A smart catalyst system for the valorization of renewable furfural in aliphatic alcohols

Article abstract of DOI:10.1039/c5cy01195g

A highly efficient and selective oxidative condensation-hydrogenation process of renewable furfural with aliphatic alcohols catalyzed by metallic platinum in a one-pot reactor is developed. A series of supported platinum catalysts including Pt/FH, Pt/H, Pt/HT, Pt/Fe₃O₄, Pt/Al₂O₃ and Pt/ZrO₂ are prepared and employed for the polarization of furfural in ethanol and n-propanol. It is found that, in the presence of Pt/FH and potassium carbonate, 93.9% conversion of furfural and 67.9% selectivity to furan-2-acrolein were obtained via oxidative condensation in the furfural-ethanol-O₂ (FEO) system, and 90.1% conversion of furfural and 90% selectivity to 3-(furan-2-yl-)-2-methylacrylaldehyde were obtained via oxidative condensation in the furfural-n-propanol-O₂ (FPO) system. Moreover, the oxygen in the FPO system is completely replaced by molecular hydrogen to allow the further conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde, while the catalytic system was kept unchanged. During this process, 87.3% conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde and 73.2% selectivity to 3-(furan-2-yl-)-2-methylpropanol were obtained via a hydrogenation reaction with the Pt/FH catalyst. Moreover, several common bases as promoters were investigated in detail. All the catalysts were characterized by XRD, TEM, SEM, TPD and BET methods to reveal their catalytic nature in the reaction.

Full text of DOI:10.1039/c5cy01195g

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A smart catalyst system for the valorization of
renewable furfural in aliphatic alcohols
Cite this: DOI: 10.1039/c5cy01195g
*
Zonghui Liu, Xinli Tong, Jinbiao Liu and Song Xue
A highly efficient and selective oxidative condensation–hydrogenation process of renewable furfural with
aliphatic alcohols catalyzed by metallic platinum in a one-pot reactor is developed. A series of supported
platinum catalysts including Pt/FH, Pt/H, Pt/HT, Pt/Fe3O4, Pt/Al2O3 and Pt/ZrO2 are prepared and employed
for the polarization of furfural in ethanol and n-propanol. It is found that, in the presence of Pt/FH and
potassium carbonate, 93.9% conversion of furfural and 67.9% selectivity to furan-2-acrolein were obtained
via oxidative condensation in the furfural–ethanol–O2 (FEO) system, and 90.1% conversion of furfural and
90% selectivity to 3-(furan-2-yl-)-2-methylacrylaldehyde were obtained via oxidative condensation in the
furfural–n-propanol–O2 (FPO) system. Moreover, the oxygen in the FPO system is completely replaced by
molecular hydrogen to allow the further conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde, while the
catalytic system was kept unchanged. During this process, 87.3% conversion of 3-(furan-2-yl-)-2-methyl-
acrylaldehyde and 73.2% selectivity to 3-(furan-2-yl-)-2-methylpropanol were obtained via a hydrogenation
reaction with the Pt/FH catalyst. Moreover, several common bases as promoters were investigated in detail.
All the catalysts were characterized by XRD, TEM, SEM, TPD and BET methods to reveal their catalytic
nature in the reaction.
