(643e) Gas–to–Liquid Conversion On Co/Al2O3 Catalyst – Pretreatment Effect Studies
AIChE Annual Meeting
Thursday, November 7, 2013 - 9:50am to 10:10am
Due to high activity of cobalt metal in syngas conversion to higher hydrocarbons, supported cobalt catalysts have been widely used for gas-to-liquid (GTL) conversion. Pretreatment conditions have significant effect on catalyst activity and product selectivity. In this study we investigated effect of cobalt phases, determined by X-ray diffraction (XRD), on catalytic performance of unpromoted cobalt on alumina catalyst (15 wt%Co/Al2O3) in a fixed bed reactor. Catalytic performance has been correlated with characterization results from XRD and temperature-programmed experiments coupled with mass spectroscopic measurements (TPH/TPO-MS).
It has been known  that carbidization of Co0 fcc produce mainly Co2C, which is inactive in FTS, but the latter can be hydrogenated and transformed to a very active Co0 hcp form [2,3]. The challenge is to achieve industrially relevant carbidization-reduction conditions that yield the highest amount of Co0 hcp without producing free carbon and/or Co2C. In the present study we have used two variations of a two-step activation procedure (H2 reduction, followed by CO carbidization and H2 reduction) in addition to a standard (baseline) H2reduction procedure (648 K, 1 bar for 12 h).
It was found that the baseline activation procedure results in the highest activity (59. 1% CO conversion) and the lowest methane selectivity (8.9%). The other two activation procedures yielded CO conversions of 48.4 – 54.8%, and methane selectivities of approximately 11%. H2-CO-H2 activations resulted in the formation of Co0 hcp, but their activity/selectivity was affected by the presence of surface carbide sites, CoxC (x = 2, 3).
 Hofer, L.J.E., Crystalline phases and their relation to Fischer-Tropsch synthesis, in Catalysis, P.H. Emmett, Editor. 1954, Reinhold Pub. Corp.: New York. p. 373-441.