Selective hydrogenation of bio-based 5-hydroxymethyl furfural to 2,5-dimethylfuran over magnetically separable Fe-Pd/C bimetallic nanocatalyst

Article abstract of DOI:10.1016/j.mcat.2018.12.009

There is an ever increasing need to innovate and provide alternative energy sources to reduce the overdependence on conventional fossil fuels. 2, 5-Dimethylfuran (DMF), a bio-based chemical, has gained a lot of attention due to its potential application as a biofuel additive and is synthesized through hydrogenation of 5-hydroxymethylfurfural (HMF). Bimetallic nano-catalysts have gained importance in recent years due to their excellent selectivity and activity. In this paper, a magnetically separable Fe-Pd/C bimetallic nano-catalyst was developed which not only showed excellent selectivity to DMF but also helped reduce the noble metal consumption, thereby making the catalyst cheaper. Using XPS, XRD and TPR characterizarion techniques, the Fe-Pd/C catalyst was found to exist as bimetallic containing a partially oxidized Fe and reduced Pd atoms. It exhibited 85% selectivity towards DMF with 100% conversion of HMF. The reaction was conducted in a liquid-acid-free environment, thus making the process environmental friendly. The oxidized Fe imparts magnetic properties to the catalyst making it easy to recover. The catalyst was found to be robust and showed excellent activity on repeated use. Overall a highly efficient, economic and green process for DMF synthesis was developed based on biomass as feedstock.

Full text of DOI:10.1016/j.mcat.2018.12.009

MolecularCatalysis465(2019)1–15
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Selective hydrogenation of bio-based 5-hydroxymethyl furfural to 2,5-
dimethylfuran over magnetically separable Fe-Pd/C bimetallic nanocatalyst
Abhijit D. Talpade, Manishkumar S. Tiwari, Ganapati D. Yadav⁎
Department of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai, 400 019, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
There is an ever increasing need to innovate and provide alternative energy sources to reduce the over-
dependence on conventional fossil fuels. 2, 5-Dimethylfuran (DMF), a bio-based chemical, has gained a lot of
attention due to its potential application as a biofuel additive and is synthesized through hydrogenation of 5-
hydroxymethylfurfural (HMF). Bimetallic nano-catalysts have gained importance in recent years due to their
excellent selectivity and activity. In this paper, a magnetically separable Fe-Pd/C bimetallic nano-catalyst was
developed which not only showed excellent selectivity to DMF but also helped reduce the noble metal con-
sumption, thereby making the catalyst cheaper. Using XPS, XRD and TPR characterizarion techniques, the Fe-
Pd/C catalyst was found to exist as bimetallic containing a partially oxidized Fe and reduced Pd atoms. It
exhibited 85% selectivity towards DMF with 100% conversion of HMF. The reaction was conducted in a liquid-
acid-free environment, thus making the process environmental friendly. The oxidized Fe imparts magnetic
properties to the catalyst making it easy to recover. The catalyst was found to be robust and showed excellent
activity on repeated use. Overall a highly efficient, economic and green process for DMF synthesis was developed
based on biomass as feedstock.
2,5-Dimethylfuran
5-Hydroxymethyl furfural (HMF)
Fe-Pd/C
Bimetallic catalyst
Selective hydrogenation
Green chemistry
Introduction
ethanol which is miscible with water [8].
For synthesis of DMF by hydrogenation of HMF, hydrogen must
There is an increasing demand for alternative energy sources due to
the ongoing issues like global warming and reduction in reserves of
conventional fossil fuels. Biofuels have emerged as an option to these
problems. Biofuel additives such as furanic ethers and esters, or 2,5-
dimethylfuran can be derived from simple processes like condensation
and hydrogenation of 5-hydroxymethylfurfural (HMF), which could be
derived from various simple and complex sugars like glucose, fructose,
etc. [1–3].
The presence of two functional groups in the furan ring of HMF
molecule provides an opportunity of converting it into various value-
added chemicals that find applications in various fields [4,5]. The
products obtained by hydrogenation of HMF typically are 2,5-dihy-
droxymethyl furan (DHMF), 2, 5-dimethylfuran (DMF), and ring-
opened products [6,7]. Scheme 1 gives the reaction products of hy-
drogenation of HMF.
react selectively with the formyl and hydroxyl groups attached to the
furan ring and avoid excessive hydrogenation or ring-opening of the
furanic molecule, as shown in Scheme 1, to prevent formation of ad-
ditional by-products [9]. Thus, the main aim in the case of hydro-
genation is to control the selectivity of the desired product using a
highly active and selective catalyst. This can be achieved by main-
taining optimum reaction conditions and by designing catalysts that
show high selectivity. Commonly used catalysts for the conversion of
HMF to DMF are CuRu/C and Pd/C. Román-Leshkov et al. [10] pro-
duced DMF from fructose using one-pot synthesis, wherein HMF was
synthesized from fructose using an acid catalyst and then transformed it
to DMF by using CuRu/C catalyst. The catalyst was found to deactivate
and required regeneration. Also, the bimetallic CuRu/C catalyst was
found to be affected to a certain extent by the chloride ions present in
the system. A milder pathway to produce DMF in excellent yield was
reported by employing an acidic reagent such as formic acid and Pd/C
as catalyst [11]. However, there was a need to use corrosive formic acid
and H2SO4 to obtain high yields making it a polluting process. Chi-
dambaram and Bell [12] produced DMF from glucose using a two-step
reaction with an acidic catalyst for dehydration followed by a metallic
Of all these products, 2, 5- dimethylfuran (DMF) is more promising
due to its superior properties such as ideal boiling point (92–94 °C),
high energy density (30 kJ cm−3), and high research octane number
(RON = 119). Furthermore, it blends easily with gasoline and is im-
miscible with water; and thus it proves to be a better additive than
⁎ Corresponding author.
E-mail address: gd.yadav@ictmumbai.edu.in (G.D. Yadav).
https://doi.org/10.1016/j.mcat.2018.12.009
Received 21 October 2018; Received in revised form 6 December 2018; Accepted 12 December 2018
2468-8231/©2018ElsevierB.V.Allrightsreserved.

