Higher Fischer–Tropsch Synthesis Activity Research Articles

Facet sensitivity of iron carbides in Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) is a structure-sensitive reaction of which performance is strongly related to the active phase, particle size, and exposed facets. Compared with the full-pledged investigation on the active phase and particle size, the facet effect has been limited to theoretical studies or single-crystal surfaces, lacking experimental reports of practical catalysts, especially for Fe-based catalysts. Herein, we demonstrate the facet sensitivity of iron carbides in FTS. As the prerequisite, {202} and {112} facets of χ-Fe5C2 are fabricated as the outer shell through the conformal reconstruction of Fe3O4 nanocubes and octahedra, as the inner cores, respectively. During FTS, the activity and stability are highly sensitive to the exposed facet of iron carbides, whereas the facet sensitivity is not prominent for the chain growth. According to mechanistic studies, {202} χ-Fe5C2 surfaces follow hydrogen-assisted CO dissociation which lowers the activation energy compared with the direct CO dissociation over {112} surfaces, affording the high FTS activity.

Fischer–Tropsch Synthesis for Light Olefins from Syngas: A Review of Catalyst Development

Light olefins as one the most important building blocks in chemical industry can be produced via Fischer–Tropsch synthesis (FTS) from syngas. FT synthesis conducted at high temperature would lead to light paraffins, carbon dioxide, methane, and C5+ longer chain hydrocarbons. The present work focuses on providing a critical review on the light olefin production using Fischer–Tropsch synthesis. The effects of metals, promoters and supports as the most influential parameters on the catalytic performance of catalysts are discussed meticulously. Fe and Co as the main active metals in FT catalysts are investigated in terms of pore size, crystal size, and crystal phase for obtaining desirable light olefin selectivity. Larger pore size of Fe-based catalysts is suggested to increase olefin selectivity via suppressing 1-olefin readsorption and secondary reactions. Iron carbide as the most probable phase of Fe-based catalysts is proposed for light olefin generation via FTS. Smaller crystal size of Co active metal leads to higher olefin selectivity. Hexagonal close-packed (HCP) structure of Co has higher FTS activity than face-centered cubic (FCC) structure. Transition from Co to Co3C is mainly proposed for formation of light olefins over Co-based catalysts. Moreover, various catalysts’ deactivation routes are reviewed. Additionally, techno-economic assessment of FTS plants in terms of different costs including capital expenditure and minimum fuel selling price are presented based on the most recent literature. Finally, the potential for global environmental impacts associated with FTS plants including atmospheric and toxicological impacts is considered via lifecycle assessment (LCA).

Recent developments in catalyst pretreatment technologies for cobalt based Fisher–Tropsch synthesis

Abstract Stringent environmental regulations and energy insecurity necessitate the development of an integrated process to produce high-quality fuels from renewable resources and to reduce dependency on fossil fuels, in this case Fischer–Tropsch synthesis (FTS). The FT activity and selectivity are significantly influenced by the pretreatment of the catalyst. This article reviews traditional and developing processes for pretreatment of cobalt catalysts with reference to their application in FTS. The activation atmosphere, drying, calcination, reduction conditions and type of support are critical factors that govern the reducibility, dispersion and crystallite size of the active phase. Compared to traditional high temperature H2 activation, both hydrogenation–carbidisation–hydrogenation and reduction–oxidation–reduction pretreatment cycles result in improved metal dispersion and exhibit much higher FTS activity. Cobalt carbide (Co2C) formed by CO treatment has the potential to provide a simpler and more effective way of producing lower olefins, and higher alcohols directly from syngas. Syngas activation or direct synthesis of the metallic cobalt catalyst has the potential to remove the expensive H2 pretreatment procedure, and consequently simplify the pretreatment process, which would make it more economical and thus more attractive to industry.

