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The low effectiveness factor of catalyst pellet caused by high internal diffusion limitation is a common issue in fixed‐bed reactor. Nevertheless, hierarchical structured catalyst provides a promising solution for the contradiction between reaction activity and diffusion efficiency in large catalyst pellets. Herein, we studied the effect of pore structure parameters of the meso‐macroporous catalyst on Fischer–Tropsch synthesis performances through experiment and pellet scale reaction–diffusion simulation. The pellet simulation firstly elucidated the reason for the significant improvement on activity and product selectivity for the meso‐macroporous catalyst observed in our experiment. Further optimization via pellet simulation indicated the critical influences of wax filling degree and that the perfect matching between reaction and mass transfer rates by increasing macropore size and adjusting porosity within pellet enables the C5+ space–time yield to the maximum. This work could provide a theoretical guideline for the engineering design of the hierarchical structured catalyst pellet. [ABSTRACT FROM AUTHOR]

A simple and effective method to modify Co/Al2O3 catalyst to improve the catalytic performance in Fischer‐Tropsch synthesis reaction is described. It is found that the electron density on the cobalt surface increases via electron donation from the dopant Ba and CN species, leading to an enhanced C5+ selectivity and C3 o/p ratio. However, the presence of Ba increases the cobalt crystalline size while the introduction of CN species leads to the formation of smaller cobalt nanoparticles and greatly increases their dispersion, thus resulting in a different distribution of heavy hydrocarbon products. Our work offers a new avenue to obtain catalyst with high activity and selectivity. [ABSTRACT FROM AUTHOR]

The modification of the equilibrium morphology to expose active facets of cobalt nanoparticles is essential for tailoring and controlling its catalytic performance. Periodic density functional theory (DFT) was applied to systematically investigate the structure and stability of exposed facets of hcp Co nanoparticles induced by Ru promoter in order to clarify the facet‐dependent equilibrium morphology of hcp Co nanoparticles stabilized by Ru promoter. The adsorption and migration of Ru atom can give rise to the change of the surface energy of exposed facets, thus affecting the equilibrium morphology of the hcp Co nanoparticles. Selectively exposed the high Miller index facets, such as Co(10‐12), Co(11‐20) and Co(11‐21) surfaces, can be tuned by adding Ru promoter. Our theoretical calculation results show that Co(11‐21) becomes the predominantly exposed facet accompanied with the decrease of exposed Co(10‐10) and Co(10‐11) with the increase of Ru loading. Further experimental studies suggest that the area of selectively exposed the Co(10‐11) surface for uniform Co nanoplates loaded with 3.0 wt % Ru will be reduced, which is in agreement with the theoretical predicted result. This work is helpful to design the desired Co‐based FTS catalysts rationally with well‐controlled surface structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hierarchical micro-meso-macroporous Beta zeolite (HB) was developed by a steam-assisted crystallization method using meso-macroporous silica as the precursor and was employed for cobalt Fischer-Tropsch synthesis，exhibiting excellent catalytic performances. • The hierarchical micro-meso-macroporous Beta zeolite (HB) supported catalyst, on the one hand has a wealth of acidic sites, increasing the selectivity of isoparaffins; on the other hand has a good macroporous structure, which is favour for reducing the internal diffusion limitations, reducing the methane selectivity. • In this paper, we examined the effect of macroporoes on reducing internal diffusion limitations, confirming that macropores have good mass transfer and diffusion effects in large pellet catalysts. Large pellet catalysts were used in the evaluation process, which was very close to industrial production. A hierarchical micro-meso-macroporous Beta zeolite (HB) was developed by a steam-assisted crystallization method and was employed for cobalt Fischer-Tropsch synthesis. Meso-macroporous silica (HS), alumina modified meso-macroporous silica (HAS) and conventional Beta zeolite (CB) were used for comparison. Structural characterization indicated that the as-synthesized HB exhibited nanosized Beta zeolite crystallites and a hierarchical micro-meso-macroporous structure. The HB supported catalyst showed very high isoparaffins selectivity because of the isomerization reaction at the strong acidic sites of the Beta zeolite, while due to its good macroporous structure, which is in favor of reducing the internal diffusion limitations, the methane selectivity was kept as low as HAS supported catalysts. In this paper, we use large particle catalysts for evaluation, which are very close to industrial condition. And the conclusions obtained may be very important for the design of new Fischer-Tropsch catalysts. [ABSTRACT FROM AUTHOR]

