J. Qiu et al.
with a length of 20–100 mm, and the N2 BET surface area was 50–
60 m2 gÀ1. Before loading catalyst, the CNFs were treated in 4.0n HNO3
under reflux at 1208C for 4 h.
The catalytic performance of CNF-supported Co nanopar-
ticles with 7.4 wt% loading in the hydroformylation of 1-
octene is shown in Figure 6. The results show that at 1308C
Preparation of CNF-supported Co catalysts: The CNF1 catalyst was pre-
pared according to the procedure shown in Figure 5. To get a colloidal
solution of cobalt, the pH of cobalt nitrate (20%) in EG was adjusted to
13 by using NaOH (2.5m in EG). The solution was refluxed at 1808C for
3 h to ensure the complete reduction of Co (the obtained sample was
termed as Co1 hereafter). After cooling the Co1 sample to room temper-
ature, its pH value was adjusted to 4 (the obtained sample was termed as
Co2hereafter) by adding HCl (2.5 m in EG). Then, the CNFs was sus-
pended in EG and mixed with the Co2sample under ultrasonic stirring
for 30 min. The mixture was refluxed at 1008C for 24 h to ensure the
complete deposition of Co colloids onto the CNFs (the obtained sample
was termed as Co3 hereafter). The CNF-supported Co catalysts were fil-
tered and washed with deionized water and absolute ethanol in sequence,
and then dried at 708C in air for 8 h. In comparison to other synthesis
methods,[15–16] in our case the pH value of the colloidal solution was ad-
justed to <7 and the mixture of CNFs and colloidal solution was heated
under controlled conditions, which were found to be critical for deposit-
ing Co colloids onto the CNFs, and for controlling the Co particle size
distribution.
Figure 6. Hydroformylation of 1-octene over Co/CNF catalyst with cobalt
loading of 7.4 wt%
Following the same procedure described above, three more catalysts
(CNF2, CNF3, and CNF4) were synthesized under identical conditions as
for the CNF1 catalyst; the only differences were as follows: for CNF2, no
heat treatment was adopted; for CNF3 and CNF4, the pH value was ad-
justed to 6 and 8, respectively.
and 5.0MPa of syngas pressure, the main products of the 1-
octene hydrogenation are C9-aldehyde with other products
being isomers of 1-octene that can be circulated for further
hydroformylation after being separated from the product.
Under the conditions adopted in this study, the Co/CNF cat-
alyst with a loading of 7.4 wt% is found to be highly active
and stable, which is better than the Co catalyst with a load-
ing of 8.7 wt% that was prepared by the traditional impreg-
nation method.[23] It is assumed that the higher catalytic per-
formance of Co/CNF catalysts for 1-octene hydroformyla-
tion are due to the high dispersion of cobalt particles on
CNFs, implying that the homogeneous distribution of cobalt
metal particles on CNFs is the key to the better perfor-
mance of Co/CNF catalysts. The excellent catalytic activities
might be also attributed to the unique structure, electrical
properties, and the high external surface of CNFs.[9,15,23–24]
Characterization: UV-visible spectroscopy (V-550, Japan) was used to
monitor the deposition process of cobalt colloids in EG. FTIR spectra of
samples were recorded on
a Thermo FTIR spectrometer (Nicolet
NEXUS 470, USA). All catalyst samples were examined by using trans-
mission electron microscopy (TEM, Philips Tecnai G2 20, operated at
200 kV) and XRD (D/max-2400, operated at 40 kV and 100 mA, CuKa ra-
diation).
1-Octene hydroformylation: The hydroformylation of 1-octene was con-
ducted at 1308C and 5MPa in a fixed-bed reactor in flowing gas of H2/
CO (50:50 v/v) with a space velocity of 0.1716 hÀ1. 1-Octene mixed with
cyclohexane in a volume ratio of 5:95 was continuously injected into the
reactor by using a high-pressure liquid pump. Before the reaction, the
catalyst was reduced in flowing hydrogen, during which the reactor was
first ramped at 28CminÀ1 to 3508C, and then was kept at 3508C for 2h.
After the reduction, the catalyst bed was cooled to reaction temperature.
For each run, 500 mg of catalyst was used. The reactants and products
were analyzed by using GC-MS (Agilent 6890N GC/5973mSD, equipped
with a HP-INNOWAX capillary column and FID detector). The loading
amount of Co metal in catalysts was measured by using inductively cou-
pled plasma emission spectrometry (ICP-OES).
Conclusion
In summary, a modified EG process has been used to syn-
thesize a highly dispersed Co/CNF catalyst under mild con-
ditions. It has been found that adjusting pH and heating the
mixture of CNFs and colloidal solution are necessary steps
to control the deposition and distribution of cobalt colloids
on CNFs. A possible mechanism of cobalt colloids deposi-
tion onto carbon nanofiber (CNFs) is discussed. The as-syn-
thesized Co/CNF catalysts show excellent activity and regio-
selectivity for the 1-octene hydroformylation. It can be ex-
pected that this work will lead to a new approach for
making carbon-nanofiber-supported metals that are of po-
tential use as catalysts for the hydroformylation of olefins.
Acknowledgements
This work was partly supported by the Natural National Science Founda-
tion of China (No. 29976006, 20376011), the Natural Science Foundation
of Liaoning Province (No. 9810300701, 2001101003), the National Basic
Research Program of China (No. G2003CB615806), and the Program for
New Century Excellent Talents in Universities of China.
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Experimental Section
Materials: CNFs used in this study were purchased from Shenzhen Nano-
tech Port (NTP; China). The CNFs had an outer diameter of 40–60 nm
[5] M. Chen, J. P. Liu, S. H. Sun, J. Am. Chem. Soc. 2004, 126, 8394.
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Chem. Eur. J. 2006, 12, 2147 – 2151