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Although considerable efforts towards directly converting syngas to liquid fuels through Fischer–Tropsch synthesis have been made, developing catalysts with low CO2 selectivity for the synthesis of high‐quality gasoline remains a big challenge. Herein, we designed a bifunctional catalyst composed of hydrophobic FeNa@Si‐c and HZSM‐5 zeolite, which exhibited a low CO2 selectivity of 14.3 % at 49.8 % CO conversion, with a high selectivity of 62.5 % for gasoline in total products. Molecular dynamic simulations and model experiments revealed that the diffusion of water molecules through hydrophilic catalyst was bidirectional, while the diffusion through hydrophobic catalyst was unidirectional, which were crucial to tune the water‐gas shift reaction and control CO2 formation. This work provides a new fundamental understanding about the function of hydrophobic modification of catalysts in syngas conversion. [ABSTRACT FROM AUTHOR]

In order to investigate the enhancement of Zr in FTS performance, a series of Zr-modified 20 wt% Co/Al 2 O 3 catalysts has been prepared by regulating the Zr and Co impregnation order and Zr amount and then the catalytic performance were evaluated in a fixed reactor. The Zr addition leads to a significant increase in activity, olefin/paraffin ratio for C 3 and C 4 at a similar CO conversion, and selectivity to C 5 + compared with the Co/Al 2 O 3 catalysts. The co-impregnation of Zr and Co shows the most attractive catalytic performance. This can be attributed to the higher reducibility of the catalyst as well as the formation of Co–Zr interface. The introduction of Zr can enhance the interaction between C∗ and cobalt active sites and weaken the C O bond, making CO easier to be dissociated and the selectivity of C 5 + is improved. • The addition of Zr leads to a significant increase in activity, olefin/paraffin ratio for C 3 and C 4 at a similar CO conversion. • The introduction of Zr can promote the ability of CO dissociation and then improve the selectivity of C 5 +. • The improvement of Zr-modified Co/Al 2 O 3 catalytic performance is determined by the reducibility of the catalyst and the formed Co–Zr interface. [ABSTRACT FROM AUTHOR]

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]

Whether Co-ZrO 2 interfacial sites have a beneficial effect on Co-based Fischer-Tropsch synthesis is still controversial. In this paper, different quantities of Co-ZrO 2 interfacial sites were fabricated by changing the impregnation sequence of Zr added to Co/SiC catalysts. The effect of the Co-ZrO 2 interfacial sites was investigated by nitrogen adsorption, X-ray diffraction (XRD), hydrogen chemisorption (H 2 -TPD), temperature-programmed reduction (H 2 -TPR) and TEM-EDS- mapping analyses. It was found that when zirconium was on the surface of cobalt, more Co-ZrO 2 interfacial sites were formed, and a higher selectivity of long-chain hydrocarbons was observed. In addition, the formation of Co-ZrO 2 interfacial sites significantly increased the conversion frequency of CO. This work is of great significance for understanding the role of Co-ZrO 2 interfacial sites and guiding the design of related catalysts in Co-based Fischer-Tropsch synthesis. • Different content of Co-ZrO 2 interface active sites in Co/SiC catalysts were created. • Co/SiC catalysts with higher content of Co-ZrO 2 interfacial active sites have higher selectivity of long chain hydrocarbon. • This study provides support for the application of interface theory in catalysts in the future. [ABSTRACT FROM AUTHOR]

In this work, the partial carbonization conversion of hcp-Co was carried out to obtain hcp-Co@Co 2 C compound with strong synergy, which exhibited high selectivity of higher alcohols owing to the obtained interface between hcp-Co and Co 2 C. [Display omitted] • The hcp-Co@Co 2 C catalyst was obtained by partial carbonization of hcp-Co. • There was a strong synergy between hcp-Co and Co 2 C due to the Co-Co 2 C interface. • Ethyne was used as a carbon source to dissociate on the surface of hcp-Co, and then Co was carbonized into Co 2 C. • The degree of carbonation conversion and synergy was easily controlled. • The hcp-Co@Co 2 C exhibited high selectivity of higher alcohols. The hcp-Co@Co 2 C catalysts were prepared by partial carbonization conversion of hcp-Co, which possessed rich Co-Co 2 C interface and strong synergy between hcp-Co and Co 2 C, compared with fcc-Co. The degree of carbonization conversion was easy to control, for ethyne was used as carbon source to dissociate on the surface of cobalt to form carbon species, and then carbonization conversion took place and hcp-Co@Co 2 C formed. The prepared hcp-Co@Co 2 C catalysts exhibited high selectivity of higher alcohols, compared with hcp-Co, owing to the rich interface and strong synergy between hcp-Co and Co 2 C. [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]

