Dehydration of fructose to HMF in presence of (H3O)xSbxTe(2-x)O6 (x?=?1, 1.1, 1.25) in H2O-MIBK

Article abstract of DOI:10.1016/j.mcat.2018.12.025

The pyrochlores (H₃O)_xSb_xTe_(2-x)O₆ (x = 1, 1.1 and 1.25) obtained by ion exchange from K_xSb_xTe_(2-x)O₆ oxides were used as catalysts for the conversion of fructose to 5-hydroxymethylfurfural (HMF) in H₂O/Methyl isobutyl ketone (MIBK). The structure of the resulting compounds as well as the location of the H₃O⁺ units inside the three-dimensional network, were determined by XRD from powder samples. The effect of factors such as reaction time and temperature on the formation of HMF was studied. A fructose conversion of 99% and a yield of 59% were achieved after 120 min of reaction time and at 150 °C temperature. The percentage of substitution of the cations Sb and Te in the position B of the pyrochlore was determinant to achieve the maximum incorporation of H₃O ⁺ ions in the pyrochlore structure, which allowed to correlate the density of acidic sites present in the materials and their catalytic activity.

Full text of DOI:10.1016/j.mcat.2018.12.025

MolecularCatalysisxxx(xxxx)xxx–xxx
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Editor’s choice paper
Dehydration of fructose to HMF in presence of (H3O)xSbxTe(2-x)O6 (x = 1,
1.1, 1.25) in H2O-MIBK
Sergio F. Mayera, H. Falcónb,⁎, R. Dipaolac, P. Ribotac, L. Moyanod, S. Morales-delaRosae,
R. Mariscale, J.M. Campos-Martíne, J.A. Alonsof, J.L.G. Fierroe
a NANOTEC (Centro de Investigación en Nanociencia y Nanotecnología), Universidad Tecnológica Nacional-Facultad Regional Córdoba, Córdoba, Argentina
b CITeQ (Centro de Investigación y Tecnología Química), Universidad Tecnológica Nacional-Facultad Regional Córdoba, Córdoba, Argentina
c Instituto Superior de Investigación, Desarrollo y Servicios en Alimentos (ISIDSA)-UNC, Córdoba, Argentina
d INFIQC, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5016 Córdoba, Argentina
e Grupo de Energía y Química Sostenible (EQS), Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie, 2 Cantoblanco, 28049 Madrid, Spain
f Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain
A R T I C L E I N F O
A B S T R A C T
Keywords:
Biomass
Biofuels
Fructose
5-Hydroxymethyl-furfural (HMF)
Pyrochlore
The pyrochlores (H3O)xSbxTe(2-x)O6 (x = 1, 1.1 and 1.25) obtained by ion exchange from KxSbxTe(2-x)O6 oxides
were used as catalysts for the conversion of fructose to 5-hydroxymethylfurfural (HMF) in H2O/Methyl isobutyl
ketone (MIBK). The structure of the resulting compounds as well as the location of the H3O+ units inside the
three-dimensional network, were determined by XRD from powder samples. The effect of factors such as reaction
time and temperature on the formation of HMF was studied. A fructose conversion of 99% and a yield of 59%
were achieved after 120 min of reaction time and at 150 °C temperature. The percentage of substitution of the
cations Sb and Te in the position B of the pyrochlore was determinant to achieve the maximum incorporation of
+
H3O
ions in the pyrochlore structure, which allowed to correlate the density of acidic sites present in the
materials and their catalytic activity.
1. Introduction
ethoxymethylfurfural (EMF), furfural, furfuryl alcohol, Dimethylfuran
(DMF), etc.), representing a very important group for the economy of a
biorefinery [4–8].
The search for alternatives to fossil fuels has received great interest,
as a measure that tends to provide solutions to energy crisis due to the
growing demand for transportation fuels that is accelerating the fall of
proven oil reserves. In addition, the emission of greenhouse gases
produced by combustion engines has attracted increasing interest in the
protection of the environment faced with the threat of Global Warming,
which makes it imperative finding alternative renewable sources such
as biomass [1,2].
