Deactivation behavior of Co/TiO₂ catalysts during fischer-tropsch synthesis

Here we report on the preparation of Co/TiO₂ catalysts (8 and 16 wt % Co) using deposition precipitation by ammonia evaporation (DPA) and incipient wetness impregnation with subsequent static drying (IWI-S) and fluidized bed drying (IWI-F). Although the initial cobalt oxide dispersions were similar for catalysts with the same metal loading, the distribution of the nanoparticles over the support surface was found to increase in the order IWI-S < IWI-F < DPA. Initial activities during Fischer-Tropsch synthesis at 493 K, 20 bar were found to increase in the same order, whereas the C₅₊ selectivities were significantly higher for catalysts prepared by DPA. After 200 h of Fischer-Tropsch synthesis at 35% X_CO, all systems studied had lost about 20% of their initial activity, which could be completely attributed to a loss in active metal surface area, as shown by TEM histogram analysis. Deactivation constants determined using second-order deactivation kinetics were in the same order of magnitude as for Co/SiO₂ catalysts studied previously, but surprisingly, they were not affected by the distribution of cobalt. Catalysts tested at higher X_CO were found to show significantly faster deactivation, which could also be attributed to cobalt particle growth.