Fischer–Tropsch synthesis over alumina supported cobalt catalyst: Effect of promoter addition

Shimura, Katsuya; Miyazawa, Tomohisa; Hanaoka, Toshiaki; Hirata, Satoshi

doi:10.1016/j.apcata.2015.01.017

Cited by 70 publications

(47 citation statements)

References 64 publications

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“…From these observations, we assume that the different catalytic activities measured on these five systems are related to the amount of metallic Co obtained upon reduction, which stems from the reducibility of CoO and is hampered significantly on 3 %Mg/γ‐Al 2 O 3 ‐500 °C and 3 %Si/γ‐Al 2 O 3 ‐CLD. Mg 2+ has been reported previously to decrease the reducibility and, consequently, the activity of Co catalysts in the FT reaction, supposedly by the insertion of Mg 2+ ions into cobalt oxide . This would explain why the catalyst supported on 3 %Mg/γ‐Al 2 O 3 ‐900 °C, in which Mg 2+ is located deep in the support is more active than its counterpart calcined at 500 °C, in which surface Mg 2+ is available for reaction with Co phases during impregnation or calcination in good agreement with the results of Gallagher et al .…”

Section: Resultssupporting

confidence: 87%

Inhibition by Inorganic Dopants of γ‐Alumina Chemical Weathering under Hydrothermal Conditions: Identification of Reactive Sites and their Influence in Fischer–Tropsch Synthesis

et al. 2017

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Understanding how alumina degradation to boehmite AlOOH can be prevented under hydrothermal conditions is key to design more stable catalysts supported on alumina for Fischer–Tropsch synthesis. We compare the effect of four inorganic dopants to inhibit γ‐alumina chemical weathering under hydrothermal conditions: three metal ions: Mg2+, Zr4+, Ni2+, introduced by impregnation, and nonmetal Si, introduced by the grafting of tetraethyl orthosilicate. Boehmite is formed by a mechanism of dissolution–precipitation. A significant decrease of alumina weathering to boehmite is evidenced for all dopants. For metal ions, the thermal conversion of doped γ‐Al2O3 into an alumina‐rich mixed oxide or the coverage of the alumina surface by particles of a poorly soluble oxide such as NiO contribute to the stabilization of the solid. Alumina dissolution and degradation are only inhibited fully through Si grafting. IR spectra in the OH stretching region suggest that the most reactive alumina sites toward dissolution are basic Al−OH sites located on lateral facets that are blocked upon Si introduction. Fischer–Tropsch reactivity shows that Co catalysts prepared on Mg2+‐ and Si‐doped supports are less active or, at best, as active as a reference Co/γ‐Al2O3 catalyst, which is explained by a lower reducibility of CoO on doped supports. The Co catalyst prepared on Mg2+‐doped γ‐Al2O3 calcined at 900 °C exhibits the best combination of catalytic activity, ease of preparation, and hydrothermal stability.

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Section: Resultssupporting

confidence: 87%

Inhibition by Inorganic Dopants of γ‐Alumina Chemical Weathering under Hydrothermal Conditions: Identification of Reactive Sites and their Influence in Fischer–Tropsch Synthesis

et al. 2017

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“…Osa et al observed a greatly improved the diesel selectivity with addition of Ca to the cobalt based catalyst. However, Ca promoted catalyst yield a higher amount of methane at 242°C than the Na promoted sample [57]. In the present study, as estimated of the H 2 -TPR result, reduction degree of the catalyst decreased with Na loading.…”

Section: Kinetic Modeling and Derivation Rate Reactioncontrasting

confidence: 44%

Impact of Na Promoter on Structural Properties and Catalytic Performance of CoNi/Al2O3 Nanocatalysts for the CO Hydrogenation Process: Fischer–Tropsch Technology

2015

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This work deals with the effect of adding Na to bimetallic sol-gel derived alumina supported Co/Ni nanocatalysts in Fischer-Tropsch synthesis. The catalyst activity and selectivity changed with different levels of Na, and the catalyst with 2 % Na loading was selected as an optimal catalyst to compare with un-promoted Co/Ni/ Al 2 O 3 catalyst. Na reduced the methane selectivity by increasing the chain-growth probability (a-value) at 12 bar. The results of physico-chemical characterizations show that the Na promoter plays a significant role in the catalytic structure. Additionally, the kinetic behavior was considered in absence and presence of Na over CoNi/Al 2 O 3 catalysts. We applied an enolic approach, which was developed based on the interaction between adsorption HCO and dissociated adsorption hydrogen, through the Langmuir-Hinshelwood-Hougen-Watson (LHHW) adsorption theory. Kinetic parameters, including the rate constant (k) and activation energy (E a ) of the catalysts, were also determined. The results show that, by adding Na, the activation energy (E a ) decreases and the reaction rate (-R CO ) increases. Graphical Abstract

