Studies of the Fischer-Tropsch Synthesis. XVIII.Influence of Catalyst Geometry on Synthesis on Iron Catalysts

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

“…The generic Fe phase changes for a Fe-based catalyst follow the following order: [1,25,31] The initial FTS reaction catalyst material is commonly in a form of a Fe oxide, mainly either as α-Fe 2 O 3 (hematite), γ-Fe 2 O 3 (maghemite) or Fe 3 O 4 (magnetite). [25] The Fe oxides are not active for the hydrocarbon-forming FTS reactions (Reaction 2 and Reaction 3), [54][55][56] and are commonly reduced to α-Fe (metallic Fe) prior to starting the FTS reaction. Upon exposure to H 2 : CO in the FTS reaction, the α-Fe then readily reacts to form various Fe carbide phases (Fe x C, x = 2-3).…”

“…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.…”

“…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. [56] As Fe 3 O 4 is active for the WGS, but not for the FTS reaction, [1,32,33] with sufficient reaction temperature (> 310°C), the catalyst may become a bifunctional catalyst where the Fe x C catalyst partially re-oxidizes to Fe 3 O 4 , which works as a WGS catalyst and the remaining Fe x C part acts as the FTS reaction catalyst. At lower (< 310°C) temperatures, the Fe 3 O 4 phase is a less efficient WGS reaction catalyst.…”

Pore size effects in high-temperature Fischer–Tropsch synthesis over supported iron catalysts

“…Previously, the effect of catalyst pore size on FT synthesis was principally assessed for bulk iron catalysts. Anderson et al [24] in 1950s attributed the influence of pore size on the catalytic activity of fused iron catalysts to mass transport phenomena. More recently, the effect of intraparticle pore-diffusion limitations on the productivity of fused iron catalysts was evaluated by Post [25] and Bukur [26,27] in a more quantitative manner.…”