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Nomenclature
KA
Equilibrium constant for the adsorption reaction of A (L/
mol)
A
Reactant species A, 5-hydroxymethyl furfural (HMF)
rHD
KH
Rate of chemisorption reaction of H (mol L−1 min−1
)
S
Catalyst active site
Equilibrium constant for the adsorption reaction of H (L/
mol)
AS
HS
B
Chemisorbed species A
Chemisorbed hydrogen (dissociative adsorption)
First intermediate product, 2,5- dihydroxymethyl furan
(DHMF)
k1
k1’
k2
k2’
k3
k3’
-r1
-r2
-r3
K1
Reaction rate constant for forward reaction of A to B
Reaction rate constant for backward reaction of A to B
Reaction rate constant for forward reaction of B to C
Reaction rate constant for backward reaction of B to C
Reaction rate constant for forward reaction of C to D
Reaction rate constant for backward reaction of C to D
BS
W
Chemisorbed species B
Water
C
CS
D
DS
CA
CAS
CH2
CHS
Second intermediate product, hydroxymethyl furan
Chemisorbed species C
Final product,2,5- dimethyl furan (DMF)
Chemisorbed species D
Rate of surface reaction 1, A to B (mol L−1 min−1
Rate of surface reaction 2, B to C (mol L−1 min−1
Rate of surface reaction 1, C to D (mol L−1 min−1
)
)
)
Concentration of A, (mol/L)
equilibrium reaction constant for reaction 1, A to B, di-
mensionless
Concentration of A at solid (catalyst) surface, (mol/g-cat)
Concentration of hydrogen, (mol/L)
Concentration of hydrogen at solid (catalyst) surface,
(mol/g-cat)
K2
Equilibrium reaction constant for reaction 2, B to C, di-
mensionless
-rD
KD
Rate of desorption reaction of species D (mol L−1 min−1
)
CB
Concentration of B, (mol/L)
Equilibrium constant for the adsorption reaction of D (L/
mol)
CBS
CW
CC
CCS
CD
CDS
CS
CT
Concentration of B at solid (catalyst) surface,(mol/g-cat)
Concentration of water, (mol/L)
k”
S
w
Consolidated rate constant in Eq. (31) (L g-cat−1min−1
Vacant active sites
)
Concentration of C in liquid phase (mol/L)
Concentration of C at solid (catalyst) surface,(mol/g-cat)
Concentration of D in liquid phase, (mol/L)
Concentration of D at solid (catalyst) surface,(mol/g-cat)
Concentration of vacant sites, (mol/g-cat)
Total concentration of sites, (mol/g-cat)
Catalyst loading (g-cat/L)
Acronyms
HMF
DMF
5-Hydroxymethylfurfural
2,5-Dimethylfuran
rAD
Rate of chemisorption reaction of A (mol L−1 min−1
)
catalyst for HMF to DMF conversion. Maat et al. [13] studied the
synthesis of DMF by combining Pd/C catalyst and HCl as an activator in
alcohol as solvent. It is seen that most of the reports require use of an
acid as a reagent to improve yields of DMF. Recent reports on carrying
out the transformation of HMF to DMF using catalysts like Ru/Co3O4
have yielded high yields of up to 94% while using mild conditions [8].
Current reports based on Ni catalysts have shown that high selectivity
of DMF along with high HMF conversions can be achieved [14,15].
As given in Scheme 1, due to different functionalities in HMF mo-
lecule, an array of products can be formed during the process of hy-
drogenation leading to reduction in yields of DMF and thus increasing
product purification costs. Exploration of bimetallic catalysts could be
considered as one of the approaches for improved DMF yield. For ex-
ample, Cu addition in bimetallic catalyst, CuRu/C, helps in improving
the selectivity of DMF with 71% yield. These experiments were per-
formed at 220 °C and 6.8 bar H2 pressure [10]. Wang et al. have ob-
tained 98% DMF yield at 180 °C and 10 bar hydrogen pressure using Pt-
Co catalyst [16]. Nishimura et al. [17] have employed Pd-Au/C and HCl
as catalyst at very moderate operating conditions (60 °C) and at
atmospheric hydrogen pressure and achieved exceptional yields of
DMF. Recent reports involving bimetallic catalysts using cobalt as a
metal have also shown promise [18,19].
Bimetallic systems help provide an added degree of freedom for
tuning the catalytic performance by modifying the electronic and geo-
metric structures of these materials which can be done by changing the
composition and size of the materials used [16,20]. Bimetallic catalysts
help in improving the selectivity, stability and activity as compared to
monometallic counterparts and are active even under mild conditions
[21–30]. Bimetallic nanomaterials are turning out to be the most pro-
mising catalysts due to their superior catalytic properties. As most of
the catalytic reactions take place on the surface of nano-sized catalysts,
their interior atoms are often rendered useless. This poses a serious
problem when costly noble-metals such as Pd or Pt-based catalysts are
used. The noble metals in the central core could be replaced by alloying
with other transition metals like Cu, Fe, Co and Ni, which not only help
reduce the catalyst cost but also show a marked improvement in the
catalytic activities due to the synergistic effects resulting from geo-
metric and electronic interactions of the two metals used [28,29].
Metals such as iron are available in abundance and show excellent
magnetic properties. On successfully employing these metals in the
catalyst, it is possible to obtain materials that are cheap to produce and
easy to recover by using an external magnetic field, due to magnetic
properties exhibited by them [28,31].
We report here the selective hydrogenation of 5-hydro-
xymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) using magneti-
cally separable bimetallic nano-catalysts synthesized using the se-
quential reduction method. Different bimetallic combinations have
been tried by combining iron with other metals (like Pd, Cu) as it
provides the additional advantage of easier separation using external
magnetic field. Various parameters have been optimised to obtain
maximum yield of DMF. The reaction mechanism and kinetics have
been proposed. Unlike the usual processes, the process has been per-
formed in an acid-free environment, thus making it greener. High yields
Scheme 1. Products from hydrogenation of HMF.
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A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
of DMF are obtained using bimetallic nano-catalysts which also show
excellent reusability characteristics.
(CuCl2) keeping the mole ratio of Pd:Cu constant as before (Pd:Cu ratio
1:20). During synthesis, to make Cu partciles on 100 mg carbon, 212 mg
CuCl2 (anhydrous) was dispersed in 30 mL water and sonicated for
10 min. The remaining procedure is the same as described in the section
above.
Experimental
Materials
Copper-iron on carbon catalyst synthesis
Ferrous chloride anhydrous, cuprous chloride, activated charcoal
pellets and sodium borohydride, n-butanol, n-decane and 5% w/w Pd/
C, were procured from SD Fine Chemicals Limited, Mumbai, India.
Palladium chloride was procured from Sigma Aldrich, Mumbai.
Tetrahydrofuran and 1, 4-dioxane was procured from Thomas Baker,
Mumbai. All these chemicals were of analytical grade and required no
purification before their use. HMF used in the experiments was syn-
thesized in the lab through a biphasic method developed in the la-
boratory. The purity assay of the HMF synthesized was studied using
1H-NMR and was found to be 98% pure.
This catalyst was synthesized with a view to see whether noble
metals could be replaced completely by transition metals to carry out
the reduction of the substrate. The molar ratio of Cu:Fe was maintained
at 1:1. In this case, initially 200 mg activated carbon was sonicated to
remove all of the impurities present in it. Excess NaBH4 (more than
stoichiometric requirement) was added to the solution to ensure com-
plete reduction of both the precursors. Then, solution of 212 mg CuCl2
(anhydrous) in 30 mL water was added drop-wise to the carbon solu-
tion. After ensuring complete reduction of copper precursor to Cu(0),
FeCl3 solution (289.3 mg FeCl3 in 30 mL water) was added to this
mixture to form Cu-Fe bimetallic nanocatalysts. The remaining proce-
dure is the same as described in the section above.
