Deactivation kinetics of bulk and nano-structured microemulsion prepared iron catalysts were studied in Fischer-Tropsch synthesis (FTS), from fitting of data to a generalized power-law expression (GPLE), r(d) = k(d) (a -a(infinity))(m). Conventional bulk iron catalyst was prepared by general bulk co-precipitation method and nano-structured iron catalyst was prepared by microemulsion method. A deactivation model involving parallel paths is proposed, i.e. simultaneous conversion of (a) atomic to polymeric to graphitic carbon and (b) active carbon-rich carbides to inactive carbon-poor carbides. Compositions of bulk iron phase and phase transformations of carbonaceous species during catalyst deactivation in FTS reaction were characterized by temperature-programmed surface reaction with hydrogen (TPSR-H-2), XRD and TEM techniques. (C) 2010 Elsevier B.V. All rights reserved.