Novel catalysts for valorization of biomass to value-added chemicals and fuels

Article abstract of DOI:10.1007/s12039-014-0577-0

Key furan compounds such as 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid (FDCA) and 2,5-dimethylfuran (DMF) were synthesized from renewable feedstocks. Dehydration of fructose was carried out in biphasic conditions employing several solid acid catalysts by targeting selective formation of HMF. Its selectivity is linearly dependent on total acidity clearly revealing that lower acidity favours selective formation of HMF. Oxidation and hydrogenolysis of HMF has been explored using 2 wt% Ru-K-OMS-2. The catalysts used for each transformation were subjected to detailed characterization using XRD, BET surface area, temperature-programmed desorption and transmission electron microscopy. The effect of various reaction parameters was also investigated for obtaining high yields of desired chemical intermediates. High FDCA yields of 93.4 mol% and 66 mol% were achieved in alkaline and base-free conditions, respectively. The 2 wt% Ru-K-OMS-2 is a versatile catalyst as it also catalyses HMF hydrogenolysis giving 33 mol% of DMF. Thus, utility of various novel materials as catalysts has been demonstrated in the multistep transformations of hexoses to furan-based fuels and chemicals.

Full text of DOI:10.1007/s12039-014-0577-0

J. Chem. Sci. Vol. 126, No. 2, March 2014, pp. 403–413. ꢀc Indian Academy of Sciences.
Novel catalysts for valorization of biomass to value-added chemicals
and fuels
NISHITA LUCAS, NARASIMHA RAO KANNA, ATUL S NAGPURE, GANESH KOKATE
∗
and SATYANARAYANA CHILUKURI
Catalysis Division, National Chemical Laboratory, Dr Homi Bhabha Road, Pune 411 008, India
e-mail: sv.chilukuri@ncl.res.in
MS received 15 July 2013; revised 27 October 2013; accepted 18 November 2013
Abstract. Key furan compounds such as 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid
(
FDCA) and 2,5-dimethylfuran (DMF) were synthesized from renewable feedstocks. Dehydration of fructose
was carried out in biphasic conditions employing several solid acid catalysts by targeting selective formation
of HMF. Its selectivity is linearly dependent on total acidity clearly revealing that lower acidity favours selec-
tive formation of HMF. Oxidation and hydrogenolysis of HMF has been explored using 2 wt% Ru-K-OMS-2.
The catalysts used for each transformation were subjected to detailed characterization using XRD, BET sur-
face area, temperature-programmed desorption and transmission electron microscopy. The effect of various
reaction parameters was also investigated for obtaining high yields of desired chemical intermediates. High
FDCA yields of 93.4 mol% and 66 mol% were achieved in alkaline and base-free conditions, respectively. The
2
wt% Ru-K-OMS-2 is a versatile catalyst as it also catalyses HMF hydrogenolysis giving 33 mol% of DMF.
Thus, utility of various novel materials as catalysts has been demonstrated in the multistep transformations of
hexoses to furan-based fuels and chemicals.
Keywords. Fructose; dehydration; 5-hydroxymethylfurfural; 2,5-dimethylfuran;2,5-furan dicarboxylic acid.
1
. Introduction
Synthesis of HMF through dehydration of hexoses is
extensively studied due to importance of HMF as a plat-
4
Dwindling reserves of fossil fuels calls for the develop-
ment of novel, renewable, environment-friendly chemi-
cals and fuel sources. In this context, effective utiliza-
tion of biomass for the production of fuels and chemi-
cals has emerged as an important area of research. Sac-
charides have attracted greater attention as a promis-
ing carbon-based alternative source as it is a renew-
able chemical feedstock.1 Hexoses are carbohydrates
which are most abundant monosaccharides found
in nature. Hence, their conversion to useful chemi-
form chemical. Potential applications of HMF includes
5
,6
its selective oxidation to FDCA, hydrogenolysis to
7
DMF, reduction to 2,5-bishydroxymethylfuran and
8
,9
2,5-bis(hydroxymethyl)tetrahydrofuran.
The latter can serve as alcohol components in the
production of polyesters. Levulinic acid, a product
obtained by rehydration of HMF, is an important
chemical building block with versatile applications.1
Moreover, numerous phenolic resins and polymeriz-
able furanic compounds with promising properties have
,2
0,11
3
12,13
cals has been intensely explored. Catalytic transfor-
been prepared from HMF.
As a result of the above
mation of hexoses into furans is highly interesting
and challenging, as it is a multistep process includ-
ing dehydration, hydrolysis, isomerization, reform-
ing, aldol condensation, hydrogenation, oxidation etc.
Among the various furanic compounds involved in
this strategy; 5-hydroxymethylfurfural (5-HMF), 2,5-
furandicarboxylic acid (FDCA) and 2,5-dimethylfuran
described versatile applications, successful efforts were
made to produce HMF using a variety of reaction sys-
14,15
tems, for e.g., ionic liquids,
high boiling organic
16 ,17
18
solvents such as dimethylsulphoxide,
water and
using both homogeneous and het-
19,20
biphasic systems,
erogeneous catalysts. Ionic liquid-based systems have
emerged as excellent medium for selective formation
of HMF but suffer drawbacks such as mass transfer
limitations and high cost. Reactions in water medium
offer a green protocol for HMF preparation, but HMF
yields are lower as rehydration to LA is favourable;
whereas, in DMSO, formation of LA is suppressed
(DMF) are highly important compounds as they can be
used as starting materials for new products as well as
replacement of oil-derived chemicals.
