Highly Active Cu Based Catalysts on Carbon nanofibers for Isopropanol
Dehydrogenation
Ingvar Kvande1, De Chen1, Magnus Rønning1, Hilde J. Venvik2, and Anders Holmen1
1
Departmet of Chemical Engineering, Norwegian University of Science and Technology
(NTNU), N-7491 Trondheim, Norway. 2SINTEF Applied Chemistry, N-7465 Trondheim,
Norway.
Introduction
Copper chromite is generally used as catalyst in industrial process for the dehydrogenation
of alcohols to aldehydes or ketones. However, new EPA restrictions now prohibit the disposal
of chromite in landfills. Thus, there has been a renewed attention to develop new Cu catalysts
which contain no chromium. Research has recently been focused on carbon supported copper
catalysts [1]. Carbon nanofibers (CNFs) have recently received increasing interests in
applications as catalyst supports, since CNFs have many unique properties [2]. The present
work deals with preparation, characterization of Cu based catalysts on different CNF
supports. The modification of Cu catalyst with CeO2 is studied to increase activity.
Experimental
For types of carbon nanofibers synthesized in our laboratory, namely platelet (P), carbon
filaments(CF), herring bond (HB) and irregular CNF, are used as catalyst supports. The CNFs
were purified and some of samples are oxidised by HNO3 or air. The 10wt% Cu catalysts are
prepared by incipient wetness impregnation and deposition-precipitation. The CeO2 modified
Cu catalysts were prepared by incipient wetness impregnation. The catalysts are calcined at
250 °C for 1 hr in air and reduced in 50% H2 for 6 hr. The catalysts have been characterized
by temperature-programmed oxidation (TPO), XRD, SEM and TEM. The surface area of Cu
were measured by means of N2O decomposition by using both TPR titration and gravimetric
measurement. The activity tests are performed by means of temperature scanning experiments
at a partial pressure of isopropanol of 4.4 kPa in a quartz reactor coupling with MS.
Results and Discussions
Table 1 shows that the dispersion of Cu on CNF is typically about 2-5%, which is in good
agreement with literature values both on activated carbon [1] and CNFs [2]. However, it is
lower than one on our reference support of activated carbon. The activation energy of Cu on
CNFs is between 21-28 kcal/mol, which is also in good agreement with the previously
reported value [1]. The selectivity to acetone is almost 100% on most of Cu/CNF catalysts,
which is higher than our reference catalyst.
Table 1. Catalyst properties and activities at 448K PIpa=4.4kPa.
Catalysts
Dispersion%
Activity
TOF
(mol/g,s) (s-1*100)
0.26
0.60
0.04
0.27
0.08
0.29
0.5
1.85
2.8
15.25
4.25
2.02
4.4
-
E
(kcal/mol)
23.3
21.8
28.8
27.5
16.5
15.0
SAcetone%
423 K
100
SAcetone%
473K
96.5
TW/HB
3.2
DP/HB-HNO3
1.6
DP/CF
2.5
100
100
DP/P-HNO3
4.6
0
0.45
Cu12Ce5/P-air
1.2
100
92
Cu17Ce17/P-air
12.4
73
45
Cu17Ce17/CF83
55
air
IW/AC
8.4
0.6
0.5
23.6
90
74
CuO
1.7
9.9
Cu0
2.3
11.7
100
99.7
Cu2O
0.04

HNO3 and air indicate oxidant used in preparation, AC is active carbon, Cu12Ce5/Pair indicates 12wt%Cu and 5%Ce on platelet support, which was oxidised by air.
Results clearly indicate that adding
CeO2 to Cu catalysts can significantly
increase the activity and that the
selectivity depends on the ratio of
Cu/Ce. The best catalysts found in the
present work is Cu12Ce5/P-air with high
activity
and
selectivity.
with
Further
almost
100%
increasing
amount of CeO2 increases activity,
200 nm
50nm
Fig. 1 TEM image of Cu/CeO2/CNF, Cu: 17wt% and Ce 17 wt%
but decreases selectivity. Both XRD and TEM indicate a low crystallinity of Cu and CeO2 and
a TEM image is shown in Fig. 1. It shows a rather uniform layer deposited on the CNF
surface. The activation energy on Cu/CeO2/CNF (about 16 kcal/mol) is found to be lower
than one on Cu/CNF catalysts (about 25 kcal/mol), indicating a different reaction mechanism
on Cu/CeO2/CNF.
In conclusion, the Cu/CeO2/CNF is a highly active catalyst with high selectivity. It can
possibly be further optimised to increase the activity. Therefore, it might be a good candidate
for replacing copper chromite.
References:
1. Rioux, R. M. and Vannice, J. Catal. 216 (2003) 362.
2.Ma, J. Park, N, Rodriguez, N. M. and Baker, T. K., J. Phys. Chem. B. 105 (2001) 11994.