On the superior activity and selectivity of PtCo/Nb2O5 Fischer Tropsch catalysts

Abstract

In this study Co/Nb2O5 catalysts and the effect of Pt-promotion thereon are investigated in comparison with γ-Al2O3- and α-Al2O3-supported catalysts for the Fischer Tropsch (FT) synthesis. Upon Pt-promotion of Co/Nb2O5 the cobalt-weight normalized FT activity was found to increase by a factor of 2.4, while the high C5+ selectivity of 85wt% was maintained. Based on environmental TEM results no indications were found that Pt affected the cobalt particle size in Co/Nb2O5 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/Nb2O5 catalysts upon Pt-promotion. Pt was tentatively proposed to bring about more efficient promotion of Co by NbOx being present as smaller clusters.