∗
For correspondence
4
03

4
04
Nishita Lucas et al.
leading to high yields of HMF. However, this approach were subjected to detailed characterization to under-
necessitates difficult and energy intensive product iso- stand the relationship between reactivity and selectivity
lation procedures.19 In this context, biphasic systems during reaction. Various process parameters were also
are superior in terms of high HMF yields and energy optimized aiming for higher yields of targeted furan
efficiency.
compounds.
In chemical conversion process, compounds such as
HMF, FDCA and DMF are interrelated by reaction
network. Indeed FDCA has been found to be useful
as corrosion inhibitor, fungicide and melting agent for
2
. Experimental
2.1 Materials
foundry sands as well as intermediate in pharmaceutical
and photography fields.2
0,21
It has also gained interest
Fructose, methyl isobutyl ketone (MIBK), 25% NH3
solution, zirconium oxychloride (ZrOCl .8H O), dode-
as a monomer of new polymeric materials for special
2
2
22 ,23
applications.
Additionally, it has large potential as a
catungstophosphoric acid (TPA), orthophosphoric
acid, aluminium sulphate, 1-butanol, sodium borohy-
dride, ammonium nitrate were purchased from Loba
Chemie Pvt. Ltd., aluminuim chloride, tetraethyl
orthosilicate (TEOS) and poly(ethylene glycol)-block-
poly(propylene glycol)-block-poly(ethylene glycol)
replacement to terephthalic acid, a widely used compo-
nent in various polyesters such as polyethylene terepha-
24–26
late (PET) and polybutyleneterephthalate (PBT).
It can also serve as starting material for the produc-
tion of succinic acid whose consumption rate is large
enough. Thus, the potential of FDCA is visible and it
is identified as one of the 12 building block compounds
that can be produced from sugars via biological or
chemical processes.27 Several heterogeneous catalysts
have been explored for the synthesis of FDCA in alka-
(average molecular weight, 5800), triethylamine, hexa-
methyleneimine, pseudobohemite, HMF, DMF, 2,5-
dimethyltetrahydrofuran, 2-methyltetrahydrofuran and
FDCA were procured from Sigma-Aldrich. 2-
Methylfuran was purchased from Alfa Aesar. Sodium
hydroxide was procured from SD Fine Chemi-
cals and sodium silicate (60% SiO , 18% Na O)
was purchased from Riedel-deHaen. All the chemi-
cals were of research grade and were used after
drying following standard procedures. Zeolites NH -
28,29
30
line conditions
and in base-free conditions using
molecular oxygen as oxidant. Researchers have used
metal-supported catalysts for the conversion of HMF to
2
2
31,32
FDCA.
Since the above reaction is base-promoted;
there is need to choose support that has basic properties.
In this context, a basic support namely K-OMS-2 (K-
exchanged octahedral molecular sieve-2) was chosen,
exchanged with Ru and explored for HMF oxidation.
DMF obtained through hydrogenolysis of HMF is
a good candidate as a sustainable liquid fuel. Com-
pared to bioethanol, DMF has 30% higher energy den-
+
4
+
mordenite (Si/Al=10) and NH -beta were (Si/Al=19)
4
+
obtained from Zeolyst International, USA. NH -ZSM5
4
(
Si/Al=28) was obtained from catalysts pilot plant,
National Chemical Laboratory, India. All the zeolites
◦
were calcined at 450 C for 4 h in air before using.
−1
sity than ethanol (23 MJL ) and also has high research
2.2 Catalyst preparation
33
octane number (RON = 119). Moreover, DMF is
immiscible in water and easier to blend with gaso- 2.2a Synthesis of AlPO-5 and SAPO-5: The AlPO -5
4
line. It has been successfully tested as a biofuel in a and SAPO-5 molecular sieves were synthesized as per
3
7,38
single-cylinder gasoline direct-injection (GDI) research reported procedures.
In a typical AlPO -5 synthesis;
4
34
engine. The performance of DMF was satisfactory 5.51 g of pseudoboehmite was added to dilute phospho-
against gasoline in terms of combustion, ignition and ric acid (9.22 g of H PO in 55 g of water) slowly under
3
4
emission characteristics. Several attempts have been stirring. After the addition of aluminium source, stirring
made to synthesize DMF. Nobel metals supported on was continued for 30 min. To this mixture, 4.73 g of tri-
carbon as well as basic supports such as hydrotalcites ethylamine was added under vigorous stirring. The gel
35,36
◦
favour selective formation of DMF.
aspect, the above-mentioned Ru exchanged K-OMS-2 autogeneous pressure without any stirring. The crys-
was screened for synthesis of DMF. talline product obtained was filtered and washed with
Visualizing this thus obtained was autoclaved at 180 C for 24 h under
Thus, the present study describes selective dehy- double distilled water. The crystals were dried for 12 h
◦
dration of sugars to HMF, in biphasic systems using at 110 C and the template was removed by heating the
◦
solid acid catalysts. Further, transformation of HMF to sample in air at 550 C for 12 h. In case of SAPO-
FDCA by selective oxidation and its hydrogenolysis to 5, synthesis procedure remained the same, except that
DMF are also investigated by Ru supported on K-OMS- required fumed silica was added to the gel followed by
2. For each transformation, the synthesized materials triethylamine addition.

Novel catalysts for valorization of biomass
405
◦
2
.2b Synthesis of H-MCM-22: The catalyst Al- at 200 C in vacuum for 4 h before N physisorption
2
MCM-22 (Si/Al=15) with MWW topology was pre- measurements. Surface area of the material was calcu-
pared by hydrothermal synthesis according to the pro- lated by BET and t-plot methods. Pore volumes were
3
9
43
cedure given in literature. The crystalline product was calculated using De Boer’s t-plot method.
