2,5-DMF production through hydrogenation of real and synthetic 5-HMF over transition metal catalysts supported on carriers with different nature

Article abstract of DOI:10.1016/j.cattod.2016.02.019

Catalytic hydrogenolysis reaction of 5-hydroxymethylfurfural platform molecule to produce 2,5-dimethylfuran conversion was studied. For that purpose noble (Pt and Ru) and non-noble (Ni and Cu) metal catalysts supported on acid (HYAl₂O₃ and Al₂O₃) and basic (ZrO₂ and TiO₂) supports were used. All of the tested catalysts were able to convert completely HMF. However, among the mentioned catalysts, the Cu catalyst supported on ZrO₂ showed the best behavior in terms of DMF selectivity, probably due to the neutral nature associated to ZrO₂ support. Moreover, this catalyst was studied in order to know the influence of some reaction parameters on DMF selectivity. As results obtained with CuZr catalyst concluded, a temperature increase had not influence on the aforementioned parameter because the reaction is exothermic. However, the type of feed, the increment of the pressure and the space velocity decrease improved the DMF selectivity.

Full text of DOI:10.1016/j.cattod.2016.02.019

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2,5-DMF production through hydrogenation of real and synthetic
5-HMF over transition metal catalysts supported on carriers with
different nature
A. Iriondo∗, A. Mendiguren, M.B. Güemez, J. Requies, J.F. Cambra
School of Engineering, University of the Basque Country (UPV/EHU), c/Alameda Urquijo s/n, 48013 Bilbao, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Catalytic hydrogenolysis reaction of 5-hydroxymethylfurfural platform molecule to produce 2,5-
dimethylfuran conversion was studied. For that purpose noble (Pt and Ru) and non-noble (Ni and Cu)
metal catalysts supported on acid (HYAl2O3 and Al2O3) and basic (ZrO2 and TiO2) supports were used. All
of the tested catalysts were able to convert completely HMF. However, among the mentioned catalysts,
the Cu catalyst supported on ZrO2 showed the best behavior in terms of DMF selectivity, probably due to
the neutral nature associated to ZrO2 support. Moreover, this catalyst was studied in order to know the
influence of some reaction parameters on DMF selectivity. As results obtained with CuZr catalyst con-
cluded, a temperature increase had not influence on the aforementioned parameter because the reaction
is exothermic. However, the type of feed, the increment of the pressure and the space velocity decrease
improved the DMF selectivity.
Received 1 December 2015
Received in revised form 22 February 2016
Accepted 24 February 2016
Available online xxx
Keywords:
2,5-Dimethylfuran
5-Hydroxymethylfurfural
Hydrogenation
Copper
Neutral-basic supports
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
and bioethanol, they had a great introduction on transportation
sector until a few years ago. However, their production from food
Nowadays fossil resources, such as petroleum, coal and natu-
ral gas, are the most important suppliers to world energy system,
around 80% of the primary energy consumption [1,2]. This fact
involves serious problems related to the concerns about depletion
of this kind of energies [2–5], energy security and economics due
to their centralized production, and greenhouse emissions, which
are related with the increase of global warming [5,6]. However, it is
important to remark that petroleum plays dominant role in chemi-
cal industry because of its use in a wide range of products including
plastics, carpets, curtains, wall paints, varnishes, soaps, perfumes
and hairsprays [7], and in transportation sector in which properties
of the used fuels are fulfilled by non-renewable petroleum-derived
liquids fuels [8]. In order to reduce the problems derived from uses
of petroleum, searching and developing of sustainable and envi-
ronmental friendly energy sources have become essential topics to
achieve.
crops came in conflicts with food industry [10]. Moreover, these
biofuels present several drawbacks that limit their use as trans-
portation fuels, such as low oxidation stability, corrosive nature and
poor cold flow properties [11]. This fact leads to the development
of a second generation of biofuels or fuels bioadditives, which are
derived from non-food residual lignocellulosic biomass [4,10,11].
Although there is a wide variety of chemical building blocks
obtained from lignocellulosic biomass, 5-hydroxymethylfurfural
(HMF), which is also considered “chemical platform”, seems
to be the most promising intermediate as it can be produced
from different raw materials (glucose, fructose, sucrose), and it
can also be converted into biofuels, such as 2,5-dimethylfuran
(DMF), and other fine chemical molecules (levulinic acid (LA), 2,5-
furandicarboxilic acid (FDCA), ethyl levulinate (EL)) [1,3,8,9,12].
The production of HMF dates back to 19th century when the HMF
was separated from reaction mixture of fructose, sucrose and oxalic
acid [12]. Nowadays, the most extended reaction to produce HMF is
dehydration of the aforementioned carbohydrates over acid, homo-
geneous or heterogeneous catalysts [1,8,9,12], because its high
volume production from petroleum derived feedstocks suppose a
great cost and therefore a low availability [13].
