Selective hydrogenation of 2-hydroxymethyl-5-furfural to 2,5-bis(hydroxymethyl)furan over gold sub-nano clusters

Article abstract of DOI:10.1039/c2ra22190j

We report a gold sub-nano cluster supported on Al₂O₃ catalyzed hydrogenation of 2-hydroxymethyl-5-furfural without furan ring hydrogenation and its opening reaction, which resulted in excellent conversion to 2,5-bis(hydroxymethyl)furan (>96% yield), Fig. 1(a). The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c2ra22190j

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Selective hydrogenation of 2-hydroxymethyl-5-furfural
to 2,5-bis(hydroxymethyl)furan over gold sub-nano
clusters3
Cite this: RSC Advances, 2013, 3, 1033
Received 18th September 2012,
Accepted 2nd November 2012
ab
a
c
c
Junya Ohyama,* Akihiko Esaki, Yuta Yamamoto, Shigeo Arai
DOI: 10.1039/c2ra22190j
ab
and Atsushi Satsuma
www.rsc.org/advances
We report a gold sub-nano cluster supported on Al
2
O
3
catalyzed
hydrogenolysis of HMF results in 2,5-dimethylfuran (DMF), which
is a gasoline alternative with higher energy density than ethanol;
hydrogenation of the aldehyde produces 2,5-bis(hydroxymethyl)-
furan (BHF), which can be used in a broad field of applications
such as resin additives, polymers, and intermediates for drugs and
hydrogenation of 2-hydroxymethyl-5-furfural without furan ring
hydrogenation and its opening reaction, which resulted in
excellent conversion to 2,5-bis(hydroxymethyl)furan (.96%
yield), Fig. 1(a).
3,15,16
crown ethers.
Dumesic et al. showed an excellent strategy for
Global warming and diminishing oil resources have driven society
to find renewable alternatives, where biomass has attracted much
attention due to the potential to produce valuable organic
the production of DMF from fructose by catalytic dehydration and
hydrogenation using HCl aq. and CuRu/C, respectively. Very
6
recently, they reported the total hydrogenation of HMF to 2,5-
bis(hydroxymethyl) tetrahydrofuran (BHTF) over supported Ru
1–4
compounds, fuels and chemicals.
Hydrogenation is a major
6
process for the refinement of biomass, because of its high oxygen
catalysts. Tomishige et al. reported the total hydrogenation of
5–7
content.
In a biomass derived compound, oxygen is often
furan derivatives over Ni–Pd/SiO
2
, and HMF was converted to
BHTF in high yield. Descotes et al. reported the hydrogenation of
HMF using carbon supported Pt, Ru, and CuO–Cr catalysts to
7
present in more than one functional group, thus the selective
hydrogenation of a targeted functional group is required for the
2 3
O
6–8
8
production of the desired compounds. Selective hydrogenation,
however, remains a challenging objective, because a multifunc-
tional molecule can potentially bind to the catalyst surface in a
obtain BHF in good yield.
Supported gold catalysts often show remarkable selectivity
towards hydrogenation of compounds with multiple functional
groups, as represented by the hydrogenation of a,b-unsaturated
6,7
variety of ways and react through any functional groups. To
attain selective hydrogenation, many scientists have devoted much
effort to design and synthesize sophisticated heterogeneous
catalysts, such as metal clusters with a well-controlled size on an
appropriate support with respect to acid–base properties, metal–
1
9–22
aldehydes to the corresponding alcohols.
reported that Au/ZrO and Au/ZnO catalyze the selective hydro-
genation of crotonaldehyde. It has also been reported that Au/
Hutchings et al.
2
19
20
2 3
Fe O shows high selectivity in the hydrogenation of citral. These
9–14
support interaction, and so on.
-Hydroxymethyl-5-furfural (HMF), which can be synthesized
by dehydration of hexoses, is one of the most promising platform
studies inspired us to apply gold catalysts to the hydrogenation of
HMF to produce BHF.
We prepared various metal oxides supported gold with ca. 1
wt% of Au loading by the deposition impregnation method
2
15–18
chemicals in the biorefinery process.
The hydrogenation of
reported elsewhere (the loading amount of Au/Al O , evaluated by
HMF can produce a variety of valuable compounds: for example,
2 3
a sequential inductively coupled plasma (ICP) spectrometer, was
2
3
a
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
0.8 wt%.). Fig. 1 (b) shows the results of the hydrogenation of
HMF (0.1 M aqueous solution, 2 mL) over various metal oxide
E-mail: ohayama@apchem.nagoya-u.ac.jp; Fax: +81 52 789 3193;
Tel: +81 52 789 3191
supported gold catalysts (10 mg) under 3.8 MPa of H at 413 K. As
a result, gold supported on c-Al
selectivity toward BHF. Au supported on La
2
b
Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University,
2
O
3
showed high activity and
and CeO also
Katsura, Kyoto 615-8520, Japan
c
O
Ecotopia Science Institiute, Nagoya University, Nagoya, 464-8603, Japan.
