Highly selective low-temperature hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol catalysed by hectorite-supported ruthenium nanoparticles

Article abstract of DOI:10.1016/j.catcom.2011.05.024

Metallic ruthenium nanoparticles intercalated in hectorite (particle size ～ 4 nm) were found to catalyse the hydrogenation of furfuryl acohol to give tetrahydrofurfuryl alcohol in methanolic solution under mild conditions. The best results were obtained at 40 °C under a hydrogen pressure of 20 bar (conversion 100%, selectivity > 99%). After a total turnover number of 1423, the hectorite supported ruthenium nanoparticles are deactivated but can be recycled and regenerated.

Full text of DOI:10.1016/j.catcom.2011.05.024

Catalysis Communications 12 (2011) 1428–1431
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Highly selective low-temperature hydrogenation of furfuryl alcohol to
tetrahydrofurfuryl alcohol catalysed by hectorite-supported
ruthenium nanoparticles
a
b
a,
Farooq-Ahmad Khan , Armelle Vallat , Georg Süss-Fink ⁎
a
Institut de Chimie, Université de Neuchâtel, CH-2000 Neuchâtel, Switzerland
Service Analytique Facultaire, Université de Neuchâtel, CH-2000 Neuchâtel, Switzerland
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 April 2011
Received in revised form 19 May 2011
Accepted 20 May 2011
Available online 27 May 2011
Metallic ruthenium nanoparticles intercalated in hectorite (particle size~4 nm) were found to catalyse the
hydrogenation of furfuryl acohol to give tetrahydrofurfuryl alcohol in methanolic solution under mild
conditions. The best results were obtained at 40 °C under a hydrogen pressure of 20 bar (conversion 100%,
selectivity N99%). After a total turnover number of 1423, the hectorite supported ruthenium nanoparticles are
deactivated but can be recycled and regenerated.
©
2011 Elsevier B.V. All rights reserved.
Keywords:
Ruthenium nanoparticles
Ruthenium-modified hectorite
Furfuryl alcohol hydrogenation
1
. Introduction
required. Nobel metals (Pd, Pt and Rh) supported catalysts are less
efficient than Ni-supported catalysts [14–19]. In this paper, we report
ruthenium nanoparticles (~4 nm) intercalated in hectorite to be a
highly efficient (conversion 100%, turnover number 1423) and highly
selective (selectivityN99%) reusable catalyst for the hydrogenation of
FA to give THFA under mild conditions (methanol solution, 40 °C,
The design of nanocomposites consisting of functional metals and
adequate matrices is a challenge for the fabrication of recyclable
catalysts. Highly active metallic nanoparticles must be stabilized by a
suitable support in order to prevent aggregation to bulk metal [1].
Hectorite is, just as montmorillonite, a naturally occurring clay, which
can be defined as layers of negatively charged two dimensional
silicate sheets held together by cationic species in the interlaminar
space, which are susceptible to ion exchange [2–4]. Ruthenium-
supported hectorite obtained by ion exchange has been reported by
2
20 bar H ).
2. Experimental section
2.1. Syntheses
2
+
Shimazu et al. using [Ru(NH
3
)
6
]
cations [5] and by our group using
2
+
2+
[(C
6
H
6 2
)Ru(H O)
3
]
cations [6] or [(C
6
H
6 4
) Ru
4
H
4
]
cations [7] for
White sodium hectorite (1) was prepared according to the method
of Bergk and Woldt [20]. The sodium cation exchange capacity,
determined according to the method of Lagaly [21], was found to be
104 mEq per 100 g. The dimeric complex [(C H ) RuCl ] was synthe-
the intercalation. These materials show high catalytic activity for the
hydrogenation of olefins [5] and of aromatic compounds [8,9].
The hydrogenation of furfuryl alcohol (FA) to give tetrahydrofur-
furyl alcohol (THFA) is of great importance [10–13], but little
information is available in this regard. A brief literature survey
shows that nickel-based catalysts (alloys or Raney-nickel, promoted
or supported) are generally used for this reaction. With these
catalysts, the yields are generally high, but the reaction is not very
selective. Moreover, drastic pressure and temperature conditions are
6
6
2
2 2
sized following the procedure reported by Arthur and Stephenson [22].
2.1.1. Preparation of the ruthenium(II)-containing hectorite 2
The neutral complex [(C H ) RuCl ] (83.8 mg, 0.17 mmol) was
6
6
2
2 2
dissolved in distilled and Ar-saturated water (50 mL), giving a clear
yellow solution after intensive stirring for 1 h. The pH of this solution
was adjusted to 8 (using a glass electrode) by adding the appropriate
amount of 0.1 M NaOH. After filtration this solution was added to 1 g
of finely powdered and degassed (1 h high vacuum, then Ar-
saturated) sodium hectorite 1. The resulting suspension was stirred
for 4 h at 20 °C. Then the yellow ruthenium(II)-containing hectorite 2
was filtered off and dried in vacuo.
⁎
Corresponding author at: Institut de Chimie, Université de Neuchâtel, Avenue de
Bellevaux 51, CH-2000 Neuchâtel, Switzerland. Tel.: +41 32 7182400; fax: +41 32
7
1
182511.
E-mail address: georg.suess-fink@unine.ch (G. Süss-Fink).
566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.05.024

