and etherication of reaction under microwave irradiation. As
shown in Table 1 (entry 1), HPW4Mo10Ox catalyst exhibited
Scheme 1 Decreasing of boiling-point after removable of an oxygen atom from fructose.
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Table 1 One-pot catalytic dehydration and etherification of mono-sugar
Product distribution selectivity
S. no
Substrate
Catalyst
Time (min)
Conversion (%)
Yielda (%)
HMF
EMF
EL
Othersb
1
2
3
4
5
6
7
Glucose
Glucose
Glucose
Glucose
Glucose
Fructose
Fructose
A
A
A
B
B
A
B
10
20
30
10
20
20
20
84
97
56
78
73
31
76
84
89
22.45
8.95
0
35.95
50.12
0
42.68
26.25
2.40
15.25
26.76
1.2
12.82
51.67
84.95
3.48
7.10
87.86
7.40
6.10
10.13
11.60
1.32
7.20
10.83
7.15
ꢂ100
56
92
ꢂ100
ꢂ98
54.65
28.80
a
b
Isolated mol% yield. Other ¼ LA, formylated HMF, FA. AHPW4Mo10Ox, B¼ HPW4Mo10Ox-Cys, other reaction condition: catalyst ¼ 20 mg,
temperature ¼ 170 ꢁC, solvent (6 : 2 : 2) THF : H2O : EtOH, substrate ¼ 100 mg.
glucose conversion predominantly decided by the acidity of as- production of EL (Table 1, entry 7). In summary, HPW4Mo10Ox
synthesized materials and times, whereas the distribution of is suitable for EL and EMF synthesis and HPW4Mo10Ox-Cys,
dehydration and etheried products is evidently inuenced by suitable for HMF synthesis due to the presence of strong and
the acidity and morphological structure of the as-synthesis medium acid sites and 3-dimensional structure.
catalyst for glucose conversion. It is noteworthy that capping
agent based HPA nanomaterials with lesser acid density
3.4 Effect of catalyst loading
(0.63 mmol gꢀ1) exhibit higher HMF selectivity in the order to
HPW4Mo10Ox (3D), higher acidic materials (0.84 mmol gꢀ1).
To further elucidate the catalyst amount of HPW4Mo10Ox,
This result suggests HPW4Mo10Ox can favor the rehydration of
a conversion of glucose monitored with different catalyst-dose,
result shown in Fig. 9. Compared with 5 mg catalyst loading,
furanics intermediate and the production of EL. Besides the
45.6% glucose conversion achieved with 31 mol% of isolated
acidity, the substrate, which is main dehydration intermediate
yield, moreover, when the catalyst-loading increased 10 mg,
(fructose), is another important factor affecting the conversion
74.01% conversion with 46 mol% of isolated yield occurred, we
and selectivity of the desired product (Table 1, entries 6 and 7).
observed an even higher conversion of glucose (86%) and 97%,
when catalyst-amount increased from 15 and 20 mg respectively
with 78 and 67 mol% of isolated yield at 170 ꢁC for 20 min,
under microwave-irradiation. The increase in the glucose
conversion and isolated yield with increasing catalyst loading
could be attributed to an increase in the availability and
We observed that HMF and the etheried product can be
produced in high yields by HPW4Mo10Ox or HPW4Mo10Ox-Cys
catalyzed dehydration and etherication of fructose under
microwave reactor using low boiling solvents (THF), reactive
aqueous phase (water) and etheried solvent (ethanol). It
suggests that the stronger acidity of HPW4Mo10Ox could cause
number of catalytically active sites during dehydration and
the rehydration of EMF to EL (87.86%, Table 1, entry 6), whereas
etherication of glucose. However, a further increment of
the weaker one of the HPW4Mo10Ox-Cys is not benecial to the
catalyst loading 25 mg, no signicant increment of yield (78 to
rehydration of EMF or HMF, thus this is disfavour the selective
81%) achieved under same reaction condition. Further incre-
ment of 30 mg, decreasing trend of isolated product observed,
indicating other side products formed like humins under a high
acid concentration.
3.5 Comparative studies of alcohols for glucose conversion
and respective etherication
The versatility of as-synthesized HPW4Mo10Ox-Cys catalyst
towards dehydration and etherication reactions was further
explored using methanol, n-propanol, isopropanol, n-butanol,
and 2-butanol (Fig. 10). Ethanol and methanol showed a similar
conversion and isolated yield, whereas propanol, isopropanol,
n-butanol, and 2-butanol were less reactive compared to
ethanol. Since, utilization of higher alcohol and synthesis of
respective AMF and AL from glucose is an exciting development
in the production of higher chain furanics and its derivative,
which would have higher energy density and nd wider appli-
Fig. 9 Dehydration and etherification of glucose at different catalyst
cation as solvent, plasticizing agent and other bio-based
chemicals. The results show in Fig. 10, tolerance and
loading, other reaction condition: glucose 100 mg, temperature
170 ꢁC, time 20 min.
