Fischer-Tropsch Synthesis Activity Research Articles

Ruthenium Modification on Mn and Zr-Modified Co/SiO2 Catalysts for Slurry-Phase Fischer-Tropsch Synthesis

The addition of Ru to Mn and Zr-modified Co/SiO2 catalysts, while applying different preparation orders and loading amounts, was investigated as a means of enhancing the Fischer-Tropsch synthesis reaction. The coimpregnation of Zr/SiO2 with Co, Mn and Ru gave the most attractive catalytic properties. This can be attributed to the higher dispersion of Co metal resulting from the coimpregnation of Co and Mn as well as enhanced reducibility due to the presence of Ru. The addition of a moderate amount of Ru together with the appropriate order of addition affected both the Co reducibility and the catalytic activity, primarily because of increased reducibility. The addition of even 0.1 wt.% Ru resulted in an obvious enhancement of Fischer-Tropsch synthesis activity.

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

The characterization of micro-structure of cobalt on γ-Al2O3 for FTS: Effects of pretreatment on Ru–Co/γ-Al2O3

Ruthenium-promoted γ-Al2O3-supported cobalt catalysts were prepared by different slurry impregnation methods and calcined in a hydrogen/air atmosphere. The prepared catalysts were well characterized by N2 physisorption, TPR, XRD, TEM and XPS techniques. The addition of Ru caused the reduction peaks to shift towards lower temperatures due to the spillover of hydrogen from the Ru species. The ruthenium-promoted catalyst calcined under a hydrogen atmosphere leads to metallic cobalt with an HCP structure and shows good catalytic activity for Fischer Tropsch Synthesis under the reaction conditions studied. The catalyst calcined under an air atmosphere leads to metallic cobalt with FCC structures and showed lower catalytic activity. It was also found that the calcination atmosphere and structure of the catalyst have a profound effect on the activity and selectivity for FT synthesis.

Microstructure of FTS studies over spherical Co/γ-Al2O3

Cobalt supported alumina catalysts were prepared by slurry impregnation method and calcined the catalysts in different atmosphere. The prepared catalysts were characterized by N2 physisorption, TPR, XRD, TEM, FT-IR and XPS techniques. The catalyst calcined under hydrogen atmosphere leads to the metallic cobalt of HCP structure and shows the good catalytic activity for Fischer–Tropsch synthesis under the reaction condition.The catalyst calcined under air atmosphere led to the metallic cobalt of FCC structures and shows lower catalytic activity. It was also found that calcination atmosphere and structure of the catalyst have profound effect on the activity and selectivity for Fischer Tropsch synthesis.

Fischer–Tropsch synthesis: Iron-based catalysts supported on nitrogen-doped carbon nanotubes synthesized by post-doping

A new approach was developed to prepare nitrogen-doped carbon nanotubes (N-CNTs) by a post-doping method at 700–900°C. In this technique acetonitrile is passed over pre-synthesized CNTs in a CVD tube so that N (and C) deposit on the CNT surface. Our results showed that no significant change in the morphologies between CNT and the synthesized N-CNTs at temperatures up to 800°C were observed. This indicates that N-CNTs produced by in-situ (contains a bamboo structure) and post-doping procedures (hollow tube) have different morphologies. When the post-doping temperature was increased to ≥850°C, spherical carbon was formed on the N-CNTs. The N-CNT yield and nitrogen content in the N-CNTs increased almost linearly with increasing post-doping temperature, whereas the surface areas of the N-CNTs decreased with increasing temperature due to tube cavity shrinkage and the deposition of spherical carbon. Raman spectroscopy data showed a decreased ID/IG ratio up to 850°C, suggesting a change in the graphitic structures with temperature. TEM-electron energy loss spectroscopy (TEM-EELS) mapping and XPS showed that the nitrogen atoms were homogeneously dispersed on the N-CNTs and they were pyridinic N atoms, quaternary N atoms and N atoms from pyridinic oxide. Fe catalysts supported on both CNTs and N-CNTs (containing 1.75% nitrogen) functionalized under both mild and harsh acid conditions were prepared in order to investigate the effect of the doped-nitrogen atoms on the performance of the Fe catalysts in Fischer–Tropsch synthesis (FTS). It was found that the incorporation of nitrogen atoms into CNTs did not significantly change the Fe oxide particle sizes. The Fe/CNT and Fe/N-CNT catalysts prepared under a mild pretreatment had large Fe oxide particles, while the Fe/CNT and Fe/N-CNT catalysts pretreated using harsh conditions presented small iron oxide particles. For Fe catalysts supported on CNT and N-CNT pretreated at mild or harsh conditions, the Fe/N-CNT catalysts are less reducible than the corresponding Fe/CNT catalysts due to the incorporation of nitrogen atoms. The interactions between iron oxides and carbon supports significantly affected the FTS performance: the Fe/N-CNT catalysts have superior FTS activity than Fe/CNT catalysts, irrespective of whether they were pretreated at mild or harsh condition. Furthermore, the pretreatment conditions affected the FTS activity of both Fe/CNT and Fe/N-CNT catalysts and the Fe catalysts pretreated at harsh conditions presented an improved FTS activity over the iron catalysts pretreated at mild conditions.

