Fischer-Tropsch Synthesis Activity Research Articles

Construction of three-dimensional nitrogen-doped graphene aerogel (NGA) supported cobalt catalysts for Fischer-Tropsch synthesis

Abstract Co/NGA catalysts were one-step hydrothermal synthesized during the construction of three-dimensional nitrogen-doped graphene aerogel (NGA). The structure and properties of the catalysts were characterized by TGA, Raman, FTIR, XRD,TEM, SEM, XPS and H2-TPR, and their catalytic performance was tested by Fischer-Tropsch synthesis (FTS) reaction. Characterization and reaction results showed that higher cobalt dispersion was found on the catalyst with higher cobalt loading, and majority of cobalt species in the freeze-dried samples was fcc phase Co°. Excessive cross linking originated by high Co2+ concentration during the construction of 3D NGA led to the restraint of mass transfer of reactants to cobalt active sites, and therefore, lower FTS activity was observed on the catalysts with higher cobalt loadings. The fcc phase Co° in fresh Co/NGA catalysts was transformed in to hcp phase Co° during FTS reaction, and as a result, catalytic activity was increased with increasing time on stream.

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.

Plasma Assisted Preparation of CoPt/SiO2 Fischer‐Tropsch Catalysts: A Comparison of the Precursor Pre‐Thermal Treated Temperatures

AbstractA series of amorphous silica supported Co‐based catalysts were prepared using traditional incipient wetness impregnation methods followed by thermal treatment at different temperatures. Glow discharge plasma effects on cobalt species in the forms of cobalt nitrate, mixture of cobalt nitrate and Co3O4, and pure Co3O4 were compared and investigated by various characterizations and Fischer‐Tropsch synthesis (FTS) tests. Plasma enhancing metal dispersion effect was mostly happened during the decomposition of cobalt nitrate in plasma field; when cobalt species was already in the form of Co3O4, no apparent particle size change by plasma treatment was observed. Under the promotion of Pt, all the catalysts maintained at high reduction degree, thus the cobalt dispersion was almost linearly related to the number of active sites. The CoSi‐100D+P catalyst with both high cobalt dispersion and high cobalt reducibility, had the maximum number of active sites, and presented the highest FTS activity. Meanwhile, the product selectivity could also be affected by plasma treatment, hydrocarbons were shifted to lower carbon numbers. This effect could be observed even on the CoSi‐400C+P sample, in which the precursor was pre‐thermal treated at high temperature (400 °C), and cobalt species was already all transformed into Co3O4.

Intrinsic Kinetics of Fischer–Tropsch Synthesis over Co/CNTs Catalysts: Effects of Support Interaction

The activities of cobalt catalysts prepared by the microemulsion impregnation method on carbon nanotubes (CNTs) and functionalised carbon nanotubes (FCNTs) supports were evaluated in the Fischer–Tropsch synthesis (FTS). The catalysts were characterised by transmission electron microscopy, X-ray diffraction and Brunauer–Emmett–Teller surface area methods. The results show that the cobalt particles in the FCNTs support are mostly located inside the tubes of the CNTs and show a narrower particle size distribution. The experimental results show that the cobalt catalyst supported on FCNTs leads to a higher CO conversion and FTS activity compared to that supported on normal CNTs. Calculated kinetic results show that the activation energies fall within the narrow range of 101.1–107.1 kJ mol−1 and the heat of hydrogen adsorption was calculated to be −40.2 and −26.2 kJ mol−1 for Co/CNTs and Co/FCNTs catalysts respectively. FCNTs, as a catalyst support of Co nanoparticles, maintain high dispersion which can be attributed to a hydrogen spillover effect of functional groups on the CNT surface.

