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Effect of Ti and Al addition via direct synthesis to SBA-15 as support for cobalt based Fischer-Tropsch catalysts
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
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2012 (English)In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 443-444, 76-86 p.Article in journal (Refereed) Published
Abstract [en]

Different mesoporous SBA-15 supports doped with Ti and Al at 5 and 10 wt% have been synthesized by means of direct synthesis. The supports have been characterized by N 2-adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), NH 3-temperature programmed desorption (NH 3-TPD), H 2-chemisorption, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM). Titanium doped materials showed to have much shorter channels than the pristine SBA-15, while aluminum addition did not have a significant effect on channel length. After impregnation with 12 wt% Co, the catalysts were further characterized and tested in the Fischer-Tropsch synthesis at industrially relevant process conditions (483 K, 20 bar, H 2/CO ratio = 2.1, pellet size: 53-90 μm) with and without external water addition. The S C5 + values of the different SBA-supported catalysts were low, especially at low conversion levels (i.e. low water partial pressure), suggesting that CO diffusion limitations increased the H 2/CO ratio inside the 1-dimensional (1D) porous network. The selectivity data showed a correlation between the channel length and the extent of CO-diffusion limitations at much shorter diffusion distances than those for conventional 3D porous supports. Water partial pressure showed to increase the syngas diffusion rate (i.e. removal of diffusion limitations on reactants’ arrival), to have a positive kinetic effect on the rate and to favor longer chain hydrocarbons.

Place, publisher, year, edition, pages
2012. Vol. 443-444, 76-86 p.
Keyword [en]
Diffusion limitations, Doping, Fischer-Tropsch, SBA-15, Water
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-102309DOI: 10.1016/j.apcata.2012.07.026ISI: 000309644400009Scopus ID: 2-s2.0-84866053813OAI: oai:DiVA.org:kth-102309DiVA: diva2:552283
Note

QC 20121017

Available from: 2012-09-13 Created: 2012-09-13 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Fischer-Tropsch Synthesis over Cobalt-based Catalysts for BTL applications
Open this publication in new window or tab >>Fischer-Tropsch Synthesis over Cobalt-based Catalysts for BTL applications
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fischer-Tropsch synthesis is a commercial technology that allows converting synthesis gas, a mixture of CO and H2, into fuels and chemicals. This process could be one of the actors in the reduction of oil dependency of the transportation sector. In fact, it has great potential for producing synthetic fuels also from renewable sources, such as biomass, after its thermochemical conversion (gasification) into synthesis gas. Concerning the quality of a diesel fuel produced with this technology, it has a lower local environmental impact than conventional diesel, since it is practically free of sulphur and nitrogen compounds and yields lower exhaust emissions of hydrocarbons, CO and particulates. The present study focuses on the use of cobalt-based catalysts for the production of diesel. In particular, it looks upon correlation between product selectivities when varying the catalyst properties and the effect of process parameters, such as a low H2/CO ratio, typical of a biomass-derived synthesis gas, and the water partial pressure.

Different cobalt-based catalysts, with different properties, such as conventional 3-dimensional porous network supports (γ-Al2O3, α-Al2O3, TiO2, SiO2), Co-loading, preparation technique, etc., were investigated in the Fischer–Tropsch reaction at industrially relevant process conditions. For a set of process conditions, a linear relationship seems to exist between the selectivity to methane (and other light products) and higher hydrocarbons (identified by the industrially relevant parameter SC5+, selectivity to hydrocarbons with more than 4 carbon atoms) indicating a common precursor.

Ordered mesoporous materials (SBA-15), characterized by a 1-dimensional mesoporous network, were tested as model supports and showed the possibility of occurrence of CO-diffusion limitations at diffusion distances much shorter than those required for conventional 3-dimensional porous network supports. The linear relationship mentioned above, derived for conventional supports, was shown to be an efficient tool for indicating whether measured selectivities are affected by CO-diffusion limitations. Some of the catalysts were exposed to H2-poor syngas and to external water addition and the effects on the selectivity relationships were investigated.

Furthermore, the possibility of internal water-gas shift of a H2-poor syngas with mixtures of Co/γ-Al2O3 and a Cu/ZnO/Al2O3 catalyst was investigated both as a technical solution for direct use of a model bio-syngas in the Fischer-Tropsch synthesis, and as a means to study the effect of indigenous water removal on the reaction rate to hydrocarbons. It was found that removal of indigenously produced water slows down the reaction rate significantly. Lastly, the effect of water partial pressure on the Fischer–Tropsch rate of the Co catalyst supported on narrow-pore γ-Al2O3, on its own, was studied. Inlet water partial pressure was varied by external water vapor addition at different H2/CO molar ratios ranging from 1 to 3. The effect of water showed to be positive on the rate for all the H2/CO ratios, but more significantly at H2-poor conditions. The nature of this positive effect on the rate seems to be unrelated to changes in amounts of amorphous polymeric carbon detectable by temperature-programmed hydrogenation of the spent catalyst.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 95 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:36
Keyword
cobalt, Fischer-Tropsch, syngas, selectivity
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-102304 (URN)978-91-7501-446-3 (ISBN)
Public defence
2012-09-28, Q2, Osquldasväg 10 NB, KTH, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20120914

Available from: 2012-09-14 Created: 2012-09-13 Last updated: 2012-09-14Bibliographically approved

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