Single pot selective hydrogenation of furfural to 2-methylfuran over carbon supported iridium catalysts

Article abstract of DOI:10.1039/c8gc00284c

Various iridium supported carbon catalysts were prepared and screened for the direct hydrogenation of furfural (FFR) to 2-methyl furan (2-MF). Amongst these, 5% Ir/C showed excellent results with complete FFR conversion and highest selectivity of 95% to 2-MF at a very low H₂ pressure of 100 psig. Metallic (Ir°) and oxide (IrO₂) phases of Ir catalyzed the first step hydrogenation involving FFR to FAL and subsequent hydrogenation to 2-MF, respectively. This was confirmed by XPS analysis and some control experiments. At a low temperature of 140 °C, almost equal selectivities of FAL (42%) and 2-MF (43%) were observed, while the higher temperature (220 °C) favored selective hydrodeoxygenation. At optimized temperature, 2-MF was formed selectively while higher pressure and higher catalyst loading favored ring hydrogenation of furfural rather than side chain hydrogenation. With the combination of several control experimental results and detailed catalyst characterization, a plausible reaction pathway has been proposed for the selective formation of 2-MF. The selectivity to various other products in FFR hydrogenation can be manipulated by tailoring the reaction conditions over the same catalyst.

Full text of DOI:10.1039/c8gc00284c

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Single Pot Selective Hydrogenation of Furfural to 2-Methylfuran
Over Carbon Supported Iridium Catalysts
Received 00th January 20xx,
Accepted 00th January 20xx
Nandan S. Date a,b, Amol M. Hengne c, K-W Huang c, Rajeev C. Chikate b*, Chandrashekhar V. Rode
a*
DOI: 10.1039/x0xx00000x
Various iridium supported carbon catalysts were prepared and screened for direct hydrogenation of furfural (FFR) to 2-
methyl furan (2-MF). Amongest these, 5% Ir/C showed excellent results with complete FFR conversion and highest
selectivity of 95% to 2-MF at very low H2 pressure of 100 psig. Metallic (Iro) and oxide ( IrO2) phases of Ir catalyzed first
step hydrogenation involving FFR to FAL and subsequent hydrogenation to 2-MF,respecively. This was confirmed by XPS
analysis and some controlled experiments. At low temperature of 140 oC, almost equal selectivities of FAL (42%) and 2-MF
(43%) were observed, while higher temperature (220 oC) favored selective hydrodeoxygenation. At optimized
temperature, 2-MF formed selectively while higher pressure and higher catalyst loading favored ring hydrogenation of
furfural rather than side chain hydrogenation. With combination of several control experimental results and detailed
catalyst characterization, a plausible reaction pathway has been proposed for selective formation of 2-MF. The selectivity
to various other products in FFR hydrogenation can be manipulated by tailoring the reaction conditions over the same
catalyst.
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subsequent hydrogenation of aromatic ring to produce furfuryl
alcohol, tetrahydrofurfuryl alcohol, pentanediols, 2-methyl
furan, methyl tetrahydrofuran, cyclopentanone etc. (Scheme
1)7,8 which constitute the key fuel additives and starting
monomers.
Introduction
Transformation of lignocellulosic biomass into fine chemicals
and various workable merchandises is gaining more
importance in pursuit of alternatives for petroleum based fuels
and chemicals.1-3 Among the variety of bio-derived feedstock
options, abundantly available lignocellulosic material at a
lower cost can be easily converted into a variety of platform
molecules. Efficient transformation of these platform
molecules with maximum selectivity to a useful product in a
multiproduct reaction becomes a very interesting challenge in
2,4
terms of catalyst design and process competitiveness.
According to DOE report of 2004, furfural is considered as a
key platform moiety in the development of lignocellulose
based bio-refinery. It is mainly derived by acid dehydration of
arabinose and xylose which are obtained from unused
5,6
agriculture waste such as corncobs, wood residue etc.
Furfural is a major component of biomass derived bio oil and
its current global production is almost 50,00,000 tpa. However
limited intensification techniques and tedious isolation
problems are the main drawbacks in efficient conversion of
6-7
FFR into C5 chemicals.
Main hydrogenation products of
Scheme 1: General furfural hydrogenation scheme
furfural are obtained by the reduction of C=O bond and
For example, 2-MF is a fine chemical arising from furfural via
selective hydrogenation of C=O bond. Being considered as a
green solvent, it has vast uses in bio-refinery as well as in
chemical industries. Its water miscible nature and solubility in
many organic solvents makes it useful for the formation of
building blocks in the pharmaceutical industry. 2-MF is also
a.N. S. Date, Dr. C. V. Rode* CEPD, CSIR-NCL, Dr Homi Bhabha Road, Pashan, Pune-
411008.
b.N.S. Date, Prof. R. C. Chikate* Post-graduate & research centre, Department of
Chemistry, M. E. S.’ S Abasaheb Garware college of Arts and Science, Karve road,
Pune-411004.
c. A. M. Hengne, K-W Huang. KAUST Catalysis Center and Division of Physical
Sciences and Engineering, King Abdullah University of Science and Technology,
Thuwal, 23955-6900, Kingdom of Saudi Arabia.
† Corresponding author: cv.rode@ncl.res.in
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used as a starting material in the production of toluene on a Furfural, furfuryl alcohol, tetrahydrofurfuryl alcohol, 2-
commercial scale. It shows good combustion performance and methylfuran, 2-methyltetrahydrofuran, pentanediols along
high energy density similar to 2-MeTHF, also RON of 2-MF is with Al2O3, SiO2 and TEOS were purchased from Sigma Aldrich,
greater than that of gasoline, which can be a good alternative Bangalore, India. IrCl3.3H20 was purchased from Johnson
4
to gasoline.9-1 Efficient and selective conversion of furfural to Matthye. Sodium hydroxide and sodium borohydride were
other by-products mainly depends on appropriate catalyst purchased from Thomas Baker, India. Hydrogen gas was
design and substrate-metal/support interactions or adsorption obtained from Vadilal Chemicals Pvt. Ltd
of substrate.