Fructose and glucose represent 75% of carbohydrates in the biomass
that are renewed annually. For example, acid hydrolysis of poly-
saccharides can be combined with the dehydration of monosaccharides
to obtain platform compounds. Dumesic et al. [3] have described and
detailed a variety of chemical processes that can be applied to the
transformation of biomass, among which it stand out as primary stages
the hydrolysis and dehydration of carbohydrates, as well as other sec-
ondary reactions. Various chemicals can be obtained, among which are
the furan compounds (for example, 5-hydroxymethylfurfural (HMF), 5-
The production of 5-hydroxymethylfurfural (HMF), through the
dehydration reaction of sugars, is one of the most important approaches
to transform biomass into useful chemicals [9]. HMF is considered an
important precursor for the production of high-value polymers, such as
polyurethanes and polyamides, as well as biofuels [10].
HMF is produced by the dehydration of hexoses like glucose and
fructose. The general agreement is that reaction happens through
fructose. Although evidence exists supporting both the open-chain and
the cyclic fructofuransyl intermediate pathways [11,12], it is clear that
the reaction intermediates and the HMF product degrade by means of
processes such as fragmentation, condensation, rehydration, reversion,
and/or additional dehydration reactions.
According to van Putten et. Al [13], a proposed pathway of cyclic
dehydration of fructose and later rehydration to levulinic acid, formic
acid and an alternate way of formation of side-product Humins is pre-
sented below (Fig. 1).
⁎ Corresponding author. Present address: Centro de Investigación y Tecnología Química (CITeQ), Universidad Tecnológica Nacional-Facultad Regional Córdoba,
X5016ZAA Córdoba, Argentina.
E-mail address: hfalcon@frc.utn.edu.ar (H. Falcón).
https://doi.org/10.1016/j.mcat.2018.12.025
Received 6 June 2018; Received in revised form 3 December 2018; Accepted 29 December 2018
2468-8231/©2019ElsevierB.V.Allrightsreserved.
Pleasecitethisarticleas:Mayer,S.F.,MolecularCatalysis,https://doi.org/10.1016/j.mcat.2018.12.025

S.F. Mayer et al.
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Fig. 1. Reaction pathway of cyclic dehydration of fructose and later rehydration.
Van Dam et al. [14] found that the reactions performed in the
irradiation at 200 °C, producing moderate HMF yields (38.1% and
18.6% respectively) [26,27]. Better yields to HMF have been obtained
with high-boiling-point aprotic solvents, such as dimethylsulfoxide
(DMSO), which suppresses unwanted side reactions and generates high
yields of HMF (90%); however, the separation of HMF from even trace
amounts of these high-boiling point solvents is difficult and requires
energy-intensive isolation procedures [28,29].
aqueous solution provoke the degradation of 5-HMF and that its poly-
merization occurs in aqueous media, through removing three water
molecules of hexoses in the acid-catalyzed dehydration reaction. In the
aqueous system, 5-HMF enters into a consecutive reaction sequence
taking up two molecules of water, and forms levulinic and formic acid
as semifinal products [15].
