Cobalt-based Fischer Tropsch Research Articles

Novel Approach to Organization of Structured Cobalt-Based Fischer–Tropsch Catalyst

Structured Fischer–Tropsch synthesis catalysts were tested in tubular reactors of industry-standard diameters of 0.5 or 0.75 inches. The structured catalyst bed was manufactured by the obturation of a straight bunch of graphite-based extrudates (D = 1.5 mm, L = 30 mm). A conventional loose bed of granulated catalyst (D = 1.5 mm, L = 3 mm) was tested as a reference. In a 1000–3000 h−1 syngas space velocity range, structured and loose catalyst bed testing showed no significant differences in their main catalytic parameters. Nevertheless, their C5+ hydrocarbon group composition was quite different, i.e., the alkene fraction rose from 9 to 23%, while n-alkanes dropped from 81 to 64%. This could be a result of secondary reaction intensification in the conventional loose bed due to its zeolite acid site’s higher availability. Further FTS testing of the structured catalysts in 4000–6000 h−1 manifested distinctive limits in C5+ productivity for 0.5 and 0.75 inches of 512 kg C5+/(m3 reactor·h) and 362 kg C5+/(m3 reactor·h), respectively. This may be explained by limitations in structured bed thermal conductivity. It suggests that the arrangement of extrudates in the structured catalyst can significantly affect the reaction heat and mass transfer conditions and affords new opportunities for group composition control by means of catalyst bed organization.

Effect of different alkaline earth metals on the adsorption and catalytic behavior of cobalt Fischer–Tropsch synthesis

Alkali earth metals are effective promoters in cobalt-based Fischer–Tropsch synthesis. To compare the similarity and difference of the effect of the same main group of alkali earth metals on Fischer–Tropsch reaction, a series of alkali earth metals-modified alumina was prepared and applied as the supports for Co catalysts. Promotion of Co/Al2O3 catalyst by alkali earth metals achieved a low CH4 selectivity,high C5+ selectivity and C3 o/p due to the lower H*/CO* ratio and enhanced CO dissociation on the surface of catalyst than the unmodified one.

Enhancing the stability of a cobalt-based Fischer–Tropsch synthesis catalyst using g-C3N4-coated SBA-15 as support

BackgroundThe design and synthesis of catalysts with high stability, activity and selectivity in Fischer–Tropsch synthesis (FTS) have been attracting extensive research attention. Maintaining high catalytic stability and activity is the best strategy for improving the catalyst efficiency and economic benefits. MethodsIn this study, graphitic carbon nitride (g-C3N4)-coated SBA-15 was utilised as a support material to prepare cobalt-based FTS catalysts. The catalysts coated with g-C3N4 were studied via TEM, XPS, XRD, H2-TPR, TG, N2 adsorption–desorption, and tested in a fixed-bed reactor. Significant findingsThe catalysts coated with g-C3N4 were considerably more stable than the Co/SBA-15 catalyst without g-C3N4 coating during a 100 h test period. Furthermore, the CO-conversion performance of the Co/SBA-15 catalyst decreased continuously. Notably, the activity of the Co/SBA-15@0.5C3N4 catalyst with a low g-C3N4 loading was higher than that of the Co/SBA-15@1C3N4 catalyst with a relatively high g-C3N4 loading. g-C3N4 can significantly strengthen the interaction between the cobalt species and the support, thereby increasing the catalyst stability. Therefore, a highly stable catalyst with good activity can be achieved by employing a small amount of g-C3N4 for surface modification. The results highlight the effectiveness of the proposed strategy for preparing highly stable, cobalt-based catalysts with good activity.

Enhancement of C5+ selectivity in photothermal Fischer–Tropsch synthesis by an inorganic heteropoly acid catalyst promotor

The C5+ product selectivity of cobalt-based Fischer–Tropsch synthesis catalyst was significantly improved from 65% to 93% under photothermal conditions by using heteropoly acid (H3PW12O40) as a catalyst promotor.

Hydrogen spillover effects in the Fischer–Tropsch reaction over carbon nanotube supported cobalt catalysts

Support (CNTs) surface defect-induced hydrogen spillover significantly impacted the catalytic activity (turnover frequency, TOF) and methane selectivity evolution in cobalt-based Fischer–Tropsch synthesis.

MOFs-assisted synthesis of robust and efficient cobalt-based Fischer–Tropsch catalysts

The supported catalyst featuring highly dispersed active species is a challenge for industrial catalyst even with high loadings. The traditional impregnation method generally results in large particles due to the particle migration and coalescence or Ostwald ripening process. Herein, a Metal-Organic Frameworks (MOFs) strategy was proposed to assist the manufacture of supported CoOx/SiO2 catalyst. The classic organic ligand (e.g., 2-methylimidazoles) was coordinated with cobalt ions dispersed in advance on silica support, which was post-treated as a sacrificial and protective agent in different atmosphere. These operations can effectively restrain the growth of cobalt particles, yielding the high dispersion of Co metal active sites. The prepared catalyst (CoOx/SiO2-A#) exhibits superior activity, C5+ selectivity and stability in Fischer–Tropsch synthesis. It reveals that the high dispersion as well as the increased number of surface-exposed Co sites contribute to superior activity. As demonstrated by TG-MS and Raman characterizations, a large amounts of carbon species in CoOx/SiO2-N catalyst impeded the accessible active sites. The existence of Co2SiO4 verified by TPR and XPS characterizations means the strong metal-support interaction, that contributes robust performance in long-term stability test. This sacrificial MOFs strategy paves the way for the design of highly dispersed and robust FTS catalysts.

