For Fischer–Tropsch Synthesis Activity Research Articles

Modulating Co reduction degree and Fischer-Tropsch synthesis performance by reducing cobalt silicate at different conditions

It is always hard to reduce Co2SiO4 to active Co0 on supported Co-based catalyst for Fischer-Tropsch synthesis (FTS). Here, amorphous Co2SiO4 material was prepared by in-situ doping TMOS during synthesis of ZIF-67, which was then reduced at different temperature and time to obtain ReX-2h (X = 400, 450, 500, 550, 600) and Re500-Yh (Y = 2, 4, 8) catalysts. The effects of reduction temperature and time on Co reduction degree and FTS performance were investigated. Results indicated that the ReX-2h and Re500-Yh catalysts exhibited low CH4 selectivity due to no obvious Co microcrystal found. The reduction degree of ReX-2h increased with reduction temperature, which led to enhanced FTS activity. However, both Re550-2h and Re600-2h exhibited poorer stability than Re500-2h, so the effects of reduction time on Re500-Yh were done. The reduction degree and FTS activity of Re500-Yh were also promoted with extending reduction time. The Re500-8h exhibited higher FTS activity with good stability.

MOF-Derived Ru1Zr1/Co Dual-Atomic-Site Catalyst with Promoted Performance for Fischer-Tropsch Synthesis.

Cobalt-based catalysts have been widely used for Fischer-Tropsch synthesis (FTS) in industry; however, achieving rational catalyst design at the atomic level and thereby a higher activity and more long-chain-hydrocarbon products simultaneously remain an attractive and difficult challenge. The dual-atomic-site catalysts with unique electronic and geometric interface interactions offer a great opportunity for exploiting advanced FTS catalysts with improved performance. Herein, we designed a Ru1Zr1/Co catalyst with Ru and Zr dual atomic sites on the Co nanoparticle (NP) surface through a metal-organic-framework-mediated synthesis strategy which presents greatly enhanced FTS activity (high turnover frequency of 3.8 × 10-2 s-1 at 200 °C) and C5+ selectivity (80.7%). Control experiments presented a synergic effect between Ru and Zr single-atom site on Co NPs. Further density functional theory calculations of the chain growth process from C1 to C5 revealed that the designed Ru/Zr dual sites remarkably lower the rate-limiting barriers due to the significantly weakened C-O bond and promote the chain growth processes, resulting in the greatly boosted FTS performance. Therefore, our work demonstrates the effectiveness of dual-atomic-site design in promoting the FTS performance and provides new opportunities for developing efficient industrial catalysts.

Bimetal–Organic Framework-Derived CoMn@C Catalysts for Fischer–Tropsch Synthesis

Introducing promoters to cobalt-based catalysts for Fischer–Tropsch synthesis (FTS) has been found to be efficient in adjusting their performance in converting syngas into long-chain hydrocarbons. High spatial proximity of the promoter and reactive metal is desired to maximize the effectiveness of the promoters. In this work, CoMn@C composites were synthesized by the one-step carbonization of bimetal–organic frameworks (BMOFs: CoMn-BTC). BMOF-derived catalysts naturally exhibited that cobalt nanoparticles (NPs) are confined in the carbon matrix, with a concentrated particle size distribution around 13.0 nm and configurated with MnO highly dispersed throughout the catalyst particles. Mn species preferentially bind to the surfaces of Co NPs rather than embedded into the Co lattice. The number of Mn–Co interfaces on the catalyst surface results in the weakened adsorption of H but enhanced adsorption strength of CO and C. Hence, the incorporation of Mn significantly inhibits the production of CH4 and C2–C4 paraffin boosts light olefin (C2–4=) and C5+ production. Furthermore, the FTS activity observed for the Mn-promoted catalysts increases with increased Mn loading and peaks at 2Co1Mn@C due to the abundance of Co–Mn interfaces. These prominent FTS catalytic properties highlight the concept of synthesizing BMOF-derived mixed metal oxides with close contact between promoters and reactive metals.

