DYNAMIC X-RAY-DIFFRACTION STUDY OF AN UNREDUCED IRON-OXIDE CATALYST IN FISCHER-TROPSCH SYNTHESIS

As a result of a previous in situ DXRD study of Fischer-Tropsch synthesis over an unsupported, reduced iron catalyst, a similar study has been undertaken with an unreduced iron oxide catalyst. At 543 K and with H2/CO = 3.2, the initial α-Fe2O3 is immediately reduced to magnetite (Fe3O4), which is in turn, slowly converted to χ-Fe2.5C via a shrinking core process. Catalytic activity appeared to be directly correlated with the formation of the χ-carbide and it is postulated that this isthe catalytically active species. Significantly lower deactivation rates are observed with the unreduced iron catalyst, and it is concluded that this is due to the direct formation of χ-carbide in unreduced iron catalysts, which precludes the ε ’-carbide → χ-carbide transformation and avoids the production of the nucleate carbon arising from that transformation. © 1993 Academic Press, Inc.