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materials for dehydration and etherication, its occurrence in
nature is limited. This drives our more intrest to use a more
abundant carbohydrate fraction, glucose, as the starting mate-
rials for further reaction.
3.7 Reusability of catalyst
To further analysis the stability of the as-synthesized and het-
erogenized HPW4Mo10Ox-Cys catalyst, with time on dehydration
and etherication of glucose was successfully tested for ve
consecutive cycles. Recycling experiments show comparable
activity of HPW4Mo10Ox-Cys, in terms of glucose conversion and
EMF yield, in the rst cycle under optimal reaction conditions
(Fig. 11). The reaction was carried out at 170 ꢁC under the MW-
irradiation for 20 minute duration with 20 mg of catalyst and
100 mg of glucose. Aer each cycle, the catalyst was ltered,
washed and activated through calcinations before used for next
cycle. The next cycle using the recovered catalyst was carried out
under similar condition by adding fresh glucose and THF,
ethanol, and water as solvent (6 : 2 : 2) ratio. As the end of the
reaction, the product was analyzed by GC, HPLC, UV and NMR.
The results as shown in Fig. 11 suggest that the activity of
catalyst aer ve cycles, in terms of conversion and selectivity
results demonstrated that the only 9% conversion and 7% yield
of desired product decreased aer ve cycles.
Fig. 10 The catalytic effectiveness of HPW4Mo10Ox-Cys for the
selective dehydration of glucose and further etherification with various
aliphatic alcohols. Reaction conditions: glucose ¼ 100 mg, catalyst
20 mg, time ¼ 20 min.
effectiveness of HPW4Mo10Ox-Cys catalyst with methanol (75%,
96%), n-propanol (72%, 89%) and n-butanol with (68,
72%) mol% yield and conversion of glucose.
3.6 Effect of substrate
The effectiveness of the catalyst was further evaluated by the
exploring some more complex sugar to intermediate platform
chemicals at optimum condition. A reaction under the condi-
tion of 100 mg of starting substrate, 20 mg of catalyst loaded in
3.8 UV-visible method
The UV-visible spectrum of pure HMF solution has a distinct
peak at 286 and 228 nm in water with corresponding molar
ꢁ
microwave tube, closed and set run for 20 min at 170 C, ach-
extinction coefficient (3) value of 1.66 ꢃ 10ꢀ4 Mꢀ1 cmꢀ1
.
ieved quantitative conversion of fructose, sucrose, and HMF
were more than 99% with 84, 81 and 89% of desired product
yield (Table 2, entries 1, 3, and 5). Other complex biomass
(crystalline cellulose) was tested for dehydration and ether-
ication reaction, we are failed to achieve desired product at
optimised reaction condition. Maybe due non-solubility of
cellulose in water or THF. Therefore, we were added 10% ionic
liquid (1-allyl-3-methylimidazolium chloride) for the dissolu-
tion of cellulose at optimum conditions and 67% conversion
and 42% of the desired yield achieved (Table 2, entry 7). We
have also tested furfuryl alcohol as starting substrate for
etherication reaction, and 92% conversion with 87% isolated
yield was achieved. Although fructose is the preferred raw
HMF has two functional group, carbonyl, and alcohol, and
therefor in carbonyl group (n to p and p to p*) transition are
possible and in alcohol (n to s*) transition possible. UV
absorption spectra for HMF show two transition to p* and p to
p*. Characteristic absorption peaks of HMF (286 nm) aer
etherication as shown in Fig. 12. The spectra of pure HMF, and
aer etherication were easily distinguished by UV-visible.
Results indicate that the absorption due to p to p* transition
decrease (286 nm) along with increasing n to p transition
intensity (225 nm) (Fig. 12, 2 h). As the reaction time increases
Table 2 Substrate scope for dehydration and etherification
S. no
Substrate
Conversion (%)
Isolated yield (%)
1
2
3
4
5
6
7
Fructose
Glucose
Sucrose
Furfural alcohol
HMF
>99.9
92
84
76
81
87
89
93
42
ꢂ99
92
>99.9
>99.9
67
LAa
Celluloseb
a
b
Fig. 11 Reusability study of HPW4Mo10Ox-Cys catalyst for glucose
dehydration and yields of products. Other reaction condition: glucose
¼ 100 mg, catalyst ¼ 20 mg, at 170 ꢁC for 20 min.
Esterication. 10 mol% ILs was used, other reaction parameter are
same.