◦
dried at 120 C for 10 h and subsequently calcined in
air at 550 C for 7 h. The calcined materials were ion- using PANalytical X’Pro dual goniometer diffractome-
exchanged thrice with 0.1M NH NO solutions and ter equipped with an X’celator solid state detector. Ni-
Wide angle powder XRD patterns were collected
◦
4
3
◦
then dried overnight at 110 C. They were calcined in air filtered Cu Kα (λ = 1.5406 Å, 40 kV, 30 mA) radiation
◦
at 450 C for 3 h prior to their catalytic evaluation.
was used and data collection was carried out using a flat
holder in Bragg–Brentano geometry. Data was recorded
in 2θ range of 10–90 with 0.02 step size. Low-angle
X-ray diffraction patterns were collected in the 2θ range
◦
◦
2
.2c Synthesis of AlSBA-15: The support SBA-15
was prepared using procedure reported by Stucky and
coworkers. AlSBA-15 was prepared by post-synthesis
method in which anhydrous AlCl was dissolved in dry
40
◦
of 0.5–5 , with the above instrument at a scan rate of
◦
−1
3
0.5 min .
ethanol (25 mL). To this solution, SBA-15 (1 g) was
added and refluxed for 10 h under stirring. The material
was then filtered, washed repeatedly with dry ethanol
and dried at room temperature followed by calcination
Acidity of the catalysts was investigated by
temperature-programmed desorption of NH (NH -
3
3
TPD) using a Micromeritics Autochem-2920 instru-
ment. Prior to TPD run, the sample was activated at
◦
◦
−1
at 550 C for 5 h to get Al-SBA15 catalyst.
4
50 C in He flow (40 mL min ) for 1 h. Subsequently,
◦
the temperature was brought down to 80 C and NH was
3
2
.2d Synthesis of 15 wt% TPA on ZrO : This catalyst
2
sorbed by exposing the samples to a stream of 10% NH3
was prepared by wet impregnation following the pro-
−1
in He (30 mL min ) for 0.5 h. Temperature was then
cedure described elsewhere.41 The support zirconium
◦
◦
raised to 100 C and flushed with He for 1 h at 100 C to
remove the physisorbed NH . Desorption of NH was
oxyhydroxide was prepared by adding 5 wt% NH solu-
3
3
3
tion to 0.5M solution of ZrOCl . 8H O, dropwise under
−1
2
2
carried out in He flow (40 mL min ) by increasing the
temperature to 550 C at 10 C min , while monitor-
continuous stirring till a final pH of 9.5 was reached.
The precipitate was filtered, washed repeatedly (till
◦
◦
−1
ing the concentration of NH desorbed using a thermal
3
◦
free from chloride ions), dried at 110 C for 14 h and
conductivity detector.
crushed to obtain white zirconium oxyhydroxide pow-
der. To methanolic solution of TPA, zirconium oxyhy-
droxide was added and stirred for 12 h at room tem-
perature. The solvent was evaporated to dryness, dried
Transmission electron microscopy of 2 wt% Ru-K-
OMS-2 was carried out using FEI Technai TF-30 instru-
ment operating at 300 kV. Samples for TEM measure-
ments were prepared by placing a droplet of the sample
suspension, prepared in isopropyl alcohol using ultra-
sonification on a carbon-coated copper grid by leaving
them for drying at room temperature.
◦
◦
at 80 C overnight and calcined at 750 C to get 15 wt%
TPA/ZrO 750 (hereafter 15TZ750).
2−
2.2e Synthesis of 2wt% Ru-K-OMS-2: Support K-
OMS-2 material was prepared by procedure described
42
2
.4 Catalytic activity
in literature. Ruthenium-exchanged K-OMS-2 was
prepared by ion exchange. In a typical synthesis, 2 g
of K-OMS-2 was dispersed in 20 mL of distilled water
along with 8 mL of ruthenium chloride solution (Ru
content is 5 mg/mL), the above mixture was stirred
Dehydration reaction was carried out in 300 mL Parr
SS 316) autoclave with a teflon liner. Hydrogenoly-
(
sis and oxidation reactions were carried out in 100 mL
and 50 mL Parr (SS 316) autoclaves, respectively.