Development of an Iron-Based Fischer—Tropsch Catalyst with High Attrition Resistance and Stability for Industrial Application

In order to develop an iron-based catalyst with high attrition resistance and stability for Fischer–Tropsch synthesis (FTS), a series of experiments were carried out to investigate the effects of SiO2 and its hydroxyl content and a boron promoter on the attrition resistance and catalytic behavior of spray-dried precipitated Fe/Cu/K/SiO2 catalysts. The catalysts were characterized by means of N2 physisorption, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectroscopy (XPS), H2-thermogravimetric analysis (H2-TGA), temperature-programmed reduction and hydrogenation (TPR and TPH), and scanning and transmission electron microscopy (SEM and TEM). The FTS performance of the catalysts was tested in a slurry-phase continuously stirred tank reactor (CSTR), while the attrition resistance study included a physical test with the standard method and a chemical attrition test under simulated reaction conditions. The results indicated that the increase in SiO2 content enhances catalysts’ attrition resistance and FTS stability, but decreases activity due to the suppression of further reduction of the catalysts. Moreover, the attrition resistance of the catalysts with the same silica content was greatly improved with an increase in hydroxyl number within silica sources, as well as the FTS activity and stability to some degree. Furthermore, the boron element was found to show remarkable promotion of FTS stability, and the promotion mechanism was discussed with regard to probable interactions between Fe and B, K and B, and SiO2 and B, etc. An optimized catalyst based on the results of this study was finalized, scaled up, and successfully applied in a megaton industrial slurry bubble FTS unit, exhibiting excellent FTS performance.

Preparation of SiO2 immobilized Co-based catalysts from ZIF-67 and the enhancement effect for Fischer-Tropsch synthesis

ZIF-67-derived Co@C catalysts show great potential for Fischer-Tropsch synthesis (FTS) due to high cobalt (Co) loading and proper cobalt crystalline size, while improving the FTS activity and stability is still a major challenge. In this work, SiO2 was embedded to immobilize Co particles by introducing a silicon source into ZIF-67 using ex-situ or in-situ methods to prevent cobalt particles from aggregating. Due to exposure of more active cobalt sites and elimination of microcrystalline Co on the ex-situ soaking catalysts, increased FTS activity and decreased CH4 selectivity were achieved, but undesirable stability was observed due to the weak immobilization ability of SiO2. To enhance the immobilization effect of SiO2, E-ZIF-67@nSiO2 precursors were prepared by an in-situ soaking method in which the formation of ZIF-67 and introduction of SiO2 occurred simultaneously. The obtained E-Co3O4@4SiO2 catalyst exhibits not only much high FTS activity but also good stability.

Fischer–Tropsch Synthesis: ZIF-8@ZIF-67-Derived Cobalt Nanoparticle-Embedded Nanocage Catalysts

The preparation of highly active and stable catalysts for syngas conversion is a major challenge for Fischer–Tropsch synthesis (FTS). Herein, we report a strategy to prepare a highly dispersed Co-embedded porous carbon nanocage (CoPCN) structure derived from a core–shell metal–organic framework (MOF) ZIF-8@ZIF-67 precursor. High Co loading (over wt 30%) is achieved while maintaining an optimal dispersion and particle size of the active Co phase when a ZIF-8@ZIF-67 is pyrolyzed at 920 °C. Besides, the porous channels and hollow structures of the CoPCN strengthen the diffusion of reactants and the hydrocarbon product, enhancing the C5+ selectivity and CO conversion. The CoPCN shows high stability in FTS with a CO conversion of 18.3%, 80.2% selectivity for long-chain hydrocarbons (C5+), and 8.9% selectivity for short-chain hydrocarbons (C2–C4) after 100 h time on stream. Compared with other MOF-derived FTS catalysts, CoPCN-920 can achieve higher C5+ selectivity at a lower reaction temperature. The present work uncovers the relationship between the porous structure and catalytic performance, providing an efficient method to prepare promising materials for enhanced FTS stability, activity, and selectivity.

