Highly selective and active niobia-supported cobalt catalysts for fischer-tropsch synthesis

The performance of Co/Nb₂O₅ was compared to that of Co/γ-Al₂O₃ for the Fischer-Tropsch synthesis at 20 bar and over the temperature range of 220-260°C. The C₅₊ selectivity of Nb₂O₅-supported cobalt catalysts was found to be very high, i.e. up to 90 wt% C₅₊ at 220°C. The activity per unit weight cobalt was found to be similar for Nb₂O₅ and γ-Al₂O₃-supported catalysts at identical reaction temperature. However, due to the low porosity of crystalline Nb ₂O₅, the cobalt loading was limited to 5 wt% and consequently the activity per unit weight of catalyst was lower than of Co/γ-Al₂O₃ catalysts with higher cobalt loadings. This low activity was largely compensated by increasing the reaction temperature, although the C₅₊ selectivity decreased upon increasing reaction temperature. Due to the high intrinsic C₅₊ selectivity, Nb₂O₅-supported catalysts could be operated up to ~250°C at a target C₅₊ selectivity of 80 wt%, whereas γ-Al₂O₃-supported catalysts called for an operation temperature of ~210°C. At this target C₅₊ selectivity, the activity per unit weight of catalyst was found to be identical for 5 wt% Co/Nb₂O₅ and 25 wt% Co/Al₂O₃, while the activity per unit weight of cobalt was a factor of four higher for the niobia-supported catalyst.