The reactants and catalyst were charged and the
closed vessel was purged with nitrogen (for dehydra-
tion), hydrogen (for hydrogenolysis) and with mole-
cular oxygen (for oxidation). The reactions were con-
ducted at the desired temperatures and pressures. At
the end of reaction, the aqueous samples were fil-
tered using 0.22 µm filter and the filtrate was ana-
◦
for 3 h at 80 C. The sample was then filtered, washed
thoroughly using deionised water and dried in oven at
◦
1
00 C for 10 h. Ion exchange material was reduced by
excess NaBH , in ethanol solution followed by drying
4
◦
in an oven at 100 C for 10 h. Ruthenium content of the
sample was estimated using ICP-OES (Spectro Arcos).
2.3 Characterization
lysed using HPLC, equipped with RI detector and
+
Specific surface area of the catalysts was measured by Rezex ROA-Organic Acid H column (300 × 7.8 mm)
N physisorption at liquid nitrogen temperature using with 5 mM H SO as the mobile phase at a flow
2
2
4
−1
Quantachrome Autosorb IQ. Samples were degassed rate of 0.6 mL min . The organic product samples

4
06
Nishita Lucas et al.
Table 1. Textural and physiochemical properties of catalysts in dehydration of fructose to HMF.
SA
(m /g)
Acidity
(mmol/g)
Fructose conv.
(mol %)
HMF Sel.
(%)
2
Catalyst
Si/Al
PD (Å)
AlPO-5
SAPO-5
SBA-15
Al-SBA15
H-MCM-22
−
−
320
330
808
549
409
0.74
0.74
60.5
0.127
0.78
0.002
0.267
1.02
30
71
−
83
42
−
−
19
15
53.7
66
78
62
36
0.51 × 0.55
0
.53 × 0.56
H-ZSM5
H-Beta
28
19
10
−
360
700
490
53
0.54 × 0.56
0.58
0.796
1.380
70
93
82
84
47
43
53
28
4
5
0
.55 × 0.51
5.7 × 7.5
4
5
6
.5 × 5.6
H-Mordenite
6.5 × 7.0,
45
2
.6 × 5.7
1
5TZ750
−
0.290
◦
Reaction conditions: Fructose = 1 g (in 10 mL water), temperature = 165 C, catalyst = 0.15 g, water: MIBK = 1: 5 (v/v),
reaction time = 1 h
Legend: SA = Surface area, PD = Pore diameter, Conv. = Conversion, Sel. = Selectivity
were analysed by Agilent 7890 gas chromatograph framework leads to reduction in surface area which may
equipped with a flame ionization detector. Products be due to presence of extra framework species, these
44
were separated using a CP Sil 8 CB capillary col- results are consistent with earlier findings. Among the
umn (30 m length, 0.25 mm diameter) coated with a microporous catalysts, the order of the surface area val-
2
−1
−1
2
−1
−1
−1
0
.25 mm thick stationary phase. Product identification ues is H-beta (700 m g ), H-mordenite (490 m g ),
2
2
was done with the help of GC/MS and confirmed with H-MCM-22 (409 m g ), H-ZSM-5 (360 m g ),
2
−1
2
reference compounds, which were also used to develop SAPO-5 (330 m g ), and AlPO -5 (320 m g ).
4
calibration curves for quantitative GC analysis.
These materials due to their porous nature exhibited
high surface areas. On the other hand, 15TZ750 has
lowest surface area of 53 m g , owing to its non-
porous nature.
2
−1
3
3
3
. Results and discussion
Specific surface area values of K-OMS-2 and 2% Ru-
K-OMS-2 are given in table 2. The support K-OMS-2
.1 Characterization of catalysts
2
−1
has surface area of 97.5 m g , which has increased to
2
−1
.1a Surface area: Specific surface areas of the 109.6 m g on exchanging with Ru. This increase in
catalysts were obtained from low-temperature nitro- surface area may be due to replacement of exchange-
+
gen sorption isotherms; the values are depicted in able K ions with larger Ru (undoped) compared to
table 1. Mesoporous SBA-15 shows high surface area the parent metal oxide. However, internal surface area
2
of 808 m /g. Incorporation of aluminium in the silica of the exchanged material has decreased due to the
Table 2. Textural and physiochemical properties of 2 wt% Ru-K-OMS-2.
2
SA (m /g)
External#
Micropore
volume (cc/g)
TPV* (cc/g)
Catalyst
BET
Internal#
APD (Å)
#
K-OMS-2
97.5
109.6
80.8
107.1
16.6
2.52
68.8
32.6
0.0069
0.0004
0.16
0.17
2
wt%-Ru-K-OMS-2
*
#
TPV for pores with diameter less than 205 Å at P/Po = 0.9
Legend: SA = Surface Area, APD = Average pore diameter, TPV = Total pore volume
Estimated from t-method

Novel catalysts for valorization of biomass
replacement of potassium by heavier Ru leading to the
407
partial blockage of pores. This also accounts for reduc-
tion in average pore diameter and total pore volume of
the exchanged sample.
