| 1. |
- Tsakoumis, Nikolaos E., et al.
(författare)
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Structure-Performance Relationships on Co-Based Fischer-Tropsch Synthesis Catalysts : The More Defect-Free, the Better
- 2019
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Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 9:1, s. 511-520
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Tidskriftsartikel (refereegranskat)abstract
- Understanding and utilizing structure-performance 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 a predominantly hexagonal close-packed structure via the use of a Co2C 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 lies between removal of lattice carbon, that remains from the Co2C precursor, and the initiation of stacking disorder, because of a 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, because of the existence of either lattice carbon or stacking faults. Therefore, catalyst preparation and activation procedures probably should be designed targeting defect-free Co crystallites.
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| 2. |
- Rytter, Erling, et al.
(författare)
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Hydrophobic catalyst support surfaces by silylation of gamma-alumina for Co/Re Fischer-Tropsch synthesis
- 2018
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Ingår i: Catalysis Today. - : Elsevier. - 0920-5861 .- 1873-4308. ; 299, s. 20-27
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Tidskriftsartikel (refereegranskat)abstract
- Eight different silanes with chloro or methoxy active ligands have been examined to modify the surface of a standard.-alumina support to investigate the effect of surface acidity and hydrophobicity in Fischer-Tropsch synthesis (FTS) at common operating conditions (210 degrees C; 20 bar; H-2/CO = 2.1). Silanes were impregnated prior to cobalt (Pre) or after cobalt impregnation and calcination (Post). Samples were characterized by standard techniques (FTIR, XRD, TPD, TPR, TGA, BET). In the Post series, cobalt crystallite size is maintained, while it is reduced when cobalt impregnation is performed on a partly hydrophobic surface. Both series of catalysts have FTS performances that deviate significantly from a reference catalyst and, in combination with characterization data, the silanes have modified all the 15 examined catalysts. The Pre series offer options for improved selectivity to higher hydrocarbons in FTS. The effects of silylation on FT performance mechanisms are discussed in terms of gas diffusion limitations, strain in cobalt particles and partial blocking of CO activation sites.
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