Fischer-Tropsch Synthesis Conditions Research Articles

Eco-friendly solid-state synthesis of Na-promoted Mn-Fe/ZrO2 catalyst for Fischer-Tropsch synthesis

The advancement of large-scale and environmentally-friendly solid-state synthesis methods is of paramount importance for the production of precipitated catalysts, notably Fe-based catalysts utilized in Fischer-Tropsch synthesis (FTS). In this study, we present an innovative solvent-independent, wastewater-free solid-state approach for the synthesis of highly efficient Fe/ZrO2 catalysts, elucidating the mechanisms of promotion within this specific methodology. The prepared catalysts underwent rigorous evaluation under industrially-relevant FTS conditions (230–270 °C, 20 bar, and WHSV = 5400 mL/(gcat⋅h)). A comprehensive suite of characterization techniques was employed to establish the intricate interplay between catalytic activity and structural attributes. We meticulously examined the impact of Na as an alkali promoter and the role of transition metals (Cu and Mn) in enhancing FTS catalytic performance. The catalytic outcomes obtained clearly demonstrate the pivotal role of the synergistic interaction between Mn and Na within the Na-Mn-Fe/ZrO2 catalyst system in driving the FTS reaction. This synergism significantly enhances FTS performance, yielding an impressive CO conversion rate (89.91 %) while maintaining low selectivity to CH4 (7.75 %). The incorporation of Mn and Na into the catalyst matrix enhances the dispersion of Fe2O3, thereby improving the reducibility of Mn/Fe oxides and elevating the electron density on the catalyst surface. These factors facilitate the formation of active Hägg iron carbide (χ-Fe5C2), stimulating chain propagation and ultimately leading to the generation of valuable C5+ hydrocarbon products, which underscores its potential as an optimal candidate for future industrial applications in Fe-based Fischer-Tropsch synthesis.

Fischer‐Tropsch Synthesis by a Cobalt‐Based Carbon Aerogel Catalyst

AbstractCarbon aerogel (CA) as a novel catalyst support in Fischer‐Tropsch synthesis (FTS) was synthesized by polymerization of a resorcinol‐formaldehyde (RF) precursor through an ambient pressure drying route. The cobalt‐doped CA was synthesized by three main strategies: (a) impregnation of the metal precursor on the CA (Co‐CA‐I), (b) carbonization of cobalt‐doped organic RF aerogel (Co‐CA‐II), and (c) addition of the cobalt precursor to the RF mixture (Co‐CA‐III). The pores and cobalt particle size increased in the order of Co‐CA‐I > Co‐CA‐II > Co‐CA‐III and cobalt particles wrapped between the graphite layers when cobalt was added to the RF mixture. The CA as the catalyst support presented high CO conversion and high stability under FTS conditions. The CH4 selectivity increased by reducing the size of the cobalt particles. Hydrogen spillover from the support to metallic particles was observed in the case of Co‐CA‐I and Co‐CA‐III catalysts. This phenomenon improved the reducibility and also resulted in higher hydrogenated products being produced.

Formulation of KMoFe/CNTs catalyst for production of light olefins and liquid hydrocarbons via Fischer-Tropsch synthesis: Fixed-bed reactor simulation

Light olefins and C5+ are strategically important products of Fischer-Tropsch synthesis (FTS) over Fe catalysts. In the present work, FTS performance of 0.5K5Mo10Fe/CNTs (DOE 2) and 2 K0.5Mo30Fe/CNTs (DOE 5) catalysts was assessed in terms of CO conversion, C5+ selectivity, and C2-C4 selectivity under industrially relevant FTS conditions (H2/CO = 1.0; GHSV = 2000 h−1; T = 280 ℃; P = 4.13 MPa). The C2-C4 selectivity increased in DOE 2 catalyst to 51.2% with respect to DOE 5 catalyst (2.9%). Meanwhile, the selectivity toward C5+ hydrocarbons decreased from 93.1% in DOE 5 to 8.3% for DOE 2 catalyst. DOE 5 catalyst was more hydrophobic than DOE 2 as confirmed by the water contact angle measurement, lowering CO2 selectivity and water gas shift rate. H2-TPR and CO2-TPD indicated an increase in reducibility and basicity of DOE 5 compared with DOE 2 catalyst, which enhanced iron carbide formation and chain growth probability. The highest amount of metallic Fe in DOE 5 calcined and spent catalysts obtained by XPS and XAS spectra also suggested higher degree of carburization in DOE 5. Additionally, COMSOL Multiphysics software package was employed to provide a 2-dimensional simulation of the FTS fixed-bed reactor. Simulation results were validated using the experimental data for FTS over DOE 2 and DOE 5 catalysts. Effects of temperature on CO conversion as well as distribution of H2, CO, and ethylene were discussed. The simulation illustrated the effects of the fixed-bed reactor wall on both velocity and temperature profiles.