Fischer–Tropsch Synthesis over Cobalt/CNTs Catalysts: Functionalized Support and Catalyst Preparation Effect on Activity and Kinetic Parameters

The effect of carbon nanotubes (CNTs) functionalization as a support on cobalt catalyst activity in Fischer–Tropsch synthesis (FTS) was investigated. The CNTs functionalized with hydrogen peroxide and sonicated via a pulsing method with different pulse time. The cobalt catalysts synthesized by the impregnation method. Confinement of concise Co particle inside the functionalized CNTs at a shorter time of sonication (Co/FCNTs-10 with 10-s pulses of sonication) was confirmed by TEM analysis. The Co/FCNTs-10 catalyst show higher FTS activity than nonsonicated Co/CNTs and Co/FCNTs-20 with 20-s pulses of sonication. The activation energies obtained through the kinetic results for FTS reaction over Co/FCNTs-10, Co/FCNTs-20, and Co/CNTs are 92.1, 98.8, and 102.7 kJ/mol. The heat of hydrogen adsorption is calculated −40.8, −34.2, and −21.4 (kJ/mol) for Co/CNTs, Co/FCNTs-20 and Co/FCNTs-10 catalysts, respectively. Co/FCNTs-10 catalyst shows higher hydrogen spillover than nonsonicated Co/CNTs catalyst.

Effects of ordered mesoporous bimodal structures of Fe/KIT-6 for CO hydrogenation activity to hydrocarbons

Highly ordered mesoporous bimodal structures of KIT-6 with average pore diameters of 3.6 and 5.4 nm originated from its different wall thickness were newly synthesized and applied for CO hydrogenation to hydrocarbons through Fischer-Tropsch Synthesis (FTS) reaction using the supported iron nanoparticles. The ordered bimodal mesopore structures of the KIT-6 with smaller than 5.4 nm in size showed a significantly enhanced FTS activity by selectively forming heterogeneous bimodal crystallite size distributions of iron nanoparticles. The positive effects of the mesoporous bimodal structures of the KIT-6 were mainly attributed to the facile formation of the spatially confined smaller iron nanoparticles, which can be strongly interacted with the structurally stable ordered mesoporous KIT-6 with the co-presence of the larger iron nanoparticles on the outer surfaces of the mesoporous bimodal KIT-6. After adding small amount of potassium promoter with 2 wt%K on the mesoporous bimodal Fe/KIT-6, a slight increase of CO conversion as well as C5+ selectivity with less extent of CO2 formation was observed due to the suppressed activity of water-gas shift reaction. However, the structurally unstable monomodal KIT-6 having a relatively larger mesopore above 7.3 nm showed a lower FTS activity by preferentially forming an inactive amorphous carbon species. A superior FTS activity on the ordered mesoporous bimodal Fe/KIT-6 was attributed to the easy formations of smaller iron carbides, where the active smaller iron carbides were strongly interacted and spatially confined inside of the highly ordered mesoporous bimodal KIT-6 surfaces.

Water as key to activity and selectivity in Co Fischer-Tropsch synthesis: γ-alumina based structure-performance relationships

Thirteen γ-alumina supports with different pore sizes and pore size distributions have been impregnated with cobalt and rhenium. The catalysts were tested for Fischer-Tropsch synthesis (FTS) under dry and enhanced water vapor pressure conditions. It is shown that there is a positive correlation between pore size and cobalt crystallite size of the reduced catalyst after incipient wetness impregnation as long as the pore size distribution is sufficiently narrow. There is a concurrent increase in C5+ with pore diameter due to higher chain propagation probabilities α3+. Higher α values are ascribed to larger cobalt crystallites that promote CO activation resulting in higher surface coverage of CHx monomers. Adding water vapor to the syngas feed has a strong positive effect on selectivity to higher hydrocarbons and activity. Water imposes a significant enhancement of α1 that is attributed to higher relative cobalt surface coverage of H2O(OH−) and CHx relative to hydrogen. Small pores are susceptible to condensation of water during FTS.

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.

