Effects of K adsorption on the CO-induced restructuring of Co(11-20)

Strømsheim, Marie Døvre; Svenum, Ingeborg-Helene; Farstad, Mari Helene; Li, Zheshen; Gavrilović, Ljubiša; Guo, Xiaoyang; Lervold, Stine; Borg, A.; Venvik, Hilde J.

doi:10.1016/j.cattod.2017.05.086

Cited by 9 publications

(28 citation statements)

References 65 publications

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“…Provided that stacking faults formed during the fcc transition are terminated as cus, terrace sites will be disrupted rendering the surface unable to reconstruct forming nano-islands to the same extent. Inhibition of surface reconstruction has been found on Co surfaces after ppm alkali addition 76 that results in reaction rate loss in similar levels to the current study.…”

Section: Figure 2 Structural Evolution Obtained From Refinement Of Isupporting

confidence: 91%

Structure–Performance Relationships on Co-Based Fischer–Tropsch Synthesis Catalysts: The More Defect-Free, the Better

et al. 2018

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Understanding and utilizing structureperformance relationships in catalytic nanomaterials is the epitome of catalysis science. Knowledge at the atomic level can potentially allow rational design of more selective and energy efficient catalytic materials. Fischer-Tropsch synthesis on cobalt is an example of a complicated system that operates in a narrow process regime, and the nature of the reaction product is governed by numerous parameters. On an industrial model catalyst, we have simplified the structure of the active, metallic nanoparticles into predominantly hexagonal close packed structure via the use of a Co 2 C precursor. By varying the final reduction temperature, we could mildly modify catalyst microstructural properties at the nanoparticle (NP) level. Catalytic materials, although with minimal structural differences, showed significantly different performance. Evidently there is a narrow window for complete utilization of the hexagonal close packed Co crystallites that lays between removal of lattice carbon, that remains from the Co 2 C precursor, and the initiation of stacking disorder, due to transition to the face centered cubic Co structure. Fischer-Tropsch synthesis performance indicators show that Co NPs with minimum number of crystal defects outperform catalysts with lattice defects, either due to the existence of lattice carbon or stacking faults. Therefore, catalyst preparation and activation procedures probably should be designed targeting defect free Co crystallites.

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Section: Figure 2 Structural Evolution Obtained From Refinement Of Isupporting

confidence: 91%

Structure–Performance Relationships on Co-Based Fischer–Tropsch Synthesis Catalysts: The More Defect-Free, the Better

et al. 2018

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“…Recent DFT work in our group indicated K atoms to be mobile on the most relevant Co facets but not across steps and edges, thereby likely deactivating sites central to the activity of the Co particles under reaction conditions 31 . Furthermore, investigating Co(11-20) as an experimental model system we found that small amounts of metallic K deposited by evaporation is mobile at ambient temperature and prefers step edge locations on the surface 32 .…”

Section: Characterization Resultsmentioning

confidence: 93%

Deactivation of Co-Based Fischer–Tropsch Catalyst by Aerosol Deposition of Potassium Salts

Gavrilović

Brandin

Holmén

et al. 2018

Ind. Eng. Chem. Res.

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A 20%Co/0.5%Re/γAl2O3 Fischer-Tropsch catalyst was poisoned by four potassium salts (KNO3, K2SO4, KCl, K2CO3) using the aerosol deposition technique, depositing up to 3500 ppm K as solid particles. Standard characterization techniques (H2 Chemisorption, BET, TPR) showed no difference between treated samples and their unpoisoned counterpart. The Fischer-Tropsch activity was investigated at industrially relevant conditions (210 °C, H2:CO = 2:1, 20 bar). The catalytic activity was significantly reduced for samples exposed to potassium, and the loss of activity was more severe with higher potassium loadings, regardless of the potassium salt used.A possible dual deactivation effect by potassium and the counter-ion (chloride, sulfate) is observed with the samples poisoned by KCl and K2SO4. The selectivity towards heavier hydrocarbons (C5+) was slightly increased with increasing potassium loading, while the CH4 selectivity was reduced for all the treated samples. The results support the idea that potassium is mobile under FT conditions. The loss of activity was described by simple deactivation models which imply a strong non-selective poisoning by the potassium species.

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“…Pederson et al recently performed DFT calculations on CoMnO systems for the production of light olefins and they found that selectivities can be attributed to an inhibited hydrogenation activity demonstrated by the increased barriers for CH 3 and CH 4 formation 22 . Strømsheim et al recently showed that the restructuring of Co surface under CO exposure with K pre-adsorbed proceeded on the terraces rather than from the step edges 38 . Other notable theoretical studies on multiple elemental surfaces include ZnO/Cu, Co 2 C/Co, Cu/Co 39–41 .…”

Section: Resultsmentioning

confidence: 99%

Promoted cobalt metal catalysts suitable for the production of lower olefins from natural gas

et al. 2019

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Due to the surge of natural gas production, feedstocks for chemicals shift towards lighter hydrocarbons, particularly methane. The success of a Gas-to-Chemicals process via synthesis gas (CO and H2) depends on the ability of catalysts to suppress methane and carbon dioxide formation. We designed a Co/Mn/Na/S catalyst, which gives rise to negligible Water-Gas-Shift activity and a hydrocarbon product spectrum deviating from the Anderson–Schulz–Flory distribution. At 240 °C and 1 bar, it shows a C2-C4 olefins selectivity of 54%. At 10 bar, it displays 30% and 59% selectivities towards lower olefins and fuels, respectively. The spent catalyst consists of 10 nm Co nanoparticles with hcp Co metal phase. We propose a synergistic effect of Na plus S, which act as electronic promoters on the Co surface, thus improving selectivities towards lower olefins and fuels while largely reducing methane and carbon dioxide formation.

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Effects of K adsorption on the CO-induced restructuring of Co(11-20)

Cited by 9 publications

References 65 publications

Structure–Performance Relationships on Co-Based Fischer–Tropsch Synthesis Catalysts: The More Defect-Free, the Better

Structure–Performance Relationships on Co-Based Fischer–Tropsch Synthesis Catalysts: The More Defect-Free, the Better

Deactivation of Co-Based Fischer–Tropsch Catalyst by Aerosol Deposition of Potassium Salts

Promoted cobalt metal catalysts suitable for the production of lower olefins from natural gas

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