3.1b X-ray diffraction: Structural aspects of the cata-
lysts used for dehydration reactions was determined
by powder and X-ray diffraction and depicted in
figure 1a. The X-ray powder diffraction patterns of
H-beta, H-mordenite, H-ZSM5 and H-MCM-22 are
in agreement with the patterns typically found for
45
these zeolites in literature. Microporous aluminophos-
phate SAPO-5 sample showed X-ray diffraction pat-
terns corresponding to that of the AFI topology reported
46
previously. Additionally, peak intensity of the XRD
patterns was retained implying that incorporation of Si
into the framework had no profound effect on the crys-
tallinity of the samples. The XRD patterns of meso-
porous SBA-15 and AlSBA-15 samples are shown in
figure 1b. These consist of three well-resolved peaks
◦
in the 2θ range of 0.8–1.8 , which are similar to those
recorded for SBA-15 in literature.40 The presence of
one strong reflection of (100) plane at 2θ = 0.8 and
two weaker reflections of (110), (200) at higher 2θ
are associated with the p6mm hexagonal symmetry in
the materials. Similarity in XRD patterns of AlSBA15
and SBA-15 clearly shows that no perturbation of the
hexagonal mesoporous structure occurred after modi-
fication. Figure 1a (inset) shows the XRD patterns
of 15TZ 750 which are predominantly in the tetra-
gonal phase. Pure zirconia calcined at high tempera-
ture mainly exists in monoclinic phase with very lit-
tle tetragonal phase.47 Addition of the surface species
results in stabilization of the tetragonal phase of zirco-
◦
nia. Additionally, peaks were obtained in 2θ = 22–25
region revealing decomposition of heteropoly acid at
higher temperatures.
Structure of K-OMS-2 and 2% Ru-K-OMS-2 is
depicted in figure 1c. Diffraction pattern of K-OMS-2
shows the presence of (110), (200), (310), (211) planes
which are typical of cryptomelane structure,4 which
are retained after Ru exchange. In fact, the XRD peaks
are sharper after Ru exchange, showing better crys-
tallinity. This has also resulted in increase of surface
area of the sample. Additionally, no peaks of Ru O
8
2
3
were observed in the XRD.
3
.1c TPD of NH : Acidity of the catalysts employed
3
Figure 1. (a) X-ray diffractograms of (a) AlPO-5, (b)
SAPO-5, (c) H-ZSM-5, (d) H-beta, (e) H-MCM-22 and (f)
H-mordenite (inset) 15TZ750. (b) X-ray diffractograms of
for dehydration reaction was determined by TPD of
NH . Total acidity of materials is expressed in mmol
3
−
1
g
of desorbed NH and these values are listed in (a) SBA-15 and (b) AlSBA-15. (c) X-ray diffractograms of
3
table 1. Among the catalysts, zeolites were highly (a) K-OMS-2 and (b) 2 wt% Ru-K-OMS-2.

4
08
Nishita Lucas et al.
acidic and their acidity can be ranked as H-Mordenite (∼50%). Conversion depends on the acidity; high con-
1.38 mmol/g) > H-MCM-22 (1.020 mmol/g) > H- versions are obtained for catalysts with high acidity,
(
Beta (0.796 mmol/g) > H-ZSM-5 (0.579 mmol/g). only exception being H-beta. Superior catalytic perfor-
There is an increase in acidity with decreasing mance of H-beta is attributed to smaller crystallite size
Si/Al ratio. For aluminophosphate samples, SAPO- which facilitates easier diffusion of reactants/products,
5
5
has higher acidity (0.78 mmol/g) than AlPO4- leading to higher conversion. Results of the catalytic
(0.147 mmol/g) as framework P (V) is replaced activity of zeolites are in good agreement with the
by Si (IV), imparting a net negative charge to the earlier findings which shows that targeted furan com-
4
9
framework. On the other hand, the acidity in AlPO - pounds undergo humin formation in the intrazeoloitic
5
4
50
is attributed to very weak acidity due to presence channels thus lowering its yield. For microporous alu-
of P-OH groups. Mesoporous SBA-15 has very weak minophosphate catalysts, SAPO-5 gave higher conver-
acidity (0.002 mmol/g) due to the presence of surface sion of 71 mol% than AlPO-5 (30 mol%), due to higher
silanol groups. However, this acidity is very low as acidity of the former. However, the selectivity of AlPO-
compared to aluminium-containing AlSBA-15 sample 5 (83%) was much higher than SAPO-5 (42%). Meso-
(0.267 mmol/g), suggesting the formation of acid sites porous AlSBA-15, was also superior to zeolites for
on post-modification with aluminium.
selective formation of HMF. Conversion of 66 mol%
and selectivity of 62 mol% is obtained for AlSBA-
1
5. This mesoporous catalyst gave maximum yield of
3
2
.1d TEM: The TEM images of 2 wt% Ru-K-OMS-
is shown in figure 2. The figure shows nanoscale size
HMF. In order to furnish insights into interplay of aci-
dity; selectivity of HMF was plotted against total aci-
dity. The result is shown in figure 3, HMF selectivity
decreases with increasing total acidity clearly reveal-
ing that lower acidity favours selective formation of
HMF. Since HMF is a highly reactive compound, it
can undergo condensation reactions on acid sites with
medium to strong acidity to give humins, thereby low-
ering its yield. Researchers demonstrated that hetero-
cyclic compounds are strongly adsorbed on the strong
fibers of the parent KOMS-2. The lattice fringes shows
d spacing of 0.47 nm which corresponds to (200) plane
of cryptomelane structure. The lattice fringes of Ru par-
ticle (d spacing of 0.21 nm) can easily be distinguished
from that of the support.