According to the literature [1,9], the biorefinery, and therefore
highly abundant and carbon-neutral biomass [4], can be a good
alternative to the current needs of energy, chemicals and uncon-
ventional fuels. Regarding to the first generation biofuels, biodiesel
Regarding the DMF, it is produced from selective hydrogena-
tion of HMF [11] under H2 atmosphere, also called hydrogenolysis
process [2,8]. This reaction involves different pathways [1,11,14] in
∗
Corresponding author.
E-mail address: aitziber.iriondo@ehu.eus (A. Iriondo).
http://dx.doi.org/10.1016/j.cattod.2016.02.019
0920-5861/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: A. Iriondo, et al., 2,5-DMF production through hydrogenation of real and synthetic 5-HMF over transition
metal catalysts supported on carriers with different nature, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.02.019

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Fig. 1. Desirable main route to transform HMF into DMF through hydrogenolysis reaction.
Fig. 2. Reaction mechanism for the conversion of HMF.
which dehydration and hydrogenation reactions are predominant.
These pathways are shown in Fig. 1. Nevertheless, according to
the literature [2,15,16], apart from dehydration and hydrogenation
reactions, secondary reactions could occur during the HMF con-
version, such as demethylation and decarbonylation. Fig. 2 shows
a complete reaction scheme of HMF conversion, which have been
adapted from the aforementioned literature.
DMF high-quality fuel is considered, as ethanol, an ideal renew-
able and sustainable substitute or additive of the conventional
gasoline [2], because of its high energy density, similar to that
of gasoline and higher than ethanol [3,11], and research octane
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3
Table 1
Composition and textural properties of calcined catalysts.
a
Catalyst
Metal content (wt%)
Pt
SBET (m2/g)
Pore volumea (cm3/g)
Ru
–
Cu
Ni
PtHYAl
NiAl
CuAl
CuZr
RuTi
0.78
–
–
–
–
–
–
–
165.0 (162.0)
146.9 (227.2)
152.9 (227.2)
101.1
44.7 (66.6)
n.a.
0.51 (0.53)
0.35 (0.81)
0.58 (0.81)
0.07
0.08 (0.15)
n.a
36.11
–
–
30.01
23.70
–
–
–
–
–
0.074
0.068
RuCuTi
–
4.80
n.a.: not available.
a
Values inside parenthesis correspond to the bare support.
CuZr
RuCuTi
0
200
400
600
800
1000
0
200
400
600
800
1000
Temperature (ºC)
Temperature (ºC)
Fig. 3. TPR-H2 profile for the CuZr and RuCuTi fresh calcined catalysts.
0.2
PtHYAl
120
NiAl
CuAl
100
CuZr and RuCuTi
80
60
CuZr
RuCuTi
0.1
0.0
40
20
0
-20
0
100
200
300
400
500
600
700
800
900
0
100
200
300
400
500
600
700
800
900
Temperature (ºC)
Temperature (ºC)
Fig. 4. TPD ammonia profiles for the calcined catalysts.
number, higher than gasoline [1]. Moreover, DMF shows very low
solubility in water and therefore it can be used as a blender in trans-
portation fuels [11,16]. In this sense, some literature reports the
good performance of the DMF as a fuel on direct injection spark
ignition (DISI) type engines [3,6] without important modifications
of the engine.
by autoclave systems [1–3,8,14,16,17], it means, in discontinuous
systems, using synthetic HMF as reactant and noble, such as Pd,
Pt, Ru, Rh and Au [1,2,14,16,17], and non-noble, such as Cu, Co, Ni
and Fe [3], metal-based catalysts. Only few research works report
information about hydrogenolysis of HMF over continuous systems
[8,18] using real feed of HMF [18].
As reported in the recent literature about this topic, DMF pro-
duction from HMF catalytic hydrogenolysis is mainly carried out
Based on this background, the aim of this work was to com-
pare the activity toward the production of 2,5-DMF from 5-HMF of
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metal catalysts supported on carriers with different nature, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.02.019

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catalysts containing noble and non-noble metals supported on car-
riers showing different degrees of acidity and basicity.
the procedure reported in the literature [21,22] in order to achieve
nominal contents of 35 wt% of Ni and Cu. In the case of the CuZr
catalyst, this catalyst was prepared by co-precipitation of aqueous
solution of Cu(NO3)2·5H2O and ZrO2(NO3)·xH2O salt precursors.
The amount of metal precursor was selected to achieve a content
of approximately 30 wt% of Cu. Then the solution was stirred at
500 rpm, meanwhile NH4OH aqueous solution (excess of 20%) was
added in order to achieve a pH above 9, followed by aging, vacuum
filtering and washing at pH around 7. Finally, catalyst was dried at
110 ◦C overnight and calcined at 300 ◦C for 1 h.