CeO 2 has obvious crystal selection effects on supported cobalt catalysts, the Co 3 O 4 supported on CeO 2 with nanorods, nanocubes, and nanopolyhedrons dominantly exposed (2 2 0), (1 1 1), and (3 1 1) planes, respectively, and the reduced Co dominantly exposed (10–11), (0001), and (1 1 1) planes, respectively, showing different catalytic performance for FTS. [Display omitted] • Supported Co 3 O 4 with exposing specific planes were obtained by varying CeO 2 planes. • Supported Co with exposing specific planes were obtained by varying CeO 2 planes. • Co(10–11) supported on rod CeO 2 exhibited the optimal catalytic performance for FTS. The exposing planes of carrier play an essential role in determining the exposing planes and catalytic performance of supported metal catalysts. In this work, Co 3 O 4 nanoparticles were supported on the CeO 2 nanorods, nanocubes, and nanopolyhedrons, with dominantly exposing CeO 2 (1 1 0), (1 0 0), and (1 1 1) planes, respectively. High resolution transmission electron microscope graphs clearly confirmed that CeO 2 has obvious crystal selection effects on supported cobalt, the corresponding supported Co 3 O 4 dominantly exposed (2 2 0), (1 1 1), and (3 1 1) planes, respectively, and the reduced Co dominantly exposed (10–11), (0001), and (1 1 1) planes, respectively. Their catalytic behaviors for Fischer–Tropsch synthesis (FTS) were studied in detail, and the optimal catalytic performance was obtained over the cobalt catalyst supported on CeO 2 nanorods, mainly due to its exposed Co (10–11) plane with low reaction barrier (-0.83 eV) after reduction. The laser Raman spectra, X-ray photoemission spectroscopy, temperature-programmed reduction, and in situ CO Fourier transform infrared spectroscopy further confirmed the effects of carriers with exposing different planes on the supported cobalt catalysts, explaining the reason for the significantly differences in FTS catalytic performance. [ABSTRACT FROM AUTHOR]

Nitrogen-doped ordered mesoporous carbons (OMCs) were prepared by using a post-synthetic method with cyanamide as a nitrogen source; they were used as supports for the fabrication of the cobalt-based Fischer-Tropsch synthesis (FTS) catalysts. The obtained composites were well characterised by using nitrogen physisorption, Raman spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, hydrogen chemisorption, X-photoelectron spectroscopy, thermogravimetry-MS, and in situ XRD to investigate the effects of nitrogen on the dispersion of cobalt species and successive autoreduction behaviour of cobalt oxide as well as the catalytic performance in the FTS. The results indicate that the doped nitrogen atoms, especially the pyridine-like nitrogen, actually serve as the anchoring sites for cobalt species. Consequently, the more uniform cobalt particle size is observed for the catalysts with nitrogen-doped OMCs as supports in comparison with their counterparts based on the pristine OMCs. In contrast, the autoreduction temperature of cobalt oxide in the as-synthesised catalysts lowers considerably after nitrogen doping, although slightly increased autoreduction temperature is observed for the catalysts with relatively high nitrogen content owing to the metal-support interaction. Dictated by the balance between decreasing particle size of cobalt and increasing strength of the metal-support interaction, the cobalt specific activity of the nitrogen-doped catalysts reaches a maximum and then decreases in the FTS with increasing nitrogen content. Notably, under optimum conditions, the cobalt specific activity on the nitrogen-doped sample with medium nitrogen content is 1.5 times higher than its analogue on the pristine OMC without compromising the selectivity to C5+ hydrocarbons. [ABSTRACT FROM AUTHOR]

