| dc.description.abstract | The Fischer-Tropsch process for the production of fuels and chemicals from alternative carbon containing feedstocks have become of increasing interest in recent years. Special attention towards the the production of light olefins have been drawn in order to meet the constantly growing demands. The aim of this work is to develop and investigate cobalt based bimetallic catalysts to enhance the production of such light olefins in Fischer-Tropsch synthesis.
Monodisperse, spherical cobalt nanoparticles with average particle size in the range of 6.4 to 7.1 nm is synthesized through a heat-up method. Subsequent deposition of MnO, in various amounts, on the cobalt particle surface through thermal decomposition is applied in the attempt of forming Co/MnO core/shell nanoparticles. However, the preparation of bimetallic nanoparticles gave inconsistent results.
Catalysts are prepared by depositing the nanoparticles on a supporting material of siliceous mesocellular foam, resulting in a variety of colors and compositions. The catalysts are then examined with XRD, XRF, XPS and TGA analysis to further investigate their properties. The catalytic activity of the synthesized catalysts is tested, monitoring the CO conversion and product selectivity.
The prepared catalysts can be divided into two groups. The first group consist of brown catalysts which exhibit CoO peaks in their \gls{xrd} spectra, have reduction temperatures of 350-400 C, and shows no catalytic activity before they are reduced. In contrast, the other group is black in color, displays the presence of Co in their XRD spectra, are reduced at 480-530 C, and show catalytic activity before reduction. In addition, these catalysts exhibit poorer CO conversion and higher methane selectivity during Fischer-Tropsch reaction.
During the reaction, non of the tested catalysts exhibit properties applicable for direct ethylene production. For C3 and C4 excess olefins are produced and somewhat higher selectivities are reached. This opens, at best, for olefin extraction of the straight run products for Co/MnO(100%) and Co/MnO(300%) which display high CO conversion, low methane formation and high production of C5+. The correlation between the amount of manganese and the catalytic activity is inconclusive.
The difference in the catalysts properties may be possibly caused by either the oxidation state of the cobalt particles or deviations in the subsequent shell-formation step, resulting in a variety of bimetallic structures consisting of different cobalt and manganese species. Further work should be conducted to enhance the reproducibility of the synthesis and ensure which bimetallic structures are present before any conclusions can be drawn. | en |
