For The Fischer-Tropsch Synthesis Research Articles

Fischer-Tropsch synthesis to α-Olefins with low CO2 selectivity on a Co2C catalyst

A Co2C catalyst with low CO2 selectivity for the Fischer-Tropsch to Olefins (FTO) was derived from a precursor catalyst prepared by a “melting” method. Co-Mn composite oxide, MnCo2O4.5, was identified as the dominant composition in the catalytic material before it was activated. The catalyst showed a weak interaction between Co and Mn with the presence of Na. Therefore, Co could be liberated easily from MnCo2O4.5 with H2 reduction at a usually used condition for Co-based catalyst for the Fischer-Tropsch Synthesis (FTS). A clear carburization of Co0 to Co2C was observed during the initial period of reaction, and this transformation could be achieved within 6 h. Four different crystal facets, (210), (020), (111), and (101) for Co2C, were identified once Co0 has been successfully carburized during the reaction. A limited amount of Co0 also transformed to Co3O4 during Co2C formation when H2O was produced by the FT reaction. The prepared catalyst demonstrated outstanding performance in terms of product selectivity. Its selectivity to lower olefins (C2-C4) was as high as 60.26 % with an average olefin/paraffin ratio of 26.69. Additional to high olefin selectivity, the CO2 selectivity was as low as 11.49 %, and that of C1 (CO2 + CH4) could be controlled at 16.44 % with optimal Co/Mn ratio and operating conditions. It was also found that transient state Co0 with Mn and Na as promoters demonstrated similar high olefin to paraffin ratios when compared to Co2C.

Classifying and understanding the role of carbon deposits on cobalt catalyst for Fischer-Tropsch synthesis

There is less agreement on the role of carbon deposits during FT reaction. Identifying and characterizing carbon species of cobalt catalyst is highly challenging for the Fischer-Tropsch Synthesis (FTS). Here, a serial of predeposited composite carbon and single carbon are constructed, and their roles in F-T synthesis are investigated on metal cobalt catalyst excluding the texture influence of the promoter and the support. Different carbon deposits are introduced on cobalt-based catalysts under different carbon-containing reducing atmospheres utilizing the pretreatment method. Atomic carbon, polymeric carbon, graphitic carbon, and combinations of them were distinguished by the characterization techniques of TPH, Raman and XPS. A significant difference occurred in both the catalytic activity and selectivity to methane after predeposited carbon on the Co-based catalysts. The p-Co-5 % syn-3 g-24 h-250-RO catalyst with single atomic carbon shows a remarkably low methane selectivity (4.03 %), high C5+ selectivity (76.38 %), and more importantly, excellent stability (TOS = 144 h) in FTS. Moreover, all of the Co-based catalysts containing the predeposited carbon can be directly used in the FT reaction without reduction procedure.

Influence of temperature during pyrolysis of Fe-alginate: Unraveling the pathway towards highly active Fe/C catalysts

Transition metals supported on carbons play an important role in catalysis and energy storage. By pyrolysis of metal alginate, highly active catalysts for the Fischer-Tropsch synthesis (FTS) can be produced. However, the evolution of the carbon (alginate) and transition metal (Fe3+) during pyrolysis remains largely unknown and was herein corroborated with several advanced in situ techniques. Initially, Fe3+ was reduced to Fe2+, while bound to alginate. FeO nucleated above 300 °C, destabilizing the alginate functional groups. Increasing temperatures improved carbonization of the carbon support, which facilitated reduction of FeO to α-Fe at 630 °C. Catalysts were produced by pyrolysis between 400 and 700 °C, where the highest FTS activity (612 µmolCO gFe−1 s−1) was achieved for the sample pyrolyzed at low temperature. Lower metal loading, due to less decomposition of alginate, moderated sintering and yielded larger catalytic surface areas. The results provide valuable knowledge for rational design of metal-alginate-based materials.