. Mumbai, India.
2-MF production is possible by selective hydrodeoxygenation Pre-treatment of carbon
of FFR without affecting the furanic “O” as well the ring double
5g charcoal was dispersed in 100 mL of 10 % sulphuric acid
solution and stirred for 6h at 65 OC. The solid was filtered and
washed successively with DI water till neutrality. This cake was
dried at 85 OC for overnight and used for preparation of
catalysts.
bonds.7 In the last decade, various types of catalyst systems
were developed for the synthesis of 2-MF from furfural either
via direct hydrogenation using H2 or via catalytic transfer
hydrogenation using IPA. Catalysts containing chromium were
reported to be very efficient for selective conversion of FFR to
2-MF but have a problem of their inherent toxicity.15 Recently,
Ni-Cu or Fe-Cu, Fe-Ni alloy catalysts have been reported for
synthesis of 2-MF with high yield but they possess serious
deactivation problems.16-19 Sitthisa et al. have reported various
silica supported nickel and copper catalysts for selective
conversion of furfural to 2-methyl furan.20-22 Catalyst systems
containing Cu, Cr, Zn with varying metal compositions showed
excellent performance giving 98% FFR conversion with more
than 90% selectivity to 2-MF, with excellent stability and
recyclability.23,24 Vlachos et al. reported a carbon supported
Ru catalyst system where 61% yield of 2-MF was achieved
through CTH using IPA.25 The same group recently reported a
nano-porous Cu-Al-Co ternary alloy catalyst system where 66%
yield of 2-MF was possible at higher temperature of 240 OC.26
In a similar manner, Hermans et al. also reported CTH of FFR to
2-MF over Pd/Fe2O3 giving 62% 2-MF yield.27 Various reports
are also available on Cu containing bimetallic catalysts in
Catalyst preparation for Ir/C
All the catalysts were prepared by wet impregnation method
as per previously reported procedure.35 For the preparation of
1g of 5 % Ir/C catalyst, 91mg of IrCl3 was first dissolved in 50ml
DI water and stirred for 10 min. To this, slurry of 0.95 g
activated carbon in water was added slowly with constant
stirring and whole mixture was stirred for 2 h. 5M NaOH
solution was then added to the above solution till pH was close
to 7 and stirring was continued for further 30 minutes. To the
above solution, 0.5g NaBH4 was added in small portions and
mixture was stirred for 30 min under inert atmosphere. The
catalyst was filtered, washed several times with DI water and
kept for drying in oven at 110 OC. Similar procedures was
adopted for preparation of 1-6 % Ir/C catalysts. Similar
protocol was adopted for the synthesis of 5 % Ir on various
supports like Al2O3, SiO2, Mont K10, TiO2.
combination with another oxophilic metal showing
a
Catalyst characterization
comparable selectivity to 2-MF from FAL through HDO
process.28-31 Recently, a new catalyst based on molybdenum is The X- ray diffraction measurement was carried out on
considered to be very active and selective for furfural Shimadzu 6100 using Cu-Kα for crystallinity and the phase
conversion to 2-MF where 2-MeF selectivity of 60% is reported purity analysis of Ir/C samples. HR-TEM images of catalysts
at low temperature.32,33 In recent papers, DFT study were were obtained the particle size and morphology were studied
carried over different catalysts.34 In our recent study of furfural using transmission electron microscope model JEOL 1200 EX.
hydrogenation over boron doped Pd/C catalysts, 2-MF BET surface area and ammonia TPD of all Ir-supported
selectivity achieved was only 35-45%. It was found that the catalysts were obtained using the DFT method on
a
selectivities could be switched to ring hydrogenated and Quantachrom3 iQ2. XPS analysis was carried out on Thermo
decarbonylation products by controlling the catalyst particle Fisher Scientific Instrument. The spectra were excited by low
size however, achieving the highest selectivity to only power Al Kα X-ray source and analyzer was operated in the
hydrodeoxygenation product like 2-MF was not possible over constant analyzer energy (CAE) mode. Pyridine FT-IR spectra of
35
Pd/C catalyst. Hence in the present work, we focused our the prepared catalysts were recorded on a Perkin Elmer 2000
efforts on developing
a
catalyst system for furfural FTIR spectrometer in the 4000–400 cm−1 wave number range
hydrogenation to 2-methylfuran with a maximum selectivity using the KBr pellet technique.
up to 95 %. Not only the structure activity correlation was
established for our novel Ir based catalyst system by detailed Typical procedure for catalytic hydrogenation of furfural
characterization but also the product selectivity could be
Catalytic hydrogenation of furfural was performed in a 300 ml
tuned by varying the different reaction conditions.
stainless steel autoclave equipped with overhead stirrer, a
pressure gauge and automatic temperature control apparatus.
In a typical experiment, 2.5 g furfural in 95 ml IPA, and catalyst
Experimental
(0.25 g) were loaded into the reactor. It was then sealed and
Materials
purged with H2 for 2 times to exclude air. H2 was charged into
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the reactor, when the autoclave temperature reached to were observed. This suggests that Ir dispersion on carbon was
desired temperature. The samples were withdrawn from time of an amorphous nature or overlap of the characteristic peaks
to time for monitoring the progress of the reaction with GC of iridium with those of carbon. Amorphous nature of catalyst
analysis.
in which formation of small cluster of active sites on the
surface results in small particle sizes could be responsible for
high activity towards furfural hydrogenation to give 2-MF.38
Further study was done with 5% Ir/C catalyst.
Product analysis
Timely samples were collected and analyzed on Thermo TRACE
700 GC using HP-5 capillary column having dimensions 30 m x
0.32 mm x 0.25 µm with a flame ionization detector. The
following temperature program method was used for GC
analysis: 40 OC (3 min), 1 OC/min, 45 OC (1 min), 100 OC/min, 60
O
(0 min), 200 C/min, and 250 (1 min). Performance of 5 % Ir/C
analyst was evaluated in terms of (%) conversion of FFR and
(%) product selectivity that are defined below.
