Several excellent reviews have been published on the Fischer
Tropsch Synthesis and some concepts have been established [3e6].
Most existing catalysts designed to obtain a high selectivity to
waxes in the FTS use cobalt as main active metal supported on a
porous inorganic oxide (SiO2, Al2
O3, TiO2), together with one or
more promoters. The activity of these catalysts is proportional to
the concentration of Co surface, which depends essentially on two
parameters: the reduction degree (RD) of cobalt oxide reached
during the catalyst reduction step prior to the FTS and the dispersion
of the reduced cobalt. These two parameters are generally
related to each other and are largely determined by the Co-support
interaction. Thus, when TiO2 is used as support, the strong interaction
between Co and TiO2, favors a high metal dispersion but
results in the formation of low reducibility of Co species, giving rise
to a low concentration of active sites. In contrast, the weak interaction
between CoeSiO2 favors Co particles reduction. However,
they tend to agglomerate leading to relatively low dispersions. The
behavior of Co supported on Al2O3 is generally intermediate between
that shown by Co on TiO2 and SiO2. It has also been established
that the efficiency of this reaction can be greatly improved by
designing new thermally stable catalysts with good mechanical and
heat transfer properties, minimizing hot spots developed in the
catalyst bed, which promote metal particle sintering.