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]

Co/SiO2 catalysts were prepared by sol-gel method with varied en (ethylenediamine)/Co molar ratios under the same pH. Their physical-chemical properties were compared with those prepared with similar en/Co molar ratios at natural pH or without adding ethylenediamine. Regardless of pH, the catalysts prepared using ethylenediamine possessed high microporosity, which led to a better selectivity to C5–18 hydrocarbons, versus the catalyst possessing higher mesoporosity which showed slightly higher C18+ selectivity. As enough positions in the coordination sphere were blocked by ethanediamine ligands, the formation of cobalt silicate disfavored for (en/Co=2) catalysts, which resulted in the higher activity in FT reaction. Whereas the catalysts prepared with lower or higher en/Co molar ratio both showed lower activity due to the formation of [(SiO)Co(en)(EtOH)3] species or the electronic adsorption of cobalt complexes in the negatively charged silica surface, respectively. However, for the catalyst without using ethylenediamine, the lowest activity and the highest CH4 selectivity obtained due to its much lower reducibility. [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]

Modified alumina carriers were obtained by pre-coating cobalt aluminate on the surface of common alumina. Next, supported cobalt catalysts were obtained by incipient wetness impregnation, and their FTS performances were evaluated in a fixed-bed reactor. In situ XRD results suggested that HCP Co was obtained after reducing the aluminate-modified alumina-supported cobalt catalysts, as opposed to FCC Co, which was supported on common alumina. H 2 -TPR results demonstrated that the modified catalysts possessed lower reduction temperatures. CO-TPD and in situ CO-FTIR characterizations indicated that bridged rather than linear CO adsorption occurred on the modified catalysts. The evaluation results indicated that the aluminate-modified catalysts possessed higher CO conversion rates, higher C 5 + selectivity, higher cobalt specific activity, higher C 5 + space-time yields (STYs), and lower methane selectivity than conventional catalysts in the FTS process. [ABSTRACT FROM AUTHOR]

Directly converting syngas to α-olefins via the Fischer-Tropsch synthesis reaction serves as a competitive alternative to the traditional petroleum route, which has attracted much recent attention. However, achieving high catalytic activity over the iron-based catalyst remains a grand challenge, due to the easy oxidation of the iron carbides active phase by the water produced during reaction. Herein, we present a porous graphite-carbon encapsulated iron-based catalyst, in which the iron carbides remain stable even under harsh reaction conditions of high CO conversion or high reaction temperature. Due to the excellent anti-oxidation ability of active phase, an ultrahigh activity for producing C 4+ α-olefins of 11.35 g·g cat −1·h−1 can be obtained. This work provides a promising strategy to develop iron-based Fischer-Tropsch synthesis catalysts with high catalytic activity and stability by rationally stabilizing iron carbides. [Display omitted] • A strategy to stabilize iron carbides during syngas to α-olefins was proposed. • Porous graphite-carbon encapsulated pure iron carbides was successfully prepared. • The rigid graphite-carbon protected iron carbides from oxidation by water. • Ultrahigh activity for producing C 4+ α-olefins of 11.35 g·g cat −1·h−1 was achieved. [ABSTRACT FROM AUTHOR]

Abstract: SiO2 was modified by various organic groups before the impregnation of cobalt precursor. These modified supports and the corresponding catalysts were characterized by BET, 29Si CP MAS NMR, XRD, Raman, XPS and H2-TPR. These characterizations clearly show the changes of morphology as well as reducibility of the catalysts. The organic modification of SiO2 remarkably influences the reducibility and catalytic properties of Co catalysts. Co catalyst supported on (CH3)3-modified SiO2 exhibits high activity and C5 + hydrocarbon selectivity. However, COOH-, NH2-, and NH2(CH2)2NH-modified SiO2 distinctly suppress the catalytic activity of Co catalysts. [Copyright &y& Elsevier]