Results and discussion
Main goal of the present work was to achieve maximum
selectivity to 2-MF in
a
single step catalytic
hydrodeoxygenation of FFR. This transformation involves
firstly, hydrogenation of FFR to FAL with simultaneous
hydrodeoxygenation to 2-MF with loss of one water molecule.
In our previous work on catalyst screening for FFR
hydrogenation, Ir supported on C showed 83 % selectivity to 2-
MF with suppression of by-products formation.35 In
continuation, detail catalyst characterization for understanding
the observed highest selectivity to 2-MF is discussed below.
Figure 1: XRD graphs of 1% to 6% Ir/C catalysts
XPS
In order to examine chemical composition as well as
electronic states of the metal functions in various catalyst
samples, XPS study was carried out and the results are shown
in Figure 2.
Catalyst characterization
BET surface area
A series of iridium C supported catalyst were prepared with
varying metal loadings from 1% to 6% and their surface area
values are presented in Table S1. BET surface area of bare
carbon support was 108 m2/g, with increase in metal loading
from 1% to 6%. There was gradual increase in surface area
from 117 m2/g to 215 m2/g. Linear increase in surface area
may be due to agglomeration of iridium nanoparticles on the
surface of carbon, surface modification of carbon pore
structure during pre-treatment of carbon support and time of
reduction with NaBH4.36
XRD
X-ray diffraction of 1-6 % Ir/C catalyst with bare carbon
support is shown in figure 1. A broad characteristics peak at 2θ
=
24.80o corresponds to (002) plane, representing the
amorphous phase of layered graphitic carbon. A second peak
was observed at 2
= 44.15o, representing a characteristic
θ
Figure 2A: XPS spectra of Fresh 5% Iridium/ Carbon-Iridium 4f
plane of (100) of rhombohedral structure of carbon. These
planes resemble the planes of turbostratic carbon peak or the
presence of graphitic carbon.35,37 After impregnation of Ir on
carbon support, no any characteristic peaks of iridium species
The binding energy values (B.E.) for all the catalysts were
interpreted after applying the charge correction using C1s
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spectra (B.E. 284.6 eV). Figure 2A shows XPS spectra of Ir 4f of Figure S1 depicts the C1s core level spectra of monometallic
5% Ir/C catalyst, where splitting of Ir 4f peak into 4f5/2 and 4f7/2 fresh 5% Ir/C with corrected C1s at B.E. 284.6 eV. After
is due to spin orbit coupling of the 4f orbital (3.1 eV). deconvolution, four different peaks appeared with B.E. at
Additionally, satellite peaks were observed in the 4f5/2 region 284.16 eV, 284.59 eV, 284.78 eV and 286.33 eV. Out of these,
of spectrum, which is 4 eV above the region of 4f 7/2, this is peaks at BE
= 284.13 eV, 284.59 eV and 284.78 eV
mainly due to the structured electron–hole pair excitation. corresponded to the presence of adventitious carbon and C-C
More intense peak as a doublet was observed at BE of 60.98 bond, respectively. While, the peak at BE = 286.33 eV
eV implying that iridium monolayer formed was of rutile type represents the existence of C-OH or C-O-C bonds.46 However,
and was confirmed by the presence of metallic Ir peak at BE = there is no detectable C=O and O-C=O species at BE of 287.9
60.86 eV which is analogous to the previous literature.39 After eV and 288.8 eV on the catalyst surface. Contribution of the
deconvolution, total 9 peaks of the core level Ir 4f spectra above peaks suggests the even deposition of iridium particles
were observed among which seven peaks could be ascribed to over carbon supports which existed in metallic as well as its
4f7/2 and 4f5/2 along with two satellite peaks. In 4f7/2 region, 3 different oxide states.
overlapping peaks were obtained at BE = 60.9 eV, 61.5 eV and
62.21 eV which were corresponding to the metallic Ir, IrO2 and TEM
IrO3, respectively.39,40 Similarly, the 4f5/2 region showed peaks
The particle size and morphological features of fresh and spent
at BE = 63.94 eV, 64.41 eV and 64.53 eV. Shifting of these
Ir/C catalysts were determined by TEM as shown in Figures 3A
peaks at lower binding energy suggests that there was absence
and 3B.
of bulk oxide species.41,40 The peaks observed at BE = 66.31 eV
and 69.21 eV were considered as satellite peaks of iridium.
Figure 2B: XPS spectra of Fresh 5% Iridium/ Carbon- Oxygen 1s
Deconvulated oxygen 1s core level spectra in Figure 2B, shows
three distinct peaks of oxygen 1s spectra at B.E. = 529.92 eV,
531.31 eV and 533.01 eV. Both peaks at B.E. = 529.92 eV and
531.3 eV correspond to the lattice oxygen in the from oxide
and hydroxide form of Ir. From the reported literature, peak at
B.E. of 531.3 eV could be responsible for the presence of Ir-O
or Ir-OH bond in the catalyst. Also, peak at B.E. = 531.3 eV was
attributed to various oxygen defects present in the catalyst,
which arise from O2-, O- or surface adsorbed oxygen species.44
Presence of larger peak at BE = 533.01 eV could be assigned to
adventitious carbon species which originate from diminutive
fraction of oxygen components present in carbon.42,43 These
observations suggest that oxygen defect sites in this catalyst
system may help to produce H2 and oxygen via splitting of H2O
involved in the mechanistic pathway during furfural
hydrogenation to 2-MF. This is analogues with water gas shift
reaction and oxygen evolution reactions by using Ir catalysts
systems.45
Figure 3: TEM analysis of 5% Iridium/Carbon with SAED pattern (inset figures
A] Fresh Ir/C B] Used Ir/C]
Supported Ir particles on carbon showed uniform distribution
having spherical morphology and particle size in the range of
2.4 to 3.6 nm.47 SAED pattern shown as inset of Fig 3A with
distinct diffuse rings was in close agreement with XRD results.