Received 28th July 2015,
Accepted 16th September 2015
DOI: 10.1039/c5cy01195g
www.rsc.org/catalysis
chemicals or biofuels derived from FUR as replacement for
fossil resources is very attractive. Actually, FUR could be
1. Introduction
In recent years, an increasing interest in developing renew-
able energy resources as alternatives to replace the
diminishing supply of fossil fuels has grown in the chemical
field. As a green, sustainable and cheap resource easily avail-
able in nature, biomass feedstock can be directly converted
into various chemical products and energy materials.1–3 Par-
ticularly, there is intensive research on the use of lignocellu-
lose as a raw material for producing fine chemicals and liquid
fuels.4–7 It has been verified that roughly 75% of biomass is
in the form of carbohydrates which can be employed to pre-
pare furanic derivatives as platform compounds.8 Obviously,
the selective transformation of biomass or bio-based platform
compounds via catalytic cascade reactions is beneficial to
improve the efficiency and cut the energy consumption in
large-scale and sustainable industrial production.9 Furfural
(FUR), a C5 compound, can be obtained through the hydroly-
sis of pentose which comes from agricultural raw materials
including corncobs, wheat bran, sawdust, etc. Molecular FUR
contains a furan ring and an aldehyde group which is improv-
able and considered as an intermediate for producing useful
chemicals in industry. Therefore, exploring the value-added
employed to synthesize a variety of chemicals via simple
processes including hydrogenation, oxidation, reductive
amination, nitration, decarbonylation, condensation, etc.10,11
For example, the efficient aldol condensation of FUR with
acetone has been proposed as a key intermediate step to
synthesize second generation biofuels obtained from lignocel-
lulosic biomass.12–17 Similarly, the condensation reaction of
furfural and aldehyde is also feasible to impel two carbon
molecules together and produce longer hydrocarbon chains
and low volatile liquid fuels. Herein, acetone and aldehydes
can be produced from the oxidation of secondary and pri-
mary alcohols in the presence of molecular oxygen.18 For
example, the efficient oxidative condensation of FUR with
n-propanol using gold and a suitable base as the catalyst to
prepare a FUR-containing long chain aldehyde has been
reported.19 On the other hand, the oxidative esterification of
furfural was also reported to produce alkyl furoates which
can be applied as flavour and fragrance components.20–24 It
is shown that FUR can be converted to methyl furoate by oxi-
dative esterification with methanol in the presence of a Au/
TiO2 catalyst and NaCH3O as an additive.20 Obviously, oxida-
tive condensation and oxidative esterification are the com-
petitive processes in the FUR–alcohol–O2 system which is
shown in Scheme 1.
Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion,
School of Chemistry and Chemical Engineering, Tianjin University of Technology,
No. 391 Binshuixi Road, Tianjin 300384, PR China. E-mail: tongxinli@tju.edu.cn,
tongxli@sohu.com; Fax: +86 22 60214259; Tel: +86 22 6024259
Very recently, Faba et al.25 investigated the hydrogenation
of FUR–acetone condensation adducts with an alumina-
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filtered, washed repeatedly with deionized water until the
solution became neutral, freeze-dried and calcined at 400 °C
for 5 h. The final white powder was hydroxyapatite and
denoted as H.
2.1.3 The preparation of calcined hydrotalcite (HTc). 30.76
g of MgIJNO3)2·6H2O and 15 g of AlIJNO3)3·9H2O were dissolved
in 400 mL of water, followed by the addition of 72 g of urea
under stirring. After being boiled for 8 h, the mixture was
placed at room temperature for 12 h to allow complete pre-
cipitation, filtered, washed with a large amount of water,
dried at 60 °C overnight, and finally calcined at 500 °C for 3
h. The sample obtained was denoted as HTc (molar ratio of
Mg/Al is 3).
2.1.4 The preparation of ferriferrous oxide. Fe2IJSO4)3 (0.01
mol) and FeSO4 (0.01 mol) were respectively dissolved in a
three-neck bottle. The mixture was heated to 45 °C in a water
bath, and then ammonia solution was dropped to adjust the
pH value to between 10 and 11. The reaction was kept for 1
h. Then, the magnetic substrates were separated by magnetic
separation and washed with distilled water to achieve neu-
trality. Finally, the obtained solid was dried in a vacuum oven
overnight at a temperature of 80 °C.
2.1.5 The preparation of alumina (Al2O3). Certain amounts
of AlIJNO3)3·9H2O and (NH4)2CO3 were respectively dissolved
in deionized water, and then transferred to a 250 mL three-
neck flask rapidly, where the pH value of the solution was
controlled at about 8.5. After being mixed equally, the solu-
tion was stirred for 2 h. The obtained white solid precipitates
were filtered and washed repeatedly with deionized water.
After being dried at 100 °C for 24 h, the solid materials were
calcined at 600 °C for 2 h.