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Fig. 12 UV absorption spectra for the HMF at zero h and after etherification (2 h).
beyond this initial period, the UV spectra begin to show an competitive with fossil fuels. The US Department of Energy
increase in absorbance at wavelengths lower than 230 nm, selected top-10 biomass-based chemicals on the basis of the
along with a decrease in absorbance observed for wavelengths well-stabilized reaction process, economics, industrial viability,
above 284 nm and therefore no appearance of alcohol peak. size of markets and ability the compound to serve as a platform
Fig. 12 shows a spectrum of HMF at zero h and 2 h, in view of chemicals for the transformation of other valuables chemicals
the spectra where increase in absorbance can be seen as deep- and fuels.1 The as-synthesized materials show the promising
ness of the valley increased.
result in these regards, as shown in Table 2, that anchored HPA
has a better selectivity and efficiency and relatively low humins
formation. Accordingly, we designed a process and conducted
a techno-economic study to determine the feasibility of using
the HPW4Mo10Ox and HPW4Mo10Ox-Cys as catalysts, in
comparison to mineral acid, and nano-material as catalyst for
carbohydrate dehydration, etherication, and rehydration. In
comparison to biomass transformation published literature our
catalytic results reveal that as-synthesized materials have better
acidity controlled and better efficiency to transform the carbo-
hydrate to valuable chemicals and fuel at economical cost and
sustainable manner and attuned with the fossil-based market.
Our materials design for catalytic reaction and analysis studies
conclude that: (i) catalytic route design for the synthesis of
HMF, EMF and alkyl levulinate from carbohydrate can be easily
scalable up to pilot-plant level. (ii) Utilization of MW energy can
reduce the reaction time and energy per capita cost. (iii) Utili-
zation of glucose and sucrose as starting substrate can also,
decrease the starting raw materials cost. (iv) True heteroge-
neous nature and better recovery of the catalyst aer reaction
can provide the relatively lower cost of materials and total
production cost. The heating value of various alcohol and fur-
anics mentioned in Table 3, indicate that furanics have poten-
tial to replace the fossil fuel in the future.55
3.9 Techno-economic analysis
The biorenery based chemical is a green concept advancing
chemistry and chemical engineering to synthesize and use
biofuels in place of fossil fuels (oil and gas). The major focus of
this research work is to developed cost-effective catalytic route
for the synthesis of renewable sources of energy that can be
Table
3 Comparative energy density of gasoline, alcohols, and
biomass-derived furanics55
Lower heating
Boiling point
(ꢁC)
Compound
value (MJ Lꢀ1
)
RON
Gasoline
Ethanol
n-Propanol
Iso-propanol
n-Butanol
Iso-butanol
n-Pentanol
MTHF
DMF
MF
EL
BL
30–33
21.4
24.7
24.1
26.9
26.6
28.5
28.2
30.1
27.6
24.8
27.1
25.9
26.2
27–225
78
88–98
109
104
106
98
105
78
86
119
103
110
98
105
100
97.2
82.3
117.7
107.9
137.8
78
94
64.7
206
237.5
126
218–220
MP
GVL
4. Conclusion
a
MTHF ¼ 2-methyltetrahydrofuran, DMF ¼ 2,5-dimethylfuran, MF ¼ 2-
methylfuran, EL ¼ ethyl levulinate, BL ¼ butyl levulinate, MP ¼ methyl
pentanoate, GVL ¼ g-valerolactone.
Highly stable, 3D hexagonal hollow core–shell structure of HPA
has been synthesized. The use of capping agent, changes in the
morphology is obtained. Structural characterization and acidity
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Conflicts of interest
There are no conicts to declare.
23 B. Zhang, H. Asakura, J. Zhang, J. Zhang, S. De and N. Yan,
Angew. Chem., Int. Ed., 2016, 55, 8319–8323.
24 S. Dutta, S. De, M. I. Alam, M. M. Abu-Omar and B. Saha, J.
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Acknowledgements
This work was carried under a DST-SERB-sponsored project. 25 D. A. Kotadiaa and S. S. Soni, Catal. Sci. Technol., 2013, 3,
Dinesh Gupta and C. Mukesh acknowledges SERB-DST (SERB
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le no. PDF/2016/000458) and (SERB le no. PDF/2016/003943) 26 J. Y. G. Chan and Y. Zhang, ChemSusChem, 2009, 2, 731–734.
for National Postdoctoral Fellowship respectively. Prof. K. K. 27 S. Budhi, C. Mukarakate, K. Iisa, S. Pylypenko,
Pant, acknowledged for project research grant, DST-SERB,
government of India.
P. N. Ciesielski, M. M. Yung, B. S. Donohoe, R. Katahira,
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28 J. R. Dethlefsen, D. Lupp, A. Teshome, L. B. Nielsen and
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