Fischer-Tropsch Catalysis Research Articles

Perspective—Concerning a New Mechanistic Model Toward the Catalytic Ammonia Synthesis

A reasonable catalytic mechanistic model should refer to a widely range of catalytic reaction. We believe that all types of catalytic reaction on heterogeneous catalysis should follow a general mechanism, and it is our opinion that with the hall-filled valence orbitals, the atom of catalysts could convert the reactant into reactive radical and/or support the formation of new chemical bond between two reactants via radical dimerization. In our recent publications this new mechanistic model on the catalytic Fischer-Tropsch reaction (the conversion of CO and H<sub>2</sub> to hydrocarbons), electrochemical hydrogen evolution reactions, and hydrogen combustion in various metal catalysts is discussed, and which seems to provide a reasonable interpretation to those catalytic reactions. In the present work it is discussed that this new mechanistic model is suitable to the Haber-Bosch process (catalytic ammonia synthesis) on various transition metal catalysts, and a reasonable explanation is provided on the catalytic property of various transition metal for ammonia synthesis.

Formation of Methanol via Fischer-Tropsch Catalysis by Cosmic Iron Sulphide.

Chemical reactions in the gas phase of the interstellar medium face significant challenges due to its extreme conditions (i. e., low gas densities and temperatures), necessitating the presence of dust grains to facilitate the synthesis of molecules inaccessible in the gas phase. While interstellar grains are known to enhance encounter rates and dissipate energy from exothermic reactions, their potential as chemical catalysts remain less explored. Here, we present mechanistic insights into the Fischer-Tropsch-type methanol (FTT-CH3OH) synthesis by reactivity of CO with H2 and using cosmic FeS surfaces as heterogeneous catalysts. Periodic quantum chemical calculations were employed to characterize the potential energy surface of the reactions on the (011) and (001) FeS surfaces, considering different Fe coordination environments and S vacancies. Kinetic calculations were also conducted to assess catalytic capacity and allocate reaction processes within the astrochemical framework. Our findings demonstrate the feasibility of FeS-based astrocatalysis in the FTT-CH3OH synthesis. The reactions and their energetics were elucidated from a mechanistic standpoint. Kinetic analysis demonstrates the temperature dependency of the simulated processes, underscoring the compulsory need of energy sources considering the astrophysical scenario. Our results provide insights into the presence of CH3OH in diverse regions where current models struggle to explain its observational quantity.

Insights into Fischer–Tropsch catalysis: current perspectives, mechanisms, and emerging trends in energy research

Fischer–Tropsch (FT) synthesis is an important module for the production of clean and sustainable fuels and chemicals, making it a topic of considerable interest in energy research. This mini-review covers the current literature on FT catalysis and offers insights into the primary products, the nuances of the FT reaction, and the product distribution, with particular attention to the Anderson–Schulz–Flory distribution (ASFD) and known deviations from this fundamental concept. Conventional FT catalysts, particularly Fe- and Co-based catalysis systems, are reviewed, highlighting their central role and the influence of water and water–gas shift (WGS) activity on their catalytic behavior. Various mechanisms of catalyst deactivation are also investigated, and the high methanation activity of Co-based catalysts is illustrated. To make this complex field accessible to a broader audience, we explain conjectured reaction mechanisms, namely, the carbide mechanism and CO insertion. We discuss the complex formation of a wide range of products, including olefins, kerosenes, branched hydrocarbons, and by-products such as alcohols and oxygenates. The article goes beyond the traditional scope of FT catalysis by addressing topics of current interest, including the direct hydrogenation of CO2 for power-to-X applications and the use of bifunctional catalysts to produce tailored FT products, most notably for the production of sustainable aviation fuel (SAF). This mini-review provides a holistic overview of the evolving landscape of FT catalysts and is aimed at both experienced researchers and those new to the field while covering current and emerging trends in this important area of energy research.