Catalyst synthesis
Iron-palladium on carbon catalyst synthesis
Catalyst characterization
Fe-Pd bimetallic catalyst, supported on carbon was synthesized
using the sequential reduction process as described in prior art with a
few modifications [28].Firstly the activated charcoal (100 mg) was
sonicated at room temperature in 30 mL water for 30 min for high
dispersion of . To this mixture, excess NaBH4 (676.2 mg) was added. For
formation of Fe in the Fe-Pd bimetallic catalyst (molar ratio Pd:Fe =
1:20), 289.6 mg FeCl3 was dispersed in 30 mL water and sonicated for
10 min. FeCl3 solution was then added into the mixture drop-wise to
bring about reduction of Fe from Fe3+ to Fe°. The mixture was then
agitated for 30 min to ensure complete release of hydrogen. PdCl2 so-
lution was prepared by taking 27 mg of PdCl2 in 20 mL water. To aid
the dissolution of PdCl2 salt in water, small amount of NaCl (500 mg)
was added. The prepared PdCl2 solution was further added to Fe/C
solution, drop-wise, and stirred for 1 h. It was found that some of the Fe
atoms present on the outer-layer were sacrificed to bring about Pd re-
duction form Pd2+ to Pd°. Bimetallic nanoparticles were then separated
magnetically (Fig. 1) and excess sodium borohydride was removed by
several washings with water and ethanol. After every water and ethanol
washing, a pH paper was used to make sure that the solution (con-
taining the catalyst) was neutral in nature. The subsequent washings
were stopped only when the solution was found to be pH neutral. The
catalyst was then dried at 50 °C overnight using a vacuum oven.
The synthesized catalysts were characterized using various techni-
ques [32–34]. Among all catalysts studied in this work, Fe-Pd bimetallic
catalyst was found to be the best (as seen in Fig. 8)and was thus,
characterized in further detail.
Scanning electron microscopy (SEM)
Surface characteristics of the catalyst were studied using SEM
(JEOL, Japan, Camera SU 30 microscope). Initially, the samples to be
tested were dried and then loaded on specimen studs followed by
sputter coating with a thin gold film to avoid charring. Topographical
images were assembled from back scattered primary or low-energy
secondary electrons.
Transmission electron microscopy (TEM)
TEM images were taken on the JEOL JEM 2100, Japan. The images
were taken at 200 kV with copper grids of 3 μm thickness. The grids
were impregnated with the solid catalyst dispersed in ethanol, and then
allowed to dry using UV lamp. The grid was loaded on the loading arm
and the electron gun was started.
X-ray diffraction technique (XRD)
Copper-palladium on carbon catalyst synthesis
The X-ray scattering measurements were studied using a Bruker
AXS, D8 Discover instrument with Cu-K (1.54 A°). The scattered in-
tensities were collected from 5 to 80° (2θ) with a counting time of 0.5 s
at each step.
Copper-palladium bimetallic nanocatalysts were synthesized using
the same procedure as stated in the previous section except that the iron
precursor (FeCl3), used previously, is replaced by a copper precursor
Fig. 1. Magnetically separable Fe-Pd/C bimetallic structured nanoparticles.
3

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Temperature programmed reduction (TPR)
of sample would be collected free of catalyst. This sample was then
subjected to centrifugation to prevent any catalyst particles from in-
terfering with further analysis.
Temperature programmed reduction (TPR) was performed by using
a Micromeritics AutoChem 2920 (USA) instrument. 30–100 mg of
sample was initially treated under helium to the temperature of 500 °C
to get rid of any impurities present. The sample was flushed with he-
lium. Temperature was then reduced to 50 °C. The sample was then
given dose of hydrogen using 10% v/v H2-Ar at 500 °C and maintained
there for 30 min. The temperature was brought down to 50 °C. The
sample was flushed with He to remove physisorbed hydrogen and then
subsequently the furnace temperature was increased from 50 to 900 °C
at a heating rate of 10 °C/min under He flow. The amount of H2 con-
sumed by the sample was measured by TCD and quantified by cali-
bration.
Analysis
The sample was analyzed using GC (Chemito model, 1000, FID
Detector) using a BP-1 capillary column. The product obtained, DMF,
was confirmed using GC–MS (Perkin Elmer Clarus 500).
Results and discussions
Catalyst characterisation
Scanning electron microscopy (SEM)
Surface area and porosity analysis
Fig. 2 depicts the SEM images of Fe-Pd catalyst. The images were
obtained at 1000x and 4000x magnification to indicate that the parti-
cles are nano-sized, falling in the range of 10–50 nm. It also shows that
they are no agglomerates present at the surface. Fig. 2 c contains the
selected area elemental analysis grayscale mapping of Fe, C and Pd. It
shows the coexistence of C, Fe and Pd in the prepared material with low
concentration of Pd compared to Fe on C.
The analysis of surface area and pore size distribution was carried
out by using Micromeritics ASAP 2010 instrument by N2 adsorption at
−197 °C, after subjecting the sample to high vacuum at 450 °C for 4 h.
X-ray photoelectron spectroscopy (XPS)
The chemical composition and oxidation state of Fe and Pd in the
synthesized catalyst were studied using an XPS analysis. The analysis on
the samples was performed at the CSIR-National Chemical Laboratory,
Pune, India.
Transmission electron microscopy (TEM)
Fig. 3 shows the transmission electron microscopy images of Fe-Pd/
C catalyst at 50 nm and 10 nm resolution. It indicates the formation of
nanoparticle structures. The formation of bimetallic structures of Fe-Pd
atoms is also seen. The images are in concurrence with some of the
previous reports [28].
Hydrogenation experiments
The hydrogenation reaction was carried out in a 100 mL Haste Alloy
C autoclave (Amar Equipments Pvt Ltd, Mumbai). The autoclave was
fed with appropriate quantities of HMF, internal standard (I.S.), solvent
and the catalyst. The reactor was initially flushed with nitrogen to
ensure that no air or oxygen was trapped in the autoclave. After
achieving the desired temperature, the hydrogen pressure in the reactor
was set and agitation was started. In a typical experiment, 2 mmol
(0.26 g) HMF, 20 mL reaction solvent, 0.3 mL internal standard (n-de-
cane) and 200 mg catalyst were charged into the autoclave. Samples
were drawn periodically for analysis. The typical Pd metal to substrate
mole ratio was 1:20 at optimized condition.
X-ray diffraction (XRD)
The diffraction pattern for the Fe-Pd catalyst was obtained. The
recycled catalyst was also characterized using XRD (Fig. 4). There is
hardly any difference in the patterns of both the catalysts proving that
the crystallinity fidelity are maintained.
The XRD pattern of both fresh and reused Fe-Pd/C bimetallic nano-
catalyst show diffraction lines with low intensities as the particle size
was small (Fig. 4). However, a distinct diffraction line is seen at around
40.01° due to the face centred cubic (FCC) structured Pd corresponding
to its (111) reflections. Small lines are observed around 46° and 68°,
Samples were withdrawn from the reactor through a sampling port
present on it by stopping the agitation momentarily. Typically, 0.5 mL
Fig. 2. SEM topography images of Fe-Pd/C catalyst. (a) at 4000x magnification and (b) at 1000x magnification (c) Elemental mapping of Fe, Pd and C on the catalyst
surface.
