Effects of Reaction Variables on Fischer–Tropsch Synthesis with Co-Precipitated K/FeCuAlO x Catalysts

Abstract

The effects of reduction temperature and reaction temperature, pressure and space velocity on iron-based K/FeCuAlO x Fischer-Tropsch catalysts prepared by co-precipitation were investigated. The catalyst reduced at 150°C deactivated quickly due to an abundance of unreduced iron species. With increasing reduction temperature, the iron oxide's phase transformed from hematite (a-Fe 2 O 3 ) to magnetite (Fe 3 O 4 ) and finally to metallic iron (a-Fe). The induction period to reach steady-state catalytic activity was reduced at increased reduction temperatures due to in situ reduction by syngas during reaction. CO conversion increased with increasing reaction temperature, and selectivity to C 5 ? decreased with increasing reaction pressure and space velocity. At reaction temperatures up to of 300°C, CO 2 formation by the water-gas shift reaction was linearly correlated with the extent of CO conversion, and CO 2 formation was slightly suppressed at C350°C by a reverse water-gas shift reaction.

Highly Ordered Mesoporous Fe2O3–ZrO2 Bimetal Oxides for an Enhanced CO Hydrogenation Activity to Hydrocarbons with Their Structural Stability

“…From the results of XPS analysis on the used FeZr catalysts as shown in supplementary Figure S7 and summarized in Table , the BEs of the Fe 2p 3/2 peak on the used FeZr catalysts shifted to the much higher BE regions from ∼711 eV on the fresh FeZr catalysts to 712.2–712.9 eV on the used ones. This observation strongly suggests the possible formations of the active iron carbides ,,, with the strong interactions of the Fe 2 O 3 with ZrO 2 promoter on the used FeZr catalysts. However, BEs of the Zr 3d 5/2 appeared at ∼182 eV on the fresh and used FeZr catalysts were not significantly altered due to its intrinsically irreducible characters.…”

“…On the FeZr(0), CO conversion was significantly lower around 5.6% due to a fast initial deactivation by complete structural disintegrations and significant coke depositions (such as dense amorphous heavy hydrocarbons), which was similar to our previous mesoporous Co 3 O 4 catalyst. − Interestingly, the most active FeZr(0.3) without any additional chemical promoter addition showed the smallest formation of CH 4 and light C 2 –C 4 hydrocarbons due to the well-preserved mesoporous Fe 2 O 3 –ZrO 2 crystalline phases. It can be originated from an easy formation of the active iron carbides such as the well-known χ-Fe 5 C 2 phases with less formation of unstable and deformed iron carbide species such as the γ-Fe 4 C phases (verified by Mössbauer analysis in the next section), where the strong adsorption natures of CO molecules on the edge/corner defect sites are responsible for a higher CH 4 formation rate on the various transition metal catalysts. ,− A relatively higher CO conversion to CO 2 was found to be proportional to the CO conversion in the range of 38.3–46.5% on all the FeZr catalysts due to an enhanced WGS activity, which are similar results with our previous work . Especially, the observed higher CO 2 formation on the FeZr(0) can be attributed to the deformed iron phases covered with heavy coke layers, which can enhance the activity of the WGS reaction .…”

“…It can be originated from an easy formation of the active iron carbides such as the well-known χ-Fe 5 C 2 phases with less formation of unstable and deformed iron carbide species such as the γ-Fe 4 C phases (verified by Mössbauer analysis in the next section), where the strong adsorption natures of CO molecules on the edge/corner defect sites are responsible for a higher CH 4 formation rate on the various transition metal catalysts. ,− A relatively higher CO conversion to CO 2 was found to be proportional to the CO conversion in the range of 38.3–46.5% on all the FeZr catalysts due to an enhanced WGS activity, which are similar results with our previous work . Especially, the observed higher CO 2 formation on the FeZr(0) can be attributed to the deformed iron phases covered with heavy coke layers, which can enhance the activity of the WGS reaction . With an increase of ZrO 2 content such as on the FeZr(0.5) and FeZr(1), the longer induction period to approach a steady-state FTS activity was observed due to the difficult transformations of the metallic iron crystallites to the active iron carbides, which can be also prohibited by a significant structure disintegration with a larger heavy hydrocarbon deposition during FTS reaction.…”

“…In general, the hydrocarbon distributions from FTS reaction depends on the pore structures as well as its sizes, and CH 4 selectivity can be significantly increased on the iron-based FTS catalyst having a small pore size. It can be explained that H 2 /CO ratio can be increased inside of the small pores due to the suppressed diffusion rates of CO molecules compared with those of the H 2 reactant through a liquid-like waxy hydrocarbon layers. , The extents of active surface iron carbides on the stable mesoporous Fe 2 O 3 –ZrO 2 structures seem to be further important to obtain a higher CO conversion and C 5 + selectivity. , The formations of the active iron carbide phases (Fe x C) were identified from the XRD analysis on the used FeZr catalysts as shown in supplementary Figure S6, where the Fe x C species seems to be in the formed of the active cementite carbide (θ-Fe 3 C), Hagg carbide (χ-Fe 5 C 2 ), or hexagonal iron carbide (ε-Fe 2 C) and so on . In general, alkali metal components such as Na and SiO 2 have been well-known as the chemical promoters to improve the catalytic activity and selectivity to olefins on the iron-based FTS catalysts by easily forming active iron carbide phases .…”

Supercritical Fischer-Tropsch Synthesis: Heavy Aldehyde Production and the Role of Process Conditions

“…Increasing the reaction temperature in FTS is generally known to increase catalytic activity while decreasing heavy product selectivity and increasing methane selectivity. 9,10 For HTFT, increasing the temperature also decreases the alcohol content of the syncrude. 11 In contrast to cobalt-based catalysts, increasing the reaction pressure over iron-based LTFT catalysts appears to have little effect on the overall carbon number distribution of the product.…”