Elucidating deactivation of titania-supported cobalt Fischer-Tropsch catalysts under simulated high conversion conditions

The study of titania-supported cobalt nanoparticles is relevant for industrial Fischer-Tropsch synthesis (FTS). Herein, we report about various deactivation pathways of cobalt supported on P25 titania (cobalt loading 2–8 wt%) under simulated high conversion conditions using in situ Mössbauer spectroscopy. A fraction of metallic cobalt was oxidized under humid FTS conditions. The absolute amount of oxidized cobalt was ∼ 1.2 wt% independent of the cobalt loading, indicating that specific cobalt-titanol interactions are involved in the oxidation process. The formation of cobalt-titanate-like compounds was only observed under very high water-to-hydrogen ratios in the absence of carbon monoxide. Steam considerably enhances cobalt sintering under FTS conditions. As such, deactivation under humid FTS conditions is not only caused by cobalt oxidation but also by enhancing sintering of the active phase.

Cobalt Catalyzed Fischer-Tropsch Synthesis with O2-Containing Syngas

Provision of sustainable transportation fuels is required for the energetic transition. A new process is presented for the production of synthetic sulfur free maritime fuel. This fuel is produced by Co-catalyzed Fischer-Tropsch synthesis (FTS) using syngas based on a plasma technology that contains traces of O2. Gravimetric experiments and steady state measurements with a Co/Pt/Al2O3 catalyst at low temperature FTS conditions (10–30 bar, 180–230 °C) show that, with H2 present in the system, the catalyst remains active for FTS, and shows no influence on the distribution of C2+-hydrocarbons. O2 is only converted to H2O and CO2 in varying proportions (H2O: 70–80%, CO2: 20–30%), whereby a higher CO concentration increases the CO2 selectivity. This work may wield a new CO2 source for carbon-neutral fuels.

Single-Phase θ-Fe3C Derived from Prussian Blue and Its Catalytic Application in Fischer-Tropsch Synthesis

Elucidation of the intrinsic catalytic principle of iron carbides remains a substantial challenge in iron-catalyzed Fischer-Tropsch synthesis (FTS), due to possible interference from other Fe-containing species. Here, we propose a facile approach to synthesize single-phase θ-Fe3C via the pyrolysis of a molecularly defined Fe-C complex (Fe4[Fe(CN)6]3), thus affording close examination of its catalytic behavior during FTS. The crystal structure of prepared θ-Fe3C is unambiguously verified by combined XRD and MES measurement, demonstrating its single-phase nature. Strikingly, single-phase θ-Fe3C exhibited excellent selectivity to light olefins (77.8%) in the C2-C4 hydrocarbons with less than 10% CO2 formation in typical FTS conditions. This strategy further succeeds with promotion of Mn, evident for its wide-ranging compatibility for the promising industrial development of catalysts. This work offers a facile approach for oriented preparation of single-phase θ-Fe3C and provides an in-depth understanding of its intrinsic catalytic performance in FTS.