2. Experimental procedure
2.1. DMF production from HMF hydrogenolysis
Two types of feeds were used in the DMF production designed
as “real” and “synthetic” HMF. The first one was obtained from syn-
thetic fructose (Sigma-Aldrich, ≥99%) dehydration over Amberlyst
70 catalyst in autoclave reactor, where an organic phase contain-
ing around 0.7 wt% of HMF in 1-butanol was obtained. Taking into
account this result, the second feed was prepared using 0.7 wt%
of “synthetic” HMF (Sigma-Aldrich, 99%) diluted in 1-butanol. This
compound was selected as most of the studies about DMF pro-
duction reported in the literature [8,16–18] used it as a solvent
agent.
The gas phase hydrogenolysis of the different HMF feeds was
carried out in a continuous bench-scale fixed bed reactor in
which 0.2 and 0.5 g of catalyst were diluted with inert SiC (cata-
lyst/SiC = 1:9 wt), corresponding to WHSV (g of HMF/g of catalyst h)
of 0.12 h−1 and 0.06 h−1, respectively. Prior to hydrogenolysis reac-
tion, all tested catalysts were pretreated and non-pretreated. The
pre-treatment were performed in-situ under 100 Nml/min of H2 at
0.1 MPa and 400 ◦C for 2 h.
2.3. Catalysts characterization
The calcined catalysts were characterized by several physic-
chemical techniques such as plasma atomic emission spectroscopy
(ICP-AES), surface area (BET method), temperature-programmed
reduction (H2-TPR), temperature-programmed desorption of NH3
(NH3-TPD) and temperature-programmed desorption of CO2 (CO2-
TPD). Analyses conditions of these techniques and the used
equipments for characterization of calcined PtHYAl, NiAl, CuAl and
RuTi are published elsewhere [19–22]. In the case of the CuZr and
RuCuTi catalysts, the characterization equipment and conditions
are explained below.
2.3.1. Plasma atomic emission spectroscopy
HMF conversion was carried out for 4 h under a feed flow of
0.1 ml/min, temperatures of 200 and 225 ◦C and pressures from 0.5
to 3 MPa. These pressures were achieved using 37 Nml/min of pure
H2. The feed and output liquid streams were collected and ana-
lyzed by off-line high-performance liquid chromatography (HPLC)
and gas chromatography (GC). Concretely, HMF quantity on feed
and liquid product stream was analyzed by an Agilent HPLC chro-
matograph (1260 Infinity) equipped with Hi-Plex H column and
infrared detector, and DMF and other products on the liquid prod-
uct stream were quantified using a Hewlet Packard GC equipped
with Suprawax 280 capillary column.
Metal contents were determined by ICP-AES, using a Perkin-
Elmer Optima 3300DV apparatus, previous dissolution of the
ground samples in acid solutions.
2.3.2. Textural properties
BET surface area and pore characteristics of the calcined
fresh catalysts were evaluated from the N2 adsorption–desorption
isotherms obtained at 77 K over the whole range of relative pres-
sures. In the case of the CuZr catalyst, this sample was characterized
using Autosorb®-1-C/TCD (Quantachrome, USA) after outgassing
solid samples at 300 ◦C for 3 h.
For better understanding of catalytic activity and product distri-
bution, parameters such as HMF conversion (%) and DMF selectivity
(%) were calculated.
2.3.3. H2-TPR analysis
This technique was used to study the reducibility of the calcined
catalysts. The measurements were carried out using an AutoChem II
instrument (Micromeritics, USA) equipped with a TCD detector. TPR
profiles were obtained by heating the samples from room temper-
ature to 900 ◦C at a linearly-programmed rate of 10 ◦C/min, while
50 ml/min of reduction gas (5% v/v H2 diluted in Ar) was passed
through the sample.
in
HMF
out
N
(mol/min) − N
(mol/min)
HMF
Conversion(%) =
Selectivity(%) =
(1)
(2)
out
N
(mol/min)
HMF
out
N
(mol/min)
DMF
in
HMF
out
N
(mol/min)-N
(mol/min)
HMF
2.2. Catalysts preparation
2.3.4. NH3-TPD analysis
Temperature programmed desorption of NH3 was used in order
to know the acid characteristics of the calcined samples. The used
equipment was AutoChem II instrument. First of all, samples were
flushed by He at 250 ◦C for 30 min, followed by cooling at 40 ◦C and
loading of NH3 for 30 min. Then the physically absorbed NH3 was
removed using He at 85 ◦C until no further desorption was recorded
and release of chemically adsorbed NH3 was collected increasing
temperature from 85 ◦C to 800 ◦C at a rate of 10 ◦C/min.