F.-A. Khan et al. / Catalysis Communications 12 (2011) 1428–1431
1429
2
.1.2. Preparation of the ruthenium(0)-containing hectorite 3
The same catalytic procedure was followed for the recycled and
The ruthenium(0)-containing hectorite 3 was obtained by reacting
regenerated ruthenium(0)-containing hectorite 3.
a suspension of the yellow ruthenium(II)-containing hectorite 2
50 mg, 0.01592 mmol Ru) in a magnetically stirred stainless-steel
autoclave (volume 100 mL) under a pressure of H (50 bar) at 100 °C
(
3. Results and discussion
2
for 14 h using different solvents and different volumes. After pressure
release and cooling, 3 was isolated as a black material.
Synthetic sodium hectorite (1) is a white solid of the general
+
formula Mg5.5Li0.5Si
8
O
20(OH)
4
Na · n H
2
O which contains Na cations
+
in the interlaminar space. These Na cations can easily be exchanged
in water by other water-soluble inorganic, organic or organometallic
cations. The dinuclear complex benzene ruthenium dichloride dimer
dissolves in water with hydrolysis to give a mixture of mononuclear
benzene ruthenium complexes being in equilibrium [23]. The dication
2
.1.3. Regeneration of the ruthenium(0)-containing hectorite 3
Regenerated ruthenium(0)-containing hectorite 3 was obtained
by reacting a suspension of recycled ruthenium(0)-containing
hectorite in a magnetically stirred stainless-steel autoclave (volume
2+
[
(C
6
H
6 2
)Ru(H O)
3
]
, which has been isolated as the sulfate and
1
00 mL) under a pressure of H
2
(50 bar) at 100 °C for 14 h using
structurally characterized [24], is the major species present in the
hydrolytic mixture over the pH range from 5 to 8 according to the
NMR spectrum. When the yellow solution obtained from dissolving
methanol (18 mL).
2
.2. Catalysis
The selective hydrogenation of FA was carried out in a magnet-
the dinuclear complex [(C
6 6 2 2
H )RuCl ] in water after adjusting the pH
to 8 by NaOH is added to white sodium hectorite (1), the main
2+
hydrolysis product [(C
6
H
6 2
)Ru(H O)
3
]
intercalates into the solid,
ically stirred stainless-steel autoclave. The air in the autoclave was
displaced by purging three times with hydrogen prior to use. The
experiments were carried out at different operating conditions.
replacing the appropriate amount of sodium cations, to give the
yellow ruthenium(II)-modified hectorite 2. This material, which can
be dried and stored in air, reacts with methanolic solution of 2 under
Quantitative chemical analysis of hydrogenation products was done
hydrogen pressure (50 bar) at 100 °C by reduction of [(C
H O) ]
2 3
6
H
6
)Ru
to give the black ruthenium(0)-modified hectorite 3
Scheme 1).
The ruthenium loading of the black hectorite 3 was assumed to be
by 1H NMR spectroscopy in CDCl
using Bruker DRX-400 MHz
®
2+
3
(
(
spectrometer and by GC-MS analysis. The GC separation was carried
out on a ZB-5MS column (30 m x 0.25 mm, 0.25 μm) using a
temperature program of 25-200 °C at 5 °C/min. The instrument used