In the present work, CoZr catalysts without support have been prepared to investigate the nature of the Zr promotion. Evidences from multiple techniques shows that Zr prefers to locate on the coordinately unsaturated sites of nano-Co 3 O 4 , then enters the lattice of Co metal after reduction, leading to the lattice expansion. Benefitting from Zr induced structural changes of the Co metal, CO adsorption and dissociation have been enhanced. Besides, due to the strong interaction between Co and Zr, the growth of the Co metal crystal size during reduction and O atoms adsorption on the reduced catalysts surface are inhibited obviously, which makes more Co atoms available during FTS reaction. As a result, the catalytic performances are improved significantly. [Display omitted] • CoZr catalysts without support have been prepared under a wide range of Zr/Co molar ratio. • Zr prefers to locate on the coordinately unsaturated sites of nano-Co 3 O 4 , then enters the lattice of Co metal after reduction, leading to the lattice expansion. • The growth of the Co metal crystal and O atoms adsorption on the reduced catalysts surface are inhibited significantly. • The CoZr catalysts exhibits high activity and C 5 + selectivity. It is reported that Zirconium (Zr) is an effective promoter of cobalt-based catalysts for Fisher-Tropsch synthesis (FTS). Numerous studies have been conducted to explore the nature of the promotion. However, many of these studies focus on oxide-supported cobalt-based catalysts, in which the support effects may have partially enhanced or masked the influences of Zr. In the present work, CoZr catalysts without oxide support have been prepared across a wide range of Zr/Co molar ratio from 0.04 to 0.33 to investigate the nature of the Zr promotion. Comparing with the nano-Co 3 O 4 , the promoted catalysts exhibit excellent performance. The reaction temperature required to convert the same amount of syngas on the same amount of cobalt has decreased by about 40 °C. The selectivity of C 5 + has increased from 70∼81% to over 85% at the same CO conversion, and even higher than 90% on the CoZr catalysts with high Zr/Co ratio. Evidences from multiple techniques, including in situ XPS, CO-DRIFTs, CO-TPD, NH 3 -TPD, Py-IR, HRTEM, Raman and XRD, shows that Zr tends to occupy the coordinately unsaturated sites of nano-Co 3 O 4. After reduction, Zr enters the lattice of Co metal, leading to the lattice expansion. Benefitting from the Zr induced structural changes of the Co metal, CO adsorption and dissociation on the CoZr catalysts have been enhanced. Besides, due to the strong interaction between Co and Zr, the growth of the Co metal crystal during H 2 reduction and O atoms adsorption on the reduced catalysts surface are inhibited significantly, which make more Co atoms available during FTS reaction. As a result, the catalytic performances are improved obviously. [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]

[Display omitted] • Three single types of deposited carbon (atomic carbon, polymeric carbon and graphitic carbon) on Co-based catalyst are successfully constructed. • The Co catalyst with atomic carbon exhibits very high Fischer-Tropsch activity and low methane selectivity. • Polymeric carbon and graphitic carbon are detrimental to the Fischer-Tropsch reaction performance. 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 C 5+ 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. [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]

• Structured cobalt-based catalysts for FTS are reviewed. • Carbon and silicon carbide supported cobalt catalysts for FTS are reviewed. • The Al 2 O 3 @Al supported cobalt catalysts for FTS are introduced. • The industrial application of the Co/Al@Al 2 O 3 is prospected. The fixed-bed reactor is a good choice for the cobalt-based Fischer-Tropsch synthesis (FTS) to produce hydrocarbons. However, the heat transfer limitation of the fixed-bed reactor greatly threatens the safe operation of the reactor and modifies the overall products selectivity on account of the strong exothermic property of FTS. Therefore, it is urgent to strengthen the heat transfer for FTS in the fixed-bed reactor. In this review, the utilizations of the structured catalysts as well as the high thermal conductive carbon and silicon carbide supported cobalt catalysts to improve the heat transfer for FTS are summarized. More importantly, the research progress on the utilization of the novel, high thermal conductive Al 2 O 3 @Al as support for the cobalt-based FTS is emphatically introduced. It demonstrates that the heat transfer efficiency value k eff of the reactor bed packed with the Co/Al 2 O 3 @Al catalysts is 2–3 times higher than that of the conventional Co/Al 2 O 3. As a consequence, the heavy hydrocarbon selectivity is significantly increased for Co/Al 2 O 3 @Al, which makes it very promising for industrial application. The possible technical problems in large-scale industrial applications and their solutions over the Co/Al 2 O 3 @Al are also prospected in this review. [ABSTRACT FROM AUTHOR]