The selected catalysts to carry out HMF hydrogenolysis were
noble and non-noble metal catalysts supported on acid (Al2O3
designed as Al) and neutral-basic (TiO2 and ZrO2 designed as Ti and
Zr, respectively) supports. The noble metal catalysts were PtHYAl,
RuTi and RuCuTi. The Pt catalyst was prepared by wet impreg-
nation of a physical mixture of HY zeolite and ␥-Al2O3 (Girdler
Sudchemie) [19]. This HYAl support was prepared by suspension
of HY (Conteka) and ␥-Al2O3 powder. The Ru and RuCu cata-
lysts were prepared by incipient wetness impregnation [20]. In
particular, 2Ru5CuTi catalyst was prepared by sequential impreg-
nation of TiO2 (Degussa, Aeroxide titanedioxide P25) with copper
(Cu(NO3)2·3H2O (Alfa Aesar, 98%)) precursor salt. After drying,
the solid was impregnated with RuCl3 (Johnson Matthey, metal-
lic phase Ru 40%) precursor salt and then calcined at conditions
reported in the literature [20]. The nominal content for the afore-
mentioned metal catalyst was 1 wt% of Pt, 2 wt% of Ru and 5 wt%
of Cu. Regarding non-noble catalysts, these were designed as NiAl,
CuAl and CuZr. The NiAl and CuAl catalysts were prepared following
2.3.5. CO2-TPD analysis
The basicity of calcined samples were determined by tempera-
ture programmed desorption of CO2 probe molecule. The CO2-TPD
measurements were carried out also with AutoChem II instrument
and the same procedure as NH3-TPD. First of all, samples were
flushed by He at 250 ◦C for 30 min, then cooled down to 40 ◦C and
loaded with CO2 for 30 min. Then the physically absorbed CO2 was
removed using He at the same temperature until no further des-
orption was recorded. Finally, the samples were heated from 40 ◦C
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0.40
5
to 600 ◦C at a rate of 10 ◦C/min, while the release of CO2 data was
collected.
0.35
2.3.6. SEM and TEM analysis
CuZr
RuCuTi
PtHYAl
The morphological appearance of the fresh and used catalysts
was studied by SEM analysis in a JEOL JSM-6400 with W fila-
ment and a resolution of 3.5 nm, and TEM images were obtained
in a Philips SuperTwin CM200 apparatus operated at 200 kV and
equipped with LaB6 filament and EDAX EDS microanalysis sys-
tem. The fresh and used samples were prepared via dispersion into
ethanol solvent and placed on a carbon-coated copper grid (300
Mesh) followed by drying under vacuum.
0.30
0.25
0.20
0.15
0.10
0.05
3. Results and discussion
3.1. Characterization results
0.00
0
100
200
300
400
500
600
700
3.1.1. Chemical and textural properties of catalysts
Table 1 shows the metal content measured by ICP-AES and
the specific surface area (SBET) and pore volume data from N2
physisorption for the calcined catalysts. The PtHYAl and NiAl cata-
lysts showed experimental metal loads close to the nominal ones
[19–22]. In the case of the CuAl catalyst, the active metal content
was slightly lower than the theoretical one. The same phenomenon
was also detected for CuZr catalyst, because the measured load was
23.7 wt%, 5 points lower than the theoretical one. In the case of
RuTi and RuCuTi catalysts, the measured Ru content was around
0.07 wt%, while in the case of Cu, the metal loading was similar to
the theoretical one.
Regarding the BET surface area of the catalysts, the incorpora-
tion of Ni, Cu and Ru metal phase to the Al and Ti supports reduced
the surface area. This fact suggested that metal deposition was pref-
erentially produced into pores of the support, and resulted in lower
pore volume when compared with bare supports. In the case of
PtHYAl catalyst, the BET area increased slightly when compared
with the bare support and a lower reduction of pore volume was
observed, suggesting that low metal load did not influence the sup-
port surface area and/or the specific area could be compensated by
the exposed area of the added metal species [23]. Regarding the
CuZr catalyst, it presented a surface area within the values reported
in the literature [24–27]. The BET surface area of Cu/ZrO2 catalysts
prepared by coprecipitation method is typically reduced when the
catalysts calcination temperature is increased because crystal size
of copper and encapsulation of zirconium increase with the rise of
the calcination temperature [27].
Temperature (ºC)
Fig. 5. TPD CO2 profiles for the calcined catalysts.
peaks could be ascribed to reduction of copper, as explained above,
and ruthenium species. As it is reported in literature [35–37], reduc-
tion peaks detected at low temperatures, normally below 200 ◦C,
were ascribed to reduction of well dispersed RuOx and RuO2 par-
ticles to Ru◦. This last conclusion can also be applied to the RuTi
catalyst, for which TPR profile had already been reported [20].