Average interlayer spacing calculated as 0.2112 nm was for the
characteristic phase of graphitic carbon or iridium monolayer
formed on the carbon surface. Similar findings were observed
for spent 5% Ir/C catalyst sample. Interestingly, particle size in
the used catalyst was slightly reduced in the range of 2.1 to 3.3
nm.47 Indeed, increase in intensity of three diffuse rings in
SAED pattern implied the formation of crystalline phases over
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the support. The crystallinity observed may be due to supported Ir catalyst gave selectivity of 46% to 2-MF and 52%
intercalation of iridium with the carbon support with d spacing to THFAL. Both Al2O3 and MMT-K10 supported catalysts
of around 0.2095 nm.48,49
preferentially formed FAL (35%) along with 2-MF up to only
21% with THFAL still remaining higher at 52%. However,
incorporation of Ir on MMT-K10, resulted in significant (27%)
formation of open chain product like 1,2-PeDO which could be
ascribed to the presence of parent surface acidity of MMT K10.
Ammonia TPD
Since hydrodeoxygenation of furfural to give 2-MF is favoured
by acid catalysis25
, total acid strength of 5% Ir/C catalyst was
50
Among all the catalysts screened very interestingly, 4% Ir/C
determined by NH3-TPD and the results are shown in Figure S2
and Table S2. Fresh catalyst showed three distinct peaks in all
three regions. Typical broad desorption peak in the
temperature range of 40-200 °C with maxima centred at 64 oC
indicated the presence of weak acid sites. The desorption peak
catalyst was found to be the best catalyst for selective
production (80%) of 2-MF via furfural hydrogenation in a single
step. In order to further maximize 2-MF selectivity, initially
metal loading effect was studied in the range of 1% to 6%.
o
present in the range of 200-400 °C centred at 347 C implied
Table 1: Effect of metal loading
the presence of medium acidic sites while, strong intense peak
observed above 400 °C cantered at 714 °C implied the
presence of very strong acidic sites. Total acidity in terms of
ammonia desorbed per unit weight of catalyst for the fresh
catalyst was 0.1633 mmol g-1 while for the spent catalyst, it
was slightly higher as 0.1669 mmol g-1. The reason for such
significant acid strength was due to the presence of oxide
species of iridium the presence of which was confirmed by
XRD and XPS as discussed above. Brönsted acidity was
confirmed by Py-IR technique where, distinct absorption band
at 1541 cm-1 clearly confirmed the presence of Brönsted
acidity, as shown in Figure S3.
Sr Metal Conv.
Selectivity,%
.
load,
%
,
II
IV
V
VI VII TON
TOF
h-1
N
o
%
+
VIII
1
2
3
4
5
1
2
4
5
6
90
94
99
99
99
48
28
18
-
-
-
52
70
80
95
87
-
-
-
2
2
-
280
208
128
158
130
560
416
256
316
264
-
-
1
5
4
8
-
-
Reaction conditions: furfural, 2.5g; solvent (IPA), 95ml; loading, 0.25g, temperature,
220oC; H2 pressure, 100 psig; Agitation speed, 1000, time, 5h.
Activity testing
Table 1 shows that increasing Ir loading from 1 to 4% favoured
increase in 2-MF selectivity from 52% to 80% at the cost FAL
selectivity which depleted from 48% to 18% (entries 1-3).
Subsequent increase in metal loading up to 5% resulted in
complete consumption of FAL with concomitant formation of
2- MF to the extent of about 95% (Table 1, entry 4). Further,
increase in Ir loading up to 6% influenced the selectivity of 2-
MF to drop down to 87% with increase in next step ring
hydrogenated products (Table 1, entry 5). Thus, appropriate Ir
metal loading favoured selective formation of 2-MF, above
which further hydrogenation of 2-MF takes place due to
availability of higher amount of active sites. Respective
catalytic activity calculated in terms of TON and TOF at low
conversion levels are given in Tables 1 and S3. A typical
conversion and selectivity Vs time profile of FFR hydrogenation
over 4% Ir/C is shown in Figure 5. Both conversion and 2-MF
selectivity linearly increased with progress in reaction time. At
the end of first hour, 71% FFR conversion was achieved which
steadily reached to 99% until the reaction reached to 5th h.
Initially in the first hour, 56% selectivity to FAL was observed
which then decreased linearly to 4% during 4th hour and finally
diminished after 5th hour of the reaction. Similarly, 2-MF
selectivity of 43% observed during 1st hour of reaction time
steadily enhanced to 95% at the end of 5th hour. On the other
hand, formation of 2-MeTHF and THFAL was very negligible
and remained almost constant throughout the reaction. These
results certainly indicate that 5% Ir/C was highly selective to 2-
MF formation which proceeded through FAL intermediate. In
order to confirm the later, hydrogenation of the intermediate
Among several products possible from FFR, formation of 2-MF
is via selective removal of oxygen from formyl group through
selective hydrodeoxygenation suppressing the competitive
ring hydrogenation as well as ring opening products. For
achieving this, initially catalysts with iridium on different
supports like C, Al2O3, MMT, and ZrO2 were screened for
furfural hydrogenation and the results are given in Figure 4.
Figure 4: Metal on different support. Reaction conditions: furfural, 2.5g; solvent
(IPA), 95ml; catalyst (4% Ir), 0.25g, temp., 220oC; `H2 pressure, 100 psig; Agitation
speed, 1000 rpm, time, 5h.
It was observed that 4% Ir on different supports showed near
about similar furfural conversion while, the selectivity to 2- MF
was in the following order, C>ZrO2>Al2O3=MMT. ZrO2
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FAL was carried out under standard optimized reaction 95% with complete conversion of furfural was observed. This
conditions which gave maximum selectivity to 2-MF and small increase in 2-MF selectivity with increase in temperature was
amount of THFAL (5%) and 2-MeTHF (10%) (Table S4). accompanied by decrease in FAL selectivity from 68% to nil.