Relationship between Iron Carbide Phases (ε-Fe2C, Fe7C3, and χ-Fe5C2) and Catalytic Performances of Fe/SiO2 Fischer–Tropsch Catalysts

The influence of different iron carbides on the activity and selectivity of iron-based Fischer–Tropsch catalysts has been studied. Different iron carbide phases are obtained by the pretreatment of a binary Fe/SiO2 model catalyst (prepared by coprecipitation method) to different gas atmospheres (syngas, CO, or H2). The phase structures, compositions, and particle sizes of the catalysts are characterized systematically by XRD, XAFS, MES, and TEM. It is found that in the syngas-treated catalyst only χ-Fe5C2 carbide is formed. In the CO-treated catalyst, Fe7C3 and χ-Fe5C2 with a bimodal particle size distribution are formed, while the H2-treated catalyst exhibits the bimodal size distributed e-Fe2C and χ-Fe5C2 after a Fischer–Tropsch synthesis (FTS) reaction. The intrinsic FTS activity is calculated and assigned to each corresponding iron carbide based on the phase composition and the particle size. It is identified that Fe7C3 has the highest intrinsic activity (TOF = 4.59 × 10–2 s–1) among the three candidat...

Nitrogen-rich mesoporous carbon supported iron catalyst with superior activity for Fischer-Tropsch synthesis

Superior iron-based Fischer-Tropsch synthesis (FTS) catalysts (Fe/NMCs) were developed by impregnating high amount of iron (40 wt%) over nitrogen-rich mesoporous carbons (NMCs) with high porosities. The large pore volumes and specific surface areas of NMCs realized the high loadings and proper dispersions of iron while the nitrogen-containing groups enhanced the basicities of the catalysts. Weak metal-support interactions were observed in Fe/NMCs, which improved the reduction, carburization of iron, and further the FTS activities. FTS tests indicated a medium amount of nitrogen (≤8.3 wt%) did not show obvious effect on the activity of the catalyst, but a much higher amount of nitrogen (≥16.5 wt%) could result in a significant decrease of activity. Nitrogen-containing groups could effectively suppress the methane selectivity and improve the lower olefins selectivity in the FTS reaction. The hydrocarbon productivity of the Fe/NMCs was up to 0.62 g HC/(h·g cat.) at 260 °C, 1 MPa, and H2/CO ratio of 1, much higher than that of any other iron catalyst reported under similar conditions. As a result of the superior performance, Fe/NMCs could be one of ideal candidates for iron-based FTS catalysts in the future.

Effect of strain on the performance of iron-based catalyst in Fischer-Tropsch synthesis

The role of strain on metal catalysis has been widely investigated by theoretical calculations. It is hard to prove by direct experimental strategies. In this work, we show how the strain can be adjusted experimentally to modulate Fischer-Tropsch synthesis (FTS) activity. The strain value is derived from the X-ray diffraction (XRD) line broadening method. The d-band occupancy (nd) is calculated semi-quantitatively by magnetic characterization on a vibrating sample magnetometer (VSM). A volcano curve is correlated between strain and FTS activity. The combination of physical property such as mechanics, magnetization, hardness and density functional theory (DFT) calculations is proposed to elucidate a general strain induced reactivity behavior. Such a strain dependent behavior is related to the variation in d-band electronic property of the metal.

Effect of graphitic carbon modification on the catalytic performance of Fe@SiO2-GC catalysts for forming lower olefins via Fischer-Tropsch synthesis

Mesoporous silica-encapsulated iron materials contribute to the suppression of self-aggregation and thereby enhances the Fischer-Tropsch synthesis activity. However, constructing Fe-based supported catalysts with high activity and selectivity in the Fischer-Tropsch synthesis to lower olefins (FTO) by a conventional mesoporous silica support has been proven challenging due to its low hydrothermal stability and low reducibility. Herein, we developed a core-shell Fe@SiO2-GC structure with an optimized interface of the catalyst by introducing graphitic carbon (GC) that weakened the Fe-SiO2 interaction. Transmission electron microscopy and nitrogen adsorption-desorption characterization proved GC-modified catalysts had well-defined core-shell structures. The Fe@SiO2-GC-2 containing the optimal GC content had the largest surface area and pore volume, and outperformed Fe2O3@SiO2 in terms of CO conversion (60.1%) and C2-C4 olefin selectivity (40.7%) within 100 h. The significant improvement of FTO performance was attributed to the rigid porous framework of GC, which allowed free access of syngas and inhibited mesoporous channel collapse during FTO, so the catalytic activity and stability were improved by the synergism between higher Fe dispersion and reducibility. Moreover, the narrow well-defined mesoporous channel also exerted a modest spatial restriction effect, which inhibited the formation of long-chain hydrocarbon and tailored the product distribution toward lower distillate, thus improving the selectivity toward C2-C4.