3.2 Catalytic activity in dehydration
Dehydration of fructose to HMF was used as a model acidic sites of microporous catalyst leading to their
51
reaction for testing catalytic activity and selectivity decomposition. This may be the probable reason for
of various catalysts. This reaction can yield nume- lower selectivity of zeolites and SAPO-5. Superior cata-
rous products (scheme 1), but we had selectively tar- lytic performance of AlSBA-15 reveals that low total
geted HMF. Results of the catalytic activity are given acidity and mesoporosity is advantageous for selective
in table 1. We have used microporous zeolites and alu- formation of HMF from bulky reactants such as hexo-
minophosphates and mesoporous AlSBA-15. Under the ses. On the other hand, when we employed 15TZ750
reaction conditions employed, the zeolites with higher (tungstated zirconia) as catalyst, which has no pore con-
total acidity gave higher fructose conversion (93, 82, straints, fructose conversion was 84 mol% while HMF
7
8, 70 mol% for beta, mordenite, MCM-22 and ZSM-5, selectivity was only 28%. This shows that surface aci-
respectively), but resulted in lower selectivity for HMF dity has to be optimum in terms of strength and type
Figure 2. TEM images of 2 wt% Ru-K-OMS-2.

Novel catalysts for valorization of biomass
409
Scheme 1. Dehydration of C-6 sugars to HMF.
(Bronsted or Lewis) for attaining good HMF selecti- 3.3 Catalytic activity in oxidation of HMF to FDCA
vity. Thus, it can be inferred that high acidity and pro-
bably strong acid sites does not favour selective forma-
tion of HMF under the reaction conditions employed.
Presence of low acidity is vital for HMF formation
which is an important finding as it will be helpful for
synthesizing new catalyst systems which aim a higher
yields of HMF.
Selective oxidation of HMF to FDCA by using KOMS-
family of catalysts is being reported for the first time.
2
Liquid phase oxidation of HMF to FDCA reaction was
studied on 2 wt% Ru-K-OMS-2, by varying the reac-
◦
tion temperatures in the range of 90–120 C. Results
are shown in figure 4 with time on stream. There is
no significant effect of temperature on HMF conversion
30
as it is always close to 100% after 2 h. As the tem-
◦
◦
perature is increased from 90 to 120 C, an increase
in FDCA yield was observed, which reached maxi-
mum after a certain duration on stream at each tem-
perature. However, further increase in reaction time led
to a decrease in FDCA yield because of the condensa-
tion of acid (FDCA) and alcohol (HMFCA), catalysed
4+
by acidic Mn ion (scheme 2). Initial product in the
reaction is HMFCA which further oxidizes to the FFCA
and finally to FDCA. The time taken to convert HMF
to HMFCA is not significant, but the time required to
convert HMFCA to FDCA is higher. So, oxidative con-
version of HMFCA to FDCA was found to be the rate
determining step in this reaction sequence.
Effect of catalyst amount on HMF oxidation was
investigated and results are given in figure 5. Increase
in catalyst weight has profound effect on FDCA yield
Figure 3. Fructose conversion and HMF selectivity vs.
total acidity.

4
10
Nishita Lucas et al.
Figure 4. Effect of temperature on oxidation of HMF over Figure 5. Effect of catalyst weight on HMF oxidation over
2
(
8
wt% Ru-K-OMS-2. Reaction conditions: HMF = 0.126 g 2 wt% Ru-K-OMS-2. Reaction conditions: HMF = 0.126 g
◦
1 mmol), NaOH = 0.16 g (4 mmol), catalyst weight = (1 mmol), NaOH = 0.16 g (4 mmol), temperature = 120 C,
0 mg, water = 20 mL, O2 pressure = 20 bar.
water = 20 mL, O2 pressure = 20 bar.
as complete conversion of HMF was observed at higher 66 mol% of FDCA. So, the above catalyst can also be
catalyst contents. With increase in catalyst amount, the used without addition of external base, though it com-
time taken to achieve maximum yield has reduced. promises FDCA yield to some extent. Further studies
With the increase in catalyst content, more active on base-free process of this catalyst are in progress. In
sites are available to drive the reaction for an early order to study the effect of support; parent K-OMS-2
completion.
was also used as the catalyst. Though complete conver-
The above HMF oxidation reactions are conducted sion of HMF was obtained on this catalyst, formation
in presence of added base (NaOH) as a promoter in of HMFCA was observed instead of FDCA (scheme 2).
order to deprotonate the alcohol moiety of HMFCA Major part of the catalyst has Mn in +4 oxidation state.
to form alkoxy intermediate.52 However, aiming for a Since Mn /Mn is a good redox couple, it drives the
green process, reactions were conducted in base-free oxidation of much reactive aldehyde to acid to form
conditions (figure 6), which gave a maximum yield of HMFCA. However, the above redox couple potential is
4+
3+
53
O
HO
O
HO
O
HO
O
O
O
O
O
O
O
2
O
O
2
O
2
OH
OH
Fast
Slow
OH Fast
HMF
HMFCA
2,5-FDCA
FFCA
O
O
O
O H
O H
O
O
O
O
+
O
H O
O
O
O
H O
O
O
O
OH
OH
HMFCA
FFCA
=
=
Hydroxymethyl furancarboxylic acid
Formyl furancarboxylic acid
Scheme 2. Oxidation of HMF to FDCA.

