Studies of the Fischer—Tropsch Synthesis. IX. Phase Changes of Iron Catalysts in the Synthesis

Carbon Pathways, Sodium‐Sulphur Promotion and Identification of Iron Carbides in Iron‐based Fischer‐Tropsch Synthesis

“…The conversion of Fe x C phases into Fe 3 O 4 takes place if either of the H 2 O:H 2 or CO 2 :CO ratios are above critical molar ratios. [1,32,33,56,62,[75][76][77] In general, H 2 O is more potent Fe oxidant than CO 2 . [32,62,77] When moving along a fixed bed reactor towards the FTS reactor outlet, [64,78] or towards the inner core of the Febased catalyst material particle, [56] the reducing H 2 : CO mixture is progressively converted into H 2 O and CO 2 .…”

“…Due to the increasing H 2 O and CO 2 concentrations, the oxidation potential towards forming Fe 3 O 4 from Fe x C increases. [1,56,75,76] Up to around 100-200 μm depth from the particle surface, the Fe-based catalyst particle might remain under reductive environment at FTS reaction conditions. For depths beyond > 200-400 μm from the particle surface, the environment may become oxidative and Fe x C oxidation to Fe 3 O 4 can take over.…”

“…The conversion of Fe x C phases into Fe 3 O 4 takes place if either of the H 2 O:H 2 or CO 2 :CO ratios are above critical molar ratios . In general, H 2 O is more potent Fe oxidant than CO 2 .…”

“…When moving along a fixed bed reactor towards the FTS reactor outlet, or towards the inner core of the Fe‐based catalyst material particle, the reducing H 2 : CO mixture is progressively converted into H 2 O and CO 2 . Due to the increasing H 2 O and CO 2 concentrations, the oxidation potential towards forming Fe 3 O 4 from Fe x C increases . Up to around 100–200 μm depth from the particle surface, the Fe‐based catalyst particle might remain under reductive environment at FTS reaction conditions.…”

Identification of Iron Carbides in Fe(−Na−S)/α‐Al2O3 Fischer‐Tropsch Synthesis Catalysts with X‐ray Powder Diffractometry and Mössbauer Absorption Spectroscopy

“…[20] The Fe-based FTS catalysts have the tendency to re-oxidize to WGS catalyzing Fe 3 O 4 over time. [20,26,59,60,86,98,99] The catalyst re-oxidation could explain the formation of the θ-Fe 7 C 3 phase at later stages of the catalyst life-time at Sasol along the WGS catalyzing Fe 3 O 4 , [20] as the WGS reaction releases CO 2 . [86,98] The formation of the θ-Fe 7 C 3 phase with catalyst treatment 340 h.p.…”