4

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Fig. 3. TEM image of the Fe-Pd/C bimetallic structured nanocatalysts.
accounting for the Pd (200) and (220) planes [28]. The diffraction lines
at around 30.31°, 35.71°, 57.31° and 63.01° are also observed for γ-
Fe2O3 and/or Fe3O4 phases (FexOy) and these diffraction lines corre-
spond to the reflections of planes (220), (300), (511) and (440) re-
spectively [35]. Peak at 43° corresponds to presence of reduced Fe in
the prepared catalyst [28,36]. This also indicates that not all Fe parti-
cles have been sacrificed to reduce Pd from Pd2+. Peaks corresponding
to iron and iron oxide confirm the presence of magnetic components in
prepared sample. The crystallite size of Fe-Pd/C sample is 13.54 nm and
of the recycled catalyst is 15.9 nm as obtained by applying the Scher-
rer’s equation [37]. It is difficult to distinguish between the γ-Fe2O3 and
Fe3O4 phases using the XRD technique alone as these two phases share
the same inverse spinel structure and show similar d spacing. However,
finding the exact composition of these phases is not important as both
these phases exhibit magnetic properties.
Temperature programmed reduction (TPR)
H2-TPR of bimetallic sample was performed to see the reduction
behaviour and interaction between two metal species of the catalyst.
For the Fe-Pd/C catalyst in consideration, Fig. 5 gives TCD signal for the
catalyst versus temperature. TPR profile showed a sharp negative peak
at 80 °C corresponding to the decomposition of palladium hydrate
phase i.e. β-PdHx, which confirms the presence of reduce Pd nano-
particle in the sample. The decomposition temperature of palladium
hydrate phase ranges between 65–85 °C [38–40]. It also exhibits addi-
tional three peaks at 360 , 578 and 640 °C. The reduction peaks at
360 °C corresponds to change of phase of Fe2O3 to metallic Fe3O4 while
peaks at 578 °C correspond to reduction of Fe3O4 to FeO. The observed
peak at 640 °C represent the reduction of FeO to metal Fe particles. As
reported earlier by Espro et al. [39], the corresponding reduction
temperature for iron oxides supported on carbon is 335 °C (Fe2O3 to
metallic Fe3O4), 495 °C (Fe3O4 to FeO) and 561 °C (FeO to metal Fe)
[38]. The shift in reduction temperature of different phases of Fe in
Fig. 4. XRD diffraction patterns of (a) fresh catalyst and (b) recycled catalyst.
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MolecularCatalysis465(2019)1–15
Fig. 5. H2-TPR profiles of Fe-Pd/C.
Fig. 6. Adsorption-desorption isotherm of the fresh Fe-Pd/C catalyst.
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A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
present catalyst is due to high content of Fe in the catalyst as reported
earlier [39]. Usually, the presence of a noble metal (here Pd) in the
bimetallic catalyst with Fe results in a decrease in the reduction tem-
perature of Fe atoms. This is due to the interaction of two metals which
can be corelated to the formation of alloys with the two metals [39,40].
Using the current synthesis method, no shifts in the reduction tem-
perature have been observed for Fe, indicating that the alloy formation
does not take place.
Table 1
BET surface area and porosity analysis of fresh and reused catalysts.
Catalyst
BET Surface
area (m2/g)
Single point adsorption
pore volume (cm3/g)
Adsorption average
pore width, nm
Fe-Pd
167.97
148.51
171.20
0.25
0.215
0.224
5.94
5.8
5.2
Fe-Pd 1st use
Fe-Pd 2nd
use
Surface area and porosity analysis
Effect of different parameters on conversion and selectivity
The conversions of HMF in all cases was found to very high. Thus, to
maximise the yields of DMF, it was necessary to improve the selectivity
of DMF. A systematic study was undertaken to optimize the reaction
parameters. The standard experiments were replicated three times and
the experimental data was found to lie within a standard percentage
error of 3%.
The adsorption desorption isotherms for the Fe-Pd/C catalyst with
Pd:Fe 1:20 showed characteristic of microporous solids (Fig. 6).
Characteristic nitrogen BET surface area, pore size and pore volume
for the fresh catalyst and the catalyst after 1st and 2nd use are given in
Table 1. There is marginal change in the pore width, pore volume and
the surface area of the catalyst, before and after its use, thereby proving
the fidelity of the catalyst.
Catalyst screening
X-ray photoelectron spectroscopy (XPS)
The hydrogenation of HMF was carried out using four different
catalysts. Three of them were synthesized in the lab and other was
commercially available (Fig. 8). Palladium proves to be a very efficient
catalyst yielding good conversions in most of the reactions where it is
employed due to its high hydrogen adsorbing capacity [43,44]
Iron is considered as a cheaper source for replacement of palladium
and has been employed for application in various reduction reactions
[45]. Copper metal shows good selectivity and reactivity even at lower
temperatures [44]. Our main aim of preparing bimetallic combinations
was to improve the desired product yield. It was observed that the
commercial catalyst 5% Pd/C and the bimetallic catalyst Cu-Pd/C
carried out ring hydrogenation of DMF, thereby reducing its yield. The
yield observed was much higher in the case of Fe-Pd/C as compared to
Cu-Fe/C. Lower activity of the latter may be due to absence of noble
metal in the catalyst. Thus, Fe-Pd/C catalyst was used in further studies.
The full elemental survey using an XPS shows the presence of
oxygen, carbon, palladium and iron and no other impurities (Fig. 7a).
Binding energies for the peaks at 338.1 eV and 343.1 eV can be assigned
to the Pd3d electrons corresponding to the presence of Pd° state [28,41]
(Fig. 7b). This confirms the presence of metallic state of Pd on the iron
surface and absence of palladium oxide in the sample. Further, the
peaks at different binding energies for Fe species at 706.8ev, 710.8 eV
and 723.2 eV correspond to Fe° (Fe2p3/2), oxidized Fe2p3/2 and Fe2p1/
2 electron (Fig. 7c). The shoulder at 719 eV is due to the overlapping of
shakeup satellite for oxidized Fe2p3/2 and Fe0 (2p3/2) [42]. The peaks at
710.8 eV and 723.2ev confirm the presence of double and tri valent iron
atoms in the prepared bimetallic catalyst [28,41]. The results confirm
the presence of bimetallic nature of the catalyst with reduced Pd on iron
oxide [28] without formation of a metal alloy.
Fig. 7. XPS spectra of Fe-Pd NPs (a) full scan survey, (b) Pd 3d-electrons of palladium-containing nanoparticles, (c) Fe 2p-electrons.
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MolecularCatalysis465(2019)1–15
Fig. 8. Effect of different catalysts on conversion of HMF and selectivity of DMF.
Reaction Conditions: HMF 2 mmol, THF 20 mL, IS 0.3 mL, catalyst 10 g/L, temperature 150 oC, pressure 20 bar, speed of agitation 1000 rpm.
Tetrahydrofuran was a better solvent. When n-butanol and 1, 4-di-
oxane were used as solvent, the analysis was very difficult. The product
could not be identified due to close boiling point difference between
DMF and these solvents.
Effect of agitation speed
The agitation speed was varied from 600 to 1200 rpm to study the
effect of external mass transfer resistance (Fig. 9). Complete conversion
of HMF was possible and the DMF selectivity increased, only slightly,
with time when the agitation speed was increased from 600 to
1200 rpm (from 79% to 87%). Speeds higher than 1000 rpm show
Fig. 9. Effect of Speed of Agitation on conversion of HMF and selectivity of DMF.
Reaction Conditions: HMF 2 mmol, THF 20 mL, IS 0.3 mL, catalyst 10 g/L, temperature 150 oC, pressure 20 bar.