2
3
2
E-mail: y.yamamoto@esi.nagoya-u.ac.jp; Fax: +81 52 789 3174;
Tel: +81 52 789 3631
catalyzed the selective hydrogenation to BHF, although the
reactivity was low. These three Au catalysts supported on basic
metal oxides exhibited high selectivity toward BHF, but almost no
BHF was obtained on those supported on acidic metal oxides,
TiO , ZrO , Ta O , TiO –SiO (TS), and sulfated zirconia (SZ). It is
2 2 2 5 2 2
suggested that the ring-opening reaction proceeds on the acid
3
Electronic Supplementary Information (ESI) available: Experimental procedures;
results of the hydrogenation over Pt, Pd, Ag, and Cu supported on Al , and 0.1 and
.5 wt% Au/Al ; the number of Au single atoms per unit surface area of Al
HAADF STEM image of 0.1 and 0.5 wt% Au/Al ; recoverability and reusability of
Au/Al -473H and the Au loading after the reaction; See DOI: 10.1039/c2ra22190j
2 3
O
0
O
2 3
2 3
O ;
2 3
O
2
O
3
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Scheme 1 Hydrogenation of HMF.
Fig. 1 Results of the hydrogenation of HMF over (a) Au sub-nano clusters
2 h and then decreased. At the same time, the ring opened
products (B1), and the other unknown by-products increased. This
time course profile suggests that the aldehyde group of HMF was
hydrogenated first and then the furan ring opened as shown in
Scheme 1. We also investigated the dependence of HMF
supported on Al
2
O
3
(Au/Al
2
O
3
-473H) under 6.5 MPa of H
2
at 393 K and (b) Au
at 413 K in water.
catalysts supported on various metal oxides under 3.8 MPa of H
2
sites. Thus, metal oxide supports with basic properties are
necessary for gold to show high selectivity for the hydrogenation
of HMF to BHF. This result is consistent with a recent report by
Dumesic et al. who achieved hydrogenation of HMF to BHTF
conversion and BHF yield on reaction temperature and H
2
pressure as represented in Fig. 3. High temperature caused an
increase in the conversion, but a decrease in the selectivity
(Fig. 3(a)). The profile of temperature dependence was similar to
6
using Ru supported on materials with high isoelectric points.
that of the time course (Fig. 2), which indicates that the reaction
temperature varies only the overall reaction rate without affecting
The hydrogenation reactions were also conducted using Al
supported Pt, Pd, Cu, and Ag metal catalysts (1 wt%) under 3.8
MPa of H at 413 K for 4 h (Table S1 ). Pt and Pd/Al showed low
2 3
O
the selectivity. On the other hand, an increase in H
enhanced both the HMF conversion and the BHF selectivity. Thus,
the enhancement of adsorption of H on gold would be important
to obtain BHF with high selectivity even at high HMF conversion.
The chemisorption of H on Au particles depends on their
Thus, we prepared Au/Al O at various calcination
2
pressure
2
3
2 3
O
selectivity toward BHF (Pt: 0%, Pd: 20%), although HMF was
completely converted to the other products over both catalysts. On
2
2 3
the other hand, Ag/Al O exhibited high selectivity toward BHF (ca.
2
22,24,25
1
00%), but much lower reactivity compared to Au/Al O (HMF
2
3
size.
temperatures (473–873 K) and atmosphere (H
2
3
conv.: 5%). As for Cu/Al
proceed at all. Therefore, Au/Al
hydrogenation to BHF.
Fig. 2 shows the time course of conversion and yield for HMF
hydrogenation over Au/Al . The yield of BHF increased for up to
2 3
O , the hydrogenation reaction did not
2
or air) to control
2 3
O
is suitable for the selective
the Au particle size. Fig. 4 shows high angle annular diffraction
scanning transmission electron microscope (HAADF STEM)
images of a series of Au/Al O obtained using JEOL-200 kV Cs-
2 3
2 3
O
corrected S/TEM with atomic resolution. The particle size analysis
revealed that calcination under air or increasing calcination
temperature gave larger Au nanoparticles, and Au/Al O prepared
2
3
2 2 3
under H at 473 K (denoted as Au/Al O -473H) has the smallest
gold particles with sub-nanometer diameter, 0.88 ¡0.30 nm
Fig. 2 Time course of conversion and yield for HMF hydrogenation over Au/Al
under 3.8 MPa of H at 413 K.