2.1.6 The preparation of zirconium dioxide (ZrO2). The
support ZrO2 was prepared by dissolving 0.01 mol of ZrIJNO3)4
·5H2O or zirconium oxychloride (Alfa corporation) in 100 mL
of deionized water. The mixture was stirred at room tempera-
ture, and then ammonia solution was added until the pH
was adjusted to 10. The gel was aged for 72 h, filtered and
washed with deionized water till the pH value became 7. The
obtained solid was dried at 120 °C for 24 h and calcined at
600 °C for 3 h.
Scheme 1 The reaction of FUR with alcohol in the presence of
dioxygen.
supported noble metal catalyst to prepare biofuels. Moreover,
the aldol condensation–hydrogenation reaction of FUR with
acetone has also been proposed using a supported Pd/
CN@MgO catalyst.26 In this article, we employ a smart cata-
lyst system to achieve the oxidative condensation and further
hydrogenation of FUR with aliphatic alcohols in a one-pot
reactor. Several typical supported platinum catalysts and
bases are chosen as catalysts for the reaction. Based on the
experimental results, it is found that using Pt/FH as a catalyst
and potassium carbonate as an additive, 93.9% conversion of
furfural and 67.9% selectivity to furan-2-acrolein were
obtained via oxidative condensation in the furfural–ethanol–
O2 (FEO) system; moreover, 90.1% conversion of FUR and
90% selectivity to 3-(furan-2-yl-)-2-methylacrylaldehyde were
obtained in the FUR–n-propanol–O2 (FPO) system, while
87.3% conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde and
73.2% selectivity to 3-(furan-2-yl-)-2-methyl propanol were
obtained under H2 atmosphere in the same catalytic system.
2. Experimental section
2.1 Synthesis of different metal oxides as supports
2.1.1 The preparation of FeOx–hydroxyapatite (FH). At
room temperature, an aqueous solution of Fe3+ and Fe2+
(mole ratio was 2 : 1) obtained by dissolving FeCl3·6H2O (3.7
mmol) and FeCl2·4H2O (1.85 mmol) in deoxygenated water
(30 mL) under nitrogen atmosphere was added dropwise to
25% ammonia solution (15 mL) under vigorous stirring. After
being stirred for 15 min, two 80 mL aqueous solutions of Ca-
IJNO3)2·4H2O (33.7 mmol) and (NH4)2HPO4 (20 mmol) were
added slowly at the same time to keep the pH value at about
10.3. The prepared grey suspension was heated to 90 °C
immediately, stirred for 2 h, cooled to room temperature and
then aged overnight. The obtained red brown precipitate was
filtered, washed repeatedly with deionized water until the
solution became neutral, freeze-dried and calcined at 400 °C
for 5 h. The obtained brown powder was FeOx modified
hydroxyapatite which was denoted as FH.
2.1.2 The preparation of hydroxyapatite (H). At room tem-
perature, two 80 mL aqueous solutions of CaIJNO3)2·4H2O
(33.7 mmol) and (NH4)2HPO4 (20 mmol) were simultaneously
added dropwise to a 25% ammonia solution (15 ml) under
vigorous stirring to adjust the pH value to about 10.3. The
resultant milk-like suspension was heated to 90 °C immedi-
ately, stirred continuously for 2 h, cooled to room tempera-
ture and then aged overnight. The white precipitate was
2.2 The preparation of supported platinum catalysts
In a typical synthesis of the 5% Pt/FH catalyst, 1 g of FH and
14 mL of 0.01 g mL−1 HPtCl4 solution were mixed together in
a three-neck flask, and then 5 mL of deionized water was
added under ultrasound treatment for 10 h. The bottle was
put into an oil bath for heating. When the temperature
reached 105 °C, 5 mL of a newly prepared NaBH4 solution
(20 mg mL−1) was dropwise added to the above mixture to
obtain a 5% Pt loading, and the mixture was refluxed for 5
hours. The resultant product was filtered and further washed
with deionized water several times. After being vacuum dried,
the desired Pt/FH catalyst was prepared successfully for the
next reaction. In addition, Pt/H, Pt/HT, Pt/Fe3O4, Pt/Al2O3,
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and Pt/ZrO2 catalysts were synthesized for comparison using
a similar method.