Alumina Coated Silica Nanosprings (NS) Support Based Cobalt Catalysts for Liquid Hydrocarbon Fuel Production From Syngas.

The effects of Al2O3 coating on the performance of silica nanospring (NS) supported Co catalysts for Fischer–Tropsch synthesis (FTS) were evaluated in a quartz fixed-bed microreactor. The Co/NS-Al2O3 catalysts were synthesized by coating the Co/NS and NS with Al2O3 by an alkoxide-based sol-gel method (NS-Al-A and NS-Al-B, respectively) and then by decorating them with Co. Co deposition was via an impregnation method. Catalysts were characterized before the FTS reaction by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction, transmission electron microscopy, temperature programmed reduction, X-ray photoelectron spectroscopy, differential thermal analysis and thermogravimetric analysis in order to find correlations between physico-chemical properties of catalysts and catalytic performance. The products of the FTS were trapped and analyzed by GC-TCD and GC-MS to determine the CO conversion and reaction selectivity. The Al2O3 coated NS catalyst had a significant affect in FTS activity and selectivity in both Co/NS-Al2O3 catalysts. A high CO conversion (82.4%) and Σ > C6 (86.3%) yield were obtained on the Co/NS-Al-B catalyst, whereas the CO conversion was 62.8% and Σ > C6 was 58.5% on the Co/NS-Al-A catalyst under the same FTS experimental condition. The Co/NS-Al-A catalyst yielded the aromatic selectivity of 10.2% and oxygenated compounds.

Microstructure Evolution of a Co/MnO Catalyst for Fischer‐Tropsch Synthesis Revealed by In Situ XAFS Studies

AbstractCo−Mn catalysts have long been considered as a promising catalyst for Fischer‐Tropsch synthesis (FTS). However, the promotional role of Mn and its interaction with Co remain unclear and controversial. In situ characterization of the structural change of FTS catalysts is a powerful way to reveal the reaction mechanisms. Nevertheless, there are significant difficulties because of the harsh reaction conditions. Here, the microstructure evolution of Co/MnO catalysts during FTS is monitored by in situ X‐ray absorption fine structure (XAFS) spectroscopy under real FTS atmosphere up to 6 bar for the first time. Combined with in situ X‐ray diffraction (XRD), ex situ high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and H2 chemisorption characterizations, we reveal that the metallic Co liberated from Mn1−xCoxO during FTS leads to activity enhancement. The presence of Mn improves the Co dispersion. However, an initial association of Mn with the Co phase hampers the cobalt reducibility. We also find that increasing the reaction pressure enhances the oxygen dissociation on the Mn surface, which leads to an increased number of exposed Co sites and consequent FTS activity improvement.

Novel Cobalt Catalysts Supported on Metal–Organic Frameworks MIL‐53(Al) for the Fischer–Tropsch Synthesis

Metal–organic framework of MIL‐53(Al) (Al(OH)‐[O2C‐C6H4‐CO2]) with exceptional thermal stability (as high as ≈550 °C in dynamic conditions) are synthesized via a solvothermal method, which serve as a porous host matrix of Co‐based catalysts for Fischer–Tropsch synthesis (FTS). MIL‐53(Al) shows large micropores and lattice dynamic flexibility, which make this material a promising support for active cobalt species. The as‐synthesized Co/MIL‐53(Al) catalysts with different cobalt loadings are characterized by powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), X‐ray photoelectron spectroscopy (XPS), thermogravimetry (TG), Fourier‐transform infrared (FT‐IR) spectroscopy, and temperature programmed reduction. The results show that the immobilization of Co nanoparticles on the MIL‐53(Al) support could be beneficial to obtain novel effective catalysts for FTS. Moreover, compared with the Co/γ‐Al2O3 catalyst of the same cobalt loading, the catalytic performance of Co/MIL‐53(Al) catalyst shows higher FTS activity. Interestingly, the gasoline selectivity over the Co/MIL‐53(Al) catalyst is much higher than that of the Co/γ‐Al2O3 catalyst, close to the optimal value for maximum gasoline and diesel production.

