Total hydrogenation of furan derivatives over silica-supported Ni-Pd alloy catalyst

Article abstract of DOI:10.1016/j.catcom.2010.09.003

The Ni-Pd bimetallic catalysts supported on silica were prepared by co-impregnation method. The catalyst with Ni/Pd = 7 showed the best catalytic performance for the hydrogenation of 5-hydroxymethyl-2-furaldehyde (HMF). The catalyst was more active than commercial Raney Ni and more selective than Pd/C. The yield of 2,5-bis(hydroxymethyl)tetrahydrofuran reached 96%. Hydrogenation of other furanic compounds, cyclohexanone, phenol, and alkenols also proceeded. Characterizations by TEM and XRD revealed that Ni-Pd alloy particles were formed on Ni-Pd/SiO₂ (Ni/Pd = 7).

Full text of DOI:10.1016/j.catcom.2010.09.003

Catalysis Communications 12 (2010) 154–156
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Total hydrogenation of furan derivatives over silica-supported Ni–Pd alloy catalyst
⁎
Yoshinao Nakagawa, Keiichi Tomishige
Department of Applied Chemistry, School of Engineering, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980–8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 June 2010
Received in revised form 30 July 2010
Accepted 2 September 2010
Available online 15 September 2010
The Ni–Pd bimetallic catalysts supported on silica were prepared by co-impregnation method. The catalyst with
Ni/Pd=7 showed the best catalytic performance for the hydrogenation of 5-hydroxymethyl-2-furaldehyde
(HMF). The catalyst was more active than commercial Raney Ni and more selective than Pd/C. The yield of 2,5-bis
(hydroxymethyl)tetrahydrofuran reached 96%. Hydrogenation of other furanic compounds, cyclohexanone,
phenol, and alkenols also proceeded. Characterizations by TEM and XRD revealed that Ni–Pd alloy particles were
formed on Ni–Pd/SiO2 (Ni/Pd=7).
Keywords:
Hydrogenation
Biomass
© 2010 Elsevier B.V. All rights reserved.
Furan derivatives
Nickel
Palladium
1. Introduction
necessary. Moss et al. have reported that Ni–Pd alloy catalysts with
large Pd content (Ni/Pd≤3) are more active than monometallic Ni or
Hydrogenation is one of the most basic chemical transformations
of organic substances. The importance of hydrogenation is even
growing, since biomass-derived materials with high content of
oxygen have been expected to play substitutes for petroleum as the
sources of chemical products [1–4]. In this context, hydrogenations
of unsaturated aldehyde such as furfural have been extensively
studied in recent years [5–8]. The conversion processes from the
hydrogenated products such as tetrahydrofurfuryl alcohol to more
valuable compounds such as α,ω-diols have been also studied [9–11].
5-Hydroxymethyl-2-furaldehyde (HMF) can be synthesized by the
dehydration of hexoses or even cellulose and is one of the most
promising intermediates in the transformation of biomass into
valuable products [12–21]. The hydrogenation of HMF has been
tested by several groups using conventional catalysts such as Raney
Ni, copper chromite, and carbon-supported noble metals (typically
Pd) [22–24]. The products depend on the catalysts and reaction
conditions, and are typically 2,5-bis(hydroxymethyl)furan (BHF),
2,5-bis(hydroxymethyl)tetrahydrofuran (BHTF), 2,5-dimethylfuran
[23], and ring-opened products [22] (Scheme 1). The production of
BHTF is important because BHTF is a key intermediate to convert
renewable resources to 1,6-hexanediol, which is currently produced
from petroleum and massively utilized in the manufacture of
polymer plastics [25]. High yields of BHTF in the hydrogenation of
HMF require harsh conditions (e.g. 433 K [22]) or large amount of
catalysts [24], and the development of a more active catalyst may be
Pd catalysts in hydrogenation of ethylene, and the best composition
is 70% Pd [26]. Recently, Bertolini et al. have reported that Pd layers
on the surface of Ni or Ni-rich Ni–Pd alloy show much higher TOFs in
butadiene hydrogenation than the surface of bulk Pd [27–30].
However, attempts to prepare supported Ni-rich Ni–Pd bimetallic
catalysts with higher performance than Pd have met with little
success [31–34]. In this paper, we report that SiO2-supported Ni–Pd
alloy catalyst with Ni/Pd ratio of 7 catalyzes total hydrogenation of
furanic compounds including HMF at low temperature (313 K) with
high activity and selectivity.
2. Experimental
2.1. Preparation of catalyst
The catalysts were prepared by impregnating SiO2 (G-6, Fuji Silysia
Chemical Ltd., BET surface area 535 m2/g, granular size b100 mesh)
with mixed aqueous solutions of Ni(NO3)2·6H2O (WAKO Pure
Chemical Industries, Ltd.) and PdCl2 (Soekawa Chemical Co., Ltd.).
After evaporating, they were dried at 383 K overnight and calcined in
air at 773 K for 3 h. The reduction was conducted in H2 flow from room
temperature to 773 K (hold 0.5 h) at a heating rate of 10 Kmin−1. After
cooling, the reduced catalyst was passivated with 2% O2/He flow for
2 h. Loading of Pd was 2 wt.%. The ratio of Ni to Pd was optimized to
maximize the conversion of HMF and yield of the total hydrogenation
product in hydrogenation catalysis, and was determined to be Ni/
Pd=7 (molar basis). X-ray diffraction (XRD) patterns were recorded
by a Philips X'pert diffractometer. TEM images were taken with a
HITACHI HD-2700 microscope. Average particle size was calculated by
⁎
Corresponding author. Tel./fax: +81 22 795 7214.
E-mail address: tomi@erec.che.tohoku.ac.jp (K. Tomishige).
1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.09.003