Evolution of cobalt species in glow discharge plasma prepared CoRu/SiO2 catalysts with enhanced Fischer-Tropsch synthesis performance

Glow discharge plasma was applied to substitute thermal calcination during catalyst preparation. Evolution of cobalt particles in cobalt-ruthenium based catalysts at different stages (fresh prepared, reduced, after Fischer-Tropsch synthesis (FTS) reaction) were studied using a series of characterization techniques. Glow discharge plasma can be developed as an efficient technique to decompose metal salt. Cobalt dispersion was greatly enhanced by glow discharge plasma treatment, and higher initial cobalt dispersion was found on the one with lower treating intensity. However, cobalt crystallites generated by plasma treatment below certain intensity had poor thermal stability, they were tended to aggregate into large particles during reduction and reaction processes, and thus severe deactivations were observed during FTS tests. Besides cobalt sintering, mass transfer limitation at high FTS activity due to the pore plugging by long-chain hydrocarbons was also one of the important reasons for deactivation. The CRS-P140 catalyst with higher plasma treating intensity combined relatively high cobalt dispersion, high cobalt reducibility and relatively stable cobalt distribution during reduction or reaction, showed a high FTS activity with less activity loss.

Fischer-Tropsch reaction on Co-containing microporous and mesoporous Beta zeolite catalysts: the effect of porous size and acidity

• The most active catalyst was Red-Me-CoSiBeta with CO conversion of 91%. • Red-Mi-CoSiBeta was less active than Red-Me-CoSiBeta. • With CO conversion of 71.6% and selectivity towards liquid products of 86.6%. • Red-Mi-CoSiBeta more selective towards isoalkanes than Red-Me-CoSiBeta. • Formation of the bigger cobalt nanoparticles is the key factor of FTS. This work deals with the investigation of the influence of the preparation procedure on the activity of microporous and mesoporous CoBeta zeolite in Fischer – Tropsch synthesis (FTS). The series of CoSiBeta, CoAlSiBeta and CoAlBeta zeolites were prepared by: i) two-step postsynthesis procedure (CoSiBeta with totally dealuminated Beta and CoAlSiBeta with partially dealuminated Beta) and ii) classical wet impregnation (CoAlBeta with undealuminated Beta), respectively. The calcination of as prepared CoSiBeta, CoAlSiBeta and CoAlBeta zeolites at 500 °C, for 3 h in the air and then reduction by treatment in flowing H 2 at 400 °C for 1 h allows to obtain Red-C-CoAlBeta, Red-C-CoAlSiBeta and Red-C-CoSiBeta catalysts with different properties in Fischer – Tropsch reaction. The two-step postsynthesis method allowed obtaining very active, more stable and more resist to carbon deposition catalysts. Two series of zeolite catalysts were prepared using microporous (Mi) and mesoporous (Me) supports. The most active catalysts in Fischer-Tropsch synthesis was Red-Me-CoSiBeta with high CO conversion of 91% and selectivity towards liquid products of 88.9% and Red-Mi-CoSiBeta with CO conversion of 71.6% and selectivity towards liquid products of 86.6%. Such results seem to be related to the formation of the larger cobalt nanoparticles on SiBeta support than on HAlSiBeta and HAlBeta supports. Larger particles exhibit weaker interaction with the support and hence, higher activity in Fischer-Tropsch synthesis. Red-Mi-CoSiBeta zeolite catalyst shows much higher selectivity towards isoalkanes than Red-Me-CoSiBeta with the ratio isoalkanes/n-alkanes of 1.32 for Red-Me-CoSiBeta and of 2.38 for Red-Mi-CoSiBeta.

Tuning interaction between cobalt catalysts and nitrogen dopants in carbon nanospheres to promote Fischer-Tropsch synthesis

N-doped carbon supports are promising to improve reduction degree and dispersion of metal catalysts in Fischer-Tropsch synthesis (FTS). However, it is a great challenge to reasonably construct desired N dopants on FTS catalysts. Herein, we report the high FTS performance of the Co catalysts supported on N-doped carbon nanospheres synthesized by using a facile strategy. Through precisely tailoring the N dopants, we discover that the interaction between cobalt catalysts and supports is significantly strengthened via donation electron function of N atoms, especially for pyrrolic N. It improves the dispersion of cobalt species to generate more electron-enriched cobalt sites, which can strongly adsorb CO and accelerate CO dissociation to C*, resulting in the enhanced catalytic activity. In addition, these in turn increase C* concentration on the surface of the active cobalt sites, which is favorable to form a high concentration of chain initiators CH2 to stimulate carbon-chain growth, inducing the high selectivity towards the C5+ products in FTS. Accordingly, the Co/NCS-500 catalyst with the high content of pyrrolic N presents the high FTS activity and C5+ selectivity. Our work provides a new avenue in rational development of other related heterogeneous catalysis.