8

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
minimum changes in product yield. Thus 1000 rpm was considered as
the optimum speed toovercome the external mass transfer resistance. A
theoretical analysis proved that there was no external mass transfer
resistance as discussed in some of our earlier work [46]
out the hydrogenation of HMF to DMF. At higher temperatures and
pressures, it is observed that the hydrogen molecule dissociates into
atomic form. Its degree of dissociation increases, thereby allowing it to
bind successfully [43]. The effect of temperature was studied by
varying the temperature from 130 °C to 190 °C (Fig. 12). As the tem-
perature increased, the rate of reaction increased leading to higher
conversions. The selectivity for DMF increases from 83% at 130 °C to
88% at 150 °C. After 150 °C, however, even though the reaction rate
seems to be increasing, an increase in the formation of the by-products
(2,5-dimethyltetrahydrofuran) occurred along with DMF. This led to
reduction of DMF yield (86% at 190 °C). Thus, 150 °C was considered as
the optimum condition.
Effect of catalyst loading
The role of catalyst loading for the selected catalyst was studied by
varying the loading from 2.5 to 20 g/L (Fig. 10). As the loading of the
catalyst in the reaction mixture was increased, the number of active
sites increased, which led to increased initial rates of reaction. The
selectivity of DMF increased from 83% at 2.5 g/L to 87.5% at 20 g/L.
However, at very high catalyst loadings (higher than 10 g/L), there was
no significant change in DMF yield even though the number of available
sites increased. Further, the increase in catalyst amount also results in
side reaction of the DMF to by-products. Thus 10 g/L was found to be
the optimum catalyst loading for obtaining high yields of desired pro-
duct.
Effect of pressure
The pressure effects were studied by varying total hydrogen pres-
sure from 10 to 25 at m (Fig. 13). Pressure had an impact on the yield of
DMF. With increase in the hydrogen pressure, the concentration of
hydrogen inside the liquid phase increases which leads to higher rate of
reaction. As seen, the DMF selectivity was changed significantly with
increase in the hydrogen pressure from 80% at 10 atm to 88% at
20 atm. In this paper, we have performed experiments at 25 atm
(highest pressure) but it was found to favour by-product formation
through ring hydrogenation mechanisms leading to products such as 2,
5-dihydroxy-tetrahydrofuran (DHTHF) and 2, 5-dimethyltetrahy-
drofuran (DMTHF). Thus 20 atm was found to be the optimum pressure
for this reaction.
Effect of substrate concentration
The effect of substrate concentration on DMF yield was studied by
varying it from 0.05 to 0.2 mmol/mL (Fig. 11). As concentration of the
substrate increased, the rate of reaction increased. Higher yield of DMF
was obtained at higher substrate concentrations (from 83% at
0.05 mol/L to 88% at 0.2 mol/L). The increase in HMF concentration
increases the number of HMF available and hence the rate of conversion
is also increased. However, no significant increase was observed after
0.1 mol/L substrate concentration which may be due to competitive
adsorption of HMF.
Catalyst reusability
The catalyst reusability studies were done over three runs, including
the fresh catalyst (Fig. 14). Since the catalyst was magnetically separ-
able, it could settle in presence of the magnetic field. The catalyst was
Effect of temperature
The reaction temperature is an important parameter while carrying
Fig. 10. Effect of Catalyst Loading on conversion of HMF and selectivity of DMF.
Reaction Conditions: HMF 2 mmol, THF 20 mL, IS 0.3 mL, temperature 150oC, pressure 20 bar, speed of agitation 1000 rpm.
9

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Fig. 11. Effect of substrate concentration on conversion of HMF and selectivity of DMF.
Reaction Conditions: THF 20 mL, IS 0.3 mL, catalyst 10 g/L, temperature 150oC, pressure 20 bar, speed of agitation 1000 rpm.
separated by decanting the reaction mixture. The catalyst was then
refluxed with THF to remove any adsorbed impurities and vacuum
dried overnight. There is a slight loss in catalyst amount during hand-
ling. The recovered catalyst was then directly used as described in ex-
perimental section. It was observed that there was no loss in the mag-
netic properties of this catalyst even after consecutive uses. The slight
decrease in the DMF yield is due to the decrease in the amount of
catalyst fed in next cycle. Further, to test the leaching of catalyst, hot
filtration test was done at same condition and the catalyst was removed
after 30 min. The reaction was further carried out for 2 h at given
condition. There was very slight increase in yield of DMF from 56.8% to
58.2% which can be considered as an experimental error. Thus, there is
no leaching of active sites and catalyst was reusable and robust. Reused
catalyst was also characterized by XRD which shows identical peaks as
in the case of fresh catalyst. This confirms that there is no change in the
catalyst structure and prepared catalyst is reusable and stable.
reaction follows the Langmuir-Hinshelwood-Hougen-Watson (LHHW)
type model.
While considering this model, the following assumptions were
made:
5-Hydroxymethyl furfural (HMF) and hydrogen adsorb on the ad-
jacent metallic site.
•
Hydrogen adsorbs by dissociative mechanism.
•
A general derivation for the hydrogenation of the substrate is at-
tempted by using a mono-functional catalyst that contains only one
type of active site ‘S’. The substrate and hydrogen, both, are assumed to
be absorbed on this active site.
Adsorption of HMF
Chemisorption of HMF (A) on site S can be shown as:
K
A
(1)
(2)
A + S ⇄ AS
Kinetic modeling
The rate of this above chemisorption reaction is given by,
Reaction mechanism
CAS
KA
′
rAD = kaCACS − kaCAS = ka (CA CS −
)
Hydrogenation of HMF involves series of steps. The reactant and
hydrogen get absorbed on the metallic site of the catalyst. The inter-
mediate formed then converts into the final product i.e. DMF accom-
panied by water release. The reaction mechanism for the reaction
system is proposed (Scheme 2).
Adsorption of hydrogen
Assuming dissociative adsorption of H2
K
H
H2 + 2S ⇄ 2HS
(3)
Development of mathematical model
Preliminary interpretation of the rate data suggested that the
The rate for the above reaction can be written as:
10

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Fig. 12. Effect of Temperature on conversion of HMF and selectivity of DMF.
Reaction Conditions: HMF 2 mmol, THF 20 mL, IS 0.3 mL, catalyst 10 g/L, pressure 20 bar, speed of agitation 1000 rpm.
C2
KH
CH2S
KH
Thus Eq. (8) reduces to:
rHD = kh PH CS − khCHS = kh (PH CS2 − HS ) = kh (PH CS2 −
)
2
2
′
2
2
2
(4)
CAS CHS
CS
CBS = K1
(12)
(13)
Surface reaction
It is a series reaction wherein the intermediate is ultimately con-
verted into the final product. The first hydrogen atom attacks the al-
dehyde end of the HMF molecule as shown in the mechanism leading to
the formation of the first intermediate (Scheme 2). This first inter-
mediate is then subject to hydrogenation again thereby yielding the
second intermediate which gets ultimately hydrogenated to the final
product.
And from Eq. (9) reduces to,
CBS CHS
CCS = K1
CWS
The controlling rate then reduces to
CAS CH3S
− r3 = k3K1K2
CS CWS
(14)
K
1
(5)
(6)
(7)
AS + HS ⇄ BS + S
Desorption
K
2
For the sake of simplicity, we have assumed only one product, final
product i.e. ‘D’.