The dehydration of sugars by heterogeneous catalysis has fostered
the search for suitable catalysts for these processes, being of vital im-
portance because they are more secure and environmentally more
sustainable according to the principles of green chemistry. These in-
clude heteropoly acids (HPA), the importance of which lies in their
unique properties such as well-defined structure, the possibility of
modifying their acidity by changing their chemical composition, the
ability to accept and release electrons and their high proton mobility
[16]. Davis et al. [17] described the combined use of Zeolite Sn-Beta
and acidic catalysts, in a biphasic reactor system to synthesize HMF
from carbohydrates such as glucose, cellobiose, and also starch, with
conversion and selectivity greater than 70% using a process in "one
-pot". The key to the process lies in the ability of the Sn-Beta zeolite to
isomerize glucose into fructose. On the other hand, sulfated ZrO2 [18]
has also been used in the dehydration reaction of sugars. Other catalysts
used for this purpose include, resins [19] and metal oxides such as
Ta2O5 [20] and Nb2O5 [21]. On the other hand, the mesoporous sub-
strates AlSBA-15, allow to incorporate different proportions of Al in the
structure, giving rise to a good linear correlation between a moderately
strong acidity and the selectivity to HMF [22,23]. Jain et al. [24] also
proposed the transformation of carbohydrates into HMF through me-
soporous zirconium phosphate (ZrP). Due to the high surface area, this
catalyst exhibited excellent catalytic performance for hexose transfor-
mation to HMF with high yield. On the other hand, titanium oxides
represent another important group of acid catalysts. Porous TiO2, with
a high surface area and adequate morphology of the particles, can be an
efficient catalyst in this reaction [25].
Jain et al. studied the catalytic activity of mesoporous ZrP in the
conversion of fructose to HMF in water/organic solvent (saturated with
NaCl, 1:3, v/v) (40 mL), and at 150 °C for 4 h. The yield of HMF in
water–MIBK solvent system was found to be 9% [30]. Carlini and co-
workers evaluated the activity of solid acid catalysts. In that report,
niobium phosphate could catalyze fructose dehydration with very high
HMF selectivity (85–100%), in batch experiments at 100 °C [31]. The
selectivity was, however, only obtained at fructose conversions between
25 and 35%. At higher conversions, the selectivity dropped sign-
ificantly. The highest reported selectivity at 50% conversion was
around 60%. Mercadier et al. published a three-part study on fructose
dehydration in biphasic water–organic systems, catalyzed by ion-ex-
change resins [32]. An aqueous fructose solution of about 25 wt % was
reacted in the presence of Lewatit SPC 108 and SPC 118 at 88 °C for 5 h.
In the absence of extraction solvent, the HMF yield was 10% at 69%
conversion, whereas in the presence of 9 eq. MIBK the HMF yield was
28% at 45% conversion. Moreau and co-workers ventured into zeolite
catalyzed sugar chemistry [33,34]. In a water/MIBK (1:5 v/v) system,
several zeolites were tested: H–Y faujasites and H-mordenite catalysts
with diff ;erent Si/Al ratios, H-beta, and H-ZSM5. The best result of 69%
HMF yield at 76% conversion was obtained after 60 min using H-
mordenite with an Si/Al ratio of 11. A recent publication by Ordomsky
et al. on zeolite catalyzed dehydration of fructose in water and water/
MIBK systems showed significantly lower selectivity to HMF at com-
parable conversion with H-mordenite with an Si/Al ration of 11.7, re-
porting 42% yield at 64% conversion [35]
Interesting candidates as acid catalysts are certain open-framework
systems, among them especially oxides with pyrochlore (H3O)B2O6
structure (B = octahedrally coordinated transition or p-block metals)
Multiple reaction systems have been reported for the production of
HMF using different solvents. ZrO2 and TiO2 catalyzed the conversion
of D-fructose into HMF in aqueous medium under microwave
[36–38], which exhibit
a remarkable catalytic behavior for the
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hydrolysis attributable to the reachability of the reactants to the in-
ternal acid contents of the solid [39]. The use of open-framework cat-
alysts presents important advantages over conventional ones, due to a
better diffusion of reagents and products within the interconnected
tunnels or channels present in the structure. It has been reported that
HNbMoO6 has good catalytic activity for the reactions of hydration and
hydrolysis [40,41]. Due to strong acid sites in the interlayer, the cata-
lytic activity of HNbMoO6 is significantly higher than the molecular
sieve and niobate in the process of esterification and hydrolysis. The
difference of the interlayer proton activity and the laminate negative
charges make the layered solid acids have the shape-selectivity for
different reactants.
