Study of deactivation of iron-based Fischer-Tropsch synthesis catalysts

Attempts to correlate the catalytic activity of unpromoted and potassium-promoted iron Fischer-Tropsch catalysts to their bulk phase compositions as determined using Mossbauer spectroscopy are reported. The CO-conversion of both catalysts declined with time-on-stream. Samples of the unmpromoted catalyst were primarily Fe(5)C(2) and this phase gradually decreased to become essentially pure Fe(3)O(4) after 450 hours time-on-stream. In contrast, the potassium-promoted catalyst was primarily Fe(2+)C after pretreatment and remained this phase during 400 hours of synthesis. Thus, both Fe(5)C(2) and Fe(2+)C phases are about equally active for Fischer-Tropsch synthesis but exhibit much different stability during the course of the synthesis reaction.