Gas Chromatograph-Mass Spectrometer (GC-MS) instrument.
In addition, the nuclear magnetic resonance (NMR) spectra
were recorded on a Bruker 400 MHz spectrometer.
2.3 General procedure for the oxidative condensation–
hydrogenation reaction of furfural and aliphatic alcohols
3. Results and discussion
In a typical oxidative condensation–hydrogenation reaction of
furfural with aliphatic alcohol, 15 mL of aliphatic alcohol
was thoroughly mixed with 0.05 g of Pt/FH, 0.05 g of K2CO3,
and 0.2 g of furfural. The mixture was charged into a 120 mL
autoclave equipped with a magnetic stirrer and an automatic
temperature control system. The solution was then stirred for
4 h at 140 °C under 0.3 MPa of O2 for the oxidative condensa-
tion step. After this reaction, the autoclave was cooled to
room temperature and a small amount of solution was
diluted with CH3CN solvent and analyzed by GC and GC-MS
after the excess gas was purged. Moreover, the hydrogenation
step was further performed, in which the remaining mixture
was transferred into a high pressure reactor and replaced
with nitrogen and hydrogen in turn to remove the remaining
oxygen. Then, pure hydrogen was charged into the reactor,
and the solution was stirred at 220 °C for 4 h under 5.0 MPa
of H2. When the hydrogenation reaction was finished, the
solution was cooled down and the remaining H2 was
removed by a careful venting process and the liquid mixture
obtained was also analyzed by GC and GC-MS.
3.1 Characterization of the supported platinum catalysts
3.1.1 XRD patterns. Fig. 1 shows the XRD patterns of the
different supported platinum catalysts. As we can observe
from it, for the Pt/ZrO2 catalyst, the main peaks are attrib-
uted to the diffractions of the ZrO2 support, and the charac-
teristic diffraction peaks of Pt are weak, which indicates that
the crystallites of Pt in Pt/ZrO2 have irregular or very small
particle sizes. For the Pt/FH or Pt/H catalyst, it is found that
the characteristic peaks of the Pt crystal distinctly appear, in
which the peaks at 2θ = 39.8°, 46.2° and 67.5° are assigned to
the diffraction of the (1 1 1), (2 0 0) and (2 2 0) lattice planes.
In addition, the other diffraction peaks should be attributed
to the diffractions of the hydroxyapatite support. For the Pt/
Fe3O4, Pt/Al2O3 and Pt/HTc catalysts, the peaks of the plati-
num crystal are also very distinct, and the other peaks can be
attributed to the diffractions of the metal oxide supports.
3.1.2 BET detection of the different platinum supported
catalysts. The textural properties of the supported platinum
catalysts derived from nitrogen physisorption are shown in
Table 1. It can be seen that the surface area of the Pt/Al2O3
and Pt/HTc catalysts is 363.1 m2 g−1 and 101.7 m2 g−1, respec-
tively. Moreover, the BET surface area of Pt/FH, Pt/H and Pt/
Fe3O4 is 81.7 m2 g−1, 66.7 m2 g−1 and 70.5 m2 g−1, respec-
tively. However, the surface area of Pt/ZrO2 is only 22.0
m2 g−1 and its pore volume is only 0.05 m3 g−1, which is
smaller than those of the other catalysts. Besides, the average
pore diameter of these Pt supported catalysts is between 35.0
nm and 86.5 nm.