Ru-M (M = Fe or Co) Catalysts with high Ru surface concentration for Fischer-Tropsch synthesis

Ru-Co/Al2O3 and Ru-Fe/Al2O3 have been prepared by the reduction-deposition method. This approach favours the interaction between Ru and Fe or Co in the final catalysts, while increasing surface enrichment of Ru. Their performance for the Fischer-Tropsch Synthesis (FTS) has been evaluated in a fixed bed reactor. Ru-Co/Al2O3 displays the highest activity in the series, doubling the steady-state CO conversion rate of a Ru/Al2O3 catalyst with 3 times higher Ru loading. Ru-Fe/Al2O3 displays higher initial CO conversion and -CH2- productivity than Ru/Al2O3, but its activity declines during operation reaching lower conversion rates than Ru/Al2O3. In addition to CO2, Ru-Fe/Al2O3 produces oxygenated products, mainly alcohols. To a lesser extent, the formation of oxygenates over Ru-Co/Al2O3 and Ru/Al2O3 is also observed, and ascribed to the small crystallite size of the Ru particles. The evolution of CO2 during time on stream indicates that Fe is segregated to the surface of this catalyst during the FTS.

Role of CoO-Co nanoparticles supported on SiO2 in Fischer-Tropsch synthesis: Evidence for enhanced CO dissociation and olefin hydrogenation

The role of mixed CoO-Co nanoparticles dispersed on a SiO2 support for the Fischer-Tropsch synthesis (FTS) has been evaluated. The multiphase CoO-Co/SiO2 demonstrated high activity for the Fischer-Tropsch (FT) reaction, water-gas shift (WGS) and hydrogenation reactions. The results were the experimental evidence that the CoO-Co interface assisted both the activation of CO and the hydrogenation of R-CHx intermediates. A new mechanism, “CoO-Co H-assisted CO dissociation”, was hypothesized to explain the high CO reactivity and selectivity to linear paraffinic products. The synergistic effect between CoO and Co° promotes the FT activity, which provides the valuable information for the design of the commercial FT cobalt-based catalysts.

Stabilizing Optimal Crystalline Facet of Cobalt Catalysts for Fischer–Tropsch Synthesis

Developing efficient catalysts with a stable optimal crystalline facet is highly promising yet challenging for the Fischer-Tropsch synthesis (FTS). Here, we demonstrate a coating strategy to fabricate a stable optimal cobalt-facet catalyst. The catalyst (Co@C-SiO2) is composed of a single crystalline core, a wrapped carbon layer, and an amorphous silica shell. The moderate metal-support interaction endowed by carbon, combining the confined effect of the silica shell, protects and maintains the single-crystal structure and optimal crystalline facet of the core, that is, Co(10-11). Due to the unique core-shell nanostructure and optimal cobalt facets, our Co@C-SiO2 catalyst shows a remarkable low methane selectivity (5.3%), high activity (TOF = 4.0 × 10-2 s-1), C5+ selectivity (88.9%), and more importantly, excellent stability (TOS = 168 h) in FTS.

Studies on the Fischer-Tropsch synthesis over RuCo/SiC-Al2O3 structured catalyst

RuCo/SiC-Al2O3 catalysts were with enhancing thermal conductivity for the Fischer-Tropsch Synthesis (FTS) were designed and manufactured. The SiC-Al2O3 support was extruded by Lab scale extruder and then foamed by the marumerizer. Catalysts were prepared by an incipient wetness impregnation method. All the prepared catalysts were characterized by SEM-EDX, XRD, TPR, TPD, XPS, ICP and N2-physisorption techniques. The catalytic performance was evaluated at T = 210–230 °C, P = 20 bar and GHSV of 1,000 h−1 in a fixed bed reactor system. The CO conversion over RuCo/nSiC-Al2O3 catalysts was increased by 10% compared to RuCo/Al2O3 catalyst at 210 °C. Furthermore, the selectivity of methane was similar or less than RuCo/Al2O3 catalyst. It was shown that the CO conversion increased with increasing the SiC content from 5 to 15 wt%, and then decreased. The RuCo/15SiC-Al2O3 catalyst showed higher CO conversion than other catalysts under the tested conditions. This is because the 15 wt.% SiC addition ratio is the most advantageous between thermal conductivity improvement and aggregation of cobalt particles.