A series of core-shell-structured catalysts that consist of different-sized Co3O4 nano-particles and silica shells were prepared by an in situ coating method. The reduced catalysts displayed uniform core sizes that ranged from 5.5-12.7 nm as ascertained by TEM, which concurred well with XRD analysis. The BET results revealed the highly mesoporous nature of the silica shell, which contributes to the facile access of the reactant gas to the active sites on the core particles. The degree of reduction of the calcined catalysts studied by H2 temperature-programmed reduction was enhanced with increased Co particle size. In the Fischer-Tropsch synthesis, a volcano-like curve was plotted as the CO conversion and Co-time-yield revealed a rapid growth if the particle size increased from 5.5 to 8.7 nm and then decreased with further increased particle size to 12.7 nm, which is an effect of the combination of Co dispersion and reducibility. However, the turnover frequency remained invariant for catalysts with particle sizes larger than 8.7 nm. If we consider the product selectivity, generally, larger particles led to a longer chain length of hydrocarbons with a larger chain-growth probability. The selectivity towards methane decreased and the corresponding heavy hydrocarbons (C19+) increased continuously with the increase of particle size. The catalyst with a particle size of 8.7 nm exhibited the highest selectivity and the maximum space-time-yield towards middle distillates (C5-C18) because of the modest chain-growth probability. [ABSTRACT FROM AUTHOR]

Highlights: [•] In situ coating method is developed to prepare silica coated core–shell catalysts. [•] An uncoated catalyst with cobalt particles outside silica beads is also obtained. [•] Silica coating leads to diffusion restrictions of reactants, which lowered molecular weight of hydrocarbon products. [•] Silica coating increases product selectivity toward middle distillates and olefins. [ABSTRACT FROM AUTHOR]

Ordered mesoporous carbon supported cobalt-based catalysts (Co/MC) were synthesized via incipient wetness impregnation with different amounts of furfuryl alcohol (FA) as carbon precursor. The characterizations of obtained Co/MC were subjected to N adsorption, XRD, XPS, TEM, H-TPR, H-TPD and H-TPSR. The results indicate that the reducibility and dispersion of Co active species vary significantly due to the difference of FA amount. By simply tuning the FA content from 25 to 100 wt%, the reduction temperature of deriving metallic Co shifts gradually to lower. The catalytic performance of Co/MC was evaluated for Fischer-Tropsch (FT) synthesis. The observed FT activity exhibits a volcano-type curve with the amount of FA due to the effect of both reducibility and dispersion of active species. As the precursor concentration overweighs 50 wt%, the ability of CO to dissociate over the active surface and the selectivity to the C products level off after experiencing an initial increase. Substantially, the catalysts with higher concentration of FA render the larger crystallites having an average size of more than 6 nm, which facilitates the CO hydrogenation by way of carbon chain propagation. It seems that the sample with FA content of 50 wt% is optimum in terms of FT activity and C selectivity. Graphical Abstract: By simply tuning the carbon precursor furfuryl alcohol (FA) content from 25 to 100 wt%, the textural property of mesoporous carbon varies significantly, which further induces the different reducibility and dispersion of Co active species and the temperature of deriving metallic Co shifts gradually to lower. The catalytic performance of as-synthesized catalysts was evaluated for Fischer-Tropsch synthesis (FTS). The observed FT activity exhibits a volcano-type curve with the amount of FA due to the effect of both reducibility and dispersion of active species. At the FA concentration of support over 50 wt%, the selectivity to the C heavy molecular maintain invariant after experiencing an initial increase. It seems that the sample with respect to 50 wt% FA is optimum in terms of FT activity and C selectivity.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Different CoZr/H-ZSM-5 hybrid catalysts were prepared by a hydrothermal synthesis method, where H-ZSM-5 was enwrapped onto the Co-ZrO2 Fischer–Tropsch synthesis (FTS) catalyst. The catalysts were characterized by BET, XRD, 27Al NMR, SEM, TEM, XPS, H2-TPR, NH3-TPD and IR techniques. The catalytic performance for the direct conversion of syngas to high-octane gasoline-range (C5–11) hydrocarbons was studied. Coke formation on the spent catalysts was measured by TGA. Compared with the base Co-ZrO2 catalyst or the physically mixed catalyst of Co-ZrO2 with H-ZSM-5, the reducibility of the hybrid catalyst was much lower due to the strong interactions of cobalt phase with zeolite and/or zirconia. The catalytic performance results showed that the as-prepared hybrid catalysts had high selectivity towards gasoline-range isoparaffins and relatively low methane selectivity in spite of the relatively low catalytic activity. The hybrid catalysts could effectively minimize the accumulation of carbonaceous deposits. The catalyst with aluminum isopropoxide as Al source exhibited excellent selectivity on the isoparaffin synthesis and relatively good stability. [Copyright &y& Elsevier]