2.4 Characterization of catalysts and product analysis
X-ray diffraction (XRD) measurement was performed by using
a diffractometer with Cu Ka radiation (0.02° resolution) in
the range from 10 to 80° [2θ]. Moreover, the surface morphol-
ogy and particle size of the platinum catalysts were obtained
by using a scanning electron microscope (SEM: JSM-6301F,
JEOL) and a transmission electron microscope (TEM: JEM-
2100, JEOL). The BET surface areas, pore volumes, and aver-
age pore diameters of the prepared samples were obtained
from N2 (77 K) adsorption measurement using a Micro-
meritics ASAP2020M system. Therein, the samples were
pretreated under vacuum at 250 °C for 4 h before measure-
ment. The average pore diameter data were calculated
according to the Barrett–Joyner–Halenda (BJH) model in
absorption and desorption periods. Ammonia temperature
programmed desorption (TPD) experiments were carried out
using a Micromeritics 2920 Autochem II Chemisorption Ana-
lyzer. The samples were first pretreated at 500 °C for 1 h
under Ar at a flow rate of 30 mL min−1 and cooled to room
temperature, then adsorption proceeded under NH3 at a flow
rate of 30 mL min−1. During the TPD experiments, the tem-
perature was set to 850 °C by means of a temperature ramp
of 10 °C min−1 using helium as the carrier gas flowing at 60
mL min−1. The effluent gas was dried by powder KOH and
the concentrations of ammonia were recorded by using a
thermal conductivity detector.
3.1.3 TPD measurement of the different Pt supported cata-
lysts. In order to study the acidic properties of the Pt solid
catalysts, NH3-TPD was performed and the experimental
results are presented in Fig. 2. It is found that the highest
peak of Pt/Al2O3 and Pt/Fe3O4 is about 230 °C, that of Pt/FH
The quantitative analysis of the product was performed on
a GC with a hydrogen ion flame detector; the qualitative anal-
ysis of the product was carried out on an Agilent 6890/5973
Fig. 1 The XRD patterns of the different platinum supported catalysts.
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Table 1 The physical properties of the different platinum supported
catalysts
different catalysts, SEM characterizations were also
performed. Fig. 3a–f show the SEM images of Pt/FH, Pt/H, Pt/
Al2O3, Pt/HTc, and Pt/ZrO2. It was found that the Pt/FH and
Pt/H materials have a flower-like surface. A lot of thin stripes
appear on the surface of the Pt/Al2O3 catalyst, while the sur-
face of the Pt/HTc catalyst appears regular and even. How-
ever, a needle-like surface is formed on the PtOx/HTc catalyst
which can be an effect of calcination at 400 °C after Pt was
loaded on the hydrotalcite support. Furthermore, tight and
rough surfaces are formed on the Pt/ZrO2 catalyst.
BET
surface
area
Pore
Average pore diameter (nm)
volume
Catalyst
(m2 g−1
)
(cm3 g−1
)
BJH adsorption BJH desorption
Pt/FH
Pt/H
Pt/HTc
Pt/Fe3O4
Pt/Al2O3
Pt/ZrO2
81.7066 0.191164
66.7383 0.186546
101.6813 0.186213
70.4899 0.131349
363.0520 0.346451
22.0419 0.058559
61.236
65.175
56.032
57.583
34.596
85.901
76.632
86.508
66.090
70.636
35.048
64.916
3.1.5 TEM images of the different Pt supported catalysts.
Moreover, the Pt supported catalysts were further character-
ized by the TEM technique. As shown in Fig. 4, the average
size of the Pt particles is 6–7 nm in the Pt/FH catalyst. The
aggregation of the platinum particles is observed in the Pt/
HTc and PtOx/HTc catalysts. Moreover, the size of the plati-
num particles is distributed between 7 nm and 9 nm on the
Pt/H catalyst, between 4 nm and 6 nm on the Pt/Al2O3 cata-
lyst and between 24 nm and 28 nm on the Pt/ZrO2 catalyst;
therefore, the catalytic activity of the Pt/FH catalyst is much
higher than those of the other catalysts in the catalytic
reaction.
3.2 The oxidative condensation reaction of FUR in aliphatic
alcohols
3.2.1 The impact of different catalytic systems. Initially,
the catalytic reaction process of FUR with ethanol and
Fig. 2 The TPD results of the different platinum supported catalysts.
is 220 °C, that of Pt/HTc and Pt/H is 200 °C, and that of Pt/
ZrO2 is 575 °C. Thus, Pt/Al2O3, Pt/FH, Pt/HTc and Pt/H mainly
have weak and middle acid sites, Pt/Fe3O4 mainly has weak,
middle and strong acid sites and Pt/ZrO2 mainly has middle
acid sites. Combined with the results of the catalytic test, it
can be concluded that the acidity distribution has no great
effect on the catalytic reaction, while the BET surface area
can be a critical factor in the activity of the platinum
supported catalysts.