Performance of hierarchical ZSM-5 supported cobalt catalyst in the Fischer-Tropsch synthesis

Uniform ZSM-5 nanoparticles (around 180 nm) were synthesized by steam assisted crystallization method (SAC), which have a hierarchically porous structure, composed of abundant open mesopores from the stacking of ZSM-5 particles and micropores in the ZSM-5 crystallites. The hierarchical ZSM-5 supported cobalt catalyst, with a cobalt loading of 15%, was then prepared through incipient impregnation and used in Fischer-Tropsch synthesis (FTS). The hierarchical ZSM-5 support and Co-based catalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 sorption. The results indicate that the hierarchical ZSM-5 supported cobalt catalyst performs excellently in FTS, since the mesoporous structure in the hierarchical ZSM-5 support can enhance the mass transfer of the reaction products and the acid sites on the microporous ZSM-5 framework can promote the hydrocracking of long chain hydrocarbon products. In comparison with the cobalt catalysts supported on bulk ZSM-5 and commercial ZSM-5, the hierarchical ZSM-5 supported cobalt catalyst exhibits much higher activity in FTS, lower selectivity to CH4, and higher selectivity to C5–20 hydrocarbons (68.9%).

Effect of CeO2 promotion on the catalytic performance of Co/ZrO2 catalysts for Fischer–Tropsch synthesis

In this paper, the effect on the physico-chemical properties and catalytic performance of CeO2-modified Co/ZrO2 catalysts were investigated in the Fischer–Tropsch synthesis (FTS) reaction. The CeO2-promoted catalysts with CeO2/ZrO2 ratios of 5wt% and 10wt% (denoted as 5 and 10) were prepared by the sequential incipient wetness method. The catalysts and/or supports were characterized by N2 adsorption-desorption, XRD, TEM, TPR, XPS, and hydrogen chemisorption techniques. The experimental results indicated that an appropriate amount of CeO2 promoter added to Co/ZrO2 catalyst could increase the active sites of the catalysts due to the increase of reducibility and dispersion, thus further lead to a high FTS activity. In the meantime, CeO2 promoter could effectively inhibit water re-oxidation as well as further the aggregation of cobalt metal particles during the reaction. Therefore, CeO2-modified Co/ZrO2 catalysts displayed a better performance against deactivation in the FTS reaction.

Fischer-Tropsch Synthesis over Skeletal Co@HZSM-5 Core-Shell Catalysts

We used skeletal Co as the core to prepare a skeletal Co@HZSM-5 core-shell catalyst by growing an HZSM-5 membrane on skeletal Co via hydrothermal synthesis. The physicochemical properties of the catalyst were determined using elemental analysis, N2 physisorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and NH3 desorption. In gas-phase Fischer-Tropsch synthesis (FTS), the skeletal Co@HZSM-5 core-shell catalyst was more efficient than a physically mixed skeletal Co-HZSM-5 catalyst in cracking long-chain hydrocarbons, giving higher selectivity for C5-C11 gasoline products. The thickness of the zeolite shell on the skeletal Co@HZSM-5 core-shell catalyst was easily tuned by adjusting the hydrothermal time. At a suitable zeolite shell thickness, the long-chain hydrocarbons were cracked completely, with high FTS activity, leading to high selectivity for the gasoline fraction. Increasing the reaction temperature resulted in higher

CO Activation Pathways of Fischer–Tropsch Synthesis on χ-Fe5C2 (510): Direct versus Hydrogen-Assisted CO Dissociation