Quantitative comparison of iron and cobalt based catalysts for the Fischer-Tropsch synthesis under clean and poisoning conditions

Abstract Quantitative data comparing iron and cobalt based catalysts for the Fischer-Tropsch synthesis (FTS) are scarce due to the fact that these two kinds of catalysts typically utilize different process conditions. This paper focuses on studying the catalytic behavior of two highly active iron and cobalt based research catalysts at clean conditions and during poisoning with common syngas contaminants. The catalyst activity and selectivity at identical conditions, the CO conversion effect, and the effect of poisons on iron and cobalt catalysts were systematically explored in a quantitative manner. At a set of identical FTS conditions, the cobalt catalyst was 2.5 times as active as the iron catalyst with higher CH4 and C5+ selectivities but much less olefins and lower CO2 selectivity. Cobalt based catalysts are more susceptible to deactivation by oxidation at high CO conversions (e.g. > 80%) due to the high partial pressure of water (PH2O) in the reactor, while the iron catalyst can be stabilized at a high conversion level. Under clean FTS conditions, the cobalt catalysts displayed a more pronounced CO conversion effect on stability and selectivity; on the other hand, a combination of effects (i.e. from CO conversion and the nature of the catalyst) were observed for the iron catalysts. The sensitivities of the Fe and Co catalysts to the typical contaminants (i.e., H2S and NH3) present in the syngas derived from coal, natural gas or biomass were compared. Iron and cobalt catalysts exhibited similar resistance to the H2S poison (i.e. threshold levels 25–50 ppb), but the iron catalyst was found to be much more resistant to ammonia than the cobalt catalyst (i.e., threshold levels of 80 ppm and 45 ppb, respectively). Co-feeding 150–200 ppm ammonia lowered CH4 selectivity and 2-olefin content (suppressing secondary reactions of 1-olefin) on both types of catalysts. In contrast, co-feeding up to 1 ppm H2S significantly increased CH4 formation only on cobalt catalysts but had a minor effect on CH4 selectivity with iron catalysts. It increased 2-olefin content (enhanced secondary reactions of 1-olefin) regardless of catalyst type. H2S and NH3 have different impacts on H2, CO adsorption, and the formation of sulfur and nitride compounds have been proposed to explain these dissimilar effects.

Characterizations and product distribution of Co-based Fischer-Tropsch catalysts: A comparison of the incorporation manner

Co-based catalysts supported on SBA-15 and ZSM-5 were prepared by various incorporation manners and evaluated for the Fischer-Tropsch synthesis (FTS). The weight ratio of SBA-15 and ZSM-5 were 1:1 and Co had a constant loading of 15 wt% in all of the finished catalysts. Their physicochemical properties and catalytic performance were investigated by the N2 adsorption–desorption, XRD, TEM, XPS, NH3-TPD, H2-TPR, H2-O2 titration, H2-chemisorption and in a high pressure fixed-bed reactor, respectively. Characterizations indicated that the main cobalt species was Co3O4 with small crystal size and high dispersion on the catalysts with SBA-15 as support, while the CoO with strong interaction with the support, as well as large particle size and low dispersion of Co3O4 was observed on the ZSM-5 supported catalyst. It was found that the catalysts with SBA-15 as main support displayed superior CO conversion (85–90%) than the catalysts with Co species mostly deposited on the ZSM-5 support (∼70%), which was arise from the easy reduction of Co3O4 with weak interaction with SBA-15 support. The consecutive hydrocracking of Co/SBA-15 primary hydrocarbons facilitated the formation of C5-C11 on the Co/S15 + Z5 catalyst with medium acid site, accordingly the selectivity of the C5-C11 hydrocarbons was enhanced from 51% to 62% in the liquid hydrocarbons. The optimum dispersion of Co3O4 and Co2+/Co3+ ratio on the Co/(S15 + Z5) catalyst facilitated the product distributions shifting to C12-C22 with the increased selectivity from 41% to 52%. Furthermore, The superior catalytic stability for Co/(S15 + Z5) could be attributed to the synergistic effect of hydrogenolysis and cracking, which suppressed the coke deposition.

Synthesis of Hydrocarbons from H2-Deficient Syngas in Fischer-Tropsch Synthesis over Co-Based Catalyst Coupled with Fe-Based Catalyst as Water-Gas Shift Reaction

The effects of metal species in an Fe-based catalyst on structural properties were investigated through the synthesis of Fe-based catalysts containing various metal species such, as Mn, Zr, and Ce. The addition of the metal species to the Fe-based catalyst resulted in high dispersions of the Fe species and high surface areas due to the formation of mesoporous voids about 2–4 nm surrounded by the catalyst particles. The metal-added Fe-based catalysts were employed together with Co-loaded beta zeolite for the synthesis of hydrocarbons from syngas with a lower H2/CO ratio of 1 than the stoichiometric H2/CO ratio of 2 for the Fischer-Tropsch synthesis (FTS). Among the catalysts, the Mn-added Fe-based catalyst exhibited a high activity for the water-gas shift (WGS) reaction with a comparative durability, leading to the enhancement of the CO hydrogenation in the FTS in comparison with Co-loaded beta zeolite alone. Furthermore, the loading of Pd on the Mn-added Fe-based catalyst enhanced the catalytic durability due to the hydrogenation of carbonaceous species by the hydrogen activated over Pd.