Ruthenium promoted cobalt catalysts prepared by an autocombustion method directly used for Fischer–Tropsch synthesis without further reduction

Ru promoted Co/SiO2 Fischer–Tropsch synthesis (FTS) catalysts with high reduction levels were synthesized through an autocombustion method using citric acid (CA) as a reductant and nitrate ions as oxidants. The as-synthesized catalysts were used directly in FTS reaction without further reduction. The effects of the ruthenium promoter, citric acid contents and reductant types on the catalyst structures and FTS performance were systematically studied. Results indicated that the introduction of a small amount of Ru (1 wt%) improved the reduction and dispersion of cobalt during the autocombustion process, and significantly enhanced the FTS activity. The CO conversion of the catalyst increased rapidly from 0.8 to 41.4% after Ru promotion. The citric acid contents (molar ratio of citric acid to nitrates: CA/N) in the precursor also played an important role in controlling the structures and FTS performance of the catalysts. With the increase of CA/N, the metal reduction level increased and the Co crystalline size decreased but the activity of the catalyst first increased and then decreased with gradually increasing CA/N. An excessive amount of the reductant could result in more residual carbon species and decrease the activity of the catalyst. For different types of reductants (at the same molar ratio of reductants to nitrates), the catalyst prepared by citric acid exhibited the highest activity whereas the catalyst synthesized by oxalic acid showed the lowest methane selectivity. The Ru promoted cobalt catalysts prepared by the autocombustion method, which omits the complex and high energy consumption reduction process, can be used directly for highly efficient FTS and thus will be more promising in the future.

Enhanced Activity and Selectivity of Fischer–Tropsch Synthesis Catalysts in Water/Oil Emulsions

Amphiphilic nanohybrid catalysts (Ru particles supported on carbon nanotube–metal oxide hybrids) enable the formation of water-in-oil emulsions and have a positive influence on the Fischer–Tropsch synthesis (FTS) activity and selectivity to desirable products in comparison with those obtained in single-phase solvents under the same reaction conditions. The reaction experiments were conducted at 473 K in a batch reactor that uses H2/CO syngas as a feed at 2.0–3.5 molar ratio and 4136.85 kPa total pressure. One of the main effects observed when using the biphasic mixture instead of a single solvent is the spontaneous separation of products by solubility differences, which affect mass-transfer-dependent secondary reactions. Another positive effect of using the biphasic system arises from the enhanced FTS activity observed in the presence of condensed aqueous phase. Finally, the presence of an emulsion seems to improve the C1/C5+ product balance, which can be explained by a dual-site model recently proposed in the literature.

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 ...

Fischer-Tropsch Performance of an SiO2-Supported Co-Based Catalyst Prepared by Hydrogen Dielectric-Barrier Discharge Plasma

A silica-supported cobalt catalyst was prepared by hydrogen dielectric-barrier discharge (H2-DBD) plasma. Compared to thermal hydrogen reduction, H2-DBD plasma treatment can not only fully decompose the cobalt precursor but also partially reduce the cobalt oxides at lower temperature and with less time. The effect of the discharge atmosphere on the property of the plasma-prepared catalyst and the Fischer-Tropsch synthesis activity was studied. The results indicate that H2-DBD plasma treatment is a promising alternative for preparing Co/SiO2 catalysts from the viewpoint of energy savings and efficiency.