Designer Biosynthetic Jet Fuels Derived from Isoprene and α-Olefins

Isoprene was hydrovinylated with a series of α-olefins (1-pentene, 1-hexene, 1-heptene, 1-octene) to produce acyclic branched C10–C13 alkenes. The process utilized CoBr2(DPPE) as the precatalyst in loadings as low as 0.1 mol % and zinc as the reducing agent. Use of the cobalt catalyst resulted in primarily 1,4-addition, with carbon coupling at the 4-position of isoprene. A significant amount (∼20%) of the coupling products at the 1-position of isoprene was also observed. Each of the discrete C10, C11, C12, and C13 products were then hydrogenated with 10% Pd/C (200 °C; 650 psi H2) to yield jet fuel blendstocks. In addition to the reactions with pure α-olefins, an equimolar mixture of the C5–C8 α-olefins was used to mimic a stream of olefins produced from ethanol dehydration/oligomerization or Fischer–Tropsch catalysis. The different fuel blends exhibited densities ranging from 0.73 to 0.76 g mL–1, gravimetric net heats of combustion (NHOC) from 43.91 to 44.13 MJ kg–1, and −20 °C kinematic viscosities from 2.4 to 6.3 mm2 s–1. The NHOC values were ∼2.9% higher than the lower limit for Jet-A, while the low-temperature viscosities were up to 70% lower than the upper limit for Jet-A. In addition to studying the suitability of the lightly branched hydrocarbons generated in this process as jet fuel blendstocks, it was of interest to explore their potential as diesel fuels. The equimolar C10–C13 fuel mixture exhibited a derived cetane number (DCN) of 56, which is 16 units higher than that required for Diesel #2 (40). The outstanding fuel properties of the isoprene-derived fuels suggest that they have applications as replacements for both petroleum-derived Jet-A and Diesel #2.

High-Ash Low-Rank Coal Gasification: Process Modeling and Multiobjective Optimization

The diversification of coal for its sustainable utilization in producing liquid transportation fuel is inevitable in countries with huge coal reserves. Gasification has been contemplated as one of the most promising thermochemical routes to convert coal into high-quality syngas, which can be utilized to produce liquid hydrocarbons through catalytic Fischer–Tropsch (F-T) synthesis. Liquid transportation fuel production through coal gasification could help deal with environmental challenges and renewable energy development. The present study aims to develop an equilibrium model of a downdraft fixed-bed gasifier using Aspen Plus simulator to predict the syngas compositions obtained from the gasification of high-ash low-rank coal at different operating conditions. Air is used as a gasifying agent in the present study. The model validation is done using published experimental and simulation results from previous investigations. The sensitivity analysis is done to observe the influence of the major operating parameters, such as equivalence ratio (ER), gasification temperature, and moisture content (MC), on the performance of the CL-RMC concerning syngas generation. The gasification performance of CL-RMC is analyzed by defining various performance parameters such as syngas composition, hydrogen-to-carbon monoxide (H2/CO), molar ratio, syngas yield (YSyngas), the lower heating value of syngas (LHVSyngas), cold gas efficiency (CGE), and carbon conversion efficiency (CCE). The combined effects of the major operating parameters are studied through the response surface methodology (RSM) using the design of experiments. The optimized condition of the major operational parameters is determined for a target value of a H2/CO molar ratio of 1 and the maximum CGE and CCE using the multiobjective optimization approach. The high-degree accurate regression model equations were generated for the H2/CO molar ratio, CGE, and CCE using the variance analysis (ANOVA) tool. The optimal conditions of the major operating parameters, i.e., ER, gasification temperature, MC for the H2/CO molar ratio of 1, and the maximum CGE and CCE, are found to be 0.5, 655 °C, and 16.36 wt %, respectively. The corresponding optimal values of CGE and CCE are obtained as 22 and 16.36%, respectively, with a cumulative composite desirability value of 0.7348. The findings of the present investigation can be decisive for future developmental projects in countries concerning the utilization of high-ash low-rank coal in liquid fuel production through the gasification route.

Electronic Promotion Effects of Metal Oxides: A Case Study of MnO Impact on Fischer–Tropsch Catalysis

Electronic Promotion Effects of Metal Oxides: A Case Study of MnO Impact on Fischer–Tropsch Catalysis

Dual catalysis by homogeneous/heterogeneous ruthenium species

In this Chem issue, Han et al. devised a system relying on tandem heterogeneous and homogeneous catalysis by ruthenium species for the CO2 hydrogenation to hydrocarbons with remarkable efficiency. In particular, 5-atom (or longer) chain hydrocarbons were obtained with remarkably high selectivity (71.1%).