Assembly and activation of supported cobalt nanocrystal catalysts for the Fischer-Tropsch synthesis.

The effect of oxidative treatments on the depostion of cobalt nanocrystals (Co-NC) onto a support and subsequent ligand removal was investigated. Deposition of ε-cobalt NC led to extensive clustering of NC and low Fischer-Tropsch synthesis activity. Low-temperature oxidation of ε-cobalt NC resulted in a very uniform CoO-NC distribution and high activity whereas high-temperature oxidation to Co3O4 led to less uniform NC distributions and lower activity.

Efficient utilization of bimetallic catalyst in low $$\hbox {H}_{2}/\hbox {CO}$$ H 2 / CO environment syngas for liquid fuel production

Application of Fischer-Tropsch synthesis (FTS) in the utilization of low $$\hbox {H}_{2}/\hbox {CO}$$ ratio (0.5–1.5) gas obtained from coal and biomass gasification can be done by selecting a catalyst system active for both FTS and WGS reaction. The enhancement of $$\hbox {H}_{2}$$ content depends on the extent of water gas shift (WGS) reaction and can be quantified by measuring usage ratio define as a mole of $$\hbox {H}_{2}$$ to CO converted. With an attempt to utilize low $$\hbox {H}_{2}/\hbox {CO}$$ ratio syngas bimetallic $$(\hbox {Fe}/\hbox {Co}/\hbox {SiO}_{2})$$ were prepared and compared with monometallic ( $$\hbox {Fe}/\hbox {SiO}_{2}$$ and $$\hbox {Co}/\hbox {SiO}_{2}$$ ) catalysts. The catalysts were tested in fixed bed reactor at industrial relevant FTS conditions (T: $$220{-}260\,^{\circ }\hbox {C}$$ , P: 2.0 MPa, GHSV-1.2 SL/gcat-h, $$\hbox {H}_{2}/\hbox {CO}$$ : 1–1.5). The incorporation of Fe-Co bimetallic catalyst facilitates both FT and WGS reaction because of the presence of iron and cobalt phases. Compared to monometallic catalyst there is a significant increase in CO conversion over the bimetallic catalyst. Also, the yield of $$\hbox {C}_{5+}$$ was significantly higher over bimetallic catalyst compared to iron catalyst, where olefin was the major product. Selected catalyst $$(\hbox {Fe}/\hbox {Co}/\hbox {SiO}_{2})$$ was tested for their activity toward WGS reaction. Effects of temperature, pressure, and feed composition on WGS reaction over bimetallic catalyst were studied. Lower value usage ratio (1.62 and 1.58) reveals the occurrence WGS reaction Fe-Co bimetallic catalyst at 240 $$^{\circ }\hbox {C}$$ and 260 $$^{\circ }\hbox {C}$$ . At 240 $$^{\circ }\hbox {C}$$ , 72% CO conversion, and 60% $$\hbox {C}_{5+}$$ selectivity show that the catalyst efficiently utilizes the increased $$\hbox {H}_{2}/\hbox {CO}$$ ratio in the production of liquid hydrocarbon. Synopsis: A novel Fe-Co catalyst combination has been optimised for the conversion of biomass derived syngas, having low $$\hbox {H}_{2}/\hbox {CO}$$ ratio (1– 1.5mol/mol). The addition of iron onto silica supported cobalt catalyst facilitates the WGS reaction activity for higher $$\hbox {H}_{2}/\hbox {CO}$$ ratio internally and thus improves FTS activity. $$\hbox {10Fe}/\hbox {20Co}/\hbox {SiO}_{2}$$ catalyst resulted optimum WGS and FTS activity with 72% CO conversion, and 60% $$\hbox {C}_{5+}$$ selectivity.