Similarly, starting with 2-MF as
a
substrate, complete With further increase in reaction temperature up to 240 oC,
selectivity to 2-MeTHF was achieved. From these results, a marginal decrease in selectivity to 2-MF from 95% to 87% was
plausible reaction pathway is shown in Scheme 2. Above observed. A small amount of THFAL (~ 5%) was observed even
transformations may be due to structural role of different at lowest temperature of 140 oC which slightly increased up to
iridium phases which are exposed during the hydrogenation, 200 oC and became almost nil at 220 oC. However, 2-MeTHF
as discussed later.
formation was observed only at 180 oC which increased
o
linearly to ~ 10 % up to 240 C. Thus ring hydrogenation of 2-
MF to some extent was facilitated only at higher temperature
over Ir/C catalyst.
Figure 5: Conversion and selectivity vs time profiles Reaction conditions: furfural, 2.5g;
solvent (IPA), 95ml; catalyst, 0.25g, temp., 220oC; H2 pressure, 100 psig; Agitation
speed, 1000 rpm, time, 5h
.
Figure 6: Effect of temperature on conversion and selectivity of furfural hydrogenation.
Reaction conditions: furfural, 2.5g; solvent (IPA), 95ml; catalyst, 0.25g; H2 pressure,
100 psig; Agitation speed, 1000 rpm, time, 5h.
Effect of H2 pressure
Figure 7 shows influence of H2 pressure in the range 100-750
psig on product distribution of furfural hydrogenation by
keeping all other parameters constant.
Scheme 2: Plausible reaction pathway
As 5% Ir/C catalyst showed maximum selectivity to 2-MF
further reaction parameter optimization studies for furfural
hydrogenation were carried out over 5% Ir/C catalyst.
Effect of temperature
Effect of temperature on conversion of furfural and product
o
distribution was studied in a range from 140-240 C. Figure 6
Figure 7: Effect of H2 pressure on conversion and selectivity of furfural hydrogenation
Reaction conditions: furfural, 2.5g; solvent (IPA), 95ml; catalyst, 0.25g, temp., 220 oC;
Agitation speed, 1000 rpm, time, 5h.
shows that at a lower temperature of 140 °C, the conversion of
furfural was 70
% with 68 % selectivity to first step
hydrogenation product, FAL while selectivity to 2-MF obtained
was 25%. With increase in reaction temperature from 140 to
220 oC, a trend of linear increase 2-MF selectivity from 25% to
Complete conversion of FFR was achieved even at lowest H2
pressure of 100 psig. While, 2-MF selectivity remained
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constant at ~95% up to 500 psig but dramatically dropped
down to 75% at enhanced pressure of 750 psig with a
subsequent increase in THFAL (17%) selectivity. This was due
to ring hydrogenation at higher H2 pressure to give 2-MeTHF.
Thus, increase in pressure to 500 psig, 2-MF selectivity was
92% with 7% selectivity to 2-MeTHF. With further increase in
pressure to 750 psig, 2-MF selectivity dropped down to 75%
with higher selectivity to THFAL (17%) and 2-MeTHF (8%).
Hence, the low H2 pressure of 100 psig would be more
favourable for furfural hydrodeoxygenation process to give 2-
MF.
Effect of catalyst loading
Catalyst loading effect in the range of 0.12g to 0.4g was
studied at 100 psig H2 keeping all other reaction conditions
constant.
Figure 9: Catalyst recycle study. Reaction conditions: furfural, 2.5g; solvent (IPA), 95ml;
catalyst, 0.25g, temp., 220 oC; H2 pressure, 100 psig; Agitation speed, 1000 rpm, time,
5h.
Initially at optimized H2 pressure 100 psig (Figure 9), after
completion of the reaction, reaction crude was separated by
decantation after settling the catalyst and fresh charge was fed
to the reactor and the reaction was continued. Catalyst was
active till 4th use. Till 3rd reuse selectivity pattern was the same
as for fresh catalyst however, after 4th reuse 2-MF selectivity
dropped down from 95% to 86% along with increase in FAL
selectivity from nil to 13 % with a negligible decrease in 2-
MeTHF from 4% to 2%. This was also associated with decrease
in conversion from 99% to 87 %. Decrease in conversion and
selectivity may be due to catalyst poisoning causing
unavailability of active metallic iridium sites. More
importantly, activity of the reused 5%Ir/C catalyst could be
regained by activating the spent catalyst in H2 environment
and the catalyst showed complete FFR conversion with similar
2-MF selectivity for next reuse. In order to compare stability of
the catalyst, catalyst recycle runs were also carried out at high
pressure (500 psig) and results are shown in Figure S5.
Surprisingly, 2-MeTHF selectivity increased during successive
recycles with decrease in 2-MF selectivity. In order to check
the possibility of iridium leaching, hot filtration test was
performed as shown in Figure 10. After 1st h, the reaction was
stopped and the catalyst was removed by filtration. The
reaction was continued with the filtrate devoid of catalyst. As
no any change in conversion of furfural was observed, it could
be inferred that the catalyst was quite stable and non-
leachable under the standard optimized reaction conditions.
Results were crossed checked by ICP-OES experiments. At the
same time, solvent reuse study were also done where almost
no change in conversion as well as in 2-MF selectivity were
observed. (Table S5)
Figure 8: Effect of catalyst loading on conversion and selectivity of furfural
hydrogenation. Reaction conditions: furfural, 2.5g; solvent (IPA), 95ml; catalyst, 0.25g,
temp., 220 oC; H2 pressure, 100 psig; Agitation speed, 1000 rpm, time, 5h.
