Abstract
In Fe-based Fischer-Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H-2 : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H(2)reduced Fe(-Na-S)/alpha-Al(2)O(3)catalyst materials, with and without Na-S promotion, were carburized under CO at 240-440 degrees C to form Fe carbides. X-ray Powder Diffractometry (XRPD) with Rietveld Quantitative Phase Analysis (R-QPA) and Mossbauer Absorption Spectroscopy (MAS) were used to identity and quantify the formed Fe carbide phases. The Fe carbides formed in order of increasing temperature are epsilon-Fe3C, eta-Fe2C, chi-Fe(5)C(2)and theta-Fe3C. theta-Fe(7)C(3)and a distorted chi-Fe(5)C(2)phase are formed at 25 bar CO (340 degrees C) from a Fe oxide precursor. Fe carbide formation was unaffected by Na-S addition, but it did increase Fe oxidation (<= 290 degrees C) and preferred formation of chi-Fe(5)C(2)over theta-Fe3C phase (>= 390 degrees C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of Na-S in the carburization process.