Both mono- and bi-modal Co-based Fischer-Tropsch Synthesis (FTS) catalysts were prepared by incipient-wetness impregnation (IWI). XRD and N physisorption revealed that the catalyst with a bi-modal distribution of 2.5-17 nm had the smallest size of cobalt crystal. In this case, the Raman absorbance shifted toward lower frequencies due to the size quantization effect. Furthermore, H-TPR indicated a lower reducibility originated from the interaction between small crystalline cobalt and silica. Such bi-modal structure catalysts showed a better FTS performance, and particularly the bi-modal mesopores catalyst presented the lowest methane selectivity, the highest activity and the highest selectivity to C-C hydrocarbons, which might be due to the confinement of mesopore to the cobalt particles. Graphical Abstract: The catalyst with a bi-modal distribution of 2.5-17 and 2.5-65 nm showed a better FTS activity, lower methane selectivity than mono-modal catalyst, particularly the bi-modal mesoporous catalyst presented the highest selectivity to C-C hydrocarbons [InlineMediaObject not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Co/SiO2 sol–gel catalysts were prepared in the presence of ethylenediamine under the same pH and characterized to have an insight into the dependence of product distribution on their structures in FT synthesis. Such catalysts prepared at the acid medium possessed high microporosity, which led to a high selectivity for middle distillates in FT synthesis. Furthermore, the activity of catalysts had a volcano-type dependence on the en/Co molar ratios. All those were closely related with the coordination state of Co precursors and their interaction with SiO2. [Copyright &y& Elsevier]

• A CO environment without CO disproportionation is constructed on the cobalt surface. • A carbon environment without CO deposition is constructed on the cobalt surface. • CO disproportionation is inevitable during carbonization reaction. • Carbon deposits can react with cobalt to form cobalt carbide. • The generated carbon via disproportionation does not participate in the carbonization reaction within the temperature range of "H 2 CO H 2 ″ processing. In the Fischer-Tropsch synthesis reaction, hcp-Co has more excellent catalytic performance than fcc-Co, thus, many studies have focused on the transformation from fcc-Co to hcp-Co via "H 2 CO H 2 ″ processing (reduction-carbonization-reduction). However, the existing form of CO during carbonization is still unclear, and it is difficult to determine whether the generated carbon via CO disproportionation participates in the carbonization reaction. In this study, the environments with CO without C and with C without CO were attempted to be constructed, respectively. The formation and evolution of Co 2 C were studied by in-situ Raman, XRD, TPH-MS and HRTEM. The results show that: (1) the transformation from fcc-Co to hcp-Co can be realized in the environment with C but no CO; (2) CO directly participate the transformation from fcc-Co to hcp-Co in the "H 2 CO H 2 ″ processing, and CO concentration and carbonization temperature jointly affect the "H 2 CO H 2 ″ processing; (3) carbon deposition is inevitable during the whole "H 2 CO H 2 ″ processing; however, the generated carbon does not participate in the reaction of forming Co 2 C within the transformation temperature range of the "H 2 CO H 2 ″ processing. In this study, the environments of CO without carbon and carbon without CO were constructed, respectively. The atoms rearrangement of CO and the formation and evolution of Co 2 C were studied by in-situ XRD, in-situ Raman and TEM. The results show that in the "H 2 CO H 2 ″ process, although carbon can be generated by CO disproportionation and react with Co to form Co 2 C, the generated carbon does not participate in the carbonization reaction within the temperature range of "H 2 CO H 2 ″ processing. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Monodispersible Co3O4 nanoparticles were prepared via a facile solvothermal route using polyvinylpyrrolidone (PVP) as the capping agent. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results, together with the N2 physisorption, indicated that those as-made Co3O4 nanoparticles of about 17nm could be used as cores to prepare core@shell nanocomposites with mesoporous silica shell. Such monodispersible Co3O4 nanoparticles were observed to be coated completely by mesoporous silica shell, and showed the higher catalytic activity and selectivity towards C5–C18 fraction than Co/mesoporous SiO2 (Co/m-SiO2) in the Fischer–Tropsch synthesis (FTS). [ABSTRACT FROM AUTHOR]