Among this family of oxides, the proton conductors (H3O)xSbxTe(2-
x)O3 (x = 1; 1.1 and 1.25) are very promising acid catalysts, with pyr-
ochlore crystal structure. It is constituted by a covalent network of
octahedral SbVO6 and TeVIO6 units randomly distributed and linked by
the vertices, forming large interconnected cavities where H3O+ units
are located, determined for the first time through Fourier synthesis
from neutron diffraction data [20,42].
equipped with a Harris Praying Mantis® as diffuse reflectance accessory
and an environmental chamber for in situ measurements and a high
sensitivity MCT-A detector. All spectra were recorded at RT with a
4 cm−1 resolution, accumulation of 128 scans and presented in units of
Kubelka-Munk. Catalysts were dried at 120 °C for 2 h under helium
flow, and then the catalysts were contacted with pyridine vapor, the
samples were flowed by helium for 30 min to eliminate the pyridine in
the gas phase and physisorbed. The catalysts were outgassed at dif-
ferent temperatures RT, 150 and 200 °C, and cooled down to record the
corresponding spectrum.
The TPD-NH3 tests were carried out in a Micromeritics Autochem II
equipment, equipped with a thermal conductivity detector (TCD). The
samples were dried “in situ” at 120 °C for 2 h under helium flow, then
the temperature was decreased to 100 °C and then the catalysts were
contacted with a flow of NH3 for 30 min. The physisorbed NH3 was
eliminated changing the gas flow to helium at 100 °C for 1 h. Then the
TPD were recorded using a heating rate of 10 °C min−1
.
2.3. Catalytic activity
During the dehydration reaction, water is produced as a by-product,
which has a negative impact on the catalyst activity; making a hydro-
phobic catalyst could be of great help to improve the catalytic activity.
In order to increase the stability of these materials in the presence of
water, specific microenvironments can be created inside their pores.
Increased hydrophobicity of the pores may also decrease the local water
concentration, thereby decreasing the tendency to form humins upon
the conversion of carbohydrates, as well as increasing the material’s
resistance to hydrolysis and subsequent loss of functional groups.
Hydrophobicity can be conveniently controlled by introduction of
stable organic bridging groups between the silicon moieties, creating a
hydrophobic microenvironment inside the catalyst pores. Hybrid or-
ganic–inorganic periodic mesoporous organosilica (PMO) materials
have gained significant attention for application in catalysis [43]. Its
synthesis involves the hydrolysis and template-assisted condensation of
bis-(trialkoxy)silane-functionalized compounds, by which highly or-
dered materials can be obtained [44,45].
The catalytic measurements were carried out in a glass stirred re-
actor with a nominal volume of 15 mL and a maximum operational
pressure of 10 bar (Ace Pressure Tube, supplied by Sigma-Aldrich). In a
typical reaction: 1.5 mL of 5 wt. % fructose in H2O solution, 3.5 mL
MIBK and 50 mg of catalyst were introduced into the immersed reactor
in a heated oil bath, with stirring. Zero time was established when the
corresponding temperature was reached. The analysis of the reaction
products was carried out in
a Shimadzu High Pressure Liquid
Chromatograph (HPLC) equipped with a refractive index detector (RID)
and a UV detector. The products were separated on a Hi-PlexH ion
exchange column (300 × 7.8 mm) (Agilent), using 0.01 M solution of
H2SO4 as mobile phase at 65 °C with a flow of 0.6 mL min−1
.
3. Results and discussion
3.1. Structural determination
The above discussion highlights the role of hydrophobic porous
framework, which renders them extraordinarily water resistant yet fully
retains their intrinsic catalytic activities under heterogeneous systems
The aim of this work is to demonstrate the performance of
(H3O)xSbxTe(2-x)O3 (x = 1; 1.1 and 1.25) oxides as acid catalysts in the
dehydration of fructose to HMF, and the study of the influence of the
different experimental parameters such as temperature and reaction
time in the yield to HMF.
