Kinetic Insights into the Effect of Promoters on Co/Al2o3 for Fischer-Tropsch Synthesis by Ssitka

The fundamentals of promoter effects in the Fischer−Tropsch synthesis over Co-based catalysts were systematically investigated by employing the Rh, Ir, Sb and Ga as promoters of Co/Al 2 O 3 . Various characterizations showed the higher dispersion and reducibility over Rh- and Ir- promoted catalysts would cause a promoted adsorption property, while the Sb- and Ga- promoted catalysts showed a contrary result because the formation of alloy suppressed the accessibility of Co species. Based on the experimental results and kinetic calculations, a linear relationship for the activation energies of these catalysts as a function of activation entropies was proposed. Besides, steady state isotopic transient kinetic analysis (SSITKA) revealed that promoters mainly affected the surface CHx concentration to alter the CO reaction rate, and the chain growth rate constants would affect the product distribution. Since CoRhA and CoIrA greatly enhanced the CH x concentration and inhibited the chain growth ability, they owned a higher CO reaction rate and CH 4 selectivity. While the CoSbA and CoGaA suppressed the CH x concentration and intrinsic activity, but enhanced the chain growth ability, thereby revealing a lower CO reaction rate and CH 4 selectivity. Furthermore, the reactivity and selectivity difference was attributed to the modification of adsorption strength dictated by the enthalpy of activation on cobalt catalysts with different promoters. These findings provide kinetic insights into the promoter effects and pave the way for optimizing catalysts