Iron carbides, especially χ-Fe5C2, among the active iron species in Fischer–Tropsch synthesis (FTS), are considered to be responsible for high FTS activity. CO activation pathways as the initial steps of FTS over χ-Fe5C2 were explored by spin-polarized density functional theory calculations. Surface energies of χ-Fe5C2 facets observed from the XRD patterns were first calculated, and then the corresponding equilibrium χ-Fe5C2 shape was obtained by Wulff construction. The thermodynamically stable (510) surface was predicted to have the largest percentage among the exposed crystal facets. Subsequently, the adsorption properties of CO on χ-Fe5C2 (510) were studied. Despite exhibiting lower binding energy than that at the 3F-4 site as the most stable configuration, CO adsorption at the 4F-1 site led to significant weakening of the C–O bond from both the structural and electronic properties’ points of view. Furthermore, two kinds of CO activation mechanisms (i.e., the direct and H-assisted CO dissociation) and ...

High performance structured platelet milli-reactor filled with supported cobalt open cell SiC foam catalyst for the Fischer–Tropsch synthesis

The Fischer–Tropsch synthesis (FTS) was evaluated on a 30wt.% Co catalyst promoted with 0.1wt.% of Ru supported on a silicon carbide (SiC) foam in a platelet structured milli-reactor (PSR). The FTS was tested under isothermal conditions according to the Mear’s criterion. The tuneable morphology of the open cell foam (cell size, macroscopic porosity, strut diameter) allows an adjustment of both axial and radial flow patterns in the reactor and ensures local fluid recirculation, which are favorable to heat and mass transfer. The large pore size, i.e. meso- and macro-pores of the support allows a rapid escaping of the liquid products leading to a high FTS activity as well a good C5+ selectivity. The catalytic results obtained in the platelet milli-reactor were compared with those obtained in a ‘conventional’ packed bed tubular reactor (TR). The PSR shows a better FTS activity compared to that obtained in the TR and the FTS activity steadily increases with increasing the GHSV. Finally, a remarkably high C5+ selectivity (∼93%) and a negligible amount of methane formation (∼1%) were also obtained at a GHSV of 1900h−1 in the PSR.

Performance of silica-nanotube-supported ruthenium catalysts for Fischer-Tropsch synthesis

Silica nanotubes (SNTs) were synthesized with carbon nanotubes (CNTs) as the template and used as the support to prepare ruthenium-based catalyst by slurry impregnation method. The catalyst was characterized by N 2 physisorption, XRD, H 2-TPR and TEM; its performance in Fischer-Tropsch synthesis (FTS) was evaluated in a fixed-bed reactor at 503 K and 1.0 MPa and compared with that of SiO 2-supported ruthenium catalyst (Ru/SiO 2). The results indicated that ruthenium oxides can be completely reduced at 623 K by H 2. For the SNT-supported ruthenium catalyst (Ru/SNT), the ruthenium particles are mainly located inside the nanotubes and are still well dispersed on SNTs after H 2 reduction. Compared with Ru/SiO 2, the Ru/SNT catalyst exhibits higher activity in FTS because of the higher dispersion of ruthenium particles in SNTs.

Activation pressure studies with an iron-based catalyst for slurry Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) was carried out with an industrial iron-based catalyst (100Fe/5Cu/6K/16SiO 2, by weight) under the baseline conditions in a stirred tank slurry reactor (STSR). The effects of activation pressure on the catalyst activity and selectivity were investigated. It was found that iron phase compositions, textural properties, and FTS performances of the catalysts were strongly dependent on activation pressure. The high activation pressure retards the carburization. Møssbauer effect spectroscopy (MES) results indicated that the contents of the iron carbides clearly decrease with the increase of activation pressure, especially for the activation pressure increasing from 1.0 MPa to 1.5 MPa, and the reverse trend is observed for superparamagnetic Fe 3+ (spm). The higher content of Fe 3+ (spm) results in the higher amount of CO 2 in tail gas when the catalyst is reduced at higher pressure. The catalyst activity decreases with the increase of activation pressure. The high quantity of iron carbides is necessary to obtain high FTS activity. However, the activity of the catalyst activated in syngas can not be predicted solely from the fraction of the carbides. It is concluded that activation with syngas at the lower pressure would be the most desirable for the better activity and stability on the iron-based catalyst.