Regarding PtHYAl and NiAl catalysts, whose TPR profiles were
previously reported [19,22], the first one showed reduction peaks
at 224 ◦C associated to the reduction of Pt4+ to Pt◦ and the sec-
ond one presented reduction peaks corresponding to reduction of
bulk nickel oxide and nickel aluminate species interacting with the
support.
3.1.3. Surface acid (NH3-TPD) and basic (CO2-TPD) properties
Acid and basic properties of the calcined catalysts were deter-
mined in order to know the influence of these characteristics on the
hydrogenolysis reactions. The amount of adsorbed ammonia for the
calcined catalysts is shown in Fig. 4. As can be observed in the figure,
CuZr and RuCuTi show a flat profile (see right part of Fig. 4) reveal-
ing that ZrO2 and TiO2 did not show significant acid properties. This
observation is in good agreement with results reported in the lit-
erature [30,38,39], which suggest that Al2O3 support generally is
more acidic support than ZrO2 and TiO2.
3.1.2. Catalysts reducibility (H2-TPR)
The ammonia desorption profile for the Al2O3 supported cata-
lysts are composed by a broad peak from 100 to 650 ◦C, indicating
that surface acid strength has a wide distribution on these catalysts
[34]. Commonly the mentioned strength of acid sites are classi-
fied as weak, medium and strong, and they appears approximately
at temperatures below 250 ◦C, temperatures in which the HMF
hydrogenolysis reaction was carried out, and 450 ◦C and, above
450 ◦C, respectively [40,41]. In this sense, the PtHYAl, NiAl and
CuAl calcined catalysts presented in general medium-strong sur-
face acidity at high reaction temperatures and weak acid sites at
temperatures similar to the ones used for activity tests. Moreover,
the incorporation of Cu to Al2O3 support reduced surface acidity
when compared with the Ni catalyst. While the Pt catalyst showed
different desorption profile probably due to the presence of HY type
zeolite.
The TPR profiles of calcined catalysts showed two reduction
regions at temperatures below and above 300 ◦C. In the case of
the CuZr catalyst (see Fig. 3), one reduction peak was detected at
around 180 ◦C. The asymmetrical form of this reduction peak indi-
cated that there were two peak contributions concretely at 173 and
188 ◦C. According to the literature [28–31], reduction peaks of Cu
catalyst supported on ZrO2 and TiO2 at temperatures below 250 ◦C
was assigned to reduction of smaller species and highly dispersed
CuO. Moreover, the presence of two peak contribution indicated
that CuO could have suffered a sequential reduction from Cu2+ to
Cu1+ and from Cu1+ to Cu◦ [24,30,32,33]. In the case of CuAl catalyst,
contribution of two peaks was detected for the broad peak of TPR
profile reported in the literature [22]. Each of these peaks could
be ascribed to the reduction of well dispersed CuO [24,30,32,33]
and to the reduction of larger particles of CuO interacting with the
support [34].
Based on these results, basic properties of the catalysts were
measured using temperature programmed desorption of CO2. The
obtained results from this characterization technique are pre-
sented In Fig. 5. As can be observed in this figure, PtHYAl and
RuCuTi catalysts showed CO2 desorption profiles, while the CuZr
As shown in Fig. 3, the reduction profile obtained for RuCuTi cat-
alyst presented a broad peak formed by the sum of different peaks
with maximum temperatures at 127, 149, 175 and 211 ◦C. These
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catalysts presented flat profile indicating that CuZr catalyst pre-
sented neutral properties. Regarding basicity properties of NiAl and
CuAl catalysts, these materials did not show signal associated to
CO2 desorption, suggesting that these catalysts did not have basic
characteristics.
The CO2-TPD profile of PtHYAl catalysts presented two peaks
contribution at around 100–380 ◦C. For RuCuTi catalysts, its profile
showed two small peaks at temperatures below 200 ◦C. According
to the literature [28], strength of basic sites can be medium if the
peaks appears at temperatures below 450 ◦C or strong if the peaks
appears at temperatures above 450 ◦C. Therefore, the strength of
basic sites in the calcined catalysts was mainly medium.
The presence of basic sites on PtHYAl catalysts could be due to
the hydrophobic characteristics of the Al2O3 support. However, the
acid characteristics of the PtHYAl catalyst overcome the basic ones,
because the total amount of desorbed NH3 (mmolNH3/g catalyst)
and CO2 mmolCO2/g catalyst), determined by the deconvolution
by Gaussian fit of TPD profiles, were 0.74 and 0.44, respectively.