• Different alkaline earth metals on the catalytic performance of Co/Al 2 O 3 catalyst for Fischer–Tropsch synthesis was reported at the first time. • The alkaline earth metals modified catalyst with a low CH 4 and high C 5 + selectivity. • The excellent catalytic performance was attributed to lower H*/C* ratio and enhanced CO dissociation ability than the unmodified one. Alkali earth metals are effective promoters in cobalt-based Fischer–Tropsch synthesis. To compare the similarity and difference of the effect of the same main group of alkali earth metals on Fischer–Tropsch reaction, a series of alkali earth metals-modified alumina was prepared and applied as the supports for Co catalysts. Promotion of Co/Al 2 O 3 catalyst by alkali earth metals achieved a low CH 4 selectivity,high C 5 + selectivity and C 3 o/p due to the lower H*/CO* ratio and enhanced CO dissociation on the surface of catalyst than the unmodified one. [Display omitted] [ABSTRACT FROM AUTHOR]

• The thermally conductive ZnAl 2 O 4 @Al composites are prepared by simultaneously combining the hydrothermal surface oxidation and temperature-programmed thermal treatment. • The composition, surface chemical property and pore configuration of ZnAl 2 O 4 @Al composites can be effortlessly modulated by controlling the preparation condition. • The Co/Zn-Al-650 catalyst exhibits the similar intrinsic FT reaction behavior, macroscopic reaction performance and heat transfer properties to the Co/SiC catalyst. The development of alternative to silicon carbide (SiC) holds great promise in energy and environmental related catalysis because the harsh preparation process and high cost limit its large-scale application. In this work, the core-shell structured ZnAl 2 O 4 @Al ceramic-metal composites (Zn-Al-T) are prepared from low cost metallic Al powder by a facile and environment-friendly approach to replace silicon carbide for Co-based Fischer-Tropsch synthesis (FTS, a typical strong exothermic heterogeneous catalytic reaction). The composition, thermal conductivity, surface chemical properties and pore configuration of the ZnAl 2 O 4 @Al composites can be easily modulated by controlling the calcination condition. Among Zn-Al-T composites, the Zn-Al-650 and Zn-Al-750 samples demonstrate optimum coupling of physicochemical properties, i.e., robust chemical stability, meso -macropore structure (wide mesopore and high macroporosity) and high thermal conductivity. Thus, the excellent FT performance (low CH 4 selectivity and high selectivity to C 5+) was obtained on the Co/Zn-Al-650 and Co/Zn-Al-750 catalysts. The heat transfer experiments were conducted on a special tubular fixed-bed reactor (I.D. = 22 mm) under near-industrial conditions. At similar reaction rates, the effective radial thermal conductivity coefficient (k eaff) in the Co/Zn-Al-650 catalyst bed is 3–4 times and 1–2 times that in the Co/Al 2 O 3 and Co/SiC catalyst beds respectively, resulting in a more uniform temperature distribution in Co/Zn-Al-650 catalyst bed. In addition, the ZnAl 2 O 4 @Al composite has wide application prospect in strong exothermic/endothermic catalytic system owing to its high thermal conductivity, adjustable physico-chemical properties, facile preparation method and low cost. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The content of SiO x C y on SiC surface decreased after nitric acid treatment. • SiO x C y had great effect on the electron density and reduction degree of cobalt species. • The decrease of SiO x C y on SiC surface allowed a significant improvement of the C 5+ selectivity of Co/SiC catalysts. Abstract Co/SiC catalysts were prepared to investigate the role of SiO x C y on SiC surface in the catalytic performance for Fischer–Tropsch synthesis. SiC was pretreated by nitric acid with different concentration, and the Co/SiC catalysts were prepared and characterized by N 2 -adsorption, H 2 -chemisorption, XRD, TPR, TPO, XPS, and TEM. It was found that the decrease of SiO x C y caused by nitric acid treatment may be related to the increase of reducibility of Co/SiC catalysts and the decrease of binding energy of cobalt. The catalytic performance revealed that the less the content of SiO x C y was, the higher the selectivity of long chain hydrocarbon was. It was concluded that the strong electronegativity of SiO x C y had great effect on the electron density of cobalt species and then on the catalytic performance of the Co/SiC catalysts. [ABSTRACT FROM AUTHOR]

