X-ray absorption, X-ray diffraction and electron microscopy study of spent cobalt based catalyst in semi-commercial scale Fischer–Tropsch synthesis

•A catalyst used for a month in a FTS unit of semi-commercial scale was studied.•Core techniques for nanoparticle size determination were applied.•Growth of cobalt nanoparticles was observed by all the applied size sensitive techniques.•The degree of reduction of the spent catalyst was higher than its fresh counterpart.•The state of rhenium before and after reaction was evaluated.

Calcined, reduced and spent Co-Re/γ-Al2O3 catalysts for Fischer–Tropsch synthesis (FTS) were characterized and compared. Co-K-edge and Re-LIII-edge X-ray absorption near edge structure (XANES), X-ray powder diffraction (XRPD), transmission electron microscopy (TEM) and H2 chemisorption were used to provide insight into structural transformations that the catalyst experiences during a month of operation in a semi-commercial FTS plant. Results from the core techniques for nanoparticle size determination suggest that sintering of the cobalt crystallites is an important deactivation mechanism in FTS performed in slurry reactors. In addition, a higher degree of reduction is observed for the spent catalytic material, while Re appears in a partially reduced state before and after reaction. The particle size distribution together with the spread of Co nanoparticles on the γ-Al2O3 surface indicates crystallite migration as the prevailing mechanism.

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