Novel catalysts for valorization of biomass
411
Figure 6. HMF oxidation over 2 wt% Ru-K-OMS-2 in
base free conditions. Reaction conditions: HMF = 0.126 g
◦
(
1 mmol), temperature = 120 C, O2 pressure = 20 bar.
not enough to oxidize the much less reactive alcohol
group of HMF which also demonstrates the necessity of
Ru metal.
3.4 Catalytic activity in hydrogenolysis of HMF
to DMF
Liquid phase hydrogenolysis of HMF was studied on
2
wt% Ru-K-OMS-2 by varying the reaction tempera-
◦
ture in the 210–230 C range. With increase in temper-
ature, there is profound effect on conversions of HMF Figure 7. Effect of temperature on HMF hydrogenolysis
(
figure 7a). Conversion increases with time on stream, over 2 wt% Ru-K-OMS-2. Reaction conditions: HMF =
0
.126 g (1 mmol), catalyst weight = 40 mg, 1-butanol =
after 8 h, it increases from 85 to 100 mol% when tem-
◦
25 mL, H2 pressure = 10 bar.
perature was increased from 210 to 230 C. However,
54
temperature also impacts DMF yields (figure 7b).
Yield increases with time on stream at all temperatures
◦
in 210–220 C range and maximum yield of 33 mol%
The effect of time was also investigated and results
◦
was obtained at 220 C after 6 h. At lower temperature are shown in figure 8. There are two paths in which
210 C), significant amount of intermediate compounds HMF can be hydrogenated. In the first path, carbonyl
scheme 3) such as 5-methylfurfuryl alcohol (MFA), group of HMF can be hydrogenated giving BHMF; and
◦
(
(
5
-methylfurfural (MF) and 2,5-bishydroxymethylfuran in the second, the alcohol group can be hydrogeno-
34
(BHMF) were obtained. With increase in temperature lysed giving MF, which can be further hydrogenated to
34
and time, theses intermediates were transformed into MFA. The first path is prominent (HMF to BHMF)
targeted product DMF. With further increase in tem- compared to the second path, as it is facilitated by
perature to 230 C, HMF conversion increases but DMF the basicity of catalyst leading to selective adsorp-
◦
yield decreased after 6 h reaction time. Higher tempera- tion of reactant molecule through carbonyl carbon of
tures favour formation of 2,5-dimethyltetrahydrofuran HMF, which enhances formation of BHMF. Thus, at the
(
DMTHF), 2-methylfuran (MFUR) and methyl tetrahy- beginning of the reaction, the formation of these inter-
◦
drofuran (MTHF). Hence, 220 C was found to be the mediates is higher. These intermediates thus formed
optimum temperature for this catalyst.
transform to DMF with increasing time on stream, i.e.,

4
12
Nishita Lucas et al.
Scheme 3. Hydrogenolysis of HMF to DMF.
from 2 to 8 h, thereby increasing yield from 12.4 to
0.5 mol%, respectively.
3
4. Conclusions
Selective formation of HMF, an important platform
chemical has been studied using solid acid catalysts.
A good linear correlation between the total acidity
and HMF selectively was clearly seen. These findings
demonstrate that the presence of optimum acidity is
crucial for selective dehydration of fructose. Success-
ful catalytic transformation of HMF to FDCA and DMF
has been achieved using 2 wt% Ru-K-OMS-2. High
FDCA yield of 93 mol% and 66 mol% is obtained in
alkaline and base-free conditions, respectively. DMF,
an important biofuel was also obtained with fairly good
yield of 33 mol%. Thus, 2 wt% Ru-K-OMS-2 was
Figure 8. Effect of reaction time on HMF hydrogenoly-
sis over 2 wt% Ru-K-OMS-2. Reaction conditions: HMF =
0
2
.126 g (1 mmol), catalyst weight = 40 mg, temperature = found to be a versatile catalyst for selective oxidation
◦
10 C, 1-butanol = 25 mL, H2 pressure = 10 bar.
and hydrogenolysis reactions. Most importantly, the

Novel catalysts for valorization of biomass
413
targeted furan compounds were successfully synthe- 27. Werpy T and Petersen G 2004 Top value added chem-
icals from biomass. Available electronically at http://
www.osti.gov/bridge
sized from renewable feedstocks.
2
2
3
8. Gorbaneb Y K, Klitgaard S K, Woodley J M,
Christensen, C H and Riisager A 2009 Chem. Sus.
Chem. 2 672
9. Pasini P, Piccinini M, Blosi M, Bonelli R, Albonetti
S, Dimitratos N, Lopez J A, Sankar M, Kiely C J,
Hutchings G J and Cavani F 2011 Green Chem. 13 2091
0. Gupta N K, Nishimura S, Tagaki A and Ebitani K 2011
Green Chem. 13 824
Acknowledgements
All the co-authors thank the Council of Scientific and
Industrial Research (CSIR), New Delhi for providing
financial support through Senior Research Fellowships.
Financial support from CSIR through network project
CSC-0122 is also acknowledged.
31. Villa A, Schiavoni M, Campisi S, Veith G M and Prati L
013 Chem. Sus. Chem. 6 609
2
3
2. Casanova O, Ibbora S and Corma A 2009 Chem. Sus.
References
Chem. 2 1138
3
3. Barlow M T, Smith D J and Steward D G 1983
EP0082689.