Synthesis of Al-SBA-15 and Its Application in Cobalt Based Fischer–Tropsch Synthesis

Synthesis of Al-SBA-15 and Its Application in Cobalt Based Fischer–Tropsch Synthesis

Role of Zeolites in Heat and Mass Transfer in Pelletized Multifunctional Cobalt-Based Fischer–Tropsch Catalysts

Role of Zeolites in Heat and Mass Transfer in Pelletized Multifunctional Cobalt-Based Fischer–Tropsch Catalysts

Sintering and Carbidisation Under Simulated High Conversion on a Cobalt-Based Fischer-Tropsch Catalyst; Manganese Oxide as a Structural Promotor

Sintering and Carbidisation Under Simulated High Conversion on a Cobalt-Based Fischer-Tropsch Catalyst; Manganese Oxide as a Structural Promotor

A highly carbon‐efficient and techno‐economically optimized process for the renewable‐assisted synthesis of gas to liquid fuels, ammonia, and urea products

Carbon dioxide conversion into beneficial products has received very much attention in recent years to decrease industrial CO2 emissions. In this context, integration of gas to liquids (GTL) process with an iron-based Fischer-Tropsch (FT) reactor with ammonia and urea synthesis plants was investigated. The main motivation of the proposed integration is to reuse a released CO2 stream from the GTL process and to enhance the commercial process economy. The required hydrogen for ammonia comes from polymer electrolyte membrane (PEM) electrolyzers running by solar power. Latin hypercube design (LHD) approach was applied to model the profitability and carbon efficiency of the process. Optimization was conducted to maximize the carbon efficiency and profit index of the overall process using the model-based calibration (MBC) toolbox of MATLAB. The results demonstrated that at the optimum case, the proposed integration is capable of producing 48 t/h of urea and also utilizing about 35 t/h of CO2 produced in the GTL process. The results were compared with another configuration in which a cobalt-based FT reactor was integrated with ammonia and urea processes. The results suggest that profitability, carbon efficiency, and urea production of the process configuration with a Co-based FT reactor is higher than the iron-based configuration while the wax production rate of the iron-based configuration is higher than that of the Co-based process. Techno-economic feasibility study of the zero CO2 emission process represents that the carbon efficiency of around 100% could be obtained.

Water-induced deactivation of cobalt-based Fischer–Tropsch catalysts

The Fischer–Tropsch product, water, is regularly hypothesized to be the driving force for catalyst deactivation. Cobalt nanoparticles may be oxidized to CoO, form mixed-metal oxides with supports, or sinter to larger particles. This Comment discusses the feasibility of these deactivation pathways, highlighting the importance of in situ characterization.

Scanning Nanobeam Diffraction and Energy Dispersive Spectroscopy Characterization of a Model Mn-Promoted Co/Al2O3 Nanosphere Catalyst for Fischer–Tropsch Synthesis

Manganese oxide is an effective promoter for enhancing the activity and selectivity of cobalt-based Fischer–Tropsch synthesis (FTS) catalysts. Previous studies suggest that Co atoms located at the Co–MnO perimeter adsorb CO more strongly and undergo C–O bond cleavage more readily than CO adsorbed on Co sites, which leads to improved C5+ selectivity. Thus, direct characterization of the formation and structure of the active interface between Co nanoparticles and MnO is essential for a full understanding of the FTS promotion effect. Scanning transmission electron microscopic (STEM) methods are well-suited for direct characterization of nanoscale features through imaging, energy dispersive spectroscopy (EDS) elemental mapping, and spatially resolved electron diffraction, a technique known as scanning nanobeam diffraction. However, these techniques require that the catalytic nanoparticles are non-overlapping and well-defined, which is not typical for nanoparticles on porous metal oxide FTS supports. In the present study, we addressed these challenges by synthesizing catalysts composed of cobalt dispersed on nonporous alumina nanospheres (Co/ANS), which yielded isolated nanoparticles that are amenable to elemental and phase mapping by STEM-EDS and scanning nanobeam diffraction. Then, manganese oxide-promoted Co/ANS (Mn–Co/ANS) was characterized using these two techniques, which provided direct evidence for the transformation of a Co–Mn oxide spinel present in the as-prepared catalyst into closely associated Co3O4 and MnO2 nanoparticles in the passivated catalyst after its use for FTS.