3.1.4 SEM images of the different platinum supported cat-
alysts. In order to obtain the structure and morphology of the
Fig. 3 The SEM images of the platinum catalysts [(a) Pt/FH catalyst, (b)
Fig. 4 The TEM images of the platinum catalysts [(a) Pt/FH catalyst, (b)
Pt/H, (c) Pt/Al2O3, (d) Pt/HTc, (e) PtOx/HTc, (f) Pt/ZrO2].
Pt/H, (c) Pt/Al2O3, (d) Pt/HTc, (e) PtOx/HTc, (f) Pt/ZrO2].
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n-propanol in the presence of molecular oxygen was carried
out with different catalysts under the same conditions. The
reaction equations are shown in eqn (1) and eqn (2). The
obtained target products are furan-2-acrolein (1) and 3-(furan-
2-yl-)-2-methylacrylaldehyde (2) in ethanol and n-propanol sol-
vent, respectively.
system, respectively. In the FPO system, the conversions of
FUR were 73.0%, 87.8%, 80.6% and 81.4% with 90.1%,
88.5%, 91.1% and 90.4% selectivities to 2, respectively
(entries 4–7). Besides, the conversion decreased to 58.9% and
31.9%, and the selectivity to 1 and 2 was 81.3% and 90.0% in
the FEO system and FPO system, respectively, when Pt/ZrO2
was used as a catalyst (entry 8). In addition, a platinum oxide
supported catalyst was also studied. In the presence of PtOx/
HT–K2CO3, only 33.7% conversion of FUR and 48.0% selectiv-
ity to 1 in the FEO system and 33.7% conversion of FUR and
63.4% selectivity to 2 in the FPO system were attained under
similar conditions (entry 9). Further, the catalytic test was
also performed in the absence of oxygen, in which 47.2%
conversion and 58.7% selectivity to 2 were obtained in the
FPO system (entry 10). It shows that oxygen was very useful
to elevate the conversion of FUR although the dehydrogena-
tion of n-propanol could happen in the presence of the Pt/
FH–K2CO3 catalyst. Thus, the high activity of several Pt cata-
lysts should be attributed to their large surface area and pore
volume, small and average sized Pt nanoparticles and numer-
ous weak acid sites, which are obtained from the BET, XRD,
TEM and TPD measurements. In addition, it is worth men-
tioning that the reaction of FUR with methanol hardly
occurred.
3.2.2 The influence of bases as additives. In order to fur-
ther reveal the influence of base as an additive, several typical
bases including Cs2CO3, Na2CO3, KHCO3, KOH and NaOH
were chosen and used in the reaction of FUR with ethanol
and n-propanol with the Pt/FH catalyst. The experimental
results with different additives are summarized in Table 3.
When Cs2CO3 and Na2CO3 were used instead of K2CO3, the
conversions of FUR were only 43.7% and 31.7% and the
selectivities to 1 were 89.7% and 85.2% in the FEO system,
while 65.5% and 31.8% conversions and 81.1% and 90.9%
selectivities to 2 were obtained in the FPO system (entries 1
and 2). Moreover, 88.0% and 86.7% conversions of FUR and
The experimental results of different catalysts are summa-
rized in Table 2. It is found that by using only Pt/FH as a cat-
alyst, 53.9% and 46.3% conversions of FUR were obtained;
however, product 1 or 2 was not obtained in the FEO or FPO
system (entry 1). When a certain amount of K2CO3 was
added, the oxidative condensation of FUR with ethanol and
n-propanol was obviously improved and 93.9% and 90.1%
conversions of FUR with 69.7% and 90.0% selectivities to 1
and 2 were obtained, respectively (entry 2). In comparison, in
the presence of K2CO3 alone, the conversion of FUR was only