Jet Fuel Synthesis from Syngas Using Bifunctional Cobalt-Based Catalysts

Advanced biofuels are required to facilitate the energy transition away from fossil fuels and lower the accompanied CO2 emissions. Particularly, jet fuel needs a renewable substitute, for which novel production routes and technology are needed that are more efficient and economically viable. The direct conversion of bio-syngas into fuel is one such development that could improve the efficiency of biomass for jet fuel processes. In this work, bifunctional catalysts based on hierarchical zeolites are prepared, tested and evaluated for their potential use in the production of actual jet fuel. The bifunctional catalysts Co/H-mesoZSM-5, Co/H-mesoBETA and Co/H-mesoY have been applied, and their performance is compared with their microporous zeolite-based counterparts and two conventional Fischer–Tropsch Co catalysts. Co/H-mesoZSM-5 and Co/H-mesoBETA showed great potential for the direct production of jet fuel as bifunctional catalysts. Besides the high jet fuel yields under Fischer–Tropsch synthesis conditions at, respectively, 30.4% and 41.0%, the product also contained the high branched/linear hydrocarbon ratio desired to reach jet fuel specifications. This reveals the great potential for the direct conversion of syngas into jet fuel using catalysts that can be prepared in few steps from commercially available materials.

Enhanced stability of a fused iron catalyst under realistic Fischer–Tropsch synthesis conditions: insights into the role of iron phases (χ-Fe5C2, θ-Fe3C and α-Fe)

The performance and stability of fused-Fe catalyst in FTS reaction are enhanced through the control synthesis of iron phases (χ-Fe5C2, θ-Fe3C and α-Fe).

Hydroconversion for Hydrocarbon Generation of Highly Overmature Kerogens under Fischer–Tropsch Synthesis Conditions

In order to explore the possibility of continuous hydrocarbon generation from highly mature organic matter, a series of simulation experiments of hydroconversion of highly over mature Yuertusi kero...

On the Cobalt Carbide Formation in a Co/TiO2 Fischer-Tropsch Synthesis Catalyst as Studied by High-Pressure, Long-Term Operando X-ray Absorption and Diffraction.

Operando X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) were performed on a Co/TiO2 Fischer–Tropsch synthesis (FTS) catalyst at 16 bar for (at least) 48 h time-on-stream in both a synchrotron facility and a laboratory-based X-ray diffractometer. Cobalt carbide formation was observed earlier during FTS with operando XAS than with XRD. This apparent discrepancy is due to the higher sensitivity of XAS to a short-range order. Interestingly, in both cases, the product formation does not noticeably change when cobalt carbide formation is detected. This suggests that cobalt carbide formation is not a major deactivation mechanism, as is often suggested for FTS. Moreover, no cobalt oxide formation was detected by XAS or XRD. In other words, one of the classical proposals invoked to explain Co/TiO2 catalyst deactivation could not be supported by our operando X-ray characterization data obtained at close to industrially relevant reaction conditions. Furthermore, a bimodal cobalt particle distribution was observed by high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray analysis, while product formation remained relatively stable. The bimodal distribution is most probably due to the mobility and migration of the cobalt nanoparticles during FTS conditions.

Unusual Effect of Support Carbonization on the Structure and Performance of Fe/Mgal2o4 Fischer–Tropsch Catalyst

Carbonization of MgAl2O4 spinel via glucose treatment is applied for preparation of spinel‐supported iron Fischer–Tropsch synthesis (FTS) catalysts. The catalysts are characterized by low‐temperature adsorption of N2, transmission electron microscopy (TEM), Mössbauer spectroscopy, in situ magnitometry, and are tested in high‐temperature FTS conditions. Surface carbonization leads to magnetite formation in the course of catalyst calcining, likely due to reductive function of surface carbon. In contrast, hematite is formed if iron precursor is deposited on pristine spinel. Support carbonization facilitates iron precursor reduction into carbide during catalyst activation step in synthesis gas flow and gives rise to highly dispersed iron nanopartilcles. Comparison of sequential and co‐impregnation approaches for support carbonization reveal that the first is preferable in terms of Hägg carbide formation during catalyst activation. Specific activity of the catalysts in high‐temperature FTS is approximately doubled due to the support carbonization. The carbonization also boosts C5+ selectivity and olefin percentage in the product hydrocarbons, while methane formation is suppressed. Adding potassium to catalyst formulation suppresses iron carbide oxidation and Fe3O4 formation, and promotes conversion of χ‐Fe5C2 into θ‐Fe7C3 in FTS conditions.