COBALT SUPPORTED ON ZSM-5 ZEOLITE USING KAOLIN AS SILICON AND ALUMINUN SOURCES FOR FISCHER-TROPSCH SYNTHESIS

The use of clay as an alternative source of raw material provides economic routes for the synthesis of ZSM-5. Therefore, the main purpose of this work was to study ZSM-5 synthesis using kaolin as Si and Al source. The zeolite using kaolin as a source of silica and aluminum has been applied as support for a 20wt% Co catalyst. Zeolite ZSM-5 was obtained with kaolin under hydrothermal synthesis at 373K for 48 hours. The kaolin was submitted to heat treatment at 973K for 2 hours before being used in synthesis. The deposition of cobalt on the support ZSM-5CK was performed by means of wet impregnation, using a 0.1-M aqueous solution of cobalt nitrate. The catalytic support and metal-loaded catalyst have been characterized and evaluated for the Fischer-Tropsch Synthesis (FTS) under controlled conditions (T = 593K, P = 20atm, H2:CO molar ratio = 2) in a fixed bed reactor for 150 hours. From the Temperature Programmed Reduction profiles, two reduction peaks were observed at 629K and 677K, corresponding to the stepwise reduction of Co3O4 particles to CoO and then to metallic Co on the support external surface. It was observed with the FTS results that the 20wt% Co/ZSM-5CK catalyst yielded a 10% conversion rate and high selectivity towards the production of C5+ (98%).

Potentials for commercialization of novel Fischer-Tropsch reactor technology

This paper comprises of a preliminary in-depth analysis of the techno-economic criteria for the Fischer-Tropsch synthesis (FTS) solvent selection. Both conventional media (i.e. gas phase FTS and liquid phase FTS) as well as non-conventional media (near-critical and supercritical phase FTS) were examined, with an emphasis on non-conventional media FTS for the design and commercialization of a novel FTS reactor technology. Supercritical and near critical fluids (SCFs) are attractive for several reasons, highlighted by their ability to overcome some of the major limitations of current commercial technologies (e.g. transport limitations in the slurry reactor, and thermal limitations in multi-tubular reactors). Due to single phase operation of SCFs, these solvents are unique media for chemical reactions as they operate with densities that are sufficient to afford substantial dissolution power, while also providing diffusivities that are higher than normal liquids and viscosities that are lower than their liquid counterparts. High temperature Fischer-Tropsch (HTFT) was the center of examinations, but LTFT was considered as well. A wide array of hydrocarbon solvents was reviewed, ranging from propane to decane, with numerous blends of two or more of the mentioned paraffins. Several fuel cuts were studied as well, such as light and heavy naphtha and diesel. Understanding the transport and thermodynamic behavior as well as economic benefit of these said solvents is essential to the success of an advanced FTS reactor model. Also, the interaction of the solvents with in-situ reaction mixture and products further insures single-phase operation and feasibility.

Formation of Co-Ru/MgO/Al2O3 catalysts for the Fischer-Tropsch synthesis: A magnetic method for the estimation of cobalt particle size

The physicochemical properties of Co-supported catalysts were studied, and the particle size of Co in Co/MgO/Al2O3 and Co-0.2% Ru/MgO/Al2O3 catalysts for the Fischer-Tropsch synthesis (FTS) was estimated using a magnetic method. It was found that a considerable fraction of superparamagnetic Co particles, which increase selectivity for C5+ hydrocarbons and decrease the yield of methane in the FTS, was present in a ruthenium-containing catalyst along with single-domain ferromagnetic particles. In this case, the catalyst activity increased by a factor of 10.

