Fischer-Tropsch Synthesis: Catalyst activation of low alpha iron catalyst

Activation with three different gases (H2, CO and synthesis gas) over an Fe100/K1.4/Si4.6/Cu2.0 catalyst was conducted to investigate the effects of pretreatment gas on Fischer-Tropsch Synthesis (FTS) activity and selectivity. Catalyst slurry was withdrawn from the reactor at increasing time intervals of FTS for Mössbauer spectroscopic analysis. Activation with CO produced the highest syngas conversion while H2 generated the lowest; syngas activation produced a slightly lower conversion than CO activation. CO activation transformed the majority of the iron into χ-Fe5C2 and Magnetite with only 12% ɛ-Fe2.2C being detected. Unlike the CO activated catalyst, the syngas activated iron catalyst resulted in a lower amount of χ-Fe5C2 than ɛ-Fe2.2C. The initial high (64%) content of ɛ-Fe2.2C decreased gradually to below 30% while CO conversion decreased from 83% to 55%. During this period, χ-Fe5C2 increased from initial 10% to 33%. Magnetite changed little during the process while the form of carbides interchanged. Hydrogen activation yielded a low CO conversion of 50% and only 8% χ-Fe5C2 and 16% ɛ-Fe2.2C was formed while Magnetite was as high as 75% after the FTS reaction rate became constant. Although activation gas type had a significant effect on syngas conversion, hydrogen, syngas and CO activations produced similar H2 to CO usage ratio, hydrocarbon product distribution, olefin fraction, alpha value and CO2 selectivity.