The samples obtained by ion exchange ((H3O)xSbxTe2-xO6, (x = 1;
1.1 and 1.25) as well as the precursors counterparts (KxSbxTe2-xO6)
exhibited excellent crystallinity, as was observed by the presence of
sharp diffraction peaks in the XRD patterns.
The XRD pattern of (H3O)SbTeO6 (Fig. 2) was indexed with a cubic
cell with a = 10.1510 (1) Å, characteristic of a pyrochlore structure
[47,48]. For the first refinement with the Rietveld method, a structural
model was used in which the atoms of Sb and Te were randomly dis-
tributed in the 16d sites, and the O1 oxygens were placed in positions
48f (u, 1/8, 1/8), with u ≈ 0.423, reaching an agreement RBragg factor
of 7.5%. In the compound with H3O+, the K+ was replaced by the O
belonging to the hydronium ion, since H atoms are invisible by XRD.
Fig. 2 (upper panel) illustrates the quality of the Rietveld fit for the
pyrochlore structure from XRD data, after final refinement. Fig. 2
(lower panel) shows a simplified structure of the pyrochlore (H3O)
SbTeO6 constituted by a randomly distributed network of SbVO6 and
TeVIO6, joined by their corners with angles (Sb, Te) -O1- (Sb, Te) of
136.2° forming a three-dimensional, strongly covalent subnetwork
containing channels or tunnels through which hydronium ions diffuse
easily, which gives a strong acid character to this compound. Recently
the crystal structure of (H3O)SbTeO6 was determined by neutron
powder diffraction (NPD), [49] including the localization of H3O+ units
in the large cages.
2. Experimental
2.1. Catalyst synthesis
The precursor KxSbxTe(2-x)O6 (x = 1; 1.1 and 1.25) pyrochlores were
obtained by reaction in solid state, from K2C2O4, Sb2O3 and TeO2
(analytical grade). The mixtures were heated in air at 750 °C for 12 h.
The ion exchange was carried out with a subsequent treatment of the
precursors in concentrated sulfuric acid in excess at 280 °C for 24 h as
have been described elsewhere [42].
2.2. Characterization
X-ray diffraction of catalysts were measured using a Brucker D8
powder diffractometer with a Cu-Kα radiation with Bragg angle be-
tween 10° and 120°, in increments of 0.02° and accumulation of 10 s in
each step. For the refinement of the X-ray profile the Rietveld method
was used [46]. Specific areas were calculated by the BET method from
the N2 adsorption isotherms at −196 °C using a Micrometric ASAP
2000 automatic instrument.
3.2. Acid sites characterization
Infrared (IR) spectroscopy undoubtedly represents one of the most
important tools in catalysis research [50]. The pyridine IR spectroscopy
adsorbed on a solid is a powerful tool to identify the nature of the acid
The FTIR spectra were obtained with a Nicolet 5700 spectrometer
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Fig. 4. TPD of NH3 adsorbed on (H3O)xSbxTe2-xO6 (x = 1, 1.1 and 0.75).
(H3O)1.25Sb1.25Te0.75O6 after the adsorption of pyridine and successive
heating at 150 and 200 °C. The bands at 1630, 1546 and 1487 cm-1 are
attributed to sites with Brønsted acidity. The first two are due only to
Brønsted acid centers, while the latter may be due to both Brønsted and
Lewis centers. Based on the published pyridine band assignments it can
be concluded that pyridine bands at 1602 cm-1 is related to Lewis-acidic
sites [53]. The intensity of these bands remains unchanged with the
thermal treatments, indicating a strong adsorption of pyridine on
Brønsted acid sites. These results indicated that the nature of the acid
sites are strong Brønsted sites.