Concretely, PtHYAl2O3 catalyst adsorbed 0.195 mmol NH3/gcat and
0053 mmol CO2/gcat at a temperature range of 85–230 ◦C, being
about 200 ◦C the temperature for the hydrogenolysis of HMF. The
aforementioned data suggest that this catalyst is more acid than
basic at the temperatures established to carry out the HMF conver-
sion into DMF. Regarding CuAl and NiAl catalysts, these presented
a similar NH3 adsorption peak at the same temperature range as
PtHYAl catalyst, indicating that the acid nature at these temper-
atures is very similar. Based on this explanation, it seems to be
obvious that ␥-Al2O3 and ␥-Al2O3 supported catalysts presented a
predominant acid nature.
3.2. Catalytic activity
3.2.1. Preliminary tests and correlation with catalyst
characterization
Before the activity measurements of CuZr catalyst, preliminary
tests were performed with PtHYAl, NiAl, CuAl, RuCuTi, RuTi and
the aforementioned CuZr catalyst, in order to establish the best
reaction conditions. The fixed conditions were real HMF, 200 mg of
catalysts (WHSV = 0.12 h−1) and 0.5 MPa for 4 h, using pretreated
and non-pretreated catalysts. The results obtained for pretreated
and non-pretreated catalysts are presented in Fig. 8, in which
the maximum DMF selectivity obtained in each experiment is
represented independently of the time on stream. In the men-
tioned figure, catalysts without selectivity toward DMF are not
presented. As can be observed, only the pre-treated PtHYAl, NiAl,
CuAl and RuCuTi showed a very low selectivity toward DMF with
high/completely HMF conversion among the all tested catalysts.
In these cases the main products were different compounds such
as; furfural (FF), 5-methylfurfural (5MF) and 2-(hydroxymethyl)-5-
methylfuran (MFA), but in small amounts. According to the reaction
mechanism shown in Fig. 2, the detected compounds, such as 5MF
and MFA, are intermediate products of HMF conversion and there-
fore precursors of DMF product. In the case of FF, which is not a
DMF precursor, it could be produced from demethylation of 5MF
in the presence of H2.
The DMF selectivity was slightly increased when the catalysts
were not pretreated, reaching the highest DMF yield with the CuZr
catalyst followed by RuCuTi and RuTi catalysts. Based on these
results, it seems that the presence of Cu and the use of neutral or low
basicity supports improve catalyst selectivity toward DMF. On the
other hand, it seems that the dispersion of the catalysts is not very
important in this reaction since the copper dispersion (TEM) was
very low. Therefore it seems that the support play a more impor-
tant role than the metal dispersion in this reaction. According to the
literature [34,42,43] non-noble metals, as Cu, and noble metals, as
Ru, were typically used for polyols hydrogenolysis because they
provided good conversion and high selectivity toward target prod-
ucts. Moreover, the addition of basic additives to catalysts used in
hydrogenolysis of polyols seems to improve the reported catalysts
performance [34]. In these sense, the non-pretreated catalysts sup-
ported on neutral-basic materials showed better selectivity toward
DMF, showing the best behavior the catalysts with neutral proper-
3.1.4. Morphological appearance
With the main objective of trying to gain more information
about the Ni, Pt, Ru, and Cu dispersion on the support surface, SEM
analyses were performed for the calcined catalysts and the obtained
results are shown in Fig. 6. In these images it can be observed how
the different metals are distributed on the samples in a different
way, mainly depending on the support. Moreover, in the case of
the used CuZr, the metal is also distributed in a different way due
to the incorporation of the Cu to the ZrO2 structure. In the case of
the CuAl, it was easier to identify the Cu particles on the support
and the morphology was similar to that of the NiAl catalyst. In the
case of the PtHYAl different region images of the catalyst at higher
magnification times were taken to analyze the presence of Pt using
the technique of Energy-dispersive X-ray spectroscopic (EDS). This
analysis allowed a differentiation between Pt and other atoms (not
shown), which was impossible neither by color nor shape, with this
technique was concluded that the Pt was highly dispersed on the
zeolite support.
ties. This type of neutral-basic supports seems to avoid the C
C
bond cleavage of tertiary carbon of the HMF raw material, avoiding
the formation of FF product. Al2O3 and zeolite type supports are
widely used in cracking process of petroleum derivatives, because
of their acid character. Moreover, according to the literature [2],
the Al2O3 and ZSM-5 supported catalysts seem to show lower DMF
selectivity. Therefore, the catalysts with acid nature could cause the
loss of one of the radicals presented in the HMF molecule and/or
the degradation of the DMF.
For a deeper analysis of the Cu dispersion in the catalysts, TEM
images were taken, which are presented in Fig. 7. Unfortunately, in
general the TEM images did not allow to make a clear distinction
between Cu particles and the support in the samples; therefore
it is very difficult to analyze the pictures. Nevertheless it can be
obtained general conclusions. The Cu dispersion in the different
supports was very low. Only in the RuCuTi it can be observed small
particles of Ru, (the small black particles) and big particles of Cu
(the big black particles). In the case of the fresh CuZr large particles
of Cu were detected, and the large Cu particle size is maintained
after use in reaction. In general, in the case of the copper catalyst
the dispersion was low. In the case of the CuAl catalyst, it can be
distinguished between Cu and Al2O3. Another conclusion was that
carbon species were not detected on the catalytic surface of the
used CuZr catalyst.