Enhanced Fischer-Tropsch synthesis performances of Fe/h-BN catalysts by Cu and Mn

A series of Fe/h-BN catalysts promoted with Cu or Mn were prepared for Fischer-Tropsch synthesis (FTS). The physicochemical properties, crystal structures and morphologies of the catalysts were characterized by N2 physisorption, FT-IR, TPR, XPS, XRD, MES and TEM. It is found that iron oxide nanoparticles are highly dispersed on h-BN matrix due to the anchoring effect of surface defects and the accommodation of porous structures of h-BN. The characterization results indicate that strong interaction between iron oxide and h-BN is present on un-promoted catalyst, which endows the h-BN supported iron catalyst with stable properties under FTS conditions but severely retards reduction of the catalyst. The addition of Cu to Fe/h-BN can to some extent overcome the strong interaction by introducing more sites for dissociating H2. It is observed that Cu promoter can increase the reduction or carburization degree and thus enhance the FTS activity. The addition of Mn to Fe/h-BN can weaken the strong interaction by altering the electron structure of iron species. And the electron-rich Fe species are responsible for easy reduction and the enhanced FTS performance. Besides, a higher activity can be realized by co-adding Cu and Mn to the Fe/h-BN catalyst. These results suggest that the synergistic effect of Mn and Cu can largely improve the performance of Fe/h-BN catalyst without impairing the stability of the catalyst. The present study paves a way to tailor the performances of FTS catalysts with h-BN as support.

Influences of ordered mesoporous silica on product distribution over Nb-promoted cobalt catalyst for Fischer-Tropsch synthesis

Nb-promoted cobalt catalysts supported on ordered mesoporous silica were prepared by sequential impregnation method and characterized by N2 physisorption, XRD, TEM, EDS-Mapping, H2-TPR, and CO-TPD. The performance of samples and the product distribution were investigated on a fixed bed reactor for Fischer-Tropsch synthesis (FTS). In respect of porous properties, the modification of supports with Nb can reduce the BET surface areas, pore volume, and pore size, possibly owing to the fact that the pore of ordered mesoporous silica was covered partially by NbOx. After the modification of Nb, both the structures of SBA-15 and KIT-6 are very stable as a catalyst support, but that of Co/Nb-MCM-41 was obviously distorted. The formation of smaller cobalt particles occurs in the narrow pore size of support. The presence of NbOx on catalyst surface can significantly weaken the cobalt-support, and accelerate the reduction of cobalt oxides. Meanwhile, NbOx can significantly enhance the adsorption stability and amount of CO adsorbed at FTS reaction condition for Co/Nb-KIT-6 sample. The CO conversion and C5+ selectivity for Co/Nb-KIT-6 sample are 92.1% and 85.1%, which are all higher than other samples supported on SBA-15 and MCM-41, and Co/Nb-KIT-6 sample has a lower CH4 selectivity up to 7.7%. Therefore, the supports with larger pore size are in favour of the formation of larger Co particles, resulting in higher FTS reaction activity. In addition, the introduction of Nb into cobalt catalysts can accelerate FTS activity and the growth of hydrocarbon chains. However, Co/Nb-MCM-41 sample with smaller pores is beneficial to the formation of oxy-compound and its selectivity to alcohols is 4.5%. Wherein, Co/Nb-KIT-6 sample has a higher selectivity to C2+-OH up to 75%. Thus, KIT-6 modified by Nb can be applied as a promising support for FTS catalysts in terms of enriching the range of FTS products.