Molecular dynamics simulation of the n-octacosane-water mixture confined in hydrophilic and hydrophobic mesopores: The effect of oxygenates

Wax and water mixtures are the main products of the Gas-To-Liquids (GTL) process through the Fischer-Tropsch synthesis (FTS), along with relatively small quantities of oxygenated compounds such as alcohols. It has been established that water production in high concentrations leads to phase segregation inside the catalyst support pores. Excess water conditions are considered responsible for sintering of catalytic nanoparticles, which reduces catalyst lifetime and increases GTL operational cost. Apart from the effects of increased water concentration in wax – water FTS mixtures, the presence of oxygenates has not been studied at the molecular level. Moreover, the effect of the surface support chemistry on the wax – water mixture inside catalyst pores is essential in understanding mixture phase behavior. All these open questions are of significant interest for the petrochemical industry. The present study focuses on simulating by means of Molecular Dynamics (MD) the n-octacosane (n-C28) – water mixture inside titanium dioxide (TiO2) and silicon carbide (SiC) mesopores at low-temperature FTS conditions (473.15 K). The presence of small alcohols such as methanol and ethanol on the n-C28 – H2O mixture's phase behavior was also evaluated. The united atom TraPPE (TraPPE-UA) force field was used for n-C28 and the alcohols, while the SPC/E was used for water. Catalyst support atoms were modeled as Lennard-Jones spheres (charged or neutral) at fixed positions. Our simulations show that inside TiO2, water molecules organize into two discrete layers on the TiO2 surface, with n-C28 occupying the pore center; mixture phase separation is completely reversed inside the SiC pore. In both cases, alcohol addition does not influence either n-C28 or H2O distribution inside the pores. Furthermore, we examine the hydrogen bonds formed between water molecules and how these are influenced upon alcohol addition and confinement. Finally, through the calculation of lateral diffusion coefficients, we provide insights on the mobility of the individual n-C28 – H2O mixture components inside the pores considered.

Insights into the Promotion with Ru of Co/TiO2 Fischer–Tropsch Catalysts: An In Situ Spectroscopic Study

Although ruthenium is a common promoter for cobalt-based Fischer–Tropsch synthesis (FTS) catalysts, the origin of Ru promotion and promoter concentration effects remains controversial. To gain a fundamental understanding of the Ru promotion effects, we herein performed an in situ spectroscopic study by X-ray absorption spectroscopy (XAS), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS)–Auger of working Co/TiO2 catalysts (ca. 12 wt % Co, pure anatase TiO2 phase) promoted with different amounts of Ru (0.1–1.2 wt %). At typical FTS conditions (220 °C, 20 bar, H2/CO = 2), the activity in terms of both metal-time-yield (MTY) and initial turnover frequency (TOF) was maximized for the catalysts promoted with 0.1–0.2 wt % Ru, for which most of the Ru was alloyed with Co in bimetallic nanoparticles. The analysis of Auger electrons evidenced that the lower (apparent) TOF of accessible Co0 sites in the absence of Ru and at Ru concentrations beyond 0.2 wt % is bridged to the development, under reaction conditions, of FTS-inactive cobalt carbide (CoCx) and cobalt oxide (CoOx) patches, respectively, at the outermost surface of cobalt crystallites.

Hierarchical porous spinel MFe2O4 (M=Fe, Zn, Ni and Co) nanoparticles: Facile synthesis approach and their superb stability and catalytic performance in Fischer-Tropsch synthesis

The environmental pollution problem and the dwindling in the crude oil resources have been driving considerable researches into alternative routes for the production of clean and low cost liquid fuels. Fischer-Tropsch synthesis (FTS) is a key-technology and a clean alternative for the production of valuable organic chemicals and high standard liquid fuels through the reaction of syngas (CO/H2). In this study, one-pot hydrothermal reaction was adopted for the synthesis of robust MFe2O4 (M = Fe, Zn, Ni and Co) nanoparticles (NPs) with hierarchical porous-structured. The as-synthesized NPs and without the reported necessary pre-calcination step were appointed as robust catalysts in FTS at various reaction temperature (240–290 °C). The obtained catalytic results have demonstrated that CoFe2O4 NPs catalyst with its inversed spinel structure exhibited the optimum catalytic activity compared with the type of normal spinel structure of ZnFe2O4 catalyst. More precisely, CoFe2O4 NPs catalyst showed the best CO conversion ratio of 96% at 290 °C and the highest light-olefin (C2–C4) selectivity value of 63%. However, Fe3O4 NPs catalyst displayed the highest selectivity toward long chain hydrocarbon product (C5+) of 50 wt%, and the lowest CH4 selectivity value of 12% at 260 °C. Notably, the obtained results from X-ray diffraction and N2-physisorption characterization for the spent ferrite catalysts demonstrated that the co-existence of the active sites of Hägg iron carbide (χ-Fe5C2) and metallic Co phases and along with the high surface area and pore diameter plays the key role for the obtained high catalytic activity in CoFe2O4 NPs. Moreover, the produced catalysts in this study exhibited good stability performance within maintained high catalytic activity for a period of at least 700 h of industrial-relevant FTS conditions.