was a ThermoFinnigan® Trace GC-Polaris Q. The data was collected by
using extracted ion chromatograms of marker m/z values for each
molecule from the total ion chromatograms (TIC).
2+
3
(
.2 wt% [6], based upon the molar ratio of [(C
6
H
6 2
)Ru(H O)
3
]
used
corresponding to 75% of the experimentally determined [21] cation
exchange capacity of 1), and the presence of metallic ruthenium was
proven by its typical reflections in the X-ray diffraction pattern. The
size distribution of the ruthenium(0) nanoparticles in 3 was studied
by a Philips CM 200 transmission electron microscope operating at
200 kV and the “ImageJ” software [25] was used for image processing
and analysis. The mean particle size of ruthenium(0) nanoparticles in
3 was found to be~4 nm having σN25% of the mean particle size
(Fig. 1).
Ruthenium nanoparticles intercalated in hectorite are highly active
and selective hydrogenation catalysts: Ruthenium(0)-containing hec-
torite 3 efficiently reduces FA to give THFA under mild conditions, the
formation of the usual side-product 2,5-bis(trimethyleneoxy)-1,4-
dioxane being avoided.
However, thecatalytic activityof 3 cruciallydepends on theway how
the ruthenium(0)-containing hectorite 3 is prepared and conditioned as
well as on the solvent used for FA hydrogenation. The effects of various
factors on the course of FA hydrogenation were evaluated in order to
determine suitable conditions for maximum FA conversion and highest
possible selectivity towards THFA. The catalytic reaction was studied
using different polar solvents: In acetonitrile, chloroform, dioxane and
2
.2.1. Catalytic hydrogenation of FA with freshly prepared 3
A freshly prepared suspension (10 mL) of the ruthenium(0)-
containing hectorite 3 in the appropriate solvent was introduced into
00 mL stainless-steel autoclave and 1.0 mL of FA was added. After
1
pressurizing with hydrogen (15–30 bar), the autoclave was subjected
to rigorous stirring at 40–60 °C. After 2 h, the pressure was released,
and the autoclave was cooled in an ice-bath. Then the solution was
decanted from the solid and analyzed.
In order to determine the catalytic productivity and selectivity, a
freshly prepared suspension of ruthenium(0)-containing hectorite 3
in methanol (18 mL) was used, 0.2 mL of FA was added, pressurized
with hydrogen (20 bar) and subjected to rigorous stirring at 40 °C.
After 1 h, pressure was released, and the autoclave was cooled in an
ice-bath. Then a sample was taken, filtered and analyzed. The turn-
over number was determined by adding 0.2 mL of FA after regular
intervals (1 h) until the catalyst became inactive, the total volume of
substrate added being 2 mL. The selectivity was checked by GC-MS.
+
]2+ cations to give ruthenium(II)-modified hectorite 2 (yellow) and reduction of
Scheme 1. Ion exchange of Na cations in sodium hectorite 1 (white) against [(C
6
6
H )Ru(H
2
O)
3
2
+
[(C
6
H
6
)Ru(H
2
O)
3
]
in 2 by molecular hydrogen gives ruthenium nanoparticles in the ruthenium(0)-containing hectorite 3.