2
O
3
Fig. 3 Dependence of HMF conversion and BHF yield over Au/Al O on (a) reaction
2
3
2
temperature under 3.8 MPa of H2 for 1 h and (b) H2 pressure at 413 K for 2 h.
1
034 | RSC Adv., 2013, 3, 1033–1036
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Fig. 4 HAADF STEM images of Au/Al
2
O
3
prepared under H
2
flow at (a) 473 K and (b) 573 K, and those prepared under air at (c) 573 K, (d) 773 K, and (e) 873 K. Some single
gold atoms in (a) are indicated by white arrows.
(
Fig. 4(a)). This size indicates the formation of a magic number
(TOF) was calculated from the surface atoms assuming that all
gold atoms form hemispherical particles. Fig. 5 shows the TOF
dependence on the size of Au particles. The TOF increased with a
decrease in the particle size, indicating that the small gold
particles have intrinsically high activity for HMF hydrogenation.
The high activity of small Au clusters is mainly due to the high
fraction of unsaturated Au atoms where hydrogen is adsorbed,
and p back donation favoring CLO adsorption on Au clusters with
26
Au13 cluster. Interestingly, we also observed a lot of single Au
atoms on Al in the HAADF STEM image of Au/Al -473H. (The
single atoms were not counted in the particle size analysis.) The
single gold atoms were also observed on the other samples, and
the number of single gold atoms decreased with the increase in
the size of gold particles (Fig. S1
Using the series of Au/Al
reaction was carried out for 15 min, and the turnover frequency
2
O
3
2 3
O
3
).
2 3
O catalysts, the hydrogenation
22,24
high d electron number.
The specific properties of Au13
clusters might also contribute to the adsorption of H and CLO
2
26–28
group and to the high activity.
In this TOF analysis (Fig. 5), the effect of single gold atoms on
the reactivity was not considered. To investigate whether the single
atoms have high activity for the hydrogenation, we prepared Au/
Al O
2 3
with 0.1 and 0.5 wt% Au loading by the same method as Au/
) and applied them to the HMF hydrogenation
reaction. As a result, 0.1 and 0.5 wt% Au/Al , which should have
a higher fraction of Au atoms than Au/Al -473H, showed lower
hydrogenation activity per all Au atoms compared to Au/Al
73H (Table S2 ). It is very likely that the highly active species for
Al O -473H (Fig. S2
3
2
3
2 3
O
O
2 3
2 3
O -
4
3
the hydrogenation are not single gold atoms, but small gold
clusters. In other words, small ensembles of gold are key to the
high activity for the selective hydrogenation. This result would
indicate a Langmuir–Hinshelwood mechanism for the selective
CLO hydrogenation and/or homogeneous dissociation of hydro-
26,27,29
gen on Au atoms.
As for the hydrogen dissociation, very
recently, Yang et al. reported a density functional theory study of
Fig. 5 TOF dependence on Au particle size of Au/Al
under 6.5 MPa of H at 393 K.
2
O
3
for HMF hydrogenation
hydrogen dissociation over Au/TiO , and showed that homolytic
hydrogen dissociation proceeds on Au atoms when the surface
2
2
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29
oxygen of TiO is passivated by OH formation. In our study, the
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1
991, 704.
HMF hydrogenation was carried out in water which would
passivate Al O surface. Thus, homolytic hydrogen dissociation
2 3
on Au atoms is likely to occur in this catalytic reaction. Further
study on the hydrogenation mechanism and the active species is
under investigation.
9
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Finally, using Au/Al O -473H which presented the highest TOF
2
3
in this study, the HMF hydrogenation reaction was performed
1
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2
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converted to BHF at greater than 96% yield for 2 h as shown in
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1
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of HMF and H to react selectively.
In conclusion, we investigated the selective hydrogenation of
HMF to BHF using Au supported on various metal oxides. The
acid–base property of metal oxide supports strongly affect the
selectivity because of the easily opening furan ring of HMF on acid
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suitable for the selective hydrogenation. The reactivity drastically
increased with a decrease in size, and Au sub-nano clusters
allowed for excellent conversion of HMF to BHF, but single gold
atoms were less active than clusters or inactive. Therefore, fine
tuning of Au size and support properties are demanded to achieve
the selective hydrogenation of HMF to BHF.
1
1
2
2
2
This work was supported by Grant-in-Aid from the Ministry of
Education, Culture, Sports, Science and Technology.
2
8
2
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