Highly dispersed cobalt on N-doped carbon nanotubes with improved Fischer–Tropsch synthesis activity

N-doped carbon nanotubes (NCNTs) were used as the support for a Co catalyst (Co/A-NCNTs). After acid treatment, the bamboo-like structure of the NCNTs disappeared and more defects were formed on the surface of the NCNTs; however there was little change in the inner diameter and N content of the nanotubes. This resulted in an improved dispersion of Co inside the cavities of the NCNTs. The Co/A-NCNT catalyst was compared with Co supported on acid treated CNTs, and the Co/A-NCNT catalyst had a smaller surface area and for Fischer–Tropsch (FT) synthesis, it had a higher CO conversion with producing a narrower distribution of low carbon number hydrocarbons. The high Co dispersion in the Co/A-NCNTs is the main reason for the improved FT synthesis performance.

Enhancement of bimetallic Fe-Mn/CNTs nano catalyst activity and product selectivity using microemulsion technique

Bimetallic Fe-Mn nano catalysts supported on carbon nanotubes (CNTs) were prepared using microemulsion technique with water-to-surfactant ratios of 0.4–1.6. The nano catalysts were extensively characterized by different methods and their activity and selectivity in Fischer-Tropsch synthesis (FTS) have been assessed in a fixed-bed microreactor. The physicochemical properties and performance of the nanocatalysts were compared with the catalyst prepared by impregnation method. Very narrow particle size distribution has been produced by the microemulsion technique at relatively high loading of active metal. TEM images showed that small metal nano particles in the range of 3–7 nm were not only confined inside the CNTs but also located on the outer surface of the CNTs. Using microemulsion technique with water to surfactant ratio of 0.4 decreased the average iron particle sizes to 5.1 nm. The reduction percentage and dispersion percentage were almost doubled. Activity and selectivity were found to be dependent on the catalyst preparation method and average iron particle size. CO conversion and FTS rate increased from 49.1% to 71.0% and 0.144 to 0.289 gHC/(gcat·h), respectively. While the WGS rate decreased from 0.097 to 0.056 gCO2/(gcat·h). C5+ liquid hydrocarbons selectivity decreased slightly and olefins selectivity almost doubled.

Enhancement of ruthenium-promoted Co/CNT nanocatalyst performance using microemulsion technique

Background: Ruthenium-promoted cobalt nanocatalysts that are supported by carbon nanotubes (CNTs) are prepared using impregnation and microemulsion techniques. Ruthenium loadings were varied from 0 to 1 wt.% while the amount of cobalt was fixed at 15 wt.%. The nanocatalysts were extensively characterized by different methods and their activity and selectivity in Fischer-Tropsch synthesis (FTS) have been assessed in a fixed-bed microreactor. The physicochemical properties and performance of the nanocatalysts were compared with the catalyst prepared by impregnation method. Results: Very narrow particle size distribution has been produced by the microemulsion technique. According to the transmission electron microscopy, pictures small Co particles (2 to 7 nm) are mostly confined inside the CNTs. Ruthenium increased the percentage reduction of the unpromoted catalyst by a factor of 25. Compared with the catalysts prepared by impregnation, using microemulsion technique with water-to-surfactant ratio of 0.5 which decreased the average cobalt oxide particle sizes to 4.8 nm, the percentage of dispersion is almost doubled and the percentage of reduction is increased by 28. Conclusions: Addition of ruthenium increased the percentage conversion and C5 selectivity of the unpromoted catalyst by a factor of 22.6 and 7, respectively. Activity and selectivity were found to be dependent on the catalyst preparation method and water-to-surfactant ratio (as well as on cobalt particle sizes). The percentage of CO conversion and FTS rate increased from 59.09 to 75.05 and 0.291 to 0.372 gr HC/gr cat/h, respectively, while the C5 liquid

Support Modification on the Catalytic Performance of Co/SiO<sub>2</sub> Catalyst in Fisher-Tropsch Synthesis

The effects of support modification on cobalt based catalysts in Fischer-Tropsch synthesis were investigated. Part of silica support was modified with ammonia solution and the other part not. The Co/SiO2 catalyst with the support surface modified by ammonia solution showed larger particle size, strong Co-Si interaction, higher activity and selectivity in Fischer-Tropsch synthesis. It could be concluded that the support acidity can be controlled thus affected the reaction property of the catalysts in Fischer-Tropsch synthesis.

