Stability of Nanocrystals:  Thermodynamic Analysis of Oxidation and Re-reduction of Cobalt in Water/Hydrogen Mixtures

Steen, Eric van; Claeys, Michael; Dry, Mark E.; Loosdrecht, J. van de; Viljoen, Elvera; Visagie, J. L.

doi:10.1021/jp045136o

Cited by 267 publications

(249 citation statements)

References 19 publications

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“…The review includes a detailed consideration and analysis of the mechanisms and processes of sintering, oxidation, aluminate formation, and coking and carbide formation and under what operating conditions each is important. They summarize their and others' previous findings that oxidation primarily occurs on small (<2 nm) cobalt crystallites and at high partial pressures of water [362][363][364][365][366]. Further, they highlight the potentially complicated transformations between CoO and aluminates [362,364,367].…”

Section: Case Study: Cobalt Based Fischer-tropsch (Ft) Catalyst Regenmentioning

confidence: 73%

Heterogeneous Catalyst Deactivation and Regeneration: A Review

2015

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Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

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Section: Case Study: Cobalt Based Fischer-tropsch (Ft) Catalyst Regenmentioning

confidence: 73%

Heterogeneous Catalyst Deactivation and Regeneration: A Review

2015

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“…Thus, when a promoter is added, the additional gain in active site density will be due in large part to the reduction of smaller cobalt oxide species having stronger interactions with the support. Depending on the loading of cobalt and method of preparation, if smaller cobalt metal crystallites (e.g., <2-4.4 nm [30,31]) within cobalt clusters are formed, they may be susceptible to reoxidation [30,32]. Some researchers have recently indicated that Co clusters less than 6-8 nm have lower intrinsic activity [33,34].…”

Section: Reoxidation Of Small Cobalt Crystallites At the Onset Of Ftsmentioning

confidence: 99%

Influence of Reduction Promoters on Stability of Cobalt/g-Alumina Fischer-Tropsch Synthesis Catalysts

Jacobs¹,

Ma²,

Davis³

2014

Catalysts

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This focused review article underscores how metal reduction promoters can impact deactivation phenomena associated with cobalt Fischer-Tropsch synthesis catalysts. Promoters can exacerbate sintering if the additional cobalt metal clusters, formed as a result of the promoting effect, are in close proximity at the nanoscale to other cobalt particles on the surface. Recent efforts have shown that when promoters are used to facilitate the reduction of small crystallites with the aim of increasing surface Co 0 site densities (e.g., in research catalysts), ultra-small crystallites (e.g., <2-4.4 nm) formed are more susceptible to oxidation at high conversion relative to larger ones. The choice of promoter is important, as certain metals (e.g., Au) that promote cobalt oxide reduction can separate from cobalt during oxidation-reduction (regeneration) cycles. Finally, some elements have been identified to promote reduction but either poison the surface of Co 0 (e.g., Cu), or produce excessive light gas selectivity (e.g., Cu and Pd, or Au at high loading). Computational studies indicate that certain promoters may inhibit polymeric C formation by hindering C-C coupling.

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“…The extent of cobalt reduction does not seem to decrease with time on-stream. It is often postulated [1,89,90] that reoxidation of small supported cobalt particles by water produced by Fischer-Tropsch synthesis is the principal reason for catalyst deactivation. The magnetic data [88] suggest however that reoxidation of cobalt metal particles in industrial Fischer-Tropsch reactors could be prevented by efficient control of water and hydrogen pressures.…”

Section: Versusmentioning

confidence: 99%

Magnetic Characterization of Fischer-Tropsch Catalysts

Чернавский

Dalmon

Перов

et al. 2009

Oil & Gas Science and Technology - Rev. IFP

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Résumé -La caractérisation par la méthode magnétique des catalyseurs Fischer-TropschCet article passe en revue les développements récents dans le domaine de la caractérisation des catalyseurs Fischer-Tropsch à base de cobalt, de fer et de nickel par la méthode magnétique. La caractérisation magnétique fournit des informations précieuses sur la réduction du catalyseur, la taille des nanoparticules ferromagnétiques, la chimisorption, ainsi que sur les réactions topochimiques qui se produisent avec les catalyseurs au cours de la genèse de la phase active et dans des conditions réactionnelles. Les possibilités et les limites de la méthode magnétique sont examinées. Abstract -Magnetic Characterization of Fischer-Tropsch Catalysts -This paper reviews recent developments in the application of magnetic methods for investigation of Fischer

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Stability of Nanocrystals: Thermodynamic Analysis of Oxidation and Re-reduction of Cobalt in Water/Hydrogen Mixtures

Cited by 267 publications

References 19 publications

Heterogeneous Catalyst Deactivation and Regeneration: A Review

Heterogeneous Catalyst Deactivation and Regeneration: A Review

Influence of Reduction Promoters on Stability of Cobalt/g-Alumina Fischer-Tropsch Synthesis Catalysts

Magnetic Characterization of Fischer-Tropsch Catalysts

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