Metal oxide promotion of Co/SiO[subscript 2] for Fischer-Tropsch synthesis

Abstract

Fischer-Tropsch synthesis (FTS) is a catalytic process which converts coal and natural gas to chemicals and clean fuels via syngas. Currently, cobalt-based catalyst is claimed to have certain advantages over other catalysts because of their high activity, long catalytic file time, low water-gas shift activity and high selectivity for long chain paraffin. The purpose of the present work was to improve the activity of cobalt-based catalyst on the silica support by the addition of aluminium oxide, titanium oxide and zirconium oxide as promoters. The effect of catalyst preparation by the sequential-impregnation and the co-impregnation methods was also investigated. The catalytic activity was examined in a semi-batch slurry-phase reactor. XRD, TPR, SEM, H [subscript 2] chemisorption and DRIFT were used to characterize the modified catalysts. The results of metal oxide addition onto the cobalt catalyst indicated the improvement on the catalytic activity of cobalt in FTS reaction by increasing the cobalt dispersion without obstruction of the cobalt reducibility. The method of preparation of Al[subscript 2]O[subscript 3] and ZrO[subscript 2] loaded into Co/SiO[subscript 2] catalyst did not affect the catalytic activity, unlike the results from the preparation of TiO2-promoted catalyst. The formation of hardly reducible CoTiO[subscript 3] from the co-impregnation method was easier than that from the sequential-impregnation method. Hydrogen spillover might be the reason for the enhancement of activity in ZrO[subscript 2]-promoted catalyst.