A series of Co Al spinel oxide modified ordered mesoporous alumina with different CoAl 2 O 4 contents were synthesized by a facile one-pot evaporation induced self-assembly (EISA) method. Then they were first investigated as supports for Cobalt-based catalysts for Fischer–Tropsch synthesis (FTS). The results from testing the catalysts clearly showed that the catalysts modified with CoAl 2 O 4 exhibited higher catalytic activity than the common ordered mesoporous alumina catalysts. A volcano-type dependence of the catalytic activity with the contents of CoAl 2 O 4 in the supports was observed. The results from in situ XRD revealed that the cobalt phase of the reduced catalysts modified with CoAl 2 O 4 were more likely to be HCP rather than FCC. As inferred from in situ CO-FTIR and CO-TPD results, the CO dissociation ability was enhanced by increasing the content of the CoAl 2 O 4 modification in the supports. Such a volcano-type dependence of catalytic activity with the contents of CoAl 2 O 4 in the supports was due to the combination of two factors. One was the generation of the HCP cobalt, which exhibited a higher CO dissociation ability. The other was the synergistic effect of lower reducibility and the degree of dispersion. Meanwhile, when the Co/Al ratios was 0.08 and 0.12 in the supports, the catalysts showed higher C5 + selectivity than other catalysts, which was mainly due to their high Co site density on the catalysts surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hybrid kinetic model for FTS over an industrial cobalt-based catalyst were developed. • CO activation paths and the rate determining step have been clarified. • The model could accurately describe the complex responses of C 19+ selectivity with process conditions. Intrinsic kinetic experiments were performed in a wide range of process conditions over an industrial Fischer-Tropsch Synthesis (FTS) cobalt-based catalyst to obtain the kinetic models, aiming at the process/engineering design and the elucidation of the reaction mechanism. A hybrid kinetic model including the CO consumption model based on the Langmuir Hinshelwood Hougen Watson (LHHW) reaction mechanism and the lump-type product distribution model-C 19+ selectivity model was developed. The obtained model, through parameters' evaluation and optimization, could provide an excellent prediction of CO conversion and C 19+ selectivity in a wide process condition range. Furthermore, it was inferred that CO activation follows direct dissociation mechanism with the hydrogenation of the dissociated C* and O* to CH* and OH* respectively as the rate determining step; and the activation energy for CO consumption rate model was obtained as 80.26 kJ mol−1. [ABSTRACT FROM AUTHOR]

High thermal conductive Al 2 O 3 @Al composite synthesized via metallic Al powders corrosion method has been applied as support for preparing Co/Al 2 O 3 @Al catalyst for high exothermic Fischer-Tropsch synthesis. The prepared Al 2 O 3 @Al composite is a hierarchical macro-mesoporous structure and consist of two parts, namely the inner metallic Al and the outer Al 2 O 3 with two kinds of morphologies. Increasing the concentration of the corrosive NaOH or extending the corrosion time could increase the specific surface area of the composite. For the prepared Co/Al 2 O 3 @Al, Co 3 O 4 phase is located on the outer plate-like Al 2 O 3 layer. The Co/Al-0.03-20 possesses higher CO conversion and C 5+ selectivity due to the appropriate cobalt reducibility, dispersion and high thermal conductivity. The thermal conductive coefficient of Co/Al 2 O 3 @Al catalysts is 13–98 times of conventional Co/Al 2 O 3 . Compared to Co/Al 2 O 3 , the Co/Al 2 O 3 @Al shows higher CO conversion and C 5+ selectivity as well as lower CH 4 and CO 2 selectivity, which is attributed to the macro-mesoporous structure and high thermal conductivity. In addition, because of the high thermal conductivity, no heat disperser should be used and a homogeneous temperature gradient maintains within the catalyst bed for Co/Al 2 O 3 @Al. [ABSTRACT FROM AUTHOR]

