Investigations of Co Catalyst Nanoparticles in the
Fischer-Tropsch Synthesis Using in situ SAXS
K. Høydalsvik1, J. B. Fløystad1, A. Voronov2, G. Voss2, M. Esmaeili1,
J. Kehres3, H. Granlund1, U. Vainio4, J. W. Andreasen5, M. Rønning2,
D.W. Breiby1
1
Department of Physics, Norwegian University of Science and Technology
Department of Chemical Engineering, Norwegian University of Science and Technology
3
DTU Center for Individual Nanoparticle Functionality, Technical University of Denmark
4
HASYLAB at DESY, Germany
5
DTU Energy Conversion, Technical University of Denmark
2
The Fischer-Tropsch synthesis (FTS) is a set of chemical reactions that forms hydrocarbon
chains from a mixture of CO and H2. The outcome can be used for petroleum substitutes,
such as synthetic diesel, see for example [1]. Typically, cobalt nanoparticles of diameter 6200 nm are used as catalyst, and optimal particle size as well as high temperature and
pressure are required for the reactions to work well.
After the syngas (H/CO2) is introduced to the system, an increase in the catalytic activity is
observed during the first few hours [1], followed by a decrease (deactivation) [2]. Until
present, a correlation between these changes in catalytic activity and the structure of the
catalyst nanoparticles has not been found. Due to their penetrating nature, X-rays are suitable
for studying catalysts during reactions, and consequently we decided to try using in situ
small-angle X-ray scattering (SAXS) for monitoring the gross structural features of the
nanoparticles during the reactions.
Figure: Characterising nano-structures from an in situ FTS experiment.
Left: A typical SAXS pattern measured during this experiment (blue).
Bottom right: The slope  found for the different conditions (top right).
SAXS measurements were performed at beamline B1 in HASYLAB (Hamburg, Germany),
whilst simultaneously monitoring by wide-angle X-ray scattering. Our experiments showed
that  increases after changing gas from H2 to syngas (see figure). To the best of our
knowledge, this is the first time a correlation has been found between the reported increase in
catalytic activity during the first few hours after introducing syngas and a measurable
parameter () that depends on the shape and surface structure of the nanoparticles.
[1] Rønning, M. et al., Catalysis Today, 2010, 155, 289-295
[2] Tsakoumis, N. E. et al., Catalysis Today, 2010, 154, 162 – 182