Crystalline niobia with tailored porosity as support for cobalt catalysts for the Fischer–Tropsch synthesis

Abstract

Structure and catalytic performance of niobia-supported cobalt catalysts were studied based on crystal phase, porosity and cobalt loading. Crystalline niobia as support proved to be a prerequisite to obtain highly active and selective Co/niobia Fischer–Tropsch catalysts, whereas amorphous niobia showed minimal activity. Crystallization changed the porous morphology of Nb2O5·nH2O resulting in a dense material with low specific pore volume and specific surface area. Multiple impregnations on crystalline Nb2O5 were necessary to achieve cobalt loadings higher than 6wt.%; this led to larger cobalt particles, diminished interaction of cobalt with niobia and therefore decreased activity per unit weight of cobalt and C5+ selectivity. Carbon deposition via sucrose pyrolysis was employed in order to partly maintain the porosity during crystallization. The obtained porous crystalline niobia was used as support for cobalt catalysts with higher metal loadings. STEM-EDX mapping characterization of the catalysts provided unique information for this kind of materials, e.g. cobalt distribution and particle size. The catalysts showed high cobalt-normalized catalytic activity and C5+ selectivity for the Fischer–Tropsch synthesis under industrially relevant conditions. Moreover, higher cobalt loadings led to an increased catalyst-weight normalized catalytic activity.