Abstract: A series of silylated Co/SBA-15 catalysts were prepared via the reaction of surface Si–OH of SBA-15 with hexamethyldisilazane (HMDS) under anhydrous, vapor-phase conditions, and then characterized by FT-IR, N2 physisorption, TG, XRD, and TPR-MS. The results showed that organic modification led to a silylated SBA-15 surface composed of stable hydrophobic Si–(CH3)3 species even after calcinations and H2 reduction at 673K. Furthermore, the hydrophobic surface strongly influenced both metal dispersion and reducibility. Compared with non-silylated Co/SBA, Co/S-SBA (impregnation after silylation) showed a high activity, due to the better cobalt reducibility on the hydrophobic support. However, S-Co/SBA (silylation after impregnation) had the lowest FT activity among all the catalysts, due to the lower cobalt reducibility along with the steric hindrance of grafted –Si(CH3)3 for the re-adsorption of α-olefins. [Copyright &y& Elsevier]

[Display omitted] • Model FTS catalyst granules with different thermal conductivity were prepared. • Overheating effect was exist within catalyst granule with low thermal conductivity. • Thermal conductivity of FTS catalyst granules could influent the catalytic performance. • Thermal conductivity could affect syngas adsorption, hydrogenation and chain growth. A series of model Fischer-Tropsch synthesis (FTS) catalyst granules with different thermal conductivity were prepared to study the influence of catalyst granule thermal conductivity on FTS performance. A clear correlation was found between catalyst granule thermal conductivity and FTS activity, CH 4 selectivity, C 5+ selectivity, mole ratio of olefin to paraffin and branched hydrocarbon selectivity at high CO conversion. This could be due to that the overheating effect occurred within catalyst granule with low thermal conductivity. On the basis of the widely accepted 'alkyl' mechanism for FTS, the overheating effect was able to affect the adsorption of H 2 and CO molecules, the hydrogenation of carbide species as well as chain growth. In addition, the overheating effect could lead to the catalyst structure reconstruction, sintering and deactivation. [ABSTRACT FROM AUTHOR]

• Process conditions have complex and abnormal influences on chain growth. • Several accordant and opposite factors contribute to the abnormal observations. • The extent of α-olefin readsorption could influence the product selectivity. A systematic study of the effects of process variables on Fischer-Tropsch synthesis product selectivity over an industrial cobalt catalyst was carried out at a broad range of industrial conditions (T = 170−215 °C, P = 1.0–5.6 MPa, H 2 /CO = 2.0–3.0, WHSV = 2.0–23.4 N L/g/h) using a fixed-bed reactor. Lower temperature and higher pressure were beneficial for suppressing methane formation. However, a volcano-shape of temperature versus C 19+ selectivity was observed. Correlations between pressure and C 19+ selectivity were closely related to the temperature. Lower space velocity and inlet H 2 /CO ratio had mild but positive effects on the product distribution. The unique C 19+ selectivity variations with temperature and pressure indicate a complicated chain growth process that stems from different aspects of the catalyst (i.e., chain propagation, chain termination and α-olefin readsorption) with process conditions. A mechanism involving several accordant and opposite effecting factors is considered for reasonably explaining the abnormal observations and providing a few reasonable interpretations of the contradictions among the related literatures. [ABSTRACT FROM AUTHOR]

• CO and H stable coverage depend on realistic condition over Co surfaces. • The gas adsorption influences surface morphology of Co catalyst. • Equilibrium morphology evolution of Co nanoparticle could predict facet distribution. Metal nanoparticles could change their shape and exposed certain facet under specific reaction conditions, resulting in greatly influence the performance of catalysts in heterogeneous catalysis. Combining spin-polarized density functional theory and ab initio atomistic thermodynamics, the equilibrium morphology evolution of FCC cobalt nanoparticle had been investigated under CO and hydrogen environments. The phase diagram clearly revealed the stable coverage could be affected by temperature and CO and hydrogen partial pressure. According to the surface energies of four surfaces, Wulff construction was introduced to characterize the morphologies of the Co catalyst at diverse temperatures and pressures. At the typical temperature (675 K) of hydrogen reduction, the estimated surface proportion ratio of the Co(3 1 1) exposed the B5 site could exist a marked increase, which was also consistent with the available Co catalyst reduced under experimental conditions. Our results would give direct insights into the understanding and quantitative description of structure evolution as well as active facets of the Co nanoparticles under the realistic FTS reaction condition. [ABSTRACT FROM AUTHOR]