Characterizing Intrinsic Deactivation in Cobalt-Catalyzed Fischer-Tropsch Synthesis

Three intrinsic deactivation modes observed in experimental cobalt Fischer-Tropsch synthesis (Co FTS) catalysts are investigated via ex-situ TEM [1]. These include: cobalt oxidation reversible by mild hydrogen treatment, cobalt agglomeration, and cobalt-support mixed oxide formation. All three mechanisms involve redox transformation of the catalytically active cobalt metal. Earlier studies [2] have shown that (a) Co 0 is the catalytically active entity in Co FTS and (b) the site activity is not influenced by the support or the metal particle size in catalysts containing metal particles larger than ~5 nm. Steady-state isotope transient studies with similar catalysts [3] confirmed these conclusions. Consequently, transformations that reduce Co 0 surface by agglomeration or by oxidizing Co particles will reduce catalytic activity. Bulk thermodynamic data [4,5] suggests that CoO would not form under typical Co FTS conditions. However, reactor studies and TEM observations prove that the behavior of nanoscale metal particles deviates from that of the bulk and that cobalt oxidation does occur during commercially relevant Co FTS conditions. The exact nature of th