21.0% and 6.1%, respectively, and product 1 or 2 was hardly
produced (entry 3). These results indicate that the coopera-
tive effect of the Pt supported catalyst and K2CO3 was respon-
sible for the whole reaction orientation in this catalytic sys-
tem. Furthermore, the catalytic performances of the Pt/H–
K2CO3, Pt/HTc–K2CO3, Pt/Fe3O4–K2CO3 and Pt/Al2O3–K2CO3
catalysts were also investigated. It was found that the conver-
sions of FUR were 92.5%, 97.2%, 93.8% and 97.1% with
68.7%, 69.1%, 71.2% and 68.6% selectivities to 1 in the FEO
Table 2 The oxidative condensation of furfural with ethanol and n-propanol catalyzed by the different supported platinum catalystsa
In FEO system
Conversionb
(%)
In FPO system
Conversionb
(%)
Selectivityb (%)
Selectivityb (%)
Entry
Catalyst
1
Othersc
2
Othersc
1
2
3
4
5
6
7
8
Pt/FH
Pt/FH + K2CO3
K2CO3
Pt/H + K2CO3
Pt/HTc + K2CO3
Pt/Fe3O4 + K2CO3
Pt/Al2O3 + K2CO3
Pt/ZrO2 + K2CO3
PtOx/HTc + K2CO3
Pt/FH + K2CO3
53.9
93.9
21.0
92.5
97.2
93.8
97.1
58.9
33.7
—
0
67.9
0
68.7
69.1
71.2
68.6
81.3
48.0
—
100
32.1
100
31.3
30.9
28.8
31.4
18.7
52.0
—
46.3
90.1
6.1
73.0
87.8
80.6
81.4
31.9
33.7
47.2
0
90.0
0
90.1
88.5
91.1
90.4
90.0
63.4
58.7
100
10.0
100
9.9
11.5
8.9
9.6
10.0
46.6
41.3
9
10d
a
Reaction conditions: 0.2 g of FUR, 0.05 g of platinum (5.0 wt% loading) catalyst, 0.05 g of K2CO3, in 15 mL of ethanol or n-propanol, under
b
0.3 MPa of O2, reaction time 4 h, temperature 140 °C. The results are obtained by the internal standard method using GC; compound 1 is
furan-2-acrolein; compound 2 is 3-(furan-2-yl-)-2-methylacrylaldehyde. c The selectivity to others is referred to the selectivity to alkyl furoates and
d
other products. The reaction was performed in the absence of oxygen, in which the main products are compound 2 and furfuryl alcohol
under 0.3 MPa nitrogen.
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Table 3 The influence of various bases in the FEO and FPO systemsa
In FEO system
Conversionb
In FPO system
Conversionb
(%)
Selectivityb (%)
Selectivityb (%)
Entry
Additives
1
Othersc
2
Othersc
(%)
1
2
3
4
5
Cs2CO3
Na2CO3
KHCO3
KOH
43.7
31.7
88.0
74.8
81.7
89.7
85.2
80.2
73.6
81.3
10.3
14.8
19.8
26.4
18.7
65.5
31.8
86.7
79.8
69.5
81.1
90.9
92.0
90.5
88.3
18.9
9.1
8.0
9.5
11.7
NaOH
a
Reaction conditions: 0.2 g of FUR, 0.05 g of Pt/FH (5 wt% Pt loading) catalyst, 0.05 g of additive, in 15 mL of ethanol or n-propanol under 0.3
b
c
MPa of O2, reaction time 4 h, reaction temperature 140 °C. The results are obtained by the internal standard technique using GC. The selec-
tivity to others is referred to the selectivity to alkyl furoates and other products.
80.2% and 92.0% selectivities to 1 and 2 were obtained
when KHCO3 was used as an additive in the FEO and FPO
systems (entry 3). Furthermore, when KOH was added, the
conversion of FUR dropped to 74.8% and the selectivity to 1
only was 73.6% in the FEO system, while 79.8% conversion
and 90.5% selectivity to 2 was obtained in the FPO system
(entry 4). In the case of NaOH, 81.7% and 69.5% conver-
sions were obtained in the FEO and FPO systems, respec-
tively (entry 5). The difference in the promotion effect of
these bases probably originated from their different basicities
and solubilities in the alcohols. Considering efficiency and
economy, potassium carbonate is the best base additive in
both FEO and FPO systems in the presence of the Pt/FH
catalyst.
