(544dw) The Use of Thermodynamics to Predict Cobalt Catalyst Speciation during Fischer Tropsch Reduction and Reaction

To understand the complexity of cobalt catalyst speciation during reduction and deactivation by oxidation during Fisher Tropsch Synthesis (FTS), thermodynamic stability diagrams were employed to illustrate predominant phases under different conditions (temperature, pressure and reducing agents). The results from the plotted stability diagrams corroborated the insitu analysis results from a number of researchers. Furthermore, during catalyst reduction, the interaction of reducing agents with the catalyst results in the formation of several gaseous components such as CO, H₂, CO₂ and H₂O depending on the reducing agent used. The stability diagrams also show that the oxidation of the cobalt catalyst is a function P_H2O/P_H2 and P_CO2/P_CO ratios. For P_H2O/P_H2 ratio of 6.25 x 10⁰⁹ and a P_CO2/P_CO ratio of 2.51 x 10¹¹ an oxygen partial pressure of 2.12 x 10^-20 bar was obtained for cobalt oxidation. The ratios obtained experimentally are of comparatively lesser magnitude hence crystalline sizes variation determines the oxidisablilty of cobalt catalyst.