Effect of La Promotion on Co/ZrO<sub>2</sub> Catalysts in Fischer-Tropsch Synthesis

The effects of lanthanum promotion on cobalt based catalysts in Fischer-Tropsch synthesis were investigated. The Co/ZrO2 catalysts promoted by lanthanum had higher activity and selectivity in Fischer-Tropsch synthesis. The catalyst with the La content 1% had the highest activity and selectivity attributed to the promotion effect of La. However, excessive La addition could depress the activity of the catalyst due to the Co-La interaction and the lower reduction degree.

Fischer–Tropsch Synthesis: Effect of K Loading on the Water–Gas Shift Reaction and Liquid Hydrocarbon Formation Rate over Precipitated Iron Catalysts

The effect of K loading on the water–gas shift (WGS) reaction and hydrocarbon formation rate during Fischer–Tropsch synthesis (FTS) was studied over 100 Fe/5.1 Si/2 Cu/x K (x = 1.25 or 3) precipitated catalysts using a 1-L continuously stirred tank reactor. The catalysts were tested over a wide range of experimental conditions: 260–270 °C, 1.3 MPa, H2/CO = 0.67 and 20–90 % CO conversions. On the low K loading (1.25 % K) Fe catalyst, the H2 deficiency required for the FTS reaction was made up by the WGS reaction only at high CO conversion level, i.e. >70 %; however, increasing potassium loading to 3 % dramatically improved the WGS reaction rate which provided enough hydrogen for the FTS reaction even at low CO conversion level, i.e. 30 %. Kinetic analysis suggests that increasing K loading resulted in significant increases in the WGS rate constant relative to that of FTS, which is a major cause of the high WGS activity on the high K loading catalyst. Both the low and high potassium containing iron catalysts have high liquid oil and solid wax formation rates, i.e. 0.78–0.93 g/g-cat/h at 260 °C, 1.3 MPa, H2/CO = 0.67 and 50 % CO conversion, but increasing potassium loading from 1.25 to 3 % shifted the primary product to wax (70 %) from oil (73.5 %). The wax fraction increased with increasing CO conversion for both iron catalysts. The effect of K loading on initial FTS activity and hydrocarbon distribution/selectivity of the Fe catalysts was also studied. High K loading, i.e. 3 % K, increased the iron carburization rate and significantly shortened the induction period of the FTS reaction. Secondary reactions of olefins were remarkably suppressed and the olefin content was greatly enhanced with increasing K loading from 1.25 to 3 %, consistent with a number of studies in the open literature.

Functional group effect on carbon nanotube (CNT)-supported cobalt catalysts in Fischer–Tropsch synthesis activity, selectivity and stability

The influence of cobalt crystallite size on catalyst performance in Fischer–Tropsch synthesis (FTS) has been investigated using functionalized carbon nanotube (CNT)-supported catalyst. The catalysts were synthesized by the core reverse micelle reactions with cobalt crystallites of various sizes. It has been shown that crystallite size is dependent to the water-to-surfactant ratio (3–10) used for the catalyst preparation. The catalysts were characterized by Brunauer–Emmett–Teller method (BET), X-ray diffraction (XRD), H2 chemisorption, temperature program reduction (TPR), and transmission electron microscopy (TEM). According to TEM analysis, small cobalt crystallites size (3–8nm) synthesized by microemulsion technique have a very narrow size distributions, and they were mostly confined inside the functionalized CNT. The deposition of cobalt nanoclusters synthesized by microemulsion technique on the functionalized CNT, shift the reduction peaks to a low temperature, indicating higher reducibility for uniform cobalt crystallites. The catalyst prepared with functionalized CNT using proposed microemulsion technique, increased the FTS rate from 0.64 to 0.78g HC/g cat./h, C5+ selectivity increased 7.4% and CH4 selectivity decreased 44%, compared to that catalyst prepared on common CNT.