Study of activated carbon supported iron catalysts for the Fischer-Tropsch synthesis

Characterization (BET and TPD) and reaction studies were conducted with activated carbon supported iron catalysts (Fe/AC) used for the Fischer-Tropsch synthesis (FTS). The TPD study showed that there existed interactions between metals and the AC surface. Greater association of Cu and K promoters with the AC surface resulted in stronger promoter to surface interaction, which enhanced the H2 desorption ability of the Cu and K promoted Fe/AC catalyst prepared under vacuum impregnation (VI). Catalytic behavior of a Fe/AC catalyst (VI-15 Fe/2 Cu/2 K/81 AC, in parts per weight) was studied in a 1-liter slurry phase continuous stirred tank reactor. The catalyst presented moderate syngas conversion (44.3-60.6%) and high gaseous selectivity (CH4, 12.8-15.1% and C2-C4, 42.4-46.1%) under 304oC, 3.0 MPa, 1.1 L(STP)/g-cat/h, and H2/CO = 2.0 during 166 h of testing. Detectable hydrocarbons up to C18 were formed on the Fe/AC catalyst.

Synthesis and catalytic properties of lanthanum nickelate perovskite materials

Characterization (BET and TPD) and reaction studies were conducted with activated carbon supported iron catalysts (Fe/AC) used for the Fischer-Tropsch synthesis (FTS). The TPD study showed that there existed interactions between metals and the AC surface. Greater association of Cu and K promoters with the AC surface resulted in stronger promoter to surface interaction, which enhanced the H 2 desorption ability of the Cu and K promoted Fe/AC catalyst prepared under vacuum impregnation (VI). Catalytic behavior of a Fe/AC catalyst (VI-15 Fe/2 Cu/2 K/81 AC, in parts per weight) was studied in a 1-liter slurry phase continuous stirred tank reactor. The catalyst presented moderate syngas conversion (44.3-60.6p) and high gaseous selectivity (CH 4 , 12.8-15.1p and C 2 -C 4 , 42.4-46.1p) under 304 o C, 3.0 MPa, 1.1 L(STP)/g-cat/h, and H 2 /CO = 2.0 during 166 h of testing. Detectable hydrocarbons up to C 18 were formed on the Fe/AC catalyst.

Fischer-Tropsch synthesis on alumina-supported ruthenium catalysts II. Influence of morphological factors

A Ru/γ-Al 2O 3 (0.87% wt./wt.) catalyst has been studied for the Fischer-Tropsch synthesis (FTS) at 5 · 10 3 Pa, 508 K with a H 2/CO ratio of 2/1. The same catalyst was also sintered at 973 K for different times in order to change the metal dispersion D M of Ru ( D M from 18 to 93%). The aim of the present work is to verify which atoms of Ru crystallites are most active in FTS. For this study a ‘model’ of truncated hexagonal bipyramid for the crystalline agglomerates has been assumed. It was verified that atoms with higher nearest neighbors i ( i,8 and 9) on flat faces and edges are more active than those on vertexes and edges at lower i values ( i,5 to 7). We found that larger crystallites decompose CO more easily than smaller ones, and that the turnover number for CO disappearance and for CH 4, C2, C3, C5–C15 formation does not depend strongly on metal dispersion. However, on the contrary, we found that light olefins (C2 and C3) are easily formed on large crystallites. The above findings reveal that FTS could be considered as a structure sensitive reaction for the initial step, but are structure insensitive for the overall reaction.

Preparation and adsorption, chemical and catalytic properties of iron boride fischer-tropsch catalysts

Sodium-free and sodium-promoted, iron borides were prepared by reducing anhydrous iron acetate with diborane/THF or NaBH 4/diglyme solution. These new preparation techniques provide straightforward pathways to preparation of high surface area iron borides without oxidation of the catalysts. The catalysts were characterized by hydrogen and carbon monoxide adsorptions, Moessbauer Spectroscopy, and X-ray diffraction (XRD). CO hydrogenation activities and selectivities of these catalysts were determined at 493 K to 577 K and 10 or 20 atm with a H 2/CO reactant ratio of 2. An in situ Moessbauer study indicates that the sodium-free, chemically reduced, iron boride interstitial consists mainly of a boron-rich FeB phase which transforms to a mixture of Fe 0, FeB and Fe 2B phases upon treating with hydrogen at 400°C; the corresponding sodium-containing catalyst contains mainly Fe 2B. Laboratory reactor data indicate that unpromoted iron borides have activity/selectivity properties similar to unpromoted iron catalysts for the Fischer-Tropsch Synthesis (FTS). Sodium significantly enhances activity and alkene selectivity of iron boride for FTS. Unpromoted iron borides are not stable under FTS conditions over long reaction times, however their stability is enhanced by sodium promotion. The rate of carbon monoxide hydrogenation and the average molecular weight of products obtained on iron boride catalysts increase with increasing pressure.