Biomass to Liquids (BtL) Process Simulation, Economics and Environmental Impact Assessment for a 3000 bbl/d Plant

The biomass to liquids process (BtL) is an interesting path to produce synthetic petroleum via biomass gasification and Fischer Tropsch (FT) synthesis. The scope of this work is to describe, to simulate and to assess the economic and the environmental impact of the BtL multistep process. The process simulation tool is CheOpe, the economics have been estimated via Aspen Process Economic Analyzer V7.2.1 and the environmental assessment via GaBi V6.0. In this study, cobalt-based catalyst kinetics are simulated in a FT slurry bubble column reactor. The feedstock for FT is the syngas obtained from biomass gasification. The first step is a syngas reforming followed by a water gas shift (WGS) section to adjust the H2 to CO ratio to about 2 (required for FT catalysis) and then by a Rectisol® island to remove the acid gases (H2S, poison for FT catalysis, and CO2, inert gas in FT reaction). Finally, after the FT reaction section, the last step is the upgrading (UPG) of FT products to produce diesel and naphtha. An estimation of CAPEX for a 3000 bbl/d capacity plant has been carried out. Estimated investment costs are about M€ 400. This result has been paired with a life cycle assessment (LCA) in order to complete a decisional frame. LCA points out the environmental advantages in the use of BtL-fuels in the reduction of CO2 global emissions, if compared to the ones relevant to fossil fuels. This result respects the recent EU Directives limits.

Supported Fe2C catalysts originated from Fe2N phase and active for Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) targeting liquid fuel products is key technology to alleviate the excessive dependence on unsustainable crude oil. Fabrication of highly active phase has long been an attractive topic in the field of Fischer-Tropsch catalysis. However, as a promising active species, the efficient formation of Fe2C phase is inhibited by kinetic barrier via traditional approaches. In this context, we firstly synthesized phase-pure Fe2N nanoparticles on Al2O3, which has similar coordination structure with Fe2C. The in-situ XRD data in time series reveal that pre-existing of interstitial N atoms in Fe2N structure leads to the effective phase transformation to Fe2C at low temperatures (280 °C). The as-prepared catalysts demonstrated highly catalytic activity without any induction period, coupling with a high selectivity of 60wt.% for desired valuable products. In addition, the corresponding structural evolution uncover the determining effect of these electron-rich Fe sites in the Fe2X (N or C) structure on superior performance.

Experimental Determination of H2 and CO Diffusion Coefficients in a Wax Mixture Confined in a Porous Titania Catalyst Support.

The ability to measure and predict molecular diffusion coefficients in multicomponent mixtures is not only of fundamental scientific interest but also of significant relevance in understanding how catalytic processes proceed. In the present work, the direct measurement of the molecular diffusion of H2 and CO gas-phase species diffusing in n-alkane mixtures using pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) methods is reported. The work is of direct relevance to Fischer-Tropsch (FT) catalysis, with the measurements being made of the gas-wax system with the wax in both the bulk liquid state and when confined within a titania catalyst support, at temperatures and pressures typical of low-temperature FT synthesis. Molecular diffusion coefficients of H2 and CO within wax-saturated porous titania in the range (1.00-2.43) × 10-8 and (6.44-8.50) × 10-9 m2 s-1, respectively, were measured in the temperature range of 140-240 and 200-240 °C for H2 and CO, respectively, at a pressure of 40 bar. The wax mixture was typical of a wax produced during FT catalysis and had a molar average carbon number of 36. It is shown that the hydrogen diffusion coefficient within this wax mixture is consistent, to within experimental error, with the hydrogen diffusion coefficient measured in pure single-component n-hexatriacontane (n-C36) wax; this result held with the waxes in the bulk liquid state and when confined within the porous titania. The tortuosity of the porous titania was also measured using PFG NMR and found to be 1.77; this value is independent of temperature. The ability of existing correlations to predict these experimentally determined data was then critically evaluated. Although the Wilke-Chang correlation was found to underestimate the molecular diffusion coefficients of both H2 and CO diffusing in the wax in both the bulk state and when confined within the porous titania, parameterized correlations based on the rough hard sphere model, having accounted for the experimentally determined tortuosity factor, predicted the H2 and CO diffusion within bulk and confined wax to within 3%.

