Genesis of active sites in silica supported cobalt Fischer-Tropsch catalysts: effect of cobalt precursor and support texture

摘要

Optimization of cobalt deposition and textural properties of catalytic support represent two different but complementary approaches to enhance the performance of cobalt silica-supported Fischer-Tropsch catalysts. It is shown that low temperature decomposition of supported cobalt complexes involves formation of small Co_3O_4 crystallites. The exothermic effect due to the decomposition of cobalt precursor seems to be a major factor responsible of cobalt silicate formation. Gentle decomposition of cobalt precursor generally leads to Fischer-Tropsch catalysts with higher activity and selectivity to higher hydrocarbons. It was found that the sizes of supported cobalt particles prepared using cobalt nitrate depended on silica pore sizes. Narrow pore size distribution in periodic mesoporous silicas allows relatively high cobalt dispersion to be maintained at high cobalt loading. This leads to higher density of active sites and more active Fischer-Tropsch catalysts.