Rh nanoparticles catalyzed hydroformylation of olefins in a thermoregulated ionic liquid/organic biphasic system

Article abstract of DOI:10.1016/S1872-2067(11)60371-9

Rh nanoparticles were investigated as a catalyst for hydroformylation of olefins in thermoregulated ionic liquid/organic biphasic systems composed of an ionic liquid, namely [CH₃(OCH₂CH₂) ₁₆N⁺Et₃][CH₃SO₃ ^-] (IL_PEG750), and an organic solvent. This enables not only a homogeneous reaction but also easy biphasic separation. Under the optimized reaction conditions, the conversion of 1-octene and yield of aldehyde were 99 and 91, respectively. The catalyst was easily separated from the product by phase separation and used eight times without evident loss of activity.

Full text of DOI:10.1016/S1872-2067(11)60371-9

CHINESE JOURNAL OF CATALYSIS
Volume 33, Issue 3, 2012
Online English edition of the Chinese language journal
Cite this article as: Chin. J. Catal., 2012, 33: 402–406.
COMMUNICATION
Rh Nanoparticles Catalyzed Hydroformylation of Olefins in a
Thermoregulated Ionic Liquid/Organic Biphasic System
ZENG Yan, WANG Yanhua*, XU Yicheng, SONG Ying, ZHAO Jiaqi, JIANG Jingyang, JIN Zilin
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, Liaoning, China
Abstract: Rh nanoparticles were investigated as a catalyst for hydroformylation of olefins in thermoregulated ionic liquid/organic biphasic
+
ꢀ
systems composed of an ionic liquid, namely [CH
3
(OCH
2
CH
2
)
16N Et
3
][CH
3
SO
3
] (ILPEG750), and an organic solvent. This enables not only
a homogeneous reaction but also easy biphasic separation. Under the optimized reaction conditions, the conversion of 1-octene and yield of
aldehyde were 99% and 91%, respectively. The catalyst was easily separated from the product by phase separation and used eight times
without evident loss of activity.
Key words: hydroformylation; rhodium; nanoparticle; olefin; thermoregulated ionic liquid/organic biphasic system
The catalytic behavior of soluble transition-metal nanopar-
ticles has been a very active research field in recent decades
because of the high efficiency and unique properties of such
catalysts. However, as is the case with traditional homogeneous
catalysts, one of the main disadvantages of soluble nanoparticle
catalysts is the problem of separating the catalyst from the
products [1,2]. A range of methods for overcoming this prob-
lem have been reported, with most studies focusing on liq-
uid/liquid biphasic systems, for example, the use of fluor-
ous/organic biphasic systems [3,4], thermoregulated
poly(ethylene glycol) biphasic systems [5], aqueous/organic
biphasic systems [6,7], and ionic liquid biphasic systems [8,9].
Recently, a novel thermoregulated ionic liquid/organic bi-
phasic system containing Rh nanoparticles stabilized by the
mylation of olefins in thermoregulated ionic liquid/organic
biphasic systems.
ILPEG750 was prepared by a method reported in the literature
[15]. Rh nanoparticles stabilized by ILPEG750 were prepared as
follows. A mixture of RhCl ·3H O (20 mg, 0.076 mmol) and
3
2
ILPEG750 (7.0 g, 7.6 mmol) was added to a 75-ml standard
stainless-steel autoclave and stirred under H (4 MPa) at 70 °C
2
for 2 h. The reactor was then cooled to room temperature and
depressurized. The Rh nanoparticle catalyst was obtained as an
ILPEG750 solution and was used for olefin hydroformylation.
The miscibility temperature of a system composed of ILPEG750
,
toluene, and n-heptane was determined by a method reported in
the literature [15].
+
ꢀ
Before reaction
Org.
During reaction
After reaction
Org.
ionic liquid [CH (OCH CH ) N Et ][CH SO ] (ILPEG750) was
3
2
2 16
3
3
3
used in the hydrogenation of olefins. This achieved a highly
efficient catalytic hydrogenation reaction and also easy sepa-
ration and reuse of the catalyst as a result of the thermoregu-
lated phase-transition properties of the ILPEG750/organic bi-
phasic system (see Fig. 1) [10].
Although Rh nanoparticle catalyzed hydrogenation has been
extensively studied, less attention has been paid to hydrofor-
mylation [11–14]. In this study, we extended the application of
ILPEG750-stabilized Rh nanoparticle catalysts to the hydrofor-
S
P
P
S
Heating
Cooling
P
Cat.
Cat.
IL
Cat.
IL
IL Org.
Recycling of catalyst
S—substrate; Cat.—catalyst; P—product;
IL—ionic liquid; Org.—organic solvent
Fig. 1. Thermoregulated ionic liquid/organic biphasic system with
ILPEG750-stabilized Rh nanoparticles.
Received 30 December 2011. Accepted 14 February 2012.
*
Corresponding author. Tel/Fax: +86-411-84986033; E-mail: yhuawang@dlut.edu.cn
This work was supported by the National Natural Science Foundation of China (21173031) and the Program for New Century Excellent Talents in University
NCET-07-0138).
(
Copyright © 2012, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved.
DOI: 10.1016/S1872-2067(11)60371-9