1430
F.-A. Khan et al. / Catalysis Communications 12 (2011) 1428–1431
a)
b)4
0
Size Distribution
Gaussian Fit
30
20
10
0
0
1
2
3
4
5
6
7
8
9
10
Size of Particle [nm]
c)
Fig. 1. TEM micrograph with SAED (a) histogram (b) and EDS analysis (c) of ruthenium(0) nanoparticles in 3.
tetrahydrofuran, the catalyst is almost inactive, but alcoholic solvents
give high conversion, the best solvent being methanol (optimal volume
Table 1
Furfuryl alcohol hydrogenation using Ru(0)-hectorite 3 in methanol by adding fresh
substrate each hour.
1
8 mL). The catalytic reaction was also studied under various hydrogen
pressures (15–30 bar) and at various temperatures (40–60 °C), the best
conditions being 40 °C and 20 bar.
The hydrogenation of FA was done by using 3, obtained by re-
duction of 2 in methanol (18 mL) under a pressure of hydrogen
Cat. Run
FA Conversion (%)
Time (h)
TON
THFA Selectivity (%)
1
2
3
4
5
6
7
8
9
100
100
100
100
100
100
100
100
94.8
100
1
1
1
1
1
1
1
1
1
2
144
142
143
144
144
144
142
142
136
142
100
98.7
99.6
99.8
99.8
99.9
98.9
98.6
99.3
98.7
(
50 bar) at 100 °C for 14 h. GC-MS analysis shows complete conversion
of FA (100%) into THFA. The commercial production of THFA by the
hydrogenation of FA over Ni-based catalysts usually results in the
formation of a number of by-products attributable to hydrogenolysis
[26] or hydrolytic ring cleavage [27]. In practice, these are separated
10
by fractional distillation, being recovered as a low-boiling fore-run
and a high-boiling residue. Formation of by-products such as 2,5-bis
(
trimethyleneoxy)-1,4-dioxane, is a common problem during cata-
It was also observed that the presence of air during the catalytic
lytic FA hydrogenation [28]. However, these side-reactions do not
occur during the catalytic hydrogenation of FA over 3, and only the
traces of 1,2-pentandiol was observed. The overall selectivity of 3
towards THFA was N99% presumably due to mild reaction conditions.
The turnover number was determined by adding 0.2 mL of FA after
regular intervals (1 h), until the catalyst became almost inactive, the
total volume of substrate added being 2 mL (Table 1).
reaction results in a loss of activity and selectivity. But this inactive
catalyst can be regenerated by reacting the thoroughly washed sus-
pension of recycled ruthenium(0)-hectorite 3 in a magnetically stirred
2
stainless-steel autoclave (volume100 mL) with H (50 bar) at 100 °Cfor
Table 2
Once the ruthenium nanoparticles became inactive, the ruthenium
Furfuryl alcohol hydrogenation using recycled Ru(0)-hectorite 3.
(
(
0)-hectorite 3 was recycled by washing three times with methanol
18 mL) (Fig. 2). The recycled ruthenium(0)-hectorite 3 regained
Cat. Run
FA Conversion (%)
Time (h)
TON
THFA Selectivity (%)
their activity by transforming FA into THFA selectively (selectivity
upto 100%). However, the reaction takes longer using recycled
nanoparticles (see Table 2).
1
2
3
100
100
100
2
2
2
142
144
144
98.7
100
100

F.-A. Khan et al. / Catalysis Communications 12 (2011) 1428–1431
1431
a)
b)
40
30
20
10
0
Size Distribution
Gaussian Fit
0
2
4
6
8
10
12
14
Size of Particle [nm]
Fig. 2. TEM micrograph (a) histogram (b) of recycled ruthenium(0) nanoparticles in 3.
[
[
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4 h in methanol (18 mL). This regenerated ruthenium(0)-containing
hectorite 3 was also able to selectively produce THFA with a selectivity
upto 100%.
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4
. Conclusion
3
[
Ruthenium nanoparticles intercalated in hectorite are found to
efficiently catalyze the hydrogenation of FA at low temperatures. The
best results were obtained at 40 °C under a hydrogen pressure of
0 bar (conversion 100%, selectivityN99%, TON=1423). Hectorite-
[
[
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2
[
[
[
supported ruthenium nanoparticles can be recycled and regenerated.
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Financial support of this work from the Fonds National Suisse de
la Recherche Scientifique (Grant No. 200021–115821) is gratefully
acknowledged. We also thank the Johnson Matthey Research Centre
for a generous loan of ruthenium(III) chloride hydrate.
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