Mechanistic insight into carbon-carbon bond formation on cobalt under simulated Fischer-Tropsch synthesis conditions

Facile C-C bond formation is essential to the formation of long hydrocarbon chains in Fischer-Tropsch synthesis. Various chain growth mechanisms have been proposed previously, but spectroscopic identification of surface intermediates involved in C-C bond formation is scarce. We here show that the high CO coverage typical of Fischer-Tropsch synthesis affects the reaction pathways of C2Hx adsorbates on a Co(0001) model catalyst and promote C-C bond formation. In-situ high resolution x-ray photoelectron spectroscopy shows that a high CO coverage promotes transformation of C2Hx adsorbates into the ethylidyne form, which subsequently dimerizes to 2-butyne. The observed reaction sequence provides a mechanistic explanation for CO-induced ethylene dimerization on supported cobalt catalysts. For Fischer-Tropsch synthesis we propose that C-C bond formation on the close-packed terraces of a cobalt nanoparticle occurs via methylidyne (CH) insertion into long chain alkylidyne intermediates, the latter being stabilized by the high surface coverage under reaction conditions.

Amphiphobic surface fabrication of iron catalyst and effect on product distribution of Fischer–Tropsch synthesis

The core-shell Fe3O4@SiO2–PFTS with amphiphobic property was prepared through successive hydrothermal process, stöber method, and silylation reaction, where perfluorodecyltrlethoxysilane (PFTS) was employed as silylation agent to form amphiphobic surface. As-synthesized Fe3O4@SiO2–PFTS catalyst was exposed to the industrially relevant Fischer-Tropsch synthesis (FTS) conditions in a fixed-bed reactor and showed altered activity and product distribution different from traditional iron catalysts. Modified Fe3O4@SiO2–PFTS reduced evidently the production of CO2 from 44% of selectivity to 12% ascribed to suppression against the water gas shift (WGS) reaction, although CO conversion on Fe3O4@SiO2–PFTS as well as on Fe3O4@SiO2 declined compared with that on Fe3O4. Surface modification also caused the disappearance of mesopores and increase in steric hindrance, which inhibited diffusion of hydrocarbons. Secondary reactions of primary olefins were thus intensified, resulting in fall in olefin selectivity but rise in production of light hydrocarbons. The catalyst exhibited good stability within 120 h of time-on-stream.

Morphological and compositional changes of MFe2O4@Co3O4 (M = Ni, Zn) core-shell nanoparticles after mild reduction

NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 core-shell nanoparticles were synthesized and reduced to be used as catalysts for the Fischer-Tropsch synthesis. The as-synthesized materials were determined to have an incomplete Co3O4 shell around the ferrite core with a maximum thickness of 3 nm. Using in-situ TEM, it was shown that reduction of these core-shell nanoparticles in pure hydrogen at 230 °C and 250 °C, respectively, resulted in the formation of small cobalt islands on the ferrite surface. Catalytic testing of the core-shell materials, NiFe2O4@Co3O4 and ZnFe2O4@Co3O4, after reduction showed a cobalt-time yield of 13.64 μmolCO·gCo−1·s−1 and 4.27 μmolCO·gCo−1·s−1 and a C5+ selectivity of 47 C-% and 68 C-%, respectively. The observed difference in cobalt-time yield and selectivity between NiFe2O4@Co3O4 and ZnFe2O4@Co3O4 core-shell nanoparticles was ascribed to a combination of effects that arose from the morphological and compositional changes that occurred after reduction and under Fischer-Tropsch synthesis conditions.

