| 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. |
- Bakhtiary-Davijany, Hamidreza, et al.
(författare)
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Analysis of External and Internal Mass Transfer at Low Reynolds Numbers in a Multiple-Slit Packed Bed Microstructured Reactor for Synthesis of Methanol from Syngas
- 2012
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 51:42, s. 13574-13579
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of mass transfer limitations in an integrated micro packed bed reactor-heat exchanger (IMPBRHE) for methanol synthesis was experimentally investigated. Experiments were performed with three different particle size distributions (50-200 mu m) of a Cu-based catalyst at 80 bar and 215-270 degrees C. Negligible effects of pore diffusion limitations on the performance of the reactor under methanol synthesis conditions for catalyst particle diameters up to 125 mu m were found. Due to a very low Reynolds numbers (similar to 1) and dominance of molecular diffusion, variation of the total pressure was applied as a suitable technique to alter the diffusivities of reactants in the gas mixture by dilution, while keeping the reactant flow and partial pressure constant. No significant change in the CO conversion was observed in the temperature range 235-255 degrees C, pressure range 50-90 bar, and for reactant contact times of 105-308 ms.g/mL. The same procedure was applied to a laboratory. fixed bed reactor with similar results. Possible heat transfer effects associated with the dilution were shown to be negligible. We therefore conclude that both reactor systems operate in the absence of external mass transfer limitations.
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| 3. |
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| 4. |
- Gavrilovic, Ljubisa, et al.
(författare)
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Fischer-Tropsch synthesis : Investigation of the deactivation of a Co catalyst by exposure to aerosol particles of potassium salt
- 2018
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Ingår i: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 230, s. 203-209
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Tidskriftsartikel (refereegranskat)abstract
- The influence of potassium species on a Co based Fischer-Tropsch catalyst was investigated using an aerosol deposition technique. This way of poisoning the catalyst was chosen to simulate the actual potassium behaviour during the biomass to liquid (BTL) process utilizing gasification followed by fuel synthesis. A reference catalyst was poisoned with three levels of potassium and the samples were characterized and tested for the Fischer-Tropsch reaction under industrially relevant conditions. None of the conventional characterization techniques applied (H2 Chemisorption, BET, TPR) divulged any difference between poisoned and unpoisoned samples, whereas the activity measurements showed a dramatic drop in activity following potassium deposition. The results are compared to previous results where incipient wetness impregnation was used as the method of potassium deposition. The effect of potassium is quite similar in the two cases, indicating that irrespective of how potassium is introduced it will end up in the same form and on the same location on the active surface. This indicates that potassium is mobile under FTS conditions, and that potassium species are able to migrate to sites of particular relevance for the FT reaction.
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| 5. |
- Gavrilovic, Lubisa, et al.
(författare)
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The effect of aerosol-deposited ash components on a cobalt-based Fischer–Tropsch catalyst
- 2019
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer. - 1878-5190 .- 1878-5204. ; 127:1, s. 231-240
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Tidskriftsartikel (refereegranskat)abstract
- The effect of ash salts on Co-based Fisher–Tropsch catalysts was studied using an aerosol deposition technique. The major elements in the ash were found to be K, S and Cl. The ash was deposited on a calcined catalyst as dry particles with an average diameter of approx. 350 nm. The loading of ash particles was varied by varying the time of exposure to the particles in a gas stream. Catalyst characterization did not reveal significant differences in cobalt dispersion, reducibility, surface area, pore size, or pore volume between the reference and the catalysts with ash particles deposited. Activity measurements showed that following a short exposure to the mixed ash salts (30 min), there were no significant loss of activity, but a minor change in selectivity of the catalyst . Extended exposure (60 min) led to some activity loss and changes in selectivity. However, extending the exposure time and thus the amount deposited as evidenced by elemental analysis did not lead to a further drop in activity. This behavior is different from that observed with pure potassium salts, and is suggested to be related to the larger size of the aerosol particles deposited. The large aerosol particles used here were probably not penetrating the catalyst bed, and to some extent formed an external layer on the catalyst bed. The ash salts are therefore not able to penetrate to the pore structure and reach the Co active centers, but are mixed with the catalyst and detected in the elemental analysis.
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| 6. |
- 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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