Moreover, the atmosphere of reaction is also an important fac-
tor in the activity of the catalysts. Due to the presence of H2 in the
reaction media, the non-pretreated catalysts could be reduced dur-
ing HMF hydrogenolysis. Based on the TPR results, the CuZr, RuTi
and RuCuTi catalysts would be completely, or nearly completely,
reduced. In the case of the non-preatreated PtHYAl, NiAl and CuAl,
the presence of H2 at 200 ◦C probably reduced a minimum part of
the reducible species. On the other hand, the pre-treatment at a
temperature higher than 200 ◦C, it means at 400 ◦C, could favor the
agglomeration/sinterization [23,27,44] of the metal phases on the
support surface, resulting in lower DMF selectivity for pretreated
catalysts. In conclusion, the catalysts without any pre-treatment
showed better DMF selectivity than pre-treated ones probably due
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7
Fig. 6. SEM images of fresh (a) PtHYAl, (b) NiAl, (c) CuAl, and (d) CuZr catalysts.
to the aggregation phenomena of metal phase in the pretreated
catalysts.
CuZr catalyst is more selective toward other type of compounds
under the mentioned conditions. Moreover, the impurities associ-
ated to the real HMF feed (mainly FF and 5MF), which were obtained
from fructose dehydrogenation/hydrogenation process in a batch
reactor, could also be the responsible of the low DMF selectivity
obtained. In this sense, HMF production from fructose could take
place through furanose type intermediate products and even HMF
could convert into soluble polymers [46]. These compounds, which
were solved in used real HMF feed, were not detected with the used
equipment.
Taking into account these results, it was decided (i) to reduce
WHSV from 0.12 to 0.06 h−1 (500 mg of catalyst), based on the
Dumesic and co-workers report [8], (ii) to use synthetic HMF,
because the impurities of the real HMF could be one of the cause of
the obtained selectivity and (iii) to increase the pressure from 0.5
to 3.0 MPa in order to determine the influence of pressure on the
hydrogenation reaction.
3.2.2. Influence of reaction conditions on performance of
non-pretreated CuZr catalyst
Based on the above results, activity measurements were carried
out with non-pretreated CuZr catalyst in order to maximize the
DMF yield. For this propose, the effect of reaction conditions, such
as temperature, pressure, space velocity, defined as WHSV, and
type of feed were analyzed in order to establish the best operation
conditions for the hydrogenolysis process.
First of all, it was decided to increase the reaction temperature in
25 ◦C, it means from 200 ◦C to 225 ◦C, remaining constant the other
operating conditions used in the preliminary tests. Fig. 9 shows the
results obtained when the temperature was increased. As can be
observed, the increase of temperature does not seem to have an
important influence on the conversion, which is close to the total
conversion, and on the selectivity, because the obtained selectiv-
ity was very similar to the previous one. These results seem are in
agreement with thermodynamic since hydrogenation reactions are
exothermic and therefore it should not expect an increase in results,
because the reaction is not thermodynamically favored at high tem-
peratures. However, a test at 150 ◦C and 0.5 MPa was performed at
the same operation conditions obtaining a conversion 10 point less
than the obtained ones at 200 ◦C and 0.5 MPa. Moreover, accord-
ing to the majority of literature based on hydrogenolysis of HMF
[4,8,17,18,45] these raw material conversion into DMF is carried
out at temperatures above 180 ◦C. And according to Kumalaputri
et al. [45] the best DMF product selectivity achieved at 220 ◦C under
the conditions reported. This fact could be probably due to that at
low temperatures reaction rate is quite low.
The data obtained for these new operation conditions are
included in Fig. 10. In this case, the CuZr catalyst was also reused
at these new operation conditions.
According to the activity results, the CuZr catalyst was able to
convert completely synthetic HMF. This result, which is the same
as the obtained under preliminary tests conditions, suggested that
the CuZr catalyst was very active in HMF transformation under dif-
ferent operation conditions. On the other hand, the DMF selectivity
obtained at 200 ◦C and 0.5 MPa was higher when compared with the
data obtained with a higher WHSV and with a real HMF. This indi-
cates that DMF selectivity improves when space velocity decrease
and HMF feed does not contain impurities. However, the selectivity
was not so high because other types of products were obtained in
the reaction, as in the case of the preliminary tests.