Nanophase iron carbides in fine‐grained rims in CM2 carbonaceous chondrites: Formation of organic material by Fischer–Tropsch catalysis in the solar nebula

AbstractTransmission electron microscope studies of fine‐grained rims in three CM2 carbonaceous chondrites, Y‐791198, Murchison, and ALH 81002, have revealed the presence of widespread nanoparticles with a distinctive core–shell structure, invariably associated with carbonaceous material. These nanoparticles vary in size from ~20 nm up to 50 nm in diameter and consist of a core of Fe,Ni carbide surrounded by a continuous layer of polycrystalline magnetite. These magnetite shells are 5–7 nm in thickness irrespective of the diameter of the core Fe,Ni carbide grains. A narrow layer of amorphous carbon a few nanometers in thickness is present separating the carbide core from the magnetite shell in all the nanoparticles observed. The Fe,Ni carbide phases that constitute the core are consistent with both haxonite and cohenite, based on electron diffraction data, energy dispersive X‐ray analysis, and electron energy loss spectroscopy. Z‐contrast scanning transmission electron microscopy shows that these core–shell magnetite‐carbide nanoparticles can occur as individual isolated grains, but more commonly occur in clusters of multiple particles. In addition, energy‐filtered transmission electron microscopy (EFTEM) images show that in all cases, the nanoparticles are embedded within regions of carbonaceous material or are coated with carbonaceous material. The observed nanostructures of the carbides and their association with carbonaceous material can be interpreted as being indicative of Fischer–Tropsch‐type (FTT) reactions catalyzed by nanophase Fe,Ni metal grains that were carburized during the catalysis reaction. The most likely environment for these FTT reactions appears to be the solar nebula consistent with the high thermal stability of haxonite and cohenite, compared with other carbides and the evidence of localized catalytic graphitization of the carbonaceous material. However, the possibility that such reactions occurred within the CM parent body cannot be excluded, although this scenario seems unlikely, because the kinetics of the reaction would be extremely slow at the temperatures inferred for CM asteroidal parent bodies. In addition, carbides are unlikely to be stable under the oxidizing conditions of alteration experienced by CM chondrites. Instead, it is most probable that the magnetite rims on all the carbide particles are the product of parent body oxidation of Fe,Ni carbides, but this oxidation was incomplete, because of the buildup of an impermeable layer of amorphous carbon at the interface between the magnetite and the carbide phase that arrested the reaction before it went to completion. These observations suggest that although FTT catalysis reactions may not have been the major mechanism of organic material formation within the solar nebula, they nevertheless contributed to the inventory of complex insoluble organic matter that is present in carbonaceous chondrites.

Surface speciation of Co based Fischer-Tropsch catalyst under reaction conditions: Deactivation by coke or by oxidation?

Loss of catalyst activity and selectivity with time-on-stream are one of the greatest limitations for the industrial use of Cobalt based Fischer-Tropsch (FT) catalysis. Despite much work on this area, there is still a lack of consensus about the causes leading to catalyst deactivation. Some of the most common hypotheses are oxidation and carbonization of the active phase. In our work we present the free energy of CαHβOγ surface deposition on Co(111) for a wide range of surface coverages under FT reaction conditions. These results present a comprehensive study in which the trends for hydrocarbon-species deposition, cobalt oxidation, and hydrocarbon-induced surface reconstruction are thoroughly compared. The formation of unavoidable branched species leads to deactivation by coke; O may be present in surface intermediates but direct Co-O interaction is unlikely at these conditions.

Effect of Co-Feeding Inorganic and Organic Molecules in the Fe and Co Catalyzed Fischer–Tropsch Synthesis: A Review

This short review makes it clear that after 90 years, the Fischer–Tropsch synthesis (FTS) process is still not well understood. While it is agreed that it is primarily a polymerization process, giving rise to a distribution of mainly olefins and paraffins; the mechanism by which this occurs on catalysts is still a subject of much debate. Many of the FT features, such as deactivation, product distributions, kinetics and mechanism, and equilibrium aspects of the FT processes are still subjects of controversy, regardless of the progress that has been made so far. The effect of molecules co-feeding in FTS on these features is the main focus of this study. This review looks at some of these areas and tries to throw some light on aspects of FTS since the inception of the idea to date with emphasis and recommendation made based on nitrogen, water, ammonia, and olefins co-feeding case studies.

