One-pot synthesis of furfural from xylose using Al2O3Ni- Al layered double hydroxide acid-base Bi-functional catalyst and sulfonated resin

Article abstract of DOI:10.1246/cl.151064

Furfural was effectively synthesized from xylose in a onepot manner by the combined use of Ni²⁺-modified γ-Al₂O₃ (Al₂O₃Ni-Al layered double hydroxide (LDH)) and a sulfonated resin (Amberlyst-15) at 373K (46% yield). The addition of Ni²⁺ onto γ- Al₂O₃ generated the bi-functional sites for Lewis acid γ- Al₂O₃ and Br?nsted base Ni-Al LDH at close boundary, and these facilitate the xylose isomerization into xylulose and/or ribulose to afford good yield of furfural after successive dehydration of generated ketopentoses on Amberlyst-15.

Full text of DOI:10.1246/cl.151064

CL-151064
Received: November 17, 2015 | Accepted: December 7, 2015 | Web Released: December 11, 2015
One-pot Synthesis of Furfural from Xylose using Al2O3-Ni-Al Layered Double Hydroxide
Acid-Base Bi-functional Catalyst and Sulfonated Resin
Mahiro Shirotori, Shun Nishimura, and Kohki Ebitani*
School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292
(E-mail: ebitani@jaist.ac.jp)
HO
Furfural was effectively synthesized from xylose in a one-
HO
O
pot manner by the combined use of Ni2+-modified γ-Al2O3
γ-Al2O3
or
HO
(Al2O3-Ni-Al layered double hydroxide (LDH)) and
a
O
OH
M2+-modified Al2O3
O
HO
HO
Amberlyst-15
-3H2O
Xylulose
O
sulfonated resin (Amberlyst-15) at 373 K (46% yield). The
addition of Ni2+ onto γ-Al2O3 generated the bi-functional
sites for Lewis acid γ-Al2O3 and Brønsted base Ni-Al LDH at
close boundary, and these facilitate the xylose isomerization
into xylulose and/or ribulose to afford good yield of furfural
after successive dehydration of generated ketopentoses on
Amberlyst-15.
OH
Isomerization
HO
HO
OH
O
Xylose
Furfural
HO
OH
Ribulose
Scheme 1. Possible reaction path for furfural synthesis via aldose-
ketose isomerization over γ-Al2O3-based catalyst and successive
dehydration on Amberlyst-15.
Conversion of biomass resources into value-added chem-
icals/fuels is an important reaction to utilize renewable
resources.1-3 Cellulose and hemicellulose, the major component
of lignocellulosic biomass, are the most abundant compounds
that are mainly composed of monosaccharides.4,5 Cellulose and
hemicellulose can be converted into monosaccharides like
glucose and xylose by the hydrolysis over activated carbons.6-9
Therefore, successive chemical conversion of saccharides into
value-added chemicals such as furans, sugar alcohols, levulinic
acid, and γ-valerolactone has attracted much attention as one of
the reactions worth conducting in biorefineries.
Furfural, a dehydration product of pentoses like xylose and
arabinose, has great potential as non-petroleum building blocks in
the production of polymers, pharmaceuticals, biofuels, and fine
chemicals.5,10-13 Conventionally, dehydration of xylose into
furfural was examined using various solid acid catalysts such
as sulfated zirconia,14 porous niobium silicate,15 sulfonic acid-
modified mesoporous shell silica beads,16 propylsulfonic SBA-
15,17 and zeolite-based catalysts.18-21 However, due to the
stability of xylose, these direct dehydrations need high reaction
temperatures (>423 K).
Herein, we focused on the modification of typical solid
Lewis acid γ-Al2O3 with M2+ ion additions. M2+ species from
aqueous solution onto γ-Al2O3 can generate M2+-Al3+ LDH-
type compounds,26 thus, the addition of M2+ onto γ-Al2O3
would easily generate bi-functional Lewis acid γ-Al2O3-
Brønsted base M-Al LDH sites. We investigated the modifica-
tion effects of adding M2+ ions onto γ-Al2O3 in the one-
pot synthesis of furfural from xylose with Amberlyst-15
(Scheme 1). The characterizations on crystal structure, crystal-
lite size, and surface area of the M2+-modified Al2O3 are
demonstrated. The Lewis acidity is estimated by the Meerwein-
Ponndorf-Verley (MPV) reduction of furfural to furfuryl alcohol
in 2-propanol (see Supporting Information (SI)).
Preliminarily, we investigated the activity of combined use
of γ-Al2O3 and Amberlyst-15 for xylose transformation (see
Experimental procedure in SI). The time courses are shown in
Figure 1. The use of γ-Al2O3 alone hardly yielded furfural at
373 K, whereas furfural was efficiently produced with the com-
bined use of γ-Al2O3 and Amberlyst-15. In the latter case, the
yield of furfural increased with time, and it became constant at
ca. 45% after 17 h of the reaction. It is noteworthy that this value
was higher than that in previous reports performed at 373 K using
solid catalysts.22,24 The HPLC profile of the reaction mixture at
8 h is shown in Figure S1. In the presence of γ-Al2O3 alone, three
peaks were observed at retention times of 7.5, 7.7, and 8.0 min,
which could be assigned to the xylose, xylulose and lyxose, and
ribulose and arabinose, respectively. These results indicated that
γ-Al2O3 significantly promoted the isomerization of xylose to
such pentoses. For combined use with Amberlyst-15, very few
amounts of such pentoses were detected because Amberlyst-15
is ineffective for dehydration of aldopentoses such as xylose
and arabinose below 373 K,22,25,27 the reaction path of one-pot
synthesis of furfural from xylose is proposed as follows: first,
γ-Al2O3 promoted the isomerization of xylose toward xylulose,
lyxose, ribulose, and/or arabinose; thereafter, Amberlyst-15
effectively dehydrated xylulose and ribulose toward furfural.
In the next stage, we prepared various M2+-modified Al2O3
catalysts (M2+/Al3+ atomic ratio = 0.05, see SI) and evaluated
To overcome this problem, one approach was developed,
merging the isomerization of xylose (aldose) into unstable
xylulose (ketose) before dehydration.22,23 Dehydration of xylose
via aldose-ketose isomerization over Lewis acid catalysts under
a mild condition (373 K) has been reported by Binder et al.23
2¹
and Suzuki et al.24 using CrCl2 with LiBr and SO4 /SnO2,
respectively. As a different expedient, we have demonstrated
that a combined use of the Brønsted solid base Mg-Al layered
double hydroxide (Mg-Al LDH) and the Brønsted solid acid
Amberlyst-15 efficiently afforded furfural from xylose in a one-
pot manner. This reaction involves aldose-ketose isomerization
by base LDH and successive dehydration of ketose by acid
Amberlyst-15.22 As advanced research studies, the bi-functional
Cr/Mg-Al LDH surface, which consists of LDH-originated
Brønsted base sites and Lewis acid sites on the dispersed Cr2O3,
was a better isomerization catalyst than bare Mg-Al LDH, where
the pair of Brønsted base and Lewis acid effectively promotes
the aldose-ketose isomerization.25
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© 2016 The Chemical Society of Japan