Fischer-Tropsch synthesis nanostructured catalysts: understanding structural characteristics and catalytic reaction

AbstractOne key goal of heterogeneous catalysis study is to understand the correlation between the catalyst structure and its corresponding catalytic activity. In this review, we focus on recent strategies to synthesize well-defined Fischer-Tropsch synthesis (FTS) nanostructured catalysts and their catalytic performance in FTS. The development of those promising catalysts highlights the potentials of nanostructured materials to unravel the complex and dynamic reaction mechanism, particularly under the in situ reaction conditions. The crucial factors associated with the catalyst compositions and structures and their effects on the FTS activities are discussed with an emphasis on the role of theoretical modeling and experimental results.

Size-dependent studies of Fischer–Tropsch synthesis on iron based catalyst: New kinetic model

In this study the effect of catalyst nanoparticle size on the Fischer–Tropsch synthesis (FTS) activity is investigated on iron catalyst. A series of iron oxide particles doped by adding cupper and lanthanum were prepared as a catalyst via precipitation by microemulsion method. Because of the role of iron carbide in FTS reaction by iron catalysts, the iron carbide particle sizes was evaluated after activation and considered as active phase in this paper. The catalytic results indicated that FTS activity increased and passed through a maximum when the iron particle size increased. A size-dependent kinetic model for FTS rates was developed using a thermodynamic analysis method. The model parameters measured by experimental results and the effect of various active sizes on these parameters was evaluated. Calculated size dependent model parameters were employed for evaluation of surface tension energy (σ) for iron catalyst and size-independent activation energy for FTS reaction.

Performance enhancement of bimetallic Co-Ru/CNTs nano catalysts using microemulsion technique

Bimetallic cobalt-ruthenium nano catalysts supported on carbon nanotubes (CNTs) are prepared using microemultion technique with water-to-surfactant ratios of 0.5–1.5. The nano catalysts were extensively characterized by different methods and their activity and selectivity in Fischer-Tropsch synthesis (FTS) have been assessed in a fixed-bed microreactor. The physicochemical properties and performance of the nanocatalysts were compared with the catalyst prepared by impregnation method. Very narrow particle size distribution has been produced by the microemulsion technique at relatively high loadings of active metals (15 wt% Co and 1 wt% Ru). According to TEM images, small Co particles (2–7 nm) were mostly confined inside the CNTs. Comparing with the catalyst prepared by impregnation, the use of microemulsion technique with water to surfactant ratio of 0.5 decreased the average cobalt oxide particle size to 4.8 nm, the dispersion was almost doubled and the reduction increased by 28%. Activity and selectivity were found to be dependent on the catalyst preparation method and water-to-surfactant ratio (as well as cobalt particle sizes). CO conversion increased from 59.1% to 75.1% and the FTS rate increased from 0.291 to 0.372 gHC/(gcath). C5+ liquid hydrocarbons selectivity decreased from 92.4% to 87.6%.

Study of Co/SBA-15 catalysts prepared by microwave and conventional heating methods and application in Fischer–Tropsch synthesis

The aim of this work was to produce a 20% (w/w) cobalt catalyst supported in SBA-15 molecular sieve, analyze it and evaluate its use in Fischer–Tropsch (FT) reaction. Two synthesis methods for the SBA-15 molecular sieves were evaluated: microwave (Co/SBA15-MW) and conventional heating (Co/SBA15-CH). The Co/SBA-15 catalysts were prepared by humidity impregnation and were characterized by X-ray diffraction, X-ray energy dispersion spectrophotometer, N2 adsorption–desorption, temperature-programmed reduction, and transmission electron microscopy. Fischer–Tropsch synthesis was carried out to evaluate the activity of the catalyst. The synthesis was carried out in a slurry reactor operating at 513K, 20atm, and 1:1 CO:H2 molar ratio. X-ray diffraction showed that the calcined cobalt catalyst did not modify the structure of SBA-15 and that Co was present under the form of Co3O4 in the precursor. The addition of cobalt in the SBA-15 decreased the specific surface area of the molecular sieve. Fischer–Tropsch synthesis activity and C5+ hydrocarbon selectivity increased with the Co/SBA15-MW. The increase in activity and selectivity were attributed to the increased number of active sites as a result of the higher reducibility. The Co/SBA-15 catalysts showed moderate conversion (40%) and high selectivity towards the production of C5+ (79%, w/w).