A robust and precious metal-free high performance cobalt Fischer–Tropsch catalyst

Slurry-phase Fischer–Tropsch catalysis is widely used in the production of synthetic transportation fuels, but places severe stresses on the catalyst due to the demanding hydrothermal and mechanical reaction conditions. In this Article we report the synthesis, characterization and catalytic performance of a robust cobalt-based Fischer–Tropsch catalyst. Combining an inert alpha alumina support with an appropriate cobalt addition method produces a material that is easy to reduce without precious metal additives and is mechanically and hydrothermally stable. Unlike many Fischer–Tropsch catalysts, this material is resistant to sintering and shows excellent selectivity and good activity in slurry-phase testing over 1,000 hours. The Fischer–Tropsch reaction is one of the key means of producing synthetic fuels. Here a deposition method to disperse cobalt nanoparticles across an alpha alumina support is shown to produce a highly stable system capable of withstanding demanding conditions while providing excellent activity.

Co-Based Catalysts Supported on Silica and Carbon Materials: Effect of Support Property on Cobalt Species and Fischer–Tropsch Synthesis Performance

The influence of different support surfaces and physical structures on cobalt species and catalytic Fischer–Tropsch synthesis (FTS) performance has been investigated by using silica or mesoporous carbon as support. All the three catalysts Co/SBA-15, Co/SiO2, and Co/CMK-3 behaved differently in the FTS test and showed characteristic cobalt species. After calcination in argon, Co3O4 was prominent on both Co/SBA-15 and Co/SiO2 because of the stronger metal–support interaction. However, the weaker metal–support interaction on Co/CMK-3 coupled with the autoreduction of cobalt oxide facilitated the formation of more CoO on the support surface. On account of the higher reducibility and specific surface area, Co/SBA-15 exhibited higher CO conversion in FTS than another two as-synthesized catalysts. SBA-15 and CMK-3 possess well-ordered channel structure which favors mass transport and diffusion while diffusion inhibits hydrocarbon chain growth. The highest C5+ and C11–17 selectivities were observed over Co/SiO2 w...

Atomically Defined Iron Carbide Surface for Fischer–Tropsch Synthesis Catalysis

With the purpose of investigating the reactivity of Fe carbide as an active phase in Fischer–Tropsch catalysis, we studied the formation of a well-defined Fe carbide surface structure resulting from carbon exposure of an Fe film on Au(111). Using two different sources of carbon (C), namely atomic carbon and ethylene gas, we used synchrotron X-ray photoelectron spectroscopy (XPS) to show that a 6 ML Fe film readily converts into a well-defined and thermodynamically stable carbide phase. Scanning tunneling microscopy (STM) showed that the surface of the Fe carbide film is crystalline and is dominated by Fe(110)-like facets perturbed into a (2 × 2) periodic structure due to insertion of C in the interstitial sites. The reactivity of the carbide film toward CO, H2, and O2 was furthermore probed by XPS under vacuum conditions. While the pristine Fe carbide surface was unreactive toward hydrogen gas at 500 K, we interestingly found that CO dissociation from a preadsorbed monolayer of CO takes place already at low temperature. This observation points to an intrinsic activity of the Fe carbide phase where additional carbon originating from CO can be placed in the Fe carbide surface. The catalytic significance of the model catalyst surface presented here is that it can be seen as a stable Fe carbide phase with intrinsically vacant sites for additional C insertion at elevated pressure, and we propose that such additional C may act as active species in C–C coupling reactions during FTS. The studies pave the way for a better understanding of FTS processes on Fe-based catalysts on the basis of a well-defined model surface.

In situ observation of phase changes of a silica-supported cobalt catalyst for the Fischer-Tropsch process by the development of a synchrotron-compatible insitu/operando powder X-ray diffraction cell.

In situ characterization of catalysts gives direct insight into the working state of the material. Here, the design and performance characteristics of a universal insitu synchrotron-compatible X-ray diffraction cell capable of operation at high temperature and high pressure, 1373 K, and 35 bar, respectively, are reported. Its performance is demonstrated by characterizing a cobalt-based catalyst used in a prototypical high-pressure catalytic reaction, the Fischer-Tropsch synthesis, using X-ray diffraction. Cobalt nanoparticles supported on silica were studied insitu during Fischer-Tropsch catalysis using syngas, H2 and CO, at 723 K and 20 bar. Post reaction, the Co nanoparticles were carburized at elevated pressure, demonstrating an increased rate of carburization compared with atmospheric studies.