Figure 8 shows that for all catalyst loadings, complete
conversion was achieved. At lower catalyst loading of 0.12g, 2-
MF selectivity was as low as 70% as FAL formation was 21%
indicating the insufficient active sites available for
deoxygenation via FAL. As the catalyst loading increased to
0.25g, 2-MF selectivity reached to 95% with decrease in FAL
selectivity from 21% to nil. This trend remained the same with
further increase in catalyst loading to 0.4g. However, minor
ring hydrogenation of 2-MF resulted in 6% selectivity to 2-
MeTHF.
Study of effect of substrate loading showed that increasing the
substrate loading from 2.5g to 7.5g, selectivity to 2-MeF
decreased from 95% to 66% as well as FFR conversion
decreased to 78% with increase in FAL selectivity to 31%
shown in Figure S4.
XRD of used 5% Ir/C catalyst (Figure S6) showed the signals at
same peak positions without any significant changes. From
TEM analysis, morphology also was found to be the same
(spherical) with particle size of 1.5 to 3 nm as that of the fresh
sample, which is discussed earlier (Figure 3B).
Above results imply that 5% Ir/C catalyst selectively prefers
only side chain hydrogenation rather than ring hydrogenation
or ring opening products and giving very high selectivity to 2-
MF through hydrodeoxygenation of furfural. Catalyst stability
and recyclability of 5% Ir/C catalyst at 100 psig was also tested
by subsequent reuse runs as shown in Figure 9.
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Moreover, after deconvolution of O1s and C1s of used 5% Ir/C
catalyst (Figures S7 & S8), the main peaks centred at B.E. of
532.8 eV consisted of six peaks as compared to fresh Ir/C
catalyst having B.E. of 531.8 eV. Among six peaks, the peak at
B.E. of 529.6 eV corresponded to lattice oxygen, while another
set of peaks at B.E. of 531.5 eV and 531.96 eV represented the
features of hydroxyl and ether groups, which may arise from
oxygen defects. Similarly, there were two peaks at B.E. of
533.06 eV and 533.86 eV that implies adsorbed C=O groups,
while peak at BE of 534.52 eV could be assigned to the
presence of C=O group originating from adsorption through π
as well as α-β unsaturated bond linkages of furfural and
furfuryl alcohol during successive recycle runs over the catalyst
surface. This is in good agreement with the results obtained by
deconvolution C1s spectrum of used Ir/C (Figure S7) catalyst.
The five different peaks with binding energies of 284.45 eV,
284.48 eV, 285.22 eV, 286.47 eV and 288.34 eV corresponded
to surface composition of C-C bond and adventitious carbon.
Another set of peaks at BE of 286.46 eV and 288.31 eV were
associated with the presence of C-OH and C=O species.
Upward shift of peaks implies the strong association of metal,
substrate and products with carbon support.44,46 Total
composition of species is calculated by corresponded area of
iridium, oxygen and carbon along with their respective
functional groups (Table S6) where increase in oxygen content
on catalysts surface clearly indicated that there was depletion
in metallic iridium content with respect to increase oxide form
of Ir, which is in line during successive recycle runs at standard
optimized conditions.
Figure 10: Catalyst leaching test. Reaction conditions: furfural, 2.5g; solvent (IPA),
95ml; catalyst, 0.25g, temp., 220 oC; H2 pressure, 100 psig; Agitation speed, 1000 rpm,
time, 5h.
In order to establish and check effect of successive catalyst
recycles on catalyst surface, XPS analysis of spent catalysts
were done shown in Figure 11.
Plausible reaction mechanism
Our catalyst possesses coexistence of all three phases of
iridium viz. Iro, IrO2, and IrO3. As shown in Scheme 3, initially,
furfural gets adsorbed on the surface through π-bond of
formyl group forming furfuryl alcohol selectively, under
hydrogenation conditions. Later interaction of FAL with IrO2
through C-OH in contrast to least absorption affinity of C=C
bond for IrO2, leads to the formation 2-MF in a single step. As
stated, iridium is well known for oxygen evolution reaction in
which water molecule splits into the H+ and OH-.40,51-53 We
hypothesized that iridium dioxide induces the splitting of FAL
into [C5H5O+] and [OH-] and then in situ reaction of [OH-] with
external H2 resulted in the formation of water molecule and
free hydride i.e. [H-]. Later in association with [C5H5O+] species
with free hydride, resulted in the formation of 2-MF. It is also
reported that defects present in oxygen as well as availability
of Ir3+ and Ir4+ sites are helpful to alter the mechanistic way
rather hydrogenation and favors hydrodeoxygenation of
furfural to give 2-MF.40 Above hypothesis was validated with
some control experiments and XPS studies of fresh and used
5% Ir/C catalyst samples (Figures S7, S8, S10 and Table S3, S5).
Use of 5% Ir/C before NaBH4 reduction showed somewhat
lower furfural conversion but high selectively to 2-MF (Figure
S9). Moreover, part of FAL molecules which were strongly
adsorbed on the surface through C=C bond led to the
formation of THFAL and 2-MeTHF which were also by-products
Figure 11: XPS spectrum of 5% Ir/C used catalyst
It was found that iridium was present as Iro, IrO2 and IrO3. The
peaks at B.E. of 60.95 eV and 63.93 eV corresponded to
metallic iridium while, those at B.E of 61.11 eV, 61.32 eV,
62.68 eV and 64.75 eV represented various oxides of iridium,
such as IrO2 or IrO3 as 4f7/2 and 4f5/2, respectively. However,
two satellite peaks observed at B.E. of 66.11 eV and 68.18 eV
could be ascribed to uneven shaking of protons.39,40,51 After
careful comparison of XPS of fresh and used 5% Ir/C catalyst, it
was observed that total percentage of metallic Ir deceased and
that of oxide increased in the used sample. It may be because
of interaction of metallic Ir with OH- species removed from
furfuryl alcohol via hydrodeoxygenation, in spite of presence
of hydrogen. This clearly suggests that Ir has a strong affinity
towards oxygen.