Temperature-programmed desorption (TPD) is one of the versatile
techniques for the determination of the total acidity and to determine
the strength of acid sites present in the catalysts [54]. TPD-NH3 deso-
rption profiles of studied catalysts (H3O)xSbxTe2-xO6, (x = 1; 1.1 and
1.25) are shown in Fig. 4. We detected three desorption regions that
correspond to three sites of different strength present on the surface of
the solid. The first centers are of a moderate acidity since they retain
Fig. 2. Upper panel) XRD diagrams of (H3O)SbTeO6 refined by the Rietveld
method and Lower pannel) Simplified view of the pyrochlore structure. Violet
spheres represent the distribution of O from the H3O+ ions in the large cages
formed by the octahedral network.
ammonia that desorb in
a relatively low temperature range
(T = 150–350 °C). The second centers are associated with a region of
moderate-strong acid sites desorption temperatures of 350 to 500 °C.
The intensity of the desorption peak in this region depends on the
catalyst. The most intense ammonia desorption peak is for the
(H3O)1.25Sb1.25Te0.75O6, clear indication that this catalyst has a higher
number of this kind of acid sites on the surface of the solid. The third
peak corresponds to the region of highest desorption temperature of
temperature higher than 500 °C. These last centers correspond to those
of very strong acid sites, and in general, the amount of these acid sites is
small for all catalysts.
sites.The assignments of the infrared bands are in concert with the well-
established correlation between the band positions and the type of in-
teraction between the pyridine and the sites on which it is adsorbed.
The original work with pyridine adsorbed on solid acids was done by
Parry [51]. A compilation of the various band assignments with this
technique has been given by Pichat et al. [52]. Liquid pyridine, pyridine
hydrogen-bonded to a surface, chemisorbed to a Lewis acid site, and
chemisorbed to a Brønsted acid site all show distinctly different regions
of absorption in the infrared.
The region of the IR spectrum of pyridine adsorbed between 1400 to
1650 cm-1 contains the characteristic bands of the different vibrational
modes of pyridine. Fig. 3 presents the DRIFTS spectra for the sample
Semiquantitative data of TPD-NH3 are compiled in Table 1. Even
though all the catalysts desorb in three regions that correspond to acid
centers of different strength, differences are observed in the desorbed
quantities. In general, it can be seen that the greater the amount of Sb in
Table 1
Quantification of TPD of NH3 on (H3O)xSbxTe2-xO6 (x = 1, 1.1 and 1.25).
Catalyst
Temperature (°C)
mmol NH3/g
desorbed
(H3O)SbTeO6
150 – 350
350 – 500
> 500
150 – 350
350 – 500
> 500
150 – 350
350 – 500
> 500
0.05
0.11
0.05
0.13
0.29
0.14
0.13
0.51
0.24
(H3O)1.1Sb1.1Te0.9O6
(H3O)1.25Sb1.25Te0.75O6
Fig. 3. DRIFT spectra of (H3O)1.25Sb1.25Te0.75O6 with pyridine adsorbed and
desorbed at 150 and 200 °C.
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Table 2
BET specific surface area of prepared catalysts (H3O)xSbxTe2-xO6 (x = 1, 1.1
and 0.75).
Catalyst
BET specific surface area (m2/g)
(H3O)SbTeO6
(H3O)1.1Sb1.1Te0,90O6
(H3O)1.25Sb1.25Te0,75O6
1.9
2.2
1.8
the composition, the more ammonia is desorbed, which is more evident
for the catalyst (H3O)1.25Sb1.25Te0.75O6. This catalyst has a high deso-
rption at moderate temperatures (350–500 °C) that corresponds to
medium-strong acid centers. The high-temperature peaks were close to
the NH3 desorption peaks obtained for layered HNbWO6 (379 °C) and
HTaWO6 (385 °C) [55], which are attributable to strong acid sites
formed in the interlayer of layered structures.
Fig. 6. Conversion of fructose (a) and yield to HMF (b) versus reaction time.
Reaction conditions: 0.050 g of catalyst (H3O)SbTeO6; 1.5 mL of 5 wt.% dis-
solution of fructose in water / 3.5 mL MIBK and T = 150 °C.
