Principles of Olefin Selectivity in Fischer-Tropsch Synthesis on Iron and Cobalt Catalysts

The selectivity in Fischer-Tropsch synthesis on iron and cobalt catalysts is studied and the fundamental principles of this process are determined.

With precipitated alkalized iron catalysts (at 250°C), 70% primary α-olefin selectivity, together with 30% primary paraffin selectivity at a steady state, is observed-after a self-organization time during which the metallic iron phase reacts to iron carbides. The rate and selectivity are influenced by potassium promotion, which controls “carbon-on-site” formation, followed by competing reactions of the formation of CH2 as a monomer, the formation of iron carbides, and the formation of a carbon phase.