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of the reaction, formed at higher catalyst loading and high particles in the range of 2 to 3 nm with an excellent dispersion
temperature. Simultaneous absorption of FAL switches the on carbon support, confirmed by respective SAED pattern
product selectivity to either 2-MeTHF or THFAL.54,55 Mass which remained almost same even after catalyst reuse.
spectrum of 2-MF is given in Figure S11.
Different phases of iridium were confirmed by XPS analysis and
respective acidity was calculated by NH3-TPD. Systematic study
with varying Ir loading results in different individual 2-MF
selectivities. Under optimized reaction conditions, 5% Ir/C
catalyst gave 95% 2-MF selectivity at low H2 pressure i.e. 100
psig suppressing other by product formation. Varying different
reaction parameters like temperature, pressure, catalyst
loading etc. product selectivity could be tuned to ring
hydrogenation products. At lower catalyst loading 1%, both
FAL and 2-MF were formed with almost equal selectivities.
Similarly, at low temperature 140 oC, conversion dropped
down to 70% with 68% selectivity to FAL while, highest
temperature of 240 oC favored ring hydrogenation product i.e.
2-MeTHF (87%). With the help of some control experiments, in
proposed reaction mechanism, crucial role of IrO2 species is
shown which facilitates the selective formation of 2-MF from
FAL. Similar way, acid mediated mechanism FR to 2-MF
mechanism is also given. The presence of relevant species
responsible for these transformations were characterized by
XPS analysis. Interestingly, catalyst was found to be very stable
at low pressure (100 psig) even after four recycles and showed
similar activity after its rejuvenation by hydrogen. No leaching
of iridium metal was observed as confirmed by hot filtration
test and by ICP-OES analysis.
Conflicts of interest
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript. “There are no conflicts to declare”.
Scheme 3: Plausible reaction mechanism over 5% Ir/C
As 5% Ir/C possesses Brönsted acidity, selective formation of 2-
MF from furfural can be explained by alternate pathway also.
Initially, furfural gets converted to FAL through hydrogenation
of C=O bond over metallic iridium sites. Subsequently, FAL gets
protonated to forms the unstable carbocation whose
subsequent dehydration followed by hydrogenation in
presence of H2 gives 2-MF selectively, as shown in Scheme 4.
Acknowledgements
One of the authors NSD gratefully acknowledges Department
of Science and Technology (DST) New Delhi, for financial
support to him.
Abbreviations:
FFR: furfural; FAL: Furfuryl alcohol; THF: Tetrahydrofuran; 2-
MF: 2-methyl furan; THFAL: Tetrahydrofurfuryl alcohol; CPO:
Cyclopentanone; 2-MeTHF: 2-Methyltetrahydrofuran; PeDO:
Pentanediols
Scheme 4: Acid catalysed plausible reaction mechanism over 5% Ir/C
References
Conclusions
1
2
J. C. S. Ruiz and J. A. Dumesic, Energy Environ. Sci., 2011, 4,
83-99 .
D.M. Alonso, J.Q. Bond and J.A. Dumesic, Green Chem. 2010,
12, 1493–1513.
Carbon supported Ir catalysts with varying Ir loadings of 1 to
6% were prepared and screened for furfural hydrogenation to
2-MF. HR-TEM revealed that the particle size of iridium
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 10 of 11
View Article Online
DOI: 10.1039/C8GC00284C
ARTICLE
Journal Name
3
4
5
6
7
8
J. A. Corma, S. Iborra and A. Velty. Chem. Rev., 2007, 107
2411- 2502.
R. D. Cortright, R.R. Davda and J.A. Dumesic, Nature., 2002,
418, 964–967.
,
38 A) R. Mane, S. Patil, M. Shirai, S. Rayalu, C. Rode, Applied
Catalysis B: Environmental, 2017, 204, 134–146. B) A. Irshad,
N. Munichandraiah, ACS Appl. Mater. Interfaces, 2015,
(29), 15765–15776
7
A. Martizez-Garcia, M. Ortiz, R. Martinez, P. Ortiz and E. 39 G.K. Wertheim and H. J. Guggenheim, Phys. Rev. B: Condens.
Reguera, Ind. Crop Prod., 2004, 19, 99–106. Matter Mater. Phys. 1980, 22, 4680–4683.
Rodiansono, S. Khairi, T. Hara , N. Ichikuni and S Shimazu, 40 S. J. Freakley, J. Ruiz-Esquius and D. J. MorganSurf. Interface
Catal. Sci. Technol., 2012, , 2139–2145. Anal., 2017, 49, 794–799.
R. Mariscal, P. M. Torres, M. Ojeda, I. Sádaba, and M. L. 41 A) V. Pfeifer, T. E. Jones, J. V. Vélez, C. Massué, M. T.
2
Granados., Energy Environ. Sci., 2016,
H. Ren, W. Yu, M. Salciccioli, Y. Chen, Y. Huang, K. Xiong,
9, 1144-1189.
Greiner, R. Arrigo and M. Hashagen, Phys. Chem. Chem.
Phys., 2016, 18, 2292-2296. B) S. J. Freakley, J. Ruiz-Esquius
and D. J. MorganSurf. Interface Anal., 2017, 49, 794–799
42 V. Pfeifer, T. E. Jones, J. J. Velasco Vélez, C. Massué, R.
Arrigo, D. Teschner and M. Hashagen. Surf. Interface Anal.,
2016, 48, 261-273.
D.G. Vlachos and J.G. Chen, ChemSusChem, 2013, 6, 798-
801.
P. Panagiotopoulou, N. Martin, D. G. Vlachos, Journal of Mol.
Cat. A: Chemical, 2014, 392, 223–228.
9
10 L. Hu, G. Zhao, W. Hao, X. Tang, Y. Sun, L. Lin, S. Liu, RSC Adv., 43 R. Kötz, H. Neff and S. J. Stucki, Electrochem. Soc. 1984, 131
2012, , 11184–11206. 72-77.