The adsorption, dissociation and desorption of CO at different coverage over two Co surfaces and the corresponding equilibrium phase diagrams under different temperatures and partial pressures have been systematically investigated; here, the results are obtained using density functional theory calculations and atomistic thermodynamics together with the periodic slab model. Our results show that the saturated adsorption on both Co(0001) and (100) surface are 7/9 ML; meanwhile, on these two surfaces, the lateral repulsive interaction has an effect on the adsorption structures and the corresponding stepwise adsorption energies of these adsorbed CO molecules, and become stronger with the increasing of CO coverage, which further leads to CO migration over Co surface; moreover, the adsorption energies decrease gradually with the increasing of CO coverage until to the saturated adsorption. According to the stepwise adsorption configurations, further calculations on CO dissociation show that only molecular adsorption CO is favored over (0001) surface; whereas on Co(100) surface, when the coverage is 1/9 ML, CO dissociation is more facile than its desorption; when the coverage is from 2/9 to 5/9 ML, only the first CO dissociation is preferred, while desorption is more favored for the left CO molecules; when the coverage is equal to or greater than 6/9 ML, CO desorption will be more favorable than its dissociation. Further, the adsorption and activation of CO under different temperatures and partial pressures from atomistic thermodynamics method well illustrate the relationship between the stable CO adsorption with the temperatures and CO partial pressure on Co(0001) and Co(100) surface, respectively. Therefore, on the basis of above results, we can obtain that the surface structures mainly affect the adsorption form of CO due to the different activity towards CO, while CO coverage will affect its adsorption energies and configurations, as well as CO dissociation on Co surfaces. The calculated stretching frequencies of CO molecule at different coverage agree with the available experimental data. This study provides a more accurate and detailed information for the process of CO adsorption and activation on Co surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • CO adsorption at lowest coverage is enhanced due to the short-range electronic effect of Ru on adsorbed CO molecular. • CO dissociation barrier depends on the adsorption site and the Ru content. • The amount of saturated adsorbed CO is increased while that of dissociated CO is decreased on the Ru-doped Co(1 0 0) surfaces at high coverage. • The adsorption model is preferred than substitution model for CO activation, as reflected by more CO molecular states for the subsequent H-assisted dissociation. CO adsorption and dissociation on Ru-doped Co(1 0 0) surfaces at different CO coverage compared to clean surface were investigated based on spin-polarized density functional theory (DFT), in order to explore the effect of the initial step of Ru promoter on CO activation in cobalt-based Fischer-Tropsch synthesis (FTS). The results show that CO adsorption is highly site-dependent, the adsorption strength of CO at different types of adsorption sites is determined by the interaction between the adsorbed CO molecule and Ru-doped Co(1 0 0) surfaces. CO dissociation is promoted at hollow sites but inhibited at top and bridge sites above the Ru atoms. In addition, the amount of saturated adsorbed CO is increased while the amount of dissociated CO is decreased on the Ru-doped Co(1 0 0) surfaces at high coverage. Combining the experimental results, it is concluded that the adsorption model is preferred than substitution model for CO activation, because the increased CO molecular states in adsorption model is facile for the subsequent H-assisted dissociation on Co surface. The present work suggests that the addition of Ru promoter can improve the CO activation on Co(1 0 0) surface and pave the way for experimental research. [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] • The synergistic effect between Ba and Ru was reported at the first time. • An improved CO conversion and excellent selectivity to high C 5 + selectivity was obtained. • The introduction of Ba induced both site poisoning and electronic effects. • The synergistic effect between Ba and Ru was responsible for the enhanced CO dissociation ability. • Other alkali earth metal promoters had a similar influence on the Co-0.1Ru/Al 2 O 3 catalysts for the FTS reaction. Alkali earth metals and Ru are famous selectivity promoters in cobalt-based Fischer-Tropsch synthesis. Ba has displayed as an effective selectivity promoter, however, the presence of Ba leads to a dropped CO conversion yield. To combine the advantages of Ba and Ru in promoting selectivity, Ba-modified alumina was fabricated and used as the supports for Co and Co-Ru catalysts. Promotion of Co/Al 2 O 3 by a combination of Ru and Ba achieved an increase of CO conversion and a low CH 4 selectivity due to the enhanced CO dissociation than unmodified and a single additive modified catalyst. The influences of other alkali earth metal additives were also investigated, which had a similar impact that of Ba on the Co-Ru catalysts for promoting FTS reaction. [ABSTRACT FROM AUTHOR]