Sintering of cobalt during FTS: Insights from industrial and model systems

Sintering of supported cobalt catalysts is an important deactivation mechanism at play during realistic Fischer-Tropsch synthesis conditions. The traditional ways of studying the mechanism of sintering by looking at cobalt particle size distributions derived from transmission electron microscope images on porous supported catalysts, does have its drawbacks. In this mini-review, we show collaborative work between Sasol and its academic partners at the University of Cape Town and Eindhoven University of Technology, in which a two-pronged approach was used to study the topic of sintering. This included the use of model systems (model catalysts and theory) as well as in-situ monitoring of real (industrial) systems for understanding this practical problem in industry. We also show with new data, that the understanding generated, can be used in the mitigation of sintering by using either process conditions, catalyst design or catalyst regeneration.

INFLUENCE OF PREPARING NANOSCALE SUSPENSIONS METHOD ON ITS PHYSICO-CHEMICAL AND CATALYTIC PROPERTIES UNDER THE CONDITIONS OF FISCHER-TROPSCH SYNTHESIS

Methods for the formation of stable iron-containing suspensions that exhibit activity in the conversion of synthesis gas to C5+ hydrocarbons by the Fischer-Tropsch method are proposed. By XRD and DLS methods it was determined that the formation of the Fe2O3 phase with a bimodal particle size distribution of 50 and 295 nm results in the formation of a suspension by the drop thermolysis method − the gradual introduction of the active metal precursor solution into the dispersion medium (mixture of hydrocarbons C19H40-C32H66). Pulsed introduction of the active metal precursor solution (flash-pyrolysis) into the reactor zone leads to the formation of the Fe3O4 phase with a particle size of 91 and 460 nm. By TEM and AFM methods it was established that, regardless of the slurry forming method, large active phase particles are agglomerates of a finer fraction of particles with an average size of 42 nm. The obtained suspensions demonstrated high activity in the Fischer-Tropsch synthesis under the slurry-reactor conditions, however, the degree of CO conversion is slightly higher in the case of the catalytic suspension prepared by the drop thermolysis method. It is shown that the method of forming the suspension significantly affects the fractional composition of the resulting reaction products. In the presence of a suspension obtained by drop thermolysis, the yield of liquid hydrocarbons reaches 130 g/m3, while a high content of C19+ hydrocarbons is observed. The system formed by the method of flash-pyrolysis makes it possible to obtain mainly the gasoline (C5-C10) and diesel (C11-C18) hydrocarbon fractions. It should be noted that the products of the reaction have a high content of unsaturated hydrocarbons, which reaches 55%. Thus, the composition of the final products of FTS can be controlled by the choice of the catalytic suspension prepared method.
 For citation:
 Kulikova M.V., Dement’eva O.S., Chudakova M.V., Ivantsov M.I. Influence of preparing nanoscale suspensions method on its physico-chemical and catalytic properties under the conditions of Fischer-Tropsch synthesis. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 9-10. P. 70-75

Fabrication of Fe2C Embedded in Hollow Carbon Spheres: a High‐Performance and Stable Catalyst for Fischer‐Tropsch Synthesis

AbstractThe Fischer−Tropsch synthesis (FTS) is a non‐petroleum‐based alternative route, which directly produces fuels and value‐added chemicals (e. g. lower olefins) from coal‐, biomass‐ or natural gas‐derived syngas. The ϵ‐iron carbide, such as Fe2C, has been predicted to be active but not stable under high‐temperature FTS conditions. In this work, we have fabricated a novel catalyst with Fe2C embedded in hollow carbon spheres (HCS) by pyrolyzing the coated polymer and Fe(NO3)3 on silica spheres and then etching the hard template. XRD, XPS, TEM and N2 physical adsorption were employed to characterize the evolution and properties of as‐prepared catalysts, which significantly depend on pyrolysis temperature. Under FTS conditions, the obtained catalysts exhibit good dispersion, robustness of geometric construction, and resistance to sintering. More importantly, Fe2C was confirmed as the dominant and stable iron carbide species. The unique chemical surrounding and confinement effect provided by carbon matrix contribute to these peculiarities that are responsible for superior activity and stability in FTS. Furthermore, we found that the products distribution could be manipulated by changing the geometric diameters of HCS, due to the tunable CO/H2 ratio.