BS + HS ⇄ CS + WS
K
3
K
D
CS + HS ⇄ DS + WS
(15)
D + S ⇄ DS
The rates of the above equation are given as follows:
Desorption rate can be written as:
′
′
− r = k1CAS CHS − k CBS CS
(8)
(9)
1
1
CDCS
− rD = kd (CDS
−
)
′
− r2 = k2CBS CHS − k2CCS CWS
KD
(16)
As the surface reaction is the rate-controlling step, the other steps
− r3 = k3CCS CHS − k3 CDS CWS
(10)
(adsorption and desorption) can be considered to be fast and in equi-
We assume that this step of conversion, second intermediate to the
final product, is the slower of the two and hence the rate determining
step. Thus, the controlling rate Eq. (10) can be modified to,
librium.
Thus Eq. (2) becomes,
′
kaCACS = kaCAS
(17)
(18)
− r3 = k3CCS CHS
(11)
kaCACS
The other two reaction steps are thus considered to be fast and in
equilibrium.
CAS
=
′
ka
11

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Fig. 13. Effect of Pressure on conversion of HMF and selectivity of DMF.
Reaction Conditions: HMF 2 mmol, THF 20 mL, IS 0.3 mL, catalyst 10 g/L, temperature 150 oC, speed of agitation 1000 rpm.
CH2S = KH PH CS2
CAS = KACACS
(19)
(20)
2
Also, Eq. (4) becomes,
Fig. 14. Effect of Catalyst Reusability on yield of DMF.
Reaction Conditions: HMF 2 mmol, THF 20 mL, IS 0.3 mL, catalyst 10 g/L, temperature 150 oC, pressure 20 bar, speed of agitation 1000 rpm.
12

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Scheme 2. Possible mechanism for transformation of HMF to DMF.
CT = CS + CAS + CHS + CDS + CWS
Table 2
Value of kinetic rate constants at different temperatures.
=CS (1 + KACA + KH PH + KDCD + KW CW )
2
(24)
(25)
Temp (°C)
Rate constant,
kp’
Adsorption equilibrium
constant, KA (L/mol)
Adsorption equilibrium
constant, KH (L/mol)
CT
CS =
(L2/mol/g.
cat/min)
1 + K C + KH PH + KDCD + KW CW
(
)
A
A
2
The controlling rate from Eq. (14) can now be converted to all the
known concentrations.
80
1.49E-02
6E-02
1E-01
5.9E-03
5.3E-03
4.7E-03
4.3E-03
6.017
5.76
5.17
4.21
100
120
140
CAS CH3S
CS CWS
1.76E-01
− r3 = k3K1K2
(26)
Substituting values from above equations, we get,
CHS
=
KH PH CS
(21)
2
(k3K1K2KACAKH3/2PH3/2)CS2
2
− r3 =
Desorption step is also considered to be in equilibrium. Thus Eq.
KW CW
(27)
(16) becomes
Substituting the value of Cs from Eq. (25), the following is obtained:
CDS = KD CD CS
CWS = KW CW CS
(22)
(k3K1K2KACAKH3/2PH3/2)CT2
2
Similarly, for water, we can write a similar equation:
− r3 =
2
KW CW 1 + K C + KH PH + KDCD + KW CW
(
)
A
A
(28)
2
(23)
Since it is assumed that the surface reaction is rate controlling, the
desorption constant will be low. Thus, the above equation reduces to,
The total balance for the catalytic sites can be written as follows:
Fig. 15. Parity plot.
13

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
Fig. 16. Arrhenius plot.
(kKAKH3/2PH3/2)CAw
Conflict of interest statement
The authors declare no conflict of interest.
dCD
dt
2
− rA
=
=
KW CW (1 + KACA + KH PH + KDCD + KW CW )2
(29)
2
Where, k = k3K1K2 and w is the catalyst loading.
Eq. (29) can be solved for obtaining values of the kinetic rate con-
stant and adsorption coefficients (Table 2). The parity plot shows that
the model developed fits the experiment data well (Fig. 15).
The high values of adsorption coefficient of hydrogen are due to the
presence of noble metals. Low values are obtained for adsorption
coefficients of the main reactant (i.e. HMF) and water. The rate equa-
tion can thus be simplified as follows:
Acknowledgements
A.D. Talpade acknowledges University Grants Commission (UGC)
for the award of UGC- Junior Research Fellowship. M. S. Tiwari ac-
knowledges University Grants Commission (UGC) for the award of BSR
Senior Research Fellowship under its SAP Program in Chemical
Engineering. G.D. Yadav acknowledges support from R.T. Mody
Distinguished Professor Endowment, Tata Chemicals Darbari Seth
Distinguished Professor of Leadership and Innovation, and J.C. Bose
National Fellowship of Department of Science and Technology, Govt. of
India.
−dCA
′
− rA
− rA
=
=
= (k KA KH PH )CAw
2
(30)
(31)
dt
−dCA
′
′
= k CAw
dt
References
Where, for constant pressure,
′
[1] Y.J. Wang, B. Bin Ying, M. Chen, W. Shen, Z.Q. Liu, An NADPH-dependent
Lactobacillus composti short-chain dehydrogenase/reductase:characterization and
application to (R) - 1-phenylethanol synthesis, World J. Microbiol. Biotechnol.
(2017), https://doi.org/10.1007/s11274-017-2311-9.
[2] Y. Zhang, Y. Chen, J. Pan, M. Liu, P. Jin, Y. Yan, Synthesis and evaluation of acid-
base bi-functionalized SBA-15 catalyst for biomass energy conversation, Chem. Eng.
J. 313 (2017) 1593–1606, https://doi.org/10.1016/j.cej.2016.11.033.
[3] R. García-Morales, O. Elizalde-Solis, A. Zúñiga-Moreno, C. Bouchot, F.I. Gómez-
Ramos, M.G. Arenas-Quevedo, Volumetric properties of 2,5-dimethylfuran in mix-
tures with octane or dodecane from 293 K to 393 K and pressures up to 70 MPa, Fuel
209 (2017) 299–308, https://doi.org/10.1016/j.fuel.2017.07.112.
′
′
k
= k KA KH PH
(32)
2
Thus Eq. (30) simplifies to a pseudo-first order equation (31). Using
the values of kinetic rate constants, the activation energy of the reaction
can be evaluated. The Arrhenius plot for the reaction was made to get
the apparent energy of activation as 11.6 kcal/mol (Fig. 16).
Conclusion
[4] E.-S. Kang, D.W. Chae, B. Kim, Y.G. Kim, Efficient preparation of DHMF and HMFA
from biomass-derived HMF via a Cannizzaro reaction in ionic liquids, J. Ind. Eng.
Chem. 18 (2012) 174–177, https://doi.org/10.1016/j.jiec.2011.11.020.
[5] Z. Yang, W. Qi, R. Huang, J. Fang, R. Su, Z. He, Functionalized silica nanoparticles
for conversion of fructose to 5-hydroxymethylfurfural, Chem. Eng. J. 296 (2016)
209–216, https://doi.org/10.1016/j.cej.2016.03.084.