Effect of Confinement in Carbon Nanotubes on the Activity of Fischer−Tropsch Iron Catalyst

Following our previous findings that confinement within carbon nanotubes (CNTs) can modify the redox properties of encapsulated iron oxides, we demonstrate here how this can affect the catalytic reactivity of iron catalysts in Fischer-Tropsch synthesis (FTS). The investigation, using in situ XRD under conditions close to the reaction conditions, reveals that the distribution of iron carbide and oxide phases is modulated in the CNT-confined system. The iron species encapsulated inside CNTs prefer to exist in a more reduced state, tending to form more iron carbides under the reaction conditions, which have been recognized to be essential to obtain high FTS activity. The relative ratio of the integral XRD peaks of iron carbide (Fe(x)C(y)) to oxide (FeO) is about 4.7 for the encapsulated iron catalyst in comparison to 2.4 for the iron catalyst dispersed on the outer walls of CNTs under the same conditions. This causes a remarkable modification of the catalytic performance. The yield of C5+ hydrocarbons over the encapsulated iron catalyst is twice that over iron catalyst outside CNTs and more than 6 times that over activated-carbon-supported iron catalyst. The catalytic activity enhancement is attributed to the effect of confinement of the iron catalyst within the CNT channels. As demonstrated by temperature-programmed reduction in H2 and in CO atmospheres, the reducibility of the iron species is significantly improved when they are confined. The ability to modify the redox properties via confinement in CNTs is expected to be of significance for many catalytic reactions, which are highly dependent on the redox state of the active components. Furthermore, diffusion and aggregation of the iron species through the reduction and reaction have been observed, but these are retarded inside CNTs due to the spatial restriction of the channels.

Preparation of highly active catalysts for ultra-clean fuels

Novel preparation methods with chelating agents for Co/SiO 2 Fischer–Tropsch synthesis (FTS) catalysts were developed in the present study. The preparation with chelating agents such as nitrilotriacetic acid (NTA) or trans-1,2-diaminocyclohexane- N, N, N′, N′-tetra-acetic acid (CyDTA) greatly improved the FTS activity of Co/SiO 2 catalyst. The surface structures of the reduced and calcined catalysts were also investigated by means of various characterization techniques. Based on these results, it was suggested that the control of the interaction between Co 2+, chelating agents and SiO 2 surface was crucial to the preparation of Co/SiO 2 catalyst with higher FTS activity.

Effects of SiO 2 and Al 2O 3 on performances of iron-basedcatalysts for slurry Fischer–Tropsch synthesis

Two spherical iron-based catalysts (Fe/Cu/K/SiO 2 and Fe/Cu/K/Al 2O 3) were prepared by the combination of coprecipitation and spray drying method for the application of slurry Fischer–Tropsch synthesis (FTS). The effects of SiO 2 and Al 2O 3 on the reduction and the carburization behaviors of iron-based catalysts were studied using temperature-programmed desorption (TPD) in H 2 and CO, isothermal reduction in syngas, and Mössbauer-effect spectroscopy (MES). The results indicate that SiO 2 suppresses the H 2 adsorption, facilitates the CO adsorption, and the carburization as compared with Al 2O 3. The FTS performances of the catalysts were evaluated in a slurry reactor under the industrial relevant reaction conditions of 260°C, 1.5 MPa, H 2/CO = 0.67, and a space velocity of 2000 h −1. This indicates that SiO 2-supported catalyst has higher FTS activity, higher water-gas shift reaction (WGS) reactivity, and higher selectivities to heavy hydrocarbons. Furthermore, the run stability of Al 2O 3 supported, iron-based catalyst is better than SiO 2 supported catalyst.