Active Fischer-Tropsch synthesis Fe-Cu-K/SiO2 catalysts prepared by autocombustion method without a reduction step

ABSTRACT The purpose of this study was to prepare iron-based catalysts supported on silica by autocombustion method for directly using for Fischer–Tropsch synthesis (FTS) without a reduction step. The effect of different citric acid (CA):iron nitrate (N) molar ratios and acid types on the FTS performance of catalysts were investigated. The CA:N molar ratios had an important influence on the formation of iron active phases and FTS activity. The iron carbide (FexC), which is known to be one of the iron active phases, was demonstrated by the X-ray diffraction and X-ray photoelectron spectroscopy. Increasing the CA:N molar ratios up to 0.1 increased CO conversion of catalyst to 86.5%, which was then decreased markedly at higher CA:N molar ratios. An excess of CA resulted in carbon residues covering the catalyst surface and declined FTS activity. The optimal catalyst (CA:N molar ratio = 0.1) achieved the highest CO conversion when compared with other autocombustion catalysts as well as reference catalyst prepared by impregnation method, followed by a reduction step. The autocombustion method had the advantage to synthesize more efficient catalysts without a reduction step. More interestingly, iron-based FTS catalysts need induction duration at the initial stage of FTS reaction even after reduction, because metallic iron species need time to be transformed to FexC. But here, even if without reduction, FexC was formed directly by autocombustion and induction period was eliminated during FTS reaction.

Structural and elemental influence from various MOFs on the performance of Fe@C catalysts for Fischer-Tropsch synthesis.

The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer-Tropsch synthesis (FTS) catalysts have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are re-engineered towards FTS catalysts by means of simple pyrolysis at 500 °C under a N2 atmosphere and afterwards characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state. We discovered that the Fe loading (36-46 wt%) and nanoparticle size (3.6-6.8 nm) of the obtained catalysts are directly related to the elementary composition and porosity of the initial MOFs. Furthermore, the carbonization leads to similar surface areas for the C matrix (SBET between 570 and 670 m2 g-1), whereas the pore width distribution is completely different for the various MOFs. The high catalytic performance (FTY in the range of 1.9-4.6 × 10-4 molCO gFe-1 s-1) of the resulting materials could be correlated to the Fe particle size and corresponding surface area, and only minor deactivation was found for the N-containing catalysts. Elemental analysis of the catalysts containing deliberately added promoters and inherent impurities from the commercial MOFs revealed the subtle interplay between Fe particle size and complex catalyst composition in order to obtain high activity and stability next to a low CH4 selectivity.

A novel nano fischer‐tropsch catalyst for the production of hydrocarbons

A novel silica nanospring (NS) supported cobalt catalyst for Fischer‐Tropsch synthesis (FTS) was synthesized and investigated, and the results were compared with those of a conventional cobalt catalyst. The NS catalyst was prepared using deposition of Co followed by thermal assisted reduction and characterized by scanning electron microscopy‐energy dispersive spectroscopy, transmission electron microscopy, N2 physisorption, X‐ray powder diffraction, X‐ray photoelectron spectroscopy, and H2‐temperature programmed reduction. FTS performance was evaluated in a quartz fixed‐bed microreactor (230°C, H2:CO ratio 2:1), and the products were trapped and analyzed with gas chromatography‐thermal conductivity detector (GC‐TCD, gases) and gas chromatography‐mass spectrometry (GC‐MS, semivolatiles) to determine the percentage of CO conversion and selectivity. Semivolatile products from both catalysts were C6‐C18 hydrocarbons. Even though the NS FTS catalyst was not fully reduced during the activation period it still showed higher FTS activity than the conventional catalyst, which is attributed to the higher accessibility of the gases to the Co on the NS surface. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 693–698, 2014

Preferential chemical vapor deposition of ruthenium on cobalt with highly enhanced activity and selectivity for Fischer–Tropsch synthesis

