Effect of Cobalt Particle Size on the Catalyst Intrinsic Activity for Fischer–Tropsch Synthesis

Azzam, Khalid G.; Jacobs, Gary; Ma, Wanhong; Davis, Burtron H.

doi:10.1007/s10562-013-1172-6

Cited by 25 publications

(16 citation statements)

References 17 publications

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“…These complications highlight a complex mechanism that may be related to chemical-assisted sintering of Co FTS catalysts through a combination of the effect of CoO reduction during the initial activation of the catalysts and water exposure during operation. First, CoO, present either due to incomplete reduction of the catalysts [368] or oxidation of the small (<2 nm) crystallites as suggested by Davis' group [369,370] can apparently increase the sintering rate due to mobility that allows them to aggregate into larger CoO clusters that are subsequently reduced to metallic Co, as inferred from evidence presented in a number of studies [79,362,[368][369][370][371]. Primarily, X-ray absorption near edge (XANES) analysis shows simultaneous increasing extent of reduction and increasing Co-Co coordination, due both to removal of oxygen and increases in particle size.…”

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

confidence: 99%

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: 99%

Heterogeneous Catalyst Deactivation and Regeneration: A Review

2015

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“…Additional investigations are needed in this area. At commercially relevant FTS conditions, a problem was identified by us in defining intrinsic activity; as chemisorption is conducted on freshly activated catalysts, any oxidation of such small Co clusters that occurs at commercially relevant conditions can mask a measurement of intrinsic activity at the level of the active site [35]. Therefore, it is important to take into account the oxidation state of Co in the working FTS catalyst.…”

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 fresh (loaded) catalyst is often in the form of cobalt oxide spinel (Co 3 O 4 )o nasupport, and this undergoes multiple steps to reach the active catalyst, all of which is inside the reactor and not observed by an operator.T he measuremento fas uccessful transformationf rom Co 3 O 4 to Co II Ot oc obalt metal ando nt ot he active surface adsorbed speciesd uringF Ti so ften measured by catalytic conversion, product selectivity or appliedo perating temperature. [2] Fischer-Tropsch (also known as gas-to-liquids, GTL) is aw ellestablished technology with an umber of operating plants aroundt he world, converting syngast ol iquid hydrocarbons using an FT converter.G iven FT produces carbon chain lengths from C 1 to over C 100 ,c racking and upgrading of the high purity/clean wax product to make fuel fractions such as diesel, gasoline or jet fuel is normally required. [3] There are aw ide range of FT catalysts described in the literature;h owever, they are rarely tested under realistic FT conditions-conversions, productivities, life time stability or optimised selectivity.…”

Section: Introductionmentioning

confidence: 99%

In Situ Diffraction of Fischer–Tropsch Catalysts: Cobalt Reduction and Carbide Formation

Paterson¹,

Peacock²,

Ferguson³

et al. 2017

ChemCatChem

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This publication highlights the effect of CO treatments on both calcined and reduced catalysts by using novel in situ techniques to track particle transformations, which are so vital to catalyst performance and activity. Cobalt carbide formation has been shown to occur readily with CO treatments on metallic cobalt particles, and in this study we have used in situ XRD and temperature‐programmed reduction (TPR) techniques to track the evolution of the carbide. We were able to show a dependence on CO partial pressures and the formation of a single hexagonal phase of cobalt as a result of the carbide step. The stability of cobalt carbide was studied and its reduction in hydrogen to cobalt metal was observed. CO was also used as the reducing gas and by using TPR and in situ XRD we were able to demonstrate the reduction of cobalt oxide (Co3O4) to cobalt carbide (Co2C) via both oxide (CoO) and metal (Co) intermediates.

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Effect of Cobalt Particle Size on the Catalyst Intrinsic Activity for Fischer–Tropsch Synthesis

Cited by 25 publications

References 17 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

In Situ Diffraction of Fischer–Tropsch Catalysts: Cobalt Reduction and Carbide Formation

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