Effect of reduction temperature on a spray-dried iron-based catalyst for slurry Fischer–Tropsch synthesis

An industrial iron-based catalyst (100Fe/5Cu/6K/16SiO 2, by weight) was characterized after reduction at different temperatures and after Fischer–Tropsch synthesis (FTS) in a stirred tank slurry reactor (STSR). The BET surface area and pore volume of the catalyst decreases with increasing reduction temperature, and the contrary trend was found for pore size. The iron phase compositions of catalysts reduced with syngas were strongly dependent on pretreatment conditions employed. Pretreatment with syngas at lower temperature prevents iron catalyst activation. Carburization was intensified with the increase in reduction temperature. The formation of iron carbides in reduced catalyst was necessary for obtaining stable high FTS activity. The relationship between the amount of CO 2 in tail gas during activation and the Fe 3+ (spm) content in the reduced catalyst was observed. The rapid carburization at high reduction temperature resulted in the formation of a superparamagnetic Fe 3+ core and an iron carbide layer of the reduced catalyst. FTS activity decreased with the increase in the reduction temperature, but the stability distinctly improved. It was found that the working catalyst loss in the heavier waxy products resulted in higher deactivation rate of the catalyst reduced at lower temperature. With the increase in the reduction temperature, the product distribution shifted towards the lower molecular weight products.

A highly active and stable Fe-Mn catalyst for slurry Fischer–Tropsch synthesis

A highly stable and active Fe-Mn catalyst for slurry Fischer–Tropsch synthesis (FTS) was prepared and scaled up for the application in the industrial pilot plant at Institute of Coal Chemistry (ICC), Chinese Academy of Sciences (CAS). One Lab-scale catalyst and one scaled-up catalyst are introduced in the present paper. The particle size of the Lab-scale catalyst is about 5–15 μm, while it is increased to 30–90 μm for the scaled-up catalyst. Simultaneously, the morphology of the catalyst was greatly improved after the catalyst being scaled up. Both the Lab-scale and scale-up catalysts show high FTS activity. CO conversion of the Lab-scale catalyst and the scaled-up one are over 70.0% (H 2/CO = 0.67, 275 °C, 1.5 MPa and 3000 h −1) and 55.0% (H 2/CO = 0.67, 260 °C, 1.5 MPa and 2000 h −1), respectively. The catalysts also possess excellent stability, no obvious deactivation was observed during stable run of 4200 h and 1200 h on stream for the two catalysts. However, the Lab-scale catalyst produced more methane (about 8–10 wt%) and C 2–4 (22–30 wt%) and less C5 + hydrocarbon (55–70 wt%). Meanwhile, the hydrocarbon distribution of the catalyst was greatly improved for after the catalyst being scaled up, and the distribution of hydrocarbon products become much preferable. The selectivity to methane was well controlled at about 5 wt%, and the sum of C 2 − 4 and C 5 + was increased to 91–93 wt%. On the whole, the scaled-up catalyst satisfies the requirements of the application for FTS in the industrial pilot plant of slurry bubble column reactor (SBCR) at ICC, CAS.

Activation Study of Precipitated Iron Fischer−Tropsch Catalysts

Slurry phase Fischer−Tropsch synthesis (FTS) was conducted with two precipitated iron catalysts (100 Fe/3.6 Si/0.71 K and 100 Fe/4.4 Si/1.0 K, atomic percent relative to Fe) at 543 K, 1.31 MPa, and a synthesis gas (H2/CO = 0.7) space velocity of 3.1 normal L h-1 (g of Fe)-1. The impact of activation gas (CO, H2/CO = 0.7, or H2/CO = 0.1), temperature (543 or 573 K), and pressure (1.31 or 0.10 MPa) on the long-term (>500 h) activity and selectivity of the catalysts was explored. Pretreatment with CO under the conditions employed gave highly active and stable catalysts. Catalyst performance when synthesis gas activation was used was found to be dependent upon the partial pressure of hydrogen in the activating gas, with low hydrogen partial pressures resulting in the highest catalyst activity. X-ray diffraction results indicate that carbon monoxide activations and synthesis gas activations with low hydrogen partial pressure result in the formation of the carbides χ-Fe5C2 and ε‘-Fe2.2C, while activation with synthesis gas with high hydrogen partial pressure results in the formation of only Fe3O4. It was found that treating the 100 Fe/3.6 Si/0.71 K catalyst activated with synthesis gas at 1.31 MPa and 543 K with carbon monoxide caused the activity to increase dramatically and the Fe3O4 to be partially converted to iron carbides. It is concluded that Fe3O4 is relatively inactive for FTS, while the presence of some bulk iron carbide is necessary for high FTS activity to be achieved.