[6] W. Zhao, W. Wu, H. Li, C. Fang, T. Yang, Z. Wang, C. He, S. Yang, Quantitative
synthesis of 2,5-bis(hydroxymethyl)furan from biomass-derived 5-hydro-
xymethylfurfural and sugars over reusable solid catalysts at low temperatures, Fuel
217 (2018) 365–369, https://doi.org/10.1016/j.fuel.2017.12.069.
[7] A.B. Gawade, M.S. Tiwari, G.D. Yadav, Biobased green process: selective hydro-
genation of 5-hydroxymethylfurfural to 2,5-dimethyl furan under mild conditions
using Pd-Cs 2.5 H 0.5 PW 12 O 40 /K-10 Clay, ACS Sustain. Chem. Eng. 4 (2016)
4113–4123, https://doi.org/10.1021/acssuschemeng.6b00426.
[8] J. Wang, J. Ren, X. Liu, G. Lu, Y. Wang, High yield production and purification of 5-
hydroxymethylfurfural, AIChE J. 59 (2013) 2558–2566, https://doi.org/10.1002/
aic.14019.
A variety of bimetallic nanoparticles comprising Fe-Pd/C, Cu-Pd/C
and Cu-Fe/C were synthesized. Magnetically separable Fe-Pd/C bime-
tallic nano-catalyst was successfully synthesized and the characteriza-
tion of the fresh and used catalyst was carried out and the fidelity of the
catalyst proved. Various parameters affecting the yield of DMF have
been studied successfully. We have been successful in obtaining high
conversions and selectivity without the use of acidic precursors, thus
making the process green. The conversions of HMF obtained are very
high (> 95%) with high selectivity towards DMF (> 85%). Optimum
conditions needed to obtain maximum yield of DMF were established. A
mechanism for the hydrogenation reaction of HMF was postulated. The
reaction system follows the LHHW type model and the experimental
data fit this model well. The values for the reaction rate constants and
adsorption coefficients were established. The value of activation energy
was evaluated using Arrhenius plot as 11.6 kcal/mol. The reaction is
kinetically controlled.
[9] J. Shi, Y. Wang, X. Yu, W. Du, Z. Hou, Production of 2,5-dimethylfuran from 5-
hydroxymethylfurfural over reduced graphene oxides supported Pt catalyst under
mild conditions, Fuel 163 (2016) 74–79, https://doi.org/10.1016/j.fuel.2015.09.
047.
14

A.D. Talpade et al.
MolecularCatalysis465(2019)1–15
[10] Y. Roman-Leshkov, C.J. Barrett, Z.Y. Liu, J.A. Dumesic, Production of di-
methylfuran for liquid fuels from biomass-derived carbohydrates, Nature 447
(2007) 982–986, https://doi.org/10.1038/nature05923.
[11] T. Thananatthanachon, T.B. Rauchfuss, Efficient production of the liquid fuel 2,5-
Dimethylfuran from fructose using formic acid as a reagent, Angew. Chem. Int. Ed.
49 (2010) 6616–6618, https://doi.org/10.1002/anie.201002267.
[12] M. Chidambaram, A.T. Bell, A two-step approach for the catalytic conversion of
glucose to 2,5-dimethylfuran in ionic liquids, Green Chem. 12 (2010) 1253, https://
doi.org/10.1039/c004343e.
Commun. 43 (2014) 75–78, https://doi.org/10.1016/j.catcom.2013.09.001.
[29] S.C. Patankar, G.D. Yadav, Cascade engineered synthesis of γ-valerolactone, 1,4-
pentanediol, and 2-methyltetrahydrofuran from levulinic acid using Pd–Cu/ZrO2
catalyst in water as solvent, ACS Sustain. Chem. Eng. 3 (2015) 2619–2630, https://
doi.org/10.1021/acssuschemeng.5b00763.
[30] S.C. Patankar, S.K. Dodiya, G.D. Yadav, Cascade engineered synthesis of ethyl
benzyl acetoacetate and methyl isobutyl ketone (MIBK) on novel multifunctional
catalyst, J. Mol. Catal. A Chem. 409 (2015) 171–182, https://doi.org/10.1016/j.
molcata.2015.08.018.
[13] L. Maat, H. van Bekkum, G.C.A. Luijkx, N.P.M. Huck, F. van Rantwijk, Ether for-
mation in the hydrogenolysis of hydroxymethylfurfural over palladium catalysts in
alcoholic solution, Heterocycles 77 (2009) 1037, https://doi.org/10.3987/COM-
08-S(F)81.
[14] C.M. Mani, M. Braun, V. Molinari, M. Antonietti, N. Fechler, A high-throughput
composite catalyst based on nickel carbon cubes for the hydrogenation of 5-hy-
droxymethylfurfural to 2,5-dimethylfuran, ChemCatChem. 9 (2017) 3388–3394,
https://doi.org/10.1002/cctc.201700506.
[15] R. Goyal, B. Sarkar, A. Bag, N. Siddiqui, D. Dumbre, N. Lucas, S. Kumar, A. Bordoloi,
Studies of synergy between metal – support interfaces and selective hydrogenation
of HMF to DMF in water, J. Catal. 340 (2016) 248–260, https://doi.org/10.1016/j.
jcat.2016.05.012.
[16] G.-H. Wang, J. Hilgert, F.H. Richter, F. Wang, H.-J. Bongard, B. Spliethoff,
C. Weidenthaler, F. Schüth, Platinum–cobalt bimetallic nanoparticles in hollow
carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfural, Nat. Mater. 13
(2014) 293–300, https://doi.org/10.1038/nmat3872.
[17] S. Nishimura, N. Ikeda, K. Ebitani, Selective hydrogenation of biomass-derived 5-
hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) under atmospheric hy-
drogen pressure over carbon supported PdAu bimetallic catalyst, Catal. Today 232
(2014) 89–98, https://doi.org/10.1016/j.cattod.2013.10.012.
[18] B. Chen, F. Li, Z. Huang, G. Yuan, Carbon-coated Cu-Co bimetallic nanoparticles as
selective and recyclable catalysts for production of biofuel 2,5-dimethylfuran, Appl.
Catal. B Environ. 200 (2017) 192–199, https://doi.org/10.1016/j.apcatb.2016.07.
004.
[19] P. Yang, Q. Xia, X. Liu, Y. Wang, Catalytic transfer hydrogenation/hydrogenolysis
of 5-hydroxymethylfurfural to 2,5-dimethylfuran over Ni-Co/C catalyst, Fuel. 187
(2017) 159–166, https://doi.org/10.1016/j.fuel.2016.09.026.
[20] J. Chen, X. Liu, F. Zhang, Composition regulation of bimetallic RuPd catalysts
supported on porous alumina spheres for selective hydrogenation, Chem. Eng. J.
259 (2015) 43–52, https://doi.org/10.1016/j.cej.2014.07.049.
[21] P.S. Kumbhar, M.R. Kharkar, G.D. Yadav, R.A. Rajadhyaksha, Geometric and
electronic effects in silica supported bimetallic nickel–copper and nickel–iron cat-
alysts for liquid-phase hydrogenation of acetophenone and benzonitrile, J. Chem.
Soc. Chem. Commun. (1992) 584–586, https://doi.org/10.1039/C39920000584.
