However, the high extent of coke lay-down observed under
the selected reaction conditions (340 C, 20 bar and H2/CO ratio
of 1) caused fragmentation of the catalyst particles and carbon filament
growth, evidencing the low mechanical stability of bulk promoted
catalysts.The combination of sodium plus sulfur as promoters for a-
Al2O3-supported iron catalysts was effective to further increase
lower olefins selectivity and decrease methane production while
enhancing catalytic activity. The combined addition of these promoters
increased carbon deposition slightly while the addition of
higher amounts of sodium resulted in a decrease in catalytic activity
possibly caused by the higher extent of carbon deposition.
The optimization of supported iron catalyst for the selective
production of lower olefins from synthesis gas relies on many
factors starting with the selection of a support material which confers
mechanical stability while allowing an intimate contact between
iron and the promoters. Additionally, the concentration of
promoters has to be balanced carefully as low amounts of these
elements have beneficial effects on catalytic performance while beyond
the optimal level these might act as poisons.
Acknowledgments