Efficient diesel production over the iron-based Fischer–Tropsch catalyst supported on CNTs treated by urea/NaOH

Due to the complex control of nitrogen (N) species in functionalizing the carbon nanotubes (CNTs), the contribution of N species to catalysis is difficult to understand. In this study, we report a facile one-pot approach for the synthesis of N-doped CNTs with N present only in the pyrrolic form using a hydrothermal method and by tailoring the treatment conditions, the N content could reach 2.3at.%. Then the N-doped CNTs are used as a support to prepare an iron-based Fischer–Tropsch synthesis (FTS) catalyst. The FTS activity and C5+ selectivity of N-doped CNTs supported iron catalyst increases with an increase of N content up to 2.1% but it decreases with higher pyrrolic N content. The enhanced FTS catalytic performance is attributed to increased electron conduction, electron donor effect and improved surface basicity due to the pyrrolic N incorporated into the carbon framework. Furthermore, a urea/NaOH co-treatment of CNTs is conducted and the treated CNTs is used as a support for preparing an iron catalyst. The results indicate that the synergistic modification effect of NaOH and urea effectively functionalizes the CNTs and leads to the incorporation of the pyrrolic N, to a high graphitization degree, to easy reduction, to a structural integrity and to a strong metal-support interaction of the supported iron catalyst. This results in an increased FTS activity, superior stability and remarkable diesel selectivity (52%). This synergistic effect shows the potential applications of carbon materials in the field of energy storage, carbon dioxide capture and catalysis, with appropriate functionalization.

Auto‐Reduction Behavior of Cobalt on Graphitic Carbon Nitride Coated Alumina Supports for Fischer–Tropsch Synthesis

AbstractGraphitic carbon nitride (g‐C3N4)‐coated alumina (CN‐Al) is investigated as a support material for a cobalt‐based Fischer–Tropsch synthesis (FTS) catalyst. The g‐C3N4 blocks the interaction between cobalt and alumina to hinder the formation of irreducible cobalt oxide species, and improves the dispersion of metallic cobalt species on the CN‐Al support. Furthermore, the coated g‐C3N4 is decomposed during the pre‐annealing process even under inert conditions to evolve reductive carbon monoxide gas that directly reduces the cobalt oxide species to metallic cobalt. Hence, the catalyst can be activated without typical hydrogen pretreatment. Moreover, reduction promotion by expensive noble metals such as Pt is not needed either. Because of the improved dispersion and reducibility of the cobalt species on the CN‐Al support, the catalytic FTS activity of Co/CN‐Al is higher compared with the conventional Co/Al2O3 catalyst.

Influence of oxalate ligand functionalization on Co/ZSM-5 activity in Fischer Tropsch synthesis and hydrodeoxygenation of oleic acid into hydrocarbon fuels

Achieving high degree of active metal dispersions at the highest possible metal loading and high reducibility of the metal remains a challenge in Fischer Tropsch synthesis (FTS) as well as in hydrogeoxygenation (HDO).This study therefore reports the influence of oxalic acid (OxA) functionalization on the metal dispersion, reducibility and activity of Co supported ZSM-5 catalyst in FTS and HDO of oleic acid into paraffin biofuel. The Brunauer–Emmett–Teller (BET) results showed that cobalt oxalate supported ZSM-5 catalyst (CoOx/ZSM-5) synthesized from the incorporation of freshly prepared cobalt oxalate complex into ZSM-5 displayed increase in surface area, pore volume and average pore size while the nonfunctionalized cobalt supported on ZSM-5 (Co/ZSM-5) catalyst showed reduction in those properties. Furthermore, both XRD and XPS confirmed the presence of Co° formed from the decomposition of CoOx during calcination of CoOx/ZSM-5 under inert atmosphere. The HRTEM showed that Co species average particle sizes were smaller in CoOx/ZSM-5 than in Co/ZSM-5, and in addition, CoOx/ZSM-5 shows a clear higher degree of active metal dispersion. The FTS result showed that at CO conversion over Co/ZSM-5 and CoOx/ZSM-5 catalysts were 74.28% and 94.23% and their selectivity to C5+ HC production were 63.15% and 75.4%, respectively at 4 h TOS. The HDO result also showed that the CoOx/ZSM-5 has higher OA conversion of 92% compared to 59% over Co/ZSM-5. In addition CoOx/ZSM-5 showed higher HDO and isomerization activities compared to Co/ZSM-5.