ZENG Yan et al. / Chinese Journal of Catalysis, 2012, 33: 402–406
In a typical hydroformylation reaction, ILPEG750 (0.25 g,
ꢀ3
containing 2.6 × 10 mmol of Rh), 1-octene (0.6 g, 5.2 mmol),
toluene (3.8 g), n-heptane (0.3 g), and n-decane as an internal
standard (0.1 g) were charged into a 75-ml stainless-steel
autoclave. The autoclave was sealed and flushed three times
Conversion of 1-octene
Yield of aldehyde
1
00
80
6
4
2
0
0
0
0
with CO at 1.0 MPa, pressurized with syngas (CO:H = 1:1) to
2
the required pressure, and held at the designated temperature,
with magnetic stirring, for a fixed length of time. The autoclave
was then cooled to room temperature and depressurized. The
upper organic phase was separated by phase separation and
immediately subjected to GC and GC-MS analyses.
1
2
3
4
5
6
7
8
GC analysis was performed on a Tianmei 7890 GC instru-
ment equipped with an OV-101 column (50 m × 0.25 mm) and
Recycle number
Fig. 2. Recycling efficiency of ILPEG750-stabilized Rh nanoparticle
catalyst for hydroformylation of 1-octene.
a flame-ionization detector; N was used as the carrier gas.
2
GC-MS measurements were performed on an HP 6890
GC/5973 MSD instrument with an HP-5MS column (30 m ×
.25 mm); He was used as the carrier gas. Transmission elec-
of aldehyde decreased a little (entry 7). It is also evident from
the data in Table 1 that prolonged reaction times led to in-
creases in the conversion of 1-octene and aldehyde yields
0
tron microscopy (TEM) images were taken with a Philips
2
Tecnai G 20 TEM (Philips, Eindhoven, The Netherlands) at an
(
entries 3, 8, and 9). The molar ratios of normal to branched
accelerating voltage of 200 kV. Inductively coupled plasma
atomic emission spectroscopy (ICP-AES) analyses of Rh were
carried out using an Optima 2000 DV (Perkin Elmer, USA).
Optimization of the reaction conditions was carried out us-
ing the hydroformylation of 1-octene as a model reaction. As
shown in Table 1, the conversion of 1-octene and the yield of
aldehyde increased with increasing reaction pressure (entries
aldehydes (n/b = 1.2–4.7) obtained with ILPEG750-stabilized Rh
nanoparticles were similar to the ratios previously reported for
reactions catalyzed by Rh nanoparticles [11,13]. It should be
noted that when n-heptane was used as the organic phase in-
stead of a toluene/n-heptane mixture, much lower conversion
was obtained (entry 10). This result implies that for reactions
carried out in a homogeneous system under heating, the choice
of an appropriate organic phase is crucial, because we observed
that ILPEG750 and n-heptane cannot mix to form a homogeneous
phase at the reaction temperature.
The recycling efficiency of the Rh nanoparticle catalyst was
investigated under the optimized reaction conditions (Table 1,
entry 3). After reaction, the lower ILPEG750 phase containing the
catalyst was separated from the upper organic phase by phase
separation and directly used in the next run. The catalyst was
used eight times without evident loss of activity, as shown in
Fig. 2.
TEM images were used to examine the morphologies of the
Rh nanoparticle catalyst before and after reaction, as shown in
Fig. 3. The mean diameter of the freshly prepared Rh
nanoparticles was 2.1 nm, with a standard deviation of 0.3 nm
(see Fig. 3(a)). Analysis of the Rh nanoparticles after eight
cycles of use showed an average diameter of 2.6 nm, with a
standard deviation of 0.7 nm (see Fig. 3(b)). TEM analysis
indicated that there was no apparent size increase.
We also studied the leaching of Rh in the upper organic
phase (see Table 2). ICP-AES analysis showed that the loss of
Rh decreases with increasing recycling number. The average
leaching of Rh was 1.1%.
1
ꢀ4). The effects of temperature on the reaction were studied.
In the range of 70ꢀ90 °C, the conversion of 1-octene and the
yield of aldehyde increased with increasing reaction tempera-
ture (entries 3, 5, and 6). Further increasing the temperature to
1
00 °C achieved a slightly improved conversion, but the yield
Table 1 Hydroformylation of 1-octene catalyzed by ILPEG750-stabilized
Rh nanoparticles
Pressure Temperature Time Conversion Aldehyde
a
Entry
n/b
o
(
MPa)
3.0
4.0
5.0
6.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
( C)
(h)
15
15
15
15
15
15
15
17
20
15
15
(%)
40
68
93
99
83
88
96
99
99
48
94
yield (%)
22
1
2
3
4
5
6
7
8
90
90
90
90
70
80
100
90
90
90
90
4.7
2.8
1.5
1.4
1.8
2.5
1.2
1.4
1.4
2.3
1.4
54
86
87
58
80
83
90
91
9
b
1
1
0
1
43
c
86
ꢀ
3
Other conditions: ILPEG750 0.25 g (containing 2.6 × 10 mmol of Rh),
toluene 3.8 g, n-heptane 0.3 g, CO:H = 1:1, substrate:Rh = 2000:1 (molar
2
ratio), internal standard n-decane 0.1 g, the miscibility temperature of the
system is 80 °C.
The molar ratio of normal to branched aldehydes.
Using n-heptane as the sole upper-phase organic solvent.
Extension of the hydroformylation reaction to other sub-
strates, including cyclohexene, 1-tetradecene, and styrene, also
afforded good conversions, as shown in Table 3.
a
b
c
Using toluene as the sole upper-phase organic solvent.
In conclusion, we have demonstrated that ILPEG750-stabilized

ZENG Yan et al. / Chinese Journal of Catalysis, 2012, 33: 402–406
40
35
30
25
20
15
10
5
0
(
a)
(2.1f0.3) nm
5
0 nm
1.0
1.5
2.0
2.5
3.0
3.5
Diameter (nm)
45
40
35
30
25
20
15
10
5
0
(
b)
(
2.6f0.7) nm
5
0 nm
1
2
3
4
5
6
Diameter (nm)
Fig. 3. TEM images of ILPEG750-stabilized Rh nanoparticles. (a) Fresh sample; (b) After eight cycles of use.
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