[22] G.D. Yadav, M.R. Kharkar, Liquid-phase hydrogenation of saturated and un-
saturated nitriles: Activities and selectivities of bimetallic nickel-copper and nickel-
iron catalysts supported on silica, Appl. Catal. A Gen. 126 (1995) 115–123, https://
doi.org/10.1016/0926-860X(95)00039-9.
[23] G.D. Yadav, Y.S. Lawate, Hydrogenation of styrene oxide to 2-phenyl ethanol over
polyurea microencapsulated mono- and bimetallic nanocatalysts: activity, se-
lectivity, and kinetic modeling, Ind. Eng. Chem. Res. 52 (2013) 4027–4039, https://
doi.org/10.1021/ie302587j.
[24] G.D. Yadav, Y.S. Lawate, Selective hydrogenation of styrene oxide to 2-phenyl
ethanol over polyurea supported Pd–Cu catalyst in supercritical carbon dioxide, J.
Supercrit. Fluids 59 (2011) 78–86, https://doi.org/10.1016/j.supflu.2011.08.008.
[25] J.W. Hong, D. Kim, Y.W. Lee, M. Kim, S.W. Kang, Atomic-distribution-dependent
electrocatalytic activity of Au – Pd, Angew. Chem.—Int. Ed. (2011) 8876–8880,
https://doi.org/10.1002/anie.201102578.
[26] S.E. Habas, H. Lee, V. Radmilovic, G.A. Somorjai, P. Yang, Shaping binary metal
nanocrystals through epitaxial seeded growth, Nat. Mater. 6 (2007) 692–697,
https://doi.org/10.1038/nmat1957.
[31] M.S. Tiwari, A.B. Gawade, G.D. Yadav, Magnetically separable sulfated zirconia as
highly active acidic catalysts for selective synthesis of ethyl levulinate from furfuryl
alcohol, Green Chem. 19 (2017) 963–976, https://doi.org/10.1039/C6GC02466A.
[32] M.S. Tiwari, G.D. Yadav, Novel aluminium exchanged dodecatungstophosphoric
acid supported on K-10 clay as catalyst: benzoylation of diphenyloxide with benzoic
anhydride, RSC Adv. 6 (2016) 49091–49100, https://doi.org/10.1039/
C6RA05379C.
[33] M.S. Tiwari, G.D. Yadav, Kinetics of Friedel–Crafts benzoylation of veratrole with
benzoic anhydride using Cs2.5H0.5PW12O40/K-10 solid acid catalyst, Chem. Eng.
J. 266 (2015) 64–73, https://doi.org/10.1016/j.cej.2014.12.043.
[34] M.S. Tiwari, T. Jain, G.D. Yadav, Novel bifunctional palladium-dodecatung-
stophosphoric acid supported on titania nanotubes : one-pot synthesis of n ‑ pentyl
tetrahydrofurfuryl ether from Furfuryl alcohol and n-pentanol, Ind. Eng. Chem. Res.
(2017) 12909–12919, https://doi.org/10.1021/acs.iecr.7b00078.
[35] K. Mori, Y. Kondo, H. Yamashita, Synthesis and characterization of FePd magnetic
nanoparticles modified with chiral BINAP ligand as a recoverable catalyst vehicle
for the asymmetric coupling reaction, Phys. Chem. Chem. Phys. 11 (2009) 8949,
https://doi.org/10.1039/b910069e.
[36] E.V. Golubina, E.S. Lokteva, T.S. Lazareva, B.G. Kostyuk, V.V. Lunin, V.I. Simagina,
I.V. Stoyanova, Hydrodechlorination of tetrachloromethane in the vapor phase in
the presence of Pd–Fe/sibunit catalysts, React. Kinet. Catal. Lett. 45 (2004)
183–188, https://doi.org/10.1023/B:KICA.0000023789.28190.1b.
[37] U. Holzwarth, N. Gibson, The Scherrer equation versus the “Debye-Scherrer equa-
tion,”, Nat. Nanotechnol. 6 (2011), https://doi.org/10.1038/nnano.2011.145
534–534.
[38] J.K. Kim, J.K. Lee, K.H. Kang, J.W. Lee, I.K. Song, Catalytic decomposition of
phenethyl phenyl ether to aromatics over Pd–Fe bimetallic catalysts supported on
ordered mesoporous carbon, J. Mol. Catal. A Chem. 410 (2015) 184–192.
[39] C. Espro, B. Gumina, E. Paone, F. Mauriello, Upgrading lignocellulosic biomasses:
hydrogenolysis of platform derived molecules promoted by heterogeneous Pd-Fe
catalysts, Catalysts 7 (2017) 78, https://doi.org/10.3390/catal7030078.
[40] J.K. Kim, J.K. Lee, K.H. Kang, J.C. Song, I.K. Song, Selective cleavage of C O bond in
benzyl phenyl ether to aromatics over Pd–Fe bimetallic catalyst supported on or-
dered mesoporous carbon, Appl. Catal. A Gen. 498 (2015) 142–149, https://doi.
org/10.1016/j.apcata.2015.03.034.
[41] K. Mishra, N. Basavegowda, Y.R. Lee, Biosynthesis of Fe, Pd, and Fe–Pd bimetallic
nanoparticles and their application as recyclable catalysts for [3+2] cycloaddition
reaction: a comparative approach, Catal. Sci. Technol. 5 (2015) 2612–2621,
https://doi.org/10.1039/C5CY00099H.
[42] X. Li, W. Zhang, Sequestration of metal cations with zero valent iron nanoparticles:
A study with high resolution X-ray photoelectron spectroscopy (HR-XPS), J. Phys.
Chem. C 111 (2007) 6939–6946, https://doi.org/10.1021/jp0702189.
[43] M.S. Tiwari, G.D. Yadav, F.T.T. Ng, Selective hydrogenation of 3,4-dimethox-
ybenzophenone in liquid phase over Pd/C catalyst in a slurry reactor, Can. J. Chem.
Eng. 92 (2014) 2157–2165, https://doi.org/10.1002/cjce.22073.
[44] N.S. Babu, N. Lingaiah, J.V. Kumar, P.S.S. Prasad, Studies on alumina supported Pd
– Fe bimetallic catalysts prepared by deposition – precipitation method for hydro-
dechlorination of chlorobenzene, Appl. Catal. A Gen. 367 (2009) 70–76, https://
doi.org/10.1016/j.apcata.2009.07.031.
[45] S. Nishimura, Handbook of Heterogeneous Catalytic Hydrogenation for Organic
Synthesis, Wiley, New York, 2001.
[27] X. Liu, D. Wang, Y. Li, Synthesis and catalytic properties of bimetallic nanomaterials
with various architectures, Nano Today 7 (2012) 448–466, https://doi.org/10.
1016/j.nantod.2012.08.003.
[46] J. Molleti, M.S. Tiwari, G.D. Yadav, Novel synthesis of Ru/OMS catalyst by solvent-
free method: Selective hydrogenation of levulinic acid to γ-valerolactone in aqueous
medium and kinetic modelling, Chem. Eng. J. 334 (2018) 2488–2499, https://doi.
org/10.1016/j.cej.2017.11.125.
[28] W. Tang, J. Li, X. Jin, J. Sun, J. Huang, R. Li, Magnetically recyclable Fe@Pd/C as a
highly active catalyst for Suzuki coupling reaction in aqueous solution, Catal.
15