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“…In the current literature, there is a large discrepancy between conditions and a manner of hydrogen chemisorption measurements, from which data are used to determine the average size of crystallites and dispersion of the metallic cobalt phase deposited on an oxide support. Although those, already old, recommendations, only in the 2015-beginning of 2016 period the much lower temperature, 293-323 K, of hydrogen chemisorption [28][29][30][31][32][33][34][35][36][37] and flow adsorption pulse and TPD methods [32][33][34][35][36][37] are used in many laboratories. The higher, 423 K, temperature of hydrogen chemisorption was also applied in the pulse method for estimation of the average size of cobalt crystallites [33].…”

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confidence: 99%

Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

et al. 2016

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Cobalt catalysts with CeO 2 support, unpromoted and promoted with potassium were prepared by an impregnation method. Reduced catalysts were subjected to hydrogen chemisorption at different temperatures in the range of 313-453 K. Studies have shown that calculated Co crystallites size depends on the temperature of chemisorption. The average of size crystallites of the Co active phase obtained from the total and strong chemisorption data were compared with those from measurements by other techniques, TEM and XRD. The results of comparison allowed us to indicate the most suitable chemisorption temperature, different for unpromoted (383 K) and potassium-promoted (413 K) catalysts to determine the proper Co crystallites size of active phase, compatible with the crystallites size determined by the most objective method, i.e. by TEM measurements. In the case of small metal crystallites of active phase (4-5 nm) the divergence of their average size determined by hydrogen chemisorption and TEM methods and particularly by the XRD method is definitely higher than that in the case of larger crystallites (~12 nm).can significantly influence on obtained results. More than 40 years ago Bartholomew et al. [23][24][25] show that the chemisorption of hydrogen over cobalt catalysts with various supports (SiO 2 , Al 2 O 3 , C, MgO, ZSM-5, TiO 2 ) and over unsupported cobalt is activated and highly reversible. The activation was a function of the interaction of cobalt with a support or promoter. Frequently used in catalysis, potassium promoter significantly increased the adsorption activation energy for hydrogen [26]. It is also proved that some methods for determining the hydrogen uptake, i.e. flow adsorption methods such as thermal desorption and pulse methods, measure only irreversible (strong) chemisorption [23,27]. No hydrogen desorption was detected for MgOand ZSM-5-supported and low-loaded (1-3 wt.%) aluminasupported cobalt catalysts using TPD method, even though those catalysts adsorbed hydrogen when the static technique was applied [23,24]. The special case is the Co/TiO 2 system, where due to the strong metal-support interactions the stoichiometry of hydrogen chemisorption is lower than one hydrogen atom per surface cobalt atom, even in static measurements. With exception of the cobalt systems in which the strong metal-support interactions take place, the static technique was recommended for estimation of the average size of cobalt crystallites on the basis of maximal hydrogen chemisorption uptake, usually at 373 K. A good correlation with TEM measurements was found for the Co/SiO 2 , Co/γ-Al 2 O 3 and Co/C catalysts. The paper [9] also shows that the volume of chemisorbed hydrogen (including strong and weak chemisorption) on the CoRe/γ-Al 2 O 3 catalyst varies with the temperature of chemisorption, and the use of different data leads to the determination of different average size of crystallites, even though the actual crystallites size remains unchanged. They obtained the best results when the total chemisorption...

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Fischer–Tropsch synthesis over alumina supported cobalt catalyst: Effect of promoter addition

Cited by 70 publications

References 64 publications

Inhibition by Inorganic Dopants of γ‐Alumina Chemical Weathering under Hydrothermal Conditions: Identification of Reactive Sites and their Influence in Fischer–Tropsch Synthesis

Inhibition by Inorganic Dopants of γ‐Alumina Chemical Weathering under Hydrothermal Conditions: Identification of Reactive Sites and their Influence in Fischer–Tropsch Synthesis

Impact of Na Promoter on Structural Properties and Catalytic Performance of CoNi/Al2O3 Nanocatalysts for the CO Hydrogenation Process: Fischer–Tropsch Technology

Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

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