An investigation using SSITKA of Chain growth on Fe and FeMnK Fischer–Tropsch synthesis catalysts

Although FTS is a simple reaction between CO and H2, its reaction mechanism is not straightforward since it involves a large number of surface species for the formation of a variety of products. In this study, steady-state isotopic transient kinetic analysis (SSITKA) was utilized to estimate the average surface residence times leading to CO2 and various hydrocarbon products in order to investigate chain growth and termination for hydrocarbon products formed on unpromoted and K- and Mn-promoted FeCuSiO2 catalysts. The addition of K and Mn to the Fe catalyst promoted significantly the catalytic activity of Fe but did not have a significant impact on the chain growth or chain termination steps. Instead, an increase in the concentration of active surface intermediates leading to hydrocarbon products was the primary cause for the improved catalyst activity. Chain termination was found to be relatively fast compared to chain growth for the Fe FTS catalysts with and without K and Mn promotion, as the average surface residence times of methane, ethane, ethylene, propane and propylene showed.