Regarding reaction pressure, its increase did not affect the
HMF conversion, but the selectivity increased specially at 1.5 MPa,
achieving after 4 h a selectivity to DMF of 45%. However, the
In terms of DMF selectivity, this was very low when compared
with the high HMF conversion. As mentioned previously, this fact
can be related to the formation of other compounds, indicating that
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Fig. 7. TEM images of fresh (a) RuCuTi, (b) CuAl, (c) CuZr, and (d) used CuZr catalysts.
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
PtHYAl (4h) NiAl (3h)
CuAl (2h) RuCuTi (4h)
CuZr (4h)
RuTi (2h)
RuCuTi (3h)
Pre-treated Catalysts
Non-pretreated Catalysts
Fig. 8. Real HMF conversion and DMF yields obtained for pretreated and non-pretreated catalysts at 0.5 MPa, WHSV = 0.12 h−1 and 200 ◦C using H2 (᭿ HMF conversion and
DMF selectivity).
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200 ºC
225 ºC
100
80
60
40
20
0
14.71
4h
14.17
4h
11.01
2h
10.73
3h
9.82
2h
9.09
3h
Time on Stream
Fig. 9. Real HMF conversion and DMF selectivity obtained with CuZr catalyst at 0.5 MPa, WHSV = 0.12 h−1 and different temperatures using H2 (᭿ HMF conversion and
DMF selectivity).
200 ºC
200 ºC
200 ºC
225 ºC
200 ºC
1.5 MPa
2.25 MPa
3.0 MPa
1.5 MPa
0.5 MPa
100
80
60
40
20
0
60.6
49.8
48.6
45.3
44.1
43.0
42.7
42.0
41.7
39.9
36.0
32.4
25.0
21.9
9.5
2h 3h 4h 2h 3h 4h 2h 3h 4h 2h 3h 4h 2h 3h 4h
Time on Stream
Fig. 10. Synthetic HMF conversion and DMF selectivity obtained with CuZr catalyst at WHSV = 0.06 h−1 and different temperatures and pressures (᭿ HMF conversion and
DMF selectivity).
increase from 1.5 MPa to 2.25 and 3.0 MPa led to selectivities of
about 41.7 and 42.7%, respectively. This means that DMF selec-
tivity remained almost constant, reaching DMF selectivity values
close to the obtained at 1.5 MPa (see the black tendency line in
Fig. 10). According to these results, pressures between 1.5–3.0 MPa
do not affect the DMF selectivity. However, the results seem to
indicate that some pressure is needed to promote hydrogenation
reaction, which commonly carries out at medium-high pressures.
In this point, it is important to mention that a pressure increase
from 0.5 to 1.5 MPa provokes that the hydrogenation reaction
take place in liquid phase. In this sense, the literature reported
[47,48] that mass transfer from gas phase to liquid phase is more
influenced by pressure, favoring the dissolution of H2 on liquid
phase. However, the increase of pressure from 1.5 to 3.0 MPa could
produce the saturation of H2 in liquid phase, resulting in similar
values of DMF selectivity.
On the other hand, the increase of temperature from 200 to
225 ◦C provoked a great decrease of DMF selectivity, achieving a
DMF selectivity of 9.5% after 4 h on reaction, corroborating the con-
clusion obtained from the preliminary activity measurements.
Finally, the catalyst was tested at 200 ◦C and 0.5 MPa in order
to close the experiment cycle. The obtained data were 33.4% (2 h),
29.1% (3 h) and 26.7% (4 h). These results were very similar to the
data presented in Fig. 10 for the aforementioned operation con-
ditions, suggesting that catalyst did not suffer a high process of
deactivation, being stable after 24 h.
Please cite this article in press as: A. Iriondo, et al., 2,5-DMF production through hydrogenation of real and synthetic 5-HMF over transition
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The main goal of this work was to investigate the hydrogenolysis
reaction of real and synthetic HMF, platform molecule, to produce
DMF, biofuel, in a continuous flow system using pre-treated and
non-pretreated noble and non-noble catalysts. For that purpose,
reaction conditions, such as temperature, pressure, type of HMF
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HMF conversion and DMF selectivity. According to the obtained
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the best DMF selectivity. This observation suggested that neutral
nature of the support and the presence of Cu influenced positively
on the selectivity toward the target product.
On the other hand, the results concluded that (i) the DMF selec-
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the presence of impurities was negligible, (ii) the increase of reac-
tion temperature did not influence on conversion and selectivity,
due to its exothermic character, (iii) the DMF selectivity improved
when the pressure was increased from 0.5 to 1.5 MPa probably due
to the improvement of mass transfer of H2 to liquid phase, in which
hydrogenolysis reaction takes place and (iv) the lower space veloc-
ity also improved the obtained DMF selectivity because the contact
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This work was supported by University of the Basque Coun-
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European Union through the European Regional Development Fund
(FEDER) (Projects: CTQ2012-38204-C03-03 and CTQ2015-64226-
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metal catalysts supported on carriers with different nature, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.02.019