3.3. Specific surface areas
Specific Surface areas of (H3O)xSbxTe2-xO6 (x = 1, 1.1 and 0.75) are
compiled in Table 2. The values are relatively low and quite similar
among them, in consequence, we do not expect any influence of the
specific surface area in the catalytic activity.
3.4. Catalytic activity
Since temperature and time are the most critical parameters, they
were initially investigated to carry out a systematic evaluation with and
without the catalyst (H3O)SbTeO6 to confirm the best conditions of the
transformation of fructose to 5-hydroxymethyl-furfural (HMF) in a two-
phase H2O/methyl isobutyl ketone system (MIBK). As shown in Fig. 5,
the highest conversion of fructose in the presence of the catalyst was
97.9% and a 47.5% yield was obtained at 170 °C for 120 min. In con-
trast, a very high yield was obtained below these values in absence of
the catalyst. It should be noted that other by-products (furfural, levu-
linic acid and formic acid) were not considered due to their very low
values. It is worth remarking that an important part of the converted
fructose yield to the formation of unidentified products. Fig. 6 shows
the results of the dehydration of fructose with (H3O)SbTeO6 at different
periods, in presence and absence of the catalyst at T = 150 °C. The
conversion of fructose (Fig. 6a) was increased when time was extended
from 60 to 120 min. to values close to 71%, increasing slightly for
150 min. The yield of HMF (Fig. 6b) increases gradually along with time
in the interval from 60 min to 120 min, going from 23.8% to 44.8%, the
Fig. 7. Conversion of fructose (a) and yield to HMF (b) with different catalysts:
(A) (H3O)SbTeO6, (B) (H3O)1.1Sb1.1Te0.9O6 and (C) (H3O)1.25Sb1.25Te0.75O6.
Reaction conditions: 0.050 g of catalyst; 1.5 mL of 5 wt.% dissolution of fructose
in water / 3.5 mL MIBK, T = 150 °C and 120 min.
yield decreases for longer reaction time.
From these results, it was then decided to study the effect of the
composition variation of Sb and Te, (H3O)xSbxTe2-xO6 (x = 1, 1.1 and
1.25) on the catalytic activity at 150 °C and 120 min of reaction (Fig. 7).
Activity results showed that the conversion of fructose depends on the
catalysts composition; the maximum conversion of fructose obtained
was for (H3O)1.25Sb1.25Te0.75O6 with a 99% (Fig. 7a). The increase in
the antimonium contents produces an increase in the yield to HMF
(Fig. 7b), the improvement of the HMF yield is clearly higher for the
Sb/Te ratio 1.25/0.75 with a yield of 58.6%. This observation is in
agreement with previous reports that observed a higher yield to HMF
with zeolites with high number of strong acid centers (TPD-NH3) [56].
Based on the activity results of the effect of the catalyst composition
on the catalytic activity (Fig. 7), it was decided to study the effect of the
reaction time with the catalyst (H3O)1.25Sb1.25Te0.75O6 on the conver-
sion of fructose and yield of HMF at 150 °C. The effect of reaction time
between 60 and 150 min was studied in the presence of the catalyst and
in its absence, at T = 150 °C for (H3O)1.25Sb1.25Te0.75O6 (Fig. 8).
The conversion to fructose increases with the reaction time. It can
be seen that in the presence of a catalyst, for all the times studied, the
conversion of fructose is practically complete, except for 60 min., while
in the absence of a catalyst the conversion is very low for the whole
study. It is observed that an increase in reaction time results in a higher
yield to HMF, from 40% to 60 min. at 51% at 120 min, and it is
Fig. 5. Conversion of fructose (a) and yield to HMF (b) in the temperature
range at 140–170 °C. Reaction conditions: 0.050 g of catalyst (H3O)SbTeO6;
1.5 mL of 5 wt.% dissolution of fructose in water / 3.5 mL MIBK and 120 min.
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—
45
76
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H-mordenite
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The authors acknowledge financial support from Comunidad de
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6