On the Superior Activity and Selectivity of PtCo/Nb2O5 Fischer-Tropsch Catalysts

Abstract In this study Co/Nb 2 O 5 catalysts and the effect of Pt-promotion thereon are investigated in comparison with γ-Al 2 O 3 - and α-Al 2 O 3 -supported catalysts for the Fischer Tropsch (FT) synthesis. Upon Pt-promotion of Co/Nb 2 O 5 the cobalt-weight normalized FT activity was found to increase by a factor of 2.4, while the high C 5+ selectivity of 85 wt% was maintained. Based on environmental TEM results no indications were found that Pt affected the cobalt particle size in Co/Nb 2 O 5 catalysts. A kinetic study indicates an increased number of active sites upon Pt-promotion whereas Steady-State Isotopic Transient Kinetic Analysis experiments show that a combination of an increased number of active sites and an increased turnover frequency is at the origin of the enhanced activity in Co/Nb 2 O 5 catalysts upon Pt-promotion. Pt was tentatively proposed to bring about more efficient promotion of Co by NbO x being present as smaller clusters.