Molecular structure and localization of carbon species in alumina supported cobalt Fischer - Tropsch catalysts in a slurry reactor

The paper focusses on the identification of molecular structure of carbon species in 15 wt.% Co/Al2O3 supported catalyst exposed to different conditions of Fischer-Tropsch synthesis in a continuously stirred tank reactor (CSTR). Characterization of wax-extracted spent catalyst by a combination of techniques showed significant carbon deposition under the conditions where the catalyst exhibited a noticeable deactivation. Carbon deposition was less important when catalyst activity was relatively stable. TPH-MS suggested the presence of different carbon species on surface. GC-MS analysis indicated that the strongly adsorbed carbon deposited on wax-extracted spent catalyst was mainly constituted of alpha-olefins, n-paraffins, branched alkanes/alkanes, 2-methyl-branched fatty aldehydes and 2-ketones. 2-Methyl-branched fatty carboxylic acids were mostly detected at high H2O pressure in the reactor. Branched alkenes/alkenes (2-methyl-alkenes/alkanes) were favored at high CO conversion. Alpha-alkyl cinnamic aldehydes were detected under hydrogen deficient conditions. STEM-EELS analysis suggests that carbon is located both on cobalt particles and on alumina support, the carbon species situated on the support being more reluctant to hydrogenation. (C) 2013 Elsevier B.V. All rights reserved.