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%).

Uniformity dispersive, anti-coking core@double-shell-structured Co@SiO2@C: Effect of graphitic carbon modified interior pore-walls on C5+ selectivity in Fischer-Tropsch synthesis

Highly dispersed Co nanoparticles with proper interaction with mesoporous support are benefit for the suppression of self-aggregation, which enhances its Fischer-Tropsch synthesis (FTs) activity. However, construct such Co based supported catalysts with high activity and stability in FTs by conventional mesoporous support, especially the common used mesoporous SiO2, has proven challenging due to their undesirable hydrothermal stability and poor reducibility. Herein, we developed a unique core@double-shell Co@SiO2@C structure with optimized interface of the mesoporous catalyst by introducing graphitic carbon layer which can weaken the interaction between metallic Co and silica. Transmission electron microscopy (TEM) images, together with Nitrogen adsorption-desorption characterization result, proved the well-defined core@double-shell structure of graphitic carbon modified catalyst. The Co@SiO2@C-2 material produced after optimizing the calcination temperature to 600°C process large surface area and pore volume, and show higher CO conversion (62.2%) and C5+ selectivity (62.2%) than Co3O4@SiO2 in a period of 100h. The significant improvement in the FTS performance of Co@SiO2@C is not only attributed to a good synergistic effect by a combination of the Co dispersion and reducibility. The unique core@double-shell structure with graphitic carbon modified interior pore-walls also contributes to the formation of heavy hydrocarbon, as well as the protecting with the metallic Co particles away from oxidation and aggregation.

Carbon Nanotubes–MnOx Nanocomposite as Support for Iron‐Based Catalysts for the Fischer–Tropsch Synthesis of Liquid Fuels

AbstractA facile one‐pot hydrothermal method is developed to synthesize a series of carbon nanotubes–manganese oxide nanocomposites (CNTs–MnOx) with different morphologies and Mn valence states. These nanocomposite materials are then utilized as catalyst supports in iron‐based Fischer–Tropsch synthesis (FTS) for the production of liquid fuels. Experimental results indicate that Fe/CNTs‐K‐190 (iron catalyst supported on the CNTs treated with KMnO4 at 190 °C) and Fe/CNTs‐KU‐190 (iron catalyst supported on the CNTs treated with KMnO4 and urea at 190 °C) display higher FTS activity than the Fe/CNTs‐K‐110 (iron catalyst supported on CNTs treated with KMnO4 at 110 °C) and Fe/CNTs‐KU‐110 (iron catalyst supported on CNTs treated with KMnO4 and urea at 110 °C). This might be due to the weak metal–support interaction and high MnO content, and the poorer stability than Fe/CNTs‐K‐110 and Fe/CNTs‐KU‐110 catalysts with nanosheet morphology might be related to the structural collapse of the nanocubes or nanorods due to MnO evolution during the FTS process. The CNTs–MnOx nanocomposite‐supported iron FTS catalysts in particular display unparalleled high C5+ selectivity (over 90 %) and very low CH4 selectivity (below 4.6 %). The unique CNTs–MnOx nanocomposites may open a new window for the understanding, design, synthesis, and optimization of iron catalysts toward high‐efficiency transport fuel production.