Table 1. Catalytic activities and surface area of M2+-modified Al2O3
50
40
30
20
10
0
Initial rate for
Initial rate for
Modified Furfural
metal ion yielda,b/%
furfural synthesisa,c MPV reductiond
S
BETe/m2 g
¹1
/mmol g¹1 h
/mmol g¹1 h
¹1
¹1
Mg2+
Co2+
Ni2+
Cu2+
Zn2+
®
38
37
46
25
33
40
0.36
0.30
0.45
0.21
0.32
0.37
2.32
2.22
2.25
0.47
1.82
2.92
154
155
158
153
136
193
0
5
10
15
20
25
30
Reaction time / h
aReaction conditions: xylose (0.67 mmol), M2+-modified Al2O3
(0.2 g), Amberlyst-15 (0.1 g), DMF (3 mL), 373 K, N2 flow
(30 mL min¹1). b8 h. c1 h. dReaction conditions: furfural (1.3 mmol),
Figure 1. Time course of furfural yield from xylose on γ-Al2O3 (
)
and combined use of γ-Al2O3 and Amberlyst-15 ( ). Reaction
conditions: xylose (0.67 mmol), γ-Al2O3 (0.2 g), Amberlyst-15
(0.1 g), DMF (3 mL), 373 K, 500 rpm, N2 flow (30 mL min¹1).
e
2-propanol (83 mmol), M2+-modified Al2O3 (0.1 g), 355K, 1 h. BET
specific surface area.
LDH
0.45
Ni2+
500
γ-Al2O3
0.40
γ-Al2O3
(f)
Mg2+
0.35
Zn2+
(e)
(d)
(c)
Co2+
0.30
0.25
0.20
(b)
(a)
Cu2+
1.0
20
40
60
80
0
2.0
3.0
2θ / degree
Initial rate for MPV reduction
/ mmolg-1h-1
Figure 2. XRD patterns of γ-Al2O3 and various M2+-modified
Al2O3; (a) Mg2+-modified Al2O3, (b) Co2+-modified Al2O3, (c) Ni2+
-
modified Al2O3, (d) Cu2+-modified Al2O3, (e) Zn2+-modified Al2O3,
and (f) γ-Al2O3.
Figure 3. Correlation of activities for MPV reduction and furfural
synthesis over various M2+-modified Al2O3 catalysts.
their catalytic performances and structural properties. The XRD
patterns of various M2+-modified Al2O3 and bare γ-Al2O3 are
shown in Figure 2. All prepared M2+-modified Al2O3 possessed
the γ-Al2O3 phase. Interestingly, XRD patterns of LDH structure
were also observed for Mg2+, Co2+, Ni2+, and Zn2+-modified
Al2O3.
Table 1 summarizes the catalytic activities for one-pot
synthesis of furfural from xylose using M2+-modified Al2O3 and
Amberlyst-15. Catalytic activity of M2+-modified Al2O3 for
the MPV reduction was estimated based on the initial rate for
the hydrogenation of furfural. BET specific surface areas of
M2+-modified Al2O3 are also listed in Table 1. It remarkably
indicated that the pairs of Ni2+-modified Al2O3 and Amberlyst-
15 showed better catalytic activities for furfural synthesis than
that of γ-Al2O3 and Amberlyst-15. Since the BET surface areas
of M2+-modified Al2O3 were almost the same values (136-
158 m2 g¹1), no significant correlation between catalytic activity
for furfural synthesis and surface area were expected in these
catalysts.
Román-Leshkov et al. have reported that the isomerization of
aldose into ketose over Lewis acid catalysts like tin-containing
zeolite proceeded via MPV reduction under hydride shift
mechanism.28 Therefore, Lewis acidity is an important factor
in M2+-modified Al2O3 catalysts. In fact, a linear trend
(R2 = 0.90) was assigned in Figure 3 except for Ni2+-modified
Al2O3 (closed circle); i.e. the initial rate for furfural production
of Ni2+-modified Al2O3 is faster than Mg2+- or Co2+-modified
Al2O3, whereas MPV reduction occurs with almost the same
rate. This result suggested that the improvement of activity for
furfural synthesis in Ni2+-modified Al2O3 catalyst was hardly
explained by Lewis acidity alone. Indeed, the activity for MPV
reduction on Ni2+-modified Al2O3 (2.25 mmol g¹1 h¹1) was
slower than that on γ-Al2O3 (2.92 mmol g¹1 h¹1).29 Thus, the
effects of generated Ni-Al LDH need to be considered.
To discuss the singularity of Ni2+ modification, basic
density of Ni2+-modified Al2O3 and crystallite size of generated
Ni-Al LDH on γ-Al2O3 were investigated. An increase of base
density of Ni2+-modified Al2O3 (0.71 nm¹2) from γ-Al2O3
(0.59 nm¹2) owing to generation of Ni-Al LDH on γ-Al2O3
was determined by N2 adsorption and titration with benzoic acid.
Interestingly, it was observed that the generated LDH (003)
plane crystallite size over Ni2+-modified Al2O3 was obviously
In contrast, the good correlation was observed between the
catalytic activities of γ-Al2O3 and Mg2+-, Co2+-, Cu2+-, and
Zn2+-modified Al2O3 for furfural synthesis and MPV reduction,
as shown in Figure 3 (open circle); the activity for furfural
synthesis increased with increasing activity for MPV reduction.
smaller (7 nm) than Mg2+-modified Al2O3 (25 nm), Co2+
-
Chem. Lett. 2016, 45, 194–196 | doi:10.1246/cl.151064
© 2016 The Chemical Society of Japan | 195

