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

Abstract

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.