• Co catalysts supported on CN-decorated Al 2 O 3 were synthesized by a facile and green strategy. • N could transmit electron to the cobalt surface and enhance the electron density of cobalt, then promoting the CO dissociation. • N-doped catalysts show the high catalytic activity, C 3 o/p and C 5 + selectivity in FTS. N-doped carbon materials have received much attention as an effective support to promote catalytic performance in FTS. However, complex and unfriendly preparation methods limit its wide application. Herein, we used a simple and harmless method to prepare CN-modified Co/Al 2 O 3 catalyst. It was found that the reducibility of catalyst was improved by the introduction of CN species and the electron density on cobalt surface was increased via the electron donation from the N dopants, especially for pyrrolic N, thus leading to the enhanced C 5 + selectivity, C 3 o/p ratio and TOF. Our work offers a new avenue to obtain high activity and selectivity catalyst. [ABSTRACT FROM AUTHOR]

[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]

• A phase transfer catalyst-assisted reversed-phase dispersive liquid–liquid microextraction has been developed. • The extractant was 100 μL 0.1 M NaOH solution. • A phase transfer catalyst (tetrabutylammonium bromide) acted as a dispersive agent. • Preconcentration of 4 organic acids in Fischer-Tropsch oil products using proposed approach. • Simplicity, low cost, short time and low LODs are advantages of the method. A method prior to using high-performance liquid chromatography (HPLC), named phase transfer catalyst-assisted reversed-phase dispersive liquid–liquid microextraction (PTC-RP-DLLME), was developed for the rapid determination of organic acids in Fischer-Tropsch synthesis (FTS) oil products. This method used sodium hydroxide solution and tetrabutylammonium bromide (TBAB) as an extractant and a disperser respectively, in which the TBAB promoted the dispersion of aqueous NaOH solutions in the organic product, and acted as a hydrogen bond receptor to enhance the extraction of organic acids via hydrogen bond interactions. Under the optimized conditions, the calibration curves in the range of 0.1–30 μg mL−1 showed correlation coefficients (r) of 0.998–0.999. Detection limits (S/N = 3) were ranged from 1.0 to 3.5 ng mL−1. The relative standard deviations of intra-day and inter-day repeatability were in the range of 2.9–5.8 % and 4.1–6.7%, respectively. The recoveries ranged from 85.4% to 105.9%. This developed method was employed for the analysis of organic acids in 6 types of oil products. This work provides an efficient and rapid pretreatment method for acid concentration prior to HPLC, and therefore saves time and cost for the quantitative analysis of FTS oil products. Moreover, precise analysis by application of this method is fairly beneficial to the FT catalyst improvement and industrial equipment material selection, and is rather significant for the proper design of the downstream processing/purification system. [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]

• Ba transfered electron to cobalt surface and then affect the adsorption of H 2 and CO on the catalyst surface. • Ba decreased CH 4 selectivity by increasing the apparent activation energy of the whole reaction. • Ba suppressed the hydrogenation of olefins by enhancing the olefins desorption. The role of Ba in Fischer-Tropsch synthesis (FTS) from syngas over Co/γ-Al 2 O 3 catalyst was investigated using a combined experimental and Density functional theory (DFT) method. The reducibility of catalysts was improved with the addition of Ba. Furthermore, the cobalt surface electronic density was increased by the existence of Ba on the surface of catalyst, leading to decrease surface H concentrations, promote CO adsorption and dissociation and then reduce the selectivity of CH 4 and enhance the selectivity of C 5 + and o/p ratio of C 3. The DFT calculation results indicate that the existence of Ba can decrease CH 4 selectivity by increasing the apparent activation energy of the whole reaction, and suppress the hydrogenation of olefins by enhancing the olefins desorption and then improve the o/p ratio of C 3. These results give mechanistic insights into why the catalytic performances of Ba-modified Co-based catalysts are better than clean Co-based catalysts and could open up new avenues for the future design of highly active and selective Co-based catalysts. [ABSTRACT FROM AUTHOR]