Transient studies of the elementary steps of Fischer–Tropsch synthesis

The pulse transient method has been used to study the kinetics of several key steps of Fischer–Tropsch (FT) synthesis over cobalt supported catalysts. These elementary steps involve chemisorption of hydrogen and propene, and chemisorption and hydrogenation of carbon monoxide. It is found that at the conditions of Fischer–Tropsch synthesis, hydrogen chemisorption is reversible and quasi-equilibrated, while carbon monoxide adsorption is generally irreversible. Chemisorption of propene on cobalt metal sites results in its rapid autohydrogenation to propane and simultaneous formation of CxHy surface species. The transient response curves produced during hydrogenation of carbon monoxide pulses in a flow of hydrogen have been analyzed using the modified Kobayashi model, which involves irreversible chemisorption and dissociation of carbon monoxide, quasi-equilibrated adsorption of hydrogen and reversible adsorption of water. The kinetic analysis suggests that oxygen-containing species are probably the most abundant surface intermediates. Desorption of water from the catalysts seems to be much slower than hydrogenation of surface carbon species.