Study of an iron-based Fischer–Tropsch synthesis catalyst incorporated with SiO2

Effects of Rare Earth Metal Promotion over Zeolite-Supported Fe-Cu-Based Catalysts on the Light Olefin Production Performance in Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis (FTS), a significant reaction for effective H2 utilization, is a promising approach for direct production of light olefins from syngas (H2 + CO). For the FT-Olefin process, an efficient catalyst restricting the product distribution of FTS to light olefins is required. Aligned with this goal, we synthesized 24 catalysts comprising Fe and Cu in combination with rare earth metals (La, Ce, Nd, Ho, Er) and zeolite supports (ultrastable Y and mordenite). FT-Olefin performances of these catalysts were screened using a high-throughput test system at atmospheric pressure, and then promising catalysts were tested under high pressure in a conventional test system. Results show that Nd increases selectivity to light olefins and Ho suppresses C5+ and coke formation. It is also demonstrated that zeolite-metal interaction, leading to a mixture of both acidic and basic sites, is significant in increasing light olefin production. The mordenite-supported 20 wt % Fe, 0.5 wt % Cu, and 0.5 wt % Ho catalyst provides the highest light olefin yield with the lowest coke and heavier hydrocarbon selectivity.

Effects of Potassium Loading over Iron–Silica Interaction, Phase Evolution and Catalytic Behavior of Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis

Potassium (K) promoter and its loading contents were shown to have remarkable effects on the Fe–O–Si interaction of precipitated Fe/Cu/K/SiO2 catalysts for low-temperature Fischer-Tropsch synthesis (FTS). With the increase in K content from 2.3% (100 g Fe based) up to 7% in the calcined precursors, Fe–O–Si interaction was weakened, as reflected by ATR/FTIR, H2-TPR and XPS investigations. XRD results confirmed that the diffraction peak intensity from (510) facet of χ-Fe5C2 phase strengthened with increasing K loading, which indicates the crystallite size of χ-Fe5C2 increased with the increase in K contents either during the syngas reduction/carburization procedure or after FTS reaction. H2-TPH results indicated that more reactive surface carbon (alpha-carbon) was obtained over the higher K samples pre-carburized by syngas. Raman spectra illustrated that a greater proportion of graphitic carbon was accumulated over the surface of spent samples with higher K loading. At the same time, ATR-FTIR, XRD and Mössbauer spectra (MES) characterization results showed that a relatively higher level of bulk phase Fayalite (Fe2SiO4) species was observed discernibly in the lowest K loading sample (2.3 K%) in this work. The catalytic evaluation results showed that the CO conversion, CO2 selectivity and O/P (C2–C4) ratio increased progressively with the increasing K loading, whereas a monotonic decline in both CO conversion and O/P (C2–C4) ratio was observed on the highest K loading sample during c.a. 280 h of TOS.

Selective olefin production on silica based iron catalysts in Fischer–Tropsch synthesis

Mixed phases of Fe3O4 and Fe5C2, interacting properly with SiO2, produce highly selective olefins from syngas.

The reduction of Fe-bearing copper slag for its use as a catalyst in carbon oxide hydrogenation to methane. A contribution to sustainable catalysis

Reduction of Fe-phases in a slag from the copper smelting process is studied for its use as a catalyst in methanation of carbon oxide (CO). This material contains 36.4 wt% Fe and the main Fe-phases in its fresh and reduced forms were identified and quantified. Chemical analysis and X-ray diffraction (XRD) for crystalline phase detection and determination of Fe dispersion were carried out. Reducibility of Fe-oxides was studied by thermal programmed reduction (TPR) under H₂ at 650 and 800 °C using 0.5 and 2 h soak time. In the fresh slag, iron was found to be in the form of Fe₃O₄ (17.4 wt%) and fayalite, Fe₂SiO₄ (43.4 wt%). The composition was experimentally determined and verified by stoichiometric balances and thermogravimetric analysis (TGA). Upon reduction at 800 °C and 2 h soak time, 87 % of the Fe-phases were reduced, leaving an activated catalyst with a 35.2 % Fe⁰, which is the active phase for CO hydrogenation to methane. An expression was derived to determine the Fe⁰ concentration in the reduced slag based on the composition of the fresh slag and its reduction degree. The catalytic activity of the reduced slag during CO hydrogenation was evaluated in a fixed bed differential reactor. The selectivity to methane, at 300 °C, was 87 %, thus confirming its catalytic activity for the selected reaction.

Activation Energies for Chain Growth Propagation and Termination in Fischer–Tropsch Synthesis on Iron Catalyst as a Function of Catalyst Particle Size

The influence of the catalyst particle size in determining Fischer–Tropsch synthesis (FTS) performance for nano-structured iron catalysts was investigated. The catalysts were prepared by a microemulsion method and to achieve a series of catalysts with different iron particle size, the water-to-surfactant molar ratio (W/S) in the microemulsion system varied from 4 to 12. The results demonstrate that by decreasing the levels of active phase of the iron catalyst, the termination rates for chain growth are increased compared to the propagation rates. In addition, the activation energy for chain propagation is lower than for chain termination, and this difference (Et – Ep) for the hydrocarbon product distributions which is characterised by α1, is lower than the hydrocarbon product distribution which is characterised by α2 The results indicate the H2 concentration on the catalyst surface is decreased by increasing the catalyst particle size. Thus, the dependence of α (α1, and/or α2) on H2 partial pressures is increased by decreasing of catalyst particle size and the dependence of α2 on H2 partial pressures is weaker than for α1.

New size-dependent kinetic equations for hydrocarbon production rates from Fischer–Tropsch synthesis on an iron-based catalyst

The effect of catalyst nanoparticle size on hydrocarbon production rates in the Fischer–Tropsch synthesis (FTS) has been investigated on an iron-based catalyst. A series of iron oxide particles was prepared via precipitation by a microemulsion method. New size-dependent kinetic models for hydrocarbon production rates were developed using a thermodynamic analysis method. Size-dependent parameters of the models were evaluated using the experimental results with a non-linear optimisation routine by minimising the mean absolute relative residual. Because of the role of iron carbide in the FTS reaction by iron catalysts, the iron carbide particle sizes was considered as an important factor in this paper. Experimental results show that the hydrocarbon product distribution shows a slight shift to lower molecular weight hydrocarbons by decreasing catalyst particle sizes and increasing the reaction temperature. The value of the surface tension energy (σ) for paraffin and olefin production on the iron catalyst is calculated in the range 1.2–0.9 J m–2 and 0.62–0.49 J m–2 respectively. These values are lower than for metals and are related to the presence of iron carbide in the catalytic reaction. Also, σ for paraffin production is higher than that for olefin production. The size- and carbon number-independent activation energies for paraffin and olefin formation are 9.1 and 14.9 kJ mol−1, respectively.