Cobalt-based Fischer–Tropsch catalysts supported on different types of N-doped carbon nanotubes

N-doped nanocarbons are promising materials for metal-free and supported catalysts. Three types of N-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor deposition (CVD), by oxidation of the CVD produced N-CNTs with nitric acid, and by post-doping of oxidized undoped CNTs with ammonia. Cobalt catalysts with 20[Formula: see text]wt.% loading supported on N-CNTs were tested in the Fischer–Tropsch synthesis. Oxidized N-CNTs containing pyridone groups demonstrated the best stabilization of cobalt nanoparticles. The catalyst on this support showed the highest selectivity towards [Formula: see text] hydrocarbons. The performance of the catalyst supported on CVD N-CNTs was the worst because of the large variation in cobalt particle size and low reduction degree. The catalysts supported on post-doped CNTs demonstrated the best activity, but high methane selectivity because of the low Co particle size ([Formula: see text][Formula: see text]nm).

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.

Stability of cobalt-based Fischer–Tropsch catalyst supported on oxidized carbon nanotubes

The stability of 20[Formula: see text]wt.% Co/CNT catalyst was tested in the Fischer–Tropsch synthesis and the structural transformations both in the catalyst and support were analyzed. The catalyst showed high conversion and stable selectivity during three weeks of the test, which was attributed to the optimal and stable cobalt particle size of [Formula: see text]13–14[Formula: see text]nm promoted by the support pre-oxidation. XPS, Raman, and nitrogen adsorption data revealed that the carefully chosen catalyst annealing and reduction conditions ensured the preservation of the support structure.

Impact of promoter on the cobalt based Fischer–Tropsch synthesis: a comprehensive kinetic study

A comprehensive kinetic model for cobalt based Fischer–Tropsch synthesis products was developed based on the recently proposed generalized mechanism for monomer formation. The model was evaluated with recent kinetic data from the literature (Co–Re/Al2O3) as well as newly obtained experimental data (Co–Zr/Al2O3). The model results were in good agreement with experimental data. Also estimated model parameters were statistically and physically significant. The model can predict the effect of promoter on the species surface coverage. According to the results, the surface of both catalysts is mainly covered with CO, monomer and carbide. At the same operating condition, carbide surface coverage was significantly higher in the case of Zr promoted catalyst (13.8%) compared to that of Re promoted catalyst (3.3%). Moreover the utilization of Zr promoter resulted in less hydrogenated carbon species (16.3%) which was about 20% in the case of Re promoter. The results also indicated that the product selectivity was mainly governed with monomer, hydrogen and vacant site surface coverage ratios.

Decoupling the deactivation mechanisms of a cobalt Fischer–Tropsch catalyst operated at high conversion and ‘simulated’ high conversion

In situ magnetometer study shows that high conversions facilitate sintering, reversible Co(ii)O and irreversible CoAl2O4 formation within cobalt-based Fischer–Tropsch systems.

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.

The effect of aerosol-deposited ash components on a cobalt-based Fischer–Tropsch catalyst

The effect of ash salts on Co-based Fisher–Tropsch catalysts was studied using an aerosol deposition technique. The major elements in the ash were found to be K, S and Cl. The ash was deposited on a calcined catalyst as dry particles with an average diameter of approx. 350 nm. The loading of ash particles was varied by varying the time of exposure to the particles in a gas stream. Catalyst characterization did not reveal significant differences in cobalt dispersion, reducibility, surface area, pore size, or pore volume between the reference and the catalysts with ash particles deposited. Activity measurements showed that following a short exposure to the mixed ash salts (30 min), there were no significant loss of activity, but a minor change in selectivity of the catalyst . Extended exposure (60 min) led to some activity loss and changes in selectivity. However, extending the exposure time and thus the amount deposited as evidenced by elemental analysis did not lead to a further drop in activity. This behavior is different from that observed with pure potassium salts, and is suggested to be related to the larger size of the aerosol particles deposited. The large aerosol particles used here were probably not penetrating the catalyst bed, and to some extent formed an external layer on the catalyst bed. The ash salts are therefore not able to penetrate to the pore structure and reach the Co active centers, but are mixed with the catalyst and detected in the elemental analysis.

The Effect of Potassium on Cobalt-Based Fischer–Tropsch Catalysts with Different Cobalt Particle Sizes

The effect of K on 20%Co/0.5%Re/γ-Al2O3 Fischer–Tropsch catalysts with two different cobalt particle sizes (small, in the range 6–7 nm and medium size, in the range 12–13 nm) was investigated. The catalyst with the smaller cobalt particle size had a lower catalytic activity and C5+ selectivity while selectivities towards CH4 and CO2 were slightly higher than over the catalyst with larger particles. These effects are ascribed to lower hydrogen concentration on the surface as well as the lower reducibility of smaller cobalt particles. Upon potassium addition all samples showed decreased catalytic activity, reported as Site Time Yield (STY), increased C5+ and CO2 selectivities, and a decrease in CH4 selectivity. There was no difference in the effect of potassium between the sample with small cobalt particles compared to the sample with medium size particles). In both cases the specific activity (STY) fell and the C5+ selectivity increased in a similar fashion.