Various amount of ruthenium was preferentially deposited on cobalt of Co/γ-Al2O3 by chemical vapor deposition (CVD) of ruthenocene and compared with a CoRu/γ-Al2O3 catalyst prepared by the usual impregnation method for Fischer–Tropsch synthesis (FTS). The Co/γ-Al2O3 was prepared by wet impregnation of cobalt nitrate aqueous solution, and then dried and calcined at 400°C for 4h. Ruthenocene was sublimated, carried by argon, and then mixed with H2 and passed over γ-Al2O3 or calcined Co3O4/γ-Al2O3 catalyst at various temperatures. The effluent gasses were passed through a gas cell of FTIR to determine the ruthenocene thermo-chemical decomposition products. In a temperature range (window) of 150–200°C the ruthenocene decomposes on Co3O4/γ-Al2O3 but not on γ-Al2O3. The catalysts were characterized by TPR, EDX, TEM, XRD and BET. The FTS activity and selectivity of the Ru-Co/γ-Al2O3 catalysts were investigated in a fixed bed microreactor. The preferential CVD of 0.3wt% ruthenium onto 15.0wt% Co/γ-Al2O3 (CoRu5-180) catalyst shifted both cobalt TPR peaks by about 120°C to lower temperatures, showed about 2.8 times higher conversion, 30% more C5+ selectivity, and 30% less selectivity of methane. The CoRu5-180 catalyst showed about 81% higher CO conversion and 12% higher selectivity to C5+ than the same catalyst composition prepared by the used impregnation of ruthenium chloride onto the 15.0wt% Co/γ-Al2O3.

Carbon nanotube-supported Fe–Mn nanoparticles: A model catalyst for direct conversion of syngas to lower olefins

Carbon nanotube (CNT)-supported monodisperse Fe3−xMnxO4 (x=0–0.5) nanoparticles in which Mn has an intimate contact with Fe were synthesized and used as a model catalyst for investigating the promotion effect of Mn oxide on the iron-based catalysts for Fischer–Tropsch synthesis (FTS) reaction. It was found that incorporation of Mn oxide (Mn/Fe=0.024–0.2) into a Fe3O4/CNT catalyst promoted the reduction of Fe3O4 to FeO, but retarded the further reduction of FeO to metallic Fe. Incorporation of small amount of Mn (Mn/Fe≤0.01) into the iron catalyst results in an increase in C5+ yield and C2–C4 olefin selectivity without any loss in FTS activity. However, the total selectivity of C2–C4 hydrocarbons is almost not affected by the addition of Mn oxide. An excess of Mn oxide in the catalysts (Mn/Fe>0.024) can lead to a significant decrease in FTS activity with no further improvement in C2–C4 olefin selectivity. The results of temperature-dependent XRD study on the Fe3O4/CNT and Fe2.73Mn0.27O4/CNT catalysts under H2/CO=1 mixture suggest that the decreasing in FTS activity on the Fe3−xMnxO4/CNT catalysts with an excess of Mn may have resulted from that the rate of carburization of metallic Fe is retarded by the Mn oxide species.

Carbon nanotubes decorated α-Al2O3 containing cobalt nanoparticles for Fischer-Tropsch reaction

A new hierarchical composite consisted of multi-walled carbon nanotubes (CNTs) layer anchored on macroscopic α-Al2O3 host matrix was synthesized and used as support for Fischer-Tropsch synthesis (FTS). The composite constituted by a thin shell of a homogeneous, highly entangled and structure-opened carbon nanotubes network and it exhibited a relatively high and fully accessible specific surface area of 76 m2·g−1, compared with that of 5 m2·g−1 of the original α-Al2O3 support. The metal-support interaction between carbon nanotubes surface and cobalt precursor and high effective surface area led to a relatively high dispersion of cobalt nanoparticles. This hierarchically supported cobalt catalyst exhibited a high FTS activity along with an extremely high selectivity towards liquid hydrocarbons compared with the cobalt-based catalyst supported on pristine α-Al2O3 or on CNTs carriers. This improvement can attribute to the high accessibility of composite surface area comparing with the macroscopic host structure alone or to the bulk CNTs where the nanoscopic dimension induced a dense packing with low mass transfer which favoured the problem of reactants competitive diffusion towards the cobalt active site. In addition, intrinsic thermal conductivity of decorated CNTs could help the heat dissipating throughout the catalyst body, thus avoiding the formation of local hot spots which appeared in high CO conversion under pure syngas feed in FTS reaction. Cobalt supported on CNTs decorated α-Al2O3 catalyst also exhibited satisfied high stability during more than 200 h on stream under relatively severe conditions compared with other catalysts reported in the literature. Finally, the macroscopic shape of such composite easily rendered its usage as catalyst support in a fixed-bed configuration without facing problems of transport and pressure drop as encountered with the bulk CNTs.

