Crystal size effect over nanosized cobalt oxide-loaded catalysts for Fischer-Tropsch synthesis

To investigate the crystal size effects in the Fischer-Tropsch synthesis (FTS), cobalt oxide nanocrystals with particle sizes of 2nm to 15nm were synthesized using oleic acid as a capping agent and the supported catalysts of 5wt% Co/Al2O3 were prepared by the impregnation of g-alumina with the colloidal solution of dispersed cobalt oxide. The synthesized nanocrystals and the supported catalysts were characterized using XRD, TEM, TPR, O2 titration, and H2 chemisorption. The FTS performances of the catalysts were examined in a fixed bed reactor. The catalytic properties such as activity and selectivity were mainly dependent on the cobalt crystal size. In the point of views of high CO conversion and selectivity toward C5+ hydrocarbons, and low conversion to CO2 and CH4, best results were obtained in the supported catalyst with 7 nm cobalt oxides. Furthermore the nanocrystal-loaded Co/Al2O3 catalysts prepared from this method exhibited much higher CO conversion and C5+ selectivity than catalysts prepared by conventional method (impregnation and precipitation).