Dissolution of CoCu catalyst step defects by Co subcarbonyl formation

In CoCu-based Fischer-Tropsch catalysis, the as-prepared nanoparticles, if allowed to self-assemble, exhibit a Co@Cu core-shell morphology that would render the catalyst inactive for CO hydrogenation. Therefore, a chemical reconstruction has to occur to create the catalytically active phase. While some of the thermodynamically-imposed driving forces for reconstruction have been identified and kinetic mechanisms experimentally probed, a thorough theoretical understanding on the molecular events has yet to be developed. Here, we employ a first-principles statistical mechanics approach to show that the reconstruction of CoCu in CO atmospheres is likely accomplished via subcarbonyl (multiple bonded CO) formation at the step and kink sites of CoCu catalysts. We find that the CO-induced antisegregation of subsurface Co atoms to step sites and the subsequent rupturing of Co subcarbonyls from these sites is thermodynamically feasible under experimentally-relevant CO pressures and temperatures. The results suggest that Co tricarbonyl formation along with its rupturing and diffusion onto the terraces is responsible for reconstruction. These Co tricarbonyls are shown to favorably dimerize, suggesting a potential route for nanoisland formation and morphological changes. Our results illustrate a strong correlation to surface carbonyl and inorganic complex chemistry of Co metal.

Carbon Chain Growth by Sequential Reactions of CO and CO2 with [W(CO)6] and an Aluminum(I) Reductant.

The formation of carbon chains by the coupling of CO x ( x = 1 or 2) units on transition metals is a fundamental step relevant to Fischer-Tropsch catalysis. Fischer-Tropsch catalysis produces energy dense liquid hydrocarbons from synthesis gas (CO and H2) and has been a mainstay of the energy economy since its discovery nearly a century ago. Despite detailed studies aimed at elucidating the steps of catalysis, experimental evidence for chain growth (C n → C n+1; n ≥ 2) from the coupling of CO units on metal complexes is, to the best of our knowledge, unprecedented. In this paper, we show that carbon chains can be grown from sequential reactions of CO or CO2 with a transition metal carbonyl complex. By exploiting the cooperative effect of transition and main group metals, we document the first example of chain propagation from sequential coupling of CO units (C1 → C3 → C4), along with the first example of incorporation of CO2 into the growing carbon chain.

Effect of Pretreatment Method on the Nanostructure and Performance of Supported Co Catalysts in Fischer–Tropsch Synthesis

Understanding precursor transformation to active catalysts is crucial to heterogeneous Fischer–Tropsch (FT) catalysis directed toward production of hydrocarbons for transportation fuels. Despite considerable literature on FT catalysis, the effect of pretreatment of supported cobalt catalysts on cobalt dispersion, dynamic atomic structure, and the activity of the catalysts is not well understood. Here we present systematic studies into the formation of active catalyst phases in supported Co catalyst precursors in FT catalysis using in situ environmental (scanning) transmission electron microscopy (E(S)TEM) with single-atom resolution under controlled reaction environments for in situ visualization, imaging, and analysis of reacting atomic species in real time, EXAFS, XAS, DRIFTS analyses, and catalytic activity measurements. We have synthesized and analyzed dried reduced (D) and dried calcined reduced (DC) Co real-world (practical) catalysts on reducible and nonreducible supports, such as SiO2, Al2O3, TiO2, and ZrO2. Comparisons of dynamic in situ atomic structural observations of reacting single atoms, atomic clusters, and nanoparticles of Co and DRIFTS, XAS, EXAFS, and catalytic activity data of the D and DC samples reveal in most cases better dispersion in the D samples, leading to a larger number of low-coordination Co0 sites and a higher number of active sites for CO adsorption. The experimental findings on the degree of reduction of D and DC catalysts on reducible and nonreducible supports and correlations between hexagonal (hcp) Co sites and the activity of the catalysts generate structural insights into the catalyst dynamics, important to the development of efficient FT catalysts.