Y. Nakagawa, K. Tomishige / Catalysis Communications 12 (2010) 154–156
155
Scheme 1. Hydrogenation of HMF.
Σnid3i /Σnidi2 (di: particle size, ni: number of particle with di). Activated
Raney Ni was supplied from Sigma-Aldrich Co., Ltd. Pd/C (5 wt.% Pd)
was purchased from N. E. Chemcat. 5-Hydroxymethyl-2-furaldehyde
(TCI) was purified by column chromatography (Silica gel 60
(Merck), methanol/ether=2/98), which procedure was essential for
reproducible results. Furfural (WAKO) was purified by distillation.
Cyclohexanone (WAKO), phenol (WAKO), 3-buten-1-ol (TCI) and
crotyl alcohol (TCI) were used as received. 2,5-Bis(hydroxymethyl)
furan (BHF) was synthesized by hydrogenation of 5-hydroxymethyl-
2-furaldehyde with sodium borohydride and checked by NMR and MS.
2,5-Bis(hydroxymethyl)tetrahydrofuran (BHTF) was separated from
the reaction mixture by column chromatography (silica gel 60,
methanol/ether=5/95) and checked by NMR and MS.
Fig. 1. (a) TEM image of Ni–Pd/SiO2 (Ni/Pd=7) and (b) size distribution of particles.
homogeneous composition by simple co-exchange method [35]. The
linewidth of the signal at 43.7° (1.6° at half maximum) was larger than
that (0.8°) calculated for 10.7 nm crystal by Scherrer's equation. It has
been reported that Pd tends to be concentrated into near-surface
layers (up to four layers [36]) in Ni–Pd alloy to lower the surface
energy [31–34,36], which might cause the broadening of the signals.
The results of the hydrogenation of HMF were summarized in
Fig. 3. Raney Ni and Ni/SiO2 catalysts showed little activity. The main
product was BHF, showing that the aldehyde group of HMF was first
hydrogenated. The Pd/SiO2 catalyst showed a higher activity than Ni
catalysts and the main product was also BHF. On the other hand, the
bimetallic Ni–Pd/SiO2 catalysts showed a much higher activity and
that with Ni/Pd=7 (molar ratio) showed the best performance. It
2.2. Activity test
Activity tests were performed in a 190-ml stainless steel autoclave
with an inserted glass vessel. An aqueous solution of substrate (0.5 M)
was put into the autoclave together with a spinner, catalyst and acetic
acid. After sealing the reactors, their air content was purged by
flushing with argon. Autoclaves were then heated to 313 K, and the
gas phase was replaced with 8 MPa hydrogen. Stirring rate was
500 rpm. After an appropriate reaction time, the autoclave contents
were transformed to vials and the catalysts were separated by
filtration. The gas phase was also collected in a gas bag. The products
were analyzed using a gas chromatograph equipped with FID. A
TC-WAX or an InertCap 5 capillary column was used for the
separation. Products were also identified using GC–MS (Shimadzu
QP 5050).
3. Results and discussion
TEM image of Ni–Pd/SiO2 (Ni/Pd=7) after reduction and passiv-
ation treatments is shown in Fig. 1. Particles with an average size of
10.7 nm were formed on SiO2 support. In the XRD pattern (Fig. 2), no
signals assignable to pure Ni (2θ=44.5 and 51.7°) or Pd (40.1, 46.7 and
68.1°) were observed. Instead, there were signals at 43.7 and 50.8°,
which corresponded to the fcc structure with a bond length of 2.53 Å.
This value agreed with the average of 7Ni (2.49 Å)+Pd (2.75 Å),
suggesting the formation of an alloy. This forms a marked contrast to
the reported difficulty in obtaining supported Ni–Pd alloy with
Fig. 2. XRD patterns of Ni/SiO2, Pd/SiO2 and Ni–Pd/SiO2 (Ni/Pd=7).

156
Y. Nakagawa, K. Tomishige / Catalysis Communications 12 (2010) 154–156
centrifugation gave 39% conversion of HMF and 21% selectivity to BHTF
in the same conditions in Fig. 3) probably because of the leaching of Ni
during the activation of oxidized particle surface with an acid. Indeed,
ICP-AES analysis showed that 16% of Ni was leached from Ni–Pd/SiO2
during the reaction of entry 1 in Table 1 while no leaching of Pd was
observed. Application of the catalyst to systems more immune to
leaching, e.g. gas phase hydrogenations, is a future work.
4. Conclusions
Co-impregnation of Ni and Pd with a Ni/Pd molar ratio of 7 on silica
and subsequent calcination–reduction procedure produced bimetallic
particles. The supported particles catalyzed the total hydrogenation of
unsaturated compounds including bio-derived HMF and furfural in
water. The catalyst was easy to prepare and handle, and was more
active than commercial Raney Ni and more selective than Pd/C.
Fig. 3. Hydrogenation of HMF over various catalysts. Conditions: HMF (0.5 M aq.,
10 ml), acetic acid (5.7 μl; 0.1 mmol), catalyst (19 μmol Pd), H2 (8 MPa), 313 K, 0.5 h.
aRaney Ni (100 mg; ca. 1.4 mmol Ni). bNi/SiO2 (10 wt.%, 100 mg; 170 μmol Ni).
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