The effect of surface acidic and basic properties of highly loaded Co catalysts on the Fischer–Tropsch synthesis

Highly loaded cobalt catalysts (80% by weight) with different supports (SiO2, Al2O3, ZrO2 and MgO) were prepared by the co-precipitation technique for Fischer–Tropsch synthesis (FTS). Microcalorimetric adsorptions of NH3, CO2, CO and H2 showed that the surface acidity/basicity significantly affected the surface properties of supported Co, as evidenced by the changes of strengths of adsorption of CO and H2 on Co, which in turn affected the FTS performance. The appropriate ratio (~ 1.2) of heats for the adsorption of CO and H2 on Co seemed important in determining the FTS activity.

Mechanistic aspects of the role of chelating agents in enhancing Fischer–Tropsch synthesis activity of Co/SiO2 catalyst: Importance of specific interaction of Co with chelate complex during calcination

Co/SiO2 catalysts (20mass%) with enhanced activities for Fischer–Tropsch synthesis (FTS) were prepared by a newly developed two-step impregnation method using several chelating agents, and the effects of the calcination temperature and chelating agent on their FTS activities were investigated to clarify the role of the chelating agent during preparation of the catalyst. Their effects upon coordination environments of Co species were also studied by in situ Co K-edge quick XAFS in conjunction with ex situ characterization techniques. The FTS activity of the catalysts increased with the calcination temperature, 473–543K, when the chelating agents with strong affinity to Co2+ such as trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CyDTA) were used for preparation. Such increase in the activity was accompanied with size reduction of Co species, while those in Co/SiO2 prepared in the absence of the chelating agents were simply agglomerated during calcination. In situ quick XAFS suggested that size reduction of Co species was associated with specific interaction between small Co oxide clusters and chelate complexes during calcination. It was also speculated that these complexes were converted to surface silicate species after combustion of carbonaceous moieties which would work as anchoring sites of Co oxide clusters, preventing agglomeration of small Co3O4 species originated from the clusters during calcination at high temperatures.

SBA‐16‐Supported Cobalt Catalyst with High Activity and Stability for Fischer–Tropsch Synthesis

AbstractSBA‐16 molecular sieves were used as support to prepare cobalt catalyst for Fischer–Tropsch synthesis (FTS). The catalysts were characterized by using TEM, power XRD, temperature‐programmed reduction, and N2 adsorption–desorption. The analyses indicate that most of the Co3O4 nanoparticles were introduced into the SBA‐16 cages, and the SBA‐16 mesostructure was retained after cobalt impregnation. The Co/SBA‐16 catalyst exhibited higher cobalt dispersion compared to the Co/SiO2 catalyst. The catalytic properties of the catalysts in FTS were evaluated in a fixed‐bed reactor. The effect of the addition of water was measured in a continuously stirred tank reactor. High FTS activity and stability were observed on the SBA‐16‐supported catalyst. The SBA‐16‐supported cobalt catalyst shows low mobility of cobalt particles in the SBA‐16 cages. Unlike silica, the SBA‐16 support can efficiently prevent the aggregation and sintering of cobalt nanoparticles.