1
2
3
. Gallezot P 2007 Green Chem. 9 295
. Lichtenthaler F W and Peters S 2004 C. R. Chim. 7 65
. Corma A, Iborra S and Velty A 2007 Chem. Rev. 107
34. Song S, Daniel R, Xu H, Zhang J, Turner D, Wyszynski
M L and Richards P 2010 Energy Fuels 24 2891
35. Chidambaram M and Bell A T 2010 Green Chem. 12
1253
36. Hansen T S, Barta K, anastas P T, Ford P C and Riisager
A 2012 Green Chem. 14 2457
2
411
4
5
6
7
8
9
. Rosatella A, Simeonov S, Frade and Afonso C 2011
Green Chem. 13 754
. Davis S E, Houk L, Tamargo E C, Datye A K and Davis
R J 2011 Catal. Today 160 55
. Gupta N K, Nishimura S, Takagaki A and Ebitani K
37. Koskela T, Jokisaari J and Satyanarayana C 2004 Micro-
por. Mesopor. Mater. 67 113
2
011 Green Chem. 13 824
38. Prakash A M, Chilukuri S V V, Bagwe R P, Ashtekar S
and Chakrabarty D K 1996 Micropor. Mater. 6 89
39. Ravisanker R, Bhattacharya D, Jacob N E and Sivsanker
S 1995 Micropor. Mater. 1 83
40. Zhao D, Feng J, Huo Q, Melosh N, Fedrickson G,
Chemlka B F and Stucky G D 1998 Science 279 548
41. Devassy B M, Halligudi S B, Hegde S G, Halgeri A B
and Lefebvre F 2002 Chem. Commun. 10 1074
. Leshkov Y R, Barett C J, Liu Z Y and Dumesic J A 2007
Nature Lett. 447 982
. Thannatthanachon T and Rauchfuss T B 2010 Angew.
Chem. Int. Ed. 49 6616
. Yang W and Sen A 2010 Chem. Sus. Chem. 3 597
1
1
1
0. Leonard R 1956 Indus. Eng. Chem. 48 1331
1. Ghorpade V and Hanna M 1996 US Patent 5859263.
2. Gandini A and Belcacem M N 1997 Prog. Polym. Sci. 42. Deguzman R N, Shen Y, Neth E J, Suib S L, Young C
2 1203
O, Levine S and Newsam J M 1994 Chem. Mater. 6 815
3. Koch H, Krause F, Steffan R and Woelk H U 1983 43. Barrett E P, Joyner L G and Halenda P P 1951 J. Am.
2
1
Starke 35 304
Chem. Soc. 73 373
1
1
4. Chan J Y and Zhang Y 2009 Chem. Sus. Chem. 2 731
5. Qi X, Watanabe M, Aida T M and Smith R L 2009 Green
Chem. 11 1327
6. Shimizu K, Uozumi R and Satsuma A 2009 Catal.
Commun. 10 1849
7. Qi X, Watanabe M, Aida T M and Smith R L 2008 Ind. 46. IZA Structure Commission: http://www.iza-structure.
Eng. Chem. Res. 47 9234 org/databases/.
8. Carlini C, Patrono P, Galleti A M and Sbrana G 2004 47. Bordoloi A, Mathew N T, Devassy B M, Mirajkar S P
Appl. Catal A: Gen. 275 111
and Halligudi S B 2006 J. Mol. Catal. A: Gen. 247 58
9. Leshkov Y R and Dumesic J A 2009 Top. Catal. 52 297 48. King’ondu C K, Opembe N, Chen C, Ngala K, Hui H,
44. Shanbhag G V, Joseph T and Halligudi S B 2007 J.
Catal. 250 274
45. Baerlocher C, Meiser W M and Olson D H 2001
Atlas of zeolite framework types: 5th revised edition
(Amsterdam: Elsevier)
1
1
1
1
2
0. Leshkov Y R, Chheda J N and Dumesic J A 2006
Iyer A, Hector F G and Steven L S 2011 Adv. Funct.
Mater. 21 312
Science 312 1933
2
1. Christensen C H, Rass-Hansen J, Marsden C C, 49. Flanigen E M, Lok B M, Patton R L and Wilson S T
Taarning, E and Egeblad K 2008 Chem. Sus. Chem. 1
83
2. Kröger M, Prübe U and Vorlop K D 2000 Top. Catal. 13
37
3. Costantin M, Hamphreys T W, Lange H B, Shew D and
Wagner J R 1963 US 3080279
1988 Stud. Surf. Sci. Catal. 39 13
50. Weingarten R, Tomsett J A, Conner W C and Huber G
W 2011 J. Catal. 279 174
2
2
2
2
2
51. Chica A, Strohmaier K G and Iglesia E 2005 Appl.
Catal. B: Environ. 60 225
52. Davis S E, Zope B N and Davis R J 2012 Green Chem.
14 143
4. Chundury D and Szmant H H 1981 Ind. Eng. Chem.
Prod. Res. Dev. 20 158
53. Serov A and Kwak C 2009 Appl. Catal. B: Environ. 90
2
2
5. Meàlares C and Gandini A 1996 Polym. Int. 40 33
6. Gandini A 2008 Macromolecules 41 9491
313
54. Zhang J, Lin L and Liu S 2012 Energy Fuels 26 4560