11 C.-C. Chang, S.K. Green, C.L. Williams, P.J. Dauenhauer, W. 44 R. D. Smith, B. Sporinova, R. D. Fagan, S. Trudel and C. P.
Fan, Green Chem. 2014, 16, 585–588 Berlinguette. Chem. Mater. 2014, 26, 1654−1659.
12 D. Wang, C.M. Osmundsen, E. Taarning, J.A. Dumesic, 45 X. Zhang, J. Qin, Y. Xue, P. Yu, B. Zhang, L. Wang and R.Liu,
ChemCatChem, 2013, 5, 2044–2050 Sci. Rep., 2014, 4, 4596-4605.
13 S. Wei, H. Cui, J. Wang, S. Zhuo, W. Yi, L. Wang and Z. Li, 46 A. Jha, D.W. Jeong, J. O. Shim, W. J. Jang, Y .L. Lee, C. V.
Particuology 2011, 9, 69–74. 13 Rode, and H. S. Roh, Catal. Sci. Technol., 2015, , 2752-2760.
14 C. Wang, H. Xu, R. Daniel, S. Shuai and X. Ma, Fuel, 2013, 47 J. F. Moulder, W. F. Stickle, P. E. Sobol and K. D. Bomben,
,
2
.
.
,
5
103, 200-.
15 X. Ma, C. Jiang, H. Xu, H. Ding and S. Shuai, Fuel. 2014, 116
Handbook
of
X-ray
Photoelectron
Spectroscopy,
,
PerkinElmer, Waltham, Massachusetts, USA, 1992.
48 T. Nakagawa, N. S. Bjorge and R.W. Murray, J. Am. Chem.
Soc., 2009, 131, 15578−15579.
49 Y. Zhao, E. A. Hernandez-Pagan, N. M. Vargas-Barbosa, J. L.
Dysart and T. E. Mallouk, J. Phys. Chem. Lett., 2011, 2,
281- 291
16 J- P. Lange, E.V.D. Heide, J.V. Buijtenen and R. Price,
ChemSusChem., 2012, , 150-166.
5
17 K. Xiong, W. Wan and J. G. Chen, Surface Science, 2016, 652
,
91–97.
402−406.
18 W. Yu, K. Xiong, N. Ji, M.D. Porosoff and J.G. Chen, J. Catal., 50 N. S. Date, R.C. Chikate, H.S. Roh and C.V. Rode. Date, N.S.,
2014, 317, 253-262.
19 A. S. Sitthisa, T. Sooknoi, Y.G. Ma, P.B. Balbuena and D.E.
Resasco, J. Catal., 2011, 277(1), 1-13.
20 S. Sitthisa and D. Resasco, Catal. Lett., 2011, 141, 784- 791
21 S. Sitthisa, W. An and D.E. Resasco, J. Catal., 2011, 284, 90-
101.
CatalysisToday,(2017),
http://dx.doi.org/10.1016/j.cattod.2017.08.002
51 A. Minguzzi, C. Locatelli, O. Lugaresi, E. Achilli, G. Cappelletti,
M. Scavini, M. Coduri, P. Masala, B. Sacchi, A. Vertova, P.
Ghigna and S. Rondinini, ACS Catal., 2015, 5, 5104-5115.
52 D. F. Abbott, D. Lebedev, K. Waltar, M. Povia, M.
Nachtegaal, E. Fabbri, C. Copéret and T. J. Schmidt. Chem.
Mater., 2016, 28, 6591-6604.
22 K. Yan and A. Chen, Fuel, 2014, 115, 101–108.
23 K. Yan and A. Chen, Energy, 2013, 58, 357–363.
24 P. Panagiotopoulou, N Martin and D.G. Vlachos J. of Mol. 53 B. Seemala, C.M. Cai, C.E. Wyman and P. Christopher, ACS
Cat. A: Chem. 2014, 392, 223–228. Catal., 2017, , 4070−4082.
25 P. Panagiotopoulou and D.G. Vlachos, Appl. Catal. A: Gen. 54 Daming Shi and John M. Vohs, ACS Catal., 2015,
2014, 480, 17–24. 2183.
26 G. S. Hutchings, W. Luc, Q. Lu, Y. Zhou, D. G. Vlachos and F. 55 Y.Nakagawa, M. Tamura and K.Tomishige, ACS Catal., 2013,
7
5, 2177-
Jiao, Ind. Eng. Chem. Res, 2017, 56, 3866-3872.
27 D. Scholz, C. Aellig, and I. Hermans, ChemSusChem, 2014,
7(1), 268-275.
3, 2655-2668.
28 L. Wang, F. S .Xiao, Green Chem. 2014, 17, 24−39.
29 J. Lee, Y. T. Kim, and G. W. Hube, Green Chem., 2014, 16
,
708−718.
30 X. Chen, H. Li, H. Luo and M. Qiao, Appl. Catal. A., 2002, 233
,
13-20.
31 John G. M. Bremner , Richard K. F. Keeys. J. Chem. Soc. 1947
1068-1080.
,
32 K. Xiong, W.-S. Lee, A. Bhan and J.G. Chen, ChemSusChem,
2014, 7(8), 2146-2149.
33 W.S. Lee, Z. Wang, W. Zheng, D.G. Vlachos and A. Bhan,
Catal. Sci. Technol., 2014, 4, 2340-2352.
34 A. Banerjee and S. H. Mushri, ChemCatChem, 2017, 9, 2828-
2838.
35 N.S. Date, N.S. Biradar, R.C. Chikate and C.V. Rode, Chemistry
Select, 2017, , 24-32.
2
36 B. J. Borah, S. J. Borah, K. Saikia and D. K. Dutta, Appl. Catal.
A: Gen., 2014, 469, 350- 356.
37 P. Devarly, Y. Kartika, N. Indraswati and S. Ismadji, Chem.
Eng. J., 2008 ,140, 32-42.
10 | J. Name., 2012, 00, 1-3
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