modified Al2O3 (33 nm), and Zn2+-modified Al2O3 (43 nm) (see
SI, Figure S2). These suggested the possibility that xylose is
successfully converted using coexistence of small basic Ni-Al
LDH with γ-Al2O3.
To verify this hypothesis, we prepared the physically mixed
catalyst of small Ni-Al LDH (5 nm) and γ-Al2O3 following to
the estimation; viz. the weight ratio of Ni-Al LDH and γ-Al2O3
in the Ni2+-modified Al2O3 is 0.16 by the XRD peak intensities
for Ni-Al LDH (003) and γ-Al2O3 (440) plane (see SI,
Figure S3), and then applied it to furfural synthesis with
Amberlyst-15. Initial rate of the physically mixed catalyst
(0.34 mmol g¹1 h¹1) is almost similar to that of bare γ-
Al2O3, and significantly smaller than Ni2+-modified Al2O3
(0.45 mmol g¹1 h¹1). Furthermore, when the physical mixture
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yielded 46% furfural from xylose in 8 h, though the pair of
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In conclusion, one-pot synthesis of furfural from xylose
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Al2O3, which contains fine Ni-Al layered double hydroxide
(LDH) crystal, and Amberlyst-15. The close boundaries between
Lewis acid γ-Al2O3 and Brønsted base Ni-Al LDH facilitated
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This work was supported by a Grants-in-Aid for Japan
Society for the Promotion of Science (JSPS) Fellows (No.
15J10050).
¹1
estimated to be 63 ¯mol g on the basis of the initial rates for
MPV reduction and Lewis acid value of γ-Al2O3 (JRC-ALO-8)
(82 ¯mol g¹1) reported in ref 30.
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196 | Chem. Lett. 2016, 45, 194–196 | doi:10.1246/cl.151064
© 2016 The Chemical Society of Japan