3.2.3 The effect of temperature. The effect of temperature
on the reaction of FUR with n-propanol was investigated with
the Pt/FH–K2CO3 system and the results are shown in Fig. 5.
It is found that the conversion of FUR gradually increased
and the selectivity to 2 slowly decreased with the increase of
temperature from 110 to 150 °C. Based on these results, it
could be concluded that, for the oxidative condensation of
FUR with n-propanol, the optimal temperature is 140 °C in
the presence of the Pt/FH catalyst.
3.3 The hydrogenation reaction of the in situ prepared
3-(furan-2-yl-)-2-methylacrylaldehyde
The following hydrogenation reaction was performed using a
one-pot method. When the oxidative condensation reaction
of furfural and n-propanol was finished, the mixture includ-
ing the liquid solution and the Pt catalyst was directly trans-
ferred into a steel hydrogenation reactor. The reaction route
is shown in eqn (3). The obtained primary products include
3-(furan-2-yl-)-2-methyl propanal (3) and 3-(furan-2-yl-)-2-
methyl propanol (4). The experimental results with different
catalytic systems are summarized in Table 4. It can be seen
that, when Pt/FH–K2CO3 and Pt/Fe3O4–K2CO3 were used as
the catalytic system, 87.5% and 89.6% conversions of 2 with
73.2% and 71.9% selectivities to 4 were obtained, respectively
(entries 1 and 2). Moreover, the conversions of 2 were 87.5%
and 89.6% using Pt/H and Pt/HT as catalysts but the selectiv-
ities to 4 dropped to 66.4% and 68.9%, respectively (entries 3
and 4). Besides, the conversion increased to 92.5% but the
Table 4 The catalytic hydrogenation of compound 2 by the different
platinum supported catalystsa
Selectivityb (%)
Conversionb
Entry
Catalyst
(%)
3
4
1
2
3
4
5
6
7c
Pt/FH+K2CO3
Pt/Fe3O4+K2CO3
Pt/H+K2CO3
Pt/HT+K2CO3
Pt/Al2O3+K2CO3
Pt/ZrO2+K2CO3
PtOx/HT+K2CO3
87.3
85.5
87.5
89.6
92.5
67.3
90.1
26.8
28.1
33.6
31.1
46.2
36.6
31.2
73.2
71.9
66.4
68.9
53.8
63.4
68.8
a
Reaction conditions: the mixture including the liquid solution and
the Pt catalyst was directly transferred into a steel hydrogenation
reactor when the oxidative condensation reaction of furfural and
n-propanol was finished; the temperature was 220 °C, under 5.0 MPa
b
of H2 pressure, for 4 h. The results are obtained by the internal
standard method using GC. The hydrogenation was performed
c
Fig. 5 The effect of temperature in the oxidative condensation of FUR
with n-propanol in the presence of the Pt/FH catalyst.
using compound 2 as the reactant.
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will provide a promising approach for efficient valorization of
biomass-derived hemicellulose in biomass transformation.
Acknowledgements
This work is financially supported by the National Natural
Science Foundation of China (No. 21003093) and the Key
Program of the National Natural Science of China (No.
21336008).
Scheme 2 The possible reaction mechanism of FUR with n-propanol.
selectivity to 4 decreased to 53.8% when Pt/Al2O3 was used as
a catalyst (entry 5). In the presence of Pt/ZrO2–K2CO3, only a
67.3% conversion of 2 with 63.4% selectivity to 4 was
attained under similar conditions (entry 6). Next, the catalytic
activity of the platinum oxide supported catalyst was also
studied, and 90.1% conversion of 2 with 68.8% selectivity to
4 was obtained (entry 7). It may be due to the fact that the
oxide is reduced to platinum atom by H2 before the hydroge-
nation reaction of the liquid mixture. Besides, it needs to be
mentioned that, following the process of entry 10 in Table 2,
the hydrogenation reaction can also be achieved under nitro-
gen atmosphere although the